CNC machining is a highly precise process compatible with many materials. The right CNC machining materials play a huge role in the manufacturing process efficiency and the quality and function of a machined part. However, choosing the right one from the multitude might be challenging.
This article explains how to select the appropriate CNC material for your project.
3-Step Guide for CNC Machining Material Selection
Before diving into the article, below is a short introduction to the 3-step guide most CNC machinists use to select a material. However, note that this is an introduction, as each step will be fully explained in subsequent sections.
· Step 1: Prioritize Your Parts Requirements
Part requirements are the core part of CNC machining, and they set the template for the type of material you can use. Common requirements include the part application, i.e., the environment where it will be used, presumed properties such as lightweight, tensile strength, and your budget.
· Step 2: Identify Potential Materials
Prioritizing materials based on the above parts requirement will lead to you identifying some materials that can fulfill all or most of them. Make a list of these materials.
· Step 3: Choose the Most Suitable Material
Choose the most suitable material by making a compromise between the part requirements. For example, you can choose cost over mechanical performance if your budget is not in range.
Step#1: Consider Your Part Requirements When Picking CNC Machining Materials
Below is an intensive study of parts requirements applicable to any CNC machining project.
· Parts Applications
Ensure the CNC material you use is compatible with the intended application or environment. For example, let’s compare stainless steel and carbon steel intended to make structural parts used in a marine environment. Both materials are machinable. However, stainless steel will be more suitable due to being corrosion resistant. If you look at a normal dry environment, carbon steel would be more suitable since it is stronger and more durable.
· Part Weight
Ensure the materials you are considering have the right weight requested based on their application. Bigger doesn’t mean better. For example, Aluminum and other low-density materials appeal strongly to the automotive and aerospace industries due to their lightweight and strength.
· Part Properties
The right CNC materials will have the necessary properties that aid effective machining without a loss of function. Therefore, you should consider the part properties you can consider.
Machinability shows how compatible material is with the CNC machining process. The right material should be highly machinable, leading to an increase in production efficiency and a reduction in destroyed CNC parts. Soft metals such as Aluminum, copper, brass, and plastics are highly machinable materials.
Hard metals and tough plastics such as metal or carbon fiber have low machinability. Therefore, this will result in low productivity and production efficiency due to the need to control the CNC machine cutting speed and feed rates. They can also damage the metal parts or require special cutting tools, as in the case of titanium.
There are different measures of strength of metal and plastic, and you should consider the following when looking for the perfect material for your project:
- Tensile strength: The resistance of the material to a pulling force
- Compression or load-bearing: The resistance of the material to a constant load
- Toughness: The ability of the material to resist tearing
- Elasticity: The ability of the material to return to its original shape after removing the load
Know the tolerable strength limit of the parts you want to make, then choose a material that resonates with such limits. Moreover, you can go online to get comprehensive technical information on the strength of different materials or talk to our personnel.
Heat resistance shows the ability of the material to resist a change in mechanical properties due to a temperature change. Ensure the materials you choose don’t expand or contract irregularly in response to temperature change.
Corrosion resistance is the ability of the material to resist foreign substances that can cause part failure. Such foreign substances are not limited to water alone. Other examples include oil, grease, and chemical reagents such as acids, salts, and alcohol. Consequently, ensure you check through the material’s technical data sheet to verify its ability to withstand chemical exposure.
Material hardness shows the its ability to withstand pinpoint surface loads and determines what materials a CNC machine can cut. Hard materials are not suitable for CNC machining as they can destroy the components of CNC machines. They also need special cutting procedures. For example, titanium needs a diamond cutting tool.
It is the materials’ overall ability to absorb stress. For example, Aluminum has no endurance limit due to its microstructure. However, its alloys should have an endurance limit of 1/3 of the tensile strength.
· Dimension Tolerance
Dimension tolerance is the permissible limit in the variation of the machine parts for effective functioning. For higher dimensional tolerance, you need highly machinable materials.
Parts made using tight tolerance are easier to assemble. Consequently, they are highly suitable for automotive and aeronautics.
Also, every CNC machine has its level of tolerance based on the manufacturer. However, the average tolerance is 0.02mm. If you are unsure of the tolerance, you can view our article about standard tolerance for CNC machining.
· Physical Appearance
Aesthetics is not at the forefront of the requirement when selecting a CNC material. However, you might need to consider it for certain products, especially consumer ones.
Physical appearance can be in terms of the smoothness and color of the final part. Metals usually have a smooth surface finish, although they have a limited range of color. Plastic materials come in different colors.
· Project Budget
Material cost is an important part of CNC material selection because CNC machining is a subtractive process, i.e., the machine chips away at the workpiece to make the final product. Therefore, the project budget is the major factor in material selection. Ensure that you choose a material with the desired properties within the range of expenditure.
Step#2: Identify Candidate CNC Machining Material
Using the part requirements highlighted above, you should be able to make a list of compatible materials for your project. Three types of materials are suitable for CNC machining: metals, plastics, and others. This section discusses the three types, their properties, and their application.
· Metal CNC Machining Materials
Metals are common CNC milling materials with unique properties. There is a wide range of metals compatible with the process. Below are the well-known options, their properties, and applications
Aluminum alloys generally have a good strength-to-weight ratio, thermal and electrical conductivity, and corrosion resistance. However, the level of these properties depends on the type of Aluminum alloy. For example, the 6061 vs. 7075 aluminum comparison shows that aluminum 6061 has lower corrosion resistance. There are also other comparisons of aluminum alloys showing the diversity in the material’s properties.
Aluminum alloys are applicable in the automotive and aeronautics industry for making parts such as frames and high-performance recreational equipment
Brass is an alloy of zinc and copper. Unlike bronze and copper, it is a cost-effective material with a low coefficient of friction, high chemical resistance, and low strength. It is highly machinable due to its softness. As a result, brass is applicable in making parts used in the medical industry (surgical tools), engineering, and music industry (strings).
– Stainless Steel
Stainless steel alloys are resistant to corrosion, distortion, and wear. Most stainless-steel alloys can be heat treated except for the 303 stainless sheets of steel used to make nuts, bolts, shafts, and gears. Another common alloy is the 304 stainless steel, known for its high machinability, corrosion-resistant, and weldability.
Stainless steel is generally applicable in the medical industry for making surgical tools and automotive and aeronautic industries.
Steel alloys have high formability, weldability, and machinability. However, the degree of these properties depends on the alloy. Steel is suitable for making materials that require strong welds, such as gears and shafts.
Titanium has a high strength, toughness, biocompatibility, and corrosion resistance. It is most time compared to Aluminum. However, unlike aluminum alloys, it is expensive and has low machinability (it requires special cutters). It also has low weldability making many machinists prefer steel steel when comparing titanium with steel.
Titanium is an important material in rapid prototyping parts used in aerospace, military, and medical device manufacturing.
Copper has a high electric conductivity and corrosion resistance, and thermal conductivity. However, it has low resistance to chemicals such as acids, halogens, sulfides, and ammonia solutions.
Copper is applicable in the electrical industry for making conductive parts and the automotive industry for making cooling systems and heat exchangers.
· Plastic CNC Machining Materials
Plastic polymers are also common materials for CNC machining and are known for their versatility and aesthetic properties. Below are the well-known options, their properties, and their applications.
ABS plastic material is a thermoplastic with high impact resistance, low electric conductivity, and high chemical resistance. It is more common in injection molding, although it is highly applicable in CNC machining due to its versatility.
ABS is applicable in making automotive components, toys, and sporting goods. However, unlike other plastic, it is less expensive and cannot withstand high temperatures for a long time.
Nylon is a polyamide polymer with high machinability, moderate flame resistance, and high strength. It is suitable for making insulators, bearings, wheels, and consumer electronic casings.
PMMA is a rigid, transparent, scratch-resistant, and impact-resistant material used as a substitute for glass. Acrylic for CNC is applicable in making display screens, lenses, clear enclosures, and food storage (due to its lack of Bisphenol-A). However, it is susceptible to heat deformation.
PEEK is a semi-crystalline polymer with excellent machinability, superior dimensional stability, chemical resistance, and adequate impact resistance. It is applicable in making parts such as test sockets, switches, and connectors.
PVC is chemically resistant and more affordable than most CNC milling materials. It is applicable in the housing industry for making water and gas pipes.
· Other CNC Machining Materials
Although metals and plastics are the more popular CNC machining materials, there are other compatible ones. Below are a few that can be suitable for your project.
Ceramics is a material known for being brittle, heat resistant, and corrosion-resistant. Therefore, it needs careful machining.
As a result of its properties, it is important for making components with heat resistance, e.g., space shuttle engine components, tank armor, and superconductors.
Wood (solid wood and plywood) has high aesthetics and wear resistance. Plywood has more dimensional stability. Consequently, it is suitable for products requiring a high tolerance level. Both materials are expensive and might require specialized cutting tools.
Foams are inexpensive, lightweight, and easily machinable materials suitable as test materials in CNC machining. There are two types: rigid and carving.
Rigid foams have a higher insulation value (they can work in temperatures between -100° and 200° F). As a result, they are suitable for making parts used in flooring and walls. They are also suitable for making products that need to withstand moisture.
Carving foam has higher flexibility. Therefore, they are applicable in making a product such as gaskets and seals.
Composites are synthetic materials made from carbon, glass, etc., bound together by thermoset or thermoplastic resin. Due to their chemical make-up, they have lower machinability. As a result, they are hard to machine and often require diamond tooling and 5-axis CNC machines. They are applicable in automotive, aerospace, and power generation applications.
Step#3: Selecting the Best CNC Machining Materials
Choosing the best CNC machining material depends on the product you envision and its applications. Since there are many materials available, you should be able to make a list of those that are suitable. Below are a few things you can consider to select the best material.
· Consider Non-Metallic Materials
Metals are not always the best option. Some non-metallic materials have properties like that of metals. For example, polycarbonate is a very strong plastic likened to metals. Also, it is lightweight, durable, and moldable. Therefore, use them if your project would fare better with a non-metallic CNC material.
· Consider Phenolics
Phenolics are hard, dimensionally stable, electrical resistant, heat resistant, and chemical resistant. That being so, they are great options for adhering to specific regulations in your projects.
· Know the Different Purposes of Foams
Foams are very important in machining due to their lightweight, durability, and rigidity. As a result, they might be the right test material, especially if you work with expensive materials. Rigid foam is suitable for parts that need high structural integrity and stability while carving foam is suitable for parts that require a high level of insulation and prototypes for molds.
Contact RapidDirect’s CNC Machining Services for Suitable Material
RapidDirect offers CNC machining services so you can create high-quality parts in a short time. They also have a wide range of CNC materials, with experts that know their properties and application. Therefore, you are guaranteed high-quality machined parts.
With our online quotation platform, you can upload your CAD file, choose your material and quantities, and get a real-time quotation and free DFM analysis within 12 hours. RapidDirect is as direct as you get. Choose us and enjoy a fast lead time and competitive pricing.
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Aluminum 6061-T6 is a popular aluminum alloy considered the standard grade for CNC machining. It is highly machinable, lightweight, corrosion-resistant, and versatile. It is applicable in the automotive and aeronautic industry
A CNC machine can cut soft metals such as Aluminum and Stainless steel, plastics such as ABS, PEEK, and PVC, and other materials such as foams and ceramics.
Both materials have properties applicable in different scenarios. Metals are expensive with good functional properties. For aesthetics, plastics are the better option. This doesn’t mean that metals don’t have aesthetic properties. You can make them look aesthetically good using surface finishing. Also, many plastics can replace metals in terms of functional properties.