Reverse compensation to prevent post-molding dimensional distortion of automobile parts manufactured using CF-SMC

• Published in: International journal of advanced manufacturing technology 2022-12, Vol.123 (11-12), p.4181-4194
• Main Authors: Yoon, Manseok, Seo, Bongkuk, Lim, Choong-Sun
• Format: Article
• Language: English
• Subjects: Automotive parts; CAE) and Design; Carbon fibers; Compensation; Computer-Aided Engineering (CAD; Cooling; Curing; Dimensional stability; Distortion; Dynamic mechanical analysis; Engineering; Extensometers; Finite element method; Glass transition temperature; Heat generation; Industrial and Production Engineering; Jigs; Material properties; Mechanical Engineering; Media Management; Original Article; Residual stress; Sheet molding compounds; Shrinkage; Temperature
• ISSN: 0268-3768; 1433-3015
• DOI: 10.1007/s00170-022-10478-8

This study suggests reverse compensation as a method to secure the dimensional stability of automotive parts manufactured using carbon fiber-sheet molding compound (CF-SMC), even after molding. After completion of molding, the uncured material undergoes shrinkage during curing, resulting in distortion of the dimensions. At this stage, the dimensions can be corrected by suppressing the distortion caused by shrinkage. This method can reduce the cost and time required for development. To evaluate the degree and condition of shrinkage of the material during curing, the shrinkage rate was measured using a dilatometer, and the curing behavior during product molding was examined by differential scanning calorimetry (DSC). After molding, the temperature change of the demolded product was inspected, and the glass transition temperature ( T g ) of the product was evaluated using dynamic mechanical analysis (DMA) to confirm that reverse compensation was possible within a certain amount of time, even for thermoset products. To examine the possibility of reverse compensation, the material properties were measured and used as input data for finite element method (FEM), in which the degree of distortion was observed after free cooling and after using reverse compensation cooling. To confirm the actual performance, a jig for reverse compensation was manufactured, and reverse compensation was performed immediately after molding. The flush values were measured after seven days, considering the possible dimensional regression caused by residual stresses. The results confirm the possibility of reverse compensation because the thermosetting product can reach temperatures higher than the mold temperature during molding owing to heat generation by curing and can maintain its temperature above the onset of T g for a certain period of time after demolding. Therefore, the dimensional quality can be improved by manufacturing an appropriate jig.