Why aren't Carbide-Tipped Drill Bits Made Completely of Carbide?
Carbide-tipped drill bits are widely used in drilling applications due to their hard and durable tips. However, it is not common to see carbide-tipped drill bits made up entirely of carbide. In this article, we will explore the reasons behind this design choice, focusing on cost, material properties, manufacturing techniques, and heat resistance.
Why not use carbide entirely?
While tungsten carbide is an excellent material for the cutting edge of drill bits, there are several reasons why it is not used for the entire bit:
Cost
Tungsten carbide is significantly more expensive than steel. Using it for the entire drill bit would greatly increase the manufacturing costs. By using a combination of tungsten carbide and steel, manufacturers can balance performance and cost effectively.
Brittleness
Carbide is brittle and prone to breaking or chipping. Although it is very hard and maintains a sharp edge, a drill bit made entirely of carbide would be more susceptible to breaking or chipping when subjected to impact or lateral forces, making it less suitable for demanding applications.
Flexibility and Toughness
Steel provides the necessary flexibility and toughness. These properties are essential for the structural integrity of the drill bit and enable it to withstand the stresses of drilling without breaking. The combination of a steel body and a carbide tip ensures that the bit is both tough and durable.
Heat Resistance
Carbide tips can withstand higher temperatures than steel, but steel is better at absorbing and dissipating heat. This means that the steel body of a carbide-tipped drill bit can prevent overheating and extend the life of the bit during prolonged use.
Manufacturing Techniques
It is easier to manufacture and attach a carbide tip to a steel body than to create a bit entirely from solid carbide. Solid carbide drill bits would require different machining processes, making them more difficult and costly to produce. The technique of attaching a carbide tip to a steel body is more efficient and practical for most applications.
Alternative Solutions: Solid Carbide Drill Bits
There are solid carbide drill bits, but these are more expensive and more sensitive to bending loads since carbide is more brittle than steel. This limits their usefulness in certain applications where the drill bit may be subjected to bending or impact.
Complexity of Solid Carbide Drill Bits
Solid tungsten carbide (WC) drill bits do exist but they are composite materials made of fine WC particles cemented in a hard cobalt or nickel metal matrix. This composite is known as a metal-matrix composite (MMC) or cermet. The process involves pressing and sintering, allowing the creation of complex shapes. Despite being called 'solid' WC, these bits are not entirely made of tungsten carbide and are more durable and less brittle than pure WC.
Applications for Solid Carbide Drill Bits
Solid WC composite bits are mainly used in highly rigid CNC machining equipment and for automated drilling of difficult-to-machine materials like titanium, nickel alloys, duplex stainless steel, and hardened alloy steels like AR-500. These materials can cause traditional steel drill bits to dull quickly, leading to frequent replacement and sharpening, which is not practical for automated processes.
Brittleness and Durability
While solid carbide composite bits are tough and durable, they can easily fracture if abused. These bits are also more expensive than alloy steel drill bits, making them a less economical choice for general use.
Flexibility of Steel Drill Bits
Steel drill bits are more tolerant of vibration, bending, and other forms of unintended punishment due to their reasonable ductility. They provide a balance between durability and the ability to withstand misuse.
Compromise for Special Applications
For applications where a drill bit faces heavy abrasion, such as drilling in masonry or rock, adding a carbide tip can provide a compromise between steel and solid carbide. The bit remains resistant to misuse and bending while the carbide tip lasts significantly longer.
Summary
The combination of a carbide tip with a steel body optimizes performance, cost, and durability, making carbide-tipped drill bits a practical choice for many drilling applications. While solid carbide drill bits offer superior performance for specific tasks, their higher cost and brittleness limit their broader use.