The NSE cylinder head production line is one of the most advanced metal processing systems globally, known for its high efficiency and precision. However, despite its technological sophistication, the pass rate during the initial leak test has remained low. This paper presents a case study that explores how addressing the issue of plug overflow significantly improved the cylinder head’s first-time pass rate.
One of the primary causes of failure in the leak test is the overflow of sealing glue from the screw plugs. According to statistical data, approximately 83.05% of all leakage failures are attributed to this issue. Solving this problem could dramatically enhance the overall pass rate. To meet industry standards, the target for the first-time pass rate was set at 96%. Through brainstorming sessions, we identified several root causes and created a fishbone diagram (see Figure 1) to visualize them.
After analyzing each factor, we confirmed that the main issues were the lack of a glue removal function in the equipment and the oversized diameter of the screw plugs. A countermeasure table (see Table 4) was developed to address these two critical factors.
To resolve the issue of excess glue, a brushing step was added between the screw plug assembly and the leak test. A pneumatic wire brush was installed on the testing station to remove any excess sealant from the 5502 hole before the test. The installation involved designing a custom tool to hold the brush and ensuring it operated automatically during the process. The brush was set to a depth of 3 mm to optimize the cleaning effect without interfering with the production cycle.
Additionally, the screw plug supplier was required to adjust their quality control measures, ensuring that the thread diameter was maintained within the middle of the tolerance range. After implementing these changes, the first-time pass rate improved significantly, as confirmed by SPC analysis showing a Ppk value of 1.86, which exceeds the required threshold of 1.67.
To sustain the improvements, the supplier updated their inspection specifications, while the production team revised the device check card and process guide to include routine maintenance procedures for the brushing system. These steps ensured long-term reliability and consistent performance, leading to a substantial increase in the cylinder head's first-time pass rate.
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Zhejiang Huafeng new material Co., Ltd. , https://www.cnhfpipe.com