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Analysis and review of different tools to calculate the production economics in injection molding Abstract The purpose of this work is to make a small review of computer-aided software based mainly on the calculation of the injection molding cost. Only a representative portion will be discussed in this paper. 40981
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An injection molding machine can produce thousands of pieces per day, depending on many factors. A small improvement in the cost per piece can have a significant impact on the industry. These factors have to be carefully considered by the software in order to make accurate estimations.
A total of 5 programs are fully analyzed in this contribution, and this is useful to achieve good cost estimation for the injection
molding process. The main characteristics and/or features of each of them are also described.
Keywords: Cost; software; injection moulding; injection molding
1. Introduction
The injection molding process is used worldwide in plastics industry. Basically all kind of polymers, known sometimes as resins, can be used. This includes all thermoplastics, and some elastomers and thermosets. The quantity of polymers that can be used in this process is growing up every year.
The plastics industry is of enormous scale worldwide. The companies are very competitive and want calculate with precision the cost of producing a single piece to millionths of a cent because of the high production rate.
The mold (sometimes known as die) refers to the tooling used in injection molding. The molds are mostly made of steel, but aluminum can also be used. Aluminum molds cost much less than steel molds. The cost of manufacturing these molds depends on several factors: size, number of cavities, surface finishes, complexity of the pieces, etc. The cost is big at the beginning,but the cost per piece is low, so with large quantities, the unit price decreases.
The whole injection process cost involves many other variables, not only the cost associated to the mold. These are, for example: the material used, labor, power consumption, cycle time (including the flow rate, pressure,
temperature, time of cooling,…), etc.
2. Previous research efforts on cost estimating calculation
Some authors have focused their cost studies on the design stage, and this can be erratic in further cost analysis. Chen and Liu [1] made a classification of product design concerns. They proposed a procedure for computer-aided design for cost effectiveness, piding the design stage into three parts: feature design, preliminary design and detail design. Injection feature evolution in these continuous stages can lead to the modification of cost-related parameters, which include materials, technologies and mold manufacture. This procedure was implemented using the C++ as programming language, but the problem was how to quantify all the variables and aspects considered.
An extended review of a total of 19 programs was made by Maier [2]. Some of those programs are no longer available and others have new improved versions. His study separated the designers and manufacturer’s needs. The“Kazmer Injection Molding Cost Estimator” (a Java application) from the University of Massachusetts Lowell and Boothroyd Dewhurst’s “DFM Concurrent Costing” were used as good examples of products done basically for the design stage.
Maier analyzed the software sophistication and program delivery providing some examples of programs. His study finished considering that the developing of appropriate models for cost estimating is an art, since they have to be simple and precise; and gave also some advice for a possible new product development.
Pearce [3] focused only on the mold cost estimation. He developed a procedure based on artificial intelligence and heuristic methods. The knowledge based constructed for this purpose was achieved using statistical survey analysis, rather than interviews with experts.