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STAMP OUT WASTE

With the right planning and forethought, coil processors can reduce their material, time, floor space, and dollars waste with an efficient pressroom.

Introductory photo: Dallas standard feed line with multiple gag feed options

The erratic ups and downs of the economy affecting the manufacturing sector lately have just about everyone scrambling to find financial and operational stability. It requires an intricate balance of controls, efficiencies, and productivity to remain profitable and stable. Many organizations, however, quickly implement the obvious policies of cost reductions without giving enough consideration to these policies’ overall, long-term impact. In many instances, merely cutting costs results in higher expenses later on.

That's why productivity savings is not only a more appropriate term to use, but also an easy-to-justify approach to the problem. By taking a hard look at all relevant elements of the process, coil processors may be able to find the right path to improvement.

For the stamping industry, and coil processing in particular, productivity savings can be found in five general areas: Better material use, more efficient labor utilization (including safety practices), time efficiency, better-quality parts, and maximized floor space usage. While improvements in these areas may require initial investments, they should show productivity gains immediately and provide returns long after the economy rebounds. Many of the options suggested improve performance in several, overlapping areas.

Figure 1 Dallas SpaceSaver 20,000 lb. X 42” wide Zig-Zag line with PC based control

It’s Staggering
The first option to consider is zig-zag, or stagger, feeding of the coil stock to the press. This technology is designed to obtain the maximum number of parts from the minimum amount of material. A zig-zag operation provides a second direction of feed travel, perpendicular to the infeed motion, that allows improved nesting to reduce waste (see Figure 1).
For example, specifying stock for zig-zag feeding that is approximately 1-1/2 times wider than the diameter of a circular blank and offsetting the placement of the parts can provide material savings of 7 to 14 percent, as opposed to stamping out a straight line of blanks. The process is not limited to circular blanks, and in almost every application, some amount of stock will be saved.

A Gag Order
Another area for a productivity upgrade is to use gag tooling in combination with servo feeds and gag control. This alliance allows coil processors to do more work than typically could be accomplished in one die by turning various tools on and off as needed and by moving the material through the die at different feed lengths.
The ability to punch many sizes and shapes of holes plus perform an array of forming and bending operations will help eliminate or minimize the need for second hit/second operations, reduce part handling and in-process inventory costs, and open up equipment and operators (of eliminated subsequent processes) for other uses. The single handling and setup of a gag tooling operation also might help to improve output quality and reduce scrap.

In a gag system the feed control provides multiple feed lengths per part and multiple numbers of each feed length linked with programmed outputs to engage various individual tools or combinations of tools within one die (see introductory photo). In some systems, reverse feeds can be programmed to optimize process performance.

Figure 2: Dallas Cut-to-Length line 15,000 lb. X 50” wide with notcher, shear and destacker

A manufacturer of heating, ventilation, and air conditioning (HVAC) units, for example, has put a gag system to the test to stamp out one-piece front-panel enclosures for residential and commercial furnaces. The line employs a gag die and an electronic servo feed incorporating gag feed and tool control. The system provides 24 separate feed lengths with from one to 100 cycles for each length, and it has capacity for 24 tool outputs. Operations include punching mounting and screw holes, which are both round and elongated; punching ventilation louvers; notching and bending the four sides; and embossing an area for attaching a nameplate and information label. All of these operations are performed in one gag die with coil fed stock using a servo feed and the appropriate controls.

More Productivity Savings
Another possible area for productivity savings is coil joining – splicing the end of the current in-process coil to the leading edge of the next coil with a butt-joint weld. This allows coil processors to obtain more parts per coil because parts can be stamped out closer to the ends of the coil used. Plus coil joining might help to reduce threading time significantly, depending on where in the feed line the coil joining takes place.

A stamper that wants to add a coil joining mechanism to a feed line can place the device at the exit end of a power straightener in the line, before the material feeds into the die. As the trailing end of the in-process coil exits the straightener, the material is held by the joining equipment and the edge is sheared to square the end. The next coil in line is threaded to and jogged through the straightener to the joiner, where its edge is also sheared. The two ends are brought together and welded. The feed line then is put back to automatic operations and, with the proper loop control, press operations may not even be affected. At the very least, rethreading the stock through the feed unit and die is eliminated, thus increasing uptime.
Auxiliary equipment enhancements to the actual feed line can also help save material and time and create a safer work environment.

Peeler/Hold-Down Roller. One such device is a combination peeler and a coil hold-down roller. The two form a system that helps increase productivity by making the threading process easier and faster, while improving operator safety. Without a peeler/hold-down roller, threading a new coil into the next process is time-consuming and can be hazardous. Done manually, this operation requires two people to hold and guide the material to the next operation while jogging the coil rotation.

Figure 3: Dallas SpaceSaver line helps conserve floor space but still can handle up to .625” thick material

First the coil hold-down roller prevents the newly loaded coil from springing open, which is especially important when a coil reel is in use. As the coil is rotated, the peeler lifts the leading edge from the coil and provides the proper direction and approximate height for alignment with the next piece of equipment, typically a straightener, or the feed unit itself. That's the scenario for thin gage stocks.

Coil End Debender. For thicker materials or high-strength alloy stock, additional help in the way of a coil end debender probably is needed. Thicker or higher-strength material tends to hold its coil curvature, increasing the difficulty of threading to and through the various stages of the line. Frequently operators have to use pry bars to force the stock into the next line component; other times they prop the material on a stand and strike it with a sledge hammer or anything handy to remove the bend from the leading end of the coil.

A coil end debender simplifies the process by using air or hydraulic power to flatten the coil end, which eases the way for threading to the next step. The results of using a coil end debender include an increased margin of safety by limiting the amount of operator involvement in the process and possible material savings because the leading edge is uniformly flattened and no longer ingrained with kinks and hammer marks. At the very least, the threading operation is faster to help increase uptime.

Cut-To-Length Feed Line. For some applications, a cut-to-length feed line may be in order for saving material, improving productivity, and possibly eliminating outside costs. [WHAT ARE THESE OUTSIDE COSTS?] (purchased blanks, added transportation costs for example) A cut-to-length line typically incorporates a shearing process along with other preliminary processes, such as punching or notching, giving users the high speed of coil handling with the accuracy and flexibility of a blanking line. This type of system can help reduce or eliminate multiple, separate processes; the slow handling and feeding of individual blanks; and free other equipment from secondary operations. A cut-to-length line also may integrate blank handling stackers, destackers, and straighteners that flatten the coil stock to precise tolerances (see Figure 2).

Figure 4:Dallas Pull-Through straightener mounted to a servo feed

Bigger’s Not Better
A final equipment option available for some stamping applications is a combination of technologies and concepts that provides a more efficient use of floor space – from one-third to one-half the length of a conventionally designed feed system with similar capacity (see Figure 3). Thus, a line that usually requires 40 to 50 feet of real estate could require as little as 18 ft.

These smaller-footprint feed lines eliminate large gaps between elements required for loops or free slack in the material and prevent the stock from binding up. One of the key elements of a space-saving line is a pull-through straightener coupled with a high-power, heavy-duty feed (see Figure 4).

A small-footprint in press feed system design also can include cradle-style decoilers that payout the material so that the loop (there is only one loop) goes up and over the cradle, then back down to the straightener or feed unit. Today the extensive use of servo-drive technology in feed units has increased control capabilities, allowing for not only precise feed lengths, but also more exacting loop control. When servo motors are incorporated with power cradle rotation or motorized reels, payout of material can be easily synchronized with feed lengths and cycles, resulting in a substantial reduction in loop length and the elimination of loop pits.

Among the steps to save material and improve productivity is the need for continuing education and operator training programs that will help to simplify implementation of these technologies, and achieve optimum performance from the equipment, and eradicate unsafe operation practices.

Just the Beginning
These areas for potential productivity savings are just beginning into a thorough examination of the equipment and processes that will help lower costs yet also enhance productivity, save material, improve operator efficiency, and open up valuable floor space for added productivity. When choosing new or replacement press feeding systems and equipment, it’s important for stampers to consider a combination of objectives carefully, including not only initial investment, but also quality of part production, equipment reliability, flexibility, and future work load capacity.