CNC machining is a process of creating parts of various shapes and sizes by removing excess material from a solid block. It is one of the most efficient techniques for parts production and is used in many industries, such as automotive, aviation, or medicine. When it comes to CNC machining, the choice of material is crucial for obtaining the perfect part. This article will help you understand the requirements of CNC machining and the criteria for choosing the right material for your project. CNC machines are equipped with specialized cutting tools, such as drills and mills, which are used to cut and shape the material according to the CAD program. Cutting tools are usually made of high-quality materials, such as tungsten carbide, which can cut even the hardest materials. CNC machining is capable of producing parts with complex shapes and narrow tolerances.
Understanding the requirements for processing
When considering CNC machining requirements, it is important to be aware that depending on the type of raw material, the material may require specialized methods such as heat treatment, annealing, or coating. These are necessary to meet the desired performance requirements. Heat treatment is used to change the properties of the material, such as strength or hardness, by altering its microstructure. The annealing process is used to reduce stress in the material and improve its plasticity. Coating is used to improve wear resistance and reduce friction.
Material Selection Criteria
Several factors need to be considered when choosing a material for CNC machining.
- It must be able to withstand the temperatures and pressures associated with the machining process.
- The material needs to withstand the cutting forces generated by the CNC machine.
- It must maintain the desired shape and size.
- Its easy availability and cost-effectiveness are essential.
- Must meet all requirements for application performance.
Popular materials for CNC machining
There are several materials commonly used for CNC machining:
- Steel and its alloys are among the most popular. This is because steel is strong, corrosion-resistant, durable, and economical, making it an ideal material for many applications. Another important argument in favor of steel is the ease with which it can be processed by CNC, and its high susceptibility to heat treatment in order to obtain the desired properties. However, there is another extremely important feature that makes this material a popular choice, and that is its magnetism. This aspect is leading when a product with such properties is required.
- Aluminum and its derivatives are second in terms of materials used during processing. They are lightweight and resistant to corrosion, which also makes them useful in many industries. A particular contrast to steel is its complete non-magnetism, which makes it particularly useful for products that require it.
- Plastics and their composites are also used in this process. The products obtained from their use are lightweight, inexpensive, and easy to process.
- The last of the popular materials in CNC machining is titanium and its alloys. It is strong, lightweight, and corrosion-resistant, which also makes it useful in many applications, however, it should be noted that it is also difficult to process and requires specialized tools and cutting techniques.
Stainless Steel (Austenitic)
They are made up of the 200 and 300 series. Their general characteristics include:
- Excellent corrosion resistance.
- Highly formable.
- Non-magnetic.
- Hardened cold (cannot be heat treated).
- Excellent weldability.
- Ability to operate in extreme temperatures.
- Susceptibility to stress corrosion cracking.
They are obtained by adding elements such as nickel, manganese, and nitrogen. The chromium content usually varies between 16 and 26%. The carbon content ranges from 0.03 to 0.08%. Chromium provides some resistance to oxidation, as well as molybdenum in some of its alloys. Stainless steel is used in products such as shafts, valves, screws, bushings, nuts, chemical equipment, hospital equipment, marine applications, aircraft components, food and beverage processing equipment, architectural decorations, cryogenic vessels, temporary prosthetics, and many other industrial products.
Great strength to weight ratio
Aluminum is lighter than most metals, so if you want to reduce weight, it's a good choice. Although pure aluminum has a tensile strength less than 100 MPa, it can be hardened in several ways:
- Altering properties by mixing with other elements to improve grain structure.
- Heat treatment — Reheating and then cooling at a specific rate to produce crystals of the ideal size.
- Strain hardening — Deliberate deformation of metal to change the grain structure. This usually occurs during heat treatment, during rolling, but it can also be done later, for example by forging.
Wide range of alloys and material properties
In reality, aluminum is an excellent base material for processing. There are many alloys available, each with different properties and uses, tailored to your needs. They are grouped into different series, each of which is multiplied by a thousand, for example, the 6000 series. Usually, the closer the category number of aluminum is to another, the more similar they are, hence 5082 and 5083 are almost identical.
Here are some of the most popular categories:
- 2024 – An aviation genre, with high fatigue strength, converts UTS (Ultimate tensile strength) into greater plasticity/durability by adding a copper alloy.
- 5083 – Marine category, with high corrosion resistance, due to a higher magnesium content.
- 6082 - General purpose category, with a good combination of strength, ductility, and corrosion resistance, making it versatile and widely used. This is achieved by alloying it with a mixture of magnesium and silicon (also nearly equivalent to 6061).
- 7075 – An aviation grade with high durability, good balance of properties, especially in the presence of high electrostatic loads. It can undergo heat treatment and contains more zinc, as well as magnesium and chromium.
High Corrosion Resistance
Although corrosion resistance varies depending on the category, aluminum is an excellent choice if the product you are manufacturing will require it the most. Many metals and their alloys have a significant interaction with oxygen. Highly reactive metals, containing magnesium, oxidize easily, while less reactive ones form a loose oxide layer, in the form of rust on iron and steel. Instead, when aluminum is exposed, it forms a passive layer of aluminum oxide, which seals the surface and prevents oxidation and corrosion. This layer is "self-healing" even in case of scratching, so the material may not require painting or surface treatment, which allows to save production and service costs throughout the entire period of use.
High Conductivity
Although copper is often the chosen material for conduction, aluminum is frequently used for electrical components, as it is significantly cheaper and lighter. In fact, it is often used for bus bars, battery cables, and connectors, especially in automotive and electric vehicle applications. Its good thermal conductivity also makes it commonly used for heat dissipation.
Recycling
Since one of the priorities of companies is sustainable development, it is good news that about 75% of all produced aluminum is still in use. Its recycling consumes significantly less energy than its production, so as long as we can control pollution, aluminum can be continuously subjected to this regenerative process.
Aesthetics
Machining this material can provide an excellent finish. It is naturally resistant to corrosion, but to achieve other aesthetic finishes, it can be anodized to obtain various colors. This is a surface finishing process that not only increases the material's resistance to wear and corrosion but also facilitates the introduction of color. The process increases the thickness of the passive oxidized layer by applying acids and an electrolytic process. Aluminum oxide is a hard ceramic, so this coating is really durable.
Titanium Parts Processing
As a neutral, shiny metallic material, titanium easily combines with aluminum, iron, nickel, and other metals, creating many high-performance titanium alloys. Specific attributes can vary in many ways, but some of the typical properties of titanium are often cited below:
- High resistance to rust and corrosion
- No toxicity
- Plasticity
- High strength-to-weight ratio
- Biocompatibility
- High energy absorption
- Low adhesion
Summary
Choosing the right material for CNC machining can be a challenging task. It is important to consider the application and performance requirements. Steel, aluminum, plastics and their composites, and titanium and its alloys are popular materials for CNC machining. It is crucial to consider the requirements necessary for such a process when making a choice. By understanding the requirements of CNC machining and various criteria, such as selecting the right material for a given application, you can be sure that you will make the right choice for your project.