How to classify the drills?

Today I'd like to talk about the classification of drill bits. What kinds of drill bits are commonly used in mechanical processing? How are they classified and how should they be selected?

1. Classification by Material

01 High-Speed Steel (HSS) Drills

The most common ones are Cobalt-Containing HSS/ Vanadium-Containing HSS/ Powder Metallurgy HSS. By adding cobalt/ vanadium alloy elements, the toughness/ wear resistance of the material is mainly improved. For powder metallurgy high-speed steel, the material particle size is finer and more uniform, and the stability and wear resistance are further improved.

02 Carbide Drills

Most carbide drill bits will choose a grade with 10% Co binder + 0.8μm WC grain. This combination takes into account both toughness and wear resistance. However, in some special occasions, such as small micro drilling, you can choose a grade with a higher Co content to improve the drill's resistance to bending. For carbide drill bits for processing cast iron, you can choose a grade with a larger particle size to increase the drill's impact resistance (strength).

03 Super-hard material PCD Drills

In the processing of non-ferrous metals and composite materials, PCD drill bits can significantly enhance the tool life and processing parameters. Moreover, there are a wide variety of PCD grades available.

2. Classification by Internal cold drills and External cold drills

Internally cooled drills can greatly improve the life of the drill, cutting parameters and chip removal performance. The above three materials can all be made into internally cooled structures.

3. Classification by solid drills and replaceable drill bit

In addition to integrated drill bits, there are many replaceable drill bits, such as U drills and replaceable heads. Under the same diameter, integrated drill bits have higher strength (larger processing feed) and higher processing accuracy. For example, the drilling accuracy of integral alloy drill bits can reach IT8-IT7, the drilling accuracy of replaceable heads is generally IT9-IT8, and the drilling accuracy of U drills is IT11-IT9.

4. Classification by flute number

Generally, there are 2 flutes, 3  flutes, and 4- flutes. 2 flutes is the most common. As the number of flute of the drill increases, the chip space becomes smaller and chip removal becomes difficult. Generally, multi-flute drills (3 flutes/4 flutes) are mainly used for shallow hole processing (within 5 times the depth); multi-edge drills, while ensuring good chip removal, have higher drill strength than 2 flutes drills, so the cutting feed (f) can be larger.

5. Classification by length-to-diameter ratio (L:D)

Shallow hole drill and deep hole drill. Based on whether a guiding drill (centering drill) is required, approximately 8 times the diameter of the drill can be defined as a shallow hole drill, and anything above 8 times is considered a deep hole drill. The maximum processing depth that various common drills can achieve is roughly as follows:

Drill Type Capabilities:

U-Drill: 2-6xD

Exchangeable-head: 15xD

Solid carbide: 60xD

Gun drill: 300xD

6. Classification by helix angle

Divided into straight groove drill and spiral groove drill. Spiral groove drill has better chip removal performance. Straight groove drill (helix angle 0°) is generally used for shallower holes (except for special gun drills). At the production level, straight groove drill has easier size control. Some straight groove drill designs are used on some multi-step compound drills.

7. Classification by point angle

The drill with a 180° apex is called a flat-bottom drill. The application scenarios of flat-bottom drills are increasing. They can be used for drilling and reaming. In non-planar holes (inclined surfaces/curved surfaces) and intersecting holes, their processing effect is better than that of ordinary drill bits, and the edge burrs will also be better. However, due to the apex angle, the control of iron filings is not as good as that of conventional drill bits. Therefore, flat-bottom drills are mainly used for processing shallow (within 5 times) holes.