3D Printing: Process and Material Selection

*Abstract *

3D printing creates objects by adding material, subcaste by subcaste to a digital model. It is used as a prototyping process to understand the form, factor, finish, fittings, and aesthetics of the final product. As technology is developing and evolving day by day, the variety of 3D printing processes can create confusion when selecting the appropriate prototyping process and material.

This method explores various types of 3D printing and the crucial factors for material selection, based on insights from ongoing work at eInfochips.

*1.Introduction *

Manufacturing processes can be categorized into several types. Forming changes the dimensions of a material by applying force. Casting is the process of heating a solid material until it liquefies and then pouring it into a mold to achieve the desired shape. Lastly, additive manufacturing is a process in which objects are constructed by sequentially adding layers of material.

Its primary goal is to minimize process time and steps, often achieved through rapid prototyping.

Additive manufacturing uses solid modeling data to form layers with thin cross-sections, allowing the production of intricate shapes and surfaces that are difficult to achieve through traditional methods. The design is created in Computer-Aided Design (CAD) software, and 3D printers process it layer-by-layer. Once the CAD models are complete, they are converted into printer-compatible file formats like OBJ, STL, 3MF, or AMF. Engineering teams like those at eInfochips specialize in supporting these early-stage design and modeling processes with end-to-end product engineering capabilities.

3D printing is considered a future technology due to its sustainable advantages, such as reduced material waste, minimal post-processing, and lower costs, even when manufacturing complex parts. Additionally, 3D printing has the potential to recycle plastics, reduce emissions, and reuse materials. It also enables the creation of parts with complex and optimized geometries, resulting in lightweight components with improved strength-to-weight ratios. As a result, 3D printing contributes to the development of more sustainable designs.

3D printing technology is currently evolving. Though 3D printing has lot of advantages over conventional manufacturing processes, there are some drawbacks to this technology. It is time-consuming, and it needs a lot of capital investment. At present the industry majorly uses 3D printing as a prototyping process, as it provides parts within tolerance and with a good surface finish.

*1.1 3D Printing Process: *

Fig 1. 3D Printing Process

*1.2 Types *

3D printing relies on three primary methods: sintering, where the material's temperature is increased without melting to create high-resolution prototypes; melting, which uses electron beams to melt powders; and stereolithography, which employs photopolymerization using an ultraviolet laser.

*2. Stereolithography (SLA) *

It is an additive manufacturing process in which liquid polymer (Resin) is solidified or cured layer by layer with the help of a UV screen or a UV laser. The UV laser travels in the shape of a sliced layer. SLA provides superior dimensional accuracy and fine surface resolution compared to many other additive manufacturing methods.

*2.1 SLA 3D Printing Process *

*Fig 2.1. SLA 3D Printing Process *

*2.2 Applications *

• Prototyping in automotive, aerospace, and consumer goods industries
• Jewelry making
• Dental models
• Architectural models for visualization and presentation
• Art and sculpture techniques are employed to produce complex and intricately detailed works

*2.3 Advantages *

• High accuracy and resolution
• Capability to create complex and detailed components
• Variety of materials

*2.4 Disadvantages *

• Slower printing speed compared to some other processes
• Achieving the intended surface texture may require post-processing to clean off the unwanted resin left after printing
• Limited in terms of scalability for large volume production

*3. Fused deposition modelling (FDM) *

In FDM, a heated nozzle extrudes molten thermoplastic filament in successive layers to construct a 3D part. Cooling causes the extruded material to solidify, incrementally constructing the final part.

3.1 FDM 3D Printing Process

*Fig.3.1 FDM 3D Printing Process *

*3.2 Multi color 3D Printing *

Multi-color Fused Deposition Modeling (FDM) is a technique that allows users to create objects with multiple colors or materials in a single print.

FDM printers employ a single extrusion nozzle capable of depositing one material at a time. In multi-nozzle or multi-color setups, there are multiple nozzles (two or more) attached to the 3D printer's print head. Each nozzle is connected to a separate filament spool, and each filament can be a distinct color or material. Later, the software users assign these materials or colors to the required area for the model.

After slicing, the data file is provided to the 3D printer to initiate printing. This data file contains instructions for the printer to change the nozzle according to the material or color. Other than the nozzle setup, the printing process remains consistent with conventional single-nozzle FDM techniques. Multi-color printing has wide applications in prototyping and in the toy industry.

Multi-material FDM is used where more finished products are required, where one primary nozzle is made of the intended material for the object and one nozzle has the water-soluble filament. This water-soluble (PVA - Polyvinyl Alcohol) filament is used only to print supports. When the object is printed, it is dipped in water and the supports dissolve in water, and we get the finished product.

3.3 Flexible 3D Printing

Flexible filaments can be used as a substitute for standard filaments in the FDM process. This material is usually made from Thermoplastic Polyurethane or Thermoplastic Elastomer.

Printing an object with a flexible material can be tricky as it may require a printer with a direct drive extruder where the feeder motor is at the spool end and not near the printing head, to prevent stretching of the filament which may future cause printing defects. There are a lot of control parameters in flexible printing, and it is critical to maintain proper flexibility of the object. This makes the printing process slower than the usual FDM process.

For seals, grips, or shoe soles where high flexibility is required, the filament material with Shore 85A or lower is used. For gaskets and parts which need some flexibility without being too soft, the filament material with Shore 85A to 95A is used. For applications where there is structural integrity requirement with some flexibility, filament material with Shore 95A or higher is used.

*3.4 Applications *

• Rapid prototyping for product development and testing
• Educational models and prototypes for tutoring 
• Manufacturing low-cost and custom parts for various industries

*3.5 Advantages *

• Cost-effective
• Broad spectrum of materials
• Simple and user-friendly operation

*3.6 Disadvantages *

• Lower accuracy and resolution compared to some other methods
• Limited in terms of surface finish compared to processes like SLA and SLS
• Layer adhesion issues may occur, affecting a part of the strength

*4. Selective laser sintering (SLS) *

The process is known for its capability to produce strong and functional products with intricate shapes, making it a popular choice for prototyping and producing end-use components. A laser of CO2 or nitrogen is employed to solidify the layers, with selection based on the face-end type and powder specifications. During this system, a chemical powder is employed for producing the object.

Various powders can be utilized, including plastics, metal, silica, etc. When a metal powder is used, this system is known as Direct Metal Laser Sintering .

*4.1 SLS 3D Printing Process *

Fig 4.1 SLS 3D Printing Process

*4.2 Applications *

• Prototypes are designed for functional testing and validation processes
• Automotive and aerospace
• Customized products such as orthotics and prosthetics
• Manufacturing complex geometries and parts with high-strength requirements

*4.3 Advantages *

• Ability to produce functional parts with high accuracy and good surface finish
• Wide material range: plastics and metals
• Does not require the support structures

*4.4 Disadvantages *

• Higher equipment and material costs compared to some of the other processes
• Post-processing may be required

*5. Multi jet fusion (MJF) *

MJF 3D printing is renowned for its ability to produce high-quality, functional parts with fine detail and smooth surfaces, making it a popular choice for both prototyping and end-use production. The solidification of layers is achieved through the precise application of fusing and detailing agents followed by the application of heat. This method primarily uses polyamide (nylon) powders but can also employ other thermoplastic materials.

The MJF process uses an inkjet array to deposit fusing agents onto the powder bed, precisely following the data of the 3D model. A detailing agent is also applied to improve resolution and surface finish. Infrared lamps pass over the built-up area, causing the areas with the fusing agent to solidify and fuse together.

Typically, thermoplastics powder is used. However, other materials like elastomers and composites can also be used depending on the application requirements.

*5.1 MJF 3D Printing Process *

Fig 5.1 MJF 3D Printing Process

*5.2 Applications *

• Functional prototypes for product development
• End-use parts for various industries including automotive, consumer goods, and electronics
• Rapid manufacturing complex geometries
• Customized consumer products

*5.3 Advantages *

• Fast printing
• Good accuracy and surface finish
• Versatility in materials, including thermoplastics, with different properties

*5.4 Disadvantages *

• Limited in terms of part-size compared to some other processes
• Material handling and post-processing cleanup may be challenging
• Higher initial investment

6. Binder jetting (BJ)

Binder jetting is known for its speed and capability to produce large, complex components economically. It is used for producing beach moulds and cores for metal. In binder jetting, a print head deposits a binding agent onto a powder bed, replacing the UV-curing process found in other methods with a mechanical bonding approach. Ceramic and metallic powders typically undergo post-processing steps such as thermal treatment and sintering prior to functional use. Most of the plastic and metal materials are usable directly out of the printer, with minimal or no need for post-processing.

*6.1 BJ 3D Printing Process *

*Fig.6.1 BJ 3D Printing Process *

*6.2 Applications *

• Producing sand casting moulds for metal casting
• Creating metal, sand, and ceramic parts for various industries
• Rapid prototyping of complex geometries is essential
• Tooling and fixtures for manufacturing processes

*6.3 Advantages *

• Quick production process
• Versatility in materials
• Scalable for large volume production

*6.4 Disadvantages *

• Limited in terms of accuracy compared to other processes
• Not a good surface finish
• Material properties may vary depending on the type of binder used

*7.Direct energy deposition (DED) *

Direct Energy Deposition is a 3D printing technique used for a wide range of applications, including rapid prototyping, repair of existing parts, and the creation of complex, high-performance components. It can restore or refurbish previously manufactured parts. DED styles make it easier to produce products by melting material when they are deposited. Directed Energy Deposition systems utilize a deposition head, which incorporates the energy delivery mechanism along with two powder feeding nozzles for material deposition. Metal powder or metal filament can be used as raw materials.

*7.1 DED 3D Printing Process *

Fig.7.1 DED 3D Printing Process

*7.2 Applications *

• Ideal for restoring or enhancing existing components across the aerospace, automotive, and manufacturing industries
• Aerospace turbine engine parts
• Rapid prototyping of metal parts with good accuracy

*7.3 Advantages *

• Good accuracy for metal parts
• Suitable for restoring and rebuilding existing components
• Intricate parts

*7.4 Disadvantages *

• Expensive process compared to some other additive manufacturing methods
• Limited material options compared to other processes
• Post-processing may be required for achieving the desired surface finish

*8. Laminated object manufacturing (LOM) *

LOM 3D printing is known for its ability to create large and strong parts in less time. It is often used for prototyping, architectural models, and creating patterns for casting and molding processes. The process initiates with a sheet affixed to a base substrate via a heated roller. A laser or mechanical cutter is employed to define the geometry, and successive layers are similarly laminated and trimmed with high precision. Following the completion of each layer, the platform increases incrementally. A new sheet of metal is then fed into position, after which the platform returns to its build height for the subsequent layer of deposition.

8.1 LOM 3D Printing Process

Fig.8.1 LOM 3D Printing Process

*8.2 Applications *

• Prototyping for product design and development
• Construction industries
• Packaging design for testing and validation
• Educational models and teaching aids

*8.3 Advantages *

• A cost-effective process
• Capable of making durable prototypes
• Versatility in materials including paper, plastic, and composite materials

*8.4 Disadvantages
*

• Lower accuracy and resolution compared to processes like SLA and SLS
• Limited in terms of intricacy and detail compared to some other methods
• Additional post-processing is typically required to achieve the targeted surface quality and dimensional accuracy

*9. Printing Process selection *

As there are several types of 3D printing processes it becomes difficult to choose a process according to specified conditions. This section marks key parameters for selection of processes. These parameters are time, process cost, material, strength, surface finish, post processing, accuracy and applications of produced part. These parameters are mentioned below in tabular form.

*Note: *

• $* represents the cost scale for the 3D printed object.
• SLA: Uses a laser to build plastic in a layer-by-layer from liquid resin.
• FDM: Parts built from successive layers by melting and extruding plastic filaments.
• SLS: The process utilizes a laser to bond powdered material, plastic, chaining the particles to form a cohesive solid structure.
• BJ: Uses an adhesive to glue powder particles together forming successive layers.
• DED: A focused laser is used to melt and fuse materials during deposition, creating a solid structure.
• LOM: Material layers are laminated together and then precisely cut into the desired shape using either a blade or a laser.
• MJF: The process involves dispensing fusing agents onto a powder layer with inkjet arrays, followed by bonding the particles using infrared light.

Table 9 Printing Process selection

*10. Material Selection *

Material selection plays a crucial role in the 3D printing process, as the properties of the printed objects depend on the type of material used. Selection of a material is dependent on numerous factors such as type of 3D printing process, required finish, application and cost.

*10.1 Process of Material Selection
*
*10.1.1 Requirements *

Clearly defining project requirements is a crucial step in the material selection process. Factors to consider:

• Mechanical Properties
• Aesthetic properties
• Environmental conditions
• Applicational requirements

*10.1.2 Process
*
Identify the required or most suitable process. Factors to consider:

• Printing Cost
• Printing Time
• Finish required

10.1.3 Material Properties

Material properties are aligned to the project requirements. Factors to consider:

• Thermal properties
• Chemical resistance
• Cost and availability

*10.1.4 Printing Parameters *

The following printing parameters are to be considered:

• Printing speed
• Layer Height
• Bed Temperature

*10.1.5 Post Processing *

The post-processing is dependent on the project's requirements. This may be dependent on strength and the required finish. The following are some post-processing steps carried out if required:

• Curing
• Cooling
• Heating
• Sanding
• Painting

*10.2 Material Selection Table *

Below table shows comparison between each process and material used respectively:

*11. Conclusion *
Stereolithography delivers the highest level of accuracy, making it ideal for applications requiring minute details and precision, especially for small and intricate parts. However, it has drawbacks such as slower printing speeds and the need for extensive post-processing.

Direct Energy Deposition can be used for accurate metal parts. While it is an expensive method, it is primarily used for repairing or adding material to existing parts and for producing large, complex metal structures.

Binder Jetting is effective for creating sand casting molds, offering fast production and compatibility with a wide range of materials, including metals, sand, and ceramics.

Fused Deposition Modeling is a cost-effective option ideal for rapid prototyping where quick evaluation of form is important. However, this method might not offer the highest precision or surface smoothness when compared to other available technologies.

Selective Laser Sintering produces components with strong dimensional accuracy and surface quality, making it well-suited for both prototype development and functional applications. Caution is needed for thinner parts, as they may be more brittle.

Multi Jet Fusion is used for end-production parts. While it offers robust performance for many applications, it is not recommended where extremely tight tolerances are required. Multi Jet Fusion (MJF) can be used to produce finished functional parts for applications. They provide good mechanical strength and can be used directly. It cannot be used where tight tolerances are required.

*Author Details: *

Abhishek Kokare is a Product Design Engineer at eInfochips, with a postgraduate degree in Design, specializing in material selection and advanced manufacturing. His work focuses on integrating 3D printing technologies into practical, high-performance product solutions. This paper reflects his ongoing interest in the future of additive manufacturing and design innovation.

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