Drilling

Definition of Drilling

Chinese name: Drilling

English name: drilling

Other names: Drilling

Definition: The method of machining holes on a workpiece by relative motion and axial feed motion between the drilling tool and the workpiece.

Drilling is the most basic method of hole machining. Drilling is often done on drilling machines and lathes, as well as on boring and milling machines. The commonly used drilling machines include desktop drilling machines, vertical drilling machines, and radial drilling machines.

Compared to turning the outer circle, drilling is much more difficult when the working area of the drill bit is on the machined surface, which causes some special problems. For example, the stiffness and strength of drill bits, chip capacity and removal, guidance and cooling, lubrication, and sliding, etc., their characteristics can be summarized as follows:

1. The drill bit is prone to deviation

Deviation: refers to the enlargement of the hole diameter, out of roundness of the hole, or deviation of the hole axis caused by the bending of the drill bit during processing. Due to inaccurate centering of the drill bit's horizontal edge, poor rigidity and guidance of the drill bit, the drill bit is prone to deviation and bending during cutting.

2. Difficulty in chip removal

The chips drilled are relatively wide, and the size of the chip holding groove is limited. When flowing out, there is severe surface friction with the hole wall, and the hole is forced to roll into a spiral shape. Causing significant friction between chips and hole walls, squeezing, roughening, and scratching the machined surface, reducing surface quality. Even chips may block in the chip holding groove, jamming or breaking the drill bit, resulting in rapid tool wear.

In order to improve the chip removal conditions, a chip groove can be ground on the drill bit to divide the wide chips into narrow strips, which is conducive to chip removal. When drilling deep holes, suitable deep hole drills should be used for processing.

3. High cutting temperature.

Due to drilling being a semi enclosed cutting process, there is a large negative rake angle near the drill core and on the transverse edge of the main cutting edge. The heat generated during drilling is absorbed by the workpiece, and a large amount of high-temperature chips cannot be discharged in time. Cutting fluid is difficult to inject into the cutting area, and cutting heat is not easily dissipated. The friction between chips, cutting tools, and workpieces is high, resulting in higher cutting temperatures and greater tool wear, which limits the improvement of drilling volume and productivity.

4. Low accuracy

The accuracy of drilling is low, the surface is rough, and the general machining accuracy is below IT10. The surface roughness Ra value is greater than 12.5mm, and the production efficiency is also low. Therefore, drilling is mainly used for rough machining or pre machining processes.