Drilling process

Characteristics of drilling
The drill usually has two main cutting edges, which are cut while the drill is turning. The rake Angle of the bit is larger and larger from the central axis to the outer edge. The closer it is to the outer circle, the higher the cutting speed of the bit is. The cutting speed decreases to the center, and the cutting speed of the rotary center of the bit is zero. The cross edge of the drill is located near the axis of the rotary center, and the side rake Angle of the cross edge is large, there is no chip tolerance space, and the cutting speed is low, so it will produce a large axial resistance. The cutting resistance can be reduced and the cutting performance can be significantly improved if the edge of the transverse edge is polished into type A or C in DIN1414 and the cutting edge near the central axis is A positive rake Angle.

According to the workpiece shape, material, structure, function, etc., drill can be divided into many types, such as HSS drill (twist drill, group drill, flat drill), solid carbide drill, indexable shallow hole drill, deep hole drill, nesting drill and adjustable head drill.


Chip breaking and chip removal
The cutting of the bit is carried out in a narrow hole, and the chip must be discharged through the edge groove of the bit, so the chip shape has a great influence on the cutting performance of the bit. Common chip shape chip, tubular chip, needle chip, conical spiral chip, ribbon chip, fan chip, powder chip and so on.
When the chip shape is not right, the following problems will occur:

① Fine chips block edge groove, affect drilling accuracy, reduce drill life, and even make drill broken (such as powdery chips, fan chips, etc.);
② Long chips wrap around the drill, hindering the operation, causing damage to the drill or blocking the cutting fluid into the hole (such as spiral chips, ribbon chips, etc.).

How to solve the problem of improper chip shape:
① Can be used separately or jointly to increase the feed, intermittent feed, grinding edge, chip breaker and other methods to improve chip breaking and removal effect, eliminate the problems caused by chip cutting.
The professional chip breaker drill can be used for drilling. For example, adding a chip breaker blade to the groove of the bit will break the chip into more easily removed debris. Debris is removed smoothly along the trench without clogging in the trench. Thus, the new chip breaker can achieve much smoother cutting results than traditional bits.

At the same time, the short scrap iron makes the coolant flow to the drill tip more easily, which further improves the heat dissipation effect and cutting performance in the process of machining. And because the new chip breaker goes through the entire groove of the bit, it retains its shape and function after repeated grinding. In addition to these functional improvements, it is worth mentioning that the design enhances the rigidity of the drill body and significantly increases the number of holes drilled prior to a single trim.


Drilling accuracy
The precision of the hole is mainly composed of aperture size, position accuracy, coaxiality, roundness, surface roughness and orifice burr.
Factors affecting the precision of drilled holes during drilling:

(1) Bit clamping accuracy and cutting conditions, such as cutter clip, cutting speed, feed, cutting fluid, etc.;
② Bit size and shape, such as bit length, edge shape, core shape, etc.;
(3) workpiece shape, such as orifice side shape, orifice shape, thickness, clamping state, etc.

Post time: Apr-12-2022

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