September_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 | S E P T E M B E R 2 0 1 9 5 6 T he goal of heat treating is to improve in-service per- formance of steel components. For decades, heat treating has been based on experience. However, with computational power improving every year and com- puter hardware becoming less costly, simulation of complex processes and geometries is now feasible [1] . Heat treatment processes are no longer a black box, but now have become transparent and malleable with the use of heat treatment software. Commercially available DANTE heat treatment software is used successfully to improve heat treat processes and steel part characteristics [1-3] as illustrated in the follow- ing examples in which real-world challenges were solved. HEAT TREATMENT PROCESS MODELING Modeling the heat treatment process requires the solu- tion to several physical phenomena including: • Mass diffusion for the carburization process • Heat transfer for heating and cooling processes • Stress and strain to predict deformation and residual stress • Solid-state phase transformations to predict microstructural evolution DANTE heat treatment simulation software accounts for all of these phenomena [4] . The models in DANTE exist as libraries that link with commercial finite element packages ANSYS Mechanical and ABAQUS/STANDARD. The required material process data (defined as heat transfer coefficients as functions of part surface temperature) are contained in supplied databases. EXAMPLE 1: PRESS/PLUG QUENCH TOOLING DESIGN Problem . Press quenching of a carburized bevel gear was resulting in excessive radial shrinkage of the inner bore [5] . Due to the carburized case on the inner bore spline teeth, final grinding could not be used to meet dimen- sional specifications and still meet mechanical property requirements. Solution . DANTE was used to explore the effects of tool- ing constraints on radial shrinkage. Figure 1 shows the bevel gear and press quench tooling, further simplified to repre- sent a single tooth. The assumptions of cyclic symmetry and uniform cooling in the circumferential direction form the ba- sis of the single tooth model. A free immersion-quench model was executed to ob- serve the behavior of the gear upon immersion into oil in the absence of tooling constraints. Model resultswere compared to the current tooling load conditions used to process the gear. Figure 2 shows that tooling with current loading con- ditions (gray curve) was similar to that for a free oil quench (blue curve), and could have been making shrinkage of the bore worse. Use of a plug or a locked expander controls the radi- al dimension better than a loaded expander. Figure 2 also shows the results of a model using a plug (green curve) to control the radial dimension. In this instance, using a plug greatly reduced radial shrinkage and brought the radial di- mension within tolerance, while maintaining the desired mechanical properties. However, taper of the bore was still an issue. Additional design iterations reduced the taper to manageable levels by tapering the plug, shown as the red line. A contoured plug was also designed, but it did not re- duce the minor predicted curvature. SOLVING CRITICAL HEAT TREATMENT CHALLENGES WITH PRACTICAL PROCESS MODELING Application of heat treat simulation using the finite element method is ideal to troubleshoot, improve, and design heat treating processes. Justin Sims,* Zhichao (Charlie) Li,* and B. Lynn Ferguson, FASM* DANTE Solutions Inc., Cleveland 8 *Member of ASM International Fig. 1 — Simplified bevel gear, single tooth press-quench heat treat model with all tooling shown.