manufacturing technology
they’ve only got a tiny space to do it in. So this is driving the requirement to create tighter radii than we’ve done before. “Everything used to be bigger and there used to be fewer components to maneuver around. The industry is challeng- ing both us, the equipment supplier, and the raw material manufacturers to make a product that can be formed within these constraints.”
Tight Bends Require Precise Control Bending tube in a tight radius requires precise control of the material fl ow. That requires specialized tooling and multi- axis CNC, as opposed to the old technology of hydraulically controlled bending machines. Searles explains that the material on the outside of a bend “has to come from someplace. It either has to stretch, break, or pull from the end of the tube. Histori- cally, we’d allow the material to stretch, pulling material from the end of the part, and we’d often use heat to get the material to bend properly. We’d make single-bend parts, cut it off, and weld these segments together to create an assembly. As recently as fi ve years ago any fi nished tube with multiple bends would have included much more cutting and welding than needed today. “That’s because our electric machines now actually push material into the outside of the turn as the tube is bending.
The servo-controlled axis also maintains enough control to keep material from pushing on the inside of the bend, where it thickens and can cause problems like wrinkles. We can control the material fl ow so well that radii as tight as one times the diameter are doable.” But it’s a balancing act. BLM Group’s engineers have to determine the right amount of pushing required and the per- fect timing for applying the force. And they have to create a repeatable process that takes just a few seconds. With cycle times like that and full automation, these machines are push- ing out 20,000 or more fi nished tubes per day.
Cut to Length in Seconds In the vast majority of high production situations, cutting the tube to length precedes the bending operation. Searles said. “Typical cutting times are a second and a half to two seconds, depending on the material and the thickness of the wall. A three-inch tube with a quarter-inch wall might take three or four seconds.
Electric control of all axis movement, savvy programming, and specialized tooling
Electric control of all axis mo ement, savvy programming, and specialized tooling enables today’s machines to rapidly and reliably bend tubing with tight radii to satisfy space constraints.
“In the automotive world, walls are generally getting thinner to help make cars lighter. We can process these lighter tubes faster. On the other hand, the material selection plays a big role, and of course it depends on the application. For example, a structural component like tubing in the door for collision protection would likely be a thin wall tube, but a much harder material that we’d cut slower. If it’s an exhaust system it’s generally pretty soft steel, which we can cut pretty fast.” BLM Group uses either saws or lasers for the actual cutting, typically holding about 0.0050" (0.13 mm) for sawing and 0.0040" (0.1 mm) for laser cuts, both of which are perfectly ac- ceptable. The goal is to produce parts in very high volume that meet the accuracy requirement without expending unnec- essary resources. BLM Group’s CM602 automatic CNC sawing machine handles tube and bar up to 4" (102 mm) in di- ameter, and depending on the material, runs at up to 5000 rpm cutting speed. The cutting head meets the tube surface at 45° and its linear movement across
50 — Motorized Vehicle Manufacturing 2017
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