3D Printing - A Leading Edge Technology

 3D printing is a manufacturing process to fabricate physical object of materials like polymers, metals, composites, bio-materials, edibles, etc. from the object’s Computer-Aided-Design [CAD] Model i.e., its digital model.

There are two types of processes

1) Additive manufacturing processes

2) Subtractive manufacturing processes

In additive manufacturing process, the material is added to form a product while in subtractive manufacturing process, the material is removed in order to create an object.

3D printing comes in the category of additive manufacturing processes as it creates an object by layering method.

It is possible to manufacture products with wide range of size, shape, colour, rigidity, and with variety of materials which are either in powdered or melted form.

3D printing technology:

                                                     (The 3D Printing Machine Operation)

Generally following steps are followed in 3D printing.

I. 3D Modelling

II. Slicing Operation

III. Printing Operation

IV. Post Operation

Let’s have a close look at every step for better understanding the 3D printing technology.

I. 3D Modelling

This is the most fundamental step where Computer-Aided-Design [CAD] software application is used to make a 3D model i.e. a digital design model of the object to be printed. Here along with a CAD software many software like 3D scanners, Photogrammetry software (to extract geometric information from the image) becomes useful. In this step of 3D printing we can customize the design of product and look for intricate details of it to obtain high precision.

After performing a design operation of the object in CAD software, it is extracted in any of file format like STL, OBJ, AMF or 3MF

STL is nothing but Standard Triangle Language. It is very simple hence widely used. In STL file format, the object surface is represented as planar straight triangles. Each triangle shares its

edges and vertices with the other to build a platform. But this format is old and having some limitations as follows:

1. Errors such as leaks and inconsistencies.

2. Cannot support colour, material or orientation.

3. As the size of object increases, then to maintain the resolution of the file the number of triangles increases significantly resulting in a very large sized file.

AMF i.e., Additive Manufacturing File format which is recently developed in 2011 can solve such problems. It is based on XML format which stands for Extensible Markup Language (similar to HTML) which is easy to read, write and process. Also, AMF is superior to STL in supporting geometry, scale, colour, materials, lattices, orientations. One more reason for AMF to be superior to STL is that along with planar straight triangles it has curved triangles which makes a lot of difference in modelling.

Despite of these many advantages of AMF over STL, it is less adopted by 3D printing industry than STL.

To have flawless 3D printed product, following requisites can be considered while designing

i. By using an option to ‘create mesh’ in 3D design software we can add 3D mesh in the model to have watertight i.e. completely closed model.

ii. STL file resolution should not be very low to avoid pixelated print and should not be very high to avoid large sized file.

iii. The base design in the model must be strong enough to have better adhesion to the printer bed, to give good support to the whole structure and to withstand different cooling rates. Also if there are certain delicate parts then such vulnerable parts should be made thick in model to avoid damages.

iv. Minimum wall thickness of the object and printing technology limitations must be considered while 3D modelling.

v. 3D model must be designed to avoid or minimize support structures not to have uneven surfaces or any marks on it.

II. Slicing Operation:

The 3d model can’t be interpreted by the 3D printer. A 3D slicer software is used to convert digital 3D model into a set of instructions which can be easily interpreted by a specific type of 3D printer. There are many such slicing software available which can slice the 3D model into many layers. Then each layer is given a specific value. These values give instructions to 3D printer how and where to move, how much amount of material to use. In this way printer becomes ready to print the object

III) PRINTING OPERATION:

After completing the steps of 3D modelling and slicing, the actual printing starts here in this step. With the combination of digital 3D model and a particular material, printer prints the object into three dimensions.

There are different types of printing technologies available for different applications based on different working principles. Some of them are below...

1. SL-STEREOLITHOGRAPHY:

In stereo lithography, a laser beam is directed in XY axes across the surface of the resin (photopolymer resin is generally used as a material) according to the digital 3d model provided to the printer. Wherever the laser hits, that part of resin gets harden. In this way layer by layer object is built. This technique sometimes requires support structures and finishing operations.

2. DLP-DIGITAL LIGHT PROCESSING:

This process is similar to SL in operation but instead of laser beam light source such as arc lamp with a liquid crystal display panel or a deformable mirror device (DMD) is used.

3. LASER SINTERING/ LASER MELTING:

Laser moves in the XY direction across the powdered material fed then the particles melt and form bonds with each other to build a layer. The process repeats to build the object layer by layer. Here the build chamber is strictly maintained at a specific temperature which is required to fuse the particles also due to this high temperature a considerable time is required to cool down the end product.

4. MATERIAL EXTRUSION/ FDM- FUSED DEPOSITION MODELING / FFF- FUSED FILAMENT FABRICATION:

The material in this process is in the form of filament (melted material) which is extruded by heated extrusion head and build the object as per the digital 3D model supplied to the printer by layering method.

5. BINDER JETTING:

The powder of material is first spread on the build platform. Referring to the 3D model binder is jetted onto it to form first layer of the object. Then build platform is lowered, again the powder is spread and binder is deposited by the print head to build the new layer. The process repeats until the whole object is formed layer by layer.

6. MATERIAL JETTING:

The melted material is jetted from the print head on the build platform to build the object layer by layer, according to 3D model. The layers are cooled, hardened or cured by the exposure of a UV light.We can also use multiple materials from multiple print heads to build an object.

7. SDL- SELECTIVE DEPOSITION LAMINATION:

The material is in the form of sheets. The sheets are added one by one and are bonded together with the help of adhesive and applied pressure. Before adding every new sheet, the previous stack is cut by a cutting tool (Tungsten carbide blade or laser) to obtain a product according to the 3D model given to the printer.

8. EBM-ELECTRON BEAM MELTING:

The process is same as laser melting in operation but instead of laser an electron beam is used to fuse the powder of material used hence it is carried out in vacuum condition.

There are many such additive manufacturing techniques available like VAT PHOTOPOLYMERIZATION, POWDER BED FUSION, and DIRECTED ENERGY DEPOSITION, etc.

IV) POST PRINTING OPERATION:

· To produce products with a high accuracy, some subtractive manufacturing processes with high resolution may require to trim the product to its standard size as prescribed; which is originally printed a bit oversized.

· Cleaning, painting or colouring, coating and surface finishing can be required for some 3d printed products.

· Some 3D printing technologies like FDM or Material jetting need support structures while building an object, that support structure should be deleted mechanically or dissolving it in a particular solution.

· Curing is another post operation where the product is heated to a temperature to enhance its mechanical strength, aesthetic properties.

Materials:

· Polymers: Nylon (polyamide), Acrylonitrile butadiene styrene (ABS), polycarbonate (PC), polyvinyl alcohol (PVA), Alumide (mixture of polyamide and grey aluminium) various types of resins and many more polymers are used as a powder form, melted and as filaments.

· Metals: stainless steel, gold, silver, titanium, aluminium, bronze, nitinol alloy and many such metals are used in powder or molten form.

· Ceramics: glass, porcelain, silicon carbide, etc.

· Composites: Alumide, composites with carbon fibers, glass fiber, wood polymer composite (Lay Wood/WPC), concrete etc.

· Food materials

· Bio materials

· Others: paper, graphene, graphite, hybrid materials, etc.

APPLICATIONS:

· Rapid prototyping: 3D printing is well known for rapid prototyping where it is used to quickly make a scale model for any physical part or assembly.

· Medical: 3D printing can be used in bio-printing (3D printing of biomedical parts by combining cells, growth factor and biomaterials), to manufacture medical devices, knee, hip implants and prosthetics, patient specific products (like various human organs), dental products, prototypes etc.

· Automotive: 3d printing is very beneficial in terms of rapid prototyping especially in automotive and in manufacturing vehicles and their spare parts, tools, fixtures and many parts with light weight and reduced cost.

· Construction: 3D printing is used in making architectural models with high complexities. Now it has become possible to build the whole house, bridges with help of huge 3D printing machine which can be built in lesser time.

                                       (Timelapse_of_3D-printer_construction_of_the_clay_house)

· Jewellery: 3D printing industry is trying to compete traditional methods of making jewellery like casting, smithing, forging, engraving, polishing in jewellery sector but still it is under improvements.

· Food: With all hygiene taking into consideration, we can use this technology for making edible items from foods like chocolate, sugar, meat, pizza etc. NASA is planning to make use of this technology to make astronaut's food and to reduce food waste.

· Fashion: As 3d printing technology is flexible and products can easily be customized it can be proved to be very helpful in fabricating fashion products such as various accessories like hats, shoes, bags and even cloths. This can be used effectively for experimentation purpose.

· Others: Arts, sculpture, computers and robotics, 3D selfies, education, consumer products, Aerospace, etc.

ADVANTAGES AND DISADVANTAGES: Some of the important advantages and disadvantages are listed below.......

ADVANTAGES:

1. It is very flexible.

2. It is incredibly accurate and ideal for rapid prototyping.

3. It is faster and cheaper as compared to traditional manufacturing processes with good quality.

4. It can easily deal with manufacturing of objects with complex geometries.

5. Products made from it are completely customizable.

6. It allows for the creation of parts with specific properties.

7. It is Eco-friendly in nature with minimum waste.

DISADVANTAGES:

1. 3D printed products can have a lower strength than that of other tradition processes.

2. Cost increases at higher volumes of objects.

3. Limitations in materials used and size to produce.

4. Post processing is required.

Credits & references: Madhura Mahamuni(Team Tech Tuesday)

https://en.m.wikipedia.org/wiki/3D_printing

https://builtin.com/3d-printing

https://www.twi-global.com/technical-knowledge/faqs/what-is-3d-printing

https://www.sculpteo.com/en/glossary/amf-definition/

https://3dprintingindustry.com/3d-printing-basics-free-beginners-guide#03-technology

https://www.divbyz.com/3D-modeling-for-3D-printing

https://monroeengineering.com/blog/the-role-slicing-plays-in-3d-printing

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