What are carbide cutting tools made of?

The tungsten carbide cutting tools are made of different ratios of tungsten carbide and bonding metals (cobalt, nickel, etc.), and the initial form of raw materials is powder.

 

How carbide cutting tools are made?

 

Cemented carbide cutting tools are currently the mainstream cutting tools in the cutting tool market. Its quality is determined by three points: the carbide substrate, the structural shape of the blade and the coating. To make a good tool, every link is closely related, and the lack of any link will affect the final product. On the whole, it is roughly divided into five steps: powder preparation, extrusion moulding, sintering, surface treatment, and testing.

The matrix of cemented carbide is composed of two parts, One is the hardened material, which is what we often call tungsten carbide, titanium carbide, etc., and they are all in powder form at first. Tungsten carbide uses tungsten and carbon as raw materials. Dry-mix tungsten powder with an average particle size of 3~5μm and carbon black with a ball mill. After fully mixing, put it into a graphite plate, and then heat it in a graphite resistance furnace to 1400~1700°C. Tungsten carbide is formed under a high-temperature reaction.

Tungsten carbide is an extremely hard and brittle material with a melting point above 2000°C, some even exceeding 4000°C. Its existence determines the high hardness and wear resistance of the alloy.

The other part of the cemented carbide matrix is the binder metal, usually an iron group metal, and cobalt and nickel are commonly used in processing.

In the case of cobalt, tungsten carbide is mixed with cobalt, which is critical to the properties of cemented carbide. The more cobalt, the better the toughness of cemented carbide, and vice versa, the harder and more wear-resistant.

In the grinding chamber, various materials are ground to the desired particle size in an environment with the addition of ethanol, water and organic binders. This step is called wet grinding in the industry, and it is a grinding process in which organic or inorganic solvents are added as grinding aids during the grinding process.

For most materials, dry grinding can only be ground to the micron level, because below 20 μm, due to the electrostatic attraction between molecules, the agglomeration of materials is serious, and it is difficult to be ground finer. Instead, the wet grinding method is used for grinding. Under the impact of grinding aids, the material can be ground to a finer level, reaching several microns or even nanometers.

Depending on the raw material, the process of wet grinding takes about 8 to 55 hours, and the raw material after wet grinding will become a uniform suspension.

The liquid mixture is then pumped to a spray dryer, where the ethanol and water are evaporated under the action of hot nitrogen, and the dried powder is in the form of uniform granules.

After the mixed slurry is dried, the sample will be sent for quality inspection. At this time, the powder consists of a series of small balls with a diameter of 20-200 microns.

After passing quality inspection, the mixed powder is sent to the punching machine where the blade is made. Put the stamping die into the machine, control the punch and die of the stamping machine to press, and get the basic shape and size of the tool.

Depending on the blade type, the pressure required to press the blade can reach up to 12 tons. After pressing, each blade is weighed to ensure acceptable quality and precision of the blade.

In fact, the freshly pressed blades are very fragile and need to be hardened in the sintering furnace. The blade is heat-treated at 1500 degrees Celsius for 13 hours so that the molten cobalt and tungsten carbide particles are bonded together. The concept of 1500 degrees Celsius is similar to that steel pipes will melt as quickly as chocolate.

After sintering, the polyethene glycol in the blade will disappear, the volume will shrink by about 50%, and the blade also has a certain hardness.

To give the blade a certain degree of precision, the blade is honed again, grinding the top and bottom of the blade.

The hard blade after sintering will be very hard, so in the honing process, industrial diamond grinding wheels are used for fine grinding. This step has extremely high requirements for the grinding process. For example, Sweden uses the most advanced 6-axis grinding plate grinding process to meet its extremely strict tolerance requirements.

After grinding, the blades are cleaned and painted, i.e. coated, before quality inspection.

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