Distortion Engineering

AS MENTIONED in the article “Basics of Distortion and Stress Generation during Heat Treatment” in this Division, distortion is a system property, and distortion control during manufacturing processes must follow a system-oriented approach. The fact that the corresponding system is the complete manufacturing chain is very important. One answer to the question of what must be done to control size and shape changes under these conditions was given by Zoch (Ref 1). He reports about the development of a methodology called distortion engineering. Always taking into account the entire process chain, this methodology consists of three levels of investigations (Fig. 1). On Level 1, the parameters and variables influencing distortion in every manufacturing step must be identified. In general, a large number of parameters may be important. Therefore, design of experiment (DOE) techniques were used, which allow the investigation of larger numbers of parameters by a limited number of samples, enabling the identification of cross-influencing parameters as well as interdependencies. On the basis of the resulting knowledge, Level 2 focuses on understanding the distortion mechanisms by using the concept of distortion potential and its carriers (see the article “Basics of Distortion and Stress Generation during Heat Treatment” in this Volume). Modeling and simulation not only are helpful, but in many cases are necessary tools to fully understand the mechanisms governing the distortion generation. Distortion engineering aims to compensate distortion using the so-called compensation potential (Level 3). On one hand, this approach uses the conventional method to increase the homogeneity, and respectively the symmetry, of the carriers of the distortion potential. On the other hand, well-directed insertions of additional inhomogeneity/asymmetries in one or more of the distributions of the carriers can be used to compensate the resulting size and shape changes of the existing asymmetries. For example, an inhomogeneous quenching process can be used to compensate shape changes from the previous manufacturing process. In principle, a compensation of single components is possible. On this level, in-process measurement and control techniques are very important (Ref 2, 3). The Collaborative Research Center “Distortion Engineering” at the University of Bremen analyzed different manufacturing chains according to the three levels of distortion engineering and rated the results according to the success of the underlying analyses.Details of the investigated manufacturing chains and the corresponding results can be found in Ref 2 (rings, SAE 52100), Ref 4 (rings, SAE 4140), Ref 5 and 6 (shafts, SAE 5120), Ref 7 and 8 (bevel gear, 17 CrNi6 6), and Ref 9 and 10 (aircraft panel, aluminum alloy). The investigations of disks of the steel grade SAE 5120 are used in the following sections to describe distortion engineering in detail. Therefore, it is important to know that the distortion of gear teeth is strongly correlated to the size and shape changes of the base body of the gear. This is, in many cases, very similar to a disk with a hole. More details are given in the section “Influence of the Carrier Distribution of Mass— Geometry.” In the next sections are many results for disks, which behave very similarly to the base body of a gear with the same dimensions. Furthermore, and of greater importance, the application of distortion engineering is explained in detail. For rings, all details of distortion engineering are presented in Ref 2.