There are three basic conditions for drilling and selecting drill bits: material, coating and geometric characteristics.
How to choose the material of the drill bit
The materials can be roughly divided into three types: high-speed steel, cobalt-containing high-speed steel and solid cemented carbide
High Speed Steel (HSS):
Since 1910, high-speed steel has been used as a cutting tool for more than a century. It is currently the most widely used and cheapest cutting tool material. High-speed steel drill bits can be used on electric drills or A more stable environment such as drilling machines. Another reason for the endurance of high-speed steel may be that high-speed steel tools can be re-ground. Due to their low price, they are not only used to grind into drill bits, but also widely used in turning tools.
Cobalt-containing high-speed steel (HSSE):
Cobalt-containing high-speed steel has better hardness and red hardness than high-speed steel, and the increase in hardness also improves its wear resistance, but at the same time, it also sacrifices part of its toughness. The same as high-speed steel: They can all be reground to increase the number of uses.
Carbide (CARBIDE):
Cemented carbide is a metal-based composite material. Among them, tungsten carbide is used as the matrix, and some materials of other materials are used as binders to be manufactured by a series of complicated processes such as sintering by hot isostatic pressing. Compared with high-speed steel in terms of hardness, red hardness, wear resistance, etc., it has a huge improvement. However, the cost of cemented carbide tools is also much more expensive than that of high-speed steel. Cemented carbide has more advantages than previous tool materials in terms of tool life and processing speed. In the repeated grinding of tools, professional grinding tools are required.
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How to choose drill bit coating
The coating can be roughly divided into the following 5 types according to the scope of use
Without coating:
Uncoated tools are the cheapest, and are usually used to process some softer materials such as aluminum alloy and low carbon steel.
Black oxide coating:
Oxidation coating can provide better lubricity than uncoated tools, and is also better in terms of oxidation and heat resistance, and can increase the service life by more than 50%.
Titanium nitride coating:
Titanium nitride is the most common coating material and is not suitable for materials with high processing hardness and high processing temperature.
Titanium carbonitride coating:
Titanium carbonitride is developed from titanium nitride and has higher high temperature resistance and wear resistance, usually purple or blue. It is used to process cast iron workpieces in the Haas workshop.
Aluminum Nitride Titanium Coating:
Aluminum titanium nitride is more resistant to high temperatures than all the above coatings, so it can be used in higher cutting environments. For example, processing high-temperature alloys. The same applies to the processing of steel and stainless steel, but because it contains aluminum elements, chemical reactions will occur when processing aluminum, so avoid processing aluminum-containing materials.
Generally speaking, a cobalt-containing diamond plus a titanium carbonitride coating or a titanium nitride coating is a more economical solution.
Geometric characteristics of the drill bit
Geometric features can be divided into the following 3 parts
length
The ratio of length to diameter is called multiple diameter, and the smaller the multiple diameter, the better the rigidity. Choosing a drill with the cutting edge length just for chip removal and the overhang length as short as possible can increase the rigidity during machining, thereby increasing the service life of the tool. Insufficient blade length is likely to damage the drill.
Point angle
The 118° drill point angle is probably the most common in machining, and is usually used for machining soft metals such as mild steel and aluminum. This kind of angle design usually does not have the self-centering function, which means that it is inevitable to machine the centering hole first. The 135° drill tip angle usually has a self-centering function. Since there is no need to process a centering hole, it will no longer be a necessary process to drill a centering hole separately, thereby saving a lot of time.
Helix angle
The 30° helix angle is a very good choice for most materials. But for environments that require better chip removal and higher cutting edge strength, a drill with a smaller helix angle can be selected. For materials that are difficult to process, such as stainless steel, a design with a larger helix angle can be selected to transmit torque.
