Making improvements in products or in processes can be one of the most challenging tasks confronting an organization. This paper uses design of experiment (DOE) to identify causes of defects associated with plastic injection molding processes at the early phases of designing processes and operations. A detailed eight‐phase methodology is offered through which an identification of defects and effective solutions for their removal could be done. The paper also shows how the parameters of the problem could be established and how DOE could be applied to achieve the stated objectives by using the results of only 18 and ten DOE test runs. The results of the initial experiments are subjected to a verification procedure to determine their viability and accuracy. As a result of this experiment, the company was able to make the changes needed to reduce the cycle time required to produce products and thus, increase productivity while maintaining high quality standards. In conclusion, an assessment of the results is provided and the necessary conditions and prerequisites for the effective utilization of the methodology are presented.