EXPERIMENTAL MODEL OF UNIFORM THERMAL PATTERNS ON PUNCHED SURFACES FOR SHEET AHSS STEELS BY THE APPLICATION OF INDUCTION HEATING

Abstract

This thesis proposes an experimental study of heating limits for punches present in high-strength sheet steels by applying induction heating. This work aims the handling of holes, which are currently a limitation in the application of induction heating due to the saturation of Eddy currents caused by the interruption of their flow through the workpiece generating a non-uniform thermal pattern, which make inefficient a subsequent heat treatment, additionally to the characteristics of AHSS(Advanced High Strength Steels) which mostly are not manufactured to be heated. Physical prototype coils are manufactured to test the flow of eddy current for AHSS. Validation of shear condition of punches is performed between conditions, before and after applying the heating, of the coupons through optical microscopy to validate any potential defects caused during heating, additional to the time of their melting point, which is used as reference to determinate the influence of punching in the heating pattern and the ΔT present on the sample. The most common geometries of punches for structural components are selected for the experimental stage. Several variants of the process are presented in which an angular speed is applied on of the workpiece to solve overheating condition and get a uniform thermal pattern. Mathematical analysis is presented based on the results of the test, behavior equations are set to define the phenomena and a final iteration is performed delivering a good correlation and proving that the problem of thermal uniformity can be solved.