Industrial Statistics with Minitab

30.2 Steering wheel – 1

A manufacturer of steering wheels for cars had problems with the hardness of its product (a critical characteristic of the steering wheels is that they must be sufficiently hard in order not to break, as well as sufficiently soft so that they break in case of an accident and do not harm the ribs of the driver). The manufacturing process consists of injecting polyurethane into a mould.

To find out what the breakage index depends on, a 23 experiment is carried out with variables P (Injection pressure), R (ratio of the two components of the polyurethane), and T (Injection temperature). After properly choosing the levels and given the large variability detected in the hardness, it was decided to replicate the experiment. The obtained results are:

The aim consists in analyzing how each of the factors affects the hardness.

Start by creating the factorial design.

Stat > DOE > Factorial > Create Factorial Design

In replicated designs, the design matrix is repeated as many times as the number of replicates. First, the first replicates are entered, then, the second replicates, etc. Thus, all the response values are placed in the same column.

Analyze the ...