Coated Drill Bits: Explained

This latest insight from Quality Tools UK, investigates the various coating options available to the consumer for different types of drill bits. This will look into the variety of coated drills/tools, the differences and how they can be of more benefit to a user over non-coated tools.

Overview

Standard non-coated HSS Drill bits are perfectly adequate for any light metal, wood, plastic, Fibreglass and PVC applications. However, certain jobs require something more powerful and longer lasting. Options with Titanium, Aluminium, Nitrogen or Silicon elements can help to achieve a better result. Or even very simple coating of the drill bits with an oxide such as Black Oxide Drill Bits can prove to be a stronger alternative.

Titanium Nitrate (TiN)

The most common form of coating, Titanium Nitrate (abbreviated to TiN) is a chemical compound of two elements, Titanium and Nitrogen. This coating is used for extra wear protection in comparison to non-coated drill bits. TiN has a three to four times longer service life over non-coated tools. Cooling is strongly advised for this type of coating as at higher temperatures the coating can slowly be destroyed. This coating is ideal for Steel, Brass and Cast-Iron applications. It is possible to use this coating in Aluminium related applications, however it is not recommended due to the special affinity between Titanium and Aluminium. Physical diffusion processes may be triggered when pressure and heat is applied between the two materials. As a result, this can increase friction and impair the chip removal and discharge. Another disadvantage of Titanium Nitrate is that the thicker layer of coating can tend to crack, the ideal coat thickness is between 1-7 micrometre (μm).

TiN Capabilities:

• Nano Hardness of 24 Gigapascal (GPa)
• Coat Thickness of 1-7 μm
• 55 μ Co-efficient of Friction
• Maximum Temperature of 600 °C

Titanium-Carbon Nitride (TiCN)

TiCN consists of three elements of Titanium, Carbon and Nitrogen to produce the coating of Titanium-Carbon Nitride. Often, this coating is specialised for Taps in Threading Applications. This is due to the lower temperatures and coefficient friction supports involved in this application. Whilst TiCN coating can handle hard materials such as Steel, Stainless Steel, Cast Iron and materials such as Brass and Plastics, it is not best suited for high temperatures above 400°C. Because of this, cooling is strongly advised. Other applications for Titanium-Carbon Nitride is punching, forming and hobbing in high and low alloyed steels. Depending on the use of the tool, TiCN can potentially last up to four to five times longer service life over non-coated options.

TiCN Capabilities:

• Nano Hardness of 32 Gigapascal (GPa)
• Coat Thickness of 1-4 μm
• 2 μ Co-efficient of Friction
• Maximum Temperature of 400 °C

Titanium Aluminium Nitrate (TiAlN)

A chemical compound composing of three elements, titanium, aluminium and nitrogen, to offer high resistance to heat and oxidisation. This form of coating allows for much higher cutting speeds, enabling work processes to be more efficient. Another benefit of TiAlN Coated Tools is the increased life span. Typically, Titanium Aluminium Nitrate can withstand a service life 10 times longer than non-coated bits. Additional cooling can help to increase the service life, however this is not compulsory. Titanium Aluminium Nitrate is best suited for hard materials such as Steel, Stainless Steel, Titanium Alloys, Aluminium, Brass, Bronze and can also be utilised in drilling/cutting of Plastics.

TiAlN Capabilities:

• Nano Hardness of 35 Gigapascal (GPa)
• Coat Thickness of 1-4 μm
• 5 μ Co-efficient of Friction
• Maximum Temperature of 800 °C

Aluminium Titanium Nitride (AlTiN)

Similar to Titanium Aluminium Nitride, but predominately focusing on Aluminium as the primary element over Titanium. Comprising of the same three elements, Aluminium Titanium Nitride (AlTiN) has a much stronger hardness in comparison to TiAlN. This is thanks to the very high resistance to heat and oxidation levels. Tha nano hardness is more, the coefficient of friction is also higher and the maximum temperature is at 900°C compared to 800°C. This means that AlTiN can potentially achieve up to 14 times longer service life than non-coated tools and 4 times longer than TiAlN (dependant on the materials and applicational use).

AlTiN Capabilities:

• Nano Hardness of 38 Gigapascal (GPa)
• Coat Thickness of 1-4 μm
• 7 μ Co-efficient of Friction
• Maximum Temperature of 900 °C

Black Oxide

Drill Bits coated with Black Oxide are typically more cost effective than all the Titanium variants listed above. As the most basic coating option, black oxide does not offer the same service life as the Titanium coated bits but they do offer a stronger water, rust and corrosion resistance. One of the best features for Black Oxide Drill Bits is the delay of oxidation to the tool, thus causing a much stronger service life over non-coated bits. In most cases, it can last 50% longer than non-coated drill bits. However, it does not provide any more strength benefits. Black Oxide is considered more of a heat treatment over a coating.

Silicon Coated

Less so common drill bits can be coated within a Silicon Coating (SG). These are designed and shaped for more precision activities such as shaping and prep-work. Used mainly for Nail Drill Bits and Rotary Burrs. They are capable of materials with a high-density.

High-Speed Steel (Non-Coated)

The most common drilling tools of any type will be HSS (full name: High-Speed Steel) drill bits. The most cost effective, simple and easy to use and maintain drill bits with no coating on, are very popular amongst both amateur or beginner DIY consumers and professional high-end construction builders/trades personnel. Due to its increased hardness and improved wear resistance, the favourite choice enables high speeds through tough metals and other materials. Without coating, on the drill bits such as Black Oxide or one of the others listed above, Standard HSS Drill Bits can be prone to rust and shorter durability capabilities. However, for most typical DIY tasks on Light Metals, Wood, Plastics, Fibreglass and PVC materials, the standard non-coated tools are perfectly ideal at a much stronger value for money to the user.

Conclusion

Overall, there are a variety of different forms of oxide coating for drill bits and other tools. Choosing the right form of coating, or whether to have a drill bit with coating at all, depends on the application it is intended for. Factors such as cost, durability, service life and usage should all be considered. For instance, should a user require a drill bit for a simple small DIY Task, then a non-coated High-Speed Steel (HSS) drill would be perfectly adequate. However, a more heavy-duty construction build project with frequent, high temperatures and pressure usage should require some form of coating, regardless of the additional initial cost of the tool. View our entire product range at Quality Tools UK.