In machining, milling and turning tools are core tools that directly affect efficiency, cost and quality. In the face of many choices, how to accurately select the type is a key skill.

1. identify the processing object - know yourself and know the enemy, a hundred battles are not dangerous

Before choosing a tool, the first question is always: "What material do I want to process?" Different material properties determine the direction of all subsequent choices.

Steel parts (class P): The most common materials to machine, ranging from mild steel to high hardness mould steel. Good toughness and impact resistance of the tool is required.

Stainless steel (M): High toughness, poor thermal conductivity, easy work hardening. Sharp cutting edges, good chipbreaking properties and higher wear resistance are required.

Cast iron (category K): usually produces abrasive chips and high wear on the tool edge. Tools need to be wear-resistant and able to withstand some impact.

Non-ferrous metals (N): e.g. aluminium, copper, aluminium alloys. Soft material, easy to stick to the knife. Need sharp cutting edge, large chipformer and design to prevent chipformer.

High-temperature alloys/titanium alloys (S): High strength, very poor thermal conductivity, and severe work hardening. They are difficult to machine and require specialised high-performance tools and machining strategies.

Non-metallic materials: such as composites and plastics. Require special edge designs and materials to prevent delamination or overheating.

Remember the material classification codes (P/M/K/N/S), which are critical when selecting coatings and materials.

II. Tool Material Selection - The “Inner Workings” of the Tool

Tool material is to determine the basis of its cutting performance, mainly divided into the following categories:

high-speed steel (HSS)

Characteristics: good toughness, cheap, can manufacture complex shape of the tool (such as drills, taps).

Suitable for: low-speed cutting, tools with complex shapes, intermittent machining or uneven materials. It is the first choice for introductory and special tools.

2. Carbide (Tungsten Steel)

Characteristics: Mainstream choice for modern machining. High hardness and good wear resistance, but less toughness than HSS. Wear resistance and toughness are balanced by varying grain size and cobalt content.

Suitable for: semi-finishing to finishing of the vast majority of materials, especially high speed cutting. They are the absolute workhorse of milling and turning inserts.

3. Metal Ceramic (Cermet)

Characteristics: between ceramics and carbide, wear resistance is better than carbide, but the toughness is slightly worse.

Suitable for: steel and stainless steel finishing and ultra-finishing, good surface finish.

4. ceramic (Ceramic)

Features: high hardness, high heat resistance (can be cut at extremely high temperatures), but brittle, afraid of impact.

Application: high-speed machining of cast iron and high-temperature alloys, mainly for finishing and semi-finishing.

cubic boron nitride (CBN)

Characteristics: Hardness second only to diamond, high thermal stability and wear resistance.

Application: Machining of high hardness cast iron (e.g. brake discs) and hardened steel (hardness HRC45 and above).

6. Diamond (PCD)

Characteristics: Diamond (PCD) is currently the hardest substance, excellent wear resistance, but afraid of high temperatures and iron elements.

Application: Highly efficient machining of non-ferrous metals (e.g. aluminium, copper) and non-metallic materials (e.g. carbon fibre, glass fibre), very long life.

Summary: For most machining scenarios, carbide is the default and most versatile choice.

III. Coating technology - the “ultimate armour” for cutting tools

Coatings can greatly enhance the performance of carbide tools by coating the surface of the tool with an ultra-hard, heat-resistant film of a few microns, which does the following:

Increase hardness and wear resistance

Reduces the coefficient of friction and reduces chip tumours

Reduce friction coefficients and reduce chiplash Improve heat resistance, allowing for higher speeds

Common Coating Types:

TiN (Titanium Nitride): Golden yellow, general purpose coating, cost effective.

TiCN (Titanium Carbide Nitride): Blue-grey, harder and more wear resistant than TiN, good toughness, suitable for general purpose machining of stainless steel and steel parts.

TiAlN (Titanium Aluminium Nitride) / AlTiN (Titanium Aluminium Nitride): Purple-black / black. One of the most important and versatile coatings for modern machining. It produces a protective layer of aluminium oxide during cutting and is particularly resistant to high temperatures, making it ideal for high-speed machining, dry cutting or machining hard materials (steel, cast iron, stainless steel).

CrN (Chromium Nitride): Silver grey, with good anti-sticking properties, ideal for machining aluminium, copper, titanium alloys and stainless steel, which are prone to sticking to the tool.

Diamond: Similar performance to PCD, mainly used for machining non-ferrous and non-metallic materials, long life.

Selection mnemonic:

Processing steel, stainless steel, cast iron → preferred TiAlN-based coatings (e.g. AlTiN).

Soft metals such as aluminium and copper → prefer uncoated, CrN or diamond coatings.

General purpose machining for cost effectiveness → TiCN or TiN.

IV. Toolholders and interfaces - the “bridge” between precision and stability.

The toolholder connects the machine tool to the cutting edge, and its precision and rigidity directly determine the machining results.

1. Types of milling cutter shanks:

JT (Straight) / Weldon (Side-fixed): Economical and versatile, but with average precision and dynamic balance, suitable for low-speed, low-demand machining.

Heat Shrink: High clamping accuracy, high rigidity and excellent dynamic balance, the first choice for modern high speed milling.

Hydraulic shanks: High clamping accuracy and vibration damping, ideal for finishing and deep hole machining.

Face milling shanks: Used for mounting indexable inserts, with the highest rigidity, used for milling large flat surfaces.

2. Turning tool system:

Welding type turning tool: Economical, but the inserts are not replaceable, gradually eliminated.

Clamping indexable turning tool: the absolute mainstream. The inserts are clamped on the toolholder by screws, and the inserts can be indexed or replaced after wear, which is economical and efficient. The selection needs to match the clamping method of the toolholder (e.g. lever type, screw type) and the groove type of the inserts.

3. Key criteria: HSK vs BT

BT shanks: the standard for conventional machining centres, with a 7:24 taper, cost-effective.

HSK shanks: Hollow, short taper design, high speed performance, higher clamping rigidity and accuracy, ideal for modern high speed machines.

Selection advice: Where budgets allow, investing in a good toolholder (such as heat shrink or HSK) is essential to improve the quality of machining and the life of expensive tools used.

Tool selection quick checklist and summary

Materials to be machined Recommended tool materials Recommended coatings Notes

Steel (P) Tungsten carbide TiAlN, TiCN Insert flutes according to roughing/finishing operations

Stainless steel (M) Tough carbide TiAlN, TiCN Maintains sharp edges, ensures chip breakage

Cast iron (K) Carbide, CBN TiAlN, TiCN Attention to wear resistance, dry cutting or trace oil mist

Aluminium/copper (N) Cemented carbide, PCD Uncoated, CrN, diamond Large chipformer to prevent sticking of tools

High temperature alloys (S) Specialised carbides, ceramics TiAlN Low RPM, large feed, ensure cooling

Comprehensive guide to CNC machining of moulds

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Comprehensive guide to CNC machining of moulds

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Comprehensive guide to CNC machining of moulds