Dry cutting tool and its application in processing rolls (2)

3. Blade structure and geometric parameters Determination of blade shape and geometric parameters is critical to the full use of cutting performance. In terms of tool strength, the blade tip strengths of various blade shapes are from high to low: circular, 100° diamond, square, 80° diamond, triangle, 55° diamond, 35° diamond. After the blade material is selected, the blade shape with the highest possible strength should be used.

Hard turning inserts should also be selected with the largest possible tool nose arc radius, roughed with round and large radius inserts, with a tool nose radius of approximately 0.8 μm during finishing.

Hardened steel chips are red and soft forging strips, brittle, easy to break, not bonded, generally do not produce built-up edge on the cutting surface, the surface quality of the processing is high, but the hardened steel has a large cutting force, especially The radial cutting force is larger than the main cutting force, so the tool should adopt a negative rake angle (g0 ≥ -5 °) and a large relief angle (a0 = 10 ~ 15 °). The lead angle depends on the rigidity of the machine tool. Take 45 to 60° to reduce workpiece and tool flutter.

Third, the dry cutting hardened roll cutting parameters and its requirements for the process system

1. Selection of cutting parameters The higher the hardness of the hardened roll material, the smaller the cutting speed should be. Suitable cutting speeds for hard turning operations using dry cutting tools range from 80 to 200 m/min, with a typical range of 100 to 150 m/min. When using large depth of cut, or strong intermittent cutting, the cutting speed should be maintained at 80 ~ 100m / min. Under normal circumstances, the amount of back-feeding knife is between 0.1 and 0.3 mm. When the surface roughness of the machined surface is high, a small depth of cut can be selected, but it should not be too small and should be suitable. The feed rate can usually be selected between 0.05 and 0.25 mm/r, depending on the surface roughness value and productivity requirements. When the surface roughness is Ra 0.6 to 0.8 μm, it is much more economical to use a dry cutting tool for hard turning than grinding.

2. Requirements for the process system In addition to selecting a reasonable tool, the use of dry cutting tools for hard turning rolls has no special requirements for lathes or turning centers. If the lathe or turning center is rigid enough, it can be obtained when machining soft workpieces. The required accuracy and surface roughness are available for hard cutting. Since the radial force is large when processing the hardened roll, the machine tool power is required to be large, and the machine tool system is rigid, which can protect the dry cutting tool and obtain satisfactory processing results. In order to ensure smooth and continuous turning operations, the usual method is to use rigid clamping devices and medium rake angle cutters. If the roll is positioned, supported and rotated under the cutting force, it can be kept fairly stable, and the existing equipment can be hard-turned by dry cutting tools.

Fourth, it should be noted problems Dry Cutting of Hardened rolls <br> <br> Dry Cutting of Hardened roll without cutting fluid, since a large amount of heat generated by the chip away during cutting, less heat is generated in the surface Damage and thermal deformation. Conversely, the use of coolant can adversely affect tool life and surface quality.

The precision car blade is preferably made of a square or round blade with high strength. Although the cutting force is increased, the roughness value is smaller and the surface quality is better. After blunt grinding, the index can be changed. Diamond-shaped inserts are also available, with a tool nose radius of between 0.5 and 1 mm.

When the dry cutting tool is used for low speed cutting (such as v<50m/min), it not only has the same cutting performance as the hard alloy, but also easily causes the vibration of the process system, causing the tool to chip or even cut. When cutting at a high speed in a certain speed range, the increase in cutting temperature also changes the performance of the workpiece material and improves the toughness of the dry cutting tool, thereby reducing the damage. However, in the case of intermittent cutting, if the cutting speed is increased too much, the temperature difference will be large, and the generated thermal stress may also cause the tool to be damaged.

The effect of feed rate on tool breakage is greater than the cutting speed. Selecting a smaller feed rate helps prevent or reduce tool breakage. Therefore, for dry cutting tools, a smaller feed rate and the highest possible cutting speed should be used.

When clamping a dry cutting tool, the tool should be as short as possible to prevent the tool from fluttering and deforming, so that the dry cutting tool can maintain a good machining state.

For workpieces with high hardness and irregularity, dry cutting tools are brittle and fearful of impact. When the cutter is cut into and cut out from the end face of the workpiece, especially the surface is uneven, the impact is most likely to occur, and the cutting edge is broken, so that the durability is lowered. Therefore, before using a dry cutting tool, it is best to chamfer the workpiece at the cutting end to reduce the impact of the tool. The chamfering of the blank cut-in position avoids excessive impact loads when the tool is just touching the workpiece. The chamfering of the blank cut-out is mainly to prevent the cutting edge of the material from being cut when the cutter is cut off from the part.

In order to use dry cutting tools well, it is important to accurately control the quality of the workpiece and accurately judge the durability of the dry cutting tool. If the tool with severe wear is used all the time, the cutting force and cutting temperature increase and the cutting is not smooth, it is difficult to control the workpiece size and surface integrity, and even the dry cutting tool can not continue to be repaired and scrapped. In order to ensure the normal use of the tool, it is recommended that the dry cutting tool should be reground after the flank wear amount reaches 0.3-0.6mm (small value when finishing the car). However, re-grinding requires certain equipment and skills. Most factory machines do not have suitable conditions. Generally, re-grinding of dry-cutting tools should be done by professional factories.

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