Additive manufacturing (AM) is the industrial production name for 3D printing, a computer-controlled process that creates three-dimensional objects by depositing materials, usually in layers. Using computer-aided design (CAD) or 3D object scanners, additive manufacturing allows for the creation of objects with precise geometric shapes. These are built layer by layer which is in contrast to traditional manufacturing that often requires machining or other techniques to remove surplus material.
Laser metal deposition manufacturing (LMD)
There are several distinct AM processes with their own standards, which include:
This technique uses a 3d printing style head moving on x, y, and z axes to deposit alternating layers of powdered material and a liquid binder as an adhesive.
Directed Energy Deposition
Direct energy deposition AM can be used with a wide variety of materials, including ceramics, metals, and polymers. A laser, electric arc or an electron beam gun mounted on an arm moves horizontally melting wire, filament feedstock or powder to build up material as a bed moves vertically.
This common AM process uses spooled polymers which are either extruded or drawn through a heated nozzle which is mounted on a movable arm. This builds melted material layer by layer as the nozzle moves horizontally and the bed moves vertically. The layers adhere through temperature control or chemical bonding agents.
Powder Bed Fusion
Powder bed fusion encompasses a variety of AM techniques including direct metal laser melting (DMLM), direct metal laser sintering (DMLS), electron beam melting (EBM), selective laser sintering (SLS) and selective heat sintering (SHS). Electron beams, lasers or thermal print heads are used to melt or partially melt fine layers of material after which excess powder is blasted away.
"Using computer-aided design (CAD) or 3D object scanners, additive manufacturing allows for the creation of objects with precise geometric shapes"
Sheet lamination can be split into two technologies— laminated object manufacturing (LOM) and ultrasonic additive manufacturing (UAM). LOM is suited to creating items with visual or aesthetic appeal and uses alternate layers of paper and adhesive. UAM uses ultrasonic welding to join thin metal sheets; a low energy, low-temperature process, UAM can be used with various metals such as aluminium, stainless steel, and titanium.
This process uses a vat of liquid resin photopolymer to create an object layer by layer. Mirrors are used to direct ultraviolet light which cures each resin layer through photopolymerization.
Wire Arc AM
Wire arc AM uses arc welding power sources and manipulators to build 3D shapes through arc deposition. This process commonly uses wire as a material source and follows a predetermined path to create the desired shape. This method of additive manufacture is usually performed using robotic welding equipment.
AM technologies can be broadly divided into three types. The first of which is sintering where the material is heated without being liquified to create complex high-resolution objects. DMLS uses metal powder whereas selective laser sintering uses a laser on thermoplastic powders so that the particles stick together.
The second AM technology fully melts the materials; this includes DLMS which uses a laser to melt layers of metal powder and electron beam melting, which uses electron beams to melt the powders.
The third broad type of technology is stereolithography, which uses a process called photopolymerization, whereby an ultraviolet laser is fired into a vat of photopolymer resin to create torque-resistant ceramic parts able to endure extreme temperatures.
What are the Advantages of Using AM?
Similar to standard 3D printing, additive manufacturing allows for the creation of bespoke parts with complex geometries and little wastage. Ideal for rapid prototyping, the digital process means that design alterations can be done quickly and efficiently during the manufacturing process. The lack of material wastage provides cost reduction for high-value parts, while AM has also been shown to reduce lead times.
In addition, parts that previously required assembly from multiple pieces can be fabricated as a single object which can provide improved strength and durability. Additive manufacturing can also be used to fabricate unique objects or replacement pieces where the original parts are no longer produced.
TWI has one of the most definitive ranges of AM services.
What Materials can be used in AM?
There are a variety of materials used for AM, these include biochemicals, ceramics, metals, and thermoplastics.
Biochemicals used in AM include silicon, calcium phosphate, and zinc while bio-inks fabricated from stem cells are also being explored. These materials are generally used for healthcare applications.
A range of ceramics is used in AM, including alumina, tricalcium phosphate, and zirconia as well as powdered glass which can be baked together with adhesives to create new types of glass product.
A wide variety of metals and metal alloys are used for additive manufacturing, including gold and silver, stainless steel and titanium amongst others.
Thermoplastic polymers are the most commonly used of AM materials and include a variety of types with their own advantages and applications. These include acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and polycarbonate (PC) as well as water-soluble polyvinyl alcohol (PVA) which can provide temporary support before being dissolved.
Where is AM used?
Additive manufacturing is used to create a wide range of products across a growing number of industries, including:
AM is particularly suited to aerospace applications due to its weight-saving capability and ability to produce complex geometric parts such as blisks.
A variety of materials are widely additive manufactured for the automotive industry as they can be rapidly prototyped while offering weight and cost reductions.
The medical sector is finding an increasing number of applications for additively manufactured parts, especially for bespoke custom-fitted implants and devices.