Injection and Compression Molding Fundamentals

Avraam L. Isayev

• Editorial: CRC Press
• Año: 2017
• ISBN:
  9781351438315
• Edición: 1
• Categoría: Technology & Engineering
• Categoría: Materials Science

This outstanding reference presents an up-to-date account of investigations during the last10 years in the area of injection and compression molding of polymers.Injection and Compression Molding Fundamentals considers simulation andexperimentation of flow dynamics in the cavity and delivery system... discussesrheology and viscoelastic modeling... clarifies fiber orientation... delineates residualstresses and processing-property relationships in molded parts... and details computeraideddesign and manufacture of the mold.In addition, the book highlights specific features and problems related to the molding ofthermoplastics, rubbers, and thermosets... and reveals the current status of the sciencebasedtechnology related to injection and compression molding.The most detailed and authoritative reference of its type, Injection and CompressionMolding Fundamentals is an invaluable resource for plastics, mechanical, andchemical engineers; colloid, oil, and color chemists; polymer engineers and scientists;mold designers and manufacturers; rheologists; and materials scientists. The book willalso be of value for use in graduate-level courses in plastics, mechanical, chemical, andpolymer engineering, and in short courses and seminars offered by professional societies.

1

Melt-Viscosity Characterization and Its Application to Injection Molding

Cornelius A. Hieber

Sibley School of Mechanical and Aerospace Engineering

Cornell University

Ithaca, New York

I. INTRODUCTION

The scientific investigation of the injection-molding process can be traced back at least to the pioneering work of Gilmore and Spencer [1, 2] at Dow, during the early 1950s, and to Ballman and co-workers [3, 4] at Monsanto, during the late 1950s. A finite-difference formulation for numerical simulation was presented by Pearson [5] in the mid-1960s but not implemented until the early 1970s in the well-known works by Kamal and Kenig [6] and by Gogos and co-workers [[7, 8]. Since then, the application of computer simulations to the injection-molding process has clearly intensified, and its commercialization, pioneered by Austin 9], has resulted in viable computer-aided engineering (CAE) tools for mold design.

One main objective in this chapter is to present a detailed description of the basic elements involved in simulating the cavity-filling stage of the injection-molding process. This is done in Section III, with the formulation being given in terms of a fluid whose shear viscosity can have an arbitrary dependence upon shear rate, temperature, and pressure. Accordingly, a second objective is to present detailed results concerning the characterization of such viscosity. This is done in Section II. Thirdly, although a general viscosity model may not always be needed for the cavity-filling stage, Section IV shows that such a model is essential when extending the simulation to the postfilling stage.

II. MELT-VISCOSITY CHARACTERIZATION

A. Viscosity Fits Using Cross-Arrhenius Model

In modeling the flow dynamics in injection molding, the single most important polymer property is the shear viscosity η. Accordingly, this section is concerned with the characterization of η, making extensive use of a viscosity data bank which has recently been developed by the Cornell Injection Molding Program (CIMP). Currently, this data bank consists of approximately 300 sets of viscosity measurements with corresponding fits. Many of these sets are from the open literature, such as the well-known compendium of Westover [10] and the recent book Rheologie [11]. Arranged according to generic material, viscosity measurements from the following sources have been fitted: ...