Choosing the Right Material for Your CNC Machining Project

Previously published on fastradius.com on November 18, 2020

Computer Numerical Control (CNC) machining is a versatile, high-precision traditional manufacturing process that’s ideal for medium to high-volume production runs of complex parts. CNC machining is a subtractive process, meaning the machine whittles away at a solid block of material to create the finished part — rather than gradually depositing material, as is seen in additive manufacturing methods. With CNC machining, manufacturers can rapidly produce prototypes and durable parts for specific applications.

Material selection is an incredibly important part of any manufacturing process, but engineers and product teams must be especially diligent when it comes to selecting materials for CNC machining. Since this process is compatible with a wide variety of materials — from metal to fiberglass to wood — it’s easy to mistakenly choose a material that’s sufficient for the project but not the best-suited. In this article, we’ll touch on key considerations for CNC machining material selection and give an overview of some common options.

Key Considerations for Choosing CNC Machining Materials

Before getting into the particulars of material selection, product teams must first take stock of their project requirements. Start by considering these four questions:

1. How will the part be used?

Engineers must consider their part’s end-use and where it will be used, as these factors will have a significant impact on material selection. For example, stainless steel and carbon steel are both suitable for CNC machining, but only stainless steel is naturally corrosion-resistant. Choosing the wrong kind of steel here would compromise a part’s longevity. FDA, FAA, as well as any industry-specific regulations should also be top of mind.

2. Does weight matter?

If a part must be light — a common requirement when manufacturing for automotive and aerospace applications — there are plenty of low-density metal options available. Manufacturers might also consider using a plastic like ABS to keep weight down if they’re willing to sacrifice strength.

3. Does the part require high strength or heat resistance?

Strength can be measured in many different ways (tensile strength, wear-resistance, etc.), so engineers should determine what kind of strength — and to what degree it matters — is required for their part. These parameters will impact the size of the pool of viable materials. Similarly, temperature requirements will exclude certain materials from the outset. Engineers should also think about whether their part will be exposed to fluctuating temperatures, as nearly all materials expand or contract in response to temperature changes.

4. What is the project budget?

Material costs almost always influence material selection. The goal of most product teams is to select a material that maximizes desired material properties and performance while minimizing expenditure. Material costs are especially important when it comes to CNC machining because this process produces a relatively large amount of scrap material behind. Some materials — such as specialty metals — are extremely expensive, which could have a major impact on the cost-efficiency of the entire project, considering scrap material output. Engineers should carefully evaluate their budget before making any final decisions.

5 Common CNC Machining Materials

Since any material — metal or plastic — that’s hard enough for machining can be used for CNC manufacturing, product teams are spoiled for choice. This short list provides a quick gloss of some of the most common materials used in CNC manufacturing today.

1. Aluminum

Aluminum alloys are easy to machine in large volumes, have a good strength-to-weight ratio, and high thermal and electrical conductivity. They are also naturally resistant to corrosion. Aluminum 6061 is an all-purpose aluminum alloy often used for CNC machining. It is typically found in automotive parts, bike parts, sporting goods, and other recreational items. This material is highly machinable; however, it can be pricier than other metals and doesn’t hold up well in the presence of saltwater or certain chemicals. Aluminum 7075 is a step up from 6061. Ideal for aerospace frames and high-performance recreational equipment, it’s the strongest commercially available aluminum alloy.

2. Stainless Steel

Stainless steel alloys are strong and resistant to distortion, wear, and corrosion. 303 stainless steel includes sulfur for improved machinability, but this material has a number of limitations that engineers must keep in mind.

303 cannot be cold-formed, heat-treated, or welded, and special care must be taken with speed/feeds and the sharpness of cutting tools during CNC manufacturing. That said, 303 makes excellent nuts, bolts, non-marine grade fittings, shafts, and gears.

304 stainless steel is a non-magnetic, all-purpose steel for CNC machining known for its toughness. It’s readily machinable and corrosion-resistant like 303, but it can be welded. 304 is well-suited for a wide range of consumer and industrial applications, kitchen accessories, tanks and pipes, architecture, and more. 316 stainless steel is even more corrosion-resistant than 304 or 303 thanks to the addition of molybdenum. It’s strong, weldable, and one of the few marine grade stainless steels.

Since it’s impossible to tell stainless steels apart by sight alone, engineers should make sure to test the raw material to confirm the characteristics of the steel they’re using.

3. Carbon Steel

Carbon steel 1045 is a mild grade of carbon steel. Manufacturers often machine with this material because it is less expensive than most stainless steels but stronger and tougher. 1045 is easy to machine, weldable, and can be hardened or heat-treated to achieve various hardnesses.

This material is ideal for nuts, bolts, gears, shafts, connecting rods, and other strong, small mechanical parts. 1045 can also be used for architectural applications, but it must be surface-treated to prevent rust and corrosion.

4. Titanium

Known for its high strength, toughness, and corrosion resistance, titanium is often employed to manufacture parts for the most demanding aerospace, military, and industrial applications. This material is also biocompatible and suitable for use in medical device manufacturing.

However, titanium is more expensive than any other metal in its commercial form, doesn’t polish well, and is a poor conductor of electricity. Engineers should also be aware that titanium is challenging to machine, and requires special cutters.

5. Nylon

Nylon is an all-purpose, low-friction thermoplastic that is often used as an alternative to metal in CNC-manufactured parts. This material is stiff, strong, impact-resistant, chemical-resistant, but surprisingly elastic. Nylon responds well to additives and fillers, so engineers can feel free to manipulate this material to achieve their desired properties.

Popular applications for nylon include electrical molding, fuel system components, gears, food packaging, fabric, and more. However, nylon absorbs moisture easily, which may negatively impact the dimensional stability of a part.

Tap Into Expert Advice on Material Selection

This isn’t an exhaustive list, but it’s clear to see that CNC machining is an extremely versatile manufacturing process that requires thorough evaluation of project requirements in order to select a material best-suited for the part in question. Still, achieving the ideal balance of cost, quality, and time can be challenging.

With a trusted on-demand manufacturing partner like SyBridge, material selection is made easy. Our manufacturing experts have years of experience guiding product teams through the entire product development and production processes, starting with design and material selection. Let’s make something incredible together — contact us to get started.

Polyoxymethylene (POM), more commonly known as acetal or its branded name Delrin®, is an engineering plastic offering low friction, high stiffness, and excellent dimensional stability. Polyoxymethylene is a category of thermoplastics and includes many different formulations of the material, all of which vary slightly. As such, it’s important to learn as much as you can about each type before choosing one for your next project. Delrin® is a semi-crystalline engineering-grade thermoplastic widely used to create highly precise parts. In general, Delrin® provides impressive dimensional stability and sliding properties. It’s known for its high strength, wide operating temperature range (-40°C to 120°C), and excellent mechanical properties. Here’s everything you need to know about this material, from how it’s made to its best-fit applications. Inside the polyoxymethylene production process Acetal was first discovered by German chemist Hermann Staudinger in 1920 before it was commercially synthesized by research chemists at DuPont, the original manufacturers of Delrin® plastic, in 1956. Like all other plastics, acetal is created by distilling hydrocarbon fuels down into lighter groups called “fractions,” which can then be combined with other catalysts via polymerization or polycondensation to produce a finished plastic. To make an acetal homopolymer like Delrin®, anhydrous formaldehyde must be generated by causing a reaction between aqueous formaldehyde and alcohol to form a hemiformal. The hemiformal is then heated to release the formaldehyde, and the formaldehyde is polymerized by anionic catalysis. The resulting polymer is stabilized when it reacts with acetic anhydride, which creates polyoxymethylene homopolymer. Acetal comes in many different commercial varieties and formulations, each with its own advantages and disadvantages. For example, Delrin® 500 is medium-viscosity, all-purpose polyoxymethylene that has a good balance of flow and physical properties. It can be used to produce parts via CNC machining and injection molding and is frequently used to manufacture mechanical parts, fuel systems, and fasteners. Delrin® 1700P, on the other hand, is a very low- viscosity, fast-molding resin that is best suited for parts with complex shapes, thin walls, long flow paths, or multi-cavity tools. It also offers the best molding thermal stability for deposit-free molding in demanding conditions. Since there are dozens of different formulations of acetal, it’s important to do your research and make sure your prospective plastic offers all of the properties you need for your application. Delrin® plastic properties and mechanical specifications small black Delrin pieces Delrin® can also be found in all-purpose industrial equipment like bearings, gears, pumps, and meters. Acetal’s excellent mechanical properties make it extremely versatile, offering a unique blend of properties that you won’t find in most metals or other plastics. Delrin® plastic is strong, rigid, and resistant to impact, creep, abrasion, friction, and fatigue. It’s also well known for its excellent dimensional stability during high-precision machining. Acetal can also stand up to moisture, gasoline, solvents, and a wide range of other neutral chemicals at room temperature. From a design standpoint, parts made with extruded POM naturally have a glossy surface finish. Since acetal is compatible with CNC machining, injection molding, extrusion, compression molding, rotational casting, and more, product teams are free to choose the manufacturing process that works best for their budget and their needs. However, it’s worth noting that Delrin® plastic is typically very challenging to bond. Acetal material properties vary by formulation, but the mechanical properties for Delrin® 100 NC010, one of the most popular formulations, include: Tensile modulus: 2900 MPa Yield stress: 71 MPa Yield strain: 26% Density: 1420 kg/m3 Charpy notched impact strength, +23°C: 15 kJ/m2 Coefficient of linear thermal expansion, normal: 110 E-6/K Water absorption: 0.9% Delrin® does have a few limitations. For instance, even though Delrin® is resistant to many chemicals and solvents, it’s not very resistant to strong acids, oxidizing agents, or UV radiation. Prolonged exposure to radiation can warp the color and cause the part to lose its strength. Also, this material isn’t readily available in a flame-retardant grade, which limits its utility for certain high-temperature applications. Why choose Delrin® plastic? These limitations notwithstanding, there are many reasons to choose acetal over other materials. When compared to other plastics, acetal offers better creep, impact, and chemical resistance, better dimensional stability, and higher strength. It also has a lower coefficient of friction. Acetal outpaces certain metals as well. Parts built with this material have a higher strength-to-weight ratio, better corrosion resistance, and offer more opportunities for part consolidation. You can build thinner and lighter parts faster and at a lower price point with acetal than with a comparable metal. Delrin® plastic can be found in almost every major manufacturing sector. In the automotive industry, common applications include heavy load-bearing gears, fuel system components, loudspeaker grilles, and safety system components like seatbelt hardware. Delrin® can also be found in all-purpose industrial equipment like bearings, gears, pumps, and meters. In the consumer goods and appliances space, this material can be used to make anything from zippers and pens to knife handles and lawn sprinklers. Getting started with Delrin® There’s a lot for product teams to love about Delrin®. It’s strong, stable, versatile, and its excellent mechanical properties make it a good choice for a wide variety of applications in a number of industries. However, with dozens of different formulations of acetal on the market, it can be very challenging to determine which one might be the best fit for your unique project. A seasoned manufacturing partner can help demystify the material selection process. When you partner with Fast Radius, you partner with a team of on-demand manufacturing experts who have years of experience helping product teams navigate material selection. We’re well-versed in the wide range of materials that can be used for both traditional and additive manufacturing — including Delrin®. Once you’ve selected the Delrin® formulation that’s the right fit for your application, our team of experts can help facilitate the entire manufacturing process — from design and prototyping to production and fulfillment. With a full suite of manufacturing services including CNC machining and injection molding, Fast Radius can bring your vision to life quickly and easily. Contact us today to get started.

Choosing the Right Material for Your CNC Machining Project