February AMP_Digital

FEATURE A D V A N C E D M A T E R I A L S & P R O C E S S E S | F E B R U A R Y / M A R C H 2 0 1 9 5 4 2 If themechanisms and parameters of distortion are un- derstood, Step 3 of distortion engineering sometimes allows for compensation of distortion effects by inverting those influences, e.g., correction of out-of-roundness by inhomo- geneous quenching processes. The described methodology allows one to understand andminimize or counteract distor- tion phenomena, not only for steel parts. More information can be found at www.distortion-engineering.de. A corre- sponding conference series, the Quenching and Distortion Engineering of the International Federation of Heat Treat- ment and Surface Engineering and Leibniz-IWT, Germany, recently took place in Nagoya, Japan. DISTORTION ENGINEERING: NOT JUST A HEAT TREATMENT TOPIC D istortion of machine parts during manufacturing con- tinues to cause high economic losses. Heat treatment processes, especially quenching, are often thought to be solely responsible for size and shape changes that require extensive hard machining to meet the necessary accuracy and tolerances. For the past few years, treating distortion problems as a system attribute of the entire process chain has become a widely accepted approach. Following a proposal of Peter Mayr, the former head of IWT, management of those challenges is called “distortion engineering.” The corre- sponding, well-established methodology of distortion engineering takes into account the processing of rawmaterial for steel parts, e.g., ingot or continuous casting, rolling and forg- ing operations, soft machining, heat treat- ment, and hardmachining. The different stag- es of the methodology start with Step 1, the measurement of size and shape changes. This measurement depends on which geometrical deviations are decisive for the specific com- ponent, such as out-of-roundness of rolling bearing races, dishing of gears, or bending of shafts. Influencing parameters like geometri- cal symmetry or quenching speedare thende- termined experimentally and quantitatively. Step 2 tries to understand distortion mechanisms, based on so-called “carriers of distortion po- tential,” including the chemical homogeneity of steel bars or forgings, introduction of residual stresses (especially those caused by clamping during soft machining), and distribution of microstructure within the cross section of a part. Those carriers of distortion potentially act as “data storage” across the entire process chain, revealing modifications caused by subsequent processes, e.g., changes inmicrostructure distri- bution from segregation patterns of rolled steel bars to mi- crostructural symmetries of forged parts until the final heat treated component. All distortion potential carriers undergo the possibility to be released (like residual stresses) or intro- duced (like changes in symmetry by machining) during the manufacturing chain. The understanding of mechanisms should be support- ed by modeling and simulation. Here, significant effort is necessary to model those changes not only for single pro- cesses, but within all steps of a process chain. A few software packages areavailable to solve this task, at least partially, but much development is needed tomeet the required accuracy for practical application. A key issue in this case is the mate- rial data, which describes the thermal and mechanical be- havior of microstructure at all conditions during processing. GUEST DITORIAL Most research to date has been performed on conven- tional steel components—cast, rolled, turned, and heat treat- ed. We all face the increasing application of 3D printing tech- nologies, i.e., additive manufacturing (AM). Here, the total manufacturing process is a combination of local solidifica- tion, tempering and re-tempering, residual stress buildup and release, and highly dynamic temperature changes. So far, AM is mainly focused on non-heat treatable steels like austenitic stainless steels, and this process also can be treat- ed with distortion engineering methods if stress relief an- nealing is performed. However, AM will gain much more im- portance if heat treatable steels areproducedby thisprocess. Therefore, the challenges of proper heat treatment selection and distortion management for modern manufac- turing technologies are crucial for economic production and should keep materials engineers busy for the foreseeable future. Hans W. Zoch Managing Director, Leibniz Institute for Materials Engineering, IWT Bremen Professor, University of Bremen, Germany