When it comes to CNC machining, material selection is one of the most crucial decisions you’ll make. The material affects the final part’s mechanical properties. It also influences cost, machining speed, surface finish, durability, and how well it works with post-processing.
Why Material Choice is Paramount in CNC
- Performance Dictation: Material properties (strength, hardness, thermal resistance, electrical conductivity, chemical resistance) define what your part can do.
- Cost Control: Material cost varies drastically. Machinability (ease of cutting) also affects labor time and tooling costs.
- Manufacturability: Some materials are brittle, gum up tools, or warp easily under machining stresses.
- Aesthetics & Finish: The base material influences achievable surface finishes and compatibility with coatings (anodizing, plating, painting).
- Lead Time: Common materials are readily available; exotic alloys might have long lead times.
Key Factors Influencing Material Selection
1. Mechanical Properties
- Strength & Hardness: Materials like titanium alloys (e.g., Ti-6Al-4V) offer exceptional strength-to-weight ratios, ideal for aerospace and medical implants .
- Ductility: Aluminum alloys (e.g., 6061-T6) are ductile and easy to machine, making them popular for automotive and consumer electronics .
- Corrosion Resistance: Stainless steel (e.g., 316L) and Inconel are preferred for marine and high-temperature applications .
2. Machinability
- Tool Wear: Harder materials like titanium require specialized carbide tools and slower cutting speeds to reduce wear .
- Chip Formation: Aluminum produces long, stringy chips, while cast iron creates shorter, brittle chips
3. Cost & Availability
- Material Cost: Titanium is 5–10x more expensive than aluminum, while plastics like POM are budget-friendly for non-structural parts .
- Machining Time: Softer materials like aluminum machine 4x faster than steel, reducing labor costs .
4. Environmental & Functional Requirements
- High-Temperature Resistance: PEEK and Inconel excel in extreme heat (e.g., aerospace engines) .
- Biocompatibility: Medical-grade titanium and 316L stainless steel meet FDA standards for implants .
Common CNC Machining Materials:
The most commonly used materials for CNC machining are metals, plastics, and composite materials. Let’s take a closer look:
1. Metals (The Powerhouses)
| Material Category | Common Grades | Key Properties | Typical Applications | Machinability Rating (Relative) |
|---|---|---|---|---|
| Aluminum | 6061, 7075, 2024, 5083 | Lightweight, good strength-to-weight, excellent corrosion resistance, good thermal/electrical conductivity, easily machinable. | Aerospace frames, automotive parts, enclosures, heat sinks, consumer goods, prototypes. | Excellent (100%+) |
| Stainless Steel | 303, 304, 316, 17-4 PH | High strength, excellent corrosion resistance, good temperature resistance. Work hardens. | Medical instruments, food processing, marine hardware, chemical equipment, shafts, valves. | Fair to Good (40-70%) Varies |
| Steel (Carbon/Alloy) | 1018, 1045, 4140, A36 | High strength, toughness, good wear resistance. Less corrosion resistant than SS. Can be heat treated. | Gears, shafts, structural components, tooling, brackets, fasteners. | Good (70-90%) Varies |
| Brass | C360 (Free Machining) | Excellent machinability, good corrosion resistance, good electrical conductivity, aesthetic (gold-like). | Electrical fittings, plumbing components, decorative hardware, musical instruments, bushings. | Excellent (100%+) |
| Copper | C110 (Electrolytic) | Exceptional electrical & thermal conductivity. Soft, can be gummy to machine. | Electrical components, heat exchangers, bus bars, RFI shielding. | Fair (20%) |
| Titanium | Grade 2, Grade 5 (Ti-6Al-4V) | Exceptional strength-to-weight ratio, excellent corrosion resistance, biocompatible. Low thermal conductivity causes heat buildup. | Aerospace components, medical implants, high-performance automotive, chemical processing. | Poor to Fair (20-40%) |
2. Plastics (The Versatile Performers)
| Material Category | Common Grades | Key Properties | Typical Applications | Machinability Notes |
|---|---|---|---|---|
| ABS | General Purpose | Good impact strength, toughness, low cost. Fair chemical resistance. | Prototypes, enclosures, housings, automotive trim, consumer products. | Good. Can melt if overheated. |
| Nylon (PA) | 6, 66, Glass-Filled | High strength, toughness, wear resistance, good chemical resistance. Absorbs moisture. | Gears, bushings, rollers, insulators, structural parts. | Good. Requires sharp tools. |
| Acetal (POM/Delrin) | Homopolymer, Copolymer | High stiffness, low friction, excellent dimensional stability, good chemical resistance. | Precision gears, bearings, insulators, conveyor parts, snap-fits. | Excellent. Clean cuts. |
| PEEK | Unfilled, Glass/Carbon | Exceptional strength, stiffness, chemical & thermal resistance. Very expensive. | Aerospace, medical implants, semiconductor, high-temp oil & gas. | Fair. Abrasive, needs care. |
| PTFE (Teflon) | Virgin, Glass-Filled | Lowest friction, excellent chemical resistance, high-temp capability. Low strength, creeps. | Seals, gaskets, bearings, chemical liners, insulators. | Good. Soft/gummy, needs support. |
| Polycarbonate (PC) | General Purpose | Exceptional impact resistance, transparency (optical clarity), good dimensional stability. | Safety glasses, lenses, enclosures, transparent shields, housings. | Fair. Can chip/crack; sharp tools essential. |
| HDPE/UHMWPE | – | Good chemical resistance, low friction, impact resistant (UHMW). Low stiffness. | Cutting boards, wear strips, tanks, liners, low-friction parts. | Good. Can melt/gum if overheated. |
3. Composites (The Engineered Solutions)
- Phenolics (G10/FR4, G7): Glass/epoxy laminates. Excellent electrical insulation, high strength, good dimensional stability. Very abrasive on tools (use carbide!). Used for electrical insulators, circuit boards, jigs/fixtures.
- Carbon Fiber Reinforced Polymers (CFRP): Very high strength-to-weight, stiffness. Extremely abrasive. Requires specialized tooling and processes. Used in aerospace, high-performance automotive, sporting goods.
How to Choose the Right CNC Machining Material
A Step-by-Step User Guide：
- Define the Application Requirements
- Will the part bear a load?
- Will it be exposed to moisture, chemicals, or high temperatures?
- Does it need to be food-grade, biocompatible, or conductive?
- Consider Budget Constraints Some materials (like titanium or PEEK) offer great performance but are expensive to machine.
- Review Machining Capabilities Check if your supplier can machine the material efficiently without excessive tool wear or extended lead times.
- Ask for Expert Input Your CNC supplier likely has experience with similar applications and can suggest ideal material alternatives.
- Prototype First Consider using lower-cost materials like ABS or 6061 aluminum for early prototypes.
Recommendations from Topfast designers and engineers
- Prioritize Machinability for Cost: If high strength isn’t critical, easier-to-machine materials (like Aluminum 6061 or Acetal) significantly reduce production time and cost.
- Consider Substitutes: Can a lower-cost or more readily available material meet the core requirements? (e.g., 303 SS instead of 304 for better machinability if corrosion resistance allows).
- Avoid Over-Engineering: Don’t specify Inconel if 304 Stainless will suffice. Match the material to the actual operating conditions.
- Think About Scrap: Highly expensive materials generate costly scrap from machining chips. Factor this in.
- Consult Your Machinist Early: Discuss your requirements and potential material choices with your CNC machining partner during design. Their expertise can prevent manufacturability issues and suggest cost-saving alternatives.
Final Thoughts
Material selection is not just a technical decision—it’s a strategic one. The right choice leads to better performance, lower production costs, and a more efficient CNC machining process. If you’re unsure, talk to your CNC machining partner early in the design process. This can help you improve both functionality and manufacturability.
If you’d like assistance selecting the right material for your next CNC project, contact us today — our team is here to help you make the smartest choice.
