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, making them less suitable for modern high-speed machine tools and harder materials. To address this issue, this study conducted drilling tests using both standard and magnetized twist drills under identical conditions, with the number of drillable holes serving as an indicator of cutting performance. The focus was on evaluating how magnetization affects the tool’s durability.
The test involved four groups of twist drills made from high-speed steel (HSS), with a diameter of 9.8 mm. The material being drilled was a 10 mm thick Q235 steel plate. A bench drill model Z512B was used at 800 rpm with manual feed and 5% emulsion coolant. The first group (20 pieces) remained untreated, while the second group (30 pieces) was magnetized so that the cutting end became an N pole and the shank became an S pole. The third group (30 pieces) was magnetized in the opposite direction, with the cutting end as an S pole and the shank as an N pole. The fourth group (20 pieces) was magnetized and then demagnetized. To prevent interference, all magnetized tools were placed end-to-end according to their magnetic poles.
During the test, each drill bit was used until it emitted unusual noise, became severely worn, or could no longer cut effectively. The number of holes drilled by each tool was recorded.
Test results showed that the untreated group (Group 1) drilled a total of 2,234 holes, averaging 111 per tool. Group 2 (N-pole magnetized) achieved 4,596 holes, averaging 153 per tool. Group 3 (S-pole magnetized) drilled 4,461 holes, averaging 148 per tool. Group 4 (demagnetized) drilled 2,239 holes, averaging 119 per tool.
Analysis revealed that magnetization increased the average number of holes drilled by 35.2%, indicating a significant improvement in tool life. Moreover, N-pole magnetized drills outperformed S-pole ones, suggesting that the polarity of magnetization plays a role in performance. Additionally, demagnetizing after magnetization had little impact on tool life, implying that the effect of magnetization is stable over time.
Further inspection of the magnetized tools showed fewer instances of chipping and wear, suggesting that magnetization may alter the internal structure of HSS, enhancing its resistance to impact and friction. Overall, the findings demonstrate that magnetization is an effective method to extend the service life of twist drills, especially when applied with the cutting end as an N pole.
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