Distortion Engineering and CFC Fixtures

Joerg Demmel • April 20, 2019
Distortion engineering: not just a heat treatment topic

“Distortion of machine parts during manufacturing continues 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.” wrote Prof. H. W. Zoch.

The so called methodology of “distortion engineering” consider the processes of raw material for steel parts, e.g., rough-out or rolling, soft machining, heat treatment to hard machining. There are 3 stages of the methodology mentioned in the cited article: “Step 1 the measurement of size and shape changes… Influencing parameters like geometrical symmetry or quenching speed are then determined experimentally and quantitatively”. “Step 2 tries to understand distortion mechanisms, based on so-called “carriers of distortion potential,” e.g. row material chemical homogeneity, introduced stresses during soft machining steps and the parts microstructures over manufacturing steps. “All distortion potential carriers undergo the possibility to be released (like residual stresses) or introduced (like changes in symmetry by machining) during manufacturing chain.”

The Step 2 understanding distortion “should be supported by modeling and simulation”, Prof. H. W. Zoch goes on and he added: “but much development is needed to meet the required accuracy for practical application.”

High Temperature Concept's approach is here different, it’s not the time for every problem and not necessary to understand the distortion engineering 100 %, from bottom up. But, top down is promising some success for industry now! Because the main root reasons which cause distortion are clear. E. g. for soft machining metal cutting with sharp cutting edges and some optimal cutting speed avoid residual stresses or for heat treatment the arrangement of the products in the Rack (2D and 3D), a continuous heating, carburizing and quenching or cooling flow avoid stresses and after e.g. high pressure cooling and phase transformation distortion! Here we are at “Step 3 the compensation of distortion effects”. Mr. Zoch goes on with “…sometimes allows for compensation of distortion effects by inverting these influences, e.g., correction of out-of-roundness by inhomogeneous quenching process.”

Focused on experience HTC understood the main influences incl. the Fixture and Rack Material and Design as one main impact on distortion. See the Figure which shows the Coefficients of Thermal Expansion (C.T.E.) at room temperature and at 1,000 C for different heat resistant materials: for CFC there is in the fiber direction almost no expansion to high temperatures. Meaning that Fixtures made of CFC don't change their dimensions. Furthermore, CFC does not change its form as well. 


We have proved our knowledge several times in industry. HTC's Step 2 distortion understanding is directly connected with Step 3 distortion problem solving. The main contributor are custom made best-in-class CFC-Fixtures and Racks and they bring usually great benefits to our customers.


We started this methodology in the mid of the 1990s.


Let’s bring excellence and a high profitability into your everyday operations.


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 +1 941 299 9191

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Sources: HTPro, Feb/Mar 2019, No. 2, page 2 and sources/references Dr. Jorg Demmel

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