In metal grinding, it is easy to use metal materials containing chromium, nickel, tungsten, molybdenum, titanium and other elements. These materials are difficult to grind, so they are called difficult to grind materials. There are many kinds of hard to grind materials, and three types are common in general processing. Let's talk about the problems of hard to grind materials in detail.
1、 Types of hard to grind materials
The first kind of hard grinding materials have high hardness and toughness, or the hardness is not very high but the toughness is very high, such as commonly used heat-resistant alloys, titanium alloys, stainless steel, high vanadium high-speed steel, etc.
The second kind of hard grinding materials are soft and sticky, such as various non-ferrous metals and pure iron used in processing.
The third kind of hard grinding material is easy to burn and crack during grinding, or the surface roughness of the workpiece is poor.
The measures to solve the above three materials are also different. The second material can be turned with diamond turning tool, and the turning effect is better; For the third kind of material, a suitable grinding wheel can be selected, such as a coarse abrasive wheel with loose structure, a suitable grinding fluid and improved pouring method can achieve better results.
2、 Characteristics of hard to grind materials
At present, the first material is difficult to solve in production. This material has the following characteristics in grinding:
1. Workpiece surface is easy to burn
The alloy steel used in this kind of hard grinding material has high hardness, toughness, large chip deformation, large cutting resistance and high heat generation. At the same time, due to the poor thermal conductivity of this material, a large amount of heat generated in the grinding area cannot be transferred quickly through effective channels, resulting in high temperature in the grinding area, so it is easy to have surface burns.
3.The grinding wheel is easy to be blocked
When grinding this kind of material, the chips are easy to stick on the surface of the grinding wheel, making the grinding wheel lose its cutting ability and difficult to remove from the abrasive particles. The grinding wheel is blocked, the friction between the grinding wheel and the workpiece increases, and the grinding temperature rises sharply, causing workpiece burns.
4 .Workpiece is easy to deform
Grinding these hard grinding materials is easier to deform than other steels. Due to the strong work hardening trend of alloy steel materials, residual stress is easy to occur on the workpiece surface during machining. In the later processing process, the workpiece will be deformed due to the change of stress state.
For example, when grinding stainless steel slender shafts, they become waist drum shaped and distorted after grinding; The sheet workpiece is warped and uneven; It is easy to produce ellipses when grinding large diameter workpieces.
5.Chill phenomenon
Due to the severe extrusion and friction in grinding, the work hardening trend of alloy steel materials is enhanced. Therefore, the cold hardening phenomenon of the ground surface layer is more serious. It will also cause annealing on the surface of the workpiece.
In addition to the above grinding defects, the grinding of difficult grinding materials also has the problems of low metal removal rate, low grinding ratio and low durability of grinding wheels. Therefore, in the process of machining difficult grinding materials, it is necessary to understand the difficult grinding materials and solve the problems pertinently to ensure the grinding quality.