Production quality problems are expensive, with costly scrap, rework, and extra inspections. It is essential to quickly identify the root cause and implement corrective actions. This requires a disciplined root cause analysis. But engineering teams frequently skip or don’t know how to do one of the steps. The result - lingering problems and costs.
This article discusses the steps of a root cause analysis, focusing on failure analysis. The sections of the article are
Broadly, the steps for a root cause analysis of a production quality problem are:
The focus of this article is on the first step of the process.
The purpose of a failure analysis is to determine whether there is anything wrong with the materials and how the materials were affected by the manufacturing process. The findings from a failure analysis help engineering teams quickly find the root cause and identify and implement corrective actions.
The steps of a failure analysis are:
The information and data collected are used to identify the root cause. Without the information and data, people waste time guessing at the root cause, and problems linger.
Collect samples
Collect samples with the quality problem. Also, it is often helpful to evaluate known good samples for comparison.
Collect information about the problem
Key details about the problem circumstances. Includes process steps and conditions, the process step when the problem appears, materials used and their properties specifications, problem frequency, typical yields, when the problem started, and more. This information helps put the analysis data in context.
Metallurgical analysis of the item being produced
Data about the materials is obtained by analyzing the materials involved. The materials data is used to determine whether the materials meet requirements and how the materials react to the process conditions.
Determine the metallurgical reason for the problem
The metallurgical reason refers to the metallurgical factors that contributed to the problem. That is, why did the metal behave as it did?
The failure analysis findings are used to identify what happened to the metal. Based on this the source of the problem can be identified. Or at least to rule out sources. Then it is possible to focus on the area contributing to the problem and identify the root cause.
For example, a steel component had low hardness after heat treating. The metallurgical analysis revealed that the low hardness was due to the heat treating temperature being too low.
The general categories of sources of problems and examples for each category are
With the metallurgical reason for the problem now known, it is possible to identify potential categories and from there focus on finding the root cause.
For the heat treating example, it was possible to exclude material, method, measurement, and environment as possible general categories. Based on this, further investigation was conducted into the other areas. It was then determined that a furnace malfunction occurred, leading to a low furnace temperature. The malfunction occurred because a furnace component had not been replaced as required during normal maintenance because of a technician error due to insufficient training.
The final step is to identify and implement a corrective action to prevent the problem from occurring again. In the case of the furnace malfunction, the corrective action was to implement a check-off list to completed by technicians as they performed maintenance.
A client’s production line had a 15% scrap rate when bending welded steel tubing to form components. The tubing was splitting. The problem had been going on for over a year. Some lots of incoming tubing had no problems and other lots had problems. The scrap cost was about $16,000 per month. Also, an extra supply of the component (WIP) had to be made to supply downstream processes when the problem arose.
The client had samples analyzed for alloy composition and mechanical properties. The samples met the client’s specifications. So, the analyses provided no direction, and the problem lingered.
We performed a complete metallurgical failure analysis of split and good samples. This included microstructure examination, composition analysis, microhardness testing, and tensile testing. We found that samples with alloy composition at the high end of the client’s specification had the problem. Specifically, higher carbon content led to weld joint metallurgy that reduced bending properties.
So, the root cause was related to the component’s design. Specifically, the alloy selection. The corrective action was to revise the tubing specification, reducing the upper limit for carbon content in the steel. This fixed the problem, while still providing the other properties needed for the component.
The main reason engineering teams struggle with root cause analysis is that one key engineering discipline is often missing from engineering teams. Many companies do not have metallurgical engineers on staff.
So, engineers with other areas of expertise try to solve problems that involve metals. These are skilled engineers. But they lack metallurgy training and don't have expertise in materials analysis and using the data to understand problems. So, problems linger while scrap, rework, and inspection costs add up.
See these articles if you’d like to learn more about failure analysis:
We provide failure analysis consulting to help solve quality problems. We work with engineering teams to help determine the root cause of quality problems and identify corrective actions to fix the problems.
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Michael Pfeifer, Ph.D., P.E. is President of Industrial Metallurgists and a metallurgical engineering consultant with more than 30 years of experience in product design, manufacturing, failure analysis, and metallurgy training. He helps clients worldwide solve design and manufacturing problems and is the author of Materials Enabled Designs.
