3 D Printing Documentation
- 2. CONTENTS Title Page No. ACKNOWLEDGEMENT DECLARATION ABSTRACT LIST OF FIGURES 1 CHAPTER 1 INTRODUCTION CHAPTER 2 3D-PRINTER CHAPTER 3 ARCHITECTURE CHAPTER 4 i ii iii iv 1 2 3 ADDITIVE MANUFACTURING 5 4.1 EXTRUSION DEPOSITION 7 4.2 GRANULAR MATERIAL BINDING 8 4.3 PHOTOPOLYMERISZATION 9 4.4 LAMINATION 10 CHAPTER 5 PROCEDURES FOR PRINTING 11 5.1 DESIGNING USING CAD 12 5.2 CONVERSION TO STL FILE FORMAT 13 5.3 CHOOSING PRINTING 14
- 3. CHAPTER 6 ADVANTAGES & DISADVANTAGES 6.1 ADVANTAGES 15 6.2 DISADVANTAGES 16 CHAPTER 7 APPLICATIONS 17 FUTURE SCOPE 18 CONCLUSION 19 REFERENCES 20 LIST OF FIGURES Title Pages Fig.1 Block Diagram 3 Fig.2 Architecture 3 Fig.3 Additive Manufacturing 6 Fig.4 Extrusion Deposition 7 Fig.5 Granular Deposition 8 Fig.6 Photo polymerisation 9 Fig.7 Laminated object manufacturing 10 Fig.8 Procedures for 3D printing 11 Fig.9 Printing inks 14
- 4. 1 CHAPTER 1 INTRODUCTION 3D printing or additive manufacturing (AM) is any of various processes for making three object of almost any shape from a 3D model or other electronic data source primarily through additive processes in which successive layer of material are laid down under computer control. A 3D printer is a type of industrial robot. Early AM equipment and materials were developed in the 1980s. In 1984, Chuck Hull of 3D Systems Corp invented a process known as stereo lithography employing UV lasers to cure photopolymers. Hull also developed the file format widely accepted by 3D printing software, as well as the digital slicing and infill strategies common to many processes today. Also during the 1980s, the metal sintering forms of AM were being developed (such a selectively a sersintering and direct met all as reinterring),although they were not yet called 3Dprintingor AMatthetime.In1990,theplasticextrusion technology most widely associated with the term “3D printing” was commercialized by Stratasys under the name fused (FDM). In 1995, Z Corporation commercialized an MIT-developed additive process under the trademark 3D printing (3DP), referring at that time to a proprietary process binder on AM technologies found applications starting in the 1980sinproduct development, data visualization, rapid prototyping, and specialized manufacturing. Their expansion into production (job production, mass production, and distributed manufacturing) has been under development in the decades since Industrial production roles within the metalworking industries achieved significant scale for the first time in the early 2010s. Since the start of the 21st century there has been a large growth in the sales of AM machines and their price has dropped substantially. According to Wohler’s Associates, a consultancy the market for 3D printers and services was worth $2.2 billion worldwide in 2012, up 29% from 2011. Applications are many, including architecture, construction (AEC), industrial design, automotive, aerospace, military, engineering, dental and medical industries, biotech (human tissue replacement), fashion, footwear, jewelers, eyewear, education, geographic information systems, food.
- 5. 2 CHAPTER 2 3D-PRINTER 3D-Printer is a machine reminiscent of the Star Trek Replicator, something magical that can create objects out of thin air. It can“print”inplastic,metal,nylon,andoverahundred the materials. It can be use d for making nonsensical little models like the over-printed Yoda, yet it can also print manufacturing prototypes, end user products, quasi-legal guns, aircraft engine add even human organs using a person’s own cells. We live in an age that is witness to what many are calling the Third Industrial Revolution. 3D printing, more professionally called additive manufacturing, moves us away from the Henry Ford era mass production line, and will bring us to a new reality of customizable, one-off production. 3D print ensues variety of very different types of add It iceman factoring technologies, butthey all share one core thing in common: they create a three dimensional object by building it layer by successive layer, until the entire object is complete. It’s much like printing in two dimensions on a sheet of paper, but with an added third dimension: UP. The Z-axis. Each of these printed layers is a thinly-sliced, horizontal cross-section of the eventual object. Imagine a multi-layer cake, with the baker laying down each layer one at a time until the entire cake is formed. 3D printing is somewhat similar, but just a bit more precise than 3D baking. In the 2D world, a sheet of printed paper output from a printer was “designed” on the computer in a program such as Microsoft Word. The file -the Word document which contains the instruction. In the 3D world, a 3D printer also needs to have instructions for what to print. It needs a file as well. The file, a Computer Aided Design (CAD) file is created with the use of a 3D modeling program, either fromscratchorbeginningwitha3Dmodelcreatedbya3Dscanner. Either way, the program creates a file that is sent to the 3D printer. Along the way, software slices the design into hundreds, or more likely thousands, of horizontal layers. These layers will be printed one atop the other until the 3D object is done.
- 6. 3 Extruder X Motor X-axis uController Motor Driver Y Motor Y-axis Level Shifter Table Z-axis CHAPTER 3 ARCHITECTURE & S Fig.1 Block Diagram Architecture & S Fig.2 Architecture
- 7. 4 The picture shows the structure of a typical 3D printer. The print table is the platform where the objects for printing have been situated. It provides the basic support form anuf act ruing objects layer by layer. The extruder is the most important part of a 3D-Printer. As the extruders in the normal paper printers, this extruder is also used to pour ink for printing. The movements of extruder in various dimensions create the 3D print. For printing a 3d object, the extruder has to access X, Y and Z coordinates. For achieving this, many techniques are used according to the printer specification required for various applications. If the 3D-Printer is a desktop printer, the Z axis movement of the extruder can be avoided and that function can be transferred to the print table. This will avoid complexity in 3D printing as well as time consumption. When the STL file is input to the printer, the microcontroller extracts each layer from it and also extracts each line segment from each layer. Then it gives controls to the movement of the extruder at required rate. The X-direction movement of extruder smade possible by the X-motor. When the X motor rotates, the shaft also rotates and the extruder moves in X direction. The Y-direction movement of extruder is made possible by the Y-motor. When the Y motor rotates, the shaft also rotates and the extruder moves in Y direction. The X direction movement is made by the printable. In the case of desktop printers, the printing ink is usually plastic wire that has been melted by the extruder at the time of printing. While printing, the plastic wire will melt and when it fall down to the printing table. Consider printing larger objects like house using 3D printer. There will not be any X motor or Y motor in that case. An extruder which can pour concrete mix is fixed on the tip of arcane. The crane is programmed for the movement of extruder in X, Y and Z axis. The concept and structure of 3d printer changes according to the type, size, accuracy and material of the object that has to be printed.
- 8. 5 CHAPTER 4 ADDITIVE MANUFACTURING Additive manufacturing is a truly disruptive technology exploding on the manufacturing scene as leading companies are transitioning from “analog” to “digital” manufacturing. Additive manufacturing uses three dimensional printing to transform engineering design files into fully functional and durable objects created from sand, Metal and glass. The technology creates products layer by layer – after a layer’s particles are bound by heat or chemicals the next layer is added and the binding process is repeated. It enables geometriesnotpreviouslypossibletobemanufactured.Full-formpartsaremadedirectlyfrom computer-aided design (CAD) data for a variety of industrial, commercial and art applications. Manufacturers across several industries are using this digital manufacturing process to produce a range of products, including: engine components fo automotive applications, impellers and blades for aerospace use, pattern less sand moulds for pumps used in Thailand energy industry, and medical prosthetics which require easily adaptable design modifications. This advanced manufacturing process starts with a CAD file that conveys information about how the finished product is supposed to look. The CAD file is then sent to a specialized printer where the product is created by the repeated laying of finely powdered material (including sand, metal and glass) and binder to gradually build the finished product. Since it works in a similar fashion to an office printer laying ink on paper, this process is often referred to as 3D printing. The 3D printers can create a vast range of products, including parts for use in air planes and auto mobiles, to replacing aging or broken industrial equipment, orf or precise components for medical needs. There are tremendous cost advantages to using additive manufacturing. There is little to no waste creating objects through additive manufacturing, as they are precisely built by adding material layer by layer. In traditional manufacturing, object sure created in a subtractive manner as metals are trimmed and shaped to fit together properly. This process creates substantial waste that can be harmful to the environment. Additive manufacturing is a very energy efficient and environmentally friendly manufacturing option. .
- 9. 6 A large number of additive processes are now available. They differ in the way layers are deposited to create parts and in the materials that can be used. Some methods melt or soften material to produce the layers, e.g. selective laser melting (SLM) or direct metal laser sintering (DMLS), selective laser sintering (SLS), fused deposition modeling(FDM), while others cure liquid materials using different sophisticated technologies, e.g. Stereo lithography (SLA).With laminated object manufacturing (LOM), thin layer sare cut to shape and joined together (e.g. paper, polymer and metal). Each method has its own advantages and drawbacks, and some companies consequently offer a choice between powder andpolymerforthematerialfromwhichtheobjectisbuilt.Somecompaniesusestandard, off- the- shelf business paper as the build material to produce a durable prototype. Fig.4 Additive Manufacturing
- 10. 7 4.1 Extrusion Deposition Fig.4.1 Extrusion Deposition In extrusion deposition, Fused Deposition technique is used. Fused Deposition Modeling (FDM) was developed by Stratus’s in Eden Prairie, Minnesota. In this process, a plastic or wax material is extruded through a nozzle that traces the parts cross sectional geometry layer by layer. The build material is usually supplied in filament form, but some setups utilize plastic pellets fed from a hopper instead. The nozzle contains resistive heaters that keep the plasticity temperature just above its melting points that it flows easily through the nozzle and forms the layer. The plastic hardens immediately after flowing from the nozzle and bonds to the layer below. Once a layer is built, the platform lowers, and the extrusion nozzle deposits another layer. The layer thickness and vertical dimensional accuracy is determined by the extruder die diameter, which ranges from 0.013 to 0.005 inches. In theX-Y plane, 0.001 inch resolution is achievable. A range of materials are available including ABS, polyamide, polycarbonate, polyethylene, polypropylene, and investment casting wax.
- 11. 8 4.2 Granular Material Binding Fig. 4.2 Granular Deposition Another 3D printing approach is the selective fusing go format aerials in granular bed. The technique fuses part softhelayer and then moves the working are a down wards, adding no ther layer of granules and repeating the process until the piece has built up. This process uses the infused media to support overhangs and thin walls in the part being produced, which reduces the need for temporary auxiliary supports for the piece. A laser is typically used to sinter the media into a solid. Examples include selective laser sintering (SLS), with both metals and polymers (e.g. PA, PA-GF, Rigid GF, PEEK, PS, Alamode, Carbonize, elastomers), and direct metal as resent erring (DMLS). Selective Laser Melting (SLM) does not use sintering for the fusion of powder granules but will completely melt the powder using a high-energy laser to create fully dense materials in a layer wise method with similar mechanical properties to conventional manufactured metals. Electron (EBM) is a similar type of additive manufacturing technology for metal parts (e.g. titanium alloys). EBM manufactures parts by melting metal powder layer by layer with an electron beam in a high vacuum. Unlike metal sintering techniques that operate below melting point, EBM parts are fully dense, void-free, and very strong. Another method consists of an inkjet 3D printing system.
- 12. 9 4.3 Photopolymeriszation Sterility ography was patented in 1986 by Hull. Photo polymerization is primarily used in sterility graphic (SLA) to produce a solid part from a liquid. This process dramatically lyrede fined previous efforts, from the” photo sculpture" methodof Franco is William (1830–1905) in 1860(which consisted of photographing as object from a variety of angles (but all at the same distance from the subject) and then projecting each photograph onto a screen, whence a pantograph was used to trace the outline onto modeling clay) through the photo polymerization of Mitsubishi's Matsubara in1974. In photo polymerization, a vat of liquid polymer is exposed to control lighting under safelight conditions. The exposed liquid polymer hardens. The build plate then moves downinsmallincrementsandtheliquidpolymerisagainexposedtolight.Theprocessrepeats until the model has been built. The liquid polymer is then drained from the vat, leaving the solid model. The Envision TEC Per factory is an example of a DLP rapid prototyping system. Fig. 4.3 Photopolymeriszation
- 13. 10 4.4 Lamination Fig.4.4 Laminated Object Manufacturing Laminated Object Manufacturing works by layering sheets of material on top of one- another, binding them together using glue. The printer then slices an outline of the object into that cross section to be removed from the surrounding excess material later. Repeating this process build supthe object on layered a time. Objects printed during LOM are accurate, strong, and durable and generally shows no distortion over time which makes them suitable for all stages of the design cycle. They can even be additionally modified by machining or drilling afterprinting.Typicallayerresolutionforthisprocessisdefinedbythematerialfeedstockand usually ranges in thickness from one to a few sheets of copy paper. Moor’s version of the technology makes LOM one of the few 3D printing processes that can produce prints in full color. Low cost due to readily available raw material Paper models have wood like characteristics, and may be worked and finished accordingly Dimensional accuracy is slightly less than that of stereo lithography and selective laser sintering but no milling step is necessary.
- 14. 11 CHAPTER 5 PROCEDURES FOR PRINTING Fig.8 Procedure of 3d Printing There are some procedures for printing. First you must create a computer model for printing the object. For creating that, you can use Computer Aided Design Software like AutoCAD, 3DS Max etc. After the object file is created, the file need to be modified. The object file contains numerous amounts of curves. Curves cannot be printed by the printer directly. The curves have to be converted to STL (Stereo lithography) file format. The STL file format conversion removes all the curves and it is replaced with linear shapes. Then the file needs to be sliced into layer by layer.
- 15. 12 5.1 Designing Using Cad Computer-aided design (CAD) is the use of computer systems to assist in the creation, modification, analysis, or optimization of a design. CAD software is used to increase the productivity of the designer, improve the quality of design, improve communications through documentation, and to created at a base for manufacturing. CAD output is of tenanted form of electronic files for print, machining, or other manufacturing operations. CAD software for mechanical design uses either vector-based graphics to depict the objects of traditional drafting, or may also produce raster graphics showing the overall appearance of designed objects. However, it involves more than just shapes. As in the manual drafting of technical and engineering drawings, the output of CAD must convey information,suchasmaterials,processes,dimensions,andtolerances,accordingtoapplication- specific conventions. CAD may be used to design curves and figures in two-dimensional (2D) space; or curves, surfaces, and solids in three-dimensional (3D) space. CAD is an important industrial art extensively used in many applications, including automotive, shipbuilding, and aerospace in dustiest, industrial and architectural design, prosthetics, and many more. CAD is also widely used to produce computer animation for special effects in movies, advertising and technical manuals, often called DCC digital content creation. The modern ubiquity and power of computers means that even perfume bottles and shampoo dispensers are designed using techniques unheard of by engineers of the 1960s. Because of its enormous economic importance, CAD has been a major driving force for research in computational geometry, computer graphics (both hard ware and software), and discrete if perennial geometry. The design of geometric models for object shapes, in particular, is occasionally called computer-aided geometric design (CAGD). Unexpected capabilities of the seassociative relationships have led to a new form of prototyping called digital prototyping. In contrast to physical prototypes, which entail manufacturing time in the design? That said, CAD models can be generated by a computer after the physical prototype has been scanned using anindustrialCTscanningmachine.Dependingonthenatureofthebusiness,digitalorphysical prototypes can be initially chosen according to specific needs.
- 16. 13 5.2 Conversion To Stl File Format An STL file is a triangular representation of a 3D surface geometry. The surface is tessellated logically into a set of oriented triangles (facets). Each facet is described by the unit outward normal and three points listed in counterclockwise order representing the vertices of the triangle. While the aspect ratio and orientation of individual facets is governed by the surface curvature, the size of the facets is driven by the tolerance controlling the quality of the surfacerepresentationintermsofthedistanceofthefacetsfromthesurface.Thechoiceofthe toleranceisstronglydependentonthetargetapplicationoftheproducedSTLfile.Inindustrial processing, where stereo lithography machines perform a computer controlled layer by layer laser curing of a photo-sensitive resin, the tolerance may be in order of 0.1 mm to make the produced 3D part precise with highly worked out details. However much larger values are typically used in pre-production STL prototypes, for example for visualization purposes. The native STL format has to fulfill the following specifications: (i) The normal and each vertex of every facet are specified by three coordinates each, so there is a total of 12 numbers stored for each facet. (ii) Each facet is part of the boundary between the interior and the exterior of the object.Theorientationofthefacets(whichwayis``out''andwhich way is ``in'') is specified redundantly in two ways which must be consistent. First, the direction of the normal is outward. Second, the vertices are listed in counter clock wise order when looking at the object from the outside (right- hand rule). (iii) Each triangle must share two vertices with each of its adjacent triangles. This is known as vertex-to-vertex rule. (iv) The object represented must be located in the all-positive octant (all vertex coordinates must be positive). However, for non-native STL applications, the STL format can be generalized. The normal, if not specified (three zeroes might be used instead), can be easily computed from the coordinates of the vertices using the right-hand rule. Moreover, the vertices can be located in anyoctant.Andfinally, the face t convene on the interface between two objects (ortwoparts of the same object). This makes the generalized STL format suitable for modeling of 3D.
- 17. 14 5.3 Choosing Printing Inks Fig 5.3 Choosing Printing Inks
- 18. 15 Printing inks are chosen according to the need and kind of object thathastoprint.Differenttypesofinksareavailableaccordingtothesize, type, resolution and function of theobject. Colloidal Inks Three-dimensional periodic structures fabricated from colloidal “building blocks” may find widespread technological application as advanced ceramics, sensors, composites and tissue engineering scaffolds. These applications require both functional materials, such as those exhibiting Ferro electricity, high strength, or biocompatibility,and periodicity engineered at length scales (approximately several micrometers to millimeters) far exceeding colloidal dimensions. Colloidal inks developed for robotic deposition of 3-D periodic structures. These inks are also called general purpose inks. Fugitive Ink These types of inks are used for creating soft devices. The type of ink is capable for self-organizing which results in self regenerative devices. Nano particle Ink The object that has to be printed sometimes need conductor for its function. For printing conductors, special types of inks called Nano particle inks are used. Polyelectrolyte Ink Polyelectrolyte complexes exhibit a rich phase behavior that depends on several factors, including the polyelectrolyte type and architecture, their individual molecular weight and molecular weight ratio, the polymer concentration and mixing ratio, the ionic strength and pH of the solution, and the mixing conditions. So such inks are used for creating sensors, transducers etc. Sol-Gel Ink In this chemical procedure, the 'sol' (or solution) gradually evolves towards the formation of a gel-like dysphasic system containing both a liquid phase and solid phase whose morphologies range from discrete particles to continuous polymer networks.
- 19. 16 CHAPTER 6 ADVANTAGES & DISADVANTAGES 6.1 Advantages Create anything with great geometrical complexity. Ability to personalize every product with individual customer needs. Produce products which involve great level of complexity that simplycould not be produced physically in any other way. Additive manufacturing can eliminate the need for tool production and therefore reduce the costs, lead time and labor associated within. 3D printing is an energy efficient technology. Additive Manufacturing use up to 90% of standard materials and therefore creating less waste. Lighter and stronger products can be printed. Increased operating life for the products. Production has been brought closer to the end user or consumer. Spare parts can be printed on site which will eliminate shipping cost. Wider adoption of 3D printing would likely cause re-invention of a number ofalready invented products. 3D printing can create new industries and completely new professions. Printing 3D organs can revolution arise the medical industry.
- 20. 17 6.2 Disadvantages Since the technology is new, limited materials are available for printing. Consumes more time for less complicated pats. Size of printable object is limited by the movement of extruder. In additive manufacturing previous layer has to harden before creating next layer. Curved geometry will not be much accurate while printing.
- 21. 18 CHAPTER 7 APPLICATIONS Three-dimensional printing makes it as cheap to create single items as it is to produce ethos ands and thus undermines economies of scale. It may have as profound an impact on the world as the coming of the factory did. Just as nobody could have predicted the impact of possible to foresee the long-term impact of 3D printing. But the technology is coming, and it is likely to disrupt every field it touches. Additive manufacturing's earliest applications have been on the tool room end of the manufacturing spectrum. For example, rapid prototyping was one of the earliest additive variants, and its mission was to reduce the lead time and cost of developing prototypes ofnew parts and devices, which was earlier only done with subtractive tool room methods (typically slowly and expensively). With technological advances in additive manufacturing, however, and the dissemination of those advances into the business world, additive methods are moving ever further into the production end of manufacturing in creative and sometimes unexpected ways.Partsthatwereformerlythesoleprovinceofsubtractivemethodscannowinsomecases be made more profitably via additive ones. Standard applications include design visualization, prototyping/CAD, metal casting, architecture, education, geospatial, healthcare, and entertainment/retail. 3D printer came with immense number of applications. All the traditional methods of printing causes wastage ofresources.But3Dprinteronly uses the exact amount of material for printing.Thisenhancestheefficiency.Ifthematerialisverycostly,3d printing techniques can be used to reduce the wastage of material. Consider printing of a complex geometry like combustion chamber of a rocket engine. The 3D printing will enhances the strength and accuracy of the object. Conventional methods use parts by parts alignment. This will cause weak points in structures. But in the case of 3D printed object, the whole structure is a single piece. The steam engine in 1750 ortheprintingpressin1450,or the transistor in 1950. It is imp
- 22. 19 FUTURE SCOPE NASA engineers are 3-D printing parts, which are structurally stronger and more reliable than conventionally crafted parts, for its space launch system. The Mars Rover comprises some 70 3-D-printed custom parts. Scientists are also exploring the use of 3- Dprinters at the International Space Station to make spare parts on the spot. What once was theprovince of science fiction has now become a reality. Medicine is perhaps one of the most exciting areas of application. Beyond the use of3-D printing in producing prosthetics and hearing aids, it is being deployed to treat challenging medical conditions, and to advance medical research, including in the area of regenerative medicine. The breakthroughs in this area are rapid and awe-inspiring. Whe the torn other arrives- absinthe home, 3D printers have many promising areas of potential future application. They may, for example, be used to output spare parts for all manner of products, and which could not possibly be stocked as part of the inventory of even the best physical store. Hence, rather than throwing away a broken item (something unlikely to be justified a decade or two hence due to resource depletion and enforced recycling), faulty goods will be able to be taken to a local facility that will call up the appropriate spare parts online and simply print them out. NASA has already tested a 3D printer on the International Space Station, and recently announced its requirement for a high resolution 3D printer to producespacecraftpartsduringdeepspacemissions.TheUSArmyhasalsoexperimentedwith a truck-mounted 3D printer capable of outputting spare tank and other vehicle components in the battlefield. As noted above, 3D printers may also be used to make future buildings. To this end, a team at Southborough University is working on a 3D concrete printing project that could allow large building components to be 3D printed on-site to any design, and with improved thermal properties.
- 23. 20 CONCLUSION As the 3D printer is a device, it should be analyzed with the advantages and disadvantages, how the device can change the society and engineering etc in mind. The very nature of 3D printing, creating a part layer by layer, instead of subtractive methods of manufacturing lend themselves to lower costs in raw material. Instead of starting with a big chunk of plastic and carving away (milling or turning) the surface in order to produce your product. Additive manufacturing only "prints" what you want, where you want it. Other manufacturing techniques can be just as wasteful. 3D printing is the ultimate just-in-time method of manufacturing. No longer do you need a warehouse full of inventory waiting for customers.Justhavea3Dprinterwaitingtoprintyournexy order. Ontop of that, you of feral most infinite design options and custom products. It doesn’t costmoreto add accompany ogotoevery product you have ornery our customer spiceberry feature on the ir next order; the sky is the limit with additive manufacturing. Whetheryouaredesigningtennisshoesorspaceshuttles, youcan’tjustdesignwhatever you feel like, a good designer always take into account whether or not his design can be manufactured cost effectively. Additive manufacturing open up your designs to a whole new level. Because undercuts, complex geometryandth in wall edpartsare difficult manufacture using traditional methods, but are sometimes a piece of cake with 3D printing. In addition, the mathematicsbehind3Dprintingaresimplerthansubtractivemethods.Forinstance,the blades on a centrifugal supercharger would require very difficult path planning using a 5-axis CNC machine. The same geometry using additive manufacturing techniques is very simple to calculate, since each layer is analyzed separately and 2D information is always simpler than 3D. This mathematical difference, while hard to explain is the fundamental reason why 3D printing is superior to other manufacturing techniques. It almost always better to keep things simple and additive manufacturing is simple by its very nature. With so many potential benefits of 3D printing, there’s no surprise that this method is making its way through a diverse number of industries and quickly becoming a favorite tool of progressive marketers.
- 24. 21 REFERENCES www.3dprinting.com www.3dprinter.net/reference www.3dprintingindustry.com www.stratasys.com/applications www.en.wikipedia.org/wiki/3D_printing www.3ders.org/3d-print-technology.html www.zdnet.com/how-3d-printing-is-building-a-new-future-7000032248