Introduction
General Background
Rapid prototyping is a technological process which involves manufacturing a product parts by parts in three dimensional forms. Rapid prototyping is also known as layered manufacturing, rapid manufacturing, and additive manufacturing. Rapid prototyping is more of a material addition process than the traditional methods, which involves material removal to come up with a final product. It fabricates physical objects from computer aided design (CAD) directly.
The technology of rapid prototyping can be divided into four parts. There is the input, method, material and applications aspects of its development. Input involves the numerical details that describes the physical object to be produced. The methods include the various steps/strategies that will be used to produce the physical object. It also involves material selection process, and the materials to be used varies. Different vendors who are into rapid prototyping employ various strategies to come up with a final product. Lastly, Application deals with where the rapid prototyping technology is used. There are a wide range of industries and businesses that gain a lot from this technology; from education, fashion, dental technology, manufacturing of turbine blades, and a lot more engineering practices.
One of the good things about rapid prototyping is that it doesn’t involve any tool and machine operation in producing the parts. A physical part can all be produced from a Computer Aided Design (CAD). Industries view the technology as a rapid and inexpensive method for producing prototypes, this has revolutionized the way industries view their product development cycle. It has given them the chance to produce their parts at a faster pace and in bulk quantities. Industries have also been able to save a lot of time and money as they are able to quickly test and justify their designs, saving them the stress of having to produce poor designs/products. The other advantages of rapid prototyping include cheaper cost to manufacture product components, the ability to visualize their products without producing them directly, quick and early discovery of errors in design, and parts that are enhanced to meet customer’s expectations. Furthermore, Rapid prototyping also reduces the amount of material components that go to wastage.
In order to produce prototypes from a rapid prototyping technology, there are set processes to follow which are in the order of:
– Creating a CAD model of the object to be made
– Converting the CAD model of the design to a Stereolithographic (STL) formatted file.
– Processing the file
– Building the object (Prototype), and Lastly,
– After processing procedures.
These processes are just the general and important aspects to take notes of, but they also include their individual steps and procedures. There are a lot of Rapid Prototyping systems in the industry. These systems can be divided into Liquid-based, solid-based, and powder-based. Stereolithography is an example of liquid-based while 3D printing is an example of powder-based.
Three dimensional printing in the form of additive manufacturing has always been in existence for over thirty years in the technology industry. Additive manufacturing is a form of rapid prototyping. It is the manufacturing of three dimensional objects through an additive process from a digital model. It is also different from the traditional method of manufacturing that involves material removal like milling, cutting, and Lathe operations. Another name for additive manufacturing is 3D printing. 3D printing like discussed earlier, helps to create physical objects with the help of CAD using varieties of materials; concrete, polymers, papers, etc. additive manufacturing and rapid prototyping somewhat involve the same processes. The terms are just different in the sense that Additive Manufacturing is the process, while rapid prototyping is the end result of Additive Manufacturing.
In additive manufacturing, there are many technologies applied. There is laser sintering, Stereolithography, and many others. They have been applied in automobile industries, electronic devices, and some medical applications have been recorded of recent. There are so many benefits additive manufacturing brings to industries that traditional methods cannot bring.
One of the benefits is being able to customize products according to customer’s needs. Customization helps to bring back older approaches of manufacturing. It is very beneficial to the customers to the consumers and producers as well because customization doesn’t include extra cost and applying tough skills. With additive manufacturing, complex products can be achieved. Complex parts and geometries that traditional methods have never been able to produce are now being produced now. Additive manufacturing is also very environmental friendly. Making plastics and metallic objects have always been quite wasteful as about 90% of the products always go to waste, however, it is the opposite with additive manufacturing as about 90% of the materials are used in production, leaving less waste than other conventional methods. Lastly, additive manufacturing as well as the application of 3D technologies in growing industries, have helped create a lot of employment opportunities as there is a growing demand for 3D technicians.
Motivation
We would like to show appreciation to our professor, Dr. Eylem Asmatulu for encouraging us to embark on writing this research paper and helping us improve our general knowledge on the topic, Rapid Prototyping and Additive Manufacturing. Thank you for all of the guidelines and time taken to push and get us started on writing our paper, which wouldn’t have been a reality without your help.
To all our engineering professors at Wichita State University, we thank you for all of your dedication in making us the students we are now. All of the times and efforts spent on lecturing us didn’t go unnoticed. This paper was a compilation of all of the knowledge instilled on us from attending your classes.
Lastly, we are especially thankful for our parents who continuously show us their support from thousands of miles away.
Objectives
The research objective is to give an idea of what Rapid Prototyping and Additive Manufacturing is about; their applications, methods, processes and how it has evolved throughout the years. We present a few literature reviews and discuss some of the other works carried out by researchers. In chapters three and four, we highlight the experiments done on Rapid Prototyping and Additive Manufacturing in the past, some of the materials and methods that were utilized and their performance. Lastly, the paper also presents some of the future works and ongoing projects on Rapid Prototyping and Additive Manufacturing, as well as the success achieved so far.
Literature review
In the early day, layer-based rapid prototyping (RP) advancements were principally concerned about manufacturing physical parts as fast as conceivable from a design concept, for the purpose of design verification. [18]
"Stereo Lithography," or three-dimensional printing was the initial term, established by 3D Systems (Valencia, CA). The developing field has been broadly alluded to in industrial and mechanical fields as "Rapid Prototyping". These days, with the quick advancement of rapid prototyping innovations:
a) more available materials,
b) with various mechanical properties to meet a variety of applications, and
c) higher precision of parts created,
rapid prototyping advancements have been utilized for creation of various functional parts and tooling [19, 20].
As parts are made by additive processes, the properties might be in a way that are not quite similar as parts that are made by conventional manufacturing processes. It is hard to specifically look at the numerous properties of rapid prototyping parts, as these depend on the material being utilized, as well as on the direction in which the property is being estimated.
In this literature review, the properties like:
(1) dimensional accuracy,
(2) tensile property,
(3) water absorption, and
(4) Shore hardness
were studied.
It is elusive that an appealing clarification to depict the significance of the additive manufacturing can be explained. Roland Berger (2014) considers that additive manufacturing (AM) is an added substance procedure of making a three-dimensional solid object of any possible shape from a computerized model or say a digital model, where materials are placed in progressive layers under computer control. It is likewise recognized from conventional subtractive machining procedures that depend on the extrusion of the material by processes, for example, cutting or milling.
As a rule, additive manufacturing, or, in other words another name for 3D printing, is an arrangement of innovations that assemble 3D objects by including layer-by layer supply of material. In collaboration with Computer Aided-Design Software (CAD) programming, this system permits the making of new kinds of objects with selective material properties. These days, the scope of materials have extended a lot more than plastic or metal. Polymers, bio-materials, paper, edible substances, concrete are going to wind up increasingly prominent and normal, after the application purposes and advancement patterns.
The term Additive Manufacturing likewise incorporates an extensive variety of advancements, from laser sintering (SLS) to fused deposit modelling(FDM) and stereolithography and some more. These advances have been utilized in different businesses like car or automotives, buyer gadgets or significantly more as of late for medicinal applications (prosthetics, aligners, skull sections, and so forth.).
Application of rapid prototyping technology in the manufacturing of turbine blades with small diameter hole.
The rapid prototyping involves different methods and additive technology to make manufacturing a product easier and possible. It is one of the best methods to forming parts of a product. The rapid prototyping was different from the previous deductive manufacturing method. The deductive manufacturing method has its limitations as a result of its inability to machine high-order surfaces and holes with small diameter. However, with the rapid prototyping, a product element is obtained easily on the fundamentals of its spatial method using a CAD system. A product was also obtained easily by building it parts by parts with its shape and form in a three dimensional geometry.
Rapid prototyping allows the manufacturing of products with complex geometry possible. An example is manufacturing turbine blades with small diameter holes of high pressure stages to be used for ship propulsion. One of the most important elements of the turbine blades is the small diameter holes. The holes ensure the flow of a cooling medium and separation from hot gases. This article experiments with a gas turbine having different dimension holes and micro holes of 0.3mm in diameter. The blades are produced through Direct Metal Laser Sintering (DMLS) technology and was investigated for the accuracy of the holes obtained. It turned out that making such small holes was infeasible by the method of rapid prototyping. Other methods were sought out for and discussed further in the article which will be more emphasized in the experimentation aspect of the report.
Rapid Prototyping – an innovative technique in dentistry
In dentistry, rapid prototyping is used to produce three dimensional physical models of complex structures to dentists before embarking on dental interventions. The three dimensional models allow them create prototypes for their designs which is better than regular two dimensional images. The frequent technologies used in dental practice include Stereolithography, Inkjet based system (3D printers), and a few others. Rapid prototyping has so many applications in dental practice. It is used in Implantology, which is a branch of dentistry dedicated to dental implants. It is also applied in Prosthodontics. Prosthodontics is used in making prosthetics wax pattern, mold for complete dentures, all-ceramic restoration fabrication and a few more. In oral surgery, Rapid Prototyping technology provides a realistic impression of a persons tooth and all other important structures before surgery can take place. It has its application in Endodontics and Orthodontics under oral surgery.
Fabrication and characterization of Multiscale PLA structures using integrated Rapid prototyping and gas foaming technology.
Polylactic acid (PLA) is an aliphatic thermoplastic polymer that is gotten from renewable resources. It is very environmental friendly and as a result, can stand as a substitute for counterparts that are petroleum based. PLA is good for packaging, food contact, and applied in scaffolding. It has other broad range of applications. It can be thermally crystallized, stress crystallized, copolymerized and can be manufactured in most manufacturing equipments for polymers. PLA has unique advantages which provides buildings with upscale energy efficiency. In addition, it has also been identified as a good substitute to fossil resource-dependent resins. The good thing about polylactic acid is that it can be modified to add more functionalities to it unlike some polymers. In this study, PLA is fabricated in a multiscale three dimensional structure by combining three dimensional printing technology, followed by a two step gas foaming process to form nano-cellular foams within the three dimensional printed features. The mechanical effect of implanting nano foams on three dimensional printed structures will be further discussed in the experimentation section
Methodology
There are various fabrication techniques that can be classified as subtractive, additive or formative. Every fabrication technique that exists either falls totally into one of the categories we mentioned or it’s a hybrid process that may fall into more than one category.
Rapid Prototyping techniques are a combination of those technologies that are fit for playing out these procedures totally under computer control, with next to zero human intervention once the procedure has started. Burns (1993) in his book alludes to the Rapid Prototyping Technique as Automated Fabrication. In choosing whether a procedure can be classified as a Rapid Prototyping process, five criteria are determined by Burns is utilized. These five criteria are:
(i) The process should take place in raw material which is a formless material which means it has no pre-defined shape, for example, blocks, sheets or a fluid, and deliver strong and solid items or say objects with a definite shape.
(ii) The process must be carried out without a lot of human intervention.
(iii) The process must create shapes with some level of three-dimensional geometrical complexity. This standard criterion wipes out the shaping of simple tubes or rods by extrusion and cutting or drilling of basic holes in sheet material.
(iv) The process must not include the manufacturing of new instruments or tools for each unique shape to be created (part specific tooling). This type of the criteria followed by Burns in his book eliminates all types of processes like molding and casting, EDM (Electrical Discharge Machining) die sinking and copy milling.
(v) Each and every item that is produced must be a single object and should not be an assembled piece produced by joining other individual components which in turn eliminates the various other joining operations, for example, sticking or gluing, welding and riveting.
Utilizing these criteria certain established fabrication procedures can be specified such as automated and a few models are also shown in the figure below.
Various techniques for Rapid Prototyping
The Computer Numerical Control (CNC) Techniques for example, grinding, drilling and milling don't entirely adhere to the five criteria on account of the human intervention that might be required in remounting the workpiece for manufacturing the complex geometries. In any case, they are incorporated supposing that if the capabilities are joined into one flexible, multi-axis, versatile CNC machining center then such a device could give an automatic fabrication facility.
Distinctive build orientations in indicated rapid prototyping systems may have huge impacts on physical and mechanical properties.
In this project report we present a comparative study which shows a similar examination in three build orientations across four rapid prototyping frameworks:
1. Specific Laser Sintering (SLS),
2. Poly-Jet,
3. Fused Deposition Modeling (FDM), and
4. 3D Printing (3DP).
The investigations of dimensional accuracy and tensile properties testing for three build orientations have been discussed in this project report. Moreover, the experimentation process of water absorption and shore hardness over these four rapid prototyping frameworks have also been discussed.
1. Selective Laser Sintering (SLS)
The Selective Laser Sintering (SLS) process produces strong solid components utilizing a carbon dioxide (CO2) laser to heat up the powdered materials layer by layer so that the surface pressures of the grains are survived, and they fuse together. Prior to the powder is sintered, the whole chamber is heated to simply below the melting point of the material with the end goal to limit or minimize the thermal distortion and encourage fusion to the past layer [5]. The laser specifically combines, and fuses powdered materials by tracing the cross-sectional slices from a three-dimensional digital depiction of the part.
The interaction of the CO2 laser beam with the powder raises the temperature to the melting point, bringing about particle bonding, fusing the particles to themselves and the previous layer to frame a solid object [1]. The laser beam with adjustable intensity combines/fuses the powder just in regions characterized by the part's geometry. The powder not melted or combined amid the processing works as the support structure. Thus, there is no need to have support material in this type of process. After each cross-section is totally drawn, the powder bed is brought down by one-layer thickness, and an extra layer of powder is accumulated by means of a roller mechanism on top of the previous layer. The procedure can be described as:
(1) new layer deposited,
(2) laser pillar trace,
(3) whole powder bed brought down is repeated until the point when the part is finished.
Figure below indicates SLS process.
Schematic view of SLS process
After the SLS process, the build chamber is moved to a post-processing station. The powder which is loose basically falls away, and the SLS parts requires a few post-processing, for example, sanding with high pressure air and glass bead mixture, and cleaning with pressurized air.
There is an extensive variety of introductory material accessible for the SLS framework. At present, nylon, nylon composites, polycarbonates, metals, sand, wax, and earthenware materials like ceramics and cermets production are being used [1, 7].
Notwithstanding, the materials utilized by the system are sensitive to the other distinctive heating and laser parameters and every material requires indicated specified settings. The products formed from SLS framework will in general have poorer surface finish due to the generally large particle sizes of the powders utilized.
2. Poly-jet
The maker of 3D printers, Objet Geometries, was the first company to effectively jet photopolymer material utilizing its patented Poly-Jet technology to create a complex model from a 3D geometry file in the 2000 [8]. In this technology, a 20 μm thick layer of photopolymer material is injected by a composed printing head on the build tray just in the zones that correspond to the cross-sectional profile from a 3D computerized depiction of the part. At the same time, the photopolymer layer is cured by UV light after it is jetted, and each layer is changed in accordance with 16 μm by a roller that is moved over the build tray immediately after deposition [9]. The repeated addition and solidification of photopolymer material layers creates a strong and solid three-dimensional model until the point when it is complete. In order to avoid the collapse of the structures produced during the production, a support material which is gel like, also which is uniquely designed to support complex geometries, is infused together with the model material. At the point when the model is finished, the support material is effectively eliminated by hand and water jetting to leave just the solidified photopolymer material. Figure 2 demonstrates Objet's Poly-Jet innovation.
Schematic view of PolyJet process [8]
Objet's Poly-Jet gives a wide collection of materials for various geometries, mechanical properties, and colors; utilization of a similar support material for all model types makes switching material easy and fast. Furthermore, this technology of Poly-Jet Matrix allows synchronous jetting of various kinds of model materials. It can jet two distinct type of photopolymer model materials in preset combinations.
Fused Deposition Modeling (FDM)
Scott Crump, the president and CEO of Stratasys Inc, built up the Fused Deposition Modeling (FDM) process in 1988 and the patent was granted in the U.S. in 1992 [1, 3]. The FDM procedure creates parts by extruding semi-liquid material through an extrusion head that moves in X axis and Y axis to make each two-dimensional layer of the part [10]. The movable extrusion head is made out of two extrusion heads:
one for build material and the other for support material [1, 7, 11].
This procedure can be found in Figure 3. The extrusion head stores a filament of liquid material either build material or support material onto a foam base. The build material is heated to 0.5°C above its melting point with the goal that it hardens about 0.1s after extrusion and cold welds to the previous layers [7]. As a rule, an outline of the perimeter of the part is expelled from the head first and after that the inside is raster filled by the extruder head [10]. When a layer is manufactured, the platform lowers down, and the extrusion head starts to deposit another layer. The machine keeps on building the part layer by layer until the point that it is finish. At the point when the part is done, it is expelled from the machine and the support material need to move away to reveal the completed product.
There are two sorts of support material: Soluble support system and Break-Away Support System (BASS) [12]. It tends to be expelled with particular equipment using water-based sodium hydroxide solution, or otherwise it can be broken away by hand.
In the FDM procedure, there is additionally a substantial scope of colors and materials accessible, for example, investment casting wax and thermoplastic [7]. The material for the most part utilized is a thermoplastic including ABS plastic, medical grade ABS (MABS), elastomers, polycarbonate, polyphenyl-sulfone (PPSF), and Ultem 9085 [1, 14]. The main favorable advantages of utilizing FDM innovation are:
a) manufacture of functional parts,
b) minimal material wastage,
c) the ease with which the expulsion of the support material takes place, and
d) ease of material change [1].
A major disadvantage of utilizing FDM technique is that the surface finish of the parts is more terrible than other rapid prototyping systems because of the procedure’s resolution which is managed by the filament thickness [7, 15]. The other inconvenience is that the building process is very time-consuming, as the entire cross-sectional area should be loaded up with building material. Unpredictable shrinkage is an additional drawback of utilizing FDM technique. As the FDM procedure expels the build material from its extrusion head and cools them rapidly on deposition, stresses induced by such rapid cooling constantly are initiated into the model. However , shrinkages and distortions caused to the model built are a typical event and are generally hard to anticipate [1].
3D Printing (3DP – Three-Dimensional Printing)
Z Corporation popularized its first 3D Printer, the Z 402 System, in view of three-dimensional technology (3DP) in 1997 [1]. The original and main technology of 3DP was designed and patented at the Massachusetts Institute of Technology. It was along these lines, licensed and further additionally created by Z Corporation. Z Corporation was procured by 3D Systems on January 3, 2012 [16].
The 3D Printing (3DP) process is like the Selective Laser Sintering (SLS) process, but in place of utilizing a CO2 laser to sinter the powdered material, an ink-jet printing head stores a liquid adhesive which is used in the binding process of the material. The 3D Printing machine has two pistons: one for injecting the powder and the other for bringing down/raising the building chamber appeared in Figure 4.
Schematic view of 3DP process
The 3D Printing process starts with the powder supply being raised by a piston and a leveling roller dispersing a thin layer of powder to the top point of the built chamber [17]. The multi-channel ink-jet printing head at that point stores fastener arrangement onto the free powder, framing the main cross-segment [1]. These locales of powder are stuck together wherever the folio is printed. The rest of the powder stays free and backings the part amid the procedure. At the point when the cross-segment is finished, the construct cylinder is brought down, the powder feed cylinder is raised, and another layer of powder is included the past layer by the leveling roller. The procedure is rehashed and the part develops layer by layer on the assemble cylinder until the point that the part is done. At last the assemble cylinder is raised and the free powder is brushed and the part evacuated [1]. 3D Printed parts are regularly invaded with a hardener to enhance quality and surface finish.The fundamental favorable circumstances of utilizing 3D Printing innovation are shading capability,shorter construct times, and economical crude materials when contrasted with other fast prototyping frameworks [1, 6]. No help structures required is additionally favorable position of 3D Printing. The powder bed gives self-support to enable complex geometry to be made. The weaknesses of utilizing 3D Printing innovation are the printed part is relatively fragile compared to other rapid prototyping frameworks, the penetration post-preparing is required, and the surface complete is generally poor [6].