Abstract
This paper presents a framework for optimizing injection molding process parameters for minimum product cycle time subjected to constraints on the product defects. Two product defects, namely, volumetric shrinkage and warpage, as well as seven process parameters including injection speed, injection pressure, cooling time, packing pressure, mold temperature, packing time, and melt temperature, were considered. Injection molding experiments were conducted on specifically chosen test points and results were used to compute the volumetric shrinkage and warpage (at each test point). Thereafter, three relationships between the product cycle time (one relationship), the two product defects (two relationships), and the injection molding parameters were constructed using the kriging technique. An optimization problem to minimize the product cycle time (described by the first relationship) subject to constraints on the product defects (described by the latter two relationships) was then formulated. A combination set of points between the lower and upper extreme values of acceptable product defect was generated to serve as constraints for the two product defects. The optimization problem was then solved using the Fmincon function, available in the Matlab optimization toolbox. A plot of the optimization results revealed an appreciable tradeoff between the cycle time and the two product defects. To validate the optimization, an additional injection molding experiment was conducted for one of the optimization results. Results from the additional experiment showed reasonably close agreement with simulation optimization results differing in the cycle time, the warpage and volumetric shrinkage by 6.7%, 3.2%, and 8%, respectively.
Highlights
Injection molding is undoubtedly among the most important industrial plastic processing techniques
A schematic of a typical injection molding unit is shown in Figure 1. e process is an unvarying, repetitive process that involves feeding plastic to the barrel via a hopper, melting of plastic using heaters in a barrel, mixing the plastic using a rotating and reciprocating screw, injecting the molten plastic into a mold cavity, packing the molten plastic within the mold cavity, cooling of the molten plastic, and thereafter ejection of the solidified plastic part. e process is, generally divided into 3 or 4 phase [2,3,4,5] which include filling, packing, cooling, and ejection. ese phases determine the cycle time of the process, which is an important factor during production as it is directly linked to the cost of production
Summary and Concluding Remarks e work in this study sought to develop an optimization framework for determining the minimum product cycle time while placing constraints on the product defect. e process involved developing three relationships relating the defects and product cycle time, respectively, to seven process parameters. e three relationships were developed based on data obtained through actual injection molding experiments
Summary
Injection molding is undoubtedly among the most important industrial plastic processing techniques. Ese phases determine the cycle time of the process, which is an important factor during production as it is directly linked to the cost of production. It can, be argued that reducing the cycle time (even seconds) within any of these phases will lead to time and cost-savings in the long run especially in the case of mass production. Is includes fine-tuning the injection molding unit to deliver proper injection pressures and speeds (which affects the filling time), designing the product to have minimum wall thickness A combination of various steps is usually taken to reduce the cycle time. is includes fine-tuning the injection molding unit to deliver proper injection pressures and speeds (which affects the filling time), designing the product to have minimum wall thickness
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