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Difficulties and Solutions of Stainless Steel Parts Processing

The continuous emergence of new products has put forward higher requirements on the material of parts. Sometimes the required materials must meet special requirements such as high hardness, high wear resistance, and high toughness, resulting in a batch of difficult-to-machine materials and higher requirements for processing technology. Compared with high-quality carbon structural steel, stainless steel contains alloying elements such as Cr, Ni, Nb, and Mo. The addition of these alloying elements not only improves the corrosion resistance of the steel, but also has a certain influence on the machinability of the stainless steel.

This paper takes stainless steel and other difficult-to-machine materials as the object, combined with the actual problems encountered in processing, analyzes the processing difficulties of stainless steel, and proposes practical and effective solutions.

Combining the actual problems encountered in machining, this paper analyzes the difficulties of stainless steel machining, and proposes practical and effective solutions.

Analysis of Difficulties in Stainless Steel Cutting

In actual processing, cutting stainless steel is often accompanied by the occurrence of broken knives and sticking knives. Due to the large plastic deformation of stainless steel during the cutting process, the generated chips are not easy to break and bond easily, resulting in severe work hardening during the cutting process. Each operation creates a hardened layer for the next cut. After layer by layer, stainless steel enters the cutting process. As the hardness in the medium increases, so does the required cutting force.

The generation of the work-hardened layer and the increase in cutting force will inevitably lead to an increase in the friction between the tool and the workpiece, and the cutting temperature will also increase.

In addition, the thermal conductivity of stainless steel is small, and the heat dissipation conditions are poor. A large amount of cutting heat is concentrated between the tool and the workpiece, which deteriorates the machined surface and seriously affects the quality of the machined surface. Moreover, the increase of cutting temperature will aggravate the wear of the tool, causing crescent craters on the rake face of the tool and gaps on the cutting edge, affecting the surface quality of the workpiece, reducing work efficiency and increasing production costs.

Ways to improve quality

It can be seen from the above that the processing of stainless steel is difficult, and it is easy to produce a "hardened layer" during cutting, which is easy to break the tool, and the generated chips are not easy to break, causing sticking 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 start from three aspects of tool material, cutting parameters and cooling method, and try to improve the quality of stainless steel processing.

1 Selection of tool material

Choosing the right tool is the basis for 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 the parts, it is easy to cause waste and increase production costs. Combined with the characteristics of poor heat dissipation, work-hardened layer, and easy-to-stick knives during stainless steel cutting, the selected tool materials should meet the characteristics 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 elements such as W, Mo, Cr, V, and Go added. It has good process performance, good strength and toughness, and strong shock and vibration resistance. In the case of high heat (about 500 ℃) generated by high-speed cutting, it can still maintain a 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, and 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 operations. However, with the continuous improvement of the mechanical properties of various processing materials, W18Cr4V tools can no longer meet the processing requirements of difficult-to-machine materials. High-performance cobalt high-speed steel emerges from time to time. Compared with ordinary high-speed steel, cobalt high-speed steel has better wear resistance, red hardness and reliability. Suitable for high removal rate machining and interrupted cutting machining, commonly used grades such as W12Cr4V5Co5.

3 Carbide steel

Cemented carbide is a powder metallurgy sintered in a vacuum furnace or a hydrogen reduction furnace with high hardness refractory metal carbide (WC, TiC) micron powder as the main component, cobalt, nickel and molybdenum as the binder. product. Cemented carbide has a series of excellent properties such as good strength and toughness, heat resistance, wear resistance, corrosion resistance and high hardness. It remains basically unchanged at a temperature of 500 °C, and still has a high hardness at 1000 °C, which 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 carbide), YT type (tungsten titanium cobalt type), YW type (tungsten titanium tantalum (niobium) type), and the compositions of these three alloys are different. , the use is also very different. Among them, YG hardened uranium has good toughness and thermal conductivity. Optional larger rake angle, suitable for cutting stainless steel.

Selection of Cutting Geometry Parameters for Stainless Steel Tools

1 Front corner:

Combining the characteristics of stainless steel with high strength, good toughness, and the chips are not easily cut off during cutting, a larger rake angle should be selected on the premise of ensuring sufficient strength of the tool, which can reduce the plastic deformation of the processed object and reduce the cutting temperature and cutting force. Reduce the generation of hardened layers.

2 Caster angle ao:

Increasing the clearance angle will reduce the friction between the machined surface and the flank, but the heat dissipation capacity and strength of the cutting edge will also be reduced. The size of the relief angle depends on the thickness of the cut. When the cutting thickness is large, a smaller clearance angle should be selected.

Main declination angle kr, secondary declination angle k'r:

Decreasing the main declination 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, and it is easy to generate vibration. The value of kr is often taken as 50° to 90°. If the rigidity of the machine tool is insufficient, it can be increased appropriately. The secondary declination angle is usually taken as k'r=9°~15.

3 Blade inclination λs:

In order to increase the strength of the tool tip, generally take the blade inclination angle λs=7°~_ -3°.

Selection of cutting fluid and cooling method

The machinability of stainless steel is poor, and it has higher requirements for the cooling, lubrication, penetration, cleaning and other properties of the cutting fluid. common cut

There are the following types of cutting fluid:

1 Cutting fluid:

A more common cooling method with better cooling, cleaning and lubricating properties, commonly used in stainless steel blank cars.

2 Vulcanized oil:

When cutting, high melting point sulfide can be formed on the metal surface, which is not easy to be damaged at high temperature, has good lubrication effect, and has a certain cooling effect. It is generally used for drilling, reaming and tapping.

3 Mineral oils such as motor oil, spindle oil:

Has good lubricating performance, but poor cooling and permeability, suitable for external precision turning.

During the cutting process, the cutting fluid nozzle should be aimed at the cutting area, or it is better to use high pressure cooling, spray cooling and other cooling methods.

In summary, although stainless steel has the disadvantages of poor machinability, serious work hardening, large cutting force, low thermal conductivity, easy sticking, and easy to wear tools, but as long as you find a suitable processing method, use a suitable tool, and the cutting amount of the cutting method. , Choose the appropriate coolant, think hard at work, and solve the problems of difficult-to-machine materials such as stainless steel.