Model based optimization for auto body dimensional control in design and assembly.

Abstract

The focus of automobile consumers has forced manufacturers to increase efforts on quality improvement. One initiative at the forefront has been the improvement of dimensional relationships in the body build. Traditionally, statistical process control (SPC) has been used to monitor the process performance. However, the automobile assembly process is an information-intense process that overwhelms a sampling-based process control strategy such as SPC. Therefore, a model based approach to determine process adjustments is presented for two types of process improvement strategy: (1) run-by-run process adjustments and (2) individual cycle process adjustments. Also, a model for sheet metal joint design evaluation is presented as a model based evaluation technique. Run-by-run process adjustments are changes to a manufacturing process that are made on intervals called runs. Two models are developed in this dissertation for the purpose of run-by-run adjustments: (1) single input single output and (2) multiple input multiple output processes. The process performance data from the current run of production is used by the run-by-run optimization model to determine the adjustments necessary to keep the process on target. The results of the presented models clearly show an improvement in the number of parts produced outside specifications for the presented case studies. The second method of process adjustment is an individual cycle process adjustment model. Two models are presented that determine the necessary process adjustments for each individual assembly sequence, based on the data gathered from the incoming material. The two processes that are modeled in this dissertation are for the (1) sheet metal joining process and (2) multiple panel fitting operation. The goal in both presented models is to minimize the dimensional deviation of the assembly. Results from both models show that the models determined the necessary process adjustments to minimize the dimensional deviations. An added application of the individual cycle process adjustment model for sheet metaljoining is a design for manufacturability tool for sheet metal joint design. This work is a tool that can be used to isolate problem joints in a sheet metal assembly sequence. Problem joints are joints in an assembly sequence that are not robust to the incoming material dimensional deviation. Therefore, their isolation can be used as an indicator of a need to redesign the joints. Results from the examples given demonstrate the capabilities of the presented techniques.