What are the selection principles of cutting parameters?
1. General principles
The cutting amount should be selected according to the material, accuracy requirements and surface roughness requirements of the workpiece, as well as the power and stiffness of the lifted material and machine tool. At the same time, when selecting the cutting parameters, it is generally necessary to first select the cutting depth, then select the feed rate, and finally determine the cutting speed.
2. Selection of cutting depth
During rough machining, after setting aside the fine machining allowance, the rough machining allowance shall be cut off with as few times as possible when the rigidity of the machine tool tool workpiece system allows. If it cannot be cut at one time, it should be processed according to the method of unequal allowance from more to less. In order to avoid damaging the cutting tool, when cutting hard surface materials such as castings with hard skin or cutting stainless steel, the cutting depth should be deepened, and it is best to exceed the thickness of hard skin or cold hard layer.
During finishing, in order to gradually improve the machining accuracy and surface finish, the method of gradually reducing the cutting depth should be adopted. If the finishing tool is good, it can also get high precision and better surface quality under the condition of stealing a large allowance at one time.
3. Selection of feed rate
Generally, the following factors should be considered when selecting the feed rate of rough machining:
(1) For the rigidity of machine tool tool fixture system, if the system rigidity is good, the feed rate can be increased, otherwise, the feed rate should be smaller.
(2) Whether the chip is curled or broken, the feed rate can be larger. If it is curled, the feed rate should be smaller.
(3) Intermittent cutting or continuous cutting. Due to the impact of intermittent cutting, considering the strength of the tool, the feed rate should be smaller, and the feed rate of continuous cutting can be appropriately larger.
When selecting the finishing feed, the requirements of workpiece surface roughness should be mainly considered. Generally, the smaller the roughness value, the smaller the feed. However, sometimes the feed rate is too small, and the surface roughness value will increase. This is because the cutting thickness of the tool's arc edge is variable. At the auxiliary cutting edge, the cutting thickness is much smaller than the arc radius of the edge, so that some metal is not cut off and is squeezed behind the auxiliary cutting edge of the tool to wear into grooves. After cutting for a period of time, several grooves can be set, and the distance between them is equal to the feed rate. Therefore, Increase the roughness value of the added surface of the workpiece.
4. Selection of cutting speed
The selection of cutting speed should be mainly based on the material of workpiece and tool, so as to achieve a certain tool durability on the basis of the selected cutting depth and feed rate.
When selecting the cutting speed for finish machining, the cutting speed area should try to avoid the place where the chip buildup exists. When intermittent cutting is carried out, appropriately reducing the cutting speed can effectively reduce the impact and thermal stress. In the case of prone to vibration, in order to improve the stability of cutting, we should pay attention to the cutting speed to avoid the critical speed of self-excited vibration.
Cutting speed, feed rate and cutting depth are important parameters in machining, which have a far-reaching impact on machining. It is suggested that the majority of workers engaged in machining should choose these three parameters before machining to ensure the quality and accuracy of finished workpieces.