Process studies in precision injection molding. I: Process parameters and precision

Abstract

Precision injection molding is an important technology for improving productivity arid lowering costs in fields such as electronics, photonics, and medical plastics by allowing the substitution of molded plastics for more expensive metals and ceramic parts. This work is part of an effort to develop a molding technology that can deliver the micron-level precision required for these applications. Two engineering thermoplastics with glass and/or mineral fillers, polytetherimide) (PEI) and polytbenzoate-naphthoate) liquid crystal polymer (LCP), were studied. Precision was defined as the standard deviation of part mass and part dimensions as measured on a coordinate measuring machine. Robust design, or design of experiments (DOE), principles were used to determine optimal injection molding parameters. The results showed that ram position and hydraulic pressure were the most effective injection phase cut-off control methods of those studied. With regard to process parameters, those that increase melt fluidity had the greatest effect on improved precision with PEL For LCP, the effect of process parameters was f a r more complicated. The cross-sectional morphology of the liquid crystal parts was investigated in the second phase of the study to assess the influence of morphology on part precision.

Tuning and control of dimensional consistency in molded products

“…Subsequently, it is desirable to select a robust set of process conditions x j that centers y and minimizes σ y , thereby maximizing the process capability and the yield. 7 A typical tolerance in molded products is ±0.1% of the absolute dimension, 12 corresponding to a typical tolerance of ±0.1 mm for a 100 mm dimension. Dimensional tolerances lead directly to requirements on shrinkage.…”

“…Alternatively and more commonly, the dimensional properties of molded products are qualified using weight. 12 In this approach, the products are weighed as they are manufactured, with dimensional consistency assumed if the weight is within prescribed limits. This paper investigates issues pertaining to dimensional tolerancing and control in molded products.…”

An innovative regression model-based searching method for setting the robust injection molding parameters

“…A set of robust processing parameters might be obtained through certain methods, such as optimization and documentation of parameters (Nirkhe and Barry, 2003;Bozzelli, 2003), experimental designs of optimal parameters (Dowlatshahi, 2004;Viana et al, 1998;Liu and Manzione, 1996;Wu and Chen, 2006), applications of fuzzy theory (Vagelatos et al, 2001) and neural network (Sadeghi, 2000;Lau et al, 2001;Ribeiro, 1999). The flowchart of the searching method provided by this work, also illustrated in Fig.…”

A comparison of seven filling to packing switchover methods for injection molding

“…The use of switchover methods based on screw position and injection pressure has been extensively studied [6–8] but remains unresolved. For example, Liu and Manzione [8] optimized a liquid crystal polymer molding process using a switchover method based on screw position. Later, Tao [9] performed an optimization of the molding process using a Taguchi method with a switchover based on injection pressure.…”