A statistical process control (SPC) methodology establishing process control in carburizing integral power steering gear components and a case study in which this SPC technique is used to validate carburizing process changes are presented. This SPC methodology uses effective case depth (ECD) measurements from standard test bars in each heat treat load to establish process control and to detect variation in furnace atmosphere and temperature over time. By using an appropriate normalization factor, test bar ECD measurements from different carburizing cycles can be plotted on the same SPC chart. Because standard test bars are measured, this SPC method is independent of variations in component geometry and material chemistry. This paper concludes with a demonstration of the use of this SPC technique to statistically validate a change to the boost/diffuse ratio in a carburizing process of one steering gear component which resulted in a total cycle time reduction of two hours.
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