b'\x1b\x1a\x19 \x1f\x18\x1d\x17\x16Machinists CornerHOT-ROLLED VERSUS COLD-ROLLED STEELBy Brandt Taylor cold finishing process. The internalbend the bar. For a thin-walled part stress situation is important to un- made from round bar, if an axial slot S teel mill products can be classi- derstand because it can lead to un- is made, the diameter of the part fied broadly by the mill finishingintended consequences when met- becomes larger. For parts that can process, whether hot rolled or coldalworking. If the stress is removed ordeform from unbalanced internal rolled. Hot-rolled products includemodified in the metalworking pro- stress, the solution is to start with structural shapes, round and flat bar,cess, it can change the dimensions ofstress-free material for the machin-and plate. Cold-rolled products in- the part. The cold working stretchesing process. That means that one clude round, flat and hex bar stock;and hardens the steel at the surfaceshould begin with either hot-rolled plate; and sheet metal. and puts the material under tension.material or stress-relieved cold-rolled Hot-rolled products dont haveSince opposite surfaces are stressedmaterial. Stress relieving steel is a the same level of dimensional ac- equally, the material is in balanceheating process. For materials that curacyascold-rolledproductsand dimensionally stable. dont heat-treat, such as alloy 1018, and have an iron-oxide coating,For a flat bar, if one surface is re- this can be done with an acetylene but hot-rolled products dont havemoved by machining, the oppo- torch. Heat the metal to a dull red the internal stress created by thesite surface tends to contract andcolor, and then air-cool. Overheating Mersen_HiTechAd_HalfPgCTE2_20.qxp_Layout 11/13/208:43 AMPage 1Trust DS4 Ultra-FineEDM Graphite forYour Toughest Jobs The intricate EDM electrodes required to produce our audiospeaker grills take 7+ days of machining and 30+ hours of EDM burning. We needed a graphite we can trust to withstandthis demanding application. We switched to MersensDS4 ultra-fine EDM graphite a few years ago and its beenthe best performing graphite weve used. With the DS4 materialwe have also seen significant savings per electrode. Eric JacobsenHi-Tech Mold & EngineeringDS4 Delivers: Excellent surface finish Exceptionally strongIntricate detail Saves significant money Easy to machineAsk your EDM distributor for DS4!edm.mersen.com Made in U.S.A. Shaping the future of EDM10JULY 2021MachinistCorner.indd 10 6/18/21 2:38 PM'