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A Systematic Approach to Planning for a Designed Industrial

A Systematic Approach to Planning for a Designed Industrial...

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0 1993 American Statistical Association and the Amencan Society for Quality Control TECHNOMETRICS, FEBRUARY 1993, VOL. 35, NO. 1 Editor’s Note: This article and the first two discussions were presented orally at the Technometrics session of the 36th Annual Fall Technical Conference held in Philadelphia, Pennsylvania, October 8-9, 1992. The conference was cosponsored by the Chemical and Process Industries, the Statistics Divisions of the American Society for Quality Control, and the Section on Physical and Engineering Sciences of the American Statistical Association. A Systematic Approach to Planning for a Designed Industrial Experiment David E. Coleman Alcoa Laboratories Alcoa Center, ?A 15069 Douglas C. Montgomery Industrial Engineering Department Arizona State University Tempe, AZ 85287 Design of experiments and analysis of data from designed experiments are well-established methodologies in which statisticians are formally trained. Another critical and rarely taught skill is the planning that precedes designing an experiment. This article suggests a set of tools for presenting generic technical issues and experimental features found in industrial experi- ments. These tools are predesign experiment guide sheets to systematize the planning process and to produce organized written documentation. They also help experimenters discuss com- plex trade-offs between practical limitations and statistical preferences in the experiment. A case study involving the (computer numerical control) CNC-machining of jet engine impellers is included. KEY WORDS: Industrial experimental design; Measurement error; Nuisance factors; Sta- tistical consulting. 1. INTRODUCTION 1.1 A Consulting Scenario Consider the following scenario: An experimenter from the process engineering group comes to you and says: “We are manufacturing impellers that are used in a jet turbine engine. To achieve the claimed performance objectives, we must produce parts with blade profiles that closely match the engineering de- sign requirements. I want to study the effect of dif- ferent tool vendors and machine set-up parameters on the dimensional variability of the parts produced on the machines in our CNC-machine center.” Many experimental design applications in industry begin with such a statement. It is well recognized that the planning activities that precede the actual experiment are critical to successful solution of the experimenters’ problem (e.g., see Box, Hunter, and Hunter 1978; Hahn 1977, 1984; Montgomery 1991; Natrella 1979). Montgomery (1991) presented a seven- step approach for planning experiments, summarized in Table 1. The first three of these steps constitutes the preexperiment planning phase. The detailed, specific activities in this phase are the focus of this article. The emphasis is planning for a screening ex- periment, or a step in sequential experimentation on an existing product/process, off-line or on-line. Many of the issues addressed, however, also apply to new products/processes or research and development (R&D) and to various additional experimental goals,
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