Sixth ASM/ESD
Advanced Composites Conference
October 8-11, 1990, Detroit, Michigan
FIBER
ORIENTATION AND WARPAGE ANALYSIS OF COMPRESSION MOLDED PARTS
H. U. Akay,* L. G. Reifschneider
Technalysis
7120 Waldemar Drive
Indianapolis, Indiana 46268, USA
Abstract
A procedure is presented for
determining thermal and mechanical properties of sheet molding compounds
(SMC) from a fiber orientation prediction analysis of compression molded
parts. Using a finite element computer program, locally planar fiber
orientation calculations are made for compression molded parts. Following a
filling analysis of the mold, a set of transport equations for fiber
orientation state of short fiber composites is solved. The final orientation
states are used for orthotropic stress analysis of the composite material.
For a sample case of a car hood, the orthotropic thermal and mechanical
properties of SMC are determined with the predicted final orientation
distribution. To determine how an orthotropic analysis differs from an
isotropic analysis, the warpage due to cooling and the deflections due to
external loading are examined using both orthotropic and isotropic models.
Introduction
Compression molded parts
offer greater manufacturing efficiencies and weight savings when compared to
steel in the fabrication of thin walled parts. However, the design of
compression molded parts is difficult because of the anisotropic behavior of
the sheet molding compound. Because the mechanical properties can vary
greatly with the fibers within the composite [1], designing with these
materials requires more analytical tools. The recent development of
compression molding simulation methods have made the fiber orientation
predictions possible, e.g., [,3].
In this paper, a recently
developed method [4] of predicting orientation of fibers in thin walled
plastic parts of arbitrary three-dimensional shapes is extended for
determining thermal and mechanical properties. It is shown how the filling
analysis provides the basis for predicting the change of fiber orientation.
Further, it is shown how the final fiber orientation can be used to
determine the anisotropic material properties of typical compression molded
parts for performing stress analysis.
The Numerical procedure
outlined here is implemented in a finite element computer program, PLASTEC
[3]. This program is designed to analyze different phases of injection and
compression molding processes, including filling, holding, fiber
orientation, and warpage. It is aimed to allow location, insure fill, and
maximize part performance for warpage and strength before any tool steel is
cut. This reduces the time and cost compared to conventional methods of
prototyping.