What to expect for graphite machining?

Posted on Dec 23, 2020

Machining Center

Graphite machining refers to the machining processes for graphite, which requires cutting tools with sharpness and coatings, dry environment, and appropriate machining techniques, so as to ensure the smoothness of the machining processes.

What is graphite machining? 

Graphite machining is the machining process for graphite, a material that is electrically conductive, heat and corrosion-resistant, self-lubricant, and dry-lubricant. 
Despite the extraordinary features that graphite has, due to the special properties of graphite, the processes of machining this material is not common as that of other materials.

To machine graphite, there are some things to consider and to be careful about, in addition to the properties that graphite has, the sharpness, number of flutes, coatings of the cutting tools, and the machining techniques all have something to do with the make or break of graphite machining.

When it comes to machining works, there is no doubt that the main elements should be the workpieces that are made of various materials, the cutting tools that come in different forms in order to accommodate different cuts, and the appropriate machining techniques. Only when these elements are equipped that the required products can be achieved.

Unlike the metals such as steel, aluminum, or other alloys, which own certain properties that make them easy to be machined without difficulty when the above elements are prepared, the machining of graphite should meet higher standards that this material can be properly cut without fracture or dust being made, for example.
 

:: Read more : What is a horizontal machining center?

What is graphite?

Graphite is an allotrope of carbon, or can be regarded as one form of carbon, which is commonly presented as the form of graphite and diamond. No matter what kind of forms that carbon is presented, each of them has its own features that make them being applied with different usage.

Among all forms of the allotrope of carbon, graphite is the one that especially has stable, conductive, soft and brittle, and versatile properties, as what we are going to discuss below.

● stable
One of the most impressive features of graphite is that it is heat and corrosion resistant, which means that it can still be machined in the circumstances when the process produces extremely high heat, and the products that are made of graphite are able to be used without rust for a long time. In other words, graphite is such a stable material that makes either the machining processes and the products that are made of it especially durable when in use.

● conductive
In addition, graphite is one of the materials that is electrically conductive, which means that it is also suitable for the machining works that are driven with electric power, and thus make the range of the applications of this material even wider.

soft and brittle
Due to the microstructure of graphite, it is relatively softer and more brittle than other forms of carbon allotropes or metals. This makes the choice of cutting tools and the machining techniques for graphite machining matter, or the excessive consumption that is made when machining graphite would be beyond the profits for the manufacturers instead.

versatile
With the above impressive features include the stability and conductivity that graphite has, graphite is recognized as a versatile material. Whether the harsh environments of the machining sites or the electrically driven operations, they both make this material versatile in being produced with a variety of products.
 

What is a suitable tool for graphite machining?

Now that we have learned the extraordinary features that graphite has, then the second indispensable element of machining works, the cutting tools, should also be cared about before the works are really done. 
Simply put, there are two parameters to follow when choosing the right cutting tools for graphite, including the sharpness of the blade and the coatings.

sharpness of the blade
This parameter should be in conjunction with the consideration of the cutting techniques because of the properties that graphite has. Since graphite is soft and brittle, if the cutting tool is blunt, it would push on the surfaces of the material instead of cutting it, which makes the material easily fracture and the tool difficult to achieve the required geometry of the product.

Besides, when using a blunt tool with a heavy chip load, the chips that are made when machining graphite would make the tool deflect from the right track and results in the deformation of the product. In contrast, if the blade of the tool is sharp, it doesn’t have to struggle to push the material. Instead, it is only required to cut the material with lighter chip load and lower feed rate, then it can make the products that satisfy the customers.

coatings
As the cutting tools cut through aby material for several times, they would still lose their sharpness. In addition to dress on the cutting tools, there is another method that is capable of protecting the tools from being damage easily even when they get blunt, which is to coat on the tools. Coating is the outer layer of the cutting tools that is additionally added for the purpose of making the tools stronger when performing machining works. The most common coating that is applied for the tools that cut graphite is the CVD (Chemical Vapor Deposition) diamond coating.

There are some other diamond coatings that can be used for strengthening the cutting tools, while the CVD diamond coating is the one that forms the thickest layer out of the tools, which makes the strongest guard around the tools, and allows for longer tool life for performing the machining works.
 

What to consider when machining graphite?

● machining techniques
Graphite machining takes time and effort. As the above introduction has mentioned, in addition to the right cutting tools, the machining of graphite requires a lighter chip load and a smaller feed rate. The chip load and the feed rate are interrelated when it comes to the effects on the products since when the chip load is heavy and the feed rate is high, which means the speed and feed of the cutting tools are both high, there would be a lot of chips being produced and cause the deflection of the tools when cutting. Therefore, to prevent the tools malfunction when cutting graphite, the chip load should remain light and the feed rate below, so that the possibility of the production of chips can be reduced to the lowest.

● interior factors
The interior factors are related to the material, which is graphite. When the environment that graphite is in are humid, it makes the pores of graphite be fed with react with the dust that is produced when the material come in contact with the tool, and create an abrasive slurry, which blocks the way for the cutting tools to cut through the material smoothly. Therefore, before the graphite is machined, it should be remained dry, which keeps the interior of the material less likely to be fed with moisture and stable when being machined.

● exterior factors
As the above paragraphs have said, moisture should be avoided for the graphite material, which indicates that this material has the feature of self-lubrication. On the other hand, the coolant that would be involved in the normal machining works is not recommended for graphite machining, as it would react with the abrasive property of graphite as well.

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