Turning preparation of cam profile
2021-11-10

Turning preparation of cam profile

Turning camshafts, the most difficult part is the cam profile machining. Here only the software and hardware requirements for cam profile machining are discussed.


1. Selection of machine tools

According to the accuracy requirements of various camshaft parts, a CNC lathe is used to build a processing platform. The machine tool requires stable dimensions, high accuracy, and excellent performance and can be competent for processing camshafts.


2. The choice of the turning tool

The current general turning tool materials are high-speed steel and cemented carbide (diamond turning tools can also be used if cost is not considered). The composition of the two materials is different. The material of cemented carbide is WC+Co+TiC, etc. It is obtained through the powder metallurgy process and is currently the most widely used tool material. The material of high-speed steel is generally C+Cr+W+Mo+v, etc. High-speed steel should be used in situations where it is complex and difficult to form or requires sharpness and high toughness. The red hardness, wear resistance, and heat resistance of cemented carbide are higher than that of tool steel, but cemented carbide has poor toughness and cannot withstand large impact forces.


In addition, to ensure that there will be no interference during machining, the turning tool needs to grind a large auxiliary relief angle during cam turning. The tip of the tool is easily chipped during turning. Therefore, cemented carbide tools should not be used. High-speed steel tools are easy to grind sharp edges, have better toughness, withstand greater impact, and are more suitable for cam turning. But it also has its disadvantage in that it is poor in heat resistance, so it cannot be used for high-speed cutting. Generally, 20-30m/min is selected, and the maximum is not more than 50m/min.


3. Selection of tool angle

There are avoidances on both sides of the cam. The main deflection angle of the turning tool is 75º because the tool nose angle is larger, which can withstand greater cutting force and is beneficial to cutting heat dissipation. Turning processing is rough processing in cam processing. Because the blank material is 45# steel, the reference values of the front and rear angles are selected according to medium carbon steel. The front angle is 25º~30º, the back angle is 6º~8º, and the auxiliary back angle can be determined by drawing. One end of the camshaft datum plane uses the center and positioning sleeve on the hydraulic floating chuck to complete the positioning requirements of the datum, and the other end uses the live spindle structure program-controlled hydraulic tailstock center to complete the positioning requirements. A hydraulic center frame is used as extra support at the pre-machined journal.


4. Choice of tool approach

The available cutting tool feed methods are radial and axial feed from the cam structure form. Suppose the radial feed is used during the camshaft processing due to the cam's special shape. In that case, when cutting to the descending surface of the cam, it is necessary to avoid interference between the tool body and the part, so the back tool surface is ground to increase the back angle. After grinding to increase the rear angle, the tool wedge angle becomes sharp, and the tool rigidity becomes poor, the leading cutting edge that can withstand the cutting force becomes poor and easy to wear. If the axial feed is adopted, the cutting condition of the main cutting edge will be improved. The angle that needs to be sharpened is only the auxiliary relief angle of the tool, and the rake angle and main relief angle will not change during the cutting process. The length of the secondary cutting edge involved in cutting is only the amount of feed per revolution, and the tool force is better than the radial feed, so it is better to use the axial feed method for turning.


5. Determination of cutting parameters

Selecting the appropriate cutting amount is very important for the profile cutting of the camshaft, and the index of the cutting amount is the basis of CNC programming. Only when the cutting amount is selected can the tool path be determined. The cutting amount includes indexes such as back-cutting, cutting speed, and feed rate. Different cutting parameters are suitable for different cutting methods.

The selection method of cutting amount is to give full play to the processing performance of tools and equipment under the premise of ensuring the processing quality of parts and a good tool life cycle to increase productivity and reduce costs as much as possible.


(1) The choice of the amount of knife

Under the premise of fully considering the tool, workpiece, and machine rigidity, as long as it does not affect the processing quality, choose a larger amount of back-grabbing as much as possible. This way, we can improve processing efficiency and reduce the number of passes. For rough machining cam profile, 4mm is generally selected.


(2) Selection of cutting speed

To select the cutting speed of the journal, we can turn the 45 steel material according to the ordinary outer circle, which is between 0.333~0.5m/s.

When turning the cam profile, the tool material limits the cutting speed. The red hardness of high-speed steel tools is poor, and the linear cutting speed is generally between 0.333~0.5m/s, that is, between 20~30m/min.


(3) Selection of feed

The feed rate is also an important parameter of turning processing, which mainly depends on the surface roughness and processing accuracy of the part and is also affected by the part's material. The maximum feed rate is limited by the system's performance, especially the rigidity of the machine tool.

The feed selection generally follows the following principles: When the surface quality and machining accuracy must be high, the smaller feed is generally selected. The fastest feed is selected when the tool returns to the origin or the idle stroke. When the surface processing quality requirements are not high, we can choose a larger feed rate.


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