Tool selection for processing high hardness iron castings

High hardness cast iron is a brittle and hard material with high surface hardness. Turning and milling are the most commonly used methods to process this kind of castings. In order to cut high-hardness cast iron, the tool must have high hardness, good wear resistance, good impact resistance, stable chemical stability and good thermal conductivity. At present, coated carbide tools, ceramic tools and cubic boron nitride tools are used to process high-hardness iron castings.

(1) cemented carbide tool: When processing high-hardness iron castings, because the hardness of high-hardness iron castings is generally above HRC45, especially when processing large pieces, the cutting time is long, the cemented carbide tool is not wearable, and the tool changing frequency is high, which affects the processing efficiency and surface roughness, so cemented carbide is generally suitable for processing small batches of small workpieces, such as YG8 and other brands.

(2) Coated cemented carbide tool: The surface of cemented carbide blade is coated with wear-resistant thin layers such as TiC, TiN, HfN and Al2O3 to form surface-coated cemented carbide. Because the surface is coated with a layer of wear-resistant material, the tool is more wear-resistant and suitable for small batch processing. However, when processing high-hardness iron castings in large quantities, due to the long cutting time, the tool wear is as serious as that of cemented carbide tools, which leads to high tool changing frequency, which affects the processing efficiency and increases the tool cost.

(3) Ceramic tool: The hardness of ceramic tool is higher than that of cemented carbide, and it has good wear resistance, but it is brittle, with low transverse fracture strength and weak ability to bear impact load. Therefore, when the cutting hardness is below HRC55 and the feed rate is small, ceramic tools are a better choice. However, when machining large cast iron with high hardness, due to casting defects such as sand inclusion and air holes on the surface of the blank, it is easy to collapse when using ceramic tools.

(4) Cubic boron nitride cutter BN-K 1 brand: Cubic boron nitride cutter has higher hardness and better wear resistance, but it has the same shortcomings and fragility as ceramic cutter, but BN-K 1 Cubic boron nitride cutter belongs to nonmetallic adhesive. The cubic boron nitride tool specially developed for high-hardness iron castings not only increases the toughness of the tool, but also has good wear resistance and impact resistance, which can realize high-speed cutting. The hardness of cubic boron nitride tool BN-K 1 is 4 times that of cemented carbide tool and 2 times that of ceramic tool. The cutting parameters of BN-K 1 tool for cutting high-hardness iron castings are 3-5 times higher than those of cemented carbide tools.

This paper briefly introduces the situation of cubic boron nitride cutter BN-K 1 for processing high hardness iron castings.

Example of machining high chromium cast iron with BN-K 1 brand cubic boron nitride cutter

High chromium cast iron is a kind of high-alloy white cast iron with high hardness and strength, which has wear resistance and corrosion resistance. As a wear-resistant casting, high chromium cast iron has hardness above hrc45 and tensile strength of 650-850mpa without any heat treatment. However, this material is hard and brittle, and the cutting state is extremely unstable, so it is difficult to cut.

Taking the processing of high chromium cast iron industrial pump parts as an example;

Processing material: high chromium white cast iron Cr26.

Processing parts: industrial pump impeller, pump body, etc.

Hardness of material: 60HRC

Tool brand: BN-K 1

Cutting parameters: ap=3.5mm, Fr=0. 1mm/r, Vc=75m/min.

Cutting mode: dry cutting.

The comparison between BN-K 1 and ceramic blades is as follows: When the cutting speed of BN-K 1 brand is twice as high as that of ceramic blades, and the feed rate is more than 40% of that of ceramic blades, the single-edge life of BN-K 1 is more than 7 times that of ceramic blades. It not only improves the processing efficiency, but also reduces the processing cost.