3D Printing: Key Elements, Types, Risks, and Safety Tips

By Khadiga Mohammad

Khadiga is a student at the College of Engineering. She is interested in writing about manufacturing. She also likes sharing what she has learned with others.

This article covers additive manufacturing, its types, key elements when 3D printing, risks, and safety tips.

3D printing is the process of creating three-dimensional solid parts. Image source: istockphotos.com

3D Printing

3D printing, or additive manufacturing, is the process of creating three-dimensional objects from a digital file. It produces geometrically complex objects, shapes, and textures.

The starting point for any 3D printing process is a digital 3D model, which can be created using different 3D software.

The first reference to 3D printing technologies was rapid prototyping (RP). Chuck Hall invented 3D printing in 1982. After that, he developed a system in which a condensed ray of ultraviolet light, moving under computer control, “hits” the surface of a bucket filled with a photopolymer liquid. As it “hits,” this liquid turns into a kind of plastic with a fixed shape.

Nowadays, 3D printer technology is used in jewelry, industrial design, architecture, automotive, dentistry and medicine, information mapping, and civil engineering projects.

Key Elements to Consider When 3D Printing

Material Selection,
Wall Thickness,
Size,
Resolution,
Orientation.

1. Material Selection

There is now a wide range of materials available for different situations.

Nylon, or polyamide, is commonly used in powder form through the sintering process or in filament form through the FDM process. It is a strong, flexible plastic material proven to be reliable for 3D printing. It is naturally white but can be colored before or after printing. This material can also be combined with aluminum powder to produce alumide, a common 3D printing material for sintering.

PLA is a biodegradable plastic. It can be used in resin form for DLP/SL processes and in filament form for FDM processes.

ABS is a type of common plastic used in 3D printing and is widely used in entry-level FDM 3D printers as filament. It is sturdy plastic and comes in a wide range of colors.

LayWood is a 3D printing material developed for entry-level 3D printers. It is a wood/polymer composite that comes in filament form.

Metals and metal composites are used for 3D printing, such as aluminum and cobalt derivatives. Other metals are used in the 3D printing industry, such as stainless steel, gold, silver, and titanium.

Ceramics are new to 3D printing. Ceramic parts need the processes that any ceramic piece made using traditional production methods of firing and glazing would undergo.

Mcor Technologies’ proprietary SDL process uses standard A4 copier paper for 3D printing. 3D-printed models made of paper are environmentally friendly, recyclable, safe, and do not require any post-processing.

Did you know?
Numerous studies have been conducted into the potential of 3D printing biomaterials for a range of medical and other applications. Living tissue is being examined at many institutions to develop applications that include printing human organs for transplantation as well as external tissues to replace body parts. Other research in this area focuses on food development.

2. Wall Thickness

Component wall thickness is an essential design characteristic that ensures an additive manufacturing part’s stability, accuracy, and tolerance. The smaller thickness shortens build time, but too thin a thickness results in a brittle part with less accurate properties.

SLS-made parts are subjected to high temperatures and powder weighing during manufacturing. The material used in the SLS method can also shrink when it cools and hardens. With thicknesses between 1 mm and 3 mm, the geometric stability of these properties is more easily achieved.

3. Size

Each technique has an ideal shape, some smaller and some larger. The FDM machine reaches its largest size of 16 x 14 x 16 inches. If the part is larger than this, it can be split before manufacturing and then professionally glued together. Part size affects manufacturing time, as larger parts take longer to build and require more materials, resulting in higher costs.

4. Resolution

Depending on the technique used, a thinner layer can reduce imperfections or burrs that may appear on the surface of the part. The thinner the layers, the more defined the details, and the longer the manufacturing time.

SLS technology provides very good resolution, meaning 100 microns (0.1 mm). The typical FDM layer thickness is 250 microns (0.25 mm). It is possible to print at a lower resolution (330 microns, 0.330 mm). This is good for larger, less aesthetically pleasing items that can be made quickly and at a lower cost.

5. Orientation

Orientation refers to how the part is positioned on the printing platform. It can be laid flat, angled, or placed vertically. When it comes to geometric dimension and error tolerance, properly orienting components for manufacturing is an essential step that impacts overall quality. There are also direct effects on the amount of energy used and the size of the support structures needed.

3D Printing Types

The American Society for Testing and Materials (ASTM) cataloged 3D printing processes into seven groups:

Material extrusion,
The binder jetting,
Directed energy deposition,
Material jetting,
Powder bed fusion,
Sheet lamination,
Vat photopolymerization.

FDM 3D printing of a blue glass ornament. Image source: shutterstock.com

1. Material Extrusion

This process is widely used, and its costs are low. The material extrusion-based 3D printing process is used to print multiple materials and multi-color printing of plastics, living cells, or foodstuffs. Fused deposition modeling (FDM) is the first example of a material extrusion system, and this method uses polymer as the main material. FDM was developed in the early 1990s.

How does fused deposition modeling (FDM) work?

FDM builds parts layer by layer, from bottom to top, by heating and extruding thermoplastic filaments. In FDM processes, thermoplastics are heated to a semi-liquid state and deposited in the form of ultra-fine beads along the extrusion path. When support is needed, the 3D printer deposits a removable substance that acts as scaffolding.

2. The Binder Jetting

In this 3D printing process, a liquid binding agent is selectively deposited to bind powder particles. The binder-jetting technique uses a jet chemical binder on the spread powder to form the layer. The application of binder jetting will produce casting patterns, raw sintered products, or similar products with a large sand volume. Binder jetting can print various materials, including metals, polymers, sand, hybrids, and ceramics. The binder jetting process is fast, simple, and cheap, as the powder particles are glued together.

3. Directed Energy Deposition

Directed energy deposition is used to repair or add additional materials to existing components. The directed energy deposition process has a high degree of control over grain structure and can produce good object quality. In this method, the nozzle is not fixed on a specific axis and can move in various directions. This technology can be used with polymers and ceramics but is typically used with metals and metal-based hybrids in wire or powder form.

Laser-engineered net shaping (LENS) and laser deposition are two instances of this technology. Laser deposition is a new technology that can be used to make or fix parts measured in millimeters or meters. This technology is gaining attraction in the tooling, aerospace, transportation, and oil and gas sectors, as it can supply scalability and different capabilities in a single system.

The LENS process can use the heating energy of melting during casting, and the parts are finished later. This process produces shapes close to the final product to eliminate the need for the finishing process.

4. Material Jetting

Material jetting is a process in which building materials are selectively deposited, drop by drop. The print head dispenses droplets of a photosensitive material that hardens, building a part layer by layer under UV light. Material jetting creates an extremely smooth surface and high-dimensional accuracy in parts.

5. Powder Bed Fusion

This method uses an electron or laser beam to melt or fuse a powdered material. Examples of powder bed fusion technology are:

1. Selective laser sintering (SLS): Carl Deckard developed selective laser sintering (SLS) in 1987, the prime example of a powder-based 3D printing technology. This technology uses a high-power laser to sinter small particles of polymer powder into a solid structure. It also allows for printing complex parts from CAD models in a short amount of time. Examples of materials used in this method include ceramics, polymers, metals, hybrids, and composites.

2. Electron beam melting (EBM): EBM enhances the energy source to heat the material.

3. Selective heat sintering (SHS) printing techniques: The SHS process uses a head thermal print to melt the thermoplastic powder to create 3D-printed objects.

6. Sheet Lamination

Sheet lamination is a 3D printing process in which sheets of material are bonded together to produce a solid part. 3D printing technologies that use this method are:

1. Laminated Object Manufacturing (LOM): This technology can produce complex geometric objects with lower manufacturing costs and less operating time.

2. Ultrasonic Additive Manufacturing (UAM): This technique uses sound to fuse layers of metal taken from featureless foil stock.

7. Vat Photopolymerization

The main 3D printing technique used is photopolymerization, which refers to the curing of photo-reactive polymers by using light, a laser, or ultraviolet (UV). Examples of 3D printing photopolymerization are:

1. Stereolithography (SLA): It is an additive manufacturing process where a light source cures liquid resin into hardened plastic. It can create very accurate feature parts. Printed parts are being deployed in every industry as end-use products.

2. Digital light processing (DLP): This technology harnesses the power of light from a video projector to process photosensitive liquid resins into sections layer by layer, one quick flash at a time.

3D Printing Risks

Experiments have shown that plastic filaments produce volatile organic compounds (VOCs) when heated in 3D printing. Exposure to these volatile compounds can cause nausea, headaches, and irritation of the eyes, nose, and throat. Also, when the filaments are heated, they produce inhalable nanoparticles (NPs). Furthermore, the use of NP-containing media can emit respirable NPs. Preliminary research suggests that inhalation is linked to cardiovascular and lung diseases.

ABS can be softened by placing it in a sealed container filled with a small amount of acetone or other organic solvent, which evaporates and reacts with ABS plastic. These solvents are usually flammable and can cause symptoms when inhaled, such as headaches, nausea, and respiratory irritation.

ABS is a material often used in FDM 3D printing.

The support material can be removed by placing the print in a hot, corrosive bath containing sodium hydroxide or other caustic chemicals. Exposure to these chemicals can cause burns, scarring, and vision damage. Motors, heat beds, UV lamps, and print heads get hot during operation and can cause burns when touched.

Fine metal powders like steel, aluminum, and titanium can spontaneously combust under normal weather conditions, and organic solvents like acetone used in steam polishing can also combust when exposed to a heat source.

Strong Class 4 lasers are used in powder bed fusion and directed energy deposition printers, which can result in permanent eye damage from direct or reflected light. Also, eye exposure to the ultraviolet rays used in SLA printers may cause temporary or permanent vision loss.

Safety Tips

Wear a face mask to avoid inhaling fumes and volatile chemicals.
Wear gloves when handling chemicals.
Before operating your 3D printer, ensure you are familiar with its correct and safe operation and follow the manufacturer’s instructions on setting up and using the printer.
Do not place flammable liquids near 3D printers, as the hot components of these printers can cause the flammable liquid to ignite.
Store chemicals in a designated chemical storage cabinet. Do not store flammable materials, such as polymer resins, rubbing alcohol, and acetone, in refrigerators, as this could cause an explosion. The maximum distance from the ground to store large chemical bottles is two feet.
Handle sharp tools carefully, and know the location of the first aid kit because removing supporting materials using sharp tools can cause cuts.
Install and disassemble the printer according to the manufacturer’s instructions, and ensure the power cable is not damaged.
The resins used in SLA printers are flammable and should be kept away from heat sources and stored in a safe, flammable storage cabinet.

Sources

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