Additive Manufacturing (AM), also known as 3D printing, builds parts through a CAD generated 3D model by adding single layers of material and fusing the layers together. AM first emerged in 1987 and has been steadily growing ever since, with more leaps and bounds in recent years. As companies invent and introduce new AM techniques, they tend to create unique marketing terms for their process, even though the core techniques are similar. Having different names for similar methods can easily lead to confusion in the marketplace. In the post, we will identify the core techniques and their advantages and disadvantages.
Per ISO/ASTM standards, AM divides the techniques used to create the layers into seven categories, of which the first four on the list are suitable for metals.
- Binder jetting
- Directed Energy Deposition
- Powder Bed Fusion
- Sheet Lamination
- Material Extrusion
- Material Jetting
- Vat Photo Polymerization
1. Binder Jetting
Unique in AM in that it does not use heat during the materials fusing process. A binding liquid or binder is selectively deposited, which joins the powder material together to form the 3D part. Depending on the type of powder, the system being used, or customer application requirements determines the selection of the kind of binder. The process starts with the powder material being spread over the build platform using a roller and the print head deposits the binder on top of the powder where specified. The build platform lowers to allow for the next layer, and the process repeats until the item is complete. Any unbound powder gets removed.
Advantages of Binder Jetting
- Ability to make parts with a range of different colors
- Uses a range of materials: metal, polymers, and ceramics
- Faster AM process
- No warping or shrinking of parts
- Less waste by reusing any unused powder
- Features a two-material method that allows different binder-powder combinations
Disadvantages of Binder Jetting
- Parts require post-processing which adds significant time to the overall process
- Low part strength, not always suitable for structural parts
- Less accurate then Material Jetting
2. Directed Energy Deposition (DED)
DED creates 3D objects by melting and depositing either powder-based or wire-based materials from a focused thermal energy source, including laser, electron beam, or plasma arc. While the process can make metal, ceramic, and polymer parts, it is mainly used for metal parts and in more hybrid manufacturing where the substrate bed is moveable to create complex shapes. DED is also referred to as laser metal deposition (LMD), 3D laser cladding, or direct light fabrication because of the different energy sources uses and final use. Lastly, based on how the process works, it’s mainly used for repairing or reconditing existing parts by adding material where needed.
Advantages of DED
- Strong and dense parts
- Fast build rates
- Reduction in material waste
- Range of material selection: metal, ceramic, and polymer
- Materials are easily changed out
- Ability to make parts with custom alloys
- Parts built to near net shape
- Capability to build larger parts
Disadvantages of DED
- Capital cost for systems are high
- Parts have lower resolution resulting in poorer surface finish, requiring secondary processing
- Support structures are not usable during the build process
3. Powder Bed Fusion (PBF)
PBF has four categories of energy sources, laser fused, electron beam fused, fused with agent and energy, and thermally fused. The energy source melts either plastic or metal powder particles, which solidifies and fuses together in a pattern to make the object. The powder bed fusion process uses two chambers, the build chamber and powder chamber, and a coating roller. To create the objects, the coating roller moves and spreads the powder material across the build chamber to deposit a thin layer of powder. Some PDF processes will use a scrapper, blade, or leveling roller after the coating roller to ensure the thickness of the material top layer is uniform. Next, the energy source melts the deposited top layer of the metal powder base. When that layer has been scanned and fused, the build platform is incrementally lowered down, simultaneously the powder chamber is raised by the same, and the process repeats until the object completed.
Advantages of PBF
- Low cost of machines
- No or minimum support structures needed for the build
- Variety of material selection
- Multiple materials can be used
- Capable of recycling powder
Disadvantages of PBF
- Slow and long print time
- Additional post-processing time
- Weaker structural properties
- Variations of surface texture quality
- Support build plate may be needed to avoid warping
- Speed of the print process can determine if the powder is recyclable
- Thermal distortion, mainly for polymer parts
- Machines use a lot of energy to create parts
4. Sheet Lamination
AM that builds 3D objects by stacking and laminating thin sheets of material through bonding, ultrasonic welding, or brazing. To create the final shape of the object, laser cutting or CNC machining is used. Of all the AM technologies, this produces parts with the least additive resolution or amount of detail but provides low cost and faster manufacturing time for quick prototyping using readily available, low-cost material.
Sheet lamination can be categorized into seven types:
- Laminated Object Manufacturing (LOM)
- Selective Lamination Composite Object Manufacturing (SLCOM)
- Plastic Sheet Lamination (PSL)
- Computer-Aided Manufacturing of Laminated Engineering Materials (CAM-LEM)
- Selective Deposition Lamination (SDL)
- Composite Based Additive Manufacturing (CBAM)
- Ultrasonic Additive Manufacturing (UAM)
While the types of sheet lamination differ slightly, the overall principle is the same. The process starts with a thin sheet of material being fed from the roller or placed onto the build platform. The next layer may or may not be bonded to the previous sheet, depending on the process. Layering continues until it achieves the full height. Removal of the print block and all the unwanted outer edges complete the object.
Advantages of sheet lamination
- Relatively low cost
- Larger working area
- Full-color prints
- Integrates as hybrid manufacturing systems
- Ease of material handling
- Ability to layer multiple materials
- No support structures needed
- In some sheet lamination
- Depending on technique type used, the material state remains unchanged
- Faster print time, but does require post-processing
Disadvantages of sheet lamination
- Layer height can’t be changed without changing the sheet thickness
- Finishes can vary depending on the material and could require post-processing
- Limited material options available
- Removal of excess material after the laminating phase can be difficult and time-consuming
- Can generate more waste in comparison to other AM methods
- Hollow parts are challenging to produce in some types of sheet lamination
- Bonding strength is dependent on the laminating technique used
5. Material Extrusion
The most popular AM process in terms of availability for general consumer demand and quality, uses a continuous filament of thermoplastic or composite material to construct 3D parts. The material in the form of plastic filament fed through an extruding nozzle, where it heated and then deposited onto the build platform layer by layer.
Advantages of Material Extrusion
- Wide selection of print material
- Easily understandable printing technique
- User-friendly method of print material change
- Low initial and running costs
- Faster print time for small and thin parts
- Printing tolerance of +/- 0.1 (+/- 0.005″)
- No supervision required
- Small equipment size
- Low-temperature process
Disadvantages of Material Extrusion
- Visible layer lines
- Extrusion head in continuous motion or the material bumps up
- Supports may be required
- Weak part strength along Z-axis
- Increased print time with finer resolution and wider areas
- Susceptible to warping and other temperature fluctuation issues
- Toxic print materials
6. Material Jetting
A process where droplets of wax-like materials are selectively deposited on a build platform. The material cools and solidifies, allowing layers of materials to be placed on top of each other. After the build, support structures are either mechanically removed or melted away.
Advantages of Material Jetting
- Material jetting can achieve outstanding accuracy and surface finishes
- Parts are good for use in patterns for casting
Disadvantages of Material Jetting
- Limited number of wax-like materials available
- Parts are fragile because of wax-like materials
- Slow build process
7. Vat Photo Polymerization
The process used to cure photopolymer liquid resin in a vat layer by layer, turning it into hard plastic parts using an ultraviolet (UV) laser. The three most common types of this technology include Stereolithography, Digital Light Processing (DLP), and Continuous Digital Light Processing (CDLP).
Advantages of Vat Photo Polymerization
- High level of accuracy and good finish
- Relatively quick process
- Large build areas
Disadvantages of Vat Photo Polymerization
- Relatively expensive
- Lengthily post-processing time and removal from resin
- Limited to photo-resins materials
- Can still be affected by UV light after print
- May require support structures and post-curing for parts to be strong enough for structural use
Conclusion
As additive manufacturing machines become more affordable for machine shops, the flexibility in design and material properties is leading itself to providing a wide range of practical applications and uses. Aerospace, automotive, and medical industries are all seeing benefits from additive manufacturing. Quick prototyping, low volume production, and ability to repair parts are some of the reasons for the growth of this type of manufacturing.
