Basic Methods to Choose Twist Drill Bit
Let’s look at the manufacturing process of twist drill bit first —— How roboticized! It contains material selection, material cutting, friction welding, chamfering, quenching, Cylindrical grinding, Chisel Ground, Nitriding treatment and finished product inspection.
There are three basic factors for selecting drill bits: Material, Coating and Geometric Features.
Materials can be roughly divided into three types: high-speed steel, high-performance high-speed steel(containing cobalt ) and whole solid carbide alloy.
High-Speed Steel (HSS):
Since 1910, high-speed steel has been used as cutting tools for more than a century. Currently, it is the most widely used and cheapest cutting tool material. High-speed steel drill bits can be used not only in hand electric drills but also in more stable environments such as drilling machines. Another reason that makes high-speed steel products last for a long time is that high-speed steel tools can be repeatedly ground. Because of their low price, they are not only used to grind for drill bits but also widely used in turning tools.
High-Performance High-Speed Steel(containing cobalt ):
High-Performance high-speed steel has better hardness and red hardness than high-speed steel. The improvement of hardness also increases its wear resistance, but at the same time, it also sacrifices some of its toughness. The same as high-speed steel is that they can improve the using times by grinding.
Whole Solid Carbide Alloy:
Solid carbide alloy is a kind of metal-based composite material. For this material, tungsten carbide is used as the matrix, and some other materials are used as a binder, then by a series of complicated processes such as hot isostatic pressing and sintering. Compared with high-speed steel, hardness, red hardness and wear resistance are greatly improved. However, the cost of carbide tools is also much higher than that of high-speed steel. Solid carbide alloy has more advantages in tool life and processing speed than the previous tool material. Professional grinding tools are needed for regrinding.
According to the application, the coating can be roughly divided into the following 5 types:
Uncoated cutting tools are the cheapest and are usually used for soft material such as aluminum alloy and low carbon steel.
Black Oxide Coating(Nitriding Treatment):
Oxidized coatings can provide better lubricity than uncoated ones, and are better in terms of oxidation resistance and heat resistance. Not only this, the Oxidized coating can increase the service life by more than 50%.
Titanium is the most common coating material and is not suitable for materials with high processing hardness or high processing temperature.
TiCN is developed from TiN and has higher temperature resistance and wear resistance. Its color is usually purple or blue.
TiALN coating is more resistant to high temperature than all the above coatings, so it can be used in a higher temperature environment, such as high-temperature alloy. It is also applicable to the process of steel and stainless steel, but due to the element aluminum, the chemical reaction will occur when aluminum is processed, so it could not be used on material containing aluminum.
Generally speaking, cobalt drill with TiCN coating or Tin coating is a more economical solution.
- Geometric Features
Geometric features can be divided into the following 3 parts:
The ration of length to diameter is smaller, rigidity is better. Drill bit with just suitable flute length for chip removal and as short as possible flute length can improve the rigidity during processing, thus prolonging the service life of tools. If the flute is not long enough, it is likely to damage drill bit.
The angle of Drill Point
The 118 degrees point angle is probably the most common in processing, and is usually used for soft metals such as low carbon steel and aluminum. Usually there is no self-centering function for such design, which means that the centering hole must be machined first. While the 135 degrees point angle usually has the function of self-centering, because there is no need to process the centering hole, which will make it no longer necessary to drill the centering hole separately, thus saving a lot of time.
For most materials, a helix angle of 30 is a very good choice. However, for the environment that requires better chip removal and higher cutting edge strength, a smaller helix angle is better. For materials difficult to process, such as stainless steel, a larger helix angle can be selected to transmit torque.
With the above information, you will have the basic knowledge for the twist drill bit. Hope it is helpful for you.
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