1 The Definition of difficult To Grind Material

2 Features of difficult To Grind Material

2.1 Large grinding force.

 2.2 High grinding temperature.

 2.3 Serious work hardening

2.4 Large abrasives wear

2.5 Low grinding efficiency

3 Types of difficult-to-grind material

3.1Materials with high brittleness, toughness, and ductility

3.2.High hardness materials

3.3. Materials with high chemical activity

3.4 Materials with high strength at high temperature

1 The Definition of difficult To Grind Material

With the development of science and technology, a large number of high strength, high hardness, and high ductility materials have been used in machine parts, especially some multi-component, high content and high activity alloy elements (such as Ni, Cr, V, Mo, Co, Al, Ti, etc.). The grind ability of these new materials is poor, the grinding rate is low, and the processing quality is not easy to guarantee. These materials are called difficult-to-grind materials.

2 Features of difficult To Grind Material

The main features of this kind of material in grinding will be shown in the following aspects.

2.1 Large grinding force.

The reason for the large grinding force is high hardness, high strength, good plasticity, good toughness, high grinding deformation resistance for material.

 2.2 High grinding temperature.

The reason for high grinding temperature is that more deformation work is consumed during grinding, and most of them are converted into heat. Secondly, some materials have a small thermal conductivity, and the cutting heat accumulates in the cutting area, and it is not easy to emit.

2.3 Serious work hardening

With the large plasticity and high toughness of the material, it causes the large plastic deformation under the action of grinding force. And makes the lattice distorted and causes work hardening.

2.4 Large abrasives wear

There are several reasons for abrasive wear.

2.4.1Large grinding force and high grinding temperature make the probability of abrasive grain breakage much. It is easy to oxidative for abrasives, and diffusion wear.

2.4.2Dispersed hard particles and cementite will have a strong anti-grinding effect on the abrasive tool.

2.4.3The material has large plasticity, and the affinity between the material and the abrasive tool make bond wear and diffusion wear.

2.4.4Work hardening causes the boundary to wear easily.

2.4.5 With high plasticity and elasticity of the material, it increases the friction between the abrasive tools, the chips, and machined surface, and aggravates the abrasive wear.

2.5 Low grinding efficiency

The grinding wheel will be quickly passivated or blocked in the grinding process, so the durability is low. The total grinding amount is low, and the metal removal rate is low, and the grinding ratio is small in the durability cycle.

3 Types of difficult-to-grind material

There are many kinds of difficult-to-grind materials, which can be divided into the following types according to their physical, chemical and mechanical properties.

3.1. Materials with high brittleness, toughness, and ductility

This kind of material is brittle and has high hardness, and they are cracked easily under the action of grinding force and grinding heat when grinding, such as ceramic, optical glass, gemstones, agate, and etc. Austenitic stainless steel and some die steels have high

Toughness and strength, and the debris block the grinding wheel easily, and the wheel wear is large.

Copper and aluminium alloy and other non-ferrous metals have large ductility. Abrasive debris adheres to the surface of the fused alumina easily, increasing grinding resistance, causing the abrasive grains crushed and drop off. When the adhesion is serious, the abrasive grains will lose the cutting and grinding ability, and the durability of grinding wheel will be reduced sharply, and the workpiece will not easy to meet the requirements of precision and roughness.

3.2.High hardness materials

There are lots of hard spots materials dispersed in the matrix with high hardness or low hardness. The hard spot of these materials usually is close to or more than that of ordinary abrasives. For example, microhardness of tungsten carbide(WC) is 2400kg/mm², microhardness of vanadium carbide(VC) is 3200kg/mm², and their microhardness is more than the microhardness of fused alumina of 2000-2200kg/mm². Cemented carbide, steel-bonded cemented carbide, high vanadium high-speed steel and etc. are also high hardness materials.

3.3 Materials with high chemical activity

Under the action of grinding heat, the oxide film is formed on the material surface by oxidation because of high activity of some chemical elements in the material itself, when grinding. Its hardness is similar to the abrasive, which causes the grinding difficult.

Some have an intense chemical affinity with abrasives, which adhere to abrasives easily, resulting in adhesion wear of abrasive grain edge. When the adhesion is serious, the grinding wheel will be passivated quickly, and the high temperature of grinding spots will occur, and burns and crack the surface of the workpiece.

There are chemical reactions on the surface of some abrasive grains, which change the chemical composition of the abrasive surface and causes the chemical wear of abrasive grains. Titanium alloy is material with high chemical activity.

3.4 Materials with high strength at high temperature

Although the hardness of this kind of material is not very high at room temperature, it still has rather high strength at high grinding temperature. Thus it causes plastic damage to abrasive grains easily, and the grinding wheels have serious wear. When grinding such material, the grinding wheels are blocked easily and have low durability. Nickel-based or cobalt-based heat resistance alloy and iron-nickel-based heat-resistant alloy are high strength at high-temperature materials.

There are grinding wheels and sanding abrasive belts for grinding. Grinding wheels are divided into ordinary abrasive grinding wheels, diamond grinding wheels and CBN grinding wheels. Sanding abrasive belts are divided into ordinary abrasive belts, diamond abrasive belts, and CBN sanding belts.

 In future articles, we will provide some solutions for several difficult-to-grind materials. To be continued!