Revitalizing a Used Mechanical Power Press, Part 1
I urge caution when purchasing a used press. It may have a history of severe abuse, even though it appears to be in good shape. It may be full of antiquated or unsafely modified electronics. With patience and understanding one can relatively easily make good preliminary observations and with further testing, determine the condition of the various electronic devices on the press and their related mechanical motions and forces. At the least, you should know what questions to ask when contemplating a press acquisition.
Let’s imagine that you have received an auction notification about a mechanical power press that you have been salivating over for years. As a new machine it was simply out of your company’s financial reach, even during booming economic times. But hold on, the auction notice has an anticipated price for that press that could very well be within your company’s means. Or likewise, perhaps you are acquiring this press through some unimaginable series of seemingly lucky events where one of your customers just happens to have one for sale at a price that is irresistible. Whether the press is at the auctioneer’s facility or at your customer’s, or it arrives with a set of takeover dies, what should one look for during the inspections and, more importantly, what can be done once the press is in your plant to bring the press and die-protection controls up to state-of-the-art standards?
This series will address the following press electronics issues. They are not exhaustive, but represent the core electronic issues to consider, when acquiring a used mechanical power press.
1) What vintage is the press control? Is it homemade? Is it relay based, or does it use a programmable logic control (PLC) or a turnkey system from a current or defunct electronic controls supplier? More importantly, does the control system meet current OSHA and ANSI regulations and standards?
2) What electronic operator safety mechanisms are in place? If there are light curtains for this purpose, are they in compliance with current OSHA regulations? Was the press used in some unorthodox manner and wired to start automatically on its own via some external signal? Are there other unusual controls-related modifications that were job specific that are not apparent upon your first inspection?
3) What is the critical angle or minimum stopping time required for the press to fully come to a halt? What if any electronic technologies currently on the press provide you with this information? What technologies can be purchased to get this information? What information is available from the press manufacturer regarding this very important issue?
4) What can be done to check the parallelism of the ram? What electronic-sensor technologies could be used to determine the position of the ram at its four corners during the full travel of the ram—mounted with an upper die load or not? How to determine if the ram is coming down uniformly during its full travel vs. any unexpected wobbling or undulating motions that may be the result of mechanical damage caused by previous abuse, again with a load attached or not?
5) What is the tonnage distribution by the ram once it closes? Is it uniform in this force delivery from its center to its four extremities? Is this force uniformity available at various points during the ram’s travel? What technologies are available to measure this on a regular maintenance basis once the press is put into operation? What are the effects of poor tonnage distribution on the quality of stamped parts?
6) If there is a mechanical or electronic shut height display, and is it accurate? How to determine this? How to do this when the press is actually running? Likewise for the counterbalance control—is it mechanical or fully automatic and electronic? If the latter, then how does one test the electronics of automated shut height and counterbalance controls?
7) What if any die-protection control is mounted on the press? Is it homemade, relay-based, a PLC or a turnkey electronic system? How many inputs does it have and what types of signals do these inputs accept? What if any per-sensor timing options are available in this control? What are the current standards that one should look for? MF
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