Week 12

In week 12, we learnt about 3D printing and digital fabrication.

Digital Fabrication is becoming an important enabling technology in many chemical engineering fields. It allows one to make whatever they need whenever they need it.

One such example is the use of additive technology in the Oil and Gas Industry. Due to the remote and urgent nature of business, replacement parts need to be produced quickly in order to prevent the product output rate from being affected. Companies like Shell, ExxonMobil and General Electric are early adopters of 3D printing to shorten the supply chain and use generative and iterative design.

3D printing is good for prototyping as it allows for a physical evaluation of the design, and it allows for functional testing to be performed before committing to a full production run to iron out mistakes and remove errors, ensuring that the final product is suitable for release to the market. Besides prototyping, it is also good for end use parts as well. It extends the lifespan of older equipment by printing obsolete parts that are no longer being produced. Spare parts that have stopped production can be reverse-engineered to improve current designs. It also allows for customisable high value and low volume end use production of objects parts to be produced without needing any tools and jigs.

This lesson was different from other lessons as we adopted the peer-teaching model. Our group was tasked with researching common materials used in 3D printing, as well as choosing a suitable thermoplastic for Fused Depositing Modelling (FDM) 3D printing based on their physical properties and characteristics.

From the other groups' presentations, we also learned more about additive manufacturing, other forms of 3D printing, slicer settings for either quality or fast printing, as well as 3D Printing applications in the news.

Additive manufacturing (AM)

Additive manufacturing, or AM, refers to the technologies that are used to build 3D objects by adding layer-upon-layer of material. Common materials used are plastic, metal and concrete. AM is also used to refer to technologies including subsets like 3D Printing, Rapid Prototyping (RP), Direct Digital Manufacturing (DDM), layered manufacturing and additive fabrication.

AM technology makes use of a computer, 3D modeling software (Computer Aided Design or CAD), machine equipment and layering material. Once a CAD sketch is produced, the AM equipment reads in data from the CAD file and lays downs or adds successive layers of liquid, powder, sheet material or other, in a layer-upon-layer fashion to fabricate a 3D object.

The applications of AM can be considered limitless due to its flexibility. They can be used with varying degrees of sophistication to meet many different needs, including but not limited to: A visualization tool in design, a means to create highly customized products for consumers and professionals alike, as industrial tooling and to produce small lots of production parts. Today, AM is most commonly used to fabricate end-use products in aircraft, dental restorations, medical implants, automobiles, and even fashion products. In fact, it is even possible for AM to produce human organs using human tissue.

3D Printing Techniques

The first technique, Fused Depositing Modelling (FDM), is the most commonly used form of 3D printing at the consumer level. In FDM 3D printing, parts are built by melting the thermoplastic material past its glass transition temperature, and extruding thermoplastic filament in a pattern next to or on top of previous extrusions, which a printer nozzle deposits layer by layer in the build area. Common materials used for FDM are thermoplastics. FDM 3D printing is fast and require low-cost consumer machines and materials. However, FDM has the lowest resolution and accuracy compared to other 3D printing techniques, thus they are not suitable for printing complex parts or parts with intricate features. FDM is most commonly used in low-cost rapid prototyping and basic proof-of-concept models.

The second technique, Stereolithography (SLA), is the first 3D printing technique to be invented, dating back to the 1980s. SLA works by using a laser to cure liquid resin into hardened plastic in a process called photopolymerization. SLA has the one of the greatest versatilities out of all 3D printing techniques. SLA parts also have the highest resolution and accuracy, the clearest details, and the smoothest surface finish of all plastic 3D printing technologies. However, parts printed using SLA are sensitive to long exposure to UV light. SLA is widely used in a range of industries from engineering and product design to manufacturing, dentistry, jewelry, model making, and education.

The last technique, Selective Laser Sintering (SLS), is the most common additive manufacturing technology for industrial applications due to its ability to produce strong, functional parts. SLS 3D printers use a high-powered laser to fuse small particles of polymer powder. The unfused powder supports the part during printing and eliminates the need for dedicated support structures. Parts produced with SLS printing have excellent mechanical characteristics, with strength resembling that of injection-molded parts. However, parts produced using SLS have a rough surface finish, and the material selection for SLS 3D printing is limited.

Common 3D Printing Materials

Common materials used for 3D printing are usually thermoplastics.

Acrylonitrile butadiene styrene (ABS) is one of the most commonly used materials for 3D printing. This is due to its durability. On top of that, it also has a high machinability rating and strong electrical insulation capabilities. However, it has a relatively low melting point, as well as poor solvent, fatigue and UV resistance. It is most commonly used for models, prototypes, patterns, tools and end-use parts in the automotive industry, machine prototype construction. It is also used to make pipes and fittings.

Polylactic acid (PLA) is a highly versatile material. Its main selling points are its low cost due to being made from renewable sources, and its biodegradability due to being made from natural sources. It is also easy to use, do not tend to warp and have good reusability. However, it has low heat resistance due to its low melting point, and can be brittle due to its low tensile strength. It is used to make food containers, cutlery and laminations.

Polyethylene terephthalate glycol (PETG) is another commonly used material for 3D printing. Its main strength is their durability. It is also chemically resistant and flexible. However, it is not UV-resistant, and weaken considerably from exposure to UV light. It is also sensitive to moisture and humidity, due to their hydroscopic properties. It is mostly used to make food and drinks containers, mechanical components and machine guards.

Polycarbonate-ISO (PC-ISO) is an industrial thermoplastic. It is a biomaterial, meaning it is biocompatible, allowing it to be used in a wide range of medical applications. It is also easily sterilisable, strong, durable and heat resistant. However, the supports used for it during 3D printing have to be broken away and removed by hand, which may cause damage to more intricate areas of the part's design. It is most often used to make food and drug packaging, and medical devices.

Slicer Settings

A slicer is a program that turns a 3D model file (STL, OBJ, 3MF, etc.) into a G-code script, which can be interpreted by the 3D printer. Slicer settings are important as different printers and materials require different settings to achieve a good print quality. Slicer settings cover all aspects of printing, from the temperature of the heated elements to the thickness of each wall and layer. Depending on whether a high quality prints or high speed print is desired, it is important to know the primary settings to use on the slicer.

The temperature of the setup is the most important factor to consider. Too high a nozzle temperature will cause over-extrusion with blobs and zits all over the print. Too low of a temperature will cause under-extrusion, where not all the layers are fully printed. On top of that, the bed temperature is also important as it will affect the print’s bed adhesion. A hotter bed will provide better adhesion, while a cooler one could lead to warping. However, if the temperature is too high, a part could deform on the bed.

The layer height refers to the height of each layer of the print. The smaller the layer height, the more layers will be required in the overall print. This means that the printer will have more room to generate finite detail on parts like miniatures. However, having more layers also means longer print times and weaker parts.

The speed refers to the speed at which the printhead moves. It can also refer to the infill speed or wall speed. Generally, increasing print speed will reduce print times. However, if the speed is too high, it may cause nozzle run-ins where the printhead could knock over small structures while printing. In most slicers, a particular speed will be chosen based on the chosen layer height and material.

Retraction determines how much and how fast filament is sucked back into the nozzle to prevent material from oozing out when it’s not being extruded. Retraction is controlled by a few specific settings, chief among them being retraction distance and retraction speed. Retraction settings should be changed in small intervals and there should not be any significant increases made. Too much retraction can cause nozzle jams, as the filament is more aggressively pushed in and out of the nozzle.

Flow, sometimes known as the extrusion multiplier, determines the rate at which filament is extruded. Adjusting the flow affects how many steps the extruder’s motor turns per millimeter of material deposited.

An adhesion assistant is a physical feature added to a print. It is auto-generated by the slicer when instructed to do so and is designed to enhance bed adhesion. An adhesion assistant comes in the form of a skirt, brim or raft. A skirt is a distant and detached perimeter that outlines a print. Skirts provide no real adhesion assistance for a model but help get material flowing through the nozzle in time for the first layer to start. A brim is a set of lines attached to the outside of a print’s first layer, sprawling from its base. As far as adhesion assistants go, this is the first step to take if a model is having bed adhesion issues. A raft is a complete base upon which the model grows. When printing rafts, slicers generally attempt to save material by putting space between adjacent lines. A skirt takes up the least amount of material and print time, followed by a brim and then a raft.

Supports are slicer-generated are structures that hold up overhanging features on models. The overhang angle and the minimum support area have to be known. Part orientation plays a key role in how support structures are generated. Other support settings include print speed and support infill density. They can be tweaked to find a balance between sufficient support and minimum material consumed.

Cooling determines the power of the fans on the printer. The fan’s speed can typically be set and adjusted as a percentage of total power. When adjusting the speed of the part-cooling fan, the material being used for printing should be considered. If the model has overhangs, cooling can be increased to more rapidly solidify printed overhangs.

Infill is the internal filling in 3D printed parts. Infill allows for better control over the strength, weight, material consumption, and internal structure of a part without having to adjust its appearance or external features. In a slicer, infill can be controlled using infill density, set as a percentage, and infill pattern, which is the infill’s structure or form. More robust infill patterns and larger infill densities will extend printing times and consume more materials, but increase a part’s strength and weight. There are many infill patterns to choose from, each with its own design and characteristics.

Shell thickness represents the number of lines in the walls of the prints, whether they’re at the sides, on the top, or on the bottom. They are completely solid and printed concentrically. Shell thickness is usually set as a value in millimeters or as a number of layers, individually for the walls and the top and bottom layers. Shell thickness is an important setting to tune because it can significantly impact the strength of the model. The higher the shell thickness, the stronger parts will be and the longer they will take to print. The more shells there is, the more completely solid layers or walls the machine has to print.

3D Printing in the News

New Bill seeks to outlaw owning digital plans to 3D-print guns
Owning digital plans to 3D-print a gun or major gun part will become illegal in Singapore, which will also significantly raise fines for unlicensed activities involving guns and explosives. The Ministry of Home Affairs (MHA) mentioned that the threat of terrorism remains high, and noted the risk of lone wolves or extremist groups using weapons to carry out an attack in Singapore. Technological changes also pose new challenges to enforcement, said the ministry, pointing to the emergence of technologies such as 3D-printing and drones, and greater access to information online on manufacturing illegal guns and weapons. The new Bill will make it illegal to possess any digital blueprint for the manufacture of a gun or major part of a gun without authorisation. This is to mitigate the threat posed by illegal manufacturing of guns through 3D-printing, said MHA.

Using corals to 3D-print implants for bone grafts
The surgical procedure for bone grafting uses transplanted bones to repair or regenerate diseased or damaged bones. This can be taken from one's own bones, or those from the dead, or by using bone substitutes made from materials like polymers. Patients with bone disease or fractures needing a bone graft may soon have another bone substitute option, as researchers from the National University of Singapore's Centre for Additive Manufacturing (AM.NUS) have been studying the feasibility of custom 3D-printing implants with coral materials. Skeletons of Scleractinian - or stony corals from three families, the Porites, known as finger coral, Goniopora, often called flowerpot coral, and Acropora - have been used as bone substitutes. Corals have long been studied for their potential in bone grafting, given their porous micro-structures which are similar to the sponge-like pores in human bones. The porosity also makes coral materials a good carrier for cell attachment and bone ingrowth. Creating bone grafts through 3D printing allows the bone implant to be customisable to each patient, in terms of its shape and porosity.

3D Printed Autonomous Robot Increases Delivery Efficiency in Singapore
Japanese design and technology firm Final Aim, Inc. partnered with robotics startup OTSAW Digital PTE LTD to use 3D printing to solve issues with inefficient deliveries in Singapore’s logistics chain. Together, they created a last mile autonomous delivery robot, called Camello. Because of long waiting periods in both loading and unloading bays, as well as low loads, tight deadlines, and high delivery volume, package deliveries in Singapore can be inefficient, which drives shipment costs up and causes operational issues as well. After developing the concept for the robot using design sketches and CAD software, they began presenting the idea to end-users, higher-level management, and frontline members, asking for feedback that would help him further expand on the idea. 3D printing was helpful to this project because the final design would feature organically curved surfaces, and the technology can analyze the curvature of surfaces using contour layers of printouts.

S'pore firm pivoted from making 3D printers for dental use to making swabs for Covid-19 tests
Local company Structo switched from manufacturing and selling 3D printers for dental use to using them to create swabs to help out at the peak of Singapore's Covid-19 crisis. Its 3D-printers were initially geared to producing surgical guides that can be customised to each patient's teeth. The surgical guide, which is typically used by dentists to drill implants into teeth, could be produced within an hour from what used to take a couple of days. When a shortage of nasopharyngeal swabs arose in April 2020, the company swiftly pivoted to designing its own swabs in collaboration with the authorities and healthcare professionals here. Manufacturing began in June, with the company producing 4.5 million swabs in three months and allowed enough time for supply chains to open up again and injection moulding became viable.

VW starts testing 3D-printed structural parts
Volkswagen has begun certifying prototype 3D-printed structural components, with the aim of producing 100,00 parts annually by 2025. VW is teaming with Siemens and HP to industrialize 3D printing of structural parts, which can be significantly lighter than equivalent components made of sheet steel. The automaker will use an additive process known as binder jetting to make the components at its main plant in Wolfsburg, Germany. HP is providing the printers and Siemens will supply the manufacturing software.


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