Chapter 9.2, Problem 22E

According to the article “Modeling and Predicting the Effects of Submerged Arc Weldment Process Parameters on Weldment Characteristics and Shape Profiles” (J. of Engr. Manuf., 2012: 1230–1240), the submerged arc welding (SAW) process is commonly used for joining thick plates and pipes. The heat affected zone (HAZ), a band created within the base metal during welding, was of particular interest to the investigators. Here are observations on depth (mm) of the HAZ both when the current setting was high and when it was lower.

Non-high	1.04	1.15	1.23	1.69	1.92
	1.98	2.36	2.49	2.72
	1.37	1.43	1.57	1.71	1.94
	2.06	2.55	2.64	2.82
High	1.55	2.02	2.02	2.05	2.35
	2.57	2.93	2.94	2.97

a. Construct a comparative boxplot and comment on interesting features.

b. Is it reasonable to use the two-sample t test to test hypotheses about the difference between true average HAZ depths for the two conditions?

c. Does it appear that true average HAZ depth is larger for the higher current condition than for the lower condition? Carry out a test of appropriate hypotheses using a significance level of .01.