Production Machining

NOV 2018

Production Machining - Your access to the precision machining industrial buyer.

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Page 14 of 51 :: 13 ,ĞůƉŝŶŐWƌĞĐŝƐŝŽŶDĂĐŚŝŶĞ^ŚŽƉƐĞDŽƌĞWƌŽĚƵĐƟǀĞĂŶĚWƌŽĮƚĂďůĞ One of the most important aspects of successfully quoting and running a new job is to fully understand the material ëiVwV>ÌÃvÌi>ÌiÀ>ÌLi>Vi`>`Ìë>VÌ on your operations. What is it We're Going to be Machining, Exactly? Sure, we know what it is. You get a phone call. "Can you run a job in 1045 steel?" "Sure, no problem!" "No problem? Really?" What if the 1045 was hot rolled, not cold drawn? What if it was normalized and covered with a dark, heavy mill scale? What if it was turned and polished, rather than cold drawn? Material is more than a grade and size. Yes, the grade is the primary determinant of the size and other tolerances, but so is the process and condition/thermal treatment of the steel. For example, hot rolled tolerances are wider than those for cold drawn material. And the tolerances for cold drawn can change depending on thermal treatment as well. The length of the steel bars can determine which straightness ëiVwV>ÌÌi>ÌiÀ>Üii`ÌiiÌ]>`ÌÃV> impact your ability to hold tolerances and relationships on the parts you manufacture. For a 1 1 |16 inch round 1045 steel bar, the tolerances for hot rolled product (which you would not want to machine) would be +0.010 inch, -0.010 inch, and 0.015 inch out of round. Try holding that in a collet, even without considering the abrasive scale that covers the bar. For a cold drawn 1045 bar of the same dimension, the size tolerance would be +0.000 inch, -0.003 inch. And the out of round would be no more than one half the dimensional tolerance, or 0.0015 inch. That is far easier to hold in your equipment. Bar straightness is also determined by whether or not the material is hot rolled (¼ inch in 5 feet, "about as straight as a pork chop bone," according to one setup man I met back in the day) or whether it is cold drawn and then by length and thermal treatment. That bar of 1 1 |16 inch round 1045 steel, Understanding Steel Material Specifications on New Jobs By Miles Free – Director of Industry Research and Technology Continues on page 16 depending on whether it was ordered over 15 feet or less, and whether or not it is thermally treated, could be delivered with straightness of either 3 |16 inch in 10 feet or 5 |16 inch in 10 feet. You would never be able to run at commercial production speeds with the hot roll straightness tolerance of ¼ inch in 5 feet! Cold Finished or Cold Drawn Many folks in our industry use these two terms interchangeably. While it is true that all cold drawn bars >Àii}Ì>ÌiÞÀiviÀÀi`Ì>úV`wÃi`]»Ì>V` wÃi`L>ÀÃ>ÀiV``À>Ü°ƂV``À>ÜL>À>ÃLii drawn through a die to impart cold working strain, which changes the material's mechanical properties, resulting in generally improved machinability. Turning and polishing will ÀiÃÕÌ>ViÛ}ÌiÃ>iºV`wÃi`»`iÃ> tolerances, but will not alter the mechanical properties from the hot rolled condition. This means that the turned >`«Ãi`V`wÃi`]LÕÌÌV``À>Ü®>ÌiÀ> ÜÌÞi`>ÃVi>ÃÕÀv>ViwÃ>`>ÞÀiµÕÀiÀi horsepower and result in poorer tool life than a comparable cold drawn bar. Special note: In some cases, the customer will arrange to furnish material. We are seeing this more now because of the tariff issues making material supply problematic at best. It is critical that you get full disclosure from your customer as

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