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Revitalizing a Used Mechanical Press, Part 2: Is Your Ram on the Level?

By: George Keremedjiev

George Keremedjiev has been writing this column for more than 20 years. He regularly consults with metalforming companies worldwide and provides metalformers with training on the application and implementation of sensors for die protection. For more information on his seminars and consultancies, contact: Tecknow Education Services, Inc. P.O. Box 6448 Bozeman, MT 59771 tel: 406/587-4751 | fax: 406/587-9620 www.mfgadvice.com gk@mfgadvice.com

Tuesday, February 01, 2011
 
You likely have experienced the following nightmare: Production made very good stamped parts last week but cannot make any this week. Die setups are identical, and the steel is from the same coil. Lubrication is identical week to week, as are process parameters including tonnage readouts, shut-height setting, feeder program, sensor-timing programs and cam-output settings. What could possibly be wrong?

Typically, the finger pointing starts. The pressroom blames the toolroom for an unstable die. The toolroom blames pressroom personnel for lacking sufficient die-setup expertise. Both blame the forklift driver for damaging the die during transit from press to shelf, and all three blame the maintenance department for not being more watchful over the press.

The game continues, as all four then blame the die designer for designing a poor die, and all five then find blame elsewhere.

Let’s consider one possible cause of the inconsistent production quality: An operator leaves a gauge block in the die and turns the press over, closing the die on top of the block. Miraculously, the die survives, but in short order, solving the cause of poor part quality begins.

For years I have been asking my clients to regularly check ram parallelism—doing so would have avoided the above-noted quality issue. It is a total misconception on the part of many in our industry that if a die survives a hit with a foreign object inside, be it a wrench, slug or gauge block, all must be well and production should not be affected. Wrong. The press most probably, but ever so imperceptibly, has been compromised. The ram could be out of position, its four corners no longer in parallel with each other in reference to the bolster.

I know of no die designer who has, during his design process, assumed that the upper die will be left-to-right cocked 0.012 in. Yet I have seen rams out of parallel as much as 0.020 in. Just what kind of die wear can one expect from such a disaster, much less part-quality tolerances? Bushings, pilots, punches, cams, etc. all are forced to now work out of the ideal parallel and perpendicular requirements of the die designer.

An even greater tragedy: Some shops will run a new die right from the start within a press whose ram is seriously out of parallel with the bolster, of particular concern with setting the die in

Revitalizing a used mechanical press
a used press. Just what abuses have you inherited from the previous press owner? Is the ram at the specs outlined by the press manufacturer? How can one quickly assess its parallelism? Likewise, how does one, within the confines of quick die change, just-in-time and lean manufacturing, quickly check the ram?

One device for doing so that I’ve become familiar with is the Parallelism Verification Device (PVD) from Upton & Sullivan Co., Oakville, Ontario, Canada. It allows an operator to accurately identify alignment problems without removing the die from the press. It also can check the parallelism of the ram without a die being present. It’s not a measuring device; rather, it is an indicator of positions on the ram relative to one another and to the bolster. This is exactly what the doctor ordered. The PVD comes in four models, covering a wide range of ram-to-bolster and die-set gaps. Learn more at www.upton-sullivan.com. MF

 


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