Review of A Case Study on Weld Spatter and Pinholes, Part 3
In Part 3 of this series, I continued our problem-solving case study of a company that manufactures stainless steel pressurized vessels. We completed steps 5, 6, and 7 from the problem-solving roadmap and then began step 8.
The continuation of our step-by-step method
In this post, we will continue with the step-by-step method for solving the problem involving weld spatter and pinholes.
8.0 Record possible causes (continued)
The team elected to use the causal chain technique to determine potential causes of the problem. The causal chain begins with a statement of the problem with the object on top of the line and the state that it is in directly beneath it.
In this team’s causal chain, the object was the weld spatter, and its state was present. The team then asked the question “Why?” until they arrived at a potential root cause. The figure below is a series of causal chains developed by this team and, as you can see, they developed 10 separate chains. One of the chains was related to the tank roller jerking. When they asked why the tank roller was jerking, they believed that the clutch could be worn out. When they subsequently asked why the clutch was worn out, their conclusion was that no preventive maintenance was in place.
For each of the 10 individual chains, the team continued in the same manner as in this example until they arrived at a potential root cause. The team had, once again, grasped the essence of this exercise and completed the process to perfection.
9.0 Eliminate obvious non-causes
The next step for the team was to eliminate causes that they believed were not relevant to the problem involving weld spatter and pinholes. As it turned out, most of the causes listed in the causal chains were legitimate and would result in actions being taken. The only potential cause that the team actually eliminated was the gas mix being wrong at run-out. The others were all seen as process deficiencies that required actions to correct.
III. Formulate and test a causal theory
10.0 and 11.0 Develop and test hypotheses
The team narrowed the list down to a single potential root cause. They deduced that the tank-to-ring gap problem that had been recorded as a symptom earlier was probably the factor that contributed the most to weld spatter generation. They needed to develop a theory as to why the gap was present, and they did.
IV. Choose the most probable cause
12.0 Select the most probable cause
The team worked backwards through the process to better understand why the gap problem existed. After much discussion and investigation, they completed this step by concluding that asymmetry was the problem source.
V. Develop, test, and implement best solutions
13.0, 14.0 and 15.0 Develop possible solutions, test and select the best solution, and implement the best solution
Because the team was convinced that if they could fix the asymmetry, the gap would be corrected and weld spatter would be reduced. The team had the worn guides replaced and had a total preventive maintenance effort of the shear machine done. Then they had parts produced and all were found to be acceptable.
Just to be certain, the team followed the parts through the bending and rolling process and found the parts to be symmetrical and consistent from end to end. The team then followed the parts through the tank area and observed no gaps when they were mounted on the tanks. Finally, the team observed the rings being welded in place on the tanks, and to the team’s delight, the incidence of weld spatter was significantly reduced.
Coming in the next post
We will complete our journey through the problem solving roadmap by documenting what the team had accomplished and we’ll celebrate the team’s success in the final post of this series.
Until next time,
 Bob Sproull, The Problem-Solving, Problem-Prevention, and Decision-Making Guide, CRC Press, Taylor & Francis Group, 2018
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