Today in moldmaking it is very common to see a manufacturer use aluminum material over steel for their plastic injection molds. Aluminum is easier to machine, easier to handle, able to provide quicker turnaround times, and in most cases, higher quality for their injection-molded plastic products. Aluminum still has its unique characteristics that require a different machining style than that of mold steel.

With the different choices in milling cutters and geometries, how do you know which cutter and geometry is right for your aluminum application? What geometry should I use? Which insert grade do I choose? Can I get more tool life than what I am already getting?

Tips for Machining Aluminum
Choosing the right geometry: In most aluminum applications we generally want to choose a sharp geometry that should shear material off, as supposed to machining with a honed edge that pushes the material off. High positive geometries decrease the cutting load and adhesion, while increasing the tool life of the insert.

Choosing the right insert grade: Aluminum likes to stick wherever it can. The right grade can make a difference in tool life and surface roughness. Choosing a coated insert, such as a standard CVD- or PVD-coated insert could create unnecessary edge build-up. A hard, uncoated insert with a mirror buffed finish could give you longer tool life. Many manufacturers offer this type of technology or something similar.

There are however coated inserts that are specifically made for non-ferrous materials. DLC (diamond like carbon) coatings and diamond coatings are both coated inserts that use coatings to extend tool life and improve surface roughness. Although these coatings are more costly, you can expect a better surface roughness and longer tool life—about two to four times for the DLC coating and about five to seven times the tool life with a diamond coating.

When the properly combined insert is chosen with the optimal geometry and grade, you can achieve longer tool life, very good surface roughness and less adhesion. With the proper machine and holding system, you can also maximize the indexable tool’s capabilities. Some cutters are even able to reach a speed above 4,000 surface feet per minute with uncoated carbide.