Invar alloy-basic information

definition
Invar (Invar, also known as Invar, changed its name to a brand name), is a nickel-iron alloy with a composition of 36% nickel, 63.8% iron, and 0.2% carbon. Its coefficient of thermal expansion is extremely low and can Maintain a fixed length over a wide temperature range.
Common name

Invar alloy, also known as “invariant steel”, is commonly known as Invar machining in Chinese. It is an iron-nickel alloy and a special steel with 36% nickel. Because of its very small expansion coefficient, it is suitable for measuring components.

Invar alloy-processing technology

The alloy material contains nickel content as high as (31.5%,-37%). Although nickel can increase the strength, plasticity, and toughness of the material, the thermal conductivity is reduced. Although the hardness of the alloy is not high, the toughness is high, and it is soft and sticky during cutting, which significantly reduces the cutting performance. Therefore, the processing performance is poor, and it is a difficult-to-cut metal material. It has the following characteristics:

  • (1) The cutting force is large. Because the metallographic structure of the alloy in the as-cast state is austenite, the tensile strength and hardness of the material are not very high, but the toughness is good. The plastic deformation is large during cutting, the lattice distortion is high, the section shrinkage is also high, the work hardening is serious, the strength is obviously improved, and the cutting resistance increases.
  • (2) The cutting temperature is high. The material has high thermal strength and large friction coefficient, consumes large cutting deformation work and friction work during cutting, and generates a large amount of heat energy. The thermal conductivity of the material is low, and a large amount of cutting heat accumulates in the cutting zone, resulting in a high cutting temperature.
  • (3) The tool wears out quickly. Due to the characteristics of the alloy material, the large amount of heat generated during cutting is not easily taken away by the chips, and is concentrated on the tool, causing severe wear of the tool, and sometimes even plastic deformation, chipping, chipping, and peeling of the tool edge. At the same time, the material is soft, viscous and plastic, which increases the friction between the chips and the front edge of the tool during cutting, which intensifies the wear of the tool, which not only reduces the durability of the tool, but also reduces the invar machining accuracy.

By selecting appropriate tool materials and tool geometric parameters, using the correct machining technology and cooling lubricant, the cutting performance is improved and the machining accuracy of the mold is guaranteed. Tungsten carbide cemented carbide with good heat resistance, high wear resistance, low oxidation resistance and low adhesion is selected as the cutting tool material. When the mold is turned, the tool adopts a large rake angle, the cutting edge is sharp, and the cutting is brisk. The front of the tool is provided with a chip breaker and the front and rear corners have a certain roughness to make the chips and the tool difficult to stick. Cutting process parameters include cutting speed, depth of cut and feed. The cutting speed should not be too high to reduce the cutting temperature. Generally, the cutting depth should not be too small to avoid leaving the work hardened layer. The feed amount should not be too large to avoid too heavy cutting load, but it should not be too small. This will cause the tool to work in the chilled layer formed after the last invar machining, accelerate the wear of the tool, and generally control the feed. When finishing the mold surface, in order to ensure the surface finish, the cutting speed is selected as 1.8/S, and the feed rate is 0.05mm/r. In order to reduce the large amount of cutting heat generated during cutting, sufficient cooling and lubrication must be carried out. The cooling lubricant is mixed with kerosene and mechanical oil.

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