Sunday, October 1, 2006
Tools Make the Maintainer
Good tools, and effective tool control, are essential for modern maintenance needs.
The quality of maintenance workmanship depends on the technician doing the work, to be sure, but the quality of tools used plays an important role. The guiding principles at Stahlwille Tools are that the tool should be consistently accurate in their dimensions, and robust enough to stand up in repeated use.
Accordingly, all tools are built to assure dimensional accuracy, chrome stability, foreign object damage (FOD) compliance, and they are made from forgings, rather than stampings. The result is longevity. "Our tools don't wear out very often," declared Bill Baum, a Stahlwille official with the North American part of the enterprise. All tools are manufactured in Germany, to aerospace specifications. Baum claims other companies manufacture to industrial or automotive specifications. Stahlwille has been distributing tools in the U.S. since 1961, primarily to the automotive, wind power and other industrial industries; they are the factory tool for Mercedes Benz, BMW, VW, Audi and Porsche. Thirty months ago the company launched its concentrated effort in aviation and aerospace, starting with the U.S. Air Force.
As an example of the benefits of high dimensional accuracy, a properly dimensioned wrench has much less chance of skipping, or slipping, on the fastener. Also, Stahlwille's 12-point sockets are considered so accurate they can be used on 6-point fasteners, thus saving money by not having duplicate tools. "The fastener can cost 10 times more than the tool, so there's a huge cost savings in not having to remove and discard a fastener whose edges have been rounded off by a tool produced to lower tolerances," Baum explained.
The Center Piece
The real stars of Stahlwille tools are the torque wrenches. The biggest issue for torque users is abuse. Torque wrenches are used, improperly, as hammers and breaker bars (used to free up a recalcitrant fastener). Torque wrenches are over torqued, dropped and generally beat up, all in a day's work. Often, the abuse is not reported, as no one wants to be admonished or responsible for a tool going out of service.
The problem comes when a torque wrench goes in for calibration, and the laboratory calls the user, notifying that the wrench is not repairable. In other words, the tool has to be replaced. Immediately, the question is asked, what has it been used on and how long has it been so bad?
"Stahlwille torque wrenches address that question in a few very clever ways," declared Baum.
Of primary importance, there is no spring inside a Stahlwille torque wrench. This feature lends itself to some very impotant attributes. Without a spring, the user can leave a Stahlwille wrench set at a value, without any degradation in the accuracy of the setting or the wrench. Thus, if a user operates the wrench at 1,040 inch-pounds, the wrench can be left at that setting day in and day out, until calibration, and still have total accuracy (+/- 3% or 4%, depending on model).
Not having a spring, the mechanism inside the wrench is actually a beam at rest. The beam is machined and tapered to follow a precise curve, allowing not only for the accuracy, but also allowing the entire range of the wrench to be used (see box, p. 37). Hence, a wrench with a designed range of 350 inch-pounds to 1,800 inch-pounds can be used at 350 inch-pounds and at 1,800 inch-pounds as accurately as at 700 inch-pounds. As Baum explained, "This design feature surmounts a big problem with torque wrenches; technicians, especially new ones, use whatever value they see, not thinking about the standard 'cannot use 20% of the visible range of the wrench' rule" applied to more traditional designs based on a spring.
Of importance, Stahlwille torque wrenches can be used as breaker bars with no effect on the accuracy of the wrench. When a Stahlwille torque wrench is misused, the internal mechanism is taken out of the mechanical connection, and the wrench can be employed successfully as a breaker bar with no damage to the wrench or to its internal mechanism. As Baum exclaimed, "Virtually every other torque wrench on the planet is seriously damaged, and its accuracy is in question, that is if the wrench still functions after being used as a breaker bar."
Stahlwille torque wrenches come from the factory with NIST traceable certificates. More importantly, the wrenches come ready to work. "In the last 30 months of supplying torque wrenches to aerospace companies and to the U.S. military, we have not had a single wrench returned for any reason, including initial calibration tests," Baum said proudly. According to many U.S. military and commercial OEM (original equipment manufacturer) laboratories, as much as 30% of the traditional torque wrenches supplied "out of the box" cannot be calibrated. This problem is costly and time-consuming, as the wrench must be returned to the manufacturer for recalibration and certification, then sent back to the end-user's laboratory for "proofing." In the meantime, the tool was paid for but is not being put to work.
"We do not have this issue with our torque wrenches," Baum declared. He said Stalhwille is unique in that the company designs, builds, forges, machines, assembles, tests and certifies every torque wrench in-house. "We have not sent our torque wrench operations to Taiwan or mainland China, nor do we buy components from third parties and simply assemble torque wrenches," Baum said. "All the critical components are done internally. To be sure, handles, windows and such are sourced out, but Baum says these components are not critical to the torque mechanism.
Stahlwille wrenches are built to the ISO 6789 standard of one year or 5,000 active calibration cycles. A calibration cycle is generally established by the user's calibration laboratory based on long term monitoring of the tools. Twelve months or 5,000 activations is the allowed maximum by the ISO/NIST. Tools that claim longer calibration cycles are not adhering to the ISO standard and thus could expose the end-user to unnecessary liabilities, Baum asserted..
Interchangeable heads allow for greater flexibility and lower overall cost than other fixed head wrenches. One wrench can accommodate multiple heads. For example, one torque wrench can be fitted with 1/4-inch, 3/8, 1/2 or 3/4-inch drive ratchets, as well as crow's feet, crow ring, square drive or ring inserts. Moreover, specific inserts allow for specialized applications, like for the mount pins on CFM56 engines on the A319 and A320 aircraft.
Baum admitted that his company's torque wrenches sell for about 2.5 times the price of competitors spring-adjusted models. "But with the interchangeable heads, ours is only 1/3 to ½ times more expensive, and its got two big advantages: you have the flexibility of the interchangeable heads, and you have the longevity of our forged, machined-beam tool," Baum explained.
As Baum said, "Torque is a focal point of the company." In addition to the tools, the company manufactures and sells torque testing and calibration equipment.
The company's torque wrenches and other tools are designed to minimize the potential for foreign object damage (FOD) to the airplane, engine or components. However, the tools themselves, if inadvertently left in the airplane or engine, present a dangerous risk of FOD.
A U.S. Air Force Air Combat Command briefing in 2003 indicated that hardware and tools comprised a major source of damage to aircraft. "Poor hardware control" was a major driver, according to the briefing, and tools left in aircraft or engines represent a significant source of the problem.
Stahlwille has teamed with Coplan Ltd. of the United Kingdom to provide what is called intelligent tool control. The object primarily is to eliminate FOD related incidents, but also to avoid tool loss, track the usage of tools, manage tool inventory and purchasing, and to control tool calibration.
These goals are accomplished by a secure tool chest that is connected, via wireless telemetering technology, to a computer network.
The tool chest can be fixed or mounted on mobile casters, but it takes the right keypad entry or swipe-card from the user to gain access to the locked drawers.
Once open, the tools are arrayed in specially cut out foam inserts, which enables one to see at a glance which tools are out. This is known as visual tool control. The use of the foam to store the tools in shaped-receptacles is not unique. What is unique is the use of digital optical sensors, adapted from the robotics assembly industry, in each tool receptacle. The optical sensor is connected to a wired or a wireless network. Thus, management knows which tools are in use and for how long. And should the tool chest be returned with missing tools, that information is also known.
There are numerous virtues to this accountability. For one thing, tools appropriate to the job at hand should be the ones in use. Second, should any tools mistakenly be left on the aircraft or engine, the empty foam receptacle is a sure sign to the mechanic, and the absence of the correct signal to management is a back-up indication. This accountability can be a lifesaver, as aircraft can be held if a tool is indicated to be out of the box by the monitoring system.
A "standard" tool trolley, able to store 180-220 tools, costs around $7,000. This is more than the price of a standard toolbox, but includes the precision-cut foam, the sensors, the control board and the software to control multiple trolleys or cabinets. "Remember that there is another cost to consider here," said Baum. "There is the cost of FOD damage, or lost sorties, and/or revenue, when a tool cannot be located, as well as the cost of searching for a tool."
These costs can easily trump the cost of the tool control system by a considerable margin.
Thus, in the grand scheme of things, the extra cost of Stahlwille torque wrenches and Coplan's tool control system, may actually be outweighed by the costs avoided. Not having an effective and flexible tool, or not being able to locate it, may cost far more.