**2. Practical application of root cause failure analysis in brake rotor failure**

Nowadays, automakers and automotive part manufacturers are under intense pressure to avoid warranty claims/costs and litigation by elevating the quality of their products to ensure safe operation. The component that fails earlier than expected usually attracts financial liability and challenges the manufacturers to scrutinize the root cause(s) of failure to evade future recurrences. However, in some cases, if the cause of the damage cannot be recognized and resolved, it increases the service and warranty costs until the appropriate solution is accomplished.

A failure is when a component or machine cannot satisfactorily perform its intended functions correctly. A metallurgical failure analysis technique is usually adopted for determining the next step to resolving the problem. Failure analysis is a systematic, methodical process to determine the physical causes of failures. Sometimes, the failure analysis process can be complex, draws upon many different technical disciplines, and employs various observation, inspection, and laboratory techniques [25]. Performing a failure analysis is tedious and complex, and it does not necessarily conclude when the physical causes of the failure are recognized.

Consequently, a well-organized, comprehensive, and straightforward way of resolving failure analysis problems is required to achieve enhanced product quality and failure prevention. A reasonable failure analysis approach first requires a clear understanding of the problem definition and the distinction between an indicator,

a cause, a failure mechanism, and a consequence [25]. However, a complete understanding of the conditions associated with the failure would enhance the knowledge of its causes and significantly improve the ability to specify appropriate corrective measures.

The root cause failure analysis (RCFA) procedure is commonly used to discover more profound contributors to failures, such as human and hidden root causes. RCFA is a process for identifying the actual root cause of a particular failure and applying the information to set a pathway for corrective and/or preventive measures. RCFA, in combination with physical analysis, are essential steps in the general problem-solving process and are vital constituents for amending and preventing failures, achieving higher levels of quality and reliability, and ultimately enhancing customer satisfaction [25].

In solving failure or quality-related problems, it is better to visually structure the information relating to the problem because it can sometimes be challenging to see how different aspects of the issue interact. The fishbone diagram is an applicable technique for visualizing causal factors and their effect on the quality or failure of a product. This diagram is also known as the cause-and-effect diagram (**Figure 1**). The chart is a visual method for root cause analysis that organizes cause-and-effect relationships into categories [26]. The idea behind this diagram is that several factors may be responsible for the poor quality or failure of a product/component, which is hidden but can be categorized and viewed clearly from the chart. This diagram has been employed by aerospace, information technology, and medical industries for process and product quality improvement. Cause-and-effect graphs allow the visualization and organization of potential causes of a problem into an applicable framework for solving it. The charts are also helpful for incorporating cross-functional influences.

The damaged rotor in this investigation was produced by sand casting, machined to the specified dimensions, and installed in a new vehicle. The rotor had operated for approximately fifteen (15) months and covered 10,670 miles before it failed. However, the potential causal factors that possibly led to the failure of the rotor are classified and identified, as illustrated in **Figure 1**. The "fish" head represents the

#### **Figure 1.**

*Fishbone diagram illustrating the potential causes of brake rotor failure.*

problem to be studied, and each critical branch denotes a specific functional area. Based on the information presented in **Figure 1**, the failure root cause analysis was begun by critically evaluating each operational unit of the diagram. The background information provided at the beginning of the investigation assisted in eliminating the need to investigate the other branches further. The root cause investigation was focused on the manufacturing process and the application of the brake rotor.

However, in this investigation, a systematic approach of root-cause failure analysis was undertaken to understand the factors contributing to the brake rotor's failure. In addition, this chapter presents some recommendations that will improve the quality of automotive brake rotors during manufacturing and inspection and prevent future failure reoccurrence.
