How to properly select drill bits for different materials

Features of Drill Bits for Metal

Drill bits for metal are engineered to help you machine precise holes on tough materials like aluminum, non-ferrous metals, steel, and heat-resistant alloys. They are manufactured from harder materials and equipped with advanced geometry and durable coatings to resist high temperature and friction.

Why is it Crucial to Use the Correct Drill Bit? 

Using the correct drill bit means using the appropriate metal drill bit sizes, metal drill bit angles, and shapes. If you choose the wrong metal drill bits, it may cause tool breakage and imprecise holes. However, correct ones can ensure stable machining with improved efficiency and minimized safety risks to prolong the tool life and reduce overall costs.

 How to Choose the Right Drill Bits for Metal?

Step 1: Confirm the Types of Metal Drill Bits

• Cobalt Metal Drill Bits

Cobalt metal drill bits are composed of 5–8% cobalt alloyed with high-speed steel, enabling their outstanding heat and wear resistance. When drilling hard materials like cast iron and stainless steel, they can deliver consistent rigidity and stability even under extremely high temperatures up to 1,100°F. No matter the edge sharpness or durability, they all show you better advantages than high-speed steel.

• Carbide Metal Drill Bits

Carbide metal drill bits are manufactured from fine-grain solid carbide with unmatched rigidity and wear resistance. They are ideal for you to machine abrasive and tough materials like titanium and hardened steel. In heavy-duty CNC machining, carbide metal drill bits can always maintain sharpness and longer tool life.

• Titanium Metal Drill Bits

Titanium metal drill bits contain the HSS substrates with durable coatings such as TiN and TiAlN, which ensure their unmatched rigidity and minimal tool friction. In general-purpose machining, heat generation can be improved, and tool service life can be extended with their exceptional durability.

• HSS Metal Drill Bits

High-speed steel drill bits are more cost-effective tools with their optimized combination of wear resistance and toughness in high-temperature machining up to 600°F. They are perfect for machining metals like aluminum and brass with high stability, even under high-speed machining up to 1,500 RPM.

• Step Drill Bits

Step Drill Bits are designed with several stepped diameters to help you create multi-diameter holes with only one tool. They are perfect for drilling metals and plastics with advanced chip control and fewer tool changes, further improving the machining efficiency.

• Center Drill Bits

Center drill bits are also a kind of metal drill bit, which are short and rigid to machine the starter hole before drilling. They feature the innovative geometry design with dual angles to maintain excellent self-centering without deflection. In CNC machining, they are typically used to boost dimensional accuracy and consistent hole alignment.

Step 2: Match Drill Bits Perfect for the Metal Type 

Soft Metals

• Aluminum

When machining aluminum, it will be most efficient for you to choose the HSS metal drill bits because of their high helix angles and unmatched sharpness. Since aluminum is a soft metal, you don’t even need specific coatings. You only need to make full use of higher machining speeds and the unique geometry design of HSS metal drill bits, like the positive rake angle, to create smooth holes without burrs. However, if you have demanding requirements of high accuracy, choosing the carbide metal drill bits will be better.

• Brass & Copper

Specialized HSS metal drill bits are also cost-effective for machining brass and copper at lower machining speeds. You can choose the bits with a slightly negative rake angle and split point design to avoid binding and walking. As brass and copper are soft enough to be machined, HSS metal drill bits, which are uncoated or with coatings like TiN, are preferred for you to choose from.

• Mild Steel

Cobalt metal drill bits and top-quality HSS metal drill bits are all perfect for machining mild steel due to their excellent wear resistance and high toughness. Longer tool life and less tool friction can be achieved with advanced coatings such as TiN and TiAIN. You will get high-accuracy holes when machining at a moderate speed.

Hard Metals

• Cast Iron

Cast iron contains abrasive graphite content, which means cobalt and carbide metal drill bits will be more suitable for machining it. You can also select the TiAIN coating to deliver extra wear resistance and durability. If you want to achieve the most satisfying drilling performance, don’t forget to use the medium speed and dry machining environment.

• Stainless Steel

In machining stainless steel, solid carbide drill bits always demonstrate exceptional rigidity and thermal generation. Overheating can be avoided by machining at lower speeds and higher feed rates with sufficient lubrication. However, carbide metal drill bits will be more suitable for drilling tougher grades. 

• Hardened Steel

For machining hardened steel, solid carbide drill bits can always provide you with smooth cutting. Because of the high hardness of hardened steel and high machining temperature, rigid drill bits with durable coatings are essential for you to maintain consistent machining with wear and heat resistance.

• Titanium & Heat-Resistant Alloys

Solid carbide drill bits with advanced coatings like AITiN are perfect for you to machine with excellent heat resistance. In machining titanium, you should choose the ultra-sharp cutting edges and steady feed rates to boost the performance. However, cobalt bits are also suitable for light processing, while carbide drill bits play a crucial role in heavy-duty machining with high precision.

Step 3: Select Suitable Coatings

• General Metals: TiN can deliver less tool friction with enhanced durability.
• Hard Metals: TiAIN and AITiN can achieve high heat and wear resistance.
• Abrasive Metals: TiCN features greatly improved toughness.

Step 4: Consider Drill Bit Geometry

• Point Angle

The sharp 118° point angles are suitable to improve the penetration on soft metals, while 135° split points are required to enhance the sharpness for hard metals.

• Flute Design

Polished and deeper flute design enables the prevention of chip clogging for soft metals, and a strong flute design is essential for hard metals to improve the hardness.

• Helix Angle

A high helix angle is perfect for soft metals to improve the chip evacuation, whereas a low helix angle can enhance the machining stability for hard metals.

• Self-Centering 

Standard centering is enough for drilling soft metals, while self-centering is necessary for hard metals.

• Chip Evacuation

Efficient chip evacuation is crucial for soft metals to avoid chip jamming, while the controlled chip removal rate is effective for hard metals to reduce heat generation. 

• Heat Control

Less heat can be achieved under high-speed machining of soft metals, while a slower machining speed can decrease the heat on hard metals.

Step 5: Choose the Correct Feeds and Speeds

Choosing the correct feeds and speeds plays a crucial role in avoiding overheating and excessive tool wear. Higher cutting speeds and lighter feeds are fundamental in drilling soft materials such as aluminum. However, lower cutting speeds and stronger feed rates are beneficial to machining hard metals like hardened steel. The higher RPM can be withstood by solid carbide metal drill bits than HSS and cobalt metal drill bits. Correct cutting configurations can significantly improve the chip flow and hole accuracy, further boosting the cutting performance, surface quality, and tool lifespan.

Step 6: Understand the Drill Bit Life

Understanding the drill bit life is also indispensable in improving the drilling efficiency and decreasing overall tooling costs. The hardness of the material, coating properties, and cutting configurations can all affect the tool wear. When you notice the signs of tool wear, for example, the edge dulling and poor chip formation, you should replace the metal drill bits in a timely manner to protect work pieces from possible damage. Moreover, the lifespan of metal drill bits can also be extended by choosing durable materials such as cobalt and solid carbide. Additionally, drill bit life can be prolonged with regular maintenance and proper cooling.

Tips for Extending Your Drill Bit Life

• Expert Machining Techniques

Remember to use the stable feed rates and proper cutting forces to decrease tool breakage, which ensures optimal cutting performance to prolong tool service life.

• Proper Cooling & Lubrication

Using the coolants is useful for dissipating thermal generation, while cutting oil can enhance the chip evacuation. Timely cooling can improve the surface quality and extend the tool life.

• Appropriate Re-sharpening 

Re-sharpen cutting edges promptly to maintain the tool geometry. If you insist on resharpening cutting edges regularly, less tooling costs and improved hole accuracy can be attained.

• Proper Storage 

You can put the drill bits in the specialized box, which can control the temperature and humidity to avoid moisture. Coated drill bits and carbide drill bits should be stored separately to maintain smooth surfaces. 

Common Problems 

Overheating

If you find the drill bits are overheating, you should decrease the cutting speed immediately and properly use the lubrication to avoid excessive tool friction. If drilling high-heat materials is involved, don’t forget to use the coated metal drill bits to ensure smooth chip flow and minimize the heat accumulation. Of course, the carbide metal drill bits will be superior to promote thermal stability in heavy-duty machining if economic conditions permit.

Tool Chipping 

• You can significantly decrease the tool vibration by using the appropriate point angle and high-rigidity fixturing to prevent the possible edge chipping.
• Decrease the feed rates when drilling hard metals and utilize the durable coatings to reduce tool wear.
• Before drilling operations, make sure the correct alignment between the tool and the workpiece.
• Prompt replacement of worn metal drill bits can greatly reduce tool chipping.

Poor-quality Holes

• You should inspect the sharpness of cutting edges and choose a suitable geometry design of the metal drill bits according to the material.
• Keep the stable feed rates and cutting speeds to ensure dimensional accuracy.
• Optimize the chip evacuation to prevent chip clogging.
• Use the proper lubrication to deliver perfect surfaces without burrs.
• Make sure the work pieces are securely clamped to prevent excessive apertures.

 

FAQ

How can smooth drilling be attained in machining hard metals?

When machining hardened metals, you can use the controlled feed rates to maintain stable machining. In addition, less tool vibration, minimal tool wear, and perfect hole quality can be attained with smooth drilling performance, greatly extending the tool life.

What will happen if we keep using dull metal drill bits?

When you keep using dull drill bits, they may cause excessive heat formation and poor hole quality. Once you find the signs of tool wear like higher cutting resistance and poor chip formation, you’d better resharpen cutting edges immediately to continue smooth cutting.

How can we maintain the metal drill bits?

You can inspect the tool wear and chip formation regularly to avoid possible damage to work pieces and metal drill bits. Inspect the tool wear, edge chipping, and coating degradation frequently to prevent unexpected downtime.  Timely and proper maintenance can keep the metal drill bits in optimal conditions to deliver consistent drilling performance.

What are the differences between HSS, cobalt, and carbide drill bits?

• HSS: Cost-Effective & High Flexibility & Perfect for machining soft metals.
• Cobalt: Superior Thermal Resistance & Suitable for machining hard metals.
• Carbide: High Rigidity & High Wear-Resistance.

Which coating is recommended to be applied to metal drill bits?

• TiN: Perfect for general-purpose metal drill bits.
• TiCN: Ideal for hard metal drill bits with superior rigidity.
• TiAlN: Suitable for hard metal drill bits in a dry environment with outstanding heat resistance.

Why do the metal drill bits become dull so quickly?

Typical causes are the use of incorrect metal drill bits, excessively high RPM, improper feed rates, and inappropriate cooling and lubrication.

What cutting speed should be set in drilling diverse metals?

Typically, when the metal is soft, the higher RPM can be used. If the metal is harder, the RPM should be lower to decrease the heat generation.