May 2012

Novel material and process technologies for wind blade design and production are critical to increasing the competitiveness of wind power generation. As part of a Department of Energy (DOE)-funded project conducted by PPG Industries (PPG) and MAG Industrial Automation Systems (MAG), the potential of producing fiber glass composite blades using automated manufacturing was evaluated. This paper focuses on the material evaluation and corresponding impact on blade performance as part of the funded study.

During the first stage of the project, a comprehensive review of the DOE composite material database was performed. The results of this review were combined with data from PPG and publicly available information and analyzed for performance characteristics based upon material type¹.

The outcome of this analysis identified state of the art composite material technology and performance characteristics used by wind blade designers. These properties (Table 1) were the benchmark for the work performed in the remainder of this study. Some of the key conclusions of the comprehensive database evaluation included:

• Unidirectional, prepreg-based laminates made with E-Glass and epoxy resin have better tensile modulus compared to equivalent infused laminates;
• Tensile modulus values of 47 and 48 GPa have been reported for unidirectional laminates made with E-Glass prepreg and correspond to the highest tensile modulus reported for any E-Glass composites;
• Laminates fabricated with PPG’s HYBON^® 2026 roving and epoxy resin resulted in higher fatigue performance when compared to laminates produced with other roving inputs.

During the second stage of the project an experiment was conducted to evaluate the effects of fiber diameter, linear density (TEX), and fabric areal weight on material properties. The samples were produced in two distinct reinforcement formats: weft insertion fabrics with 90+ percent of the reinforcement in one direction, and by dry filament winding to mimic the reinforcement packing of a unidirectional prepreg. The glass fiber sizing chemistry and the sizing content was kept constant: PPG’s HYBON 2026 multi-compatible roving. The experiment revealed that the roving based factors considered did not have a significant effect on the mechanical properties of the laminates. However, the study showed that the fabric style/architecture and fiber volume fraction achieved using a particular reinforcement had a significant effect on the composite mechanical properties (Figure 1). Furthermore, the elimination of crimp and improvements in fiber alignment as found in resin pre-impregnated rovings can increase overall mechanical performance. A detailed description of these results was reported at a SAMPE Technical Conference in May 2011².

Using these findings, the next step was the experimental determination of mechanical properties of currently used non-crimp fabrics. As concluded from the database analysis, a set of composite laminates (uniaxial, biaxial and tri-axial) was produced and tested using the HYBON 2026 roving in commercially available non-crimp fabrics (same fiber orientation within a ply). These results were used as the lower limit considered acceptable for any new material. All laminates were produced with a standard epoxy resin (Momentive Epikote™ MGS L135/Epikure^TM MGS RIM H1366) via vacuum assisted resin transfer molding (VARTM).

The evaluation conducted on unidirectional laminates used a dry filament winding process. While not viable for the production of wind blade components, this process was used as an upper boundary for composite laminate performance because it allowed for higher fiber volume fractions² than those achieved with today’s non-crimp fabric technology. The performance result was expected to be representative of a composite laminate produced through automation.

Four independent epoxy prepreg producers were selected to manufacture the materials. After fabrication according to the laminate schedules, the laminates were laid on a flat tool using either an automated tape laying machine or a fiber placement machine (depending upon the material format requested by MAG) and were molded under vacuum at the recommended temperature defined by the prepreg producers (Figure 2). Table 2 summarizes the unidirectional (UD) material forms and laminate processes used in the study.  Tensile, compressive and fatigue properties were determined for these materials.

The tensile strength of the materials was segmented into three groups. The highest performing material was the dry wound laminate and was considered a “benchmark” because it is not a feasible wind blade manufacturing solution. The second group consisted of one UD towpreg, the UD slit tape, and the UD wide tape laminates. The third group, and lowest performers, consisted of the standard non-crimp fabric widely used for blade production and one UD towpreg material. The statistical comparison of the tensile strength by material form (Figure 3) indicated that modest improvements (0-13 percent, depending on specific material format) in tensile strength can be achieved with the prepreg/automation materials when compared to the standard non-crimp materials commonly used

The tensile modulus for the diverse material forms is shown in Figure 4. This analysis confirmed that the effect of laminate glass content, driven by the reinforcement format and manufacturing process, has a significant impact on the stiffness of the laminates. All of the UD prepreg/automation material inputs performed significantly better than the non-crimp fabric baseline and were statistically equivalent to the upper bound dry wound infusion laminates. This is a promising finding as it proves that by using automation techniques for laminate production and the state of the art reinforcements, significantly higher stiffness—up to 20 percent, in some cases—can be achieved. Therefore, longer blade lengths and improved energy generation capacity could be realized.

The compressive properties of a composite material greatly depend on the compressive performance of the resin system and fiber alignment. The compressive properties measured in most prepreg/automation materials were statistically equivalent to the standard fabric-based materials utilized in the industry. Similar trends to those observed in the UD laminates were observed with double bias laminates and do not merit additional discussion. The glass transition temperatures for the epoxy resin systems were found to be significantly higher than the infusion epoxy resin Tg.

Representative laminates of all material variants were subjected to tension-tension fatigue to determine the S-N fatigue curve using a servo hydraulic testing machine. The specimens were subjected to various levels of cyclic loading at a rate of 5 Hz with an R value of 0.1 until failure. Figure 5 shows the fatigue performance of the different materials compared to the current non-crimp technology (UD NCF infusion). While the performance of the dry wound infused laminates was not achieved, it was encouraging to note that both the Towpreg 1 laminate and slit tape laminate performed significantly better than the industry standard.

Predictive Modeling
To evaluate the impact of the composite laminates on wind blade performance, a full scale finite element blade model was developed. The model used a 33.25m long blade geometry imported from Numerical Manufacturing and Design (NuMAD) software, which was originally developed by Sandia National Laboratories into an finite element analysis (FEA) platform using ANSYS^® software. The model included detailed laminate and material information based on a composite shell element formulation for the prediction of stresses and deformations. The blade model specifications are outlined in Table 3 and Table 4 and are documented in detail in the National Renewable Energy Laboratory (NREL) report (NREL/SR-500-29492)³ and correspond to a three-blade wind turbine with rotor radius of 35m and tip speed ratio of 7 for a generation capacity of 1.5MW.

All pre-processing of the 3D FEA, model geometry creation (Figure 6), material designation (Figure 4 and Figure 5), meshing, and boundary condition definition was done using NuMAD software. The blade model wire frame geometry is shown in Figure 7.

For the model, the spar cap consisted of alternating layers of tri-axial (CDB340) and unidirectional fabrics (A260). The tri-axial fabric was composed of 50 percent ±45⁰ and 50 percent 0⁰ fibers. The spar cap mixture laminate had 70 percent unidirectional and 3 percent tri-axial fabrics by weight. Although changes were implemented to the spar cap, no changes were performed on the root or shear web sections from the NREL design. The material models described in Table 4 and Table 5 were assigned to the blade 3D model in NuMAD. The 3D model generated in NuMAD was analyzed in ANSYS using a composite shell element (SHELL281, Figure 8). SHELL281 is an eight-node structural shell with 6 degrees of freedom at each node (translations and rotations in X, Y, and Z axes).

Using the ANSYS GUI environment, a master node was defined at the tip of the blade and coupled to the blade tip edge nodes. A static load of 1,000 kg was applied at the master node, acting vertically downwards along the Y-axis of the model coordinate system, inducing flap-wise deformation to the blade. A dummy load was selected to characterize the stiffness of the blade and had no relation to the actual aero-elastic loads expected to be endured during blade service. The model was also used to calculate the weight of the different sections of the blade.

Using the baseline model, the material properties of the blade were replaced with state of the art properties from the UD prepreg using HYBON 2026 roving input and other E-glass offerings from PPG. The maximum displacement occurred at the blade tip in the flap wise direction. The weight of the new blade was calculated as 5237 kg, due to the increased fiber weight fraction of the unidirectional composite.

The focus of the modeling efforts shifted to the impact of the mechanical properties of the evaluated materials on blade weight and energy generation capacity.  For this purpose, the blade model was scaled to generate a 40m, 3MW blade. The experimentally determined mechanical properties from the analysis were used to design equivalent stiffness blades, using the highest performing automation materials. The total calculated blade weights from the FEA model and the blade lengths are summarized as follows: 

Case 1: The spar cap of the blade is produced with UD prepreg while keeping the remaining blade materials constant. The blade can be made 4 percent lighter while maintaining the stiffness of the baseline 40m blade.
Case 2: The complete blade is made by prepreg/automation using automated fiber placement. The blade has a 5 percent weight savings compared to the baseline due to the increased stiffness provided by the pre-impregnated materials.
Case 3: The blade is produced with pre-impregnated rovings using automated fiber placement but the blade length is increased without increasing tip deflection. The resulting blade is heavier, but energy generation capacity was increased by approximately 6 percent.
Case 4: The spar cap is made using automation but the blade length was increased to match the stiffness of the baseline. The blade length increased to 40.8m and resulted in an energy generation capacity increase of approximately 4 percent.

Conclusion
Materials suitable for automation were evaluated and composite laminates made using those materials demonstrated significant improvements in laminate strength, stiffness and fatigue life as compared to existing materials. The automated fiber placement process was found to be a technically feasible alternative to resin infusion to produce equivalent or higher performing composites.  The potential for higher strength, stiffness and durability compared to current materials used for the production of blades was shown. 

The materials designated as Towpreg 1 and slit tape processed via automated fiber placement resulted in increased performance and are recommended as technology capable or that requiring minor development for further evaluation.  A manufacturing trial on a scaled wind blade component is recommended at this point as these materials have proven capable of increased mechanical properties against the benchmark materials and were found to be amenable to automated processing.  

Disclaimer: This study was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Acknowledgment:
This material is based upon work supported by the Department of Energy under Award Number DE-EE0001372. 

References:
1) Watson, J.C., and J.C. Serrano. “Composite Materials for Wind Blades.” Wind Systems. September 2010: 46-51.
2) Serrano, J. C., J. Watson, S. Vennam. “Performance Drivers on Glass Fiber Composites for Wind Blades.” International SAMPE Technical Conference (2011) p. 14.
3) WindPACT Turbine Design Scaling Studies Technical Area 1. Composite Blades for 80- to 120-Meter Rotor, NREL/SR-500-29492, April 2002.

A few years ago a major operator signed a deal to operate wind farms at several locations over a multi-year period. The farms would then be turned over to a local authority once the initial service period ended. Near the end of the operator’s service period, it was determined that all of the maintenance plans and procedures would need to be conveyed to the local authorities.

The only problem was, there was no maintenance plan in place and no procedures had been documented. All that existed were piles of repair tickets that listed the scheduled and unscheduled work that had been done over the past several years—that and the combined knowledge of the maintenance staff, which was filed in the 8” space between their ears. With some outside help, the operator was able to analyze the repair tickets and build the required documentation needed to complete their contractual requirements. 

A better approach would have been to develop and implement operational strategies from the beginning that mitigate (or eliminate) the effects of unplanned maintenance events. Achieving the correct balance of scheduled and unscheduled maintenance is an ongoing quest that evolves as equipment wears and economic conditions merit. Organizing technical information (typically procedures and schematics) in a way that is easy for the field technician to comprehend and utilize—regardless of the specific machinery being maintained—is critical to the success of the operation. 
In this article we will walk through the high-level basics of defining a maintenance program and see how the operator used this approach to meet their needs.  We will discuss how to:

• Organize your procedural information in a universal manner;
• Incorporate simplified English in technical documentation;
• Understand organizational objectives and determine the correct balance between scheduled and unscheduled maintenance;
• Manage spares inventory while increasing your part availability, and;
• Implement technology that allows maintainers to work more efficiently.

Organization
The first step is to determine how your technical data will be organized so you can find the information you need efficiently. Unfortunately, there are no universally adopted standards as to how technical information is organized in the wind power industry. Instead of reinventing the wheel, the operator in our story structured their technical information similar to what is used by the commercial air transport industry (Kinnison, 2004). The information is laid out so that the top-level assembly (tower platform) is divided into major components (tower, nacelle, electrical systems, etc.), and these components are divided into subassemblies. For example, the gearbox cooler is  a component of the nacelle. Subassemblies can be further divided into components (gearbox fan, gearbox motor, gearbox radiator, etc.). The process is repeated until the lowest repairable unit is reached. At that level, the specific information can be provided that is applicable to that unit. These may include description information, inspection tasks, repair tasks, and servicing tasks. Figure 1

The organization of information is relevant for any tower platform, regardless of the manufacturer or design. This allows the maintenance staff to locate the correct information quickly regardless of the manufacturer, and enables the staff responsible for updating technical information to know exactly where the revised information belongs.

Keep It Simple
Once the information is organized, it needs to be written in a manner that makes it easy to use and maintain. Simplified Technical English (STE) is one approach that helps improve the readability and portability of your information.

The objective of Simplified Technical English (STE) is clear, unambiguous writing. Developed primarily for non-native English speakers, it is also known to improve the readability of maintenance text for native speakers. STE does not attempt to define English grammar or prescribe correct English.

This type of writing standard is also known as a controlled language because it restricts grammar, style, and vocabulary to a subset of the English language. The main characteristics of the STE standard are: simplified grammar and style rules; a limited set of approved vocabulary with one word having only one meaning; a thesaurus of frequently used terms, technical nouns, verbs, and suggested alternatives, and; guidelines for adding new technical words to the approved vocabulary.

STE attempts to limit the range of English, and many of its rules are recommendations found in technical writing textbooks. For example, STE requires writers to use the active voice, use articles wherever possible, use simple verb tenses, use language consistently, avoid lengthy compound words, and use relatively short sentences. Companies in several industries—manufacturing, mining, oil exploration and software development, for example—have produced their own controlled-language writing standards (Works, 2005). Here is an example, with the “original” text: Place the water heater in a clean, dry location as near as practical to the area of greatest heated water demand. Long un-insulated hot water lines can waste energy and water. Clearance for accessibility to permit inspection and servicing such as removing heating elements or checking controls must be provided.

And the same content in STE: Put the water heater in a clean, dry location near the area where you use the most hot water. If the hot water lines are long and are not insulated, you will use too much energy and water. For inspection and servicing, make sure that you have access to the heating elements and controls. Figure 2

Besides readability, STE offers a business advantage when creating documentation that will be translated into a number of languages. As the text volume is typically reduced by at least 20 percent and the remaining text becomes more repetitive, the use of STE normally results in 30-40 percent less translation cost. In addition, STE will reduce the number of unique terms and improve translation quality and consistency. The graph shows typical results of rewriting standard English into STE (Wijma, 2012).

Text in STE is easier to understand and may not even require translation. Where translation is needed, STE helps to drastically reduce translation cost and time-to-market, as it effectively eliminates redundant words and improves consistency. With the ever-increasing number of languages that companies need to deal with, these savings add up quickly. Content is easier to validate, technical writers will be more productive, and fewer iterations and less rework will be required.

Striking a Balance
There are some industries where unscheduled maintenance is associated with catastrophes. Air travel is one. There is no road shoulder at 30,000 feet. Nuclear power is another. Thankfully we are not in the brokerage operations market, where the cost of downtime is reported to be $107,500 per minute (Marquis, 2006). For the wind power industry, unscheduled maintenance is a bad event, but it’s also something that can be managed.

Scheduled maintenance, while allowing the operator to avert part failure, almost always results in premature part replacement. Unscheduled maintenance results in parts being replaced only once full part life has been utilized. Unplanned failures are a problem not because of the repair costs, but because of the downstream effect of loss of energy production. This makes it difficult to arrive at a cost estimate that is both accurate and believable. Figure 3

Applying industrial engineering concepts allows the operator to evaluate items such as costs and likelihood of downtime, and the cost of purchasing parts with higher reliability or having spare sub-assemblies available (which have a cost on the shelf). In some cases an operator will have a database of thousands of repairs that can be analyzed to prevent future failures before they occur through planned maintenance and condition based maintenance programs. These programs are designed to preserve and restore equipment reliability by replacing worn components before they fail. Preventive maintenance activities include partial or complete overhauls at specified periods, oil changes, lubrication and so on. In addition, workers can record equipment deterioration so they know to replace or repair worn parts before they cause system failure.

Spare Parts
The inventory of maintenance items includes all the replacement parts for machines, for tools, and for company-supplied finite-lived employee equipment such as safety glasses. This category excludes items used in manufacturing, such as washers or bolts, and this category includes consumable items for cleaning or safety, such as solvents. Maintenance storeroom management has three major goals:

• To have the item that is needed;
• To supply that item when needed, and;
• To control the overall cost of keeping items in stock.

As an example, suppose that an oil pump is typically replaced twice a year, but only when it “fails,” rather than on a pre-emptive maintenance schedule. That tower’s production will stop until the pump is replaced. If it is out of stock, there will be a significant delay in returning the tower to production. If a replacement pump is listed in the inventory, but misplaced, there is still a delay. Now suppose the response to this scenario is that a dozen pumps are purchased, with some stored near the machine and more in the storeroom. That expense represents a six-year supply. If we assume some of those pumps will be misplaced in the ensuing years, part of this investment still represents a loss of production time at best, and inventory cost if the missing pumps are never found.

One key recommendation is to consider a computerized inventory management system for the maintenance supplies. This should integrate the purchasing, storage, and stock-release functions so the system tracks pending orders, expense authorizations, where items are stored, and to whom the items are released. For scheduled maintenance, the demand for repair parts will be known in advance. Ensure that the storeroom workers are given sufficient notice of the maintenance schedule so they may pick the items and prepare maintenance “shopping carts” for each tower. This streamlines the workload for the storeroom staff, and it leads to fewer errors (Olofsson, 2011).

Implementing Technology
Perhaps the hardest part of a maintenance program is knowing when to invest in your maintenance staff through training and when to invest in tools through technology. Most organizations realize that training is required when implementing new concepts. What few organizations do well is monitor mistakes in order to better understand when training would have improved the efficiency of the maintenance staff. If similar mistakes are being repeated across the staff, training classes can reinforce best practices or clarify information.

This is an area where technology can help training. Some electronic technical manuals have a functionality that allows end users to add their comments about technical information, typically a task or procedure. In many cases the task can be improved by leveraging the knowledge of the people doing the task in a field environment, and this functionality allows that feedback. But in some cases the added suggestion is not what the person who originally developed the task had in mind. For instance, an employee suggested using a broomstick to rotate a very delicate compressor assembly to assist in the inspection. In reality, the broomstick could introduce nicks and dents to the compressor blades. There were two results of this well-meaning feedback: a warning was added to not use foreign objects (like a broomstick) to rotate the compressor; and a training session was conducted to alert the maintenance staff as to why this was not an approved maintenance method.

As a side note, the employee who made the suggestion was actually rewarded with a gift certificate for making the suggestion. Not because it was a good idea; it wasn’t. But because he was using the system to leverage his experience.

One way to get the most from your training budget is to record videos of processes that warrant it. This is likely to be the case when it is difficult to do the process correctly, or it is a common to many processes. Just as some electronic technical manuals have a “knowledge manager” that allows for field feedback, there is also the capability to embed training videos and 3D model browsers into technical documentation. Try getting a piece of paper to play a video.

While most maintenance staff will attempt to memorize procedures because of repetition or convenience, it’s difficult to memorize all the part numbers associated with scheduled maintenance tasks, and impossible for unscheduled maintenance tasks. This is what makes the Illustrated Parts Catalog (IPC) a critical piece of technical information. But even with an updated IPC, identification and ordering of spare parts can be a trouble spot. Maintenance is often delayed when the wrong parts are ordered because part numbers are identified or entered incorrectly. Use of an electronic parts catalog provides a point-and-click functionality where part numbers are automatically inserted into a shopping cart. Implementers of this technology report that creating a parts list via an electronic shopping cart is 35 percent faster than manual entry into a form, and ordering errors are reduced by more than 20 percent.

Summary
While some organizations look at their documentation as a “necessary evil” at best, in reality it can be the foundation of an efficient maintenance program that maximizes uptime and reliability and can strengthen the organization. By implementing a consistent organization and structure to your technical information, managers provide your staff a head start in finding the information they need consistently, regardless of the equipment being maintained. Implementing STE allows even the most inexperienced maintainer to more easily comprehend complex task. Building a maintenance plan that factors scheduled and unscheduled maintenance with organizational needs can save money by avoiding unnecessary maintenance. Determining which spare parts to stock—and where they should be stored—will help make parts inventory lean and efficient. Likewise, knowing when and how to leverage technology will keep a workforce on the cutting edge without being gashed by not having the information foundation in place.

And what about the operator with the eleventh-hour requirement for maintenance plans and procedures? They were delivered on time, with the information well organized and unambiguous.  

Traditional design and verification procedures in developing a new product or improving upon existing technology can be time consuming, costly, and in some cases physically impractical or risky in the field. Typically, many disciplines will be involved in the iteration loop from concept to product launch and the number of prototype and test iterations can become staggering. The application of advanced computer simulation techniques—“virtual simulation” or “virtual testing”—can help shorten the process (and enable verification and evaluation of designs at an early stage when all options are open), reduce a need for prototyping, troubleshoot for root causes when components fail and, ultimately, optimize a system’s overall performance and reliability.

Challenge: A major wind turbine manufacturer was in the process of designing a large turbine with an objective to sustain a 20-year lifecycle. The design team additionally sought documentation that the mainshaft bearing and housing arrangement would fulfill requirements of international certification bodies active in the wind industry.

Solution: Enlisting extensive experience in bearing system structural fatigue analysis and applying proprietary virtual simulation technology with the capability to evaluate the dynamic behavior of rolling bearings, SKF engineering consultants conducted a highly accurate analysis of the turbine housing, including bearing and mainframe interaction. Detailed results enabled engineers to assess the design from a system fatigue perspective and generate valuable input for future design improvements without the need to develop a prototype (or wait for 20 years to ascertain actual lifecycle performance of the turbine). Figure 1

Results: Analysis confirmed the main bearing housing design would meet extreme load and fatigue-load conditions and that the design would not lead to premature bearing failure over the required 20-year service life. Supporting documentation was compiled to apply for formal international certification of the design.

Simulating Dynamic Behavior
Rolling element bearings are a bridge between rotating and static parts and often are a key element for the behavior of the complete application. They consist of an inner ring, outer ring, and a set of rolling elements (balls or rollers). Most rolling bearings also have a cage (or cages) and a few types feature a guide ring. Most commercial simulation tools offer a bearing “representation,” usually sidelining the cage or describing in simplified models.

The dynamic phenomena that occur in rolling bearings require specialized simulation tools for evaluation. SKF has been developing simulation tools to analyze bearing and bearing systems for more than 40 years. The first tools focused on an accurate representation of a bearing by itself and were greatly limited by the computational power available.

Today’s tools allow for the accurate representation of not only the bearing, but of the complete system such as a gearbox. The SKF tool, called BEAST (for Bearing Simulation Tool), simulates the behavior of complete bearing, including cages, using a fully three-dimensional, specialized tribological contact model (which also accounts for the effects of small-scale geometric variations, such as surface roughness).

This simulation program additionally builds upon or otherwise augments commercial CADS/FEA/CFD systems enabling importing and exporting of system information that may or may not be required for an accurate description of the bearing dynamics. SKF BEAST utilizes fully transient models (generating results over a time domain), compensating for flexibility in bearing geometry (for accurate bearing load calculations), and accommodating all bearing types to develop accurate and detailed bearing models (with geometry based on exact manufacturing data).

Unleashing the BEAST
BEAST is based on multi-body techniques and with special focus on contact problems. It allows for studies of dynamic behavior of all bearing components to be carried out under general loading conditions. This includes the forces on (and motions of) the cage, skew, and tilt behavior of rollers and the skidding of balls.

Principal output data from BEAST relates to the movements of all bearing components, the contact forces between the components, and the forces with the environment. Additionally, detailed data from the contacts are produced (for example, power loss, lubricant film thickness, pressure distribution, slip-speed distribution, and wear). Figure 2

The output data can be studied in several ways. Animation of bearing components can serve as a good visual starting point (and motions can be magnified for more clarity). Force or velocity vectors can be added to the animation. Some parameters, such as contact pressure or slip velocities, can be displayed as three-dimensional images on the bodies or on parametric surfaces. All output data can be reviewed in more detail using graphical formats.

The integration of Design for Six Sigma (DfSS) into the modeling process introduces a framework for optimized evaluation of selected bearing arrangements. Utilizing the DfSS process enables a structured approach and toolbox to identify critical to performance operating parameters.

The performance of bearings will be influenced by many different system design and operating parameters. Some can be controlled during operation, while others cannot but may have a significant impact on system performance. One example of combining virtual simulation and DfSS is to generate a virtual design of experiments (DoE). Through a statistical analysis of DoE results, the robustness of a bearing system can be ascertained along with the influences that design parameters exert on performance. Figure 3

In a design of experiments, different calculation runs will be made to rank the parameters in terms of their influence on the bearing’s performance. The model allows many more parameters to be analyzed independently compared with physical assembly and testing. This type of analysis can help optimize system settings to increase robustness and reduce performance variability.

Such models can help designers narrow their choices and evaluate the various options early in the design process or beyond. Designers can strategically factor in different parameters and tolerances to understand how they will impact overall performance without use of a prototype or physical testing. As a particular example, friction and thermal models can provide an accurate temperature prediction that can help in determining bearing life and clearance, lubrication intervals and conditions, and proper lubricant selection, among other purposes.

Final Note
While virtual simulation and testing cannot necessarily replace all physical testing and prototyping, technologies offer a practical methodology to investigate parameters and test conditions too difficult to achieve otherwise. Along the way, the number of iterations on the road to a viable design can be reduced significantly. In the near future, advances in computers and simulation technology can be expected to increase capabilities and provide designers with even keener insights into how bearings and systems can (and should) perform. 

The wind industry has experienced a rapid expansion. As wind farms are aging, their operations and maintenance issues are gaining in significance. The wind industry has been affected by failures of wind turbine components such as main bearings, gearboxes, and generators. Replacement of failed components results in the high cost in energy production. Therefore, research in fault identification and condition monitoring is warranted. In this study, detecting wind turbine gearbox faults based on vibration acceleration data provided by the National Renewable Energy Laboratory (NREL) has been investigated. Data mining methods [1, 2] are applied to identify the faults in the time domain.

NREL Gearbox Test Facility
The data used in this research originate from a damaged gearbox of a test wind turbine. The gearbox was retested at the Dynamometer Test Facility (DTF) at NREL. To retest the gearbox, the complete nacelle, and the drive train of the test wind turbine were installed at the DTF. The nacelle was hard fixed to the floor without hub, rotor, and yaw bearing. Figure 1 shows the diagram of DTF.

The gearbox included three stages: low-speed stage (LSST), intermediate-speed stage (ISST), and high-speed stage (HSST). It was instrumented with over 125 sensors. Figure 2 shows the side view of the gearbox. As shown in Figure 2, the LSS is connected to the rotor and the HSS is connected to the generator.

To investigate the root cause of the gearbox damage and conduct the fault identification analysis, vibration data needed to be collected. Therefore, 12 accelerometers were mounted on the outside of the gearbox, generator, and main bearing to measure the vibration acceleration. Vibration data measured by all 12 accelerometers were collected at 40 kHz using a high-speed data acquisition system. Besides the vibration data, the corresponding torque of the low-speed shaft and the generator speed were recorded. The direction of the drive train vibration acceleration is described as a three-dimensional coordinate system and sensed by accelerometers. The origin of the coordinate system is the intersection of the planet carrier rotation axis and the plane cutting the torque arm cylinder in half along their length. The x-axis describes the system acceleration along the main shaft axis and the downwind side, and the y-axis represents the vibration acceleration direction, which is horizontally perpendicular to the x-axis. The z-axis is orthogonal to the x- and y-axes. Figure 3 illustrates the coordinate system of the vibration acceleration. Although the vibration acceleration of the system is depicted by a three-dimensional coordinate system, the mounted accelerometers can only sense one or two directions of acceleration. Table 1 presents the locations of the accelerometers, the measured directions of vibration acceleration and the units of the recorded data. Figure 4 illustrates the locations of 12 accelerometers.

Three test cases are conducted by NREL. In Case 1 the nominal speed of the high-speed shaft is set to 1800 rpm and the electricity power is set to 25 percent of the rated power. In Case 2 the nominal speed of the high-speed shaft is the same as in Case 1, but the electricity power is set to 50 percent of the rated power. This indicates that the torque in Case 2 is twice the amount of torque in Case 1. In Case 3 the generator speed is 1200 rpm and the torque is at 25 percent. The test length of all cases is the same, 10 min.

Data Processing
To analyze the gearbox vibration in the time domain, jerk is utilized. Jerk describes the rate of acceleration change, and it is often used to indicate the excitement of vibration. For the high-frequency vibration acceleration data in Section 2, the jerk is approximated in (1).

where J is jerk, a is acceleration, t is the time index, and T represents the sampling interval. 

Since the sampling frequency is high (i.e., 40 kHz), the number of data points within 10 min length is large. Therefore, vibration, the high-frequency jerk data (40 kHz), is then converted into much lower-frequency data (1/15 Hz) by computing the mean of jerk at 15-s intervals. The standard deviation and the maximum value of the jerk data in each 15-s interval are also computed.

Fault Identification Methodology
In this section, clustering analysis [1] is utilized to investigate the failed components in the gearbox. Clustering analysis is an unsupervised method of data analysis. Clustering algorithms group observations into clusters by evaluating similarities among the observed data. The component failure can be identified by examining the pattern similarity of the jerk data measured by accelerometers mounted at different locations of the drivetrain.

The clustering analysis aims at grouping data from 12 sensors using the jerk data. The time series of the jerk described in the previous section are utilized in the clustering analysis. The k-means algorithm [3] is modified in this study to establish clusters. In the original version of k-means algorithm, the number of clusters, k, should be arbitrarily set by the analyst. In this study, a clustering cost function is introduced to evaluate the cluster quality with k.

The results of clustering analysis for Cases 1 and 2 are the same and illustrated by Figure 5. As shown there, the 12 accelerometers are classified to three clusters according to the modified k-means algorithm. In Cluster 1, most of the sensors sense the vibration acceleration of the gearbox low-speed stage. Cluster 2 contains data from two sensors that monitor the acceleration of the main bearing. Sensors that measure the vibration acceleration in the intermediate- and high-speed stage make Cluster 3. To further analyze the data in the three clusters, the Euclidean distance between the centroids of clusters is calculated. The shorter the distance, the more similar the two clusters are. Figure 6 demonstrates the cluster distances for Cases 1 and 2, respectively.

Since the gearbox test experiment was conducted to examine the failure components of the gearbox, the vibration of the main bearing was considered as normal in this research. In Case 1 of Figure 6, the distance between the centroids of Cluster 1 and Cluster 2 is 2.31 while the distance between the centroids of Cluster 3 and Cluster 2 is 5.72. The Case 2 demonstrated in Figure 6 presents a similar result. Based on the results in Figure 6, the components sensed by the accelerometers in Cluster 3 are considered to be primarily failed because the distance between Cluster 1 and Cluster 2 is small. Some components sensed by the sensors in Cluster 1 are also considered as failed since the vibration data from the two sensors installed for monitoring the same stage belong to two different clusters.

Conclusion
In this article vibration acceleration data of an impaired wind turbine gearbox provided by NREL were analyzed to identify the faulty stage of the gearbox. In the analysis the vibration acceleration data were transformed to the change rate of vibration acceleration. The correlation coefficient analysis and modified k-means clustering approach were introduced to identify the faulty stage of the gearbox. The suspected faulty stages of the gearbox were proved after the inspection of the gearbox by disassembling. 

References:
1) A. Kusiak and A. Verma, A Data-Mining Approach to Monitoring Wind Turbines, IEEE Transactions on Sustainable Energy, Vol. 3, No. 1, 2012, pp. 150-157.
2) A. Kusiak and A. Verma, Prediction of Status Patterns of Wind Turbines: A Data-Mining Approach, ASME Journal of Solar Energy Engineering, Vol. 133, No. 1,  2011, pp. 011008-1 – 011008-10.
3) P.N. Tan, M. Steinbach and V. Kumar, Introduction to Data Mining, Boston, MA: Addison Wesley, 2006.

With some 60,000 of its wind turbine pitch and yaw systems installed worldwide, the Brevini Group is no stranger to wind power. Yet today the stakes, and opportunities, have never been greater. With the establishment of its Brevini Wind division—and a $90-million, 100,000 square-foot, ultramodern factory in Yorktown, Indiana—Brevini has entered the main wind turbine gearbox business in a big way. It’s expected that as many as 40,000 new wind turbines could be deployed in North America by 2015, and many will be equipped with a new generation of lighter, more-efficient, and highly reliable Brevini main gearboxes ranging in size from 0.9 to 3.5MW capacity. So when Brevini Wind USA Director of Facility Operations Dale Harder learned that a Gleason 3000GMM analytical gear inspection system was going into the new factory’s QC room, he couldn’t have been more pleased. Figure 1

“Many of us have had experience in the past with M&M Precision, which ultimately became Gleason Metrology Systems, so the brand is highly respected,” he says. “We have established very ambitious quality and throughput objectives for the large internal ring gears and sun and planetary gears we’re producing here for these new gearboxes, so you can imagine the very important role gear inspection is playing.”

Quality is Critical
A critical driver of gear quality standards at Brevini is of course the need for exceptional gearbox reliability. Wind turbine installations are often in inaccessible areas and operating in adverse conditions that make repair and maintenance both difficult and expensive. Increasingly important is the need for quiet-running wind turbines, particularly for wind towers in close proximity to populated areas. Despite their size (Brevini internal ring gears are as large as 2.2 meters in diameter with 400 mm face widths and weigh upwards of 3,000+ kg), part prints call for Brevini gears to be made to ISO Grade 6 or better, all with surface finishes to Rz 3 μm. Mr. Harder says his two new Gleason P 1600 and P 2400 Hobbers and two P 1600 G and P 2400 G Profile Grinders are easily achieving these levels, and better. The challenge, he says, is ensuring that inspection keeps up with production. “We’re keen on demonstrating, both internally and to our customers, that our new processes can achieve the highest quality levels, which puts the burden on our gear inspection system,” says Mr. Harder. “That’s what we really like about the new 3000GMM. If you can read a part print, you’re practically ready to set up the part and run the machine. It’s that fast and easy.”

A Stirring Experience
For example, Harder says that the initial “stirring in” of the part during setup is traditionally one of the most time-consuming stages of the large gear inspection process. In the case of a two or three ton internal ring gear this can consume a considerable amount of time, with several people delicately lower the part onto the worktable and work to manually “true it up”—a painstaking process of moving part datums incrementally until they’re zeroed in precisely to a pre-established starting point. But the 3000GMM eliminates much of this setup time with its “journal reference” software. This allows the operator to simply position the part anywhere to within 10 mm of the desired location—something most operators can “eyeball”—and then the journal reference software takes it from there. It automatically probes to determine the actual location of a datum such as the OD, takes a radial and axial measurement, and corrects for the new zero location so that no additional stirring in time is required. Harder says it’s just one of the many features available to his operators through the system’s extremely friendly user interface called GAMA, a software suite designed to greatly simplify the inspection process. It’s particularly easy to learn and use, with a highly intuitive Windows-based graphical user interface and a host of features including help menus, language translation, multiple security levels, and even online support. Several other important features stand out as well, including:

• A solid granite base, providing considerably more stability for, say, a 3,000+ kg gear than competitive models with cast-iron bases. Its Meehanite® cast iron slide assemblies provide vastly better damping characteristics as well.
• The use of the Renishaw® SP80H probe, which is an advanced 3D scanning probe that’s light years ahead of older model scanning probes. It acquires data faster and more accurately on even the most complex gear tooth profiles and features industry leading probe axis travels—X axis is plus or minus 1.5 mm; Y and Z axes are plus or minus 2.5 mm—with each axis driven on 20 nanometer resolution glass scales for exceptional measuring accuracies.
   
Finally, Gleason’s localized service and support network has been instrumental in the successful startup of the new technology. Gleason Metrology Systems, based in Dayton, Ohio, is in relatively close proximity to the Brevini plant and has provided onsite technical expertise and application support throughout the installation and launch period. Figure 2

“The 3000GMM is the perfect complement to the highly productive Gleason machines,” Harder explains. “Those of us employed here with Brevini Wind clearly realize what a unique opportunity we have been presented with. We are very fortunate to work for a company that is willing to make the significant investments necessary to provide us with such tremendous gear manufacturing and inspection capabilities. Figure 3

“Additionally, we are also very fortunate that Gleason has proven itself to be a very dependable partner in our startup efforts by providing us with the necessary training and applications assistance that allows us to utilize these latest technologies in the most proficient ways,” he says. “The most demanding of our gear manufacturing applications have been easily accommodated although the level of experience amongst our workforce with large gear manufacturing in the beginning was quite minimal.

“Our manufacturing team is extremely pleased with the simplicity of setting up and operating all of the Gleason equipment,” Harder says. “I don’t know how Gleason could have made this any better for our particular situation.” Figure 4

Gains in Spain
It might surprise you to learn that Spain is the world’s fourth biggest producer of wind energy, right after the United States, Germany, and China, with an installed capacity of 19,959MW at the end of 2010. And the number of wind turbine installations in Spain is expected to rise. For companies like special gear and gear reducer manufacturer Talleres Guibe, situated in the heart of northern Spain’s industrial region of Irura, Guipuzcoa, that’s good news.

But according to company officials, the enormous productivity and quality gains made possible with new Gleason grinder installations were being limited by the deficiencies found in the company’s large gear inspection system. This older system was suddenly rendered almost completely obsolete, since its measurement capabilities were far below the exceptional accuracy levels achievable on the new Gleason machines. Furthermore, spare parts and service for the old system were almost nonexistent. As a result, large gear inspection would now have to be performed elsewhere, adding to cost and delivery time; neither of which was acceptable to Talleres Guibe or its customers. Figure 5

No wonder Talleres Guibe is so excited about their new Gleason 2000GMS analytical gear inspection system. With a 2-meter workpiece diameter capacity, the new 2000GMS can handle almost any gear produced at Talleres Guibe. Better yet, it performs the complete inspection of today’s increasingly complex gear geometries up to 25 percent faster, while meeting VDI/VDE Class 1 specifications.

Powered by GAMA
Equipped with a new and improved GAMA 2.0 applications suite of software, the GMS series is unquestionably the easiest and most intuitive system of its kind to operate, empowering even less experienced operators with the ability to inspect any gear faster and more efficiently. GAMA 2.0 puts a host of powerful new features right at the fingertips of the operator, creating a simple and intuitive human/machine interface to improve their performance. Figure 6

For example, the process of creating a new program is as easy as point and click, and it can be done in just minutes in a few easy steps, and regardless of the operator’s level of experience or the gear or gear cutting tool type. This even includes an “unknown” gear, where parameters aren’t defined and even a drawing might not exist. The operator simply selects from a list of typical machine configurations, enters a part number, and clicks the “create” button. Once the necessary fields are filled out with pertinent gear data, special tests required for highly modified gear profiles and geometry, and the type of analysis required, GAMA 2.0 does the rest. It draws from a suite of applications software supporting the complete topographical inspection and prismatic measurement of any rotationally symmetrical workpiece, including cylindrical, bevel, conical and cycloid gears, shaper and shaving cutters, hobs, bevel blades, rotors, etc., and the programming process is complete. In addition, the human/machine interface has been further enhanced on the new GMS series with a newly-designed operator work station, which puts the operator in a better position to quickly, easily, and more comfortably perform tasks.

Also available is a unique handheld remote pendant workstation that allows the operator to be productive anywhere and is also ideal for large gears and particularly complex part setups. This remote pendant control comes complete with video telephony support, Internet connection, touchscreen input, and a host of other important features. 

The national unemployment rate is currently at 8.3 percent. The unemployment rate has been at or above 8.8 percent for the past 28 months. The underemployment rate has remained between 15.7 and 17.4 percent since the spring of 2009, and it currently stands at 16.1 percent. Additionally, the current skilled workforce is losing its qualified and experienced workers. On average 10,000 senior, experienced, knowledgeable, qualified workers will turn 65 years of age every day for the next 20 years, and as the 73 million folks leave the marketplace so goes their skills, talents, knowledge, and inherent trade techniques. With these kinds of numbers who would ever have thought that there was a very large unmet demand for skilled labor, or that the need for skilled labor would be in a niche marker sector like wind energy?

Since the end of World War II there has been an appreciating decline in skilled workers. This decline has grown immensely as the American economic engine has revved up. The Baby Boomers numbering in the ballpark of 73 million folks were the largest contributor to the skilled labor pool, but not large enough to meet the demands in the industry. The following generations of “X” and emerging generation of “Y” have not met the demand of the industry to date.

The Baby Boomers
By definition, a Baby Boomer is someone who was born between the years 1946 and 1964. As of right now Boomers are between the ages of 44 and 62. The Boomer generations are the folks who built and motivated the American economy for the last 60 years. Their social, cultural, and economic impact on the United States has been unprecedented in its history and is currently the single largest economic group in the United States today. The Boomers’ “work hard, play hard” mentality allowed them to have one of the highest discretionary income levels than any other age group, and it accounts for 45 percent of all consumer demand. As these Boomers retire and leave the workforce, the demands that they place on the goods and services producers and service providers will create some challenges as there are fewer folks to produce and service the retiring boomer society.

However, the Boomers have not saved very effectively for retirement, and some may be retiring early or moving into a less demanding working pattern, working less rigid jobs, playing golf on weekends, and dining at leisure all while still possessing their skills, talents, knowledge, and inherent trade techniques from a lifetime of hard work and no one to pass these skillsets on to. The exit of the Baby Boomer generation compounds an already looming crisis with the lack of qualified and skilled workers that has existed over the last 30 years. Skill levels in the U.S. workforce have stagnated, with Americans 25-34 years of age who do not possess the higher skills that their Baby Boomer parents do.

Generation X
The 46 million “X Generation” of sons and daughters of the Boomers did not wholly move into the skilled trade sectors, but instead went to college, sought professional degrees, jobs, and technical assignments, overall making much less income than their Boomer parents. They are officially the first generation to challenge the notion that that each generation will be better off than the one that preceded it. The study “Economic Mobility: Is the American Dream Alive and Well?” focuses on the income of males 30-39 in 2004 (those born April, 1964 – March, 1974) and is based on Census/BLS CPS March supplement data. The study, which was released on May 25, 2007, emphasized that in real dollars this generation’s men made less (by 12 percent) than their fathers had at that same age in 1974, thus reversing a historical trend. The study also suggests that per-year increases in the portion of father/son family household income generated by fathers/sons have slowed (from an average of 0.9 to 0.3 percent), barely keeping pace with inflation, though increases in overall father/son family household income are progressively higher each year because more women are entering the workplace, contributing to family household income.

In the next five years the X generation will make up the largest majority of the workforce in America, replacing the roughly 20 million skilled Boomers with only a third of the skilled workforce required to support the demands for goods and services. The balance of the X generation will continue to work in the professional services sector.

Generation Y
The roughly 80 million “Y Generation” folks entering the workforce today are the most technologically diverse generation in American history, but they barely make the global top 10 of educated and trainable workers. America is no longer a skill-abundant country compared with an increasing share of the rest of the world. As a result, in the coming decade America will face broad and substantial skill shortages.

The Y generation prefers to work independently with self-directed projects, responding to learning that provides interaction with their colleagues. They prefer more structure, direction, and social interaction. This generation is polite, believes in manners, adheres to strict moral code, and believes in civic action, but it also places a high value on making money—more than any other previous generation—and they see education as a means to this goal. Like the X generation before them, they seek professional careers. Studies predict that Generation Y will switch jobs frequently and will not have the passion for “the company” that older and more career established employees do. With the global booming numbers of Y generational workers added to the employment pool, economic prospects for the Y generation look bleak due to the late 2000 recession and a youth unemployment rate in the U.S. reaching a record level of close to 20 percent at the end of 2010.

As the Boomers exit, the X generation tries to fill the gap while the Y generation is looking to find a professional work environment. The question arises; Who is going physically move this country forward in the next 10-20 years?

Renewables and Labor
The resurgence of renewable energy installations possesses the potential to be a very large source of job creation. This virtually renewed industry demands highly skilled electrical and mechanical construction workers, heavy machinery operators, and professionals with a wide range of skills from chemistry, engineering, and physics to design, build, install, and maintain the infrastructure at these sites.

Since “skilled and qualified” workers of renewable infrastructure did not exist in any great numbers, the labor was pulled from the general skilled trades and the declining energy sectors to construct and maintain these sites. Because wind farms require permanent employees to maintain and operate them, wind energy produces jobs at different levels, in operation as well as in wind turbine component manufacturing and construction. These jobs, unlike other high-paying jobs in technology-based industries, are widely available in rural areas where wind farms are located.

These new jobs will require the personnel to interact with the equipment, either as a direct employee or a contractor and the ever-increasing regulatory component of the U.S. government is placing critical demands for protecting workers in the renewable energy sector, hence the ability to learn, adapt, and understand jobsite hazards is a must.

Human Resources
Unskilled native-born Americans do tend to compete with unskilled workers in the jobs marketplace, but the skilled workforce is still a challenge that has yet to be met for the growing immigrant labor pool.

The Y generation moving into the workforce may not be as motivated to take skilled labor, or “hands-on” jobs, due to their ability to easily seek education beyond high school and pursue professional careers where their income levels will be same as their X generation counterparts. It remains to be seen where this generation will end up, but whatever the outcome working long distances from home in remote isolated areas with limited communications and long workdays far away from social circles may create a challenge in retaining these folks. Since much of these renewable resources are constructed and installed in very rural areas many workers are leaving the ranch and farm to work in the industry. Many are pursuing educational opportunities from community colleges and universities that are developing renewable energy programs that offer a general education in wind, solar, and biomass engineering and maintenance technologies.

As with any resource, skilled labor will be in higher demand, which in turn will drive wages higher and demands for repairs, testing, and power generation equipment maintenance will push the skilled worker from employment with the renewable sites directly to contractors and suppliers. As these wages increase, so will labor rates for the services offered by electrical installers and repairmen. Eventually the annual incomes of skilled workers will match or outpace those of the professional worker.

If we want to build a skilled workforce in sufficient numbers to fill the jobs in the growing renewable energy industries, we will have to start before college. Students in high school who are beginning to consider career choices need to know that there are career opportunities in renewable energy. They also need to understand what workers in the renewable industries actually do on a daily basis to get a realistic idea of whether or not a job in renewable energy is right for them. That could be accomplished through internships for high school students as well as “job shadowing” opportunities during which students spend time with workers on the job, witnessing firsthand the skills and responsibilities those jobs require. To complete the process of ensuring that renewable energy firms have an adequate pool of skilled labor, we must build a strong “skill pipeline” from high school into college and to the workplace to provide an adequate number of skilled applicants for every type of position.

As the renewable market grows, opportunity will grow with it. This opportunity will be rich, with high-paying jobs that will have to compete for the qualified and skilled workers that choose to stay on their tools. Though the possibilities are endless for the Y generation to move into the skilled trades, it does not appear with the current trending to be the case anytime soon. The answer in the short term to who will fill the skilled trades’ gap may lie with international workers who possess similar skills, training and qualifications very similar to that of the native-born American counterparts.

Whatever the generational case may be, there are unfilled skilled jobs available in the renewable energy market sector, as well as those service providers who install, maintain, and repair the unique equipment that generates power from the wind and the sun—but you must be qualified to answer the call. 

It’s remarkable how tools and equipment can suddenly grow legs and walk off a wind farm or jobsite. A lost or missing tool may not seem like all that big of a deal, or a lot of money for that matter. But when a jobsite starts losing multiple tools, the replacement costs—not to mention the lost productivity—can quickly add up.

Tool manufacturers are leading the charge to help eliminate the growth of those legs and keep tools and equipment on the jobsite where they belong. A comprehensive tool management system includes organization, visibility, security, trackability, and accountability. Different applications and needs require different answers, from very low-tech solutions such as foam cutouts to visually identify if a tool is missing all the way to digital imaging software to track tool movement in real time. When implemented correctly, these jobsite tool management strategies provide an effective way to reduce tool loss, improve worker productivity, and ultimately save money. Figure 1

Low-Tech Solutions
Certainly the idea of using foam cutouts in a tool box as a way to visually inspect for any missing tools isn’t a new concept, but it is effective. Imagine trying to find a 19mm socket in a box in which tools are scattered throughout several drawers with no semblance of order. You may eventually locate the socket, but it could take awhile. A box with no organization also poses an inviting target to someone looking to take a tool home. Who’s going to know if that 19mm socket is missing from a box with tools that’s an unorganized mess? If the socket has been removed, and the next person is hunting through the box looking for it, the time wasted searching for it is keeping him from performing his job. That’s lost productivity.

Boxes with foam do provide an extra layer of security in preventing tool loss. A person is going to think twice before considering taking a tool home knowing that an empty foam cutout is showing the evidence of a missing tool. Foam also aids in alerting someone of a tool left behind on the jobsite. A quick scan of the drawers can reveal any missing tools that may have been inadvertently left behind on the job, which can then be retrieved. Figure 2

While using foam is a low-tech solution for tool control, the process of foam creation has come a long way from the days of tracing and cutting by hand. Some manufacturers cut foam to their customers’ exact specifications. One way to do this is for customers to lay out tools in a mock drawer with a camera positioned over it. The drawer is pre-sized to fit their existing tool boxes. They then arrange tools in the mock drawer to their liking, and take a photo of the layout. The process is repeated for each drawer. Once the photos are taken, they are sent to the manufacturer, where the photos are converted to a CAD drawing and fed into a CNC cut machine, and cut to the exact layout of the tools in the pictures. The foam drawers are ready to use and are cut precisely to fit their existing tools.

Another low-tech solution to tool control is using pre-made tool kits on the job site. Again, the concept of creating a kit for a specific job is nothing new, but what is different is the ability to add tool control to that kit to help ensure each tool is returned following the job.

Many companies that have created kits often include all the necessary tools to accomplish a task, but they are thrown into a bag or pouch and distributed to the technician at the tool crib. These tools can mistakenly get left behind because there’s no way of truly knowing if all the tools are in the pouch unless they’re counted. This is an inefficient process that may be skipped on the jobsite.

The better solution is a mobile mini tool chest that offers tool control. These types of boxes can be kitted to contain tools to perform specific maintenance out on a jobsite, but have drawers with foam for tool control. They’re designed with different configurations to meet different applications: two two-inch drawers plus six one-inch drawers, or three two-inch drawers plus four one-inch drawers. The drawers can be opened without having to flip the box over on its side. Figure 3

The box has wheels so it can be pulled by hand, and the drawers open and close on slides and rails and can be fully secured when not in use. Portable tool chests are ideal for applications where maintenance is being performed on more remote jobsites away from the tool crib.

Another was to prevent tool loss is simply through color. While shiny chrome tools can pose an attractive target to someone with sticky fingers, tools are available in a dull, black finish. It’s not to say that black-colored tools don’t walk away from tool boxes as well, it’s just another way for companies to reduce the appeal of tool theft.

High-Tech Solutions
Technology has greatly improved tool control to the point where a supervisor, miles from a jobsite, can track which tools are being used, and who is using them. For many tool boxes, keys are becoming a thing of the past. Tool boxes today can be accessed by someone using a badge with a bar code. Not only can a box be set up to allow specific people to access it, but there is now an electronic paper trail of a date stamp of when the box was accessed.  This way, any lost or missing tools can be traced back to the person that last accessed them. Using an electronic badge to access tools does cut down on tool theft as boxes are more secure; only those persons authorized to use the box have access to it.

Beyond bar-code entry, software is now available to fully track which tools have been removed and returned to a box using a scanner. Here’s how it works: Once a person scans their credentials to gain access to the box, any tools removed are scanned by a handheld device that captures pertinent information about that tool. For instances where multiple people are accessing the same box, any tools removed are tagged to that specific individual. Tools and equipment can be marked for single use or in quantity. For example, if a kit has been developed containing 20 tools, it can be scanned as one item to save time. All returning tools are scanned to ensure full accountability. Figure 4

The latest adaptation of this type of technology is the use of digital imaging to track and monitor tools. Digital imaging removes the need to manually scan tools as cameras mounted inside the tool box scans the drawers each time the box is accessed, recording the removal and return of tools. Additionally, software keeps track of information and can transmit data via wireless or a cable Ethernet connection to a computer for further accountability.

These tool boxes, which can hold up to 750 tools, come equipped with an LCD monitor attached to the top to give technicians a visual view of the tool activity he is using from the box. Each time a drawer is open and tools are removed, the system scans the drawer and documents which tools have been removed. The box is also voice activated and announces which tools have been removed. When tools are returned, the system scans the opened drawer again and checks off which ones have been returned and both visually and audibly alerts the technician on the status of each tool. If a tool has been placed in the wrong foam cutout in the drawer, the voice alerts the technician to the discrepancy. Figure 5

The system, along with its tracking software, can also monitor calibration cycles of tools such as torque wrenches. Another benefit of this type of box is that it reduces the need for tool crib attendants during late-night shifts when maintenance needs to be performed but an attendant may not be available. Essentially the box acts as its own tool crib as multiple users can be set up to access the box with each user’s actions being tracked.

These more high-tech technologies are useful in those industries such as wind, natural resources, and aerospace where tool control is a prime concern. Leaving a tool behind in a wind tower could pose a threat to the operation of the turbine, not to mention the time wasted to go and recover the missing tool. Monitoring tools saves money and improves efficiencies.

Mobile Tool Crib
For some applications in the wind industry where it may be more advantageous to bring the crib and its tool control directly to the jobsite, a mobile tool crib may be the answer. A mobile tool crib can be preloaded with thousands of tools and shipped directly to a remote job site and be fully operational in just a few days. When the job is finished, the crib can be loaded onto a tractor trailer and moved to the next site. This cost-saving move reduces tool costs by bringing the tools to the workers when needed.

Mobile tool cribs, which can be staffed with an attendant from a tool manufacturer, offers the same level of tool control and accountability as the technology found in individual boxes. These cribs are designed to be quickly deployed to remote locations and put tools into the hands of workers on a jobsite, yet at the same time using tool control technology to eliminate lost tools and save money.

When a new mobile tool crib is set up on a jobsite, the first thing the attendant accomplishes is entering each worker into the tool tracking software and assigning each of them a bar code. A quick scan of the employee’s barcode, followed by a scan of the tool accurately tracks the equipment that has left the crib and who’s responsible for it. This setup can be done by a designated employee, or some suppliers will even provide a trained tool crib attendant to manage the mobile tool crib onsite. Modular in design, mobile tool cribs range between 20 and 40 feet in length, include storage and control systems, cabinets, and shelving, plus electrical components that include lighting, air conditioning, and electronic entry systems. A mobile tool crib isn’t the answer for every application, but for those companies operating multiple jobsites it can become an efficient, cost-saving tactic to supplying and tracking tools for workers.

As systems and components become more complex, tooling will need to keep pace by providing the right solutions for technicians to get the job done correctly. That’s why it’s becoming more important to control those tools and keep them on the jobsite ready for use. There are several ways companies can go about implementing a tool control program. Consulting with a tool manufacturer to review your application, needs, and expectations is the best way to proceed in obtaining a tool control program that will provide the best return on your investment.