As the most common tool in hole processing, drills are widely used in mechanical manufacturing, especially for the processing of cooling devices, tube sheets of power generation equipment, steam generators and other parts. The application is particularly extensive and important.

 

 

1

Features of drilling

 

 

The drill bit usually has two main cutting edges, and during machining, the drill bit performs cutting while rotating. The rake angle of the drill is getting larger and larger from the central axis to the outer edge. The cutting speed of the drill is higher the closer to the outer circle, and the cutting speed is gradually reduced toward the center, and the cutting speed of the rotation center of the drill is zero. The chisel edge of the drill is located near the central axis of rotation, the secondary rake angle of the chisel edge is large, there is no chip space, and the cutting speed is low, which will produce a large axial resistance. If the chisel edge is ground to A-type or C-type in DIN1414, and the cutting edge near the center axis has a positive rake angle, the cutting resistance can be reduced and the cutting performance can be significantly improved.

 

According to the shape, material, structure and function of the workpiece, drill bits can be divided into many types, such as high-speed steel drill bits (twist drill, group drill, flat drill), solid carbide drill, indexable shallow hole drill, deep hole Drills, nesting drills and interchangeable bit drills, etc.

 

2

Chip breaking and chip removal

 

 

The cutting of the drill is carried out in a hole with a narrow space, and the chips must be discharged through the groove of the drill, so the shape of the chips has a great influence on the cutting performance of the drill. Common chip shapes include flake chips, tubular chips, needle chips, conical spiral chips, band chips, fan chips, powder chips and so on.

 

 

 

 

The key to drilling process-chip control

 

When the chip shape is inappropriate, the following problems will occur:

①Fine chips block the cutting edge groove, affect the drilling accuracy, reduce the life of the drill bit, and even break the drill bit (such as powdery chips, fan-shaped chips, etc.);

②Long chips wrap around the drill bit, hinder the operation, cause the drill bit to break or prevent the cutting fluid from entering the hole (such as spiral chips, ribbon chips, etc.).

 

How to solve the problem of inappropriate chip shape:

① Methods such as increasing feed rate, intermittent feed, grinding chisel edge, and installing chip breaker can be used separately or in combination to improve the effect of chip breaking and chip removal, and eliminate the problems caused by chips.

②Professional chip breaking drill can be used to make holes. For example: adding a designed chip breaker in the groove of the drill bit will break the chips into more easily cleaned chips. Debris is smoothly removed along the groove and will not block in the groove. Therefore, the new chipbreaker drill has a much smoother cutting effect than traditional drills.

 

At the same time, the short broken iron chips make it easier for the coolant to flow to the drill tip, which further improves the heat dissipation effect and cutting performance during the machining process. And because the newly added chipbreaker penetrates the entire groove of the drill bit, it can still maintain its shape and function after repeated grinding. In addition to the above functional improvements, it is worth mentioning that this design strengthens the rigidity of the drill body and significantly increases the number of holes drilled before a single grinding.

 

3

Drilling accuracy

 

 

The accuracy of the hole is mainly composed of factors such as aperture size, position accuracy, coaxiality, roundness, surface roughness and hole burrs.

 

Factors that affect the accuracy of the hole being machined during drilling:

① The clamping accuracy and cutting conditions of the drill, such as tool holder, cutting speed, feed rate, cutting fluid, etc.;

② The size and shape of the drill bit, such as the length of the drill bit, the shape of the blade, the shape of the drill core, etc.;

③The shape of the workpiece, such as the shape of the side of the orifice, the shape of the orifice, the thickness, and the clamping state.