Mon Jul 04 15:57:27 CST 2022
As with all man-made products, manufacturing cutting insert must first solve the problem of raw materials, that is to determine the composition and formula of the carbide insert material. Most of carbide insert are made of cemented carbide, the main components of which are tungsten carbide (WC) and cobalt (Co). WC is a hard particle in the insert , and Co as a binder can make the insert shape.
The easiest way to change the characteristics of cemented carbide is to change the grain size of the WC particles used. Cemented carbide materials prepared with larger particle size (3-5μm) WC particles have lower hardness and are easier to wear; smaller particle size (<1μm) WC particles can produce higher hardness and better wear resistance , But also brittle hard alloy material. When processing metal materials with very high hardness, the use of fine-grained carbide blades may obtain the most ideal processing results. On the other hand, coarse-grained carbide inserts have better performance in intermittent cutting or other processing that requires higher insert toughness.
Another way to control the characteristics of cemented carbide inserts is to change the ratio of WC to Co content. Compared with WC, Co has much lower hardness, but better toughness. Therefore, reducing the Co content will result in a higher hardness insert. Of course, it again raises the question of overall balance: a higher hardness insert has better wear resistance, but its brittleness is also greater. According to the specific processing type, selecting the appropriate WC grain size and Co content ratio requires relevant scientific knowledge and rich processing experience.
By applying gradient material technology, a compromise between insert strength and toughness can be avoided to a certain extent. This technology that has been commonly used by major global tool manufacturers includes the use of a higher Co content ratio in the outer layer of carbide insert than the inner layer. More specifically, it is to increase the Co content in the outer layer (thickness of 15-25μm) of the carbide insert to provide a "buffer" effect, so that carbide insert can withstand a certain impact without breaking. This allows the carbide insert body to obtain various excellent properties that can be achieved only by using higher-strength cemented carbide components.
Once the technical parameters such as the particle size and composition of the raw material are determined, the actual manufacturing process of the cutting insert can be started. First, put the tungsten powder, carbon powder, and cobalt powder in the proportions into a mill that is about the size of a washing machine, grind the powder to the required particle size, and mix the various materials uniformly. Alcohol and water are added during the milling process to prepare a thick black slurry. Then the slurry is put into a cyclone dryer, and after the liquid in it is evaporated, agglomerated powder is obtained and stored.
In the next preparation process, the prototype of carbide insert can be obtained. First, mix the prepared powder with polyethylene glycol (PEG). PEG acts as a plasticizer to temporarily bond the powder together like a dough. The material is then pressed into the shape of the insert in a press mold. According to different carbide insert pressing methods, a single-axis press can be used for pressing, or a multi-axis press can be used to press the shape of carbide insert from different angles.
After obtaining the pressed blank, it is placed in a large sintering furnace and sintered at high temperature. During the sintering process, PEG is melted and discharged from the blank mixture, and finally the semi-finished carbide insert remains. When the PEG is melted out, the carbide insert shrinks to its final size. This process step requires precise mathematical calculations, because the shrinkage of carbide insert varies according to different material compositions and ratios, and the dimensional tolerance of the finished product is required to be controlled within a few microns.