Why is Poly-crystalline Diamond (PCD) good on aluminium?
Polycrystalline diamond, also known as PCD, or just diamond tipped cutting tips, is one of the most common used cutting tools for industrial CNC lathes on aluminium. In this article we run you the reasons why, and whether PCD is suitable for the small workshop or hobbyist.
Advantages of PCD on aluminium
Speed -
Unlike carbide, PCD can be run at tremendously high feeds and speeds (in excess of 6000rpm), without any loss of durability. This is due to its high hardness, abrasion resistance, chemical stability and thermal conductivity, in comparison to carbide, which tends to wear and fail at higher speeds.
Longevity -
The hardness of PCD also gives it much longer lifespan than carbide.
When combined with the incredibly high throughput that PCD is capable of, this makes it an ideal choice for industry, where down time for switching out inserts can be considerably more expensive than the insert itself, due to the hourly wage cost of skilled CNC workers, capital cost and the opportunity cost of lost cutting time.
Finish -
PCD, when used on the proper set up, can leave aluminium with a mirror finish, often removing the need for any separate finishing or polishing operation. This is due to the incredibly high speeds PCD can cut with, which prevents visible cut lines from forming, provides phenomenally clean and quick chip removal, and whose heat from high speed help smooths the surface of the work.
Disadvantages of PCD on aluminium
Poor low speed performance -
When PCD can not be run at the high speeds it performs best at, it can perform worse than its carbide alternative since its geometry is designed for high speeds and resilience, and does not have the sharpness of a ground carbide insert which can cut even at low speeds, and it typically lacks any chip breaker geometry.
Higher initial cost -
PCD inserts are significantly more expensive than specialized aluminium cutting carbide insert, often 10x or more expensive per insert.
Limited versatility -
PCD inserts are less effective for interrupted cutting operations that are common in many aluminium machining tasks
More sensitive to shock loading -
PCD is brittle and can chip or fracture when subjected to vibration or unstable cutting conditions
Is PCD suitable for smaller lathes?
Older lathes with manual speed gearing especially tend to be limited in top speed compared to more modern lathes with digital speed controlled motors.