Choosing the Best Materials for Low-Volume CNC Milling

Choosing the right material for low-volume CNC milling is important. It affects the part’s durability, cost, machining time, and overall performance. Unlike high-volume production, where material costs can be spread across thousands of parts, low-volume projects need a balance between quality and affordability. The wrong choice can lead to excessive wear on tools, increased waste, or parts that fail to meet requirements.

Different materials have unique properties that influence machinability, strength, and surface finish. Some are easy to cut but may lack durability, while others are tough but demand specialized tooling. This guide will help you navigate the best material choices for low-volume CNC milling. 

What to Consider When Choosing Materials for Low-Volume CNC Milling?

Below are key aspects to consider before selecting materials for low-volume CNC milling: 

Machinability

Machinability refers to how easily a material can be cut, drilled, and shaped using CNC machines. Materials with high machinability reduce tool wear, speed up production, and lower overall costs. Aluminum, brass, and certain plastics like ABS and acrylic are some of the easiest materials to machine, allowing for smooth cutting and minimal tool changes. 

In contrast, stainless steel, titanium, and hardened alloys require slower cutting speeds, specialized tooling, and efficient cooling systems to prevent overheating and tool breakage. For low-volume production, choosing an easy-to-machine material can improve efficiency and reduce costs, especially when production time and tool longevity are key concerns. Comparing metal vs plastic machining can help in choosing the most efficient material for production.

Strength and Durability

CNC milling materials should meet the mechanical demands of the final product. Strength, impact resistance, and long-term durability must be considered based on how the part will be used. Steel and titanium provide exceptional strength and are suitable for high-stress applications where durability is critical. However, they can be difficult to machine and may not be necessary for less demanding applications. Aluminum offers a great balance between strength and weight, making it popular in industries like aerospace and automotive. 

Plastics such as PEEK and nylon are excellent alternatives for applications that require flexibility, toughness, and wear resistance without the added weight of metals. Selecting a material that aligns with the functional demands of the part ensures long-term reliability without unnecessary machining difficulties.

Surface Finish and Post-Processing

Some materials naturally produce a smooth finish, while others require additional finishing steps such as polishing, anodizing, or coating. Aluminum and brass, for example, can be machined to a highly reflective finish with minimal effort, making them ideal for applications where aesthetics matter. Stainless steel, on the other hand, often requires polishing or passivation to remove machining marks and enhance its corrosion resistance. The need for post-processing can impact production time and costs, so it’s important to choose a material that meets the required finish quality without excessive extra steps. If the part needs to be coated or anodized, selecting a material that is compatible with those treatments will ensure durability and a professional appearance.

Cost-Effectiveness

Material costs play a significant role in low-volume CNC milling since smaller production runs don’t benefit from bulk-order discounts. Choosing an expensive material for a short run can drive up costs unnecessarily. Aluminum, mild steel, and certain plastics are more affordable and offer good machinability, making them ideal choices for budget-conscious projects. Titanium, carbon fiber, and specialty alloys are more expensive due to their properties and machining challenges. 

In some cases, a lower-cost material with similar characteristics can achieve the same performance without the added expense. Balancing cost and functionality is key to ensuring a cost-effective manufacturing process without compromising quality.

Thermal and Chemical Resistance

If the final part will be exposed to extreme temperatures, moisture, or chemicals, material selection becomes even more critical. Titanium and Inconel are excellent choices for high-temperature applications since they maintain their strength even under extreme heat. Stainless steel and aluminum resist corrosion, making them ideal for humid or chemical-heavy environments. Certain plastics, such as PTFE and PEEK, offer excellent chemical resistance, making them suitable for applications in medical and industrial settings. 

Choosing a material that can withstand its working conditions prevents premature failure, ensuring long-term reliability and reducing the need for frequent replacements.

Weight Considerations

In industries like aerospace, automotive, and robotics, reducing weight is essential for improving efficiency and performance. Aluminum, magnesium, and carbon fiber composites offer strong yet lightweight solutions, making them popular for applications where weight reduction is a priority. Steel and titanium, while incredibly strong, are significantly heavier, which can be a disadvantage in projects where minimizing weight is crucial. 

Choosing a material that provides the necessary strength without adding unnecessary mass ensures optimal performance and efficiency in the final product.

Common Metal Alloys (Aluminum 6061 vs 7075, Stainless steel and titanium.)

Selecting the right metal alloy for low-volume CNC milling depends on the application, required strength, machinability, and cost. Aluminum, stainless steel, and titanium are among the most commonly used materials, each offering unique advantages. Understanding their differences helps in choosing the best option for a specific project.

Aluminum 6061 vs. 7075

Aluminum is widely used in CNC milling due to its lightweight nature, excellent machinability, and corrosion resistance. Among the different aluminum alloys, 6061 and 7075 are the most common.

Aluminum 6061 is known for its versatility. It offers a good balance of strength, corrosion resistance, and affordability. It is easy to machine and weld, making it a popular choice for structural components, automotive parts, and general-purpose applications. Its strength is lower compared to 7075, but its resistance to corrosion makes it a better choice for outdoor and marine environments.

Aluminum 7075, on the other hand, is significantly stronger and more rigid, often used in aerospace and high-performance applications where strength-to-weight ratio is crucial. However, it is harder to machine than 6061 and is more susceptible to corrosion, requiring protective coatings or anodizing in certain environments. While it is an excellent choice for parts that need maximum strength, its higher cost and lower machinability make it less ideal for general-purpose projects.

Stainless Steel

Stainless steel is chosen for applications that require strength, corrosion resistance, and durability. It is commonly used in medical, aerospace, and industrial settings where exposure to moisture or chemicals is a concern. There are various grades of stainless steel, with 304 and 316 being the most widely used.

Stainless steel 304 is the most common type, offering good corrosion resistance and mechanical properties. It is easy to clean and suitable for food, medical, and decorative applications. However, it is not as strong as some other stainless steel grades and can be challenging to machine due to its toughness.

Stainless steel 316 provides even better corrosion resistance, particularly in harsh environments with exposure to saltwater or chemicals. It is often used in marine, medical, and chemical processing applications. While stronger and more resistant to corrosion than 304, it is also more expensive and harder to machine, requiring specialized tools and cutting techniques.

Titanium

Titanium is an exceptional material known for its high strength, lightweight properties, and excellent corrosion resistance. It is commonly used in aerospace, medical implants, and high-performance automotive parts. Despite its advantages, titanium is one of the most challenging metals to machine. Its toughness generates significant heat during cutting, leading to rapid tool wear and the need for specialized machining techniques. Additionally, titanium is more expensive than both aluminum and stainless steel, making it a better choice for applications where strength and weight reduction are critical rather than cost-sensitive projects.

When choosing between aluminum, stainless steel, and titanium for low-volume CNC milling, the decision should be based on the specific needs of the application. Aluminum 6061 is an affordable and versatile option, while 7075 provides extra strength for demanding applications. Stainless steel offers durability and corrosion resistance but can be tougher to machine. Titanium excels in strength and weight reduction but comes at a higher cost and machining difficulty.

Engineering plastics (PEEK, Delrin)

Engineering plastics are an excellent alternative to metals in CNC milling, especially for applications that require lightweight, chemical resistance, or electrical insulation. Two of the most commonly used high-performance plastics are PEEK and Delrin. Each offers unique properties that make them suitable for different applications.

PEEK (Polyether Ether Ketone)

PEEK is a high-performance thermoplastic known for its exceptional strength, heat resistance, and chemical stability. It is often used in aerospace, medical, and industrial applications where metal replacement is necessary. Unlike many other plastics, PEEK can withstand continuous exposure to high temperatures—up to 250°C—without losing its mechanical properties. It is also highly resistant to chemicals, moisture, and wear, making it ideal for demanding environments such as medical implants, aerospace components, and automotive parts.

Despite its advantages, PEEK is more expensive than other plastics and requires precise machining due to its toughness. It tends to produce fine dust when milled, requiring proper ventilation and cutting strategies. However, its durability and long lifespan make it a cost-effective choice for applications that demand high performance.

Delrin (Acetal, POM)

Delrin, also known as acetal or polyoxymethylene (POM), is a versatile engineering plastic widely used in CNC machining due to its excellent machinability, low friction, and high dimensional stability. It is often chosen for mechanical components such as gears, bushings, and precision parts where smooth movement and minimal wear are required. Unlike PEEK, Delrin is easier to machine and produces clean, precise cuts, making it a preferred choice for prototyping and low-volume production.

Delrin also offers good resistance to moisture and chemicals, but it is not as heat-resistant as PEEK. It can withstand moderate temperatures but softens under extreme heat, making it unsuitable for high-temperature environments. Additionally, while Delrin has excellent impact resistance and mechanical strength, it is not as strong as metal or PEEK, so it may not be the best option for heavy-load applications. A CNC milling service can optimize cutting techniques for smooth, precise results.

Conclusion 

Choosing the right material for low-volume CNC milling is essential for achieving the desired balance of performance, cost, and machinability. Metals like aluminum, stainless steel, and titanium offer strength and durability, with aluminum being the most cost-effective and easiest to machine. Stainless steel provides superior corrosion resistance, while titanium is ideal for high-performance applications requiring strength and lightweight properties.

For applications where weight reduction, chemical resistance, or electrical insulation is necessary, engineering plastics like PEEK and Delrin provide excellent alternatives. PEEK offers high heat resistance and durability but comes at a higher cost, while Delrin is easier to machine and suitable for precision components requiring low friction and dimensional stability.

Ultimately, the best material choice depends on the specific requirements of the project. By considering factors such as machinability, strength, surface finish, cost, and environmental resistance, manufacturers can optimize their material selection for efficient and high-quality CNC milling, even in low-volume production runs.