In this series, I will discuss a case study that demonstrates how the use of a structured problem solving process not only solved two chronic quality problems, but also significantly impacted throughput within the same department. It is important to understand that when we solve problems, there are often positive side benefits that we may not have anticipated.
A quick summary of our case study subject and the problem
Our subject company is a manufacturer of stainless steel pressurized vessels used to hold a variety of liquids and gases. In their facility, sheets of stainless steel are rolled into tubes that are then welded together before structural rings are mounted and welded to the exterior of these large tubes. The welding provides the needed strength to counteract the applied pressures of the liquids and gases that are held and transported inside the tanks.
Two common problems encountered when welding products of this nature are pinholes and weld spatter. Weld spatter occurs when the welding arc virtually explodes and coats the surrounding area with bits of welding wire that must be ground off for aesthetic purposes. Pinholes are small cavity-type discontinuities formed by gas entrapment that can occur for a variety of reasons. Both of these defects are caused by many of the same culprits. This company believed that if they could solve the weld spatter problem, then pinholes would be reduced as well.
As the stainless-steel support rings were welded into place, weld spatter formed along the entire diameter of the tank, in close proximity to these structural rings. Removing the spatter took significant time and created a sizeable bottleneck in the normal process flow. This, in turn, had a negative impact on throughput. Actually for a typical tank, the amount of time required to remove the weld spatter alone averaged a bit over six hours.
Applying the problem solving roadmap to weld spatter and pinholes
The figure below1 is my problem-solving roadmap. The team used this tool to solve the related problems of weld spatter and pinholes. In this series, we will follow each of the major sections and the corresponding individual steps on this roadmap.
I. Define, describe, and appraise the problem
A team was formed that included members from the tank fabrication area, finishing where the rework is performed, quality assurance, design engineering, and finance. Their objective was to study ways to either eliminate or significantly reduce the most significant factors causing the extended time in finishing. The first deliverable in using this approach a problem statement, but before this could be created, the team had many questions to answer.
The team developed a simple system to rapidly collect information on all downtime and rework in the tank or barrel area. They collected the data and determined that during a period of approximately two weeks, weld related defects around the structural rings accounted for approximately 42 hours of rework in the tank finishing area. This accounted for about 40 percent of the total downtime hours. The team concluded that rework of this nature is typically related to the actual welding process and equipment being used, but operator technique played a significant role as well.
1.0 Define the problem and write a problem statement
The team collected lots of information about the problem and then developed this problem statement:
Pinholes and weld spatter are occurring on 100 percent of the stainless steel tanks at a rate of approximately eleven hours per day, creating significant amounts of rework. Based upon a recent study, as many as 100 hours per week of rework time have been observed for these two problems, and the trend is constant.
Coming in the next post
In Part 2 of this series, we will continue working our way through the various steps in our problem solving roadmap.
Until next time,
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