Selection of CNC Machining Materials - How to Choose the Best Materials for CNC

The right material is crucial for getting the optimal performance of the fabricated parts and products. In this article, we’ll explore various factors influencing material selection and how to choose the best material for CNC machining.

CNC Machining Material Selection Guide

Material selection for CNC machining is a multifaceted process that requires careful consideration of various factors, including cost, applications, material properties, requirements, environmental factors, and more.

CNC Machining (Material) Cost

The cost incurred during the CNC machining process has a significant effect on the selection of materials, as it influences both the initial expenses and the overall production efficiency. High-performance materials, such as titanium and Inconel, often come with higher prices compared to more common options like aluminum or plastics. This disparity arises not only from the material costs themselves but also from the machinability factors. Harder materials tend to lead to increased tool wear and longer machining times, further escalating expenses. Additionally, fluctuating market prices for raw materials can affect project budgets, manufacturers need to balance performance requirements with cost considerations when choosing materials.

Material Costs: Start from the type of materials available. High-performance options like stainless steel or titanium may offer superior mechanical properties but come at a premium. For example, while aluminum is an economical choice for prototypes due to its excellent machinability, it may not provide the strength needed for high-stress applications.
Machining Costs: Consider the complexity of the design. More intricate parts often require specialized equipment and skilled labor, which can significantly raise costs. For instance, if you’re designing a component with complex geometries, using a material like aluminum might be advantageous because it is easier to machine compared to harder materials like stainless steel, which would require more robust tooling.
Performance Requirements: The mechanical properties needed for your application are also different. If your part must withstand high temperatures or corrosive environments, investing in a more expensive material that meets these requirements can be justified. For example, while standard steel might be cheaper, it may not perform adequately under specific conditions, leading to potential failure and increased costs down the line.
Tolerance and Surface Finish: Pay attention to dimensional tolerances and surface finishing requirements. Tighter tolerances often escalate machining costs; therefore, consider whether slight adjustments can be made without compromising functionality. Additionally, intricate surface finishes might necessitate extra machining steps. For example, a polished finish on a part will require more time and resources compared to a standard finish.
Prototype Testing: Before finalizing your material choice, create prototypes using the selected materials. This allows you to test performance and functionality while controlling costs. For instance, if you’re considering a high-cost material for mass production, testing with a less expensive variant can provide insights into whether the investment is warranted.
Market Fluctuations: Be aware of market dynamics that may affect material prices and availability. Additionally, ensure that the materials comply with any relevant industry regulations, which may involve testing or certification processes that can add to costs.

Types of Materials Used in CNC Machining

When selecting a material for CNC machining, consider a range of key factors, including strength and durability, which refers to the material’s ability to withstand stress, wear, and tear; corrosion resistance, or its ability to resist corrosion and chemical reactions; machinability, which is the ease with which the material can be cut, drilled, and shaped; thermal conductivity, or its ability to conduct heat; electrical properties, such as its ability to conduct or insulate electricity; chemical resistance, or its ability to resist chemical reactions and corrosion; biocompatibility, which is its ability to be used in medical applications without causing harm; and finally, cost and availability, which takes into account the material’s cost and availability in the market.
1. Metals:

Aluminum Alloys: Lightweight, excellent thermal conductivity, good machinability, and corrosion resistance. Used in aerospace, automotive, and engineering applications.
Stainless Steel: Corrosion-resistant, high strength, and good machinability. Used in food processing, marine, and industrial applications.
Steel: High strength, toughness, and good weldability. Used in construction, machinery, and automotive applications.
Titanium: High strength-to-weight ratio, corrosion resistance, and biocompatibility. Used in aerospace, medical, and industrial applications.
Brass: Good strength, corrosion resistance, and machinability. Used in plumbing, door hardware, and musical instruments.
Copper: High conductivity, corrosion resistance, and machinability. Used in electrical and electronics applications.

2. Plastics:

ABS: Impact-resistant, scratch-resistant, and good weldability. Used in injection molding, automotive, and marine applications.
Acrylic: Transparent, hard, and resistant to weather and chemicals. Used in transparent applications such as windows and frames.
PC (Polycarbonate): Transparent, durable, and resistant to shattering and heat. Used in food and beverage packaging, medical devices, and construction materials.
PEEK: Tough, rigid, and resistant to chemicals, fatigue, and radiation. Used in medical implants, automotive parts, and electrical components.
PEEK Glass-filled: Sturdy, rigid, and resistant to chemicals and heat. Used in medical devices, automotive parts, and electrical components.
Polypropylene (PP): Low flexural modulus, high elongation, and suitable for molding large-sized products. Used in prototypes and products of PP or PE.
POM / Delrin acetal: Durable, strong, and resistant to wear, creep, and deformation. Used in industrial and mechanical parts such as pumps, valves, and bearings.
PTFE / Teflon: Slippery, resistant to extreme temperatures, and low friction. Used in producing gears, bushings, slide plates, and piston rings.
PVDF / Polyvinylidene fluoride: High strength, chemical resistant, and self-lubricating. Used in electrical insulation, automotive parts, and medical devices.
UHMW PE / Ultra-high-molecular-weight polyethene: Durable, resistant to abrasion and wear, and self-lubricating. Used in applications that require excellent wear resistance and low friction.

CNC Machining Parameters and Environmental Factors

CNC machining parameters and environmental factors significantly influence material selection by determining the suitability and performance of various materials in machining processes. For instance, harder materials such as tool steel or titanium necessitate slower machining speeds and robust cutting tools, which can elevate processing times and costs but often provide enhanced durability for critical applications. Additionally, chip formation plays a crucial role; materials like stainless steel generate long, thin chips that can complicate processing, requiring specialized tools, while cast iron produces shorter, more manageable chips. Tool life is another critical factor, as abrasive materials can lead to rapid wear of cutting tools, necessitating the use of advanced materials or coatings to prolong tool longevity.

Chip Formation: Understand how different materials behave during machining. Materials that produce long, thin chips, like stainless steel, can pose challenges that necessitate specialized tools for chip management. In contrast, materials such as cast iron, which produces shorter, brittle chips, may be easier to handle and process efficiently.
Tool Life: Consider the abrasiveness of the material. For instance, using glass-filled plastics or hardened steel can significantly reduce tool life. Opting for coated cutting tools or advanced materials like tungsten carbide can mitigate wear and extend tool longevity, ultimately reducing costs over time.
Thermal Conductivity: How a material’s thermal properties might affect machining. Materials like titanium retain heat, causing increased wear on tools, while aluminum dissipates heat effectively, allowing for faster machining speeds. Choose materials that align with your machining speed requirements and tool life expectations.
Operating Temperatures: Analyze the operating temperatures your machined parts will encounter. Ensure the materials chosen can withstand these temperatures without melting or deforming. For example, if a component will be used in a high-temperature environment, select materials known for their thermal stability to prevent warping or breakdown.
Required Fastening: If the machined components will serve as fasteners, it’s crucial to select a material that ensures a secure fit. Different materials possess unique properties such as strength and corrosion resistance, which will affect the integrity of fastened connections. Steel is commonly used, but alternatives may be necessary based on specific requirements.
Sustainable Material Choices: In today’s eco-conscious landscape, consider sustainable materials to minimize environmental impact. Recycled metals like aluminum or steel are excellent choices, as are advanced high-temperature alloys and biodegradable plastics. These options not only reduce your carbon footprint but also align with societal demands for responsible manufacturing practices.

Material Properties and End Uses of CNC Machining Parts

The selection of materials for CNC machining is profoundly influenced by the properties of the materials and the specific applications of the machined parts. Key factors such as mechanical performance, environmental resistance, and thermal characteristics dictate which materials are appropriate for a given application. For instance, components subjected to heavy loads or stresses require materials with high strength and durability, such as steel or titanium. Conversely, parts intended for lightweight applications might utilize aluminum or specific plastics that provide adequate strength without excessive weight. Additionally, considerations such as corrosion resistance are critical for parts exposed to harsh environments, which may necessitate materials like stainless steel or specialized plastics. The interplay of these properties ultimately shapes the performance, longevity, and cost-effectiveness of the CNC-machined components.

Mechanical Properties: The part’s required strength, hardness, and ductility. For example, if machining a component for an automotive engine that will face high stress, high-strength steel might be appropriate. In contrast, for a lightweight drone component, aluminum alloys could be suitable due to their favorable strength-to-weight ratio.
Environmental Resistance: Consider where the part will be used (indoors vs. outdoors). Outdoor applications may necessitate corrosion-resistant materials like 316 stainless steel or titanium, while indoor components could use less expensive materials if environmental exposure is minimal.
Thermal Considerations: Assess the thermal requirements of the application. For high-temperature environments, materials such as Inconel or ceramics may be essential. For example, components in aerospace applications often require materials that maintain structural integrity under high temperatures.
Cost and Availability: Cost-effectiveness is a crucial factor. While high-performance materials often yield better results, they can be expensive. For budget-sensitive projects, consider alternatives like coated steels or lower-grade aluminum that still meet performance needs without breaking the bank.
Machinability: Different materials have varying machinability, affecting production efficiency and cost. Materials like aluminum and brass are relatively easy to machine, so they are ideal for high-volume production. On the other hand, harder materials such as titanium may require specialized tooling and longer machining times.
Compatibility with Production Processes: Ensure the selected material is compatible with CNC machining capabilities. Some materials, such as certain plastics, may require specific CNC techniques to achieve the desired finish and tolerances.

How to choose materials based on your application:
For parts like engine mounts, use titanium or high-strength aluminum alloys due to their excellent strength-to-weight ratios and resistance to fatigue. Components such as gearboxes may be made from hardened steel to withstand high stress, while dashboard panels can be machined from ABS plastic for lightweight and aesthetic appeal. Surgical instruments often require biocompatible materials like medical-grade stainless steel or titanium to ensure safety and performance in sensitive applications.

Other Factors to Consider for CNC Material Selection