In the world of machining, two of the most commonly encountered types of drills and mills are high-speed steel, or HSS, and carbide drills. Though these drills and mills are both used to remove material from a workpiece as well as for cutting and shaping applications, they are quite different in their material composition and other attributes. Here’s what you should know, from a high level.
High Speed Steel Drills
As the name suggests, high-speed steel drills, also known as HSS, are made of steel alloy, one that is often fortified with the addition of other elements like molybdenum and tungsten which improve its strength, hardness, and wear-resistance.
As the name suggests, HSS bits were designed for high-speed cutting applications. The steel is also heat-treated so that it remains relatively flexible, which is a beneficial attribute during high-speed cutting. This gives HSS bits a fairly good ability to withstand stresses and long tool life.
HSS bits are also renowned for their impact resistance and so can also be effectively used on a wide range of relatively soft materials, including but not limited to mild steel, aluminum, and even plastic and wood.
One thing to note about HSS drills is that, despite the name, they do not exhibit the same resistance to thermal stresses incurred during certain high-speed machining applications as carbide drills, so they can’t be used at the same high speeds.
Another note is that HSS drills are generally more affordable than carbide drills, which makes them more affordable for some machinists and hobbyists.
Carbide Drills
By contrast to HSS drills, carbide drills are made of a solid carbide material, commonly tungsten carbide, which is a compound material made of carbon and a metal. In the case of tungsten carbide it would be a combination of carbon and tungsten.
Carbide drills are much harder than HSS bits, which gives them considerably better wear resistance, which generally yields longer tool life because the drills stay sharper for longer.
Carbide also has much higher thermal resistance than HSS, and as a result, can be used at much higher speeds than HSS, without deforming or losing its cutting ability. Carbide drills are also sometimes treated with advanced coatings that improve their cutting ability, boost chip evacuation, enhance resistance to high temperatures, or some combination of these attributes.
Most importantly in this case is that the superior hardness of carbide drills means that they can also be used to cut much harder and more abrasive materials than HSS bits, and will last longer when used for those applications. As a result, carbide drills are often used on harder metals like titanium, especially in CNC-machining applications in which tight tolerances are required.
The tradeoff is that the higher hardness of carbide drills also makes them more brittle, which means they are less tolerant of impact or high vibration, and carbide drills can snap or shatter if subjected to these stresses.
Because of these attributes, carbide drills are generally more expensive than HSS drills.
Shop Carbide Drills and Other Machine Tools
Want to learn more about carbide drills, or do you need to replace some aging drills or mills? Visit TMT Toolbox. They carry a wide range of drills, mills and other machining tools and accessories. You can also get in touch with their customer service team if you have any questions.
