7-Step Problem-Solving Methodology

Quality of products and processes plays a vital role in the automotive industry. To become more efficient and effective in the global market, approaches for failure diagnosis using standardized methodologies such as 7-Step Problem-Solving Methodology (7SPSM), along with 8D, PDCA, DMAIC, and Six Sigma are adopted. The present article discusses a successful case of 7SPSM in the automotive industry. The tools used in all seven phases contribute majorly toward an effective and complete understanding of the problem considering all the underlying factors. From the results experienced, it can be concluded that 7SPSM provides an effective methodology not only for solving problems but also for continual improvement by elimination of recurrences of product failure.

Step 1. Identify the Problem

The company’s foremost task is the detailed identification of the problem or failure that occurs. The problem is addressed with the 5W1H questioning method (Who, What, When Where,?Why, and How) , which helps in better understanding of the loss of function and the failure mode. Comparison is made between the current working of the system and the ideal working, and it is checked by how much the variation from the norm is tolerable. As previously problem, customers complained of noise from the exhaust system. Upon inspection, the main problem was a failure in the clamps being used, which led to leakage of exhaust gases, and hence, the noise was being produced. Data related to clamp failure location, intake and exhaust manifold configuration, stage at which failure was reported, and several other factors were collected. These activities helped in documenting a concise and quantifiable problem statement and identify the severity of the failure.

Step 2: Identify and Prioritize Possible Causes

The task here is to understand the mechanism of failure with respect to the three realities (Real Parts, Real Place, and Real Situation). The cross-functional team systematically derives all possible causes of the problem. It investigates why the problem went undetected during the design and analysis phase to understand whether the problem has occurred after eventual repairs. Step 2 is then concluded by formulating a prioritized list of possible causes of the product problem/failure mode based on the severity of damages caused by them. This involves using Pareto Charts (Fig.?1) with the data collected in the previous step to indicate the frequency of defects and their cumulative impact. Failure causes like design failures, quality defects, excessive stresses, and alignment issues are identified, and a cause-effect diagram (Fig.?2) is developed with these causes to get an idea of the inter-relationship between the causes. Using physics and logical approach, fault tree analysis is prepared to identify all the system failures and their hierarchy. Based on their severity, damage caused by them, and their effect on the system, possible assignable causes are obtained.

Step 3: Take a Short-Term Action

Since the cross-functional team is familiar with the product/process, possible short-term corrective actions must be undertaken to control the problem and prevent its expansion. These actions should be taken to protect the customer from the problem until permanent collective measures are implemented. In addition, this corrective action should make sure that no further problems arise on its implementation. This step is proposed to stop the failure outcome from proving to be irrecoverable before the problem can be solved. Replacement of the failed clamps with new clamps when the vehicles were brought to the service touch-points of the company was thought to be the best possible interim corrective action. For this, the service centers had to be stocked with spare clamps for quick replacements.

Step 4: Determine Failure Causes

This step involves systematically conducting tests to demonstrate a correlation between the possible causes and the observed failure modes using the data obtained in Step 2. This step was initiated using the boundary diagram, which helped in studying the different interactions like mass flow, fluid flow, and reaction forces between the system and its adjacent subsystems. Fault tree analysis helped to identify the causes in detail by progressing from left to right of the tree. This also helped in getting a detailed analysis of all the possible causes. The parameter diagram (Fig.?3) helped in studying the different noise sources like the piece to piece variation, external environment, change over time, customer usage, system interactions as well as the input signals, ideal functions, the error states, and the controlling factors of the system. It was observed that most of the failures were caused by excessive stresses developed on the clamp and due to flange misalignment. The different causes that were contributing to these two failures were further studied in detail. Simulation study validated that flange misalignment's led to excessive stress generation on clamp.

Step 5: Select and Verify the Solutions

After thorough analysis, the team should be able to objectively demonstrate the effect of each of the causes identified previously. This helps to understand all the aspects of the problem and helps in initiating proper corrective actions. The current system is modeled in SOLID-WORKS and simulated in Ansys. Since the main contributing factors for the excessive stresses being developed on the clamp were design and material aspects of the clamp, they were studied in greater detail. Different design alternatives with modifications in the thickness and filets were modeled and analyzed, and their results for different engine temperatures were plotted. Desirable results were also obtained by changing the material grade. To solve the issue of misalignment of flanges, different flange designs were tested. Determination of which potential solutions are more effective or ‘better’ than others is done by using the Pugh Matrix, a scoring matrix used for concept selection. All the design alternatives are rated for different parameters like size, weight, cost, manufacturability, ease of assembly, function, life, strength, and safety. The alternative that fares the best in all the parameters is selected for implementation. At the end of this step, a combination of the clamp with optimum dimensions and good strength along with the flange type that prevents misalignment was selected.

Step 6: Implement Permanent Solution

The potential solutions narrowed down with the help of Pugh Matrix were implemented in the initial system. Before the implementation, it is imperative that we thoroughly check that the problem has been understood completely, all the constraints and factors affecting the failures were taken into consideration, and all the possible alternatives were studied. This was facilitated by implementing Design Failure Mode and Effect Analysis (DFMEA). All the possible modes of failure of the existing system are listed by prioritizing them out along with their effects, severity, and frequency of occurrence. With these data, the Risk Priority Number (RPN) is calculated for each mode. Further, the same exercise is carried out for the system with our implemented corrective solution, and RPN is calculated. By comparing these two RPNs, we can effectively understand if our solution is successful in preventing the failure.

Step 7: Monitor and Prevent Recurrence

In this step, it is ensured that the underlying systemic or process issues which led to the problem have been addressed. The implemented solution is continuously monitored to check whether it is preventing failures with the help of check-sheets. The check-sheets consist of several parameters such as flow rate of gases, vibrations, and noise which are used to validate the solutions. The system is also checked for any recurrences of failures. At the end of this step, the long-term effectiveness of the permanent solution is quantified, and verification of the effectiveness of the implemented solution is confirmed.

Conclusions

Several automotive companies have started adopting standard approaches for failure diagnosis in recent years. This article discusses a case study of the successful implementation of 7SPSM in an automotive company for solving a problem in the exhaust gas flow system. The tools used in the different phases of the seven steps contribute majorly toward an effective and complete understanding of the problem considering all the underlying factors. The diagnostic process was carried out efficiently once the main causes were identified, such as the excessive axial pressure on the clamp and low yield strength of the material being used. The solution most effective, feasible, and most compatible with the system was chosen through the Pugh Matrix. The 7-step diagnosis provides a standardized, methodical, and disciplined approach to understand the root causes, identify their effects, and implement solutions that are effective and help increase the system’s efficiency. The case study shows that 7SPSM could provide an effective method for solving problems where the solution is not obvious. Considering the damage caused by the failure, it is imperative that we reach the root causes and solve them as soon as possible.