1. Introduction
CNC Machining is a high-precision manufacturing process that removes material from a solid workpiece to create tight-tolerance, structurally sound, and highly durable parts. It is widely used in aerospace, medical, automotive, and industrial applications, where material selection is critical to performance, cost, and manufacturability.
Unlike 3D printing or thermoforming, machining requires materials that can withstand cutting, milling, drilling, and turning without excessive wear, distortion, or failure. This white paper explores the best machinable metals and plastics, comparing their mechanical properties, cost, and ease of machining to help manufacturers optimize material selection for their applications.
2. Machining Metals: Strength, Durability, and Precision
Metal machining is ideal for high-strength components requiring exceptional durability, heat resistance, and corrosion protection. The choice of metal depends on application requirements, cost, and machinability.
2.1 Aluminum: Lightweight and Highly Machinable
Aluminum is one of the most commonly machined metals due to its high strength-to-weight ratio, corrosion resistance, and ease of machining. It is widely used in aerospace, automotive, and structural applications.
- 6061 Aluminum: Highly machinable, corrosion-resistant, and weldable, making it suitable for automotive and aerospace components, structural parts, and consumer goods.
- 7075 Aluminum: Stronger than 6061 but less corrosion-resistant. Used in high-strength aerospace parts, sports equipment, and military-grade applications.
Machinability: Excellent. Aluminum produces low cutting forces and minimal tool wear, making it one of the fastest and most cost-effective metals to machine.
Cost: Moderate. Aluminum is more affordable than titanium or stainless steel, but high-strength grades like 7075 are more expensive.
2.2 Stainless Steel: Corrosion Resistance with Strength
Stainless steel is widely used in medical, food-processing, marine, and industrial applications due to its high strength, corrosion resistance, and temperature stability.
- 303 Stainless Steel: Easiest stainless steel to machine due to sulfur content, used in fasteners, fittings, and precision components.
- 304 Stainless Steel: Standard corrosion-resistant grade used in kitchenware, medical devices, and industrial equipment.
- 316 Stainless Steel: Superior corrosion resistance, ideal for marine, chemical, and medical applications.
- 17-4 PH Stainless Steel: Hardenable stainless steel with exceptional strength and wear resistance, often used in aerospace, defense, and high-load industrial parts.
Machinability: Moderate to difficult. 303 stainless steel is the easiest to machine, while 316 and 17-4 PH require advanced tooling and slow feed rates.
Cost: High. Stainless steel is more expensive than carbon steel and aluminum, but its longevity and corrosion resistance can justify the investment.
2.3 Carbon Steel: Affordable Strength for Industrial Use
Carbon steel is widely used in industrial machinery, structural applications, and tools due to its high strength, affordability, and ease of heat treatment.
- 1018 Carbon Steel: Low-cost, mild steel with excellent machinability, used for shafts, gears, and general-purpose components.
- 1045 Carbon Steel: Medium-carbon steel with higher hardness and strength, used for machine parts, gears, and structural applications.
- 12L14 Carbon Steel: Leaded free-machining steel, offering exceptional machinability for high-volume production.
Machinability: Excellent for 12L14 and 1018; moderate for 1045. Carbon steel machines faster than stainless steel but requires protective coatings to prevent rust.
Cost: Low to moderate. More affordable than aluminum or stainless steel, but requires post-processing to prevent corrosion.
2.4 Titanium: High-Strength, Low-Weight Performance
Titanium is stronger than steel but 45% lighter, making it a premium material for aerospace, medical implants, and high-performance automotive parts.
- Grade 2 Titanium: Excellent corrosion resistance, used in chemical processing and marine applications.
- Grade 5 Titanium (Ti-6Al-4V): Stronger and more wear-resistant, used in aircraft, medical implants, and racing components.
Machinability: Difficult. Titanium generates high cutting forces and heat, requiring slow cutting speeds and specialized tooling to avoid tool wear and deformation.
Cost: Very high. Titanium is more expensive than aluminum and steel, with higher machining costs due to tool wear and slow processing speeds.
3. Machining Plastics: Lightweight, Wear-Resistant, and Chemical Stability
Plastics are often machined for lightweight, non-conductive, or chemically resistant applications where metals are too heavy or reactive.
3.1 Delrin (Acetal/POM): Low-Friction and Wear-Resistant
Delrin is a high-performance plastic known for its low friction, strength, and dimensional stability. It is commonly used for gears, bearings, and precision mechanical components.
Machinability: Excellent. Delrin cuts easily without melting or excessive tool wear, making it ideal for tight-tolerance components.
Cost: Moderate. More expensive than Nylon and ABS, but superior mechanical properties justify the cost.
3.2 Nylon (PA6, PA66): Impact-Resistant and Self-Lubricating
Nylon is lightweight, strong, and resistant to wear, commonly used for bushings, gears, and industrial parts.
Machinability: Moderate. Nylon tends to absorb moisture, affecting dimensional stability. It also melts easily, requiring sharp tools and low cutting speeds.
Cost: Low. One of the cheapest engineering plastics, making it a cost-effective choice for industrial applications.
3.3 PTFE (Teflon®): Extreme Chemical and Heat Resistance
PTFE is chemically inert and capable of withstanding extreme temperatures, making it ideal for seals, gaskets, and medical components.
Machinability: Difficult. PTFE is soft and can deform easily, requiring sharp tools and precise machining parameters.
Cost: High. PTFE is more expensive than Nylon and Delrin, but necessary for high-heat and chemical applications.
3.4 PEEK (Polyetheretherketone): Aerospace-Grade Performance
PEEK is one of the highest-performance plastics, offering exceptional heat resistance, strength, and chemical stability. It is used in aerospace, medical implants, and high-performance automotive parts.
Machinability: Difficult. PEEK is abrasive and generates heat, requiring coolant and carbide tools for precise machining.
Cost: Very high. PEEK is one of the most expensive plastics, but necessary for extreme applications.
4. Conclusion: Optimizing Material Selection for Machining
Selecting the right material for machining depends on cost, strength, corrosion resistance, and ease of machining.
- For high-strength, lightweight metals, aluminum and titanium are top choices.
- For corrosion-resistant applications, stainless steel and PEEK offer longevity.
- For affordability, carbon steel and nylon provide cost-effective solutions.
- For extreme environments, PTFE and titanium provide unmatched chemical and heat resistance.
At RapidMade, we specialize in precision machining services for metals and plastics, helping businesses select the best materials for durability, performance, and cost efficiency.
For custom machining solutions, visit rapidmade.com or contact [email protected].