Difficulties and Solutions of Stainless Steel Parts Processing
The continuous emergence of new products puts forward higher requirements for the material of parts. Sometimes the required materials must meet the special requirements of high hardness, high wear resistance, high toughness, etc., resulting in a batch of difficult to machine materials, which puts forward higher requirements for processing technology. Compared with high-quality carbon structural steel, stainless steel materials contain Cr, Ni, Nb, Mo and other alloy elements. The increase of these alloy elements not only improves the corrosion resistance of the steel, but also has a certain impact on the machinability of stainless steel.
This paper takes stainless steel and other difficult materials as the object, analyzes the processing difficulties of stainless steel in combination with the actual problems encountered in processing, and puts forward effective solutions.
Combined with the practical problems encountered in machining, this paper analyzes the difficulties in stainless steel machining, and puts forward effective solutions.
Analysis of Difficulties in Stainless Steel Cutting
In actual processing, cutting stainless steel is often accompanied by the occurrence of knife breaking and sticking. Due to the large plastic deformation of stainless steel in the cutting process, the chips produced are not easy to break and stick, resulting in serious work hardening in the cutting process. Each process will produce a hardened layer for the next cut. After layers of accumulation, stainless steel enters the cutting process. With the increasing hardness of the medium, the required cutting force is also increasing.
The generation of work hardening layer and the increase of cutting force will inevitably lead to the increase of friction between the tool and the workpiece, and the increase of cutting temperature.
In addition, the thermal conductivity of stainless steel is small and the heat dissipation condition is poor. A large amount of cutting heat is concentrated between the tool and the workpiece, which makes the machined surface deteriorate and seriously affects the quality of the machined surface. Moreover, the increase of cutting temperature will aggravate tool wear, which will cause crescent pits on the tool rake face and notches on the cutting edge, affecting the surface quality of the workpiece, reducing work efficiency and increasing production costs.
Methods of Improving the Processing Quality of Stainless Steel Parts
It can be seen from the above that the processing of stainless steel is difficult. When cutting, it is easy to produce a "hardened layer", which is easy to break the tool, and the generated chips are not easy to break, causing adhesion to the tool, which will aggravate the wear of the tool. In view of these cutting characteristics of stainless steel, combined with the actual production, we try to improve the processing quality of stainless steel from three aspects of tool materials, cutting parameters and cooling methods.
1 Selection of tool material
Choosing the right tool is the basis of machining high-quality parts. The tool is too poor to process qualified parts; If a good tool is selected, although it can meet the surface quality requirements of parts, it is easy to cause waste and increase production costs. In combination with the characteristics of poor heat dissipation condition, work hardening layer and easy sticking knife during stainless steel cutting, the selected tool material should meet the requirements of good heat resistance, high wear resistance and low affinity with stainless steel.
2 High speed steel
High speed steel is a high alloy tool steel with W, Mo, Cr, V, Go and other elements added. It has good processing performance, good strength and toughness, and strong impact and vibration resistance. Under the condition of high heat generated by high-speed cutting (about 500 ℃), it can still maintain high hardness (HRC is still above 60). High speed steel has good red hardness, and is suitable for making milling cutters, thorns and other milling cutters. It can meet the requirements of stainless steel cutting. Hardened layer, poor heat dissipation and other cutting environments.
W18Cr4V is the most typical high-speed steel tool. Since its birth in 1906, it has been widely manufactured into various tools to meet the needs of cutting. However, with the continuous improvement of mechanical properties of various machining materials, W18Cr4V tool can no longer meet the machining requirements of difficult to machine materials. High performance cobalt high speed steel should be produced from time to time. Compared with ordinary high speed steel, cobalt high speed steel has better wear resistance, red hardness and service reliability. Suitable for high removal rate machining and intermittent cutting. Common brands such as W12Cr4V5Co5.
2 Carbide steel
Cemented carbide is a kind of powder metallurgy, which is made of high hardness refractory metal carbide (WC, TiC) micron powder as the main component, cobalt, nickel, molybdenum as the binder, sintered in vacuum furnace or hydrogen reduction furnace. Products. Cemented carbide has good strength and toughness, heat resistance, wear resistance, corrosion resistance, high hardness and a series of excellent properties. It is basically unchanged at 500 ℃, and still has high hardness at 1000 ℃. It is suitable for cutting difficult to machine materials such as stainless steel and heat-resistant steel. Common cemented carbides are mainly divided into three categories: YG type (tungsten cobalt cemented carbides), YT type (tungsten titanium cobalt type), YW type (tungsten titanium tantalum (niobium) type). These three kinds of alloys have different compositions and applications. YG hardened uranium has good toughness and thermal conductivity. Large front corner can be selected, which is suitable for cutting stainless steel.
Selection of cutting geometric parameters of stainless steel tools
1 Front corner:
Combined with the characteristics of stainless steel, such as high strength, good toughness, and hard to cut the chip during cutting, on the premise of ensuring that the tool has sufficient strength, a large rake angle should be selected to reduce the plastic deformation of the processing object, reduce the cutting temperature and cutting force, and reduce the generation of hardened layer.
2 Caster angle ao:
Increasing the back angle will reduce the friction between the machining surface and the back face, but the heat dissipation capacity and strength of the cutting edge will also be reduced. The size of the back angle depends on the cutting thickness. When the cutting thickness is large, the smaller back angle should be selected.
Primary deflection angle kr, secondary deflection angle k'r:
Reducing the main deflection angle kr can increase the working length of the cutting edge, which is conducive to heat dissipation, but it will increase the radial force during cutting, which is easy to generate vibration. The value of kr is usually 50 °~90 °. If the rigidity of the machine tool is insufficient, it can be increased appropriately. The secondary deflection angle is usually k'r=9 °~15.
3 Blade inclination λ s：
In order to increase the strength of the tool tip, the inclination of the blade is generally taken λ s=7°~_ - 3°。
Processing of stainless steel parts
Selection of cutting fluid and cooling mode
The machinability of stainless steel is poor, and there are high requirements for the cooling, lubrication, penetration, cleaning and other properties of cutting fluid. Common cutting fluids are as follows:
1 Cutting fluid:
A more common cooling method, with better cooling, cleaning and lubrication performance, is commonly used for stainless steel blank cars.
2 Vulcanized oil:
High melting point sulfide can be formed on the metal surface during cutting, which is not easy to be damaged under high temperature, has good lubrication effect, and has a certain cooling effect. It is generally used for drilling, reaming and tapping.
3 Mineral oil such as engine oil and spindle oil:
It has good lubricating property, but poor cooling property and permeability, and is suitable for external precision turning.
During the cutting process, the cutting fluid nozzle should be aligned with the cutting area, or it is better to use high-pressure cooling, spray cooling and other cooling methods.
To sum up, although stainless steel has the disadvantages of poor machinability, severe work hardening, large cutting force, low thermal conductivity, easy adhesion, easy wear of tools, etc., as long as the appropriate processing method is found, the appropriate tool is used, the cutting amount of the cutting method is selected, the appropriate coolant is selected, and the problem of difficult to machine materials such as stainless steel is solved through careful thinking in the work.
