The material to be turned, tool material, tool angle and cutting elements are described in detail
Abstract: The turning methods suitable for various kinds of materials were introduced in this paper. The operated materials, cutter materials and angles, and cutting elements were expounded in detail, which could be as a reference for relevant people.
Key words: special steels; turning process; cutter angles; cutting elements
1 Preface
The tools and dies used in machining have complex materials, various varieties and different performances. To turn these tools and dies made of different materials, the turning tools used also require different materials, different angles and different turning methods. There is no lack of technical innovation and transformation in the summary of turning fixture and die work over the years.
2 Turning methods of several high hardness metal materials
In machining, turning metal materials with high hardness and plasticity is often encountered. Such as: turning of high-speed steel, turning of workpiece after quenching and turning of cemented carbide, etc. High hardness metal materials refer to metals with a hardness of more than 48HRC before quenching and materials and cemented carbides with a hardness of 58~62HRC after quenching. Practice has proved that reasonable selection of tool materials, geometric angles and turning parameters, and correct mastery of turning methods for high hardness metal materials are helpful to improve work efficiency. This paper introduces the specific methods of turning high hardness metal materials with ordinary lathes and domestic cutters.
2.1 Turning of high speed steel and hot die steel
2.1.1 Turning of W6Mo5Cr4V2 steel
This kind of high-speed steel is usually used to make cutting tools and cutting tools, such as turning tools, drill bits, reamers, milling cutters, etc. Before quenching, the hardness of high-speed steel is 225HB. The main metal content of this material is: tungsten 17.5~19.0%, chromium 3.8~4.4%, carbon 0.70~0.80%, molybdenum 1%, vanadium 1~1.4%. The metal elements contained are high hardness, which is not conducive to turning. When turning with cemented carbide and coolant, the service life of the tool is not ideal for both horizontal and vertical cutting. Especially for horizontal cutting, the blade of the cemented carbide tool is easy to wear and produce chip buildup, and the turning efficiency is low.
Figure 1 circular arc cutter
Through practice, it is found that the effect of transverse cutting W6Mo5Cr4V2 with high-speed steel W18Cr4V2 turning tool and coolant is better. The cutting edge of the cutter is of circular arc shape, which can avoid the blunt sharp angle of the blade in turning, improve the strength of the cutting edge and greatly improve the service life of the cutter. The circular arc cutter is shown in Figure 1.
When cutting materials, the linear speed of turning should be lower, generally V=20~30m/min is appropriate, the feed rate S=0.15mm/ revolution, and the rake face adopts a large arc shape.
2.1.2 Turning of hot die steel before quenching
Hot die steel H13, 012AL, with a hardness of 20HRC, is a die steel material developed in China in recent years. With its strength, plasticity, toughness, impact resistance, high temperature resistance and other advantages, it is widely used as hot heading dies. The die of "HBP-120, HBP-160" high-speed hot forging machine imported from Japan was localized, and H13 and 012AL were used to make hot die forging tools, replacing the import of Japanese dies, so that the service life of domestic dies reached the service life of imported dies. The turning of these two materials is very difficult. In cutting, the cutting deformation is large, the heating is serious, the fault is difficult, and it is easy to produce "chip nodules", and the cutting surface is easy to produce scale thorns. The previous cutting speed V=20~30m/min, so it is not easy to break chips and make iron chips entangle the knife in cutting. Because the cylindrical surfaces of H13 and 012AL are as irregular as forgings, the previous turning tool angle cannot be used. Instead, the large R front face shallow chip removal groove should be used, and the main, auxiliary and rear angles should not be too large, so as to increase the strength of the cutting edge and increase the cutting speed from the original V=70m/min to V=102m/min, S=0.3~0.4mm, t=3~5mm. After turning the bar, changing the fine turning tool for turning can improve the working efficiency by more than 3 times, More than 20 turning tools can be saved every year.
3 Turning of alloy steel
The domestic moulds of HBP-120 and HBP-160 high-speed hot forging machines have "bottoming punches", as shown in Figure 2.
Fig. 2 bottoming punch
The surface of the working part is overlaid with "tungsten chromium cobalt alloy". The hardness of this tungsten chromium cobalt alloy can reach 50~52HRC. The welding surface is uneven and easy to cut, which makes turning difficult. Start cutting with "YT" cemented carbide turning tools. Because this kind of knife has high hardness and poor toughness, it is easy to cut when turning, and the effect is not good. After repeated tests, "YG8" cemented carbide cutter is used for turning, and the result is very good. From turning a workpiece with several turning tools to turning a workpiece with one turning tool, it can process 2~3 workpieces, improving the work efficiency by 2~3 times. Due to the change of the angle of the turning tool (front angle γ From 0 ° to 5 °, rear angle α From 5 ° to 2 °), making the turning edge strong and sharp, ensuring the smooth cutting.
4 Turning of workpiece after quenching
4.1 Turning of quenched hot die steel
For the two metal materials H13 and 012AL mentioned above, oxide skin, oil stain and impurities appear on the metal surface after quenching, so direct grinding is very difficult. After process improvement, the quenched H13 and 012AL are finely turned first and then ground. After quenching, H13 and 012AL materials have a surface hardness of 54~56HRC. The turning tool with negative rake angle is used to cut, and the result is not good. Then the domestic "726" cemented carbide tool is used for turning, and the geometric angle of the turning tool is improved. The result is very good, and the efficiency is greatly improved. See Figure 3 for the geometric angle of the tool.
Figure 3 tool geometric angle
4.1.1 turning tool before improvement
(1) The blade material is "yt30" cemented carbide, and the cutter bar is 45 steel.
(2) The -15 ° rake angle and r0.5mm tool tip arc radius are adopted to protect the tool tip and enhance the impact resistance.
(3) V=20~30m/min, S=0.1~0.15mm/r， t=0.3~0.5mm.
(4) Process hardened carbide steel below 60HRC.
4.1.2 Improved turning tool
(1) The blade material is "YT726" cemented carbide, and the cutter bar is 45 steel.
(2) Adopt -1~-5 ° front angle, r0.3~0.5mm arc radius of the tool tip, and 5~10 ° rear angle to protect the tool tip and resist impact.
(3) V=25~40m/min, S=0.15~0.3mm/n, t=0.5~1.0mm (Figure 3 tool geometric angle). (4) Process hardened carbide steel below 62HRC.
(5) The efficiency is 3 times higher than that before improvement.
At present, this cutting method has been comprehensively promoted. Over the past few years, some quenched workpieces have been precision turned to remove oxide skin and oil stains, which has reduced the grinding amount, brought great convenience to the grinding process, shortened the grinding time, and improved labor productivity.
4.2 Turning of male and female dies after quenching
The hardness of the metal surface exceeds HRC60, so turning is extremely difficult, and the cutting edge of the tool is very easy to wear. Machining a part called "convex concave touch" (commonly known as horn bowl), as shown in Figure 4, its surface is irregular curve, and manual feeding is required during turning. The traditional turning method is to grind the tool tip into a small arc. If you don't pay attention to it when turning, the arc surface of the workpiece will be turned into a concave knife mark, which will bring trouble to the next step of polishing. The surface finish Ra1.6 can't meet the requirements, and the workpiece quality is difficult to guarantee. Work hard on the reform of cutting tools, and change the cutting edge from small arc to large arc, as shown in Figure 5.
Figure 4 diagram of punch and die
Figure 5 Comparison of tool shapes before and after improvement
During cutting, the cutting edge changes from point contact to line contact with the workpiece surface, avoiding the knife marks caused by the cutting tip cutting into the workpiece surface.
Due to the improvement of the cutting edge of the tool, the strength of the tool is greatly improved and the service life of the tool is prolonged. The roughness of the workpiece surface can also meet the requirements, which greatly facilitates the polishing process. The qualified rate of the product reaches 100%, and the service life of the product is correspondingly improved.
5 Conclusion
Although the turning of high hard metal materials is very difficult, as long as we carefully explore and dare to practice, the problem of difficult turning can be solved. We should focus on the geometric angle of the tool and the turning speed.
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