Question 9.12: The article "Experimental Design for Process Settings in Air...
The article “Experimental Design for Process Settings in Aircraft Manufacturing” (R. Sauter and R. Lenth, Statistical Case Studies: A Collaboration Between Academe and Industry, SIAM- ASA, 1998: 151- 157) describes an experiment in which the quality of holes drilled in metal aircraft pru1s was studied. One important indicator of hole quality is “excess diameter,” which is the difference between the diameter of the drill bit and the diameter of the hole. Small excess diameters are better than large ones. Assume we are interested in the effect of the rotational speed of the drill on the excess diameter of the hole. Holes will be drilled in s ix test pieces (coupons), at three speeds: 6000, 10,000, and 15,000 rpm. The excess diameter can be affected not only by the speed of the drill, but also by the physical properties of the test coupon. Describe an appropriate design for this experiment.
A randomized complete block design is appropriate, with drill speed as the treatment factor, and test coupon as the blocking factor. Since six observations can be made in each block, each drill speed should be used twice in each block. The order of the speeds within each block should be chosen at random.