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An approach towards the reduction of sink marks in sheet molding compound
Author(s) -
Smith Kenneth L.,
Suh Nam P.
Publication year - 1979
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760191203
Subject(s) - sink (geography) , sheet moulding compound , materials science , molding (decorative) , mechanics , rib cage , composite material , newtonian fluid , mold , structural engineering , engineering , physics , geography , cartography
Sink marks are shallow depressions normally observed above reinforcing ribs in molded Sheet Molding Compound (SMC) parts. In this paper, the effect of mold geometry, particularly the rib entrance shape, on the flow pattern of molding compound and the resulting sink marks in molded parts is presented. Flat plate specimens with a single reinforcing rib in the center were used in this work. Rib entrance shape was varied and its effect on both sink depth and fiber orientation measured. A reduction in sink depth from 0.0007 in. to less than 0.0001 in. was observed when comparing rounded and protruding rib entrances, respectively. The effect of inducing unequal flow rates from the two sides of the rib was also investigated and found to give a reduction in sink depth of about one‐third. A computer simulation of the flow during molding was, used to compare observed flow patterns with simple theoretical predictions. The SMC was modeled as a highly viscous Newtonian fluid and finite difference methods were used to solve the Navier‐Stokes equations. Extension of this modeling procedure to more complex geometries will aid in the design of nearly sink free molds.