China FAW Group has set plans to expand the production capacity of its vehicle assembly line. To support this growth, it is essential to improve the cycle time of the cylinder head assembly line. Currently, the leak test machine for the cylinder head operates at a slow pace—60 seconds per unit—which has become a bottleneck in the overall production process. As a result, technical upgrades and optimization efforts have been initiated to enhance productivity and meet the new production demands.
The leak test machine plays a crucial role in ensuring the quality of components by measuring their sealing performance. The "leak rate" is a key parameter used to determine whether a part meets the required standards. If the actual leak rate is below the acceptable limit, the component is considered qualified. This is done by either pressurizing the part with compressed air or creating a vacuum, followed by monitoring pressure changes over time. A drop in pressure indicates a potential leak, while a rise in vacuum level suggests the same.
In the case of engine cylinder heads, the leak tester is used to detect leaks in valve seats, oil seals, and other critical areas. The system automatically inflates, balances, saturates, measures, and discharges dry air, allowing for an accurate assessment of the gas leak rate. This method is both efficient and reliable. Key parameters involved in the testing process include the material and geometry of the workpiece, its condition, test pressure, duration, allowable leak rate, and environmental factors such as temperature.
To evaluate the current performance of the cylinder head leak test machine, a detailed analysis was conducted. The machine is responsible for testing five different sections of the cylinder head: three intake ports, three exhaust ports, two oil circuits, one water passage, and one additional air inlet/exhaust port. Each section requires specific test durations, with the total cycle time reaching up to 30 seconds. When combined with the auxiliary actions (such as loading/unloading and plugging), the total cycle time reaches 34 seconds for the main test and an additional 26 seconds for the auxiliary operations, totaling 60 seconds per unit.
Several improvement options were considered. Option 1 involved shortening the test time, but this risked inaccurate results and was therefore discarded. Option 2 suggested increasing the number of testers, which would be costly and not balanced in terms of workload. Option 3 focused on reducing the auxiliary time by optimizing the movement of parts into and out of the test station, as well as synchronizing the plugging and unblocking processes. This approach proved to be the most effective.
Under the third plan, three key improvements were implemented:
1. Synchronizing the entry and exit of the tested cylinder head and the next unit, reducing the time spent on loading/unloading by 2.5 seconds.
2. Simultaneously sealing the intake, exhaust, and fuel rail holes before the test, using the longest blocking time among the three, resulting in a 2.5-second reduction.
3. Closing all sealed areas simultaneously after the test, using the longest opening time among the three, saving 1.5 seconds.
After implementing these changes, the total cycle time was reduced from 60 seconds to 53.5 seconds. Further refinements in the second stage led to even greater efficiency, with the average cycle time dropping to 51.48 seconds per unit.
This optimization not only improved the production tempo but also ensured that the assembly line could meet the increased demand efficiently. The results demonstrate the effectiveness of process optimization in enhancing productivity and reducing costs in automotive manufacturing. Such improvements are valuable for companies worldwide looking to streamline their production lines and increase output.
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