Twist drills are among the most expensive cutting tools used in machining operations. Due to their semi-closed cutting environment and unique geometry, drilling generates higher temperatures compared to turning or milling under similar conditions. This leads to changes in cutting speed and geometric parameters of the cutting edge, ultimately reducing the service life of twist drills significantly. As a result, they struggle to keep up with modern trends such as high-speed machine tools and harder workpiece materials. To address this issue, this study conducted drilling tests using both standard and magnetized twist drills under identical conditions. The number of holes drilled before tool failure was used as an indicator of cutting performance. The focus of the research was on how magnetization affects the lifespan of twist drills.
**1. Test Conditions and Methods**
The material used for drilling was a 10mm thick mild steel plate (Q235). The twist drills used were high-speed steel (HSS) with a diameter of 9.8 mm. The drilling was performed on a bench drill model Z512B at 800 rpm, with manual feed control and a 5% emulsion coolant. A batch of twist drills was divided into four groups: the first group remained untreated (20 pieces), the second group was magnetized so that the cutting end was the N-pole and the shank end was the S-pole (30 pieces), the third group was magnetized in the opposite direction (S-pole at the cutting end and N-pole at the shank end, 30 pieces), and the fourth group was both magnetized and then demagnetized (20 pieces). To prevent demagnetization during testing, the magnetized drills were placed end-to-end according to their poles.
During the test, each drill was used to drill holes until it emitted unusual noise, became severely worn, lost its cutting ability, or suffered damage. The number of holes drilled by each tool was recorded individually.
**2. Test Results**
- **Group 1 (Untreated):** Total holes = 2,234; Average per tool = 111.
- **Group 2 (N-pole at cutting end):** Total holes = 4,596; Average per tool = 153.
- **Group 3 (S-pole at cutting end):** Total holes = 4,461; Average per tool = 148.
- **Group 4 (Magnetized and then demagnetized):** Total holes = 2,239; Average per tool = 119.
**3. Results Analysis**
When comparing Group 1 with Groups 2 and 3, it was evident that magnetization significantly improved the average number of holes drilled, increasing from 111 to 153 and 148, respectively. The overall average rose to 151, representing a 35.2% improvement. This demonstrates that magnetizing twist drills can greatly extend their service life.
Further analysis revealed that the N-pole magnetized drills outperformed the S-pole ones, indicating that the orientation of the magnetic field has an impact on performance. Additionally, when comparing Group 1 and Group 4, there was little difference in the number of holes drilled, suggesting that demagnetization after magnetization had minimal effect on the tool's lifespan.
Moreover, inspection of the cutting edges of the magnetized drills showed a much lower probability of chipping compared to non-magnetized ones. This suggests that magnetization may alter the internal atomic structure of HSS, improving its resistance to impact, friction, and localized damage.
**4. Conclusion**
Magnetization significantly enhances the service life of high-speed steel twist drills. Among the magnetized groups, those with the cutting end as the N-pole performed better than those with the S-pole. Furthermore, demagnetizing a previously magnetized drill did not substantially affect its performance. These findings suggest that magnetization is a promising technique for extending the life of twist drills in modern machining environments.
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