When it comes to 3D printing, metal 3D printing is worth discussing for the high strength and durability of metals. Primarily, metal 3D printing is synonymous with additive manufacturing, which deals with creating products by building layers one by one.
There are various metal 3D printing techniques. Thus, you can choose between material types in order to have a perfect combination of durability, cost, surface finish, and speed. Here is a complete guide to the process, working, types, and applications of metal 3D printing.
What is Metal 3D Printing Technique and How Does it Work?
Metal 3D printing is an additive manufacturing technology that produces metal parts in the form of layers by sintering, melting, and welding. Metal 3D printing typically uses metal powder for operation. Generally, a large range of metal alloys and metals, including stainless steel, aluminum, cobalt chrome, and titanium, are involved in 3D metal printing.
The working of metal 3D printing mainly revolves around SLM and DMLS. So, let’s see how it works:
Before moving towards the working of metal 3D printing, let me introduce the build platform. Usually, the metal parts are attached to them through supporting structures made from the same material as the parts. The build platform mainly prevents distortion or bending because of high temperatures.
The first step is to minimize the probability of the oxidation of metal powder by filling the build chamber with inert gas, i.e., argon. Then the build chamber is heated at optimal temperature.
After spreading the thin layer of metal powder, the cross-section of the component is scanned with a high-power laser.
Consequently, the metal particles fuse and give rise to another layer. Likewise, the complete area of the metal part is monitored to ensure the formation of a fully solid product.
As soon as the scanning process finishes, the build platform shifts downwards and spreads a second thin layer of metal using a recoater. The process keeps repeating until the formation of the final product.
Once the product is formed and the bin cools to room temperature, the excess metal powder needs to be removed manually by technicians. Afterward, the part is heat treated without detaching it from the build platform. Here, the build platform serves to relieve residual stresses of the part.
Finally, it’s time to separate the component from the build platform through machining or cutting. Now, you may use the part for further post-processing.
What are the Different Types of Metal 3D Printing Techniques?
As discussed earlier, metal powder is a key element of metal 3D printing. Therefore, the difference between all types of metal 3D printing techniques lies in the fusion of the powder into metal parts. These techniques involve different sources for the working of a metal 3D printer.
Classification of Metal 3D Printing Techniques
Powder Bed Fusion
|Binder Jetting||Material Jetting||Material Extrusion||Vat Polymerization||Direct Energy Deposition||
|Binder jetting||Material Jetting DOD||FDM
Electron Beam DED
Tungsten Carbide, Nickel-based alloys
Titanium alloys, Nickel alloys, Aluminum alloys, copper, Stainless steel
Stainless steel, Nickel alloys, titanium alloys, cobalt alloys
Paper, Metals, Ceramic, polymer,
Below, we’ll look at its significant types, their working, and uses:
1. Powder Bed Fusion
Powder bed fusion is the most frequently used metal 3D printing technique. The working principle of these machines is that they spread a fine layer of powder and use a thermal source to melt a cross-section of the part into a powder layer.
In order to learn in-depth information about this process, you should look at its popular types. Whenever it comes to metal 3D printing, the first image that appears in mind is DMLS and SLS. Typically, SLM (Selective Laser Sintering), DMLS (Direct Metal Laser Sintering), and MJF (Multi Jet Fusion) are types of powder bed fusion. Let’s discuss these types one by one:
Direct Metal Laser Sintering stands higher because you can make parts from any metal alloy by using it. Whereas other 3D printing methods are only compatible with specific metal alloys or polymer-based materials. Although the working of DMLS is quite similar to SLS, the difference lies on the molecular level. Instead of melting the metal powder, it is only sintered together. Ultimately, you get less porous parts as compared to the melting technique.
Also, less energy is required in the case of DMLS as it doesn’t require heat to melt the metal powder. The process is specifically used to create products with undercuts, cavities, and draft angles. You can find its major applications in functional prototypes, tools, and medical devices or instruments.
By using this method, you can get extremely dense and strong printed objects. Typically, a high-power laser is used to join the small powder particles into a three-dimensional part. Once a layer is fused, a roller is moved over the bed to ensure the distribution of the next powder layer. Later, the majority of loose powder is removed by manual brushing.
SLS is ideal for dealing with mechanical parts, including propellers and gears. Further, this process manufactures the parts for the automotive, aerospace, and medical industries.
Multi Jet Fusion technology deals with sweeping arms. Firstly, a sweeping arm applies the layer of powder then the second arm, which consists of inkjets, selectively deposits a binder agent over the particular workpiece. Moreover, the inkjet provides smooth and precise surfaces by applying a detailing agent around the binder.
Advantages of PBF
The following are some common advantages of the powder bed fusion method:
- You can fabricate a wide range of geometries.
- Provides the best mechanical properties to the products.
This method has certain downsides, like high expenses, limited build sizes, waste production, and dangerous handling of metal powders.
2. Binder Jetting
The binder jetting technique in 3D printing was developed in the 1990s. The purpose was to come up with low-cost metal 3D printing that could also be highly effective.
The method starts when the initial material is deposited in the printer in powder forms like sand, metal powder, ceramic, or polymer. Then the binder agent is applied through inkjet, and each layer is printed onto the build platform. As the process repeats, the powder is recoated after each layer until the printing is completed.
This technique can produce a large number of high-quality parts and machining tools in a short period. Plus, you may find its applications in manufacturing sand-casting molds, realistic models, and low-cost prototypes.
While using this technique can expect the following benefits:
- Low cost.
- 2 mm dimensional accuracy.
- Excellent color production.
Besides its remarkable benefits, results are still not up to the mark. You can only use it for low-intensity applications.
3. Material Jetting
Material jetting, also known as poly jet, is a quite popular technique in 3D printing. It uses viscous photoreactive materials like waxes and photopolymers(liquid) as commonly used materials due to their viscosity. Due to their viscous nature, they form fine droplets to form layers. Generally, the method utilizes UV light to solidify the material on parts. The product is mainly made layer by layer until it is completed.
This technique can be used in applications like prototyping to create brightly visual prototypes for different brands and medical models.
- The accuracy can be as high as 0.01 millimeters per thin layer.
- It provides a smooth surface finish.
- The process offers a wide color range for material parts.
The downsides of material jetting are that it is unsuitable for mechanical applications and is a low-speed printing process.
4. Material Extrusion
As the name suggests, this 3D printing technique works on the principle of extrusion, where the material next to its melting point is passed through a small opening. This technique works by depositing composite filaments and thermoplastic materials on a predetermined path to form layers. The materials common for material extrusion are PLA, PA, ABS, TPU, carbon fiber, and more.
Usually, material extrusion in 3D printing is applicable for electronic housings, investment casting patterns, fixtures, etc.
There are two sub-types of material extrusion:
- FDM (Fused Deposition Modeling)
- FFF (Fused Filament Fabrication)
FDM technology deals with plastic filament which is first liquified and then re-solidified into a required shape (already set by a CAD model). Typically, heating an extrusion nozzle is responsible for melting the plastic. The melted material tends to form layers and after hardening, it results in a 3D object.
FFF technology is exactly similar to FDM. However, FDM parts are considered stronger than FFF parts. When it comes to the working of FFF, it lacks a heated print environment which is a key factor in less accurate results of products.
Here are some great benefits of metal extrusion:
- You can easily operate it with high safety.
- Provide fast printing for delicate parts.
Material extrusion is not preferable in terms of accuracy and speed due to the limited radius of the nozzle. Also, technicians need to maintain the final finish quality of the product.
5. Vat Polymerization
Vat Photopolymerization is one of the additive manufacturing processes that only uses the photopolymer as a significant material for this technique. Usually, photopolymer resin is available in various colors. Typically, it uses UV light to cure the resin and provides a perfect surface finish.
In addition, the photopolymerization process occurs when the molecules of liquid photopolymers are exposed to different wavelengths of light. As a result, they quickly bond together and harden into a solid.
Vat polymerization techniques are common for producing pieces with fine details like jewelry work and different dental and clinical applications.
This 3D technique has further different types:
- SLA (Stereolithography)
- DLP (Digital Light Processing)
- CDLP (Continuous Digital Light Processing)
SLA is known best for providing tight resistances, elevated levels of detail, and smooth surface finishes. The working of this type involves a build platform that is dipped into a resin-filled container. During this, only one layer of height is left between the bottom of the resin tank and the build platform. Afterward, a galvanometer with the aid of G-code traces the laser beam in the path, which is responsible for creating a layer on the part.
Later, the cross-section of a particular part is re-coated with fresh material. Following the same steps, new coatings can be formed on this re-coated surface.
As the name suggests Digital Light Processing method uses light and photosensitive polymers for printing. It differs from the SLA only due to the light source. It uses different projected light sources, such as arc lamps. Furthermore, it is considered faster than SLA.
DLP is ideal for printing intricate patterns on resins in order to form toys, dental molds, jewelry molds, figurines, and many other products of fine details.
CLIP is the fastest VAT polymerization technique that produces smooth-sided objects of various shapes. This technology explicitly uses a UV projector, oxygen, and photosensitive resin to produce a 3D object.
The build platform is slightly submerged in a photosensitive resin well. When this build platform rises, UV light reacts with the resin, resulting in the hardening of the material. At this point, UV light and oxygen are adjusted to alter the shape of the part while it rises from the resin well. One of the significant purposes of CDLP is to generate mechanical properties in truly isotropic parts.
- It provides high-quality, detailed work.
- Plus, it offers fast printing.
In addition to the benefits of vat polymerization, it also lacks strength, and UV light may affect resin even after printing. Moreover, with time, the resin can warp and bend.
6. Direct Energy Deposition:
Direct Energy Deposition in 3D printing is a complex technique typically used in repairing industrial parts. In this process, only metal in the form of wire or powder is used. Additionally, it doesn’t require any extra support structure and uses a high-energy source like a laser or electron beam to melt the material simultaneously as printing occurs.
However, depending on different applications, this technique is also known as DMD, LENS, EBAM, etc.
The applications for this technique in the industrial sector are repairing damaged paddles or turbine blades.
- Larger parts can be manufactured with higher efficiency.
- Allow fast printing as compared to other metal 3D printing techniques.
- The process creates high-density products with excellent mechanical properties.
No doubt, the overall performance of this method is outstanding, but it is relatively very expensive. In addition, it works without using support structures, eliminating the possibility of overhangs.
7. Sheet Lamination
Sheet lamination follows the layer-by-layer phenomenon to form a 3D part. In this method, thin metal sheets are stacked and laminated, ending in a single piece that can be converted into a 3D object by cutting. The lamination may include ultrasonic welding, brazing, or bonding. Once the printing process is completed using this method, the resulting products are modified by machining or drilling.
- Materials are easy to handle
- No additional support system is required
- The use of standard material saves the cost
- After post-processing, it offers a faster print time
Sheet lamination technology offers limited material options. Also, it may be difficult to remove the excess material after lamination is done. Above all, this method leads to a lot of waste.
Characteristics of Metal 3D Printing with Respect to SLM and DMLS
1. 3D Printer Parameters
The parameters are already set in a printer by machine manufacturers. Usually, 20 to 50-micron layer height is used. On the other hand, the general build size of the system is almost 250 * 150 * 150 mm, yet larger ones are also available in the market.
Furthermore, during SLM and DMLS, less than 5% of metal powder is wasted in the form of support structures. However, the maximum powder can be recycled.
2. Layer Adhesion
The parts produced by DMLS and SLM printers have high thermal and isotropic mechanical characteristics. These solid parts feature very slight internal porosity. Whereas they possess higher strength and hardness as compared to other traditional techniques.
However, their high surface roughness makes them prone to fatigue.
3. Lightweight Structures
In metal 3D printing, a lattice structure is typically used to obtain lightweight parts. Also, you may go for topology optimization algorithms to get organic, lightweight designs.
4. Support Structures
Support structures are crucial to SLM and DMLS printers to tackle the consequences of high processing temperatures. The three significant functions of these structures are as follows:
- They serve to attach the workpiece to build plates to avoid warping.
- It helps to form the next layer to be built upon.
- They play a vital role in drawing heat away from the component. Hence, it cools at a rapid rate.
You might have observed that along with several benefits of different metal 3D printing techniques, there are certain downsides also. Especially when considering the relatively high cost of metal powders and 3D printers, the best solution is to get customized 3D prints on demand.