Ask the Stamping Expert: How can we achieve fast punch changeout halfway through a run?

STAMPING Journal November/December 2011
April 1, 2016
By: Thomas Vacca

Q: I’m a diemaker for a Detroit Three automaker. We have a job on which we have to change punches halfway through the run. Changing the punches is a lengthy operation and involves quite a bit of downtime. Does anyone in the industry make an automatic or semiautomatic punch removal system that we could implement?

A: Your question goes deeper than just changing punches; it cuts to the heart of how to reduce downtime for tooling service. It all starts early in the design stage and understanding what you can justify as an upfront investment to minimize service time as much as possible.

In a standard three-plate design, the punch holder is mounted to the top die shoe, backed up with a hardened steel plate so the punch heads do not pound a recess into the soft die shoe. A spring-loaded stripper, also mounted to the top, compresses with each stroke, allowing the punches to protrude into the die when the tool is closed.

As the tool opens, the springs push the stripper plate, stripping the raw material being stamped off the exposed punch tips. The die chase, a large block of hard steel, usually holds cutting inserts that can be knocked out for sharpening. This also is backed up with a hard steel backup plate on which cutting inserts or bushings sit.

With a die of this design, you can minimize punch changeover and service time in three ways:

1. Design in punches that are held in with a head behind the punch holder, adding a backup plate that is accessible from the top side of the shoe. Use hydraulic quick clamps to mount the top die shoe to the press ram. To change the punches, drop the ram, use the quick, unclamp of the top die shoe, raise the press ram, and remove the backup plate on the top side of the die shoe to access the punches. This changeover should take no longer than 30 min.

2. Have all the trims in one module—almost like a small die within a die. If you choose this option, you’ll need to consider it upfront in the original design review. When the trim punches need changing, you can change the whole module. The design needs to be robust to achieve repeatable location of the module during removal and reinstallation. Using half-turn quick clamps, or quick-lock clamps, you should be able to change out the module in about 15 min. and then service the tooling offline. This option requires more upfront investment than option 1, but it allows you to service the punches and dies without sacrificing production time.

As a rule, punches wear twice as fast as dies because they pass through the material twice during each stroke: once on entry and once on retraction. This can vary, however, depending on the type of materials, lubrication, and clearances you use. Be sure to consider this carefully during the original design so you can change the punches, dies, or both as needed.

3. If space allows, design the tool with two trim stations. Mount the punches on a retractable slide. Run one set until it’s dull, and change the punches by pulling on the retractable slide, allowing the punches to rise, and lowering another set by pushing in the slide.

With this method, you can service punches and die cutting stations on-the-fly in less than 5 min., but be aware that upfront design and cost are the drawbacks. This option is suitable for tooling that has a particular cutting or forming station that wears much faster than the rest, such as a shave or extrusion station. If can be convenient and cost-effective to have one punch or form duplicated for slide tooling changeout.

In all cases it is important to think upfront about potential service needs, engineered hits per service, and how to maximize efficiency. Engineering should define and address these issues in the design phase, balancing expected run volumes with higher upfront tooling investment.

Good luck and happy stamping!

Thomas Vacca

Director of Tooling and Design Engineering
Micro Stamping Corp.
Has a shop floor stamping or tool and die question stumped you? If so, send your questions to kateb@thefabricator.com to be answered by Thomas Vacca, director of tooling and design engineering at Micro Stamping Corp.

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STAMPING Journal

STAMPING Journal

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.

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