Numerical Analysis of Thermal Stress and Shrinkage of Wax Patterns: IV. Cooling Condition to Minimize the Residual Thermal Stress

The optimal cooling conditions used to minimize the residual thermal stress in wax patterns were derived theoretically from the uniaxial thermal stress equation by using Euler-Lagrange's method. This was calculated for three brands of casting waxes. The optimal condition thus obtained gave an approximately minimum stress of many conditions arbitrarily established. The optimal cooling was such that the reduced time, derived from the time-temperature superposion principle, might be long for stress relaxation in a given period. In a short time (10min and 30min), the residual stresses were not much different between the optimal cooling and spontaneous cooling, but after 5 hours, the stress under optimal cooling was half the value of the spontaneous cooling.