Big changes work their way through appliance stamping shops
May 16, 2002
Changes are taking place in stamping operations in the appliance industry, with more on the way. And the science of stamping is improving significantly as a result. In this article, appliance industry executives express their opinions of the state of this technology.
Stamping experts say sudden, revolutionary developments may not be sweeping through the appliance industry, but there are plenty of changes, with more on the way. And the science of stamping is improving significantly as a result.
These were key findings of an informal survey of stamping executives involved with the home appliance manufacturing industry. Appliance builders, equipment suppliers, and independent stampers serving appliancemakers were polled by The FABRICATOR® for their views on the state of stamping.
The companies we talked to agree on several points:
The forces that have swept through the automotive industry are driving changes in appliances as well. Low in-process inventories, just-in-time (JIT) deliveries, continuous improvement, and lean operations are the order of the day, and product quality has skyrocketed.
"For the last 10 or 15 years, no one has wanted to maintain inventory. We operate pretty much JIT. Some customers want as little as two-day turnaround on orders," noted Bill Weigand, manufacturing engineering manager for TUTCO Inc., an electric heating element manufacturer with stamping operations in Cookeville, Tenn.The industry is extremely cost-conscious, and the drive to eliminate costs at every level is intense. Suppliers are being pushed hard to innovate and become ever more cost-competitive."Appliance styling has become less like a simple white box and more complicated,? said John Meisner, project stamping engineer for Whirlpool'sClyde Div. in Clyde, Ohio. "We're seeing deeper draws, more complex geometries. This will drive changes in the way we buy our tooling: Styles will change more frequently, and we won't need to buy a die built like a tank to last forever."
Other executives agree that trends toward shorter production runs, more flexibility, and more frequent die changes are well-advanced.
Some of the technological changes in appliance stamping are being driven by alternatives in the metals used. The newer players are:
1. Prepainted steel. Over the last five to 10 years, prepainted steel has made significant inroads into the appliance field and now forms the wrappers for many major appliances. Stamping executives surveyed report that prepainted is more difficult to form than bare cold-rolled steel (CRS), often requiring a higher polish on tools, as well as handling equipment that will not mar the paint.
Some companies use heated dies to form the painted steel effectively. Prepainted steel remains popular because it saves manufacturers the considerable expense of paint lines.
"The quality of prepaint has improved dramatically," observes Ron Demonet, vice president of manufacturing for Atlas Technologies Inc., a Fenton, Mich., builder of presses and automated fabricating lines. "We can do deep drawing and stamping operations we couldn't do a few years ago."
Demonet explains that prepainted steel cannot be spot or projection welded easily. This has led appliancemakers to form refrigerator-freezer doors, for example, with plastic covers on the corners or with a small seal at the joints.
2. Stainless steel. Stainless steel is gaining ground in appliances, particularly in premium units. Applications include washer and dryer drums, refrigerator doors, and places where food touches the appliance surface.
Stainless can be difficult to form, executives report, with one of the major problems being springback, the tendency of the steel to remember its former shape after drawing. Stainless requires different tooling, which is more expensive, requires more maintenance, and has a shorter work life. Tighter tolerances and higher press tonnages are the rule with stainless.
"We keep the stainless quarantined, segregated from the CRS equipment," says Whirlpool's Meisner. "We don't want carbon to migrate from the regular steel onto the feeder rolls—it contaminates the stainless and looks like rust. We're looking at not segregating the tooling, but right now our stainless lines have dedicated equipment."
3. Galvanized steel. Many appliancemakers admit to running more galvanized steel for applications like back panels, brackets, and water-intensive units such as washers and dryers. Galvanized requires more tool maintenance, because the zinc coating can flake off and get into the dies.
4. Aluminized steel. This has applications for appliances with heating elements (ranges, heating, ventilation, and air conditioning). One stamper reports difficulties with varying hardness of steel shipped from service centers, which can significantly affect formability.
5. Others. Plastics have gained applications, executives say, and at least one appliancemaker is looking at laminated materials.
Beyond these general trends, a host of new technological developments are making news in appliance stamping. A sampling includes:
1. General movement to transfer press systems. This trend appears to be most obvious at the major manufacturers of appliances. The push to improve productivity has driven some manufacturers away from the old tandem press lines to automated transfer press systems. These new systems are designed to be flexible—the goal, one stamping executive says, is to be able to handle all refrigerator models, for example, from 17 to 27 cubic feet on a single line. The systems typically are coil-fed, with all stations computerized.
"They used to blank parts in individual presses. Today they want to go from coil and develop a part on the fly, all in one line. At the end you have a complete door, ready for foaming and wiring," says Tank Gonzalez, national sales manager for Fagor Arrasate USA Inc., a producer of sheet metal manufacturing lines with U.S. headquarters in Bensenville, Ill.
2. Quick die changes. Many appliance manufacturers have installed automated die change, retrieval, and storage systems to speed model changes. Other techniques also are used to add flexibility and cut changeover time, including toggle die systems in which cranks on the side of the press permit "model changes in a minute," according to one executive; dies located on rolling subplates for quick roll-in; and push-button controls that automatically move all equipment out of the way for free access to the dies.
"We're not at SMED [single-minute exchange of dies] yet, but we're working toward that goal," says Whirlpool's Meisner.
But the changes run deeper than that. As noted earlier, with more frequent model changes, dies are not used for continuous production as they were years ago. This has led toolmakers to use different-quality steels for tooling, depending on the anticipated length of a production run, to give the customer the lowest possible cost. Appliancemakers reportedly also are improving die protection and using coated forms, all to improve handling of their expensive investments in tooling.
3. More sensors. More monitors and sensors are being installed in and around dies to spot and prevent production problems. The goal, says one executive, is to detect any problem before the press makes a second hit, thus saving both production material and tooling."Customers appreciate this because they pay for the tooling," the exec adds.
Among these devices are tonnage monitors; in-die sensors to detect misfeeds or holes in metal; beams to detect buckling; and proximity switches that activate on overfeeds, underfeeds, or when parts fall off the dies.
4. Finite element analysis (FEA). Both appliance manufacturers and stampers are using FEA in the tooling design phase to spot problems in die designs before they become production problems.
5. Less welding. The trend to use less welding noted earlier has led to increasing use of various mechanical and other joining methods in appliance assembly, including lock seaming and several branded mechanical joining systems, some of which can be incorporated into the stamping press tooling.
6. Hydroforming. Customers are starting to ask for hydroforming, stampers and equipment suppliers report. Typical applications at this point include washer and dryer drums and various piping products. Hydroforming is viewed by some appliancemakers as slow, costly, and a high-maintenance procedure, but suppliers must meet their customers' demands.
7. Switch to servo feeders. The move away from air feeders appears to be well-advanced. "The days of air feeders are going away," one stamping executive says, because servo feeders are seen as smoother and more accurate, with less slippage.
8. In-die tapping. This process now is in use in some appliance lines. In this process, a punch with a tiny tip makes a hole in metal, and then the thicker shoulders of the punch bend the metal out around the hole. Further along, a tap that looks like a bolt threads the metal surrounding the hole so screws can be inserted in the metal later. This is all done as part of the progressive die stamping operation.
9. Nitrogen cylinders. These now are being used in place of air cushions, some manufacturers say. In the past cylinders under the press that cushion and hold the workpiece in place were charged with ordinary air. Now nitrogen is replacing the air because it often allows more tonnage per press and provides flexibility, enabling operators to move cylinders from one press to another.
With all of these changes in appliance materials and machinery, what about the human side? Almost every company interviewed agrees that workers are required to be more flexible today than ever before. Training plays a more important role.
"Workers are definitely doing more than they were 20 years ago. We're asking them to do more quality checks and to take more responsibility. And they're doing a pretty good job of it!"? reports Steve Koch, director of manufacturing engineering for Maytag, Newton, Iowa.
The picture of appliance stamping that emerges from these interviews is one of a dynamic, rapidly improving segment of the industry. Improvements are not coming in leaps and bounds but through thousands of small changes made day-to-day. Appliance stampers are being asked to cope with new materials, new appliance designs, more and faster model changeovers, and intense customer pressure for both higher quality and lower costs.
The FABRICATOR® acknowledges the contributions of the following companies in preparing this article.
Maytag Appliances, 403 W. 4th St. N., Newton, IA 50208, phone 641-787-7000, Web site www.maytagcorp.com.