Good design, set-up, maintenance can keep dies out of repair shop
Take this old maxim to heart: A stitch in time saves nine. The same goes for die maintenance and repair.
A technical society once asked me if I would be willing to write a book on stamping die maintenance. Chuckling, I told the requester that I'd have the book done by Friday.
He did a double take. "Friday?" he asked. "You must have already completed the book, huh?"
He was even more surprised when I told him that I hadn't even thought about the book. "I hope you don't expect it to be more than 30 or so pages," I said.
He seemed downright astounded as he told me that all of the books he had seen on die maintenance were several hundred pages long and proceeded to ask how, pray tell, I could possibly summarize all of this information in such a short book. (Believe me, I think his faith in my stamping knowledge dropped a few notches during that discussion.) Sensing his confusion, I explained myself.
I pointed out that, although regular die maintenance is necessary for a successful stamping operation, the unfortunate truth is that shops spend far more time on repairs than on maintenance. This should not be. One usually precludes the other.
Following is a list of a few of the most common types of die repair:
- Welding a pad back together
- Fixing or welding cracked tool sections
- Removing double metal from a cavity
- Straightening a die shoe
- Fixing chipped cutting sections
- requent polishing and resurfacing
- Replacing broken pilots
- Realigning cutting punches
- Drilling out slugs
- Very frequent sharpening of tool sections
- Remaking smashed set-up blocks
- Replacing crushed nitrogen cylinders
- Straightening bent pads and plates
- Galling of cams and slides
I could go on and on. The point is, all of these repairs are costly and usually can be prevented, or at least postponed.
Unnecessary die repair stems from several basic shortcomings, namely, poor die design, setup procedures, tool design, and maintenance techniques.
Poor Die Design. It always amazes me how many die maintenance programs revolve around a poor die design.
For example, let's say coil springs are breaking in the die every 2,000 strokes of the press. To ensure that they are replaced before breakage, you could schedule spring replacement every 1,500 strokes. The reality is that the springs should last 10 times that long, though.
The root of the problem most likely is that the die in which the spring was used was designed improperly or that the spring was deflecting far beyond its most efficient rate. The long-term solution: Fix the root problem; that is, the die.
Poor Setup. One shop I visited replaced all of the pilots in a progressive die every 2,000 hits. It was actually part of their regularly scheduled maintenance. They replaced them because they were all galled up and bent and no longer functioned properly.
Root cause: poor setup procedures. Holes were being pierced frequently with the pilots, improper progression feeds were set on the coil feeder, the die was not set up parallel to the coil feeder, and press operators were beating on pilots to remove sheet steel that was stuck to them.
Long-term solution: Educate press operators on progressive die setup and operating fundamentals. Give them ownership of the tools, as well as incentives to ensure that they are set up and run properly. Listen and seek to understand fully their setup and feeding problems. Then collectively seek a solution that you both can live with.
Poor Tool Design. Some frequent tool design problems are:
- Poor tool steel selection
- Poor part ejection
- Poor slug and scrap removal
- Low shut height
Poor Maintenance. Although most repairs can be traced back to bad design or setup procedures, poor maintenance can cause major damage. For example, overshimming an insert after sharpening or failing to place a hole in a shim for slugs to drop through, which are common mistakes, can be disastrous.
The following is a list of everyday maintenance checks — the assumption being that that the die was designed, set up, and run properly in a well-maintained press:
- Sharpen cutting sections as needed and reinstall and retime them if necessary.
- Check and tighten screws and dowels regularly.
- Wash and clean dies as needed.
- Lubricate working components such as guide pins, slides, and cams.
- Monitor cycles and replace springs before the end of their normal life expectancy.
- Inspect dies for cracked or broken sections.
- Resurface die sections worn down as a result of normal use.
- Inspect items such as scrap ejectors, slug chutes, and ejector pins to make sure they are not sticking.
A good preventive maintenance program will pay for itself many times. But keep in mind that all of the die maintenance in the world can't take the place of a properly designed tool that is run in a frequently maintained press by a well-educated press operator.
Avoid setting up a die maintenance program based on poor die design and frequent mis-hits in the press. Instead, find the root cause of your problem and fix it instead of the symptoms.
If you are one of the few who spends most of his time on true die maintenance, congratulations. I tip my hat to you and your company. For the rest of you, I applaud you and your effort to keep up with the one of the most frustrating career paths known in stamping—die repair.
Now, how about a book on die repair? Now that would be a bigbook.