Right materials make the best applications.
Material selection is a crucial step to get your CNC project right. Think of it as assembling a Subway meal based on your diet plan; you add meats if your diet chart asks for more protein, and greens for a vitamin fulfill. Similarly, selected materials must cover your design prerequisites— hardness, rigidity, thermal stability, and chemical resistance just to name a few. And your budget as well, of course.
Material characteristics are especially important when you require high precision CNC machined parts with complex designs. For instance: amorphous materials like metallic glass and polymers generally hold tighter tolerances than, say, aluminum.
In the following article, we will elaborate more on material types, their characteristics, tips and guidelines on choosing the right materials, and more. Let’s start with the basic: the material selection process.
CNC Materials Selection Process
If you’ve decided to jump the CNC machining wagon, have a valid prototype handy and your budget figured out, it’s time to select the best suitable materials for your project. The basic three steps to material selection are:
Step 1. Define your material requirements: Based on your design, make a high-level list of material prerequisites. Do you need a malleability? Or perhaps a sturdier material? Laser polishing for a surface finish? Consider all the mechanical, physical, environmental, and budget factors.
Step 2. Pin down qualified materials: Identify potential candidates that fulfill your material requirements. Notice, we’re are focusing on ‘candidates’ not ‘candidate’. There’s a solid reason behind it. Have a look:
Here’s what Ronald E. Giachetti, of National Institute of Standards and Technology, wrote in his paper on Manufacturing Process and Material Selection During Conceptual Design:
“The material and manufacturing process selection is performed early in the product development process. At this stage, it is inappropriate to select a single material or process without evaluating all the alternatives. The selection of sets of possible candidate materials and processes allow for greater flexibility in the product development process. The more alternatives, the greater the manufacturing flexibility.”
| Hack: Make sure you approach readily available materials— it’ll help cut costs and efforts. |
Step 3. Now, select the most appropriate material: The third step is the final showdown: choosing the material with maximum functionality in minimum costs. Or, the materials that check most on your prerequisites list.
In the next section, we will talk about the most popular materials and their properties.
CNC Material Selection- Guidelines
Metals
Most common metals in the CNC machining universe are:
1. Aluminum
Most popular of the bunch; used for both mechanical and aspect components.
(a) Physical properties:
● Medium physical strength (<500 MPa) (Note: Aluminium 7075 is one of the strongest metals at >500 MPa; but it’s a bit pricey)
● Corrosion resistance
● Temperature resistance (<400°C)
(b) Mechanical properties:
● High machinability. Can be machined quicker than other metals
● Readily available; inexpensive
(c) Industries:
● Automotive ( gears and shafts etc.)
● Aerospace (aircraft fittings etc.)
● Healthcare (medical equipment)
● Consumer electronics (electronic housings)
2. Cold Rolled Steel
(a) Physical properties:
● High physical strength (Increases the strength of the finished product by 20%)
● Provides perfect precision as it creates smaller products
● Can handle tighter tolerances
(b) Mechanical properties:
● Medium machinability.
● Moderately expensive
(c) Industries:
● Manufacturing (Machinery parts)
● Aerospace (aircraft fittings etc.)
● Construction
● Consumer electronics (electronic housings, Jigs & fixtures)
3. Stainless Steel
(a) Physical properties:
● Hardness
● Chemical resistance
● High strength (>500 MPa)
● Temperature resistance ( Very high >500°C)
● Corrosion resistance
(b) Mechanical properties:
● Good machinability
● Inexpensive
(c) Industries:
● Automotive
● Aerospace (aircraft fittings etc.)
● Healthcare (surgical equipment)
● Consumer electronics (electronic housings)
● Food Industry
● Marine applications
● Chemical Processing
● Marine applications
4. Brass
Used for high volume applications.
(a) Physical properties:
● Medium strength
● Natural Corrosion resistance
● Low-Temperature resistance (<250°C)
● High tensile strength
(b) Mechanical properties:
● High machinability.
● Readily available; moderately expensive
(c) Industries:
● Automotive ( mechanical parts, valves & nozzles)
● Architecture
● Healthcare (medical equipment
● Consumer goods
● Electrical hardware
Exotic alloys
1. Inconel
(a) Physical properties:
● Temperature resistance
● Corrosion resistance
● Medium strength
(b) Mechanical properties:
● Moderate machinability
● Moderately expensive
(c) Industries:
● Automotive
● Aerospace
● Healthcare
● Consumer electronics
2. Copper
(a) Physical properties:
● Highest electric conductivity
● High corrosion resistance
● Thermal conductivity
● Low chemical resistance (especially to acids, halogens sulphides, and ammonia solutions)
(b) Mechanical properties:
● High machinability. Can be machined quicker than other metals
● Readily available; moderately expensive
(c) Industries:
● Automotive (cooling systems and heat exchanger, valves and radiators etc)
● Aerospace Healthcare (medical equipment)
● Consumer electronics (electronic housings)
Outside of this wide range of metal materials, it’s also possible to use plastics, wood, and even fiberglass and foams with CNC machining technology.
Plastics
1. PVC
(a) Physical properties:
● High strength
● Corrosion resistance
● Temperature resistance
● Chemical resistance
(b) Mechanical properties:
● High machinability
● Readily available; inexpensive
(c) Industries:
● Automotive
● Aerospace
● Healthcare
● Consumer electronics
● Food Industry
● Chemical
2. Nylon
(a) Physical properties:
● High physical strength
● Good impact strength
● High corrosion and abrasion strength
(b) Mechanical properties:
● High machinability. Can be machined quicker than other metals
● Readily available; inexpensive
(c) Industries:
● Automotive (insulators, bearings)
● Aerospace
● Healthcare
● Consumer electronics
Now that you know about different materials, you can select the ones that best suit your CNC project. We, at Machining Design Associated Ltd., offer exceptional CNC machining parts with desired tolerances. Get in touch to know more!
Frequently Asked Questions
What properties are most critical in CNC material selection?
The most critical properties include strength, stiffness, hardness, density, thermal stability, machinability, corrosion resistance, and surface finish requirements. You must match these properties to your part’s function and operating conditions.
Can I prototype with a different material and switch for production?
Yes, you can prototype in a more cost-effective or machinable material (e.g. aluminum) and then move to a higher performance one (e.g. stainless) for production. Be careful of differences in thermal expansion, strength, and behavior that may impact dimensions or performance.
How do material cost and availability affect the decision?
Even if a material meets performance needs, high cost or long lead time can make it impractical. Always factor in raw material availability, supplier reliability, and batch costs when narrowing your choices.
Are plastics ever a better choice over metals in CNC machining?
Yes – plastics (like POM, ABS, Nylon, Delrin) can outperform metals when weight, chemical resistance, insulation, or damping properties are priorities. They’re also easier to machine, but typically offer lower strength and thermal stability than metals.
How can I test if a material choice is viable before full production?
You can run a small prototype or pilot batch, measuring parameters such as dimensional accuracy, surface finish, tool wear, thermal distortions, and environmental performance. Use the results to validate or adjust your material choice before scaling.