Plastic parts design process selection

When simulating the mold-filling process, the designer of a plastic part must therefore select the feed points such that the flow lines are not within regions of maximum stress load. 

A successful plastic product depends on the optimization of each of the following four principal components part design, material selection and handhng, tool design and construction, and processing/machine capabilities. 

The design of a plastic part and the selection of the plastics manufacturing process are extremely interdependent it is critical to match the plastic part design to the capabihties of the plastics manufacturing process. For example, a plastic part designed for injection molding will not be interchangeable with a... 

Risk is an inherent part of plastic product development, and the level of risk can actually increase as plastic part designs become more efficient. The reason is that as the plastic part designer improves the design, more constraints on the design become obvious. For example, consider the selection of wall thickness for the internal chassis depicted in Fig. 27.15. A large wall thickness of 5 mm can be used to provide stiffness but will tend to increase the cost of the plastic part due to excessive material costs and processing times. The plastic part designer will likely... 

Calculator An interactive process wizard that provides quick, effective material, design, processing, and cost solutions. This Engineering Calculator s capabilities include (1) Material, to select from a variety of GE Plastics materials (2) Design, which calculates minimum part thickness based upon allowable deflection (3) Processing, which calculates pressure to fill and clamp force and (4) Cost, which calculates estimated material and processing costs for the intended part. 

This book focuses on the relationships between the chemical structure and the related physical characteristics of plastics, which determine appropriate material selection, design, and processing of plastic parts. The book also contains an in-depth presentation of the structure-property relationships of a wide range of plastics, including thermoplastics, thermosets, elastomers, and blends. 

Contents Introduction to Materials. Manufacturing Considerations for Injection Molded Parts. The Design Process and Material Selection. Structural Design Considerations. Prototyping and Experimental Stress Analysis. Assembly of Injection Molded Plastic Parts. Conversion Constants. 

In the injection molding process, setting the temperature involves optimization of the temperature profile of the plasticating unit (extruder barrel), temperatures of the mnners and gates, (aU these determine the molten polymer temperature) as well as the mold temperature. The temperature setpoints depend on the material type (viscosity profile, thermal and shear stability, thermal properties) as well as machine or process considerations (machine capacity to shot size ratio, screw design, mold and part design, cycle time, etc.). Temperatures of the two basic units, the injection system and the mold, should be discussed separately since their selection stems from very different considerations. 

Physical dimensions of many processed parts must be held to fairly close tolerances to ensure proper assembly of parts into a complete structure, as, for example, molded fender panels bolted to steel chassis cars, plastic screw caps for glass jars, etc. In general, the final dimensions of the processed part will differ from the dimensions of the mold cavity or the pultrusion die. Such differences are somewhat predictable, but are usually unique to the specific material and to the specific process. The dimensions of a mold cavity for a phenolic part requiring close tolerances will often be different from dimensions of a cavity for an identical polyester part. Both the part designer and the mold or die designer must have a full understanding of the factors affecting final dimensions of the finished product, and often need to make compromises in tolerances of both part and cavity dimensions (or even in plastic material selection) in order to achieve satisfactory results with the finished product. 

The creation of a plastic part requires a series of conscious decisions regarding type of plastic, method of production, design of mold or tooling, and selection of machine or process. Reaching these decisions requires information as to the intended usage of the part and the conditions of environment (temperature, moisture, exposure to harsh atmospheres, physical and electrical requirements). Furthermore, in most cases, the cost to manufacture the part is a major consideration and is dependent on the choice of materials, the manufacturing process, and, of course, the quantities to be produced per shift, month, or year. 

As already stated, the choice of manufacturing process is influenced by both the material selected and part design. The entire manufactmlng process normally consists of primary and secondary operations. Primary operations are those that convert the raw material into a recognizable part (casting, plastic forming, powder compaction, molding, etc.), whereas secondary operations are those subsequently used to produce the finished part... 

---