Investigation of an inverse thermal injection mould design methodology in dependence of the part geometry

Abstract

The production of injection moulded components with low shrinkage and warpage is a constant challenge for manufacturers. The thermal design of the injection mould plays an important role for the achievable quality, especially the placement of the cooling channels. This design is usually based on empirical knowledge of the mould designers. The construction is supported iteratively by injection moulding simulations. In the case of thick-walled plastic optics with big wall thickness jumps, the shrinkage is compensated by injection compression moulding. In this process, the thin-walled areas freeze earlier and the necessary compression pressure introduces stresses into these areas which reduces the optical performance. An adapted cooling channel design can reduce these problems. At the IKV, Institute for Plastics Processing in Industry and Crafts at the RWTH Aachen University, a methodology was developed which inversely calculates the cooling requirement of the moulded part A demand-oriented cooling channel system is derived based on the computed results. The aim of the research projects is to minimise displacement and internal stresses by temperature control of the moulded parts according to the demand. In this paper, the methodology is applied to three different geometries, representing three classical parts for the injection moulding process. Three different quality areas in the mould for the inverse optimisation are defined and investigated. For each geometry the cooling channel designs are then validated in injection moulding simulations based on the results from the thermal optimisation. It can be shown that for different component geometries and thicknesses, different quality areas are advantageous and decrease the maximum warpage of the parts. For thin-walled ribbed components, a 2D approach leads to a 15% smaller displacement, for components with wall thickness jumps, all investigated quality ranges show no differences in displacement, but a surface in the middle of the part is preferred due to a 3 °C lower standard deviation of the temperature distribution.

Variable Offset Computation Space for Automatic Cooling Dimensioning

“…Within the optimization of the inverse mold design, the thermal boundary conditions in the mold are calculated in such a way that a thermally optimal molded part is produced at the end of the cooling phase with regard to the material models and modeling used. This methodology is based on an approach by Agazzi et al [7], was extended by Nikoleizig [18], and is further researched at IKV [17,19,20]. In this approach, a thermal optimization of the injection mold is carried out on the basis of a quality functional, which objectively quantifies the molded part quality after cooling in the injection mold.…”

“…The discussed influences (see Section 4) of the offset on the quality function are analyzed. The quality function is used to evaluate the influence of the offset, since it has been experimentally and simulatively validated that minimizing the function's result causes more dimensionally accurate parts [15,16,18,19].…”

Manufacturing Process of Helicopter Tail Rotor Blades from Composite Materials Using 3D-Printed Moulds

“…Design parameters taken in consideration for the mould of the anti-torque blade are as follows (Table 1): volume to be filled by layup process, cavity design, and clamping force required in order to evacuate the excess resin, geometrical dimensions, tolerances, and part removal when the curing process is finished. For the design of the 3D-printed mould, the following aspect was also taken into account: the minimum wall thickness should be at least 3 mm and cores with thick sections should be used to prevent thermal cracking due to curing and mould damage due to high exotherms [43,49,50]. For the design of the 3D-printed mould, the following aspect was also taken into account: the minimum wall thickness should be at least 3 mm and cores with thick sections should be used to prevent thermal cracking due to curing and mould damage due to high exotherms [43,49,50].…”

“…For the design of the 3D-printed mould, the following aspect was also taken into account: the minimum wall thickness should be at least 3 mm and cores with thick sections should be used to prevent thermal cracking due to curing and mould damage due to high exotherms [43,49,50]. For the design of the 3D-printed mould, the following aspect was also taken into account: the minimum wall thickness should be at least 3 mm and cores with thick sections should be used to prevent thermal cracking due to curing and mould damage due to high exotherms [43,49,50].…”