Die Science: How to destroy a die in 7 easy steps (or, how to work every Sunday)
Art Hedrick applies humor to a not-so-funny problem.
In the November/December 2013 issue of STAMPING Journal, I wrote an article called "How to destroy a press." I received a pretty good response from it, so I decided to write down some of my thoughts about dies are often damaged.
Please note that this article highlights the don’ts. You might laugh at some of these, but believe me, I’ve seen them all.
1. Never Perform Scheduled Die Maintenance
Avoid replacing springs, sharpening punches, and cleaning or lubricating working surfaces. Be sure to load all lubeless wear plates with extra-heavy, high-pressure lithium grease. Don’t worry about missing dowel pins, and don’t tighten any of the socket head cap screws. Never replace a gas spring until it fails to return. Don’t replace any springs; let broken springs cause your pressure pads to tilt and break die sections.
Be sure to use several different spring strengths and lengths to ensure poor pressure distribution. If a dowel is loose, just peen the hole over with a hammer. If wear surfaces are galled, just ignore them—sooner or later they will weld themselves to the mating section.
Be sure to use the wrong grinding wheel when sharpening die sections. When available, use very hard-bond, fine-grit wheels for rough grinding. This will ensure that the tool steel will be damaged. Avoid using coolant during grinding as well.
Never clean your dies. Instead, leave all of the grinding grit in them. Never inspect gas cylinders for leaks, and always overpressurize them so that they blow out seals as soon as possible. Don’t inspect the die before it goes into the press. Just assume that you took care of all of your tools and that you didn’t leave your micrometer under a pressure pad that bottoms out on the die.
2. Shim Sections Crooked
Shim cutting and forming sections crooked so you will be certain to destroy the die. Be sure to make them tilt a lot. Avoid grinding the bottoms flat; just keep shimming them crooked. Also be sure to use more than three shims under each block. If you really want cutting sections to break, use 15 shims, each 0.005 inch, under a block instead of a single 0.075-in. shim. This will ensure that the tool steel section deflects and bends under load.
Make sure that your shims overhang the slug drop area, because this will surely keep the slugs from falling through the die. In fact, to guarantee a slug up, forget putting the slug drop area in the shim altogether. Just assume that the slugs will make their own holes.
3. Weld on Tool Steel Without Preheating It First
Avoid preheating tool steel sections before welding on them, especially if they are air-hardened or CPM® grades. Weld them cold. Be sure to put on 10 times more weld than you need.
Don’t worry about postheating or drawing the tool steel back after welding it. Don’t grind out any tool steel cracks—just weld over them. Also be sure to weld the die right in the press so that weld spatter goes all over in the die.
4. Never Run Lube on Your Die
Never use lube on your die, especially if you’re doing operations such as deep drawing of stainless or high-strength steel. If you are going to use lube, mix it with the hand check method. If it feels right, it must be right. This will surely result in scoring and galling.
Don’t worry about getting lube where it is most effective—just blast the stop block will gallons of the stuff. Never lubricate both sides of the strip. And don’t forget to run heavy chlorinated lubes on solid-carbide dies. Chlorine will surely result in carbide damage.
5. Use a Poor Press
Be sure to install a high-tonnage, precision-alignment die in an old, beat-up gap-frame press. Be sure the frame of the press is cracked. Make sure you use all of the tonnage to ensure maximum press deflection, resulting in massive punch and die section breakage.
Don’t worry if the ram of the press is out of parallel with the bolster plate. Just assume that the die will make everything flat and parallel.
6. Set Your Shut Height Incorrectly
To use the stop blocks incorrectly, remove them and set your shut height based on how it sounds when the ram hits bottom. If you’re not getting a good part, keep lowering the ram until everything is just right. Heck, you might even get a “twofer” out of that one—you will break the press and the die! Use things like old cigarette butts and a matchstick to set the shut height.
7. Ignore All Die Protection Methods
If your die is equipped with die protection sensors and limit switches, unhook them; better yet, throw them out. Just assume that the press operator is really quick and will be able to avoid crashes.
I hope I haven’t sounded too cynical. I have always felt that it is just as important to know what not to do as what to do. I have just scratched the surface of the don’ts. I’m sure there are hundreds of other things that could destroy a die.
Until next time … best of luck!
STAMPING Journal is the only industrial publication dedicated solely to serving the needs of the metal stamping market. In 1987 the American Metal Stamping Association broadened its horizons and renamed itself and its publication, known then as Metal Stamping.