For a machining center, a tool is a consumable tool. During machining, it will produce breakage, wear and chipping. The wear of the tool has a huge impact on the production, and if it is serious, it will directly lead to the shutdown of a production line. The impact this brings to the enterprise can be imagined. Tool wear is inevitable, but there are also controllable reasons such as unscientific and non-standard operation and improper maintenance. What are the root causes of tool wear? Let’s find out together today.
There are often some tiny particles with extremely high hardness in the processed material, which can draw grooves on the surface of the tool, which is abrasive wear. Abrasive wear exists under various cutting speed conditions, which is the main cause of low-speed tool wear. In addition, the lower the hardness of carbide inserts, the more serious the abrasive wear.
The main method to reduce this kind of wear is to reduce the surface roughness of the cutting part of the tool and use the corresponding cutting fluid with good lubricity.
Cold welding wear
During cutting, there is a lot of pressure and strong friction between the workpiece, cutting and front and rear rake faces, so cold welding occurs. Due to the relative movement between the friction surfaces, the cold weld will crack and be taken away by one side, resulting in cold weld wear. Cold welding wear is generally more serious at moderately low cutting speeds.
Under the normal working speed of the high-speed steel tool and the low working speed of the cemented carbide tool, the conditions for cold welding can be met. Therefore, the proportion of cold welding wear is larger at this time. After increasing the cutting speed, the cold welding wear of cemented carbide tools is reduced.
Diffusion wear occurs at high temperatures. During cutting, under the action of high temperature, the molecular activity energy between the contact surfaces is large, resulting in the mutual replacement of alloy elements. For example, a high-speed tool forms a white layer containing high Cr and C on the rake face, which is continuously taken away by chips. When the cutting steel temperature is between 800 and 1000 degrees, Co, C, and W in the cemented carbide diffuse into the chips, and Fe in the steel diffuses into the cutting surface to form composite carbides with low hardness and brittleness, which accelerates tool wear. Diffusion wear is also present in diamond and cubic boron nitride.
In cemented carbide, adding TaC, NbC and VC can increase the diffusion resistance temperature of cemented carbide and reduce diffusion wear.
When the temperature rises, the surface of the tool oxidizes to produce softer oxides that are wiped off by the chips and the wear formed is called oxidation wear. Oxidative wear is related to the adhesion strength of the oxide film. The lower the adhesion strength, the faster the wear; otherwise, the wear can be reduced. Generally, air does not easily enter the chip contact area, and oxidative wear is most likely to be formed at the working boundary of the main and auxiliary cutting edges.