Industrial Statistics with Minitab

25.3 Wear

To study the possible relationship between the wear and tear of a cutting machine and both its rotation speed and the material it was made of, the data of file WEAR.MTW are provided:

Col.	Content
C1	Wear and tear after 8 hours of operation (in tenths of a mm)
C2	Rotation speed (in rpm)
C3	Type of steel (encoded as 0 and 1)

The aim is to find an equation that explains the wear and tear as a function of both variables available.

As always, we start with an exploratory analysis of the data:

Graph > Matrix Plot > Matrix of plots: Simple

Looking at the Matrix Plot, we can rule out the presence of anomalous values. Regarding the relations among the variables, we see that a higher speed is associated with a major wear, and that material 1 wears out more than material 0.

In this case, it is also a good idea to draw a scatterplot of wear versus speed stratified according to the material.

Graph > Scatterplot: With Groups

We can clearly see the relation between wear and speed as well as that material 1 wears out more than material 0. We compute the equation of the regression model:

Stat > Regression > Regression

Since the type of material is a categorical ...