February 19, 2001
An appliance plant with 80 to 100 presses in opeation is likely to buy new presses regularly. Under these circumstances, it makes good sense to pursue aggressive productivity goals inch by inch through steady advances in such prosaic concerns as machiner ergonomics, prventive maintenance, tooling efficiency, and material quality.
To the pilots of high-performance aircraft and operators of stamping equipment, one rule holds true—keep surprises to a minimum.
This is especially true for stamping operations in the appliance industry. With the exception of the development of programmable electronic controls, manufacturers have made gradual but consistent performance upgrades that have allowed them to minimize capital equipment expenditures while maximizing the performance of stamping presses, transfer feed systems, and tooling.
Recognizing that a stamping press has an average life expectancy of 20 to 25 years, an appliance plant with 80 to 100 presses in current operation is likely to buy new presses at regular intervals. Under these circumstances, it makes good sense to pursue aggressive productivity goals inch by inch through steady advances on such prosaic concerns as machine ergonomics, preventive maintenance, tooling efficiency, and material quality.
The increased operating speeds offered by transfer presses are one source of improved productivity. Another factor that influences productivity is the Quick Die Change system, which can sometimes make a pressroom feel like the flight deck of an aircraft carrier. In five minutes, quick clamps are released, the transfer rail is disconnected, tooling exits the press on one side while new tooling enters from the other side, and the press is ready to run again.
The trend toward transfer presses is largely a response to intense competition in the appliance industry. Whether the part in question is a large dryer panel or the inside liner of a refrigerator, producing 18 to 20 parts per minute (PPM) on a transfer press equipped with electronic controls is not unusual. This contrasts with speeds of 8 to 10 PPM on a typical tandem line.
Improvements in transfer press technology involve more than big ideas, such as electronic controls and Quick Die Change systems. When pneumatic lifters replaced traditional spring lifters more than 20 years ago, part quality and production speeds increased substantially.
Pneumatic lifters, charged by nitrogen, allow the stamping manager to apply pressure discretely according to the operation under way, the geometry of the part, and the material being formed. By holding the part in place, the lifters secure it for the next operation. After the operation is performed, the lifters quickly elevate the newly formed piece for transfer to the next operation.
Pneumatic lifters provide part stability and quick part release, which are important contributions to press speed. After all, a part cannot be stamped if it is bouncing around on the tooling.
Increased speed and overall press flexibility are the macro side of transfer press improvement, but the best stamping operations also benefit from improvements at the micro level.
For example, not long ago, managers bought presses, and operators ran them. Now, press purchase and installation is an open process in which the operator plays a critical role. A multitude of concerns is now weighed against the cost of a new press, and every aspect deserves consideration.
Ergonomics is more important than ever. One appliance manufacturer even builds prototype panels for the operator controls of a proposed new press to minimize wasted motion. Every operator who will be working with the panels works with the prototype to ensure that the position is proper, the functions are correct, and the buttons are in the right place. By allowing operators to get involved with the planning and design of the prototypes, the company reduces any motion that is not related to production during stamping.
The philosophy of controlling nonproductive factors even extends to controlling noise and dust. Press gates with special sound-dampening qualities help to keep a pressroom quiet while minimizing the effects of dust and grime on equipment, the labor force, blanks, and finished parts.
As competitive pressures mount and consumers demand better products, stamping equipment manufacturers can expect unusual requests from their appliance industry customers. For example, one stamping press manufacturer sends its engineers to appliance manufacturing plants to supervise press rebuilds. In the past, such projects were usually handled at the press manufacturer's plant. However, doing the job at the customer's plant eliminates the time and costs involved in shipping the press to the press manufacturer.
In this case, the press manufacturer shipped the correct materials to the customer, built to the customer's specifications, and sent engineers to supervise the customer's work force in executing the project.
The productivity of stamping operations is also boosted by using better materials. Cold-rolled and hot-dipped galvanized steel are the materials most commonly formed by appliance manufacturers. Improvements in the steel manufacturing process have lead to steel with more consistent chemistry. Continuous casting, a process developed in the 1960s, allows a mill to use additives such as aluminum to attain desired characteristics. Kilned steel is one such product that is used by appliance manufacturers.
Adding aluminum to steel de-oxidizes it and prevents it from gradually hardening, which makes it more difficult to work. Kilned steel ordered for Just-In-Time (JIT) delivery now has the same chemical properties from day to day, week to week, and month to month. Consistency in the steel eliminates many production problems such as ragged edges on parts or accelerated tool wear that used to result from age hardening of the steel.
More to the point, using a more consistent steel enables appliance product designers to use thinner-gauge steel for exterior parts. This fits well with the overall trend in the appliance industry to reduce the amount of steel that is used. Using blanks made of thinner steel also places fewer demands on the stamping equipment, thereby increasing the life of tooling and stamping presses.
Quality initiatives in the steel industry are boosting productivity. The surface of the steel being shipped to appliance manufacturers has far fewer impurities today than it did years ago. Paint adheres better to a product that is free from grit, oil, or dust. When paint adheres better, part rejects are reduced.
Sheet metal remains the go-to material, although research into plastics and prepainted metals continues. But because much of the painting equipment in large manufacturing plants has been installed, debugged, and paid for, little likelihood exists that other materials will achieve greater market share in the near term.
From better materials to improvements in press technology, die design, and tooling, stampers in the appliance industry are showing that metal forming innovations come in many shapes and sizes — and the fewer surprises, the better the results.