In metal cutting, hole machining occupies a certain proportion, and various hole machining tools are widely used.
Generally, there are two categories of hole machining knives:
One is the cutting tool for machining holes from solid materials, such as fried dough twist drill, flat drill, center drill and deep hole drill;
The other is the tool that reprocesses the existing hole, such as reamer, reamer, spot facer and boring tool.
As the most commonly used tool in hole machining, drill bit is widely used in mechanical manufacturing, especially for the machining of holes of parts such as cooling devices, tube sheets of power generation equipment and steam generators.
The drill bit has a cutting edge at the top part and a groove for discharging chips at the tool body part.
When cutting, the closer it is to the outer circle, the higher the cutting speed of the drill bit is, and the cutting speed decreases towards the center, and the cutting speed of the rotation center of the drill bit is zero.
（1） Classification of drill bits
According to the shape, material, structure and function of the workpiece, the drill can be divided into many kinds, such as high-speed steel drill (fried dough twist drill, group drill, flat drill), integral cemented carbide drill, indexable shallow hole drill, deep hole drill, nesting drill and replaceable drill.
According to the needs of hole processing and the continuous development of tool manufacturing technology.
Bits of different materials and structures have their own fields of application.
1. By tool material
According to the classification of tool materials, drills can be divided into high-speed steel drills and cemented carbide drills.
High speed steel drill, made of high-speed steel, has sharp cutting edge, high strength and low price, but it has poor thermal hardness and low service life, which is suitable for low-speed cutting.
As shown in Fig. 5-1, it is a typical fried dough twist drill;
Cemented carbide bits, made of cemented carbide, are used more and more, and have a variety of structural forms.
One of the integral cemented carbide bits is shown in Fig. 5-2.
Fig. 5-1 high speed steel drill bit
Fig. 5-2 integral cemented carbide bit
2. By tool structure
According to the structure of cutting tools, drills can be divided into integral drills, welding drills and assembly drills.
Among them, integral drills are divided into integral high-speed steel drills, group drills and integral cemented carbide drills;
The assembled bit can be divided into indexable blade bit, replaceable bit, deep hole bit, composite bit and nesting bit.
3. By tool function
According to the function of cutters, drills can be divided into ordinary drills, deep hole drills, reaming drills, spot facers, etc.
（2） Selection of drill bit
The selection process of drill bit is as follows:
(1) Determine the hole diameter and depth.
Firstly, the aperture size and depth of the workpiece are determined according to the machining condition.
(2) Select the bit type.
Select a type of drill used for rough machining or finishing holes, and check whether this type is suitable for workpiece material and processing conditions.
(3) Select the handle type.
Various drill bits have different installation forms, and the type of tool handle suitable for the processing machine tool is selected.
(4) Select the blade.
If the indexable blade bit is selected, the blade material, geometric angle and the chip breaking groove shape of the blade suitable for processing must be selected.
(5) Select the cutting amount.
According to the size and structure of the selected drill bit, the cutting parameters are reasonably selected.