INSTRUMENTATION • ELECTRONICS
Another challenge in measuring friction in the forming process is the fact that many metal surfaces are not completely fl at but angled, contoured or rounded. T e same is true of much of the machinery and tooling within the industry. “In metal forming, the only material that will have a completely fl at, horizontal surface is sheet metal. But once you start bending and machining, it is not a smooth, fl at surface anymore, which complicates traditional friction testing,” says Bogart.
THE BENEFITS OF PORTABLE FRICTION TESTING In contrast to traditional destructive incline friction testing methods performed in a lab, portable friction analysers are now available that are simple to use. T e handheld units can be used anywhere that virtually instant, in situ friction testing is needed in the metal forming process. For instance, friction can be measured on metal surfaces when receiving raw materials, in production to adjust lubrication or during QA checks further downstream. Examples of the portable friction analysers include two handheld, battery operated models, the H94Ai and H37 3D by Kett. Both units can measure the static coeffi cient of friction (SCOF) on dry, wet or lubricated metal surfaces and are designed for use with minimal training. T e operator simply places the unit on the surface to be tested, presses the “measure” key and the static coeffi cient of friction is measured to 0.001 precision in seconds, with accuracy and reliability comparable to lab models. “Basically, anyone can pull a workpiece from the production line and test the friction in multiple places with these portable units. If the item is in spec, they can put it right back on the line. If not, they can quickly adjust on the fl y,” says Bogart. For testing fl exibility, the
Portable friction testers have been developed that enable fast, non-destructive testing without specialised training
ability to exchange test fi xtures allows the unit to simulate the interaction of multiple surface materials (i.e. steel to steel, steel to aluminium, aluminium to aluminium) by simply swapping out the fi xture. T is is important not only when forming various metals but also when the metal surface of the equipment and tooling diff ers from that of the formed material. “Measuring friction is completely dependent on the two interface materials. So, quickly changing out the fi xture to accommodate the testing of diff erent metals is important,” says Bogart. He notes that exchanging test fi xtures can be used to simulate solid/solid interfaces and solid/liquid interfaces, which can be helpful in determining the frictional interaction of metals with lubricants or other liquids.
Although the H94Ai must be held level when measuring, the newer H37 3D has integrated angle adjustments that allows it to be used at any angle – from horizontal to vertical in three dimensions, even upside down. T e combination of the H37 3D’s integrated angle adjustments, along with the ability to exchange test fi xtures, enables measuring friction in angled, contoured, and rounded metal surfaces. T is facilitates more versatile, static coeffi cient of friction (SCOF) measurement
of metal surfaces, machinery and tooling, which can improve production quality and equipment longevity. “By being able to hold the instrument at any angle, you can get accurate measurements without having to worry about either orienting the piece or orienting your hand to make sure that the instrument is completely horizontal,” says Bogart. Special fi xtures can also be created for custom friction measurement applications. “By request, we manufactured a special fi xture with a ‘reverse hump’ in it. T e hump was the cutout [so it would sit on a bar] to simulate a friction test covering more surface than just the top of the rounded area,” says Bogart. In addition to the portable friction analysers, Kett off ers a full line of desktop units that can be used to test not only static friction and dynamic friction but also surface properties such as peel, wear, adhesion and scratch resistance.
In contrast to traditional destructive incline friction testing methods performed in a lab, portable friction analysers are now available that are simple to use
ENSURING QUALITY, LONGEVITY T e bottom line for the metal forming industry is that it is now easier to ensure quality and protect machinery from the problems created by either too much or too little friction in the process. With portable SCOF testing, they can ensure that all metal surfaces are within production specifi cations anywhere as needed.
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