There are hundreds of different metals and metal alloys used to make parts and products. Most metals are an alloy–a combination of two or more metallic elements. The elements are combined to create a material with specific properties. For example, some metal alloys are stronger, or have better corrosion resistance.
One of the most important properties of a metal is the hardness.
The hardness or softness of a metal affects how strong it is, how much weight it can bear, how easy it is to machine, and how resistant to wear it is.
All of these factors are important when you’re choosing which material to use for machined parts. Using the right material is essential for the functionality and longevity of your parts.
In this post, we’ll explain the difference between hard and soft metals, and what you should consider when choosing the material for your next project.
A hard metal is more rigid and stronger compared to soft metals.
The difference between hard metals and soft metals depends on the atomic structure of the elements in the metal. We won’t get too deep into the chemistry lesson here, but the different structures in the atoms of metallic elements makes them harder or softer.
The individual atoms of a soft metal move around more than a harder metal, making the material more malleable.
Gold for example, is a very soft metal. Pure gold feels more like playdough than metal, while Titanium is an extra-hard metal.
A hard metal is more difficult to machine, and less likely to scratch or lose its shape over time.
Softer metals like copper and brass are easier and faster to machine, but are more susceptible to deformation.
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Most CNC machines can effectively machine any type of metal, as long as the right cutting tools are used.
Harder metals are more difficult to machine, which makes machining them more expensive. The tools used to cut and shape the parts wear down faster, and the machining process takes longer.
Softer metals are easier to cut and machine, making them less expensive. However, using a soft metal isn’t always the best choice. In some cases, using a harder metal increases the longevity of the part, making it more cost-effective over the years.
The metal you use for your parts depends on what the part is needed for and the environment it will be in.
Aluminum and stainless steel are two metals that are commonly used for CNC machined parts.
Aluminum is a softer metal, and considered to be one of the most cost-effective choices for CNC machined parts. Because aluminum is softer, it can be precision machined and it’s easier to form complex designs with tight tolerances. Aluminum is used in a wide variety of applications, including the aerospace industry because it’s lightweight and relatively strong.
Stainless steel is another popular choice because it’s highly durable and resistant to corrosion. Stainless steel is very effective at maintaining its strength in high-stress environments like gears and fittings. Stainless steel is a harder metal, but with the right tooling and CNC machines, it can be machined fairly easily.
Titanium is usually named the hardest material to machine. Titanium is a hard metal and requires special tooling to machine it effectively. Despite being difficult, titanium parts are commonly used in the aerospace and medical industry because of its great strength-to-weight ratio and corrosion resistance.
There are also many different alloys that affect the machinability of metals. For example, Aluminum 2011 is an aluminum alloy that’s very easy to machine. But, this alloy doesn’t have the best strength or corrosion resistance. It’s commonly used for electronics and computer parts where it won’t be bearing weight or exposed to harsh environments.
Aluminum 7075 is the strongest aluminum alloy. It’s more difficult to machine, and is used in high-stress applications where higher tensile strength is needed, and is commonly used for automotive and aerospace frames.
How do you choose the right metal to use? Should you use a hard or soft metal? And which alloy should you use?
It’s always nice to have some different options, but it can be overwhelming. Here are some things to consider when choosing the right metal for your project.
What is the part going to be exposed to? Will it be in an environment with higher temperatures? Or will it be moving and sliding against other parts?
Most metals will wear down or begin to lose their shape after a few years because of high stress. This happens even faster when there are high temperatures.
Nickel, titanium, and stainless steel have the highest resistance to deformation. Aluminum tends to have lower melting temperatures, which means it will wear down much faster in high temperatures.
Being in a corrosive environment can quickly deteriorate a metal. For example, if you put a carbon steel part in water, it will immediately start to rust and deteriorate. If your part is going to be exposed to water, acids, oil, or saltwater, it’s important to know which metals can withstand the corrosion.
Brass and copper parts are often used in plumbing and appliance fittings because they have excellent corrosion resistance.
Hastelloy is a nickel alloy that is very resistant to harsh chemicals and high temperatures. Even though the metal is more expensive, the parts can last much longer in tough working conditions.
Stainless steel is made with iron, so it still rusts in water, but the process is much slower because it’s mixed with other metals. This makes it ideal for marine applications.
There are also secondary operations like anodizing aluminum parts that increase their corrosion resistance.
If you have a complex part design, it may be better to choose a material or alloy that has a higher machinability rating. Almost any metal can be machined, but the cost of machining varies quite a bit.
As we mentioned, soft metals are easier and faster to machine. This can significantly reduce your part cost.
You can visit our material page to compare the different options for your next CNC machining project. If you have any other questions about choosing the right materials, reach out to our team.
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