Precision Injection Molding of Thermoplastics

The paper reviews the state of the art of injection molding. The tolerances in terms of shrinkage and warpage are reviewed for major plastic resins. The molding process is discussed in terms of flow orientation and control of melt and machine parameters to achieve good properties and dimensions. The paper looks at automatic process control for precision parts. The use of microprocessor control is reviewed. The paper will discuss both ram velocity control and melt pressure control. The use of such a control unit in the molding of high quality optical polyurethane lenses is described. The use of computer modeling and computer aided design in the simulation of molded plastics is described from a commercial viewpoint. Also, the role of cooling of the part and the feasibility of the proposed part is described. Finally, the paper describes the need for rheological and thermodynamic data that are required for the computer modeling.