Turning is the main process of mechanical manufacturing process. Especially in the heavy-duty machining industry, the workpiece structure size is huge, the weight is as high as 60-80t, even hundreds of tons, the processing equipment heavy-duty bicycle turning diameter is 6m, and the heavy-duty vertical car can reach 10m. Compared with ordinary machining, heavy-duty turning has a large cutting depth, a low cutting speed, and a slow feed rate. The machining allowance is 35~50mm on one side, combined with the poor balance of the workpiece during the cutting process, the uneven distribution of the machining allowance, the vibration caused by the imbalance of some parts of the machine tool, etc., which makes the dynamic unbalance process of the machining consume a lot of maneuver. Time and auxiliary time. Therefore, in the processing of heavy-duty parts, to improve productivity or the utilization of machinery and equipment, we must start from increasing the thickness of the cutting layer and the amount of cutting. It is important to consider the cutting amount and tool selection, improve the tool structure and geometry, and the strength characteristics of the tool material. Take it into account to increase the amount of cutting and significantly reduce maneuver time.
1 Tool material selection
Commonly used tool materials for cutting include high speed steel, hard alloy, cubic boron nitride (CBN), ceramics, and the like. The heavy cutting depth is generally 30~50mm, the margin is uneven, the surface of the workpiece has a hardened layer, and the tool wear in the roughing stage is mainly in the form of abrasive wear: the cutting speed is generally 15-20m/min, although the speed value is in the product. The area of ​​the tumor occurs, but the high temperature of the cutting makes the contact point between the chip and the rake face in a liquid state, which reduces the friction and inhibits the formation of built-up edge. The choice of tool material is resistant to wear and impact. Ceramic tools have high hardness, but have low flexural strength and poor impact toughness. They are not suitable for heavy-duty turning with uneven margins. CBN has the same problem. Cemented carbide has a low coefficient of friction, which can reduce the cutting force and cutting temperature during cutting, greatly improve the tool durability, and is suitable for high hardness materials and heavy-duty turning roughing. Cemented carbides are classified into tungsten cobalt (YG), tungsten cobalt titanium (YT) and tungsten carbide (YW). YG-based cemented carbides have good strength and toughness when processing steel, but high-temperature hardness and high-temperature toughness are poor: the workpiece has large plastic deformation during heavy turning, severe friction and high cutting temperature, so YG is rarely used in heavy-duty turning. Carbide. YT type hard alloy has high hardness and wear resistance, high heat resistance, anti-adhesion and anti-oxidation ability, and is a commonly used tool material for heavy-duty turning, suitable for processing steel materials. However, in low-speed turning, the unevenness of the cutting process will result in poor toughness of YT-based alloys, resulting in chipping: especially when processing some high-strength alloy materials, the durability of YT-type hard alloys is rapidly reduced and cannot meet the requirements for use. In this case, YW type tools or fine-grained, ultra-fine grain alloy tools (such as 643) should be used. The fine-grained alloy has good wear resistance and is more suitable for processing chilled cast iron products, and the efficiency can be more than doubled compared with YW tools.
The use of carbide tools to increase the turning speed of heavy machining is one of the keys to increasing productivity and a favorable factor in shortening the production cycle. In the process, a large amount of cut is performed in several strokes, and the cutting depth is small each time, and the cutting speed is greatly improved by the cutting performance of the cemented carbide tool.
2 Tool angle selection
In the rough turning stage of heavy-duty turning, forging scales, cracks, shovel, casting inclusions, pores and other defects on the outer surface of the workpiece are easy to cause the tool to break, so a reasonable tool angle should be selected. Under heavy-duty processing conditions, the rough cutting is necessary to remove very thick chips. The turning tool generally adopts the rake angle g=8°~12°, and the ordinary g=15°. The cutting edge inclination angle is l=10°~18°. If the rake angle is reduced, that is, the cutting angle is increased, the strength of the cutting edge can be increased to some extent. It should be noted that: the reduction of the rake angle increases the cutting force, but when the g changes from 15° to 10°, the cutting force increases little, and the increased working rake angle and wedge angle increase the sharpness of the blade and Tip strength 3 Especially when the workpiece is heavy and the impact load is rotated, the cutting edge of the cutting edge l=10°～18° creates the most favorable cutting conditions, so the impact point of the cutting force during cutting Leaving the tip of the knife prevents the tip from breaking. At the same time, the main cutting edge has a negative chamfer of about 1mm width and a rounded corner of R2mm to improve the impact resistance of the blade, but the tool installation angle should be adjusted according to the actual situation.
3 Tool structure selection
In the roughing stage, the cutting allowance is large, and the rigidity of the tool is required to be high. In general, the overall tool stiffness is good, but the structure is cumbersome, difficult to load and unload: the machine clamp tool is flexible to disassemble, and the dynamic stiffness can also meet the processing requirements. The selection of the blade material and the clamping structure of the machine clamp tool are very important for the machining accuracy. In actual machining, it is found that the eccentric pin clamping and the hook head pressing type are not suitable for heavy rough machining because the process system vibration is large during rough machining, often making pressure The tight mechanism is loose, causing damage to the blade: the upper-pressure structure also often causes damage to the clamp due to the flow of the chip. The manufacturing precision of the machine clamp tool is also very high, because even a slight error can make the positioning mechanism become a bearing mechanism. Due to the large cutting force during the machining of heavy cutting, the tool is easily damaged. The actual machining results show that the tool shown in Figure 1 is more suitable for roughing of heavy turning.
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