CNC machining creates parts of various shapes and sizes by removing excess material from a solid block. It is one of the most efficient techniques for producing parts and is used in many industries, such as automotive, aerospace, and medical. When it comes to CNC machining, the choice of material is crucial to getting the perfect part. This article will help you understand the requirements of CNC machining and the criteria for selecting 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 material according to a CAD program. The cutting tools are usually made of high-quality materials, such as tungsten carbide, which cut through even the hardest materials. CNC machining is capable of producing parts with complex shapes and tight tolerances.
Understanding machining requirements in CNC
When considering CNC machining requirements, it is important to know 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 alter the material’s properties, such as strength or hardness, by changing its microstructure. The annealing process reduces stresses in the material and improves its ductility. The coating is used to improve wear resistance and reduce friction.
Material selection criteria in CNC
When selecting a material for CNC machining, several factors must be considered.
- It must be able to withstand the temperatures and pressures associated with the machining process.
- The material is required 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.
- It must meet all application performance requirements.
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 lends itself to CNC machining and its high susceptibility to heat treatment to achieve the desired properties. However, there is another fundamental characteristic that makes this material a popular choice, and that is its magneticity. This aspect is at the forefront when a product with these properties is required.
- Aluminum and its derivatives are in second place when it comes to materials used in machining. They are lightweight and corrosion-resistant, so they also find use in many industrial fields. A particular contrast to steel is its total non-magneticity, making it particularly applicable to products requiring it.
- Plastics and their composites are also used in this process. Products obtained using them are lightweight, inexpensive, and easy to process.
- The last popular materials in CNC machining are titanium and its alloys. It is strong, lightweight, and corrosion-resistant, so it also finds many useful applications; however, it is worth noting that it is also difficult to machine and requires specialized tools and cutting techniques.
Stainless steel (austenitic)
- It is formed by the 200 and 300 series. Their general characteristics are:
- Excellent corrosion resistance.
- Highly formable.
- Cold-hardened (cannot be heat-treated).
- Excellent weldability.
- Capable of operating at extreme temperatures.
- Susceptible to corrosion cracking.
They are obtained by adding elements such as nickel, manganese, and nitrogen. Chromium content generally ranges between 16 and 26%. Carbon content ranges from 0.03 to 0.08%. Chromium provides some of the oxidation resistance and molybdenum in some of its alloys. Stainless steel is used in products such as shafts, valves, bolts, bushings, nuts, chemical equipment, hospital equipment, marine applications, aerospace components, food and beverage processing equipment, architectural decorations, cryogenic vessels, temporary prostheses, and in many other industrial products.
Great strength-to-weight ratio
Aluminum is lighter than most metals, so it is a good choice if you want to reduce weight. Although pure aluminum has a tensile strength of fewer than 100 MPa, it can be hardened in several ways:
Changing properties by mixing with other elements to improve the grain structure.
Heat treatment – Heating and then cooling at a specific rate to produce crystals of ideal size.
Hardening by crushing – Intentionally deforming a metal to change the grain structure. This is usually done during heat treatment and rolling but can also be done later, such as by forging.
A wide range of alloys and material properties
In fact, aluminum is an excellent base material for machining. There are many alloys available, each with different properties and applications to suit your needs. They are grouped into different series, each of which is multiplied by a thousand, such as the 6000 series. Typically, the closer the aluminum category number is to another, the more similar they are, which is why 5082 and 5083 are almost identical.
Here are some of the most popular categories:
- 2024 – Aerospace grade, high fatigue strength, converts UTS (Ultimate tensile strength) to higher ductility/strength due to the addition of an alloy with copper.
- 5083 – Marine category, with high corrosion resistance due to 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 almost equivalent to 6061).
- 7075 – A high-strength aerospace grade with a good balance of properties, especially when high electrostatic charges are present. It can be heat-treated and contains more zinc, magnesium, and chromium.
High corrosion resistance
Although corrosion resistance varies by category, aluminum is an excellent choice if the product you manufacture will require it the most. Many metals and their alloys have high 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 aluminum oxide layer that seals the surface and prevents oxidation and corrosion. This layer is „self-repairing” even when scratched, so the material may not require painting or surface treatment, saving production and service costs over its lifetime.
Although copper is often the material of choice for conductivity, aluminum is often used for electrical components because it is much cheaper and lighter. In fact, it is often used for busbars, battery cables, and connectors, especially in automotive and electric vehicle applications. Its good thermal conductivity also makes it widely used for heat dissipation.
Since sustainability is one of the companies’ priorities, the good news is that about 75% of all aluminum produced is still used. Recycling uses much less energy than producing it, so as long as we can control pollution, aluminum can be continuously subjected to this restorative process.
The treatment of this material can provide an excellent finish. It is naturally corrosion resistant, but to achieve other aesthetic finishes, it can be anodized to achieve different colors. This is a surface finishing procedure that increases the material’s resistance to wear and corrosion and facilitates the introduction of color. The process increases the thickness of the passive oxidized layer through the use of acids and an electrolytic process. Aluminum oxide is a hard ceramic, so this coating is really tough.
Treatment of titanium parts
As an inert, shiny metal material, titanium easily combines with aluminum, iron, nickel, and other metals to form 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
- Lack of toxicity
- High strength-to-weight ratio
- High energy absorption
- Low adhesion
Choosing the right material for CNC machining can be a difficult 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 important to consider the requirements for such a process when selecting. By understanding the requirements of CNC machining and various criteria, such as choosing the suitable material for the application, you can be sure to make the right choice for your project.