M.S. Thesis Presentation by Sundiata Jangha
Friday, May 25, 2001

(Dr. David Rosen, advisor)

"An Ejection Mechanism Design Method for Rapid Injection Molding Tools"


One of the main issues in injection molding is the amount of time required to develop a mold once a part representation has been created. To combat this issue, rapid tooling techniques have been developed. The technique to be examined in this case is the use of the Stereolithography Apparatus (SLA). While SLA tools are much faster to fabricate than traditional steel tools, there is a strength loss that must be accounted for as well. One of the areas where this plays a major role is the ejection of the part from the mold. Hence there is a need for a system that will design a reliable ejection mechanism for a given part geometry.

There are two goals of this research. The first goal is to develop a model that effectively characterizes the forces and stresses that the mold core undergoes as a result of part ejection. The second goal is to develop a system that uses the aforementioned model to determine an ejection procedure for a part given its geometry. This ejection design system will have two main functions. First it will determine the feasibility of ejection for that particular geometry. Second it will determine the number of pins and their diameter and recommend locations for these pins and a location and orientation for the part being considered. The approach taken to accomplish this will consist of a combination of analytical, computational, and physical experiments. A specific set of tasks to achieve the goals include the following:

  1. Develop a model to characterize the ejection force in the injection molding process. This will be accomplished using a combination of analytical, computational, and physical experiments.
  2. Develop the system that will create the ejection mechanism based on the part geometry. The system itself will be created to consider a specific type of part geometry (rectangular).
  3. Verify the effectiveness of the design method for the ejection mechanism by implementing the ejection mechanism for a series of simple parts, and comparing a subset of the results to a set of results from other formulations.