16-01-2014, 03:20 PM
SEMINAR REPORT ON ADD
ADDITIVE PRINTING.docx (Size: 982.05 KB / Downloads: 25)
ABSTRACT
The last two decades ended in the midst of revolution caused by a technology that was barely noticeable at the beginning of the decade. In 1980 few would have guessed that personal computer along with desktop publishing software would fundamentally change the way of our industry did business. In 1990 again internet was known and used by a relatively small set of people. Yet by the end of the decade it was a major force in our industry and in society and in economy.Once again we are facing anew decade and we have to wonder what the next dominant technology likely to change our way of life is. While there is a number of candidates for the ”next big technology” including perennial favorite, the free energy device, our best is the technology called 3D printing which as the name implies is a technology that literally prints real 3D objects. It is used by the marketing industry to create models for marketing focus groups and pre-production sales demonstration.
INTRODUCTION
Additive manufacturing or 3D printing is a process of making a three-dimensional solid object of virtually any shape from a digital model. 3D printing is achieved using an additive process, where successive layers of material are laid down in different shapes. 3D printing is considered distinct from traditional machining techniques, which mostly rely on the removal of material by methods such as cutting or drilling (subtractive processes).A materials printer usually performs 3D printing processes using digital technology. Since the start of the twenty-first century there has been a large growth in the sales of these machines, and their price has dropped substantially. The technology is used for both prototyping and distributed manufacturing in jewelry, footwear architecture, engineering and construction (AEC), automotive, aerospace, dental and medical industries, education, geographic information systems, civil engineering, and many other fields.
The term additive manufacturing refers to technologies that create objects through a sequential layering process. Objects that are manufactured additively can be used anywhere throughout the product life cycle, from pre-production (i.e. rapid prototyping) to full-scale production (i.e. rapid manufacturing), in addition to tooling applications and post-production customization.In manufacturing, and machining in particular, subtractive methods are typically coined as traditional methods. The very term subtractive manufacturing is a retronym developed in recent years to distinguish it from newer additive manufacturing techniques. Although fabrication has included methods that are essentially "additive" for centuries (such as joining plates, sheets, forgings, and rolled work via riveting, screwing, forge welding, or newer kinds of welding), it did not include the information technology component of model-based definition. Machining (generating exact shapes with high precision) has typically been subtractive, from filing and turning to milling and grinding.
GENERAL PRINCIPLES
Modeling
Additive manufacturing takes virtual blueprints from computer aided design (CAD) or animation modeling software and "slices" them into digital cross-sections for the machine to successively use as a guideline for printing. Depending on the machine used, material or a binding material is deposited on the build bed or platform until material/binder layering is complete and the final 3D model has been "printed." A standard data interface between CAD software and the machines is the STL file format. An STL file approximates the shape of a part or assembly using triangular facets. Smaller facets produce a higher quality surface. PLY is a scanner generated input file format, and VRML (or WRL) files are often used as input for 3D printing technologies that are able to print in full color.
Printing
To perform a print, the machine reads the design from an .stl file and lays down successive layers of liquid, powder, paper or sheet material to build the model from a series of cross sections. These layers, which correspond to the virtual cross sections from the CAD model, are joined together or automatically fused to create the final shape. The primary advantage of this technique is its ability to create almost any shape or geometric feature.Printer resolution describes layer thickness and X-Y resolution in dpi (dots per inch) or micrometres. Typical layer thickness is around 100 micrometres (0.1 mm), although some machines such as the Objet Connex series and 3D Systems' ProJet series can print layers as thin as 16 micrometres. X-Y resolution is comparable to that of laser printers. The particles (3D dots) are around 50 to 100 micrometres (0.05–0.1 mm) in diameter.Construction of a model with contemporary methods can take anywhere from several hours to several days, depending on the method used and the size and complexity of the model. Additive systems can typically reduce this time to a few hours, although it varies widely depending on the type of machine used and the size and number of models being produced simultaneously.Traditional techniques like injection molding can be less expensive for manufacturing polymer products in high quantities, but additive manufacturing can be faster, more flexible and less expensive when producing relatively small quantities of parts. 3D printers give designers and concept development teams the ability to produce parts and concept models using a desktop size printer.
WORKING OF 3D PRINTER
The microcomputer is used to create a 3 Dimensional model of the component to be made using well-known CAD techniques. A slicing algorithm is used to identify selected successive slices, i.e., to provide data with respect to selected 2-D layers, of the 3-D model. Once a particular 2–D slice has been selected, the slice is then reduced to a series of one dimensional scan lines. Each of the scan line may comprise of single line segments or two or more shorter line segments. Each line segment having a defined starting point on a scan line and a defined line segment length. The microcomputer actuates the powder distribution operation when a particular 2-D slice of the 3-D model which has been created has been selected by supplying a powder “START” signal to a powder distribution controller circuit which is used to actuate a powder distribution system to permit a layer of powder for the selected slice to be deposited as by a powder head device. The powder is deposited over the entire confined region within which the selected slice is located.Once the powder is distributed, the operation of powder distribution controller is stopped when the microcomputer issues a powder “STOP” signal signifying that powder distribution over such region has been completed. Microcomputer then select a scan line i.e., the first scan line of the selected 2-D slice and then select a line segment, e.g., the first 1-D line segment of the selected scan line and supplies data defining the starting point thereof and the length there of to a binder jet nozzle control circuit. Nozzle is turned on at the start of the line segment .
ADDITIVE PROCESSES
Several different 3D printing processes have been invented since the late 1970s. The printers were originally large, expensive, and highly limited in what they could produce. A 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 sintering (SLS) and fused deposition modeling (FDM), while others cure liquid materials using different sophisticated technologies, e.g. stereolithography (SLA). With laminated object manufacturing (LOM), thin layers are cut to shape and joined together (e.g. paper, polymer, metal). Each method has its own advantages and drawbacks, and some companies consequently offer a choice between powder and polymer for the material from which the object is built. Some companies use standard, off-the-shelf business paper as the build material to produce a durable prototype. The main considerations in choosing a machine are generally speed, cost of the 3D printer, cost of the printed prototype, and cost and choice of materials and color capabilities.
INKJET PRINTING TECHNOLOGY
3D printers use standard inkjet printing technology to create parts layer-by-layer by depositing a liquid binder onto thin layers of powder. Instead of feeding paper under the print heads like a 2D printer, a 3D printer moves the print heads over a bed of powder upon which it prints the cross-sectional data sent from the ZPrint software. The system requires powder to be distributed accurately and evenly across the build platform. 3D Printers accomplish this task by using a feed piston and platform, which rises incrementally for each layer. A roller mechanism spreads powder fed from the feed piston onto the build platform; intentionally spreading approximately 30 percent of extra powder per layer to ensure a full layer of densely packed powder on the build platform. The excess powder falls down an overflow chute, into a container for reuse in the next build. Once the layer of powder is spread, the inkjet print heads print the cross-sectional area for the first, or bottom slice of the part onto the smooth layer of powder, binding the powder together. A piston then lowers the build platform 0.1016mm (0.004”), and a new layer of powder is spread on top.
CONCLUSION
3D printing has enabled the manufacturer to improve their designs and get the product to market more quickly than ever.3D printing is developing relative to the developments of CNC and 2D printers and becoming faster, easier to operate and cheaper prices. It is a method of converting a virtual 3D model into a physical object. Earlier the printing was limited to only two dimensions i.e printing on the paper but now a prototype of a three dimensional object can be prepared using layered structure by the help of this technology. Inspite of all these advantages yet there is still lot of growth to be seen in this field in near future. Various factors like Improved accuracy and surface finish, Increased size capacity ,Increase in speed etc are still needed to be improved.