When designing components for CNC machining, many times you will choose a metal material. For this, you need to consider strength requirements, chemical resistance, thermal stability, cost, and other such factors. With so many materials to choose from, it may be a little overwhelming. First define the most important features of your part. How does it work? What environment will it be exposed to? How does it interact with other components?
After understanding the above important characteristics of parts, combine the six factors that you should consider before processing hard or soft metals introduced in this article. I believe it will help you in choosing the right metal material.
Mechanical Properties Of Metals
Let’s start with the mechanical properties, which are measured by the performance of the material when different forces are applied.
The main mechanical properties of metals to be considered are:
Hardness:
Harder materials are more resistant to scratches and creasing than soft materials. Hard materials are suitable for wear parts such as bushings. Some materials can also be machined and hardened later. Remember that if the material hardens, the material properties will change. For example, hardening the material may make it more brittle. The surface of the part can also be hardened with a coating.
The following picture simply compares the hardness of common metal materials
Source from https://www.metalcraftmachining.com/services/cnc-metal-materials.html
Density:
The density of aluminum is much lower than that of mild steel, which makes it about one-third of its weight. Depending on the grade of the material, aluminum may actually be stronger than steel when compared by weight (strength to weight ratio).
Tensile Strength:
The maximum stress that a material can withstand before failure. If you design a bracket that connects two components, consider how these components interact. The tensile strength will represent the ability of the material to resist fracture.
Damping (hard metals tend to have less damping capacity)
Brittleness:
Highly brittle materials will not stretch or deform before breaking. If your parts need to be continuously bent, then brittle materials will not be a good choice.
If any of the above properties are important to your project, we recommend that you do some research to obtain the actual property rating of each material.
Wear And Fatigue Characteristics Of Metals
Generally, if you are machining parts to achieve prototype fit and function, you don’t need to worry about material wear. If you need to ensure strength or allow parts to withstand the test of environmental characteristics such as extreme temperatures, your choice of materials will be very important. Let us break down the most important fatigue characteristics to consider.
Fatigue Strength And Toughness:
This is the stress that the material can withstand within a certain number of cycles. These changes have been extensively studied to help select the appropriate materials to meet your end-use requirements. In fact, according to the research on this subject, metal fatigue is the gradual local permanent cumulative damage of materials and components under the action of cyclic stress or cyclic strain at one or several places, and cracks or sudden occurrences after a certain number of cycles The process of complete fracture. Approximately 90% of all metal failures occur quickly and without any warning, so we usually use the average of the ratios to measure the fatigue strength. When selecting materials, if you know that your parts will endure multiple stress cycles, we recommend that you evaluate the fatigue strength level.
Working Temperature Of Metal Parts
The operating temperature of the environment in which the component will operate is another important factor to consider. This is because the melting point of the CNC material used must be higher than the operating temperature. If it is not, the structure of the part may change. In addition, you must ensure that the CNC machined material can withstand extreme temperature changes. Although some materials may be able to withstand these temperature changes, some materials may experience structural changes after a period of use
There are many resources for environmental cycle testing. In most cases, materials are placed in a controlled environment and tested for high and low temperatures, high and low humidity, thermal cycling, and thermal shock.
–High temperature resistant metals: titanium and stainless steel.
–Metals that can withstand extremely cold temperatures and maintain ductility at low temperatures: copper and aluminum.
Creep resistance is defined as the ability of a material to resist “creep”, which refers to the tendency of a solid material to deform over a long period of time-due to exposure to high levels of stress. It is important to note that the creep resistance may exceed the standard stress limit of the material because it takes longer to occur. Nickel, titanium and stainless steel have the highest creep resistance to metals.
Corrosion (Oxidation) Resistance Of Metals
Due to the chemical reaction between the metal and the surrounding environment, metal corrosion is degradation or oxidation. There are many reasons for metal corrosion, it is worth noting that all metals will corrode. Pure iron usually corrodes very fast, but stainless steel that combines iron and other alloys corrodes very slowly. If you are concerned about corrosion, stainless steel is an excellent choice for metal.
Another alternative to stainless steel is anodized aluminum. This method helps reduce corrosion and is a very durable finish. Nickel-plated mild steel may be more cost-effective than using stainless steel.
Thermal Properties Of Metals
Metals can expand, melt, and conduct electricity. The most common thermal property is electrical conductivity, which is the ability of a material to conduct heat. Materials with high thermal conductivity are better at transferring heat. If your components are used for cooling applications, it is best to pay more attention to materials with high thermal conductivity.
The thermal properties of common metals are listed in the table below for reference.
Source from https://www.protolabs.com/resources/blog/hard-metals-vs-soft-metals-for-cnc-machining/
Manufacturing Performance
Machinability refers to the ease with which a material can be modified by cutting (machining). For example, aluminum is very easy to machine and does not wear tools as quickly as other materials. Therefore, the processing cost of aluminum is “cheaper” compared to materials with lower workability.
Metals have different material properties, which determine the performance characteristics of the final product. These various characteristics are great, but they should be balanced with raw material costs and processing costs. For example, if your parts are designated as stainless steel, you will find that there are several different grades of stainless steel that differ greatly in cost and material properties. In addition, some stainless steels are more troublesome to cut than others, which means that their cost on CNC machine tools will be slightly higher.