Introduction

The purpose of this thesis is to develop methodologies and procedures for the construction and use of CAD part families. This project uses the software CADDS5 created by Computervision, Inc., and its ``Family of Parts'' module. This software allows the creation of an entire family of similar parts by building a single parametric model and using a text file containing the necessary parameters for each member of the family. The software reads this text file and uses the information to create the family members.

Previously, creating such a family of parts required a great deal of effort on the part of the designer. The only way to create the group of parts was for the designer to create all of the parts individually, or create one part in the family, modify the appropriate parameters, and save the part under a new name. This part would be modified and re-saved for each member of the family. Using the method developed in this thesis, the designer can now create just one part, called a master part, and a text file containing the parameter values for each part. The CADDS5 software then creates each of the member parts, with minimal interaction with the designer.

The process involved in creating these families of parts can be much different from the process used in creating standard, one-use parts. Careful attention must be paid to the creation process; for if the parts are created improperly, the model will fail when the parameters are changed and the model regenerated. Unlike other models, the family members generally can not be modified once they are generated. Because these are generated parts, any changes made to the models would be lost if the model were regenerated. This makes the choice of modeling process critical as the parts cannot be modified later to make up for deficiencies in the original model. Thus, master parts must have the ability to create any member of the family by merely regenerating with the proper parameters.

In single use parts, spending extra time revising the model to decrease the disk space or regeneration time slightly often costs more in the designer's time creating the part than it saves in disk space or computer time. With families of parts, however, the part will be regenerated and saved many times. Any extra savings in the disk space used by the part, or the time necessary for regeneration, will result in much greater savings through the member parts. This makes it worthwhile to spend more time than usual making sure that the model is as small and efficient as possible. With this method, there will be one model of each standard part. This ensures consistency among the assemblies created by the various designers. Due to of the ambiguities in many of the specifications, different designers would more than likely create models with different dimensions. The same designer can also create the same part with different dimensions on different occasions. With only one model of each part, the part will have the same dimensions every time it is used.

Last Modified: Wed Aug 28 14:41:29 EDT 1996