For a long time, the processing efficiency of single-edge deep hole drill (gun drill) has been limited due to its low rigidity and grinding defects. Innovative and efficient single-edge deep hole drills can significantly improve the processing efficiency.
When the depth of the hole is more than 20 times the diameter of the hole, the deep hole drilling method must be used for processing. For many years, single-edged deep hole drill (gun drill) is a common tool for processing deep hole with hole diameter less than 40 mm. It can be seen from the test that the advantages of single-edge deep-hole drilling are high drilling quality and low feed speed. When tempered steel is processed, if the feed rate is increased, tool wear will increase and bad chip shape will be produced. Therefore, low processing efficiency and short tool life are the disadvantages of common single-edge deep hole drills.
The slight rounding of the edge and the overall coating can prolong the tool life without affecting the machining accuracy.
On the premise of retaining the high quality of single-edge deep hole drilling, the cutting tool is optimized to improve its processing efficiency without reducing the tool life. For example, for the processing of stainless steel, special attention should be paid not only to the design of cutting tools, but also to the study of the performance of different coating materials and coating structures. A large number of practices have proved that the tool wear of integral coating is less than that of common partial coating. In most cases, slight rounding of the cutting edge can improve tool life compared with single-edged deep hole drills with sharp edges
In order to evaluate the performance of single-edge deep-hole drills, common uncoated monolithic carbide single-edge deep-hole drills were used to process low sulfur quenched and tempered steel. Through cutting experiments, the wear condition and chip shape of common single-edge deep-hole drill with carbide as a whole show that the tool wears slightly when the drilling length reaches 30m under the condition of feed f=0.02mm. Because the cutting heat and cutting force load of the tool is small, there are only slight crescent depression wear and back face wear, and the chips produced are oblique spiral scroll chips. Easily discharged from the hole. By increasing the feed rate, after the drilling length reaches lf=9m, the tool tip at the tool's outer circle shows severe wear and tear, which makes the test have to be interrupted. In addition, the chip shape is also affected by the increase of feed rate. There is also a strip chip on the oblique spiral chip, and the flat strip chip segment will be clamped between the tool and the workpiece, causing tool damage.
From the practical application effect in industry, ordinary single-edged deep hole drills can be reliably applied to deep hole processing. However, in order to improve the processing efficiency, it must be limited by certain conditions, especially if the feed rate is increased, the tool will wear too fast. When the feed rate of single-edged deep hole drill changes, it can be seen that the measured value increases with the increase of feed rate, which is almost linear. When the feed quantity f = 0.34 mm, the feed force Ff = 950N, the torque Mb = 4.3Nm; when f = 0.36 mm, the tool will be damaged due to excessive torsional load.
In addition to cutting force load, chip shape is of great significance for deep hole drilling process. With single-edge deep-hole drill, when the feed rate f = 0.04 mm, oblique helical chips of suitable length are formed, and no unfavorable strip chips appear. When the feed rate is increased to f=0.1mm, a single chip roll appears, which is also suitable for the type and shape of chips smoothly discharged from the hole. When the feed rate is further increased to f=0.2mm, a large amount of heat load is obviously generated, the chip color changes obviously, and the shape becomes irregular. When the feed rate is further increased to f=0.3mm, this phenomenon becomes more prominent. Chips not only curl very closely, but also appear flat chips. It can be seen that the chips are very thick. The size of mechanical load can be used to judge tool wear. With the increase of wear value, the measurement value of feed force and torque also increases.
According to the expected tool life, the feed rate can be increased by 10 times. The measurement results show that within the length of 30m drilling, because ordinary single-edged deep-hole drills can reach 30m drilling length when the feed is f=0.02mm, and increase the feed rate, the wear of ordinary single-edged deep-hole drills will be accelerated. The single-edged deep-hole drills adopt a feed rate 10 times higher, that is, f=0.2mm, which still achieves the predetermined life index. Scanning electron microscopy analysis shows that the tool is still in normal wear state and can continue to use.
In addition to tool wear, hole quality is also an important index to describe deep hole drilling performance. For the eccentricity error of the hole, the measured value shows the influence of tool structure and feed rate. For different single-edge deep hole drills, the measured values are comparable. Therefore, the improvement of tool grinding has no adverse effect on the eccentricity error of holes. In addition, for single-edge deep hole drills, the eccentricity error of the hole is increased by increasing the feed rate. With the increase of feed, the value of feed force and torque increases, which leads to the increase of radial force, the offset of tool and the eccentricity error of hole.
Through the improvement of tool structure and processing technology, the hole eccentricity error can reach a very good level. In a word, the improvements in tool structure design, coating and cutting edge chamfering have proved to be effective, so that the single-edge deep hole drill can be processed efficiently.
