The flexible application of QC seven techniques in examples

QC seven techniques, also known as QC seven tools, generally refer to the old QC seven techniques, namely checklist, stratification, Plato, causality chart, histogram scatter chart and control chart, is an effective tool for quality management and improvement. In the actual analysis case, seven QC techniques are regarded as seven steps of quality analysis according to the steps and logic of quality analysis (the steps can be less than seven according to the needs of actual cases).

1 Check Sheet

1.1 Application Scenario: Record the defect type and quantity on the production line.

1.2 Case: From August 3, 2024 to September 20, 2024, defective BAC1278 products will be isolated in the process of product inspection, and the technical engineer in charge of the product will statistically confirm the daily product defects and quantity, such as: bubbles, mold sticking, deformation, edge biting, mold exit damage, flash pressing, flash adhesion and trimming damage. Through statistical analysis of the data, the product owner found that mold damage and sticky mold frequently occurred in multiple shifts, and then identified the defect as a common problem rather than an occasional problem. Therefore, it was determined that problems in process control or problems in employees' operation techniques led to more mold damage of products, and it was necessary to train employees' operation techniques to improve their operation skills.

2. Stratification

2.1 Application scenario: Classify the data according to different dimensions to find the root cause of the problem (for example, classify the data according to shift, machine, operator and mold number, identify the difference between variables, and determine whether the variable is the root cause of the problem).

2.2 Case: BAC1299 bad gas is the main problem in the production of this product. By arranging the mold holes and collecting the number of the bad product holes, we can determine whether the bad gas is concentrated in certain areas of the mold. By increasing the injection hole size in this area, we can improve the feed and solve the problem, or by increasing the exhaust holes in this area to improve the exhaust effect and solve the problem.

Conclusion: 9#, 10#, 13#, 14#, 8#, 6# are serious.

Improvement direction 1: Change the size of the injection port to improve the feeding situation and solve the problem of aeration

Improvement direction 2: Increase the exhaust hole in this area to improve the exhaust effect to solve the problem of air

3 Plato (Pareto Chart)

3.1 Application scenario: Identify major problems, also known as key management chart. According to the collected data, it is sorted and classified according to different differentiation criteria, and the proportion of each classification item is calculated in order of size, plus the graph of the cumulative value. Platonic analysis is the 80/20 law of business management; Grasp the main reason why 20% of the total proportion of 80%, 80% of the total proportion of only 20%. So the purpose of Plato's analysis is to get to the point. Only by focusing on things and finding the crux of problems can we quickly solve them and get twice the result with half the effort.

3.2 Case: From June 27, 2024 to August 18, 2024, Beratographic analysis was conducted on 23 defective products in BAC1306 production shifts, and it was found that insufficient filling, deformation and flash compression accounted for 83.68% of the total defective products. To solve the problem of insufficient filling, deformation and flash pressing is the key point to improve the qualified rate of the product.

4.1 Application Scenario: Analyze the cause of the fault.

4.2 Example: BAC1287 product viscosity deformation in August 2024. Through the analysis of human, machine, material, method, environment and measurement, the possible causes of product viscosity deformation are listed, and then checked and verified one by one, so as to obtain the real cause.

5 Histogram

5.2 Example: BAC1266 used histograms to analyze the size distribution of parts and found that the size of parts was concentrated on the left side of the median value, indicating that the mold development was unreasonable and the product size did not comply with the principle of centering. If the process changed, the size would easily exceed the lower limit and be unqualified.

6. Scatter Diagram

6.1 Application Scenario: Analyze the relationship between variables.

6.2 Example: DOE analysis can be used for process design to verify the linear relationship between vulcanization temperature, vulcanization time and product vulcanization degree (measured by international hardness value) and find the best process.

7 Control Chart

7.1 Application Scenario: Monitoring process stability.

7.2 Example: Running diagram and normal distribution diagram (capability analysis) are commonly used to determine whether the process is stable.

BAC1363 mold measured temperature running diagram