Hard Metals vs. Soft Metals for CNC Machining
Last updated: 08/28/2023 | Author: Nick Nolan | Posted in: Materials
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.
What’s the difference between hard metal and soft metal?
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. Without getting deep into a chemistry lesson here, the different structures in the atoms of metallic elements makes the metal harder or softer. The individual atoms of a softer 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.
| Soft Metal | Hard Metal |
|---|---|
|
Copper |
Carbon Steel |
|
Brass |
Stainless Steel |
|
Aluminum |
Titanium |
|
Bronze |
Monel |
|
Zinc |
Hatelloy |
What metals can be CNC machined?
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 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 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 metal 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. Aluminum 7075 is the strongest aluminum alloy. It’s harder and more difficult to machine compared to the 2011 alloy, and is used in high-stress applications where higher tensile strength is needed, and is commonly used for automotive and aerospace frames.
Choosing the right material for your parts
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.
The wear of the material
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.
Corrosion resistance
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 like the oil and gas industry.
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.
Machinability
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.
FAQs
How do the costs vary between machining hard and soft metals for similar parts?
Machining soft metals is generally faster and easier on the tooling, which translates to lower manufacturing costs. Hard metals, due to their increased wear on tools and the slower machining speeds required, can be more expensive to machine. However, it’s essential to factor in other costs, such as the raw material cost, post-machining treatments, and potential increased lifespan of harder metal parts, which can offset the higher machining costs.
Can I combine both hard and soft metals in a single component?
If you’re looking for the benefits of soft and hard metals, there are alloys around the middle of the hardness scale.
Combining hard and soft metals in a single component is also possible, especially in multi-material assemblies. Such combinations can leverage the strengths of both materials. For example, a component might use a hard metal for areas requiring high strength and a soft metal for areas where malleability or weight reduction is crucial.
However, considerations like thermal expansion, joining techniques, and corrosion between different metals need to be addressed to ensure long-term reliability.
How does weight vary between similar parts made from hard and soft metals?
Typically, soft metals are less dense and lighter than harder metals. The weight difference can have a significant impact on your product’s functionality. For instance, in the aerospace industry, lighter components (often made from aluminum or titanium) are preferred to reduce the overall weight of the aircraft. Conversely, in industries where durability and strength are a priority, heavier and harder metals are used despite the added weight.
Are there certain environments or conditions where you would strongly advise against using a soft metal (or hard metal)?
Yes. Soft metals like aluminum or copper aren’t ideal for high-temperature or high-stress environments due to their lower melting points and tensile strengths. They can deform or wear out faster under these conditions.
Certain hard metals aren’t ideal in highly corrosive environments unless they’re treated or alloyed to resist such conditions. For instance, while stainless steel offers corrosion resistance, untreated carbon steel can rust rapidly in damp or marine environments.
What is the impact of heat treatment on metal hardness?
Heat treatment can significantly alter a metal’s hardness. For instance, processes like tempering, quenching, or annealing can increase the hardness of metals like steel, making them more resistant to wear and deformation.
Certain heat treatments can also be used to increase the ductility of hard metals, making them easier to machine or shape. It’s a balance of achieving the desired properties for the specific application of the metal part.
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