Title: The Effect of External Mold Release on Sheet Molding Compound (SMC) Tensile Strength

Authors: Thomas E. Yarrington

DOI: 10.33599/nasampe/c.24.0308

Abstract: One common process for producing thermoset composites is high temperature, high pressure compression molding. Production tooling for this process is usually chromed steel, which is conducive to component release due to the nonporous, smooth surface created from the chrome plating. Prototyping and preproduction component requirements often require molding on un-chromed steel or on aluminum tooling. Excessive external mold release application is sometimes used to demold components on these preproduction tools. Scrap rates of components molded off aluminum tooling is sometimes 50 % or more during these mold trials, primarily from flow-related fractures. However, additional fracturing of post-molded components may also be an issue. During an investigation, it was postulated that excessive external mold release, an anti-stick agent by nature, resulted in extremely weak flow defects in the molded component. Internal historical data suggests that the knit line tensile strength of a sheet molding compound (SMC) laminate is approximately 75 % weaker on average than its isotropic tensile strength. Preliminary investigations suggested that the tensile strength of a knit line intentionally molded with excessive mold release is approximately 90 % weaker on average than its isotropic tensile strength. The purpose of this research paper is to investigate how an external mold release affects the tensile properties of an SMC laminate based on the chemistry of the mold release, the quantity applied to the tool, and the process of application.

References: 1. ISO 527-4:2023, “Plastics – Determination of tensile properties – Part 4: Test conditions for isotropic and orthotropic fibre-reinforced plastic composites” the International Organization for Standardization, 2023, www.iso.org 2. ISO 1183-1:2019, “Plastics – Methods for determining the density of non-cellular plastics – Part 1: Immersion method, liquid pycnometer method and titration method” the International Organization for Standardization, 2019, www.iso.org 3. ASTM Standard D638-22, 2022, “Standard Test Method for Tensile Properties of Plastics” ASTM International, West Conshohocken, PA, 2022, DOI: 10.1520/D0638-22, www.ASTM.org

Conference: CAMX 2024 | San Diego CA

Publication Date: 2024/9/9

SKU: TP24-0000000308

Pages: 15

Price: $30.00