Industrial Statistics with Minitab

12.1 Welding

To know more about the behaviour of an automatic welding procedure, 100 welds were made. The exact condition in which each weld was made was recorded. The welds were made in standard sheets and their shear stresses were tested. The file WELDING.MTW contains the data, with the following information:

Column	Content
C1 C2 C3 C4 C5	Test order Strength exerted by the electrodes Electric current measured with Bosch's ammeter Electric current measured with Miyachi's ammeter Shear breaking load

The questions to be answered are:

1. Is the exerted strength by the electrodes stable?

2. Is there a correlation between the exerted strength and the shear stress? Is there a cause and effect relation?

3. Can we say that the maximum shear stress is lower in the first 50 welds than in the last 50 welds?

4. The real value of the electric current varies from one weld to another (for various reasons it cannot remain constant). Can we say that the Bosch and Miyachi ammeters measure different?

1. Start checking if the strength exerted by the electrodes has remained stable:

Graph > Time Series plot: Simple

Place the column C2 in Series, with all other options by default:

The strength has not remained stable. There is a tendency to increase.

2. Investigate if there is a correlation between strength and shear stress:

Graph > Scatterplot: Simple

Put the shear breaking ...