How to choose the right drill bit for metal processing?

Drill bit selection process


• Determination of hole diameter and depth


First, determine the aperture size and aperture depth of the workpiece according to the processing conditions.


• Select drill type


Choose a type of drill for roughing or finishing holes, and check whether the type is suitable for the workpiece material and machining conditions.


• Select the handle type


Various drill bits have different installation forms, choose the tool holder type that is suitable for the processing machine tool.


• Selection of blades


If an indexable insert drill is selected, the insert material, geometric angle and insert chip breaker shape suitable for processing must be selected.


• Select the amount of cutting


According to the size and structure of the selected drill bit, the cutting parameters are reasonably selected.


metal processing, drill bit


1. How to choose the material of the drill bit?


The material of the drill bit can be roughly divided into three types: high-speed steel, cobalt-containing high-speed steel and solid carbide.

1) High-speed steel (HSS) drill bit


Since 1910, high-speed steel has been used as a cutting tool for more than a century. It is currently the most widely used and cheapest material for cutting tools. High-speed steel drills can be used in hand drills or in A more stable environment such as a drilling machine. Another reason why high-speed steel lasts for a long time may be because high-speed steel cutting tools can be reground repeatedly. Due to its low price, it is not only used to grind into drill bits but also widely used in turning tools.


2) Cobalt-containing high-speed steel (HSSE) drill bits


Cobalt-containing high-speed steel has better hardness and redness than high-speed steel. The increase in hardness also improves its wear resistance, but at the same time sacrifices part of its toughness. The same as high-speed steel: they can be used to increase the number of times through grinding.


3) Carbide (CARBIDE) drill bit


Cemented carbide is a metal-based composite material. Among them, tungsten carbide is used as the matrix, and some other materials are used as binders to sinter by hot isostatic pressing and a series of complicated processes. Compared with high-speed steel in terms of hardness, red hardness, and wear resistance, it has been greatly improved, but the cost of cemented carbide tools is also much more expensive than high-speed steel. Cemented carbide has more advantages than previous tool materials in terms of tool life and processing speed. In the repeated grinding of tools, professional grinding tools are required.


2 How to choose a drill bit coating


Coatings can be broadly classified into the following five types according to the scope of use.


1) Uncoated drill


Uncoated tools are the cheapest and are usually used for machining softer materials such as aluminium alloys and mild steel.


2) Black oxide-coated drill bits


Oxide coatings can provide better lubricity than uncoated tools, are also better in oxidation and heat resistance, and can increase service life by more than 50%.


3) Titanium nitride-coated drill bit


Titanium nitride is the most common coating material, and it is not suitable for materials with relatively high hardness and high processing temperature.


4) Titanium carbonitride coated drill bit


Titanium carbonitride is developed from titanium nitride, and has higher high temperature resistance and wear resistance, usually purple or blue. Used in the Haas workshop to machine workpieces made of cast iron.


5) Titanium Aluminum Nitride Coated Drill Bits


Titanium aluminium nitride is more resistant to high temperatures than all the above coatings, so it can be used in higher cutting environments. For example, processing superalloys. It is also applicable to the processing of steel and stainless steel, but because it contains aluminium elements, chemical reactions will occur when processing aluminium, so avoid processing materials containing aluminium.

In general, cobalt-containing diamonds with titanium carbonitride coatings or titanium nitride coatings are a more economical solution.


drill bit for metal processing, milling cutter


3. Geometric characteristics of the drill bit


Geometric features can be divided into the following 3 parts


1) The length of the drill bit


The ratio of the length to the diameter is called the multiple diameter, and the smaller the multiple diameter, the better the rigidity. Choosing a drill with a blade length that is just right for chip removal and a short overhang length can improve the rigidity during processing, thereby increasing the service life of the tool. Insufficient blade length is likely to damage the drill bit.


2) Drill point angle


The 118° point angle is probably the most common in machining and is usually used for machining soft metals such as mild steel and aluminium. The design of this angle is usually not self-centring, which means that it is inevitable to machine the centring hole first. The 135° drill point angle usually has a self-centering function. Since there is no need to process the centring hole, this will make it no longer necessary to drill the centring hole separately, thus saving a lot of time.


3) Helix angle

A helix angle of 30° is a very good choice for most materials. However, for environments that require better chip evacuation and stronger cutting edges, drills with a smaller helix angle can be selected. For difficult-to-machine materials such as stainless steel, a design with a larger helix angle can be selected to transmit torque.

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