As you start to get into 3D printing, it is essential to learn more about the different types of metals available and their uses. This ultimate guide will review the various types of metal, their classifications, and how you can use them in 3D printing and CNC machining.
Different Types of Metals, Properties, and Uses
The best place to start is defining the most common types of metal, their properties, and popular uses. Let’s dive in!
Aluminum is a popular metal that has a wide variety of applications. It is the most popular non-ferrous metal.
It was first developed in 1825 and boasts an impressive strength to weight ratio. This metal is malleable – meaning you can form it with ease – and does not rust. While it isn’t as strong as other options like steel, its durability, lightweight, and ease of machining make it very appealing.
Similarly, you can cut aluminum into extremely thin sheets, like what we use for foil.
Even though aluminum doesn’t rust, it can oxidize. That means that it corrodes after prolonged exposure to salt – not water. When this happens, a chalky, white residue will build upon the metal.
One of the reasons that aluminum is so popular is its versatility. You can use it for everything from soda cans and grilling trays to freshwater boats. Aluminum was even used on the space shuttle that sent a man to the moon!
Stainless steel is an alloy of iron, carbon, chromium, and several other metals. It is unique because it does not oxidize or rust, so maintenance is simple.
This metal is very sturdy and versatile, so you can also use it for furniture and fixtures. That’s why so many people opt for stainless steel appliances! Even most utensils are made out of this material.
Brass is a copper and zinc alloy. The ratio of each of these metals will vary depending on the properties you are looking for. In some cases, it can include some small amounts of lead and aluminum too.
This metal comes in many different colors, like bronze, gold, yellow, red, and brown. It is resistant to corrosion and antimicrobial, so people tend to use this for faucets and door knobs. Note that if you use harsh chemicals on it, the finish can crack, though.
You can tell the difference between brass and goals by hitting it – if it vibrates like a bell, you’ve got brass!
Other valuable applications of brass include plumbing, locks, bearings, and even musical instruments. Likewise, you can use it in flammable environments since it is intrinsically safe.
Copper is an alloy with a long history as a conductor. It is perfect for circuits since it has the best heat and electrical conductivity capabilities next to silver.
This metal does not occur naturally, so it must be smelted and extracted from the ore. It has a reddish-orange color, but as it oxidizes, it can become blue or green. Copper is easy to form too, so you can also find it in tools like cooking utensils.
Another copper alloy on our list is bronze. It contains tin, and manufacturers will often incorporate silicon, phosphorus, and aluminum to improve its properties for specific applications. Bronze has thermal and electrical conductivity properties and is also resistant to corrosion.
This metal is also hard, brittle, and can handle fatigue well. As a result, it can make electrical connectors, ship fittings, reflectors, and more.
Titanium is one of the most popular metals used for engineering since it is both lightweight and strong. It is one of the most abundant metals on earth, but refining it is difficult – that’s why it is so expensive!
This metal has the highest strength to weight ratio and strong resistance to corrosion, which is why it is ideal for airplanes and anything else that flies. Another unique property of titanium is that your body will not reject it, so it is the material of choice when manufacturing medical implants.
It also has high thermal stability, so you can also find it in military equipment and chemicals.
What Types of Metals Are Magnetic?
So, which of these metals are magnetic? Before we answer that question, it is necessary to review how magnets work.
Atoms contain electrons that move around, and this motion creates a small magnetic field. The motion of other electrons normally cancels it out since it generates an opposing magnetic field. However, when the magnetic fields spin in alignment, it creates a net field over the entire object.
In other words, rather than canceling each other out, these magnetic fields amplify each other. Magnets will have north (positive) and south (negative) poles – opposites attract one another, and matching poles repel.
When a metal has iron in it, it is called a ferrous metal. This is what gives it magnetic properties! If metal does not have any iron mixed in, it is considered non-ferrous and will not be magnetic.
Metals like iron, nickel, and cobalt are all magnetic. Stainless steel also falls into this category.
Similarly, metals can also be paramagnetic. These materials have a weaker attraction to magnets so they won’t retain their magnetic properties outside of a magnetic field. Some examples include the following:
What about metals that repel magnets? These are called diamagnetic metals.
With these materials, their electron fields work against the magnet instead of enhancing it. That is why they repel them.
Lead, copper, mercury, and silver are all diamagnetic metals.
When you think of magnets, you are likely thinking of permanent ones. Think of a refrigerator magnet – it sticks on the door no matter what, right?
Iron is the most common type of permanent magnet. Others are made from ferrite, which is a compound made from iron oxide and other metallic elements.
They can also consist of alnico alloy – a mixture of aluminum, cobalt, and nickel. Alnico alloy is popular for consumer and industrial electronics since they make strong permanent magnets.
Electromagnets are an additional type of magnet. These are made from an iron, cobalt, or nickel core that has a coil of copper wrapped around it. The wire creates a magnetic field any time electric currents move through it, but the fields disappear when it stops.
That means all electromagnets need electricity to work, but the benefit is that you can control the power of the magnetic field by adjusting the strength of the current. These magnets are used in traffic lights, switches in relays, and even junkyard cranes.
More advanced applications of electromagnets include MRI machines and particle accelerators.
Types of Metal 3D Printing
3D printers can use metal powder to create objects, parts, and more. The unique properties of the metal will determine how the 3D printers fuse it, and the process will vary based on the materials used.
Here are the various ways you can use metal in 3D printing:
Powder Bed Fusion
Powder bed fusion is the most popular type of metal 3D printing. It is also called powder bed melting since it involves selectively melting a cross-section of metal powder.
The 3D printer will spread out a thin layer of powder on the build plate, then melt part of it to create your object.
There are two ways to accomplish this process: selective laser melting or electron beam melting.
Selective Laser Melting
As we mentioned, powder bed fusion is the most common way to 3D print with metal. Of the two options available, selective laser melting, or SLM, is most frequently used. This process is sometimes called laser powder bed fusion or selective laser sintering, but the concept is the same.
These machines use high-powered lasers to fuse layers of metal into your final part. Once the print is done, you can remove it from the powder bed and begin cutting parts off the build plate. You will also need to post-process the object.
SLM is very effective for creating complex parts that require precision and have geometrical challenges. For example, there are many applications in the aerospace and healthcare industries. As a result, the build volumes can range drastically.
You can determine the precision of the machine based on the layer height and width of the laser beam. The print speed on SLM printers is moderate, so you can’t expect it to produce a large number of objects in a short timeframe.
A drawback to this option is that the post-processing requirements can be extensive. Most machines require professional operators since the process is intricate, and you will probably need to tweak the designs several times to make it work.
There are also some safety risks since SLM 3D printers use metal powder that can be dangerous – and expensive – to handle properly.
Direct Energy Deposition
A different way to 3D print metal is through direct energy deposition or DED. This type of printing works by using a laser and metal feedstock to make parts. The stock can either be powder or wire, and it sits with the laser on a single print head.
How is that different than SLM?
The key is that the print head dispenses and fuses the metal at the same time. Rather than spreading the powder throughout the print bed and using a laser to melt it, DED printers blow the metal material out and fuse it to the part simultaneously.
Another thing that makes this machine unique is that you can use it to correct imperfections on parts not printed by the machine.
However, the types of metals you can use – and the cost of the equipment – fall directly in line with those for selective laser melting printers.
Bound Powder Extrusion
This type of 3D printing can work with metal and is also called atomic diffusion additive manufacturing.
This technology is much newer than the ones we just discussed, and they are different because these machines don’t rely on loose metal powder. Instead, the material is bound with waxy polymers in a way that mimics the process for metal injection molding.
Unlike the loose powder that can be dangerous and poses a health risk, the bonded metal material can be handled safely without protective measures. Not only is the material safer, but it can also be easily extruded from a nozzle like traditional 3D printing materials.
That means that the building process is very similar to conventional plastic printing. It is effective for almost all types of geometric parts and can even create objects with an open cell infill.
After the object has been printed, you must complete two post-processing steps. The first involves a washing machine that will dissolve most of the waxy polymer – leaving behind the fused metal powder. Next, you must place the object in an oven to be sintered, where it will shrink down and yield your completed metal part.
Some models like the Metal X printing system include the 3D printer, wash station, and sintering furnace together. They are much more affordable than SLM and DED machines, with a price range of $120,000 to $200,000.
The last type of metal 3D printing technique we will review is binder jetting. This is a large-scale, high fidelity process, and many in the industry believe that it will eventually replace SLM printers as the first choice for powder-based metal printing.
It boasts speed and scalability, and the goal of the manufacturers is to improve metal additive manufacturing capabilities to production volumes.
The technology is like an inkjet printer: the machine distributes an even coating of metal powder over the print bed to create an unbound layer. The jetting head will then distribute a binding polymer in the shape of the part, which loosely adheres to the part.
This process will repeat itself until you have a completed part!
Binder jetting machines have high levels of precision and can create pieces with fine detail. While the speed is an advantage, the cost is much higher than other options.
Types of Metal CNC Machining
CNC machining, or computer numerical control machining, is the process of machining a piece of metal with a computer. The tool uses the coded and programmed instructions to control the cutting or grinding tools, so a manual operator is not necessary.
There are various ways to accomplish CNC machining in metal, including milling, solid sink EDM, wire EDM, and surface grinding.
Milling is a popular option when it comes to machining various metals. These machines hold the object in place, and the milling tool will rotate on a spindle to cut it. The spindle can use interchangeable cutting tools that move across all axes: X, Y, and Z.
This process is ideal for removing stock from asymmetrical or complicated pieces. They can also drill bores and holes, create notches and channels, and cut precise angles.
As you can imagine, the mill can heat up quickly as it rubs against the metal. You will need cutting fluid to keep the object cool, and lubrication to eliminate any metal particles.
Solid Sink EDM
Another option for CNC machining in metal is a solid sink EDM. With this method, you put a conductive electrode that is bathed in a dielectric fluid near the piece you are working on. The electrode will discharge, and this process forces metal particles away from the object.
Note that the electrode doesn’t touch the metal you are machining but rather is a sacrificial tool. As a result, you will likely need to replace it frequently.
You can use the solid sink EDM process to make holes, pockets, and other features within steel tools and other hard metals that are difficult to work with. Similarly, EDM can be used for plastic injection molds, recessed (or debossed) lettering, and other textured surfaces.
If you need to make circular and smooth features on a metal object, consider using wire EDM. This option relies on a conductor made of copper wire to create a high-voltage electric charge.
The machine feeds the wire from a spool since the conductor will erode during the cutting process. A necessary thing to note about wire EDM is that you can’t use it in a blind hole because it needs a pass-through.
Wire EDM is most often used on hardened or thick tool steel to create circular or semi-circular features that you could not create with other conventional cutting tools.
Surface grinding is the best option for making extremely flat surfaces. It uses a precision grinder in the form of a spinning disk.
Depending on your needs, you can swap out the disk to adjust the coarseness or abrasive grit of the piece. Once you select the appropriate grinder, you will need to mount the metal on the table and move it back and forth under the grinder.
Expertise is required to use surface grinding tools on metal since mechanical stress and high heat can damage the object. In other words, you must carefully control the temperature and speed of the tool to get the right results.