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**Tightening Effect Detection and Problem Analysis in Engine Components**
Cars are made up of numerous components, and bolted connections are among the most commonly used. However, manual tightening can lead to inconsistent torque levels, making it difficult to ensure assembly quality. To address this, tightening machines are widely used in automotive manufacturing, especially for critical engine parts, as they provide precise control over the tightening process.
While modern tightening machines from both domestic and international manufacturers are highly accurate and stable, there is always a possibility of minor errors. Therefore, it's essential to test the tightening effect after the machine has completed its task to ensure product quality.
This paper introduces current methods for detecting the tightening effect after using a tightening machine and analyzes real-world issues encountered during the tightening process of engine parts.
**Common Methods for Detecting Tightening Effects**
The two main control methods used globally are torque control and torque-rotation angle control. In practice, however, the tightening effect is usually assessed based on the torque value. Common detection methods include the double-tightening method and the sensor serialization method.
The **double-tightening method** involves using a high-precision torque wrench to re-tighten a bolt after it has been tightened by the machine. The torque value at the point of re-tightening is recorded as the final torque. This method is simple and cost-effective but can introduce significant errors due to operator skill, force application, and differences between static and dynamic friction.
On the other hand, the **sensor serialization method** uses a high-precision torque sensor installed between the tightening shaft and the sleeve. This allows for real-time measurement of the torque during the tightening process, resulting in more accurate readings that can be used as the final torque value.
**Torque Errors and Complex Tightening Methods**
The double-tightening method is a static detection technique that is easy to use but not entirely reliable. For non-soft connectors, the torque deviation can range from -5% to 25%, while for soft connectors, it can go as low as -20%. Therefore, this method should only be used as a reference rather than an exact measurement.
In contrast, the sensor serialization method is more accurate because it measures torque dynamically during the tightening process. It requires specialized equipment, making it more expensive, but the results are more reliable and suitable for final verification.
**Problems Encountered During Tightening**
Even when the tightening machine operates correctly and displays accurate values, discrepancies can still occur during manual inspections. Some common issues include:
1. **Discrepancy Between Manual and Machine Readings**:
- When the manually measured torque is higher than the machine’s reading, it may be due to improper zeroing, visual error, or inherent inaccuracies in the wrench.
- When the manual torque is lower, it could be due to the time elapsed since tightening or issues with the workpiece itself, such as misalignment or material inconsistencies.
2. **Torque Reaches Upper Limit, Angle Not Reached**:
This often occurs when there is poor thread quality, foreign matter in the hole, or washers that rotate during tightening, increasing friction.
3. **Torque Below Lower Limit, Angle Reached**:
This is typically caused by bolts with low yield strength or incorrect thread sizes, though such cases are rare in production.
4. **Other Issues**:
Sometimes, process specifications are too strict, leading to unnecessary rejections. It's important to understand that torque is an indirect measure of clamping force, and variations in friction can significantly affect the readings. Therefore, it's crucial to avoid overemphasizing small torque deviations.
**Case Study: Different Torque Readings for Same Workpieces**
A notable example involved engine cover tightening. When using aluminum alloy covers, certain tightening points showed higher manual readings compared to the machine. Upon inspection, it was found that the friction patterns on the cover surface affected the static friction, causing higher manual readings. When steel covers were used instead, the readings aligned better, confirming that the issue was related to the material, not the machine.
In conclusion, while tightening machines offer precision, manual checks remain necessary. However, they must be interpreted carefully, taking into account factors like friction, material properties, and timing. Understanding these nuances helps ensure accurate and reliable assembly in automotive manufacturing.
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