Injection molding process description

Although most injection molding processes are covered by the conventional process description discussed earlier in this chapter, there are several important molding variations including ... 

Based on Equation (7.33) and assuming that nP G[t(T) i l3 = k(T), one can derive Equation (7.31) with n = 4. The Nakamura equation (Eq. 7.31) has been widely used in the modeling of crystaUization in the injection molding process, for example. References [33-36], because it allows application of the results of isothermal crystallization analysis to the description of nonisothermal crystallization. It can be noticed that in isothermal conditions, for a given temperature T, k(T) = th(Ty In 2, where h is the crystallization halftime. Therefore, for nonisothermal conditions. Equation (7.31) assumes the form ... 

Numerous mathematical models have been developed by various research groups for the analysis of the injection molding process and have been implemented into commercid and scientific software. While outstanding improvements in the simulation of shrinkage and warpage codd be observed during the past decades [1-5], the simulation results mostly do not reflect the reality. Amongst others the insufficient description of the material data, especially the insufficient description of the specific volume is critical. 

Injection Molds and Molding A Practical Manual , 2nd Edition, Joseph B Dym Kluwer Academic Publishers (1987) ISBN 0442217854. Highlights include a description of CAD/CAM potential and process control capabilities, and a... 

Injection Molding. In injection molding a molten thermoplastic is injected under high pressure into a steel mold. After the plastic solidifies, the mold is opened and a part in the shape of the mold cavity is removed. General descriptions of the process and related equipment are given in References 29—34. 

For unsteady-state processes, and in particular in injection molding, initial conditions are also needed, while the boundary conditions applied inside the mold must invariably take into account the interaction between the mold and the flowing and solidifying polymer melt. The variety of such conditions makes a full description beyond the scope of this chapter. The interested reader can find useful information in the manuals of custom-made commercial computer software, such as MOLD-FLOW [44], and in a recent thesis [20]. 

The term IM is an oversimplified description of a quite complicated process that is controllable within specified limits. Melted or plasticized plastic material is injected by force into a mold cavity (Figure 4.1). The mold may consist of a single cavity or a number of similar or dissimilar cavities, each connected to flow channels or runners which direct the flow of the melted plastic to the individual cavities (Chapter 17). The process is one of the most economical methods for mass production of simple to complex products. Three basic operations exist. They are the only operations in which the mechanical and thermal inputs of the injection equipment must be coordinated with the fundamental behavior properties of the plastic being processed. These three operations also are the prime determinants of the productivity of the process since manufacturing speed will depend on how fast we can heat the plastic to molding temperature, how fast we can inject it, and how long it takes to cool (or solidify) the product in the mold. 

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