Stamping Dies: Quick Change Artists
- April 16, 2014
Hours become minutes on changeover of stamping dies
For years, those familiar with Single Minute Exchange of Die (SMED) have been hearing how efficiency expert Shigeo Shingo helped automaker Toyota reduce setup time on its 1000-ton presses, going from four hours to just three minutes. An admirable achievement, but is it really necessary to change dies faster than you can pick up a happy meal at the local drive-thru?
Probably not, but it's a sad fact that many shops waste time during set-up, and best measure their machine downtime in hours rather than minutes. This leads to oversized production runs and long lead times for finished goods, bloated inventory, product obsolescence and machine utilization figures that would have Shingo rolling in his grave.
Hopefully, your shop has already embraced some of the principles of SMED. Good shop organization, die standardization, efficient die transport and handling, making certain dies are properly maintained and ready to go—are all attributes of a well-tuned stamping house. If so, it might be time to make the move to quick die change.
Quick die change systems come in two types: hydraulic and magnetic. Like anything, each has its pros and cons, and there are proponents who will swear one is better than the other. The truth is that each has its place, and regardless of which best fits your shop, fast and accurate positioning is there for the taking. Prepare yourself for some sticker shock, though—you can plan on spending $10,000 at least to outfit a small press with quick-change, and maybe 10 times that for a large one.
George Munschauer, regional sales manager for AIDA-America Corp., Dayton, OH, explains that the level to which a shop carries its quick-change efforts (and the commensurate investment) depends on several factors, including part complexity and lot size, as well as the type of die, its weight and dimensions. For example, those shops doing simple parts and single-stroke processing are less likely to need the inherent accuracy that quick die change brings to the table. Says Munschauer, "but where automation is in place, or on progressive-type work using a coil-feeder, you'll likely need positioning within a few thousandths if you're going to assure good alignment. This is where quick die change systems really pay off."
Despite that potential pay off, Munschauer says larger presses get the most SMED attention. "A rough guess would be that 65-85 per cent of presses 400 tons and larger are equipped with some form of quick change. Below that, I don't see it used much." The reasons are simple: large, heavy dies, some with dozens of clamping points, take substantially longer to setup than their smaller cousins, thus justifying the investment in time saving devices. Still, in those situations where changeover frequency is high, shoebox-sized die sets can consume just as much set-up time as those the size of a pickup truck. "Whatever the size of the tooling, if a shop has to make five or six die changes a day, quick change should be considered," Munschauer points out.
Dave Fischer, Hilma engineering manager with Carr Lane Roemheld Mfg. Co., which offers a complete line of quick die change and handling solutions, agrees. "With smaller presses, say 100 tons and below, there's less clamping hardware to deal with, fewer nuts and bolts, less weight to jockey into position. This means shops feel less pressure to go with quick change clamping systems." That doesn't mean, however, that they shouldn't do it.
Fischer offers an example of a 100-ton press with a one-hour setup—implementing quick change could easily lop 50 per cent off that time. True, that only saves half an hour, but with frequent changeover environments, every minute adds up. But the real benefit, Fischer argues, is consistency. "Quick change systems mean easier standardization, and more consistent processes overall. For example, you don't get caught out at the machine missing a bolt or a strap, and end up wasting time walking to the tool crib for a part that cost a couple of bucks. Set-up times become very predictable."
Carr Lane Roemheld offers hydraulic and magnetic die clamp systems. "It's all about what's best for the application. For example, magnetics are very fast. We recently worked with a company making furnace components, and the ability to quickly switch from one length to the next was important—in this case, magnetics were the best choice. They're also flexible, and work great where a company still has some work to do on the standardization of their die sets—thickness is basically irrelevant. You must have a clean, flat surface for safe clamping, a way to locate the die, and you're up and running."
Fischer admits magnetic systems can get expensive, especially on very large presses. "You need a lot of magnets to safely hold a big die set during a stamping operation. Magnets are less effective than hydraulics where the clamp surface area is limited or the condition of the mating clamping surface can't be guaranteed. Applications where there may be heavy stripping or ejector forces need to be evaluated. In these cases, hydraulic clamping may be a better solution."
Duke Shelley is a member of the quick die change sales team at Kosmek USA Ltd., a distributor of powered clamping systems. Shelley can recommend a variety of tools to reduce die changeover time, including die lifters, pre-rollers, hydraulic power units and swing clamps. One example is a self-positioning clamp with built-in proximity sensors. During changeover, the clamp swings out of the way, and when the new die is in place, an air cylinder pushes it back into position against the die, eliminating the need to walk around the machine to place and tighten clamps.
Quick die change systems, says Shelley, are the genesis of efficiency. "Once people start thinking about quick die change, it affects the entire company. The engineers start thinking more seriously about standardization, so that they can utilize the new clamping system. The operators think about keeping production flowing smoothly. The setup people and programmers think about additional areas where they can save time. The byproduct is that everyone's job gets a little easier, waste is reduced, and the company becomes more profitable."
SMED has been used successfully for decades, and allows stamping houses to set-up in minutes instead of hours. Reducing set-up time has many benefits—lower inventory levels, better responsiveness to customer demands and greater profits, to name a few.
Best of all, it's a very effective tool to help keep stamping work in this country. SMT