Die Science: Unnecessary detail work can cut into your stamping profits

Pride from tool and die makers add to labor and production costs

Tool and die maker in stamping shop

Customers aren’t willing to pay for a pretty die when a cheaper, uglier one will produce the same part quality and last just as long. Learn what unneeded steps you can cut in die production to save money. Getty Images

I was recently in a tool and die shop having a discussion with one of the executives of the company. He expressed how increasingly difficult it is to be competitive in today’s global market, especially with the lower labor rates in other countries. And on top of that, he said that his die shop typically exceeds the number of hours quoted to build a job, resulting in little or no profit on the tooling.

I can say with a great deal of confidence that his shop builds very high-quality tooling. In fact, as odd as this may sound, the quality might be too high.

His toolmakers take pride in their work. Every detail of a job is meticulously crafted, fitted, polished, and machined to exacting tolerances. The dies not only function well but are a thing of beauty. And therein lies the bigger problem.

While beauty and detail are nice, some practices add little or no value to the tool but cost plenty to implement.

Unnecessary Surface Machining

More often than you can imagine, I see dies with fully machined subplates, pads, and die shoes. Although occasionally it is necessary to machine a single side of a shoe or plate for dimensional reference, machining all sides square often is time-consuming and wasteful.

Don’t worry about making the pads, shoes, or riser plates to the exact specified dimension on the print unless it obstructs the fit and function of the die.

Squaring Tool Steel Before Machining Die Details

In some die shops, when tool steel arrives from the supplier, workers take it to a wet grinder and square it up on all four sides. Usually this is wasteful and completely unnecessary.

Many die shops have omitted all presquaring of tool steel before machining by clamping the block in a vise at the mill or using magnets to hold the workpiece in place and then face milling the block to produce a flat surface. They reference one corner of the block and machine two precision reference holes into the block in positions that ensure there will be enough material to machine off and complete the block in its entirety. These reference holes, which also can serve as the centerpoint for the dowels, typically enter the tool steel only about 0.125 in. During this process, the shop also drills screw holes and starter holes for wire burning dowel holes.

After fully machining the bottom of the tool steel die section, they invert and mount it to a machining plate that contains holes the exact same size and distance apart as the two reference holes. These holes are used as reference holes for the remainder of the machining process.

Don’t bother machining or squaring up the sides of items such as stop blocks, pad balancers, and spacers that do not require squared-up surfaces to function.

Polishing and Finishing Nonfunctional Surfaces

I’ve seen shops waste hours, days, and even months on polishing and metal finishing nonfunctional tooling surfaces. Many surfaces that are machined in a die have no contact with the sheet metal or part. Contoured pressure or stripper pads often are engineered never to touch the metal.

In drawing and stretching dies, the only functioning surfaces that touch the part or metal are male convex-shaped surfaces. Male radii are good examples of convex features. Don’t waste time polishing draw die cavities unless they have male features that get formed into the part. Any feature that is concave does not need to be metal-finished unless the surface is coining on the male feature at the bottom of the press stroke.

Antiquated Polishing Techniques

During my apprenticeship, I was taught to polish in the direction of the metal’s flow when finishing a drawing pad, die face, or die entry radius. And it’s true, when you first finish a drawing pad or die face, polishing in the direction of flow is recommended and no more time-consuming than finishing in any other direction.

However, polishing the die entry radius in the direction of flow is a waste of time and typically provides no benefit. I once witnessed the die entry radius on a very large automobile body side panel get polished in the direction of flow. It took three days to polish the entire radius. The diemakers were painstakingly taking emery paper and pulling it over the radii until it was polished to what they felt was satisfactory. This entire radius polishing process could have been performed by using a series of Scotch-Brite pads followed by diamond compound on a felt bob in about four to six hours.

Keep in mind that once you obtain a certain surface finish, the direction that you polished the surface will have little or no effect on the tool’s performance.

Should you take pride in your craftsmanship? Of course! By all means, do the best work you can. But direct your attention to the things that need to be right and avoid wasting time on those that have no fit or function. Customers aren’t willing to pay for a pretty die when a cheaper, uglier one will produce the same part quality and last just as long.

About the Author
Art Hedrick

Art Hedrick

Contributing Writer

Dieology LLC

10855 Simpson Drive West Private

Greenville, MI 48838

616-894-6855

Author of the "Die Science" column in STAMPING Journal?, Art also has written technical articles on stamping die design and build for a number of trade publications. A recipient of many training awards, he is active in metal stamping training and consulting worldwide.

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