The suspension system is floorboard of the connection device between the frame and wheel axle or all the force, its function is to transfer function between the wheel and the frame of force and moment, and buffer by the uneven road surface to the impact of the frame or body, and the attenuation of the resulting vibration, in order to make sure the car was going smoothly.
In general, the automobile suspension system can be divided into the independent suspension and independent suspension, the independent suspension of the wheels on both ends of a whole axle, when the wheel side beat the other side wheels also beat accordingly, make whole body vibration or inclination;Independent suspension axle is divided into two sections, each wheel under the spiral spring independent by the installation of the frame, when the side wheels to beat the other side of the wheel is not affected, can the wheels on both sides of the independence movement, improve the stability and comfort of a car.As people demand for the car ride comfort and manipulation stability becomes more and more high, the independent suspension system already was washed out gradually
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In the trial production of parts, we carried out the turning test of 3Cr13 stainless steel according to the process of turning ordinary carbon steel. As a result, the tool wear was very serious, the productivity was extremely low, and the surface quality of the parts could not meet the requirements.
Comparing the mechanical properties of 3Cr13 steel with carbon steel such as 40 steel and 45 steel, 3Cr13 steel is higher in strength than 40 steel and 45 steel. It is a medium-carbon martensitic stainless steel with high strength and good plasticity. Due to severe work hardening during cutting, high cutting resistance and high cutting temperature, the tool wear is severe, the number of sharpening is increased, the downtime and machine adjustment time are increased, and the productivity is reduced. At the same time, it is easy to stick the knife, which causes the built-up edge, which causes the change of the workpiece size and affects the surface roughness. Moreover, the chip is not easy to be curled and broken, which is easy to damage the processed surface of the workpiece and affect the quality of the part. Therefore, the process of cutting 45 steel cannot be used to cut 3Cr13, and the processing method on the general lathe cannot be transferred to the automatic lathe. Since the automatic lathe is less loaded, it is required to achieve the required size and surface roughness of the machined surface in a single pass to ensure high productivity.
2 Main technical measures
1) Change the hardness of the material by heat treatment
The different hardness of martensitic stainless steel after heat treatment has a great influence on the turning process. Table 1 shows the turning condition of 3Cr13 steel of different hardness after heat treatment with a turning tool of YW2 material. It can be seen that although the annealed 0.10.10.1 state martensitic stainless steel has low hardness, the turning performance is poor, because the material has large plasticity and toughness, the structure is uneven, the adhesion and the fusion property are strong, and the cutting process is easy to produce a knife-shaped tumor. It is not easy to obtain a good surface quality. The 3Cr13 material with hardness below HRC30 after quenching and tempering has better turning workability and easy to achieve better surface quality. For parts made of materials with hardness above HRC30, the surface quality is good, but the tool is easy to wear. Therefore, when the conditions permit, the material can be quenched and tempered after the material enters the factory, and the hardness reaches HRC25~HRC30, and then the cutting process is performed.
2) Selection of tool materials
In the automatic lathe for turning stainless steel, the commonly used hard alloy tool materials are: YG6, YG8, YT15, YT30, YW1, YW2 and other materials.
Commonly used high speed steel knives have: W18Cr4V, W6M05Cr4V2AL and other materials. Under the same cutting parameters, we have turned the comparison test of the tools of several materials. It can be seen from Table 2 that the external turning tool with TiC-TiCN-TiN composite coated blade has higher durability and better cutting speed. High, the surface quality of the workpiece is good and the productivity is high. However, there is no cutting blade of this material. Through the comparison test of Table 2, the cutting performance of YW2 cemented carbide is also good. We use the blade of YW2 material as the cutting blade.
Table 2 Different tool materials cutting comparison test tool material tool geometry angle cutting amount tool durability
Min machining surface roughness μm
Rake angle γ back angle α main angle Kr edge angle λ ν
m/min s
Mm/r
YG8 15° 8° 90° -10 45～55 0.1 72～82 Ra3.2
YT14 15° 8° 90° -10 45～55 0.1 80～95 Ra3.2
YW2 15° 8° 90° -10 45～55 0.1 90～110 Ra3.2
Tic-TiCN-TiN
Composite coated blade 12° 8° 90° -4 45～55 0.1 128～185 Ra6.3 (for cutting)
Ra～Ra1.6
3) Selection of the geometric angle and structure of the tool
For good tool materials, choosing a reasonable geometric angle is especially important.
1) rake angle γ: It is more suitable to use 10°～20° for the front angle of the general turning martensitic stainless steel tool.
2) Back angle α: Generally, it is suitable to take 5°～8°, but the maximum is 10°.
3) Blade inclination angle λ: Generally, λ is -10° to 30°.
4) The lead angle Kr should be selected according to the shape of the workpiece, the machining position and the loading condition.
5) The surface roughness of the cutting edge should be no more than Ra0.4~Ra0.2.
In terms of structure, our external turning tool adopts an external oblique arc breaking groove. The chip has a large curl radius at the tip of the blade, and the chip has a small curl radius at the outer edge. The chip will be turned to the surface to be processed and broken. it is good. For the cutting knife, we control the secondary declination within 1o, which can improve the chip removal conditions and extend the life of the tool.
1) Reasonable choice of cutting amount [Page]
According to the cutting theory, the cutting speed v has the greatest influence on the cutting temperature and tool durability. The cutting amount is the second, and the cutting amount t is the smallest. On the automatic lathe, the surface of the workpiece is processed once, and the amount of the knife is t. The size of the part and the size of the material blank are generally 0 to 3 mm; the cutting speed of difficult-to-machine materials is often much lower than that of ordinary steel.
The amount of tool s has less influence on the durability of the tool than the cutting speed, but it will affect the chip breaking and chip removal, straining and scratching the surface of the workpiece, affecting the surface quality of the processing. Generally, when the depth of the knife is large, the amount of the tool should be reduced. Small, and the amount of cutting off is smaller than the outer circle. When the surface roughness of the machined surface is not high, s is selected from 0.1mm/r to 0.2mm/r.
In short, for difficult materials, low cutting speed and medium pass are generally used.
2) Select the appropriate cooling lubricant
Cooling lubricants for turning stainless steel should have the following characteristics:
a. High cooling performance, guaranteed to take away a lot of cutting heat.
b. The stainless steel has high toughness, and it is easy to produce knife tumor during cutting, which deteriorates the processing surface. This requires high lubricating performance of the cooling lubricating fluid and can provide better lubrication.
c. Good permeability, good chipping, diffusion and internal lubrication for chips that are not easily cut off.
The commonly used cooling lubricating fluid for processing stainless steel is as follows: sulfurized oil, vulcanized soybean oil, kerosene oleic acid or vegetable oil, carbon tetrachloride plus mineral oil, emulsion, and the like.
Considering that sulfur has a certain corrosive effect on the machine tool, vegetable oil (such as soybean oil) is easy to attach to the machine tool for crusting and deterioration. We chose a mixture of carbon tetrachloride and engine oil in a weight ratio of 1:9. Among them, carbon tetraoxide has good permeability and the lubricating oil has good lubricity. Tests have shown that this cooling lubricant is suitable for semi-finishing and finishing of stainless steel parts with low surface roughness requirements, and is especially suitable for the machining of martensitic stainless steel parts.
3 Conclusion
Due to a series of measures, our processing of 3Cr13 stainless steel material is completely normal. The number of sharpenings is only 1/3 of that of the trial production, which improves the production efficiency and the quality of the parts fully meets the design requirements.
Difficulties and countermeasures of automatic lathe turning 3Cr13 stainless steel
1 Difficulties and causes in the cutting process