Meaning
Thermal barriers at the interface of a molded part and the mold cavity wall restrict the rate of heat dissipation during solidification. The cavity contact resistance determines how quickly heat transfers from the molten material to the cooling channels. This resistance changes dynamically as the material cools, shrinks, and detaches from the mold surface.
Thermal Dissipation
Cooling rates are highly sensitive to the contact pressure between the hot material and the steel mold. Initial high pressure ensures low cavity contact resistance, facilitating rapid heat transfer. As the part solidifies and begins to shrink away from the cavity, an air gap forms, causing the resistance to rise by orders of magnitude.
Process Simulation
Accurate injection molding simulation requires detailed modeling of this variable resistance to predict cycle times and warpage. Using a constant resistance value leads to incorrect temperature histories and inaccurate predictions of residual stresses. Therefore, advanced solvers adjust the resistance based on local displacement and contact state.
Tooling Optimization
Tool makers optimize surface finish, draft angles, and cooling channel placement to manage the heat transfer variance. Adjusting these parameters helps maintain a more uniform temperature distribution across the part during cooling. A uniform cooling profile reduces internal stress, prevents part distortion, and optimizes the overall cycle time in high-volume production lines where seconds saved translate directly into increased daily output and lower manufacturing costs.
