Why is it so difficult to drill an aluminium heat sink?

Drilling an aluminum heat sink is challenging because aluminum is soft, ductile, and gummy, causing it to grab the drill bit, create excessive friction, and produce long, stringy chips that clog. Heat sinks, often made of 6061 or 6063 alloys, are also typically anodized, which adds a hard, abrasive surface layer that dulls bits rapidly.

Key Reasons for Difficulty:

• Galling and Softness: As a soft material, aluminum sticks to the cutting edge of the drill bit (galling), creating intense heat and preventing clean cutting.
• Clogging (Chip Welding): The material produces long, stringy, or powdery chips that do not evacuate properly, melting back onto the bit or clogging the hole.
• Anodized Coating: Many heat sinks have an aluminum oxide coating (anodizing) that is much harder than the base aluminum, which can quickly ruin standard high-speed steel bits.
• Thermal Expansion: Aluminum expands rapidly when heated, which can cause the hole to shrink and bind on the drill bit as it cools.

Tips for Success:

• Use Lubrication: Apply cutting oil or kerosene to prevent aluminum from sticking to the bit.
• Speed and Feed: Use higher RPMs, but maintain a consistent, firm feed rate to prevent the bit from just rubbing the surface.
• Clear Chips Frequently: Back the drill bit out often to clear chips and apply lubricant.
• Sharp Bits: Use sharp, high-speed steel or titanium nitride-coated bits to reduce heat generation.

PS: As a safety precaution, I was using N95 mask to prevent inhalation of aluminium dust and goggles to protect eyes.