Additive Manufacturing (AM) or 3D printing is basically a process that adds some materials to the previous surface via different deposition techniques that lead to different part quality, density, and geometrical accuracy.
One of the main purposes of using AM is to save manufacturing time and increase production speed. This will accelerate prototyping and reduce the time of production of spare parts and replacement parts.
The conventional processes are usually subtractive or a combination of several processes in case of complicated parts. The major drawback of conventional processes is the high amount of material waste and lack of control systems to continuously modify the processes based on the current conditions.
With the rise of computer-controlled machines, additive manufacturers currently use different techniques to solve the problems in traditional methods and widen the selection range of processes for manufacturers and customers. Each process has its own key features, advantages, and disadvantages, depending on three important key features: time, cost, and flexibility. This post will give a quick overview of different techniques used in additive manufacturing.
1. Selective Laser Melting (SLM)
Selective laser melting (SLM) is one of the most popular techniques of AM. In SLM, metallic particles are fed in different layer thicknesses, and a laser beam melts the desired regions of the surface. In the next step, a new layer of powder is distributed on the build plate, and the laser source melts the powder until the deposition finishes, and the final shape is achieved
- Materials used: Metals, ceramics
- Applications: Industrial purposes, bio-applications, implants, actuators
- Advantages: Unlimited level of geometrical complexity, a wide range of metallic and ceramic powders, clean parts, high density
- Challenges: Fine powder is needed, fabrication chamber needs inert gas, slight metal evaporation in high laser powers
- Accuracy: 50–150 µm
- Post-Processing: Heat treatment, in some cases a slight deburring
2. Metal jetting
Material jetting binds materials to the main body of a part. In this, polymers are usually melted and deposited in droplets to form the needed geometry. The molten polymers then undergo a curing process by heat, light, or chemical reactions to increase the bonding strength.
- Materials used: Polymers, plastics
- Applications: Desktop applications, research purposes, bio-applications
- Advantages: High speed of fabrication, high flexibility in the process, low cost
- Challenges: Limitations in feedstock material selection, low geometrical accuracy in complex parts, and it is not consistent
- Accuracy: 5–200 µm
- Post-Processing: Usually some slight deburring and residue removal with hand
3. Binder jetting
Binder jetting works on the same principle as material jetting. However, in binder jetting, there is a prepared bed of metallic powder laying under a jetting nozzle that disperses bonding polymers selectively on the surface of the metallic powder. After applying the polymer glue on the surface, a new layer of metallic powder is deposited, and glue dispersion occurs. This cycle continues until the final shape is achieved.
- Materials used: Polymers, ceramics, metals
- Applications: Industrial purposes, research, bio-applications
- Advantages: High quality of the final part, high geometrical accuracy, flexibility in feedstock material
- Challenges: Residual thermal stresses, unwanted porosity due to using bonding materials
- Accuracy: 50–200 µm
- Post-Processing: Sintering, heat treatment
4. Sheet lamination
Sheet lamination is another AM process, which assembles metal sheets on top of each other to form a 3D object. In this process, different glues, welding, and brazing can hold the sheets of material in place for a longer time, but ultrasonic welding is the most efficient and the most common. The sheets are fed into the building area in the needed geometry, and an ultrasonic head punches them against the previous layer and lightly welds them together. This process is cheap and fast, while the second material removal is needed after the parts are done.
- Materials used: Polymers, metals, and ceramics
- Applications: Electronics, tissue fabrication
- Advantages: High speed of fabrication, low residual stresses
- Challenges: Low accuracy of the final product, the chance of delamination under harsh thermal/mechanical conditions
- Accuracy: Depends on the thickness of the sheets
- Post-Processing: Internal material residue removal, clamping in some cases that glue is used
5. Photo-polymerization
Photo-polymerization is a process employing UV light to cure polymers layer-by-layer, and the processing speed is high while it keeps the process’s simplicity. In addition to polymers, researchers have tried to mix the polymers with ceramic particles to produce stronger mechanical objects with bio-applications.
- Materials used: Acrylonitrile butadiene styrene (ABS), epoxy, polystyrene, acrylate
- Applications: Biomedical, electronics, alpha prototyping
- Advantages: High geometrical accuracy, high surface quality
- Challenges: Limitation in feedstock material selection, low fabrication speed
- Accuracy: <10 µm
- Post-Processing: Slight deburring
6. Extrusion
The extrusion method is mostly used for thermoplastics and requires high operating temperatures. As a result, the final parts usually suffer from high porosity, but the low processing cost and flexibility in geometry increase its applications in making different mechanical parts. In addition, some researchers have tried to make ceramic-reinforced polymers with this method.
- Materials used: Thermoplastics such as ABS, Polylactic acid (PLA), polyethylene, polyether ketone, polycarbonate
- Applications: Visual aids, educational models, alpha prototypes, tooling models
- Advantages: Simplicity, low cost, high speed
- Challenges: Low geometrical accuracy, low surface finish, only for polymers and thermoplastic materials
- Accuracy: ~100 µm
- Post-Processing: Nil
