Distortion engineering

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As Distortion Engineering is called a methodical approach to engineering-based mastery of delay causes.

This approach supports, on the one hand, a distortion-compatible design and manufacture of components and, on the other hand, compensation of component distortion through the targeted use of existing distortion potential carriers (VP ​​carriers) in the process chain. An essential feature of distortion engineering is the system consideration and the knowledge that only considering the distortion as a property in the entire production chain can be successful. For this, the interactions of the influencing factors from the individual production steps on the warpage must be identified, understood with regard to their effect and incorporated into a cross-system solution approach through cooperation between the relevant specialist disciplines.

method

Fig. 1: Procedure in distortion engineering / system-oriented distortion and mechanism analysis

The procedure in distortion engineering consists of three steps (Fig. 1):

  • Determine system and manipulated variables
  • Determine the carriers of the delay potential
  • Initiate measures to compensate for delay

Step 1

Possible, significant influencing variables in the form of system and manipulated variables (system variables: machine, workpiece, tool, cooling lubrication; manipulated variable: cutting speed, feed rate, etc.) are determined along a production chain. One possible approach is the application of the Design of Experiments method ( statistical test method ). At the end of step 1, all significant influencing factors have been determined. Now, in the next step, a correlation must be established between the influencing variables and the VP carriers.

step 2

The influencing variables determined in step 1 are used for a cross-process description of the delay potential (VP). The warpage potential includes the sum of all influencing possibilities to trigger processes that can have an unfavorable influence on the dimensions and shapes of a component and is quantified by the state of different carriers of the warpage potential. The potential carriers identified so far are listed below:

  • Dimensions (geometry);
  • Chemical composition;
  • Structure;
  • (Internal) stresses;
  • Temperature ;
  • Mechanical history (solidification).

However, it is not the specified sizes per se that are decisive for the distortion, but rather their spatial distribution in the workpiece . The specified VP beams were determined using steel as the material . Other carriers may occur in other materials.

Figure 2: Influencing the warpage potential carriers in the process chain

Each sub-process of the process chain can change the status of these VP carriers either directly via the process variables or indirectly through interactions between individual VP carriers. Figure 2 shows schematically how the VP carriers are influenced in a process chain.

Which VP carrier ultimately determines the warpage depends primarily on the component geometry and the manufacturing process.

The complex interactions that occur within the workpieces can usually only be recognized by using process simulations (for the example of steel, these include the casting simulation, machining simulation, forming simulation and simulation of the heat treatment )

step 3

Fig. 3: Deformation reduction through targeted use of the compensation potential

With the knowledge from steps 1 and 2, the manufacturing process can initially be designed to be warpage. In addition, through targeted changes to selected VP carriers, a compensation potential can be generated that offsets the influence of the other VP carriers (Figure 3).

The compensation potential is defined as the sum of all influencing possibilities to trigger processes that can favorably influence the dimensions and shapes of a component. Global compensation measures are already carried out in the process planning. In addition to quality planning, the in-process measurement of the component geometry and the use of appropriate control strategies optimize the compensation for individual components during manufacture.

Practical example

Image 4: Distortion-correct turning of thin-walled workpieces
Figure 5: Reduction of roundness deviations through targeted asymmetrical gas quenching

Process design suitable for warpage can be explained using the production of thin-walled workpieces (e.g. roller bearing rings). In this case, variations in the roundness and wall thickness, which normally have to be eliminated through extensive reworking (grinding), are successively minimized in the process chain through various compensation measures.

The wall thickness variations are reduced by machining (turning process, Figure 4). During machining, the clamping force Fsp causes elastic deformation of the workpiece. The resulting inhomogeneous stock removal normally leads to wall thickness fluctuations and roundness deviations. However, by rotating the ring by 60 ° during the second clamping and adapting the clamping force according to the reduced wall thickness (compared to the first clamping), fluctuations in wall thickness are largely compensated for.

The remaining roundness deviations are then compensated for in the subsequent heat treatment using targeted asymmetrical heating and quenching conditions.

literature

  • F. Hoffmann, O. Keßler, Th. Lübben, P. Mayr: Distortion Engineering. Control of defaults in production . In: HTM . No. 57 , 2002, p. 213-217 .
  • K.-D. Thoben, T. Lübben, B. Clausen, C. Prinz, A. Schulz, R. Rentsch, R. Kusmierz, L. Nowag, H. Surm, F. Frerichs, M. Hunkel, D. Klein, P. Mayr: Distortion engineering. A system-oriented consideration of the component warpage . In: HTM . No. 57 , 2002, p. 276-282 .
  • Th. Lübben, H.-W. Zoch: Distortion Engineering. A Systematic Strategy to Control Dimensional Changes . In: Heat Treatment and Metallography Study Group of AIM (Ed.): Innovation in Heat Treatment for Industrial Competitiveness . Verona May 7, 2008 (proceedings).