Page 54 - MetalForming August 2012

Metalforming Electronics
If our sample die has a twin and each die will run in two sep- arate press systems, it is quite possible that in a typical domes- tic metalforming job shop the two presses will have two dif- ferent feed mechanisms, different oiling devices, different shut-height adjustment procedures, different ram-parallelism settings, different tonnage-distribution forces, different brake- stopping times, different scrap removal methods, different part-blowoff systems, etc. And don’t forget, two different die setters with different levels of skill training, attitude, discipline and interpretation of the setup sheets; and operators whose predictability and repeatability can be all over the map.
Now imagine a shop that may run our two dies in six press- es, rather than just two, and the situation becomes even muddier. Yes, the sensors and their installations are identi- cal on the two dies, but the relationships between the dies and their respective presses may be totally different from setup to setup—in subtle and perhaps not-so-subtle ways.
Rare is the stamping company where every press system operates identically, where every setter has been formally and equally trained on best practices for tooling setups, and where every operator has undergone the training required to ensure operations are duplicated from setup to setup. Some specific examples of the variability that can occur from press to press:
• Different feed-acceleration and speed characteristics, which leads to slightly different strip-arrival times;
• Rams that close the upper die at varying angles of par-
allelism, causing the strippers to arrive differently above the sensor blocks;
• Press-stopping times that may not be adequate enough, especially at higher speeds, to properly stop the system before the die closes on a misfeed or a double hit;
• Poor lubrication, which leads one press setup to expe- rience strip-to-guide friction while another sees its strip fly through such guiding; and
• Slight differences in the press-mounted part-blowoff tub- ing that has one die detecting the part exit at a different angle than the other die.
The above scenarios explain, in part, why there are no short cuts. Regardless of one’s level of experience with sen- sors, the harsh and unpredictable realities of the pressroom floor can be a blast of cold water in one’s face. Accounting for process variability when setting sensor timing takes time, and in our time-pressed manufacturing environments it is all too easy to skip the crucial experimentation step.
Do not simply assume that two dies running in several dif- ferent presses will operate identically in all setups. Rather, please allow your sensor experts a reasonable amount of time to experiment with every press and die sensor setup, as required. To skip this crucial step invites many of the frus- trations that often are blamed on the sensors, but truly reside with the variability present in a typical metalforming
job shop.
MF
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Yearsof 1942-2012 Excellence
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MetalForming/August 2012
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