CNC machining is the automated control of machining tools (drills, lathes, etc.) by means of a programmable computer. Today, CNC machining is widespread and almost dominates the manufacturing sector.

When your company has created a new product design, you might have wanted some prototypes for functionality & market testing of the design and to speed up your new product development cycle. Then, you probably have heard about CNC machining. 

It is a highly accurate and repeatable manufacturing process for prototyping, and small volume production runs in many industries. It is speedy and also fairly cost-effective when compared to other prototyping techniques. In addition, it can process an extensive range of materials, including plastic, metal, ceramic, wood, or composite. Many of these materials can be treated with a variety of surface finishing options in post-processing. 

Materials for CNC Prototyping

Do you need metal with exceptional mechanical properties, such as a titanium alloy? Must the material possess properties that are resistant to corrosion? Is the speed your priority, leading you to choose easy-to-machining materials such as plastic and aluminum? 

The most common material type for CNC machining is the metallic material. Now let's have a general understanding of the most common metal materials and their properties.

1. Brass

Brass has good machinability. It is recognized as one of the easiest and most economical materials to CNC machining. Due to its excellent electrical conductivity, it is widely used for application in consumer electrical hardware, medical equipment. In addition, with the low friction coefficient and high corrosion resistance, it is widely used in engineering and construction field, for products like pipe fitting, bearing, etc. It is even suitable for musical instruments.

2. Aluminum

Perhaps, aluminum is the most widely used material for CNC prototyping. It is a versatile metal and has an excellent strength-to-weight ratio, formability, and natural protection against corrosion. It can be anodized. And it is easy to machining and low-cost. Compared to other metal materials, it is the most economical and quickest option. If you need prototypes of aluminum gears, spline shafts, worm gears, electronic housings, and other similar parts, aluminum may be the best. It is commonly used for construction, marine, aerospace, and automotive industries.

3. Stainless Steel

Stainless steel has high strength, high ductility, excellent wear and corrosion resistance and can be easily welded. Many stainless steel alloys can be heat treated. It is typically used for prototyping parts that require enhanced formability, high stress, and stronger weld. It is highly suited to CNC machining parts of automobile, aircraft, medical devices, and electronics.

4. Alloy Steel

Alloy steel can be heat treated and can also be subject to both direct hardening and case hardening. If you require the CNC machined prototype with excellent performance under high stress, it is an ideal material.

5. Titanium

What makes Titanium a unique material is its high melting point. It has high ductility and good corrosion resistance. It is also excellent in protecting against salt and water. It is a lightweight, but strong and sturdy, mostly used for making aircraft components and medical implants.

In addition to metallic prototypes, plastic prototypes can also be produced through CNC machining. Here are some of the most commonly used plastic materials in CNC prototyping.

1. ABS

ABS is a plastic material with good mechanical properties. It has excellent impact strength, high heat resistance, and good machinability. It is more often used for making the pre-production prototypes of consumer products.

2. Nylon

Nylon is known as polyamide (PA). It has excellent mechanical properties, good impact strength and is highly resistant to chemicals and abrasion, water and moisture, often used for engineering applications, for products including bearings, insulators, etc.

3. POM (Delrin)

POM has the highest machinability among all CNC machining plastics materials. If your CNC machined prototype requires high precision, high toughness, low friction, low water absorption, excellence heat resistance, POM might be a decent option. It is suited to CNC prototyping of mechanical parts.

4. PTFE (Teflon)

PTFE (Teflon) can withstand the temperatures above 200℃. Few plastics can do that. It has outstanding performances of heat & chemical resistance. For the CNC prototype of electrical components, it may be the premium option.

The properties of metal and plastic materials differ greatly. Metals are mainly used for prototypes that require high strength, hardness, and thermal resistance. And plastics are more lightweight. It is often used for applications requiring chemical resistance and electrical insulation.

Factors to Consider

But what material is best suited to your CNC prototype and how to select it? Regardless of your industry, choosing the right materials for CNC machining is of great importance in finalizing your product design and promoting your new product development. As there are so many material options for CNC prototyping, it is highly likely for you to find the most suitable one for your prototyping need. Well, here are some tips on material selection.

1. Where will your prototypes be applied?

In addition to the outstanding and unique properties of materials themselves, the condition in which your CNC machined prototypes be used also has a great impact on the best choice of materials.

The indoor or outdoor uses of your CNC prototype will lead to the differences in the best option of materials. For example, when it is used outdoors, you need to consider the influence of moisture. Then the material you choose should be able to resist the impacts of oxidation, such as rusting. Materials like aluminum, stainless steel or rigid foam have good resistance to moisture and rust. And carbon steel is an appropriate option in this case. Besides, the extreme temperature in the outdoor environment, both high and low, will also eliminate some materials as the best choice.

2. How is the stress load?

Does the application require high stress load? If so, when you are considering which material for your CNC machined prototypes, you should take this factor into account. The material you choose should have the properties of excellent bearing capacity and no deformation.

3. What is the working temperature?

Low, high, and extending temperature will eliminate the options of certain materials. You should locate a material that is steady under the working temperature of your product - that is, it is able to withstand the fluctuations in the working temperature. The materials that show signs of warping, expansion, or break down under the required working temperature of your product should be not considered, even it may be lower in cost, as it may lead to the wrong or inaccurate design verification results. 

In high temperature, some materials cannot hold up well and will deteriorate or distort. For example, if the working temperature of your product is extremely high, one of the popular plastic cannot be an option for your CNC prototype - that is, PVC. The working environment of this material is about 80℃. For temperature lower 250℃, brass, PEEK, and Teflon can be selected; for temperature lower 400℃, aluminum is preferred; for the very high temperature that is above 500℃, you can choose stainless steel, alloy steel.

Make sure the working temperature of your product is well-considered when selecting a material for your CNC prototype.

4. How is the importance of the weight in your product design?

The weight of the materials should also be considered carefully. Bigger and heavier do always mean better. Heavy materials can withstand strong impact and load. For products that require great bearing capacities, such as industrial machinery, heavy materials, such as steel and cast iron, should be the better choice. But it is not a decent option for weight-sensitive products.

For weight-delicate products, such as consumer electronics, electrical hardware, lightweight material is ideal. It is lighter in weight, but still durable and strong enough to withstand a substantial amount of impact and load. But it may cost higher. If the cost is an important factor for your CNC prototyping project, considering it well. In general, for metal, standard aluminum alloys like 6061 are great, low-density options to keep weight down; for plastic, Delrin and ABS can keep weight down while maintaining high strength.

5. What is the strength required?

When it comes to strength, it is not limited to the bearing capacities or the load a product can withstand. There are many ways to measure material strength, including textile strength, hardness, endurance strength, and wear resistance.

The above is not just about telling you what properties of materials you should prioritize and what factors you should consider for your CNC prototype, but also helps you specify what elements are crucial for your design that ensures the proper and long-lasting functionality of your product.

6. Are metallic materials the only choice?

Plastic materials, such as ABS, have become increasingly popular in CNC machining, as it is lighter in weight yet strong and durable. And it is easy to machining and mold into various shapes. Compared to metallic materials, plastic materials retain more small details. Remember that the metal is not the only option. Consider the plastics materials as well. There is a wide variety of diverse plastic available. Sometimes, they may serve your CNC prototyping purpose better and more cost-effectively than metallic materials.

In Conclusion 

There are lots of factors that should be considered when choosing a material for prototyping, including machinability, formability, price, corrosion resistance, strength, heat resistance, and weight. Here are some rules of thumb:

1. Aluminum is the most commonly utilized material for CNC prototyping, with the lowest cost.

2. POM (Delrin) is the most cost-effective plastic material as it has the advantage of excellent machinability.

3. If your prototype requires high strength, hardness, or excellent thermal resistance than you could choose a metal alloy.

4. If you are looking for prototypes prior to injection molding or require a lightweight but high-strength and more cost-effective prototype, then choose plastics as the CNC machining material.

Do you have a great design and need a mock-up to verify and test it? Choosing the CNC machining technology, you will not be disappointed with the results, especially if the right material is chosen.

Whether you are designing parts of consumer electronics, automotive components, hardware fittings, insulators, or others, you can always find a material that can be CNC machined to achieve your design. Having a broad range of materials to choose from is a luxury, but it can also be confusing if you are lack of relative experience and expertise. Following the above instructions to make sure you are choosing the most accurate and efficient material. Of course, you do not have to make a choice alone. You can turn to a professional manufacturer in prototyping who can guide you through the selection process.