A Review of Additive Manufacturing

Additive manufacturing also known as 3D printing is a process in which a CAD file is converted into a STL
file to create objects by slicing and approximating drawings into layers. This technology has various field
of applications such as aerospace, medicine and architecture. Limitation of materials and accuracy issues
are some challenges that must be resolved before this process becomes standard in the manufacturing
industry. However the continuous growth and positive outcomes indicates that it has significant role in
the future of manufacturing.

Rapid prototyping:

Rapid prototyping is one of the earliest additive manufacturing process. It was initially used for making
models and prototype parts .But now it is used to create finished products. It is not widely adopted in
the manufacturing sector yet but Rapid prototyping is most used by Scientists, Doctors and Artists.
CAM ,CAD and CNC are technologies with the help of which rapid prototyping is possible. It can be used
to print 3D objects. For larger parts CNC is required and materials for rapid prototyping are limited. Thus
It is still not the best solution.

The steps involved in product development using Rapid prototyping are shown below

Stereolithography:

It was the first and most widely used process of Rapid prototyping. It is a liquid based process.
Photopolymerisation is the basic principle of stereolithography. Overcuring and scanned line shape are
the errors induced to the final piece from the process of stereolithography.

The basic parts of stereolithography machine are shown below

Standard Tessellation Language is widely used in additive manufacturing processes. It was It was
introduced by 3D systems Inc. An STL file is created by converting the continuous geometry from a CAD
file into a list of coordinates and normal vectors representing small triangles.

The data flow in the STL file section software is shown below

3DP-A 3D Printing Process in which water-based liquid binder is supplied in a jet onto a starch-based
powder .They are glued together when the binder is jetted ,similar to an inkjet printer. The main
advantage of 3DP is that it has ability to produce complex geometries with high precision and accuracy.
To print the data CAD Drawings are used. Although produced resolution and surface finish are sufficient
for some applications but post-processing and finishing methods allow for benefits such as greater
dimensional accuracy & smoother surfaces.
Fused Deposition Modeling(FDP)- A thin filament of plastic is taken where a print head melts it and
eject it in a thickness of 0.25 mm. No chemical is required in finishing and it is a cost effective
process.The main disadvantage is low resolution on Z-axis Compared to other processes. polycarbonate
(PC), acrylonitrile butadiene styrene (ABS),polyphenylsulfone (PPSF), PC-ABS blends are used in this
process. Thera are two modes of FDP; a fully dense mode and a sparse mode . Sparse mode saves time
but it reduces the mechanical properties.

Prometal-A powder based process used to build stainless steel products. Process occurs when a liquid
binder is spurt out in jets to steel powder.Powder is located in powder bed and powder bed is controlled
by pistons. If a functional part is being built than various processes are required. -Such processes are
sintering , infiltration & finishing process . In the sintering process the binder fusing with the steel is
hardened. For manufacturing of rocket nozzle carbide powder is sintered with zirconium copper alloy.

Selective Laser Sintering-A process in which carbondioxide laser beam is used to fuse powder. variety of
materials that could be used: plastics, metals, combination of metals, combinations of metals and
polymers, and combinations of metals and ceramics. composites or reinforced polymers that is
polyamide with fibreglass can also be used. They could be reinforced with metals like copper . Binder is
necessary for metals which is removed by heating it. Polyvinyl alcohol an organic binder can be used to
give strength to alumina. The main feature of this technology is the use of wide range of materials.

Electron Beam Melting-A rapidly growing process in which electron laser beam powder by high voltage
is used to melt powder. Possible use of this process is the manufacturing in outer space. The voltage
ranges from 30 to 60 KV. This process takes place in a vacuum chamber to avoid oxidation issues as it is
used to manufacture metal parts. It can also process a high variety of prealloyed metals.

Laser Engineered Net Shaping-In this process melting metal powder can built part. The powder is
molten with the use of a high-powered laser beam. The part solidifies when it is cooled down. Argon
environment is necessary for the process. Metals and combination of them like stainless steel, nickel
based alloys, titanium-6 aluminium-4 vanadium,toolingsteel, copper alloys are used in this process. It is
also used in repairing parts. The main problem of this process is the residual stress by uneven heating
and cooling process.

Laminated Object Manufacturing-It is the combination of additive and subtractive techniques to build a
part layer by layer. The different layers are bonded together by pressure and heat application and using a
thermal adhesive coating. It is highly economic process & no post processing is required. The main
drawback is the waste of material in this process. This process can be used for models with papers ,
composites, and metals.

Polyjet-In this process inkjet technologies is used to manufacture physical models. Photopolymer is
deposited on x and y axes which is cured by ultraviolet lamps. The minimum layer thickness is 16 μm .
The parts produced in this process are weaker than others. After the process is finished the material is
water jetted. For supporting the overhang feature a gel type polymer is used. This process produces
parts with multiple colours.
Applications
Lightweight Machines

Additive manufacturing technologies enable the production of lightweight parts, benefiting industries
such as automotive and aerospace. The aim is to create the lightest feasible vehicles while ensuring
safety. Additive manufacturing allows for the manufacture of complex structures like honeycomb cells,
reducing weight while maintaining strength. Methods such as the hanging method and soap film method
can be used to create lightweight structures. Selective laser sintering and electron beam melting are
utilized in aerospace industries, expanding design possibilities. Hollow structures can be produced,
reducing costs by using less material.

Architectural Modeling

Architects face challenges when creating complex architectural models using traditional hand
techniques. Additive manufacturing offers architects a powerful tool to quickly create physical models,
regardless of design complexity. It provides better resolution compared to other architectural processes.
Architects can seamlessly transition from CAD software to additive manufacturing using STL files.
Stereolithography is particularly suitable for architectural modeling due to its materials and printing
resolution.

Medical Applications

Additive manufacturing printing technologies have significant applications in the medical field. They
revolutionize medical practices by enabling the creation of rapid prototypes, high-quality bone
transplants, and models of damaged bones for analysis. These methods allow doctors to scan and
produce physical models of defective bones, aiding in better planning and cost-effective procedures.
Bone transplants can now be printed, providing practically identical replacements. Doctors have the
flexibility to create porous-controlled materials for osteoconductivity or precise metal transplants,
depending on the specific bone replacement needed.

Improving the Manufacturing of Fuel Cells

Additive manufacturing technologies offer precise deposition of thin films, crucial in manufacturing
polymer electrolyte membrane fuel cells (PEMFCs) with high utilization efficiency of platinum. Traditional
methods like screen printing compromise uniformity and time efficiency. Using 3D printing, specifically
inkjet printing, significantly improves the process, being 4 to 5 times faster than screen printing.