Date of Award


Degree Name

Doctor of Philosophy


Industrial and Manufacturing Engineering

First Advisor

Dr. Paul V. Engelmann

Second Advisor

Dr. Steven E. Butt

Third Advisor

Dr. Philip J. Guichelaar

Fourth Advisor

Dr. Azim Houshyar


The injection molding segment of the plastics industry has historically exhibited an environment of intense competition. To remain competitive, manufacturers must ensure that molds will produce defect-free parts without multiple design revisions. Designers often use computer simulations to predict design problems before the construction of tooling. These sophisticated software applications will soon have the ability to simulate the final appearance of products. However, the effects of aesthetic defects such as sink marks and splay are often difficult to simulate accurately and effectively.

It is understood that surface textures can conceal minor aesthetic defects. A well-known example is the concealment of sink marks: shallow depressions on the surface of a molded product caused by volumetric shrinkage during cooling. The relationship between surface texture and the visibility of sink marks has not been completely explored. Nor is it understood how the viewing environment changes the visibility of sink marks.

This research studied the effects surface texture and color have upon the visual detection of sink marks. A novel inspection fixture was built to comply with existing ASTM inspection standards. Human observers evaluated a series of injection-molded parts exhibiting various widths and depths of sink marks as well as various textures. Data were collected in the Plastics Processing Laboratory at Western Michigan University's Parkview Campus and at various plastics companies located in western Michigan.

The results of the research confirmed industry-held beliefs in the effectiveness of surface texture to conceal minor sink marks. The data-collection instruments developed were capable of detecting thresholds of perception of sink marks on various textures. The color of the sample plaques was found to be a significant contributor to the probability of the perception of a sink mark. The research also found that the environment surrounding a sink mark could influence the probability of visually detecting the sink mark. Factors essential for predicting sink mark visibility were identified, allowing the future development of models for designers to use to eliminate the visibility of problematic sink marks.


5th Advisor: Dr. David M. Lyth

Access Setting

Dissertation-Open Access

Included in

Engineering Commons