Generally, when machining high-precision parts, the slow wire cutting machine is widely used.
1、 Definition of drilling
Chinese name: drilling
English name: drilling
Other names: drilling
Definition: the method of machining holes on the workpiece when the drilling tool makes relative motion and axial feed motion with the workpiece.
Drilling is one of the most basic drilling methods. Drilling is often carried out on drilling machines and lathes, as well as on boring machines and milling machines. Commonly used drilling machines include bench type drilling machine, vertical drilling machine and radial drilling machine.
2、 Features of drilling:
Compared with turning excircle, it is much more difficult for drill bit to work locally on the machined surface, which causes some special problems. For example, the rigidity and strength of the drill bit, chip holding and chip removal, guiding and cooling lubrication, etc. can be summarized as follows:
1. The bit is easy to deflect
Deflection: refers to the enlargement of the hole diameter, out of round hole or deflection of the hole axis caused by the bending of the drill bit during processing, as shown in Figure 2-6.
Cause: Due to inaccurate centering of the cross edge of the drill bit, poor rigidity and guiding effect of the drill bit, the drill bit is easy to offset and bend when cutting.
2. Chip removal is difficult
The chip in the hole is relatively wide, and the size of the chip holding groove is limited. When it flows out, it will rub the surface violently with the hole wall, and the hole is forced to roll into a spiral shape. It can cause greater friction between the chip and the hole wall, extrude, roughen and scratch the machined surface, and reduce the surface quality. The chip may even be blocked in the chip holding groove, the drill bit may be stuck or broken, and the tool may wear quickly.
In order to improve chip removal conditions, a chip separation groove can be grinded on the drill bit to divide wide chips into narrow strips for chip removal. When drilling deep holes, appropriate deep hole drills shall be used for processing.
3. High cutting temperature
As drilling is a semi closed type of cutting, there is a large negative rake angle near the drill core on the main cutting edge and on the horizontal edge. The heat generated during drilling is absorbed by the workpiece. A large number of high-temperature chips cannot be discharged in time. It is difficult to inject cutting fluid into the cutting area, and the cutting heat is not easy to spread. The friction between chip, tool and workpiece is very large, so the cutting temperature is high, the tool wear is large, and the improvement of drilling amount and productivity is limited.
4. Low precision
The drilling accuracy is low and the surface is rough. Generally, the machining accuracy is below IT10, the surface roughness Ra value is greater than 12.5mm, and the production efficiency is low. Therefore, drilling is mainly used for rough machining or pre machining.
Fig.: Structure of vertical drilling machine and radial drilling machine
3、 Application of drilling
In single piece and small batch production, small holes (D<13 mm) on small and medium-sized workpieces are usually processed by bench type drilling machines, and large holes (D<50 mm) are usually processed by vertical drilling machines;
The holes on large and medium-sized workpieces shall be processed by radial drilling machine, and the holes on rotary workpieces shall be processed by lathe.
In batch and mass production, drill jigs, multi spindle drills or modular machine tools are widely used to process holes in order to ensure machining accuracy, improve production efficiency and reduce machining costs.
For small and medium diameter holes (D<50mm) with high accuracy and small roughness, after drilling, it is often necessary to use expanding and reaming for semi finishing and finishing.