The choice of material in CNC machining is one of the most important decisions in the manufacturing process of a CNC milled or turned component. It has far-reaching effects: It determines not only the functionality and performance, but also how efficiently and cost-effectively the component can be manufactured. An ideal-looking part in the CAD model may be uneconomical or even impossible to produce in reality if the material does not match the production parameters. Here is a comprehensive guide to material selection in CNC machining.
Table of contents
Introduction
This guide to materials in CNC machining provides engineers and purchasers with a valuable guide to choosing the right materials. It explains the main material groups, highlights their specific properties and analyzes their impact on cost and manufacturability. This provides a solid basis for optimizing the CNC part, from initial design to series production.
The experts at FACTUREE are also on hand to advise you on the best material decision for your specific project. Together, we examine the decisive criteria - such as mechanical requirements, weight, properties and your budget - to ensure that your component is perfectly designed from the outset.
The most important materials for CNC machining
The materials commonly used for CNC machining can be divided into five main categories: Aluminum alloys, steels, stainless steels, soft metals and plastics. Composite materials and ceramics are also gaining in importance. Each of these groups brings with it a unique set of characteristics and challenges.
1. CNC steel and metalworking
Metals are the cornerstone of CNC machining. Due to their strength, hardness and versatility, they are the preferred material for applications in mechanical engineering and aviation. Here is an overview:
Aluminum alloys
Aluminum is probably the most frequently CNC-machined metal. It is characterized by a high strength-to-weight ratio, excellent corrosion resistance and outstanding machinability.
- Aluminum 6061 (Al-Mg1SiCu): As a universally applicable alloy, it offers a balanced combination of medium strength, good weldability and high resistance to corrosion. This makes it ideal for a wide range of applications, such as general construction parts, vehicle components and bicycle frames. With a tensile strength of up to 290MPa and a density of 2.70g/cm3, it is a cost-effective choice for projects that do not require the highest strength.
- Aluminum 7075 (Al-Zn6MgCu): is characterized by its exceptional strength, toughness and fatigue resistance. With a density of only 2.81 g/cm³, it is one of the lightest and at the same time strongest commercially available aluminum alloys. Its tensile strength of up to 572MPa is significantly higher than that of 6061, making it the material of choice for high-performance aerospace applications such as aircraft wings and fuselage bulkheads. Machining is more demanding than with 6061, but thanks to its hardness it can be machined precisely without the risk of built-up edges and burrs as with softer aluminum grades.
Steel
Steel is an all-rounder in CNC machining. It offers excellent tensile strength, hardness and durability and is also very cost-effective. They are used in areas where the focus is on high mechanical loads.
- Carbon steels (e.g. C45 AISI 1045): As a "soft" steel grade, C45 is considered to be very cost-effective, easy to machine and easy to weld. It is often used in the automotive and construction industries for car bodies, frames and other components. The typical cutting speed is 70-90 m/min.
- Tool steels (e.g. 1.2842): These alloys are specially designed for their extreme hardness and wear resistance. They are the first choice for the manufacture of tools, machine parts and plastic molds that have to withstand high mechanical loads. The machining of tool steels is demanding due to their hardness and alloying element content and requires special carbide tools and controlled cooling to prevent overheating.
Stainless steel
Stainless steel is indispensable in CNC machining. They are characterized by their inherent corrosion resistance, which is achieved by a chromium content of at least 10 %. This makes them an indispensable material class for applications in the food, chemical and medical technology industries as well as in shipping. The machining of austenitic stainless steels (e.g. 304, 316) is challenging due to their tendency to work harden, as the surface hardens during machining and drastically increases tool wear. The recommended cutting speeds are only 40-60 m/min, which leads to longer machining times.
- Stainless steel 303 (1.4305): This steel is characterized by its excellent machinability, which makes it the ideal choice for large-scale production. Compared to other stainless steels, however, it is less resistant to corrosion.
- Stainless steel 304 (1.4301): As a standard material in manufacturing, this stainless steel offers an ideal combination of high corrosion resistance, solid mechanical properties and excellent weldability. These characteristics make it the preferred choice for applications such as kitchen equipment, pipe systems and sinks.
- Stainless steel 316L (1.4404): Due to its molybdenum additive, it has increased corrosion resistance compared to 304, especially in chloride-containing environments. This property makes it the ideal material for marine and medical applications. However, it is generally more difficult to machine than 304 due to the higher alloy content and costs up to 75 % more raw material.
Non-ferrous metals: brass & copper
Non-ferrous metals such as brass and copper are particularly suitable for CNC machining due to their excellent machinability and specific functional properties.
- Brass: Brass (e.g. MS58) is a very soft material with excellent machinability, which makes it ideal for the production of complex CNC parts. Its high ductility at room temperature and its good soft and hard soldering properties predestine it for applications in automotive and shipbuilding as well as for fittings and connectors.
- Copper: Copper (e.g. C101) is characterized by its excellent electrical and thermal conductivity. This property makes it an indispensable material for electronic components and heat sinks in electrical engineering. With a typical cutting speed of 150-200 m/min, it is very easy to machine, although its ductility can promote the formation of built-up edges.
Titanium
Titanium (e.g. grade 5 / Ti-6Al-4V): This light metal is characterized by an exceptional strength-to-weight ratio. Its outstanding corrosion resistance and biocompatibility make it a key material for demanding applications in aerospace, medical technology and high-performance automotive engineering.
However, machining titanium places high demands on the manufacturing process. Due to the extremely low thermal conductivity of the material, the heat generated is concentrated at the cutting edge of the tool, which leads to extremely rapid wear. To compensate for this, very low cutting speeds (20-30 m/min), special heat-resistant tools and the use of high-pressure coolant are absolutely essential. These combined factors make titanium one of the most expensive materials in CNC machining.
2. plastics: lightweight, versatile and cost-efficient
Plastics have become an established alternative to metals in CNC machining. Their advantages lie in their low weight, their electrical insulation properties, their corrosion resistance and their often excellent machinability.
- ABS: This widely used thermoplastic offers good strength, heat resistance and machinability. ABS is often used for prototypes before injection molding.
- POM (Delrin): This plastic is known for its excellent machinability. POM is very rigid, dimensionally stable, has low friction and water absorption and is therefore ideal for precision parts such as gears and bearings.
- Polycarbonate (PC): An extremely durable thermoplastic that is characterized by a higher impact strength than ABS. Due to its transparency and shatter resistance, it is often used as a substitute for glass.
- PEEK: This high-performance plastic (polyether ether ketone) offers amazing thermal stability and chemical resistance. With its excellent mechanical properties, PEEK can replace metal materials in some applications. A key advantage in medical technology is its biocompatibility and ability to withstand multiple sterilization cycles. However, machining requires special precautions to avoid internal stresses and cracks. For medical applications, dry processing is often necessary in order not to impair biocompatibility
3. specialty and composite materials
Composite materials such as carbon fiber reinforced plastic (CFRP) and glass fiber reinforced plastic (GFRP) are known for their excellent strength-to-weight ratio and high rigidity. They are widely used in the aerospace, automotive and sports equipment industries. However, machining these materials poses a particular challenge: The resulting conductive fine dust can not only be harmful to health, but can also damage sensitive electronics. For this reason, special, enclosed CNC machines with mandatory extraction concepts and compliance with strict guidelines (TRGS 900) are essential.
Comparison of typical materials used in CNC machining
The following table serves as a strategic guide to facilitate the initial material selection for CNC machining.
| Material group | Relative density | Machinability | Relative costs (€/kg) | Main advantage | The challenge of processing |
| Metals | |||||
| Aluminum alloys | Low | Excellent | Low | High strength-to-weight ratio | Heat expansion, burr formation |
| Steels | High | Good to Moderate | Very low | High strength, cost-effective | Rust (carbon steel) |
| Stainless steels | High | Moderate | Medium | Corrosion resistance | Chip removal, curing |
| Soft metals | High | Excellent | Medium | Conductivity, aesthetics | Lower strength |
| Titanium | Low | Moderate to low | High | High strength, biocompatibility | Tool wear, heat dissipation |
| Plastics | |||||
| Standard thermoplastics | Very low | Excellent | Very low | Cost efficiency, lightness | Lower strength, dimensional stability |
| High-performance plastics | Low | Good | High | Extremely high performance | Costs, special process parameters |
| Composite materials | |||||
| CFRP/GRP | Very low | Moderate | High | Extreme stiffness, lightness | Dangerous fine dust, abrasive |
Possible surface finishes and finishing methods*
| Material group | Post-processing method | Main advantage |
| Aluminum alloys | Anodizing | Corrosion protection, aesthetics |
| Polishing | Aesthetics, reflective surface | |
| Powder coating | Robustness, aesthetics | |
| Steel/stainless steel | Passivating | Corrosion resistance |
| Black oxide coating | Aesthetics, light corrosion protection | |
| Polishing | Aesthetics, function (warehouse) | |
| Powder coating | Robustness, aesthetics | |
| Plastics | Polishing | Aesthetics, transparency (e.g. acrylic) |
| General | Glass bead blasting, sand blasting | Cosmetic surface, diffuse texture |
*This is just a selection of possible surface and finishing methods offered by FACTUREE. Here you will find all surface treatments of the online paver.
How to choose the right material: A checklist
Are you unsure which material is right for your component? Use our simple guide to clarify the decisive factors and make the best choice.
What is the main requirement for your component?
[High strength / hardness / wear resistance]
[Low weight (lightweight construction)
[Maximum corrosion / chemical resistance]
[Specific electrical / thermal properties]
[Lowest possible total costs (material + processing)]
In which environment is the component used?
[Indoor, dry, normal temperature]
[Outdoor area, weather / humidity]
[Contact with salt water / aggressive chemicals]
[High or very low temperatures]
What other factors are decisive?
[Fast & cost-effective machining (high machinability)
[Complex geometry with thin walls or deep pockets]
[Particularly high surface quality / decorative look]
[A balanced ratio of all properties]
Your answers will help us to pre-select suitable materials and advise you on the best solution for your project.
Practical examples of material selection from industries
To illustrate the strategic selection of materials, the following case studies from practice are presented.
Case study 1: Aerospace
The aerospace industry places the highest demands on material performance. Here, low weight, extreme strength, fatigue resistance and reliability under extreme conditions (temperature, pressure) are of the utmost importance. Aluminum alloys, especially the high-performance grade. 7075, are the primary material for airframes, wings and fuselage bulkheads due to their high strength-to-weight ratio. Titanium is used for critical engine components and landing gear. High-performance plastics such as PEEK are increasingly being used as a metal substitute for lighter, heat-resistant parts.
Case study 2: Automotive industry
In the automotive industry, material selection is a direct conflict of objectives between cost, functionality and production volume. For car bodies and many structural components, cheaper materials are often used. Carbon steel as it offers a good balance of toughness, strength and cost-effectiveness in mass production. Aluminium alloys are used in weight-sensitive areas such as engine and chassis components. Brass is used in the automotive and marine sectors, as it is characterized by excellent machinability, durability and the possibility of quality-neutral recycling.
Case study 3: Medical technology
Medical technology requires materials that meet the highest standards of precision, durability, biocompatibility and sterilizability. For this reason, in addition to metals such as Titanium also High-performance plastics used.
The high-performance plastic PEEK has established itself as a successful replacement for titanium in the manufacture of implants such as spinal fusion devices. A decisive advantage is the material's biocompatibility, which enables limited contact with skin and tissue and allows it to be used in dental implants and prostheses. In addition, medical-grade PEEK can withstand multiple sterilization cycles without loss of quality, which is of key importance for medical instruments.
Have you found the right material for your project?
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