Metal hardness plays a crucial role in CNC machining, affecting material selection, tool choice, and machining strategies. But what makes a metal hard or soft, and how does it impact machining?
What Determines Metal Hardness?
Hardness refers to a material’s resistance to deformation. It is influenced by atomic structure, chemical bonds, and the mobility of dislocations—defects in the crystal structure that impact how a metal deforms under stress.
Metals fall into two categories:
●Hard metals (stainless steel, titanium, tool steel) resist wear and deformation, making them ideal for strength-demanding applications.
●Soft metals (aluminum, brass, zinc) are easier to machine but more prone to surface damage.
▼Hard vs. Soft Metals in CNC Machining
【Metal】 ●Hardness ○Shear Modulus ○Tensile Strength
【17-4 PH Stainless 】 ● 85 Rockwell B ◎11200ksi 200ksi
【Kovar 】 ●78 Rockwell B ◎7500 ksi 75 ksi
【Grade 2 Titanium 】 ● 80 Rockwell B ◎ 5510 ksi 49.9 ksi
【Grade 5 Titanium 】 ● 36 Rockwell B ◎ 6380ksi 138ksi
【2024 Aluminum 】 ● 75 Rockwell B ◎ 4060ksi 27ksi
【6061-T6 Aluminum】 ● 60 Rockwell B ◎3770ksi 42ksi
【6063 Aluminum 】 ●50 Rockwell B ◎3740 ksi 28 ksi
【7075-T6 Aluminum】 ● 87 Rockwell B ◎3770 ksi 83 ksi
【360 Brass】 ●80 Rockwell B ◎5370ksi 58ksi
【304 Stainless Steel 】 ●92 Rockwell B ◎12500ksi 73.2ksi
【316 Stainless Steel 】 ● 95 Rockwell B ◎11000 ksi 79.8 ksi
【Zinc 】 ● 63 Rockwell B ◎35ksi 5.3ksi
How Hardness Affects CNC Machining
1.Tooling: Hard metals require carbide or diamond-infused tools, while soft metals need careful speed control to avoid smearing.
2.Wear & Durability: Hard metals wear down tools faster, demanding optimized tool paths and coolant. Soft metals may cause tool clogging if not managed properly.
3.Machining Approach: Hard metals benefit from roughing passes before finishing to minimize heat buildup. Soft metals require precise speed adjustments to prevent deformation.
Pro-Tip for Hard Metal Machining
To reduce tool chatter and heat, use rigid tools. Ball end mills work well for finishing, while corner radius tools are useful for large flat surfaces but should be used cautiously to avoid chipping.
Final Thoughts
Choosing the right metal for CNC machining impacts efficiency, tool life, and part quality. Whether working with aerospace-grade titanium or soft aluminum, optimizing machining strategies ensures the best results.