UNIT -II AM PART 1. , types of addtve manufacturing,
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The document outlines the development and processes involved in additive manufacturing (AM) technology, highlighting its reliance on advancements in computers, CAD systems, and various associated technologies such as lasers and printing. It details the step-by-step process of AM, from conceptualization and CAD modeling to post-processing, discussing the evolution of materials and methods used in the industry. The document also notes the rise of hybrid systems that combine additive and subtractive techniques for improved precision and efficiency.
UNIT -II AM PART 1. , types of addtve manufacturing,
- 1. Development of Additive Manufacturing Technology Additive Manufacturing (AM) technology came about as a result of developments in a variety of different technology sectors. Like with many manufacturing technologies, improvements in computing power and reduction in mass storage costs paved the way for processing the large amounts of data typical of modern 3D Computer- Aided Design (CAD) models within reasonable time
- 2. 1. Computers 2. Computer-Aided Design Technology 3. Other Associated Technologies Lasers Printing Technologies Programmable Logic Controllers Materials Computer Numerically Controlled Machining Development of Additive Manufacturing Technology
- 3. Computers Like many other technologies, AM came about as a result of the invention of the computer. However, there was little indication that the first computers built in the1940s. Inventions like the thermionic valve, transistor, and microchip made it possible for computers to become faster, smaller, and cheaper with greater functionality. One key to the development of computers as serviceable tools lies in their ability to perform tasks in real-time. In the early days, serious computational tasks took many hours or even days to prepare, run, and complete.
- 4. Computers AM takes full advantage of many of the important features of computer technology, both directly (in the AM machines themselves) and indirectly (within the supporting technology), including: • Processing power • Graphics capability • Machine control • Networking • Integration
- 6. Computer-Aided Design Technology CAD technologies are available for assisting in the design of large buildings and of nano-scale microprocessors. CAD technology holds within it the knowledge associated with a particular type of product, including geometric, electrical, thermal, dynamic, and static behavior. Additive Manufacturing technology primarily makes use of the output from mechanical engineering, 3D Solid Modeling CAD software. It is important to understand that this is only a branch of a much larger set of CAD systems and, therefore, not all CAD systems will produce output suitable for layer-based AM technology.
- 7. Computer-Aided Design Technology Early CAD systems were extremely limited by the display technology. The first display systems had little or no capacity to produce anything other than alphanumeric text output. Some early computers had specialized graphic output devices that displayed graphics separate from the text commands used to drive them. Even so, the geometric forms were shown primarily in a vector form, displaying wireframe output
- 8. Other associated technologies •Lasers •Printing technologies •Programmable logic controllers •Materials •Computer numerically controlled machining
- 9. Lasers Many of the earliest AM systems were based on laser technology. The reasons are that lasers provide a high intensity and highly collimated beam of energy that can be moved very quickly in a controlled manner with the use of directional mirrors. Since AM requires the material in each layer to be solidified or joined in a selective manner, lasers are ideal candidates for use, provided the laser energy is compatible with the material transformation mechanisms. There are two kinds of laser processing used in AM; curing and heating.
- 10. Lasers With photopolymer resins the requirement is for laser energy of a specific frequency that will cause the liquid resin to solidify, or “cure.” Usually this laser is in the ultraviolet range but other frequencies can be used. For heating, the requirement is for the laser to carry sufficient thermal energy to cut through a layer of solid material, to cause powder to melt, or to cause sheets of material to fuse. For powder processes, for example, the key is to melt the material in a controlled fashion without creating too great a build-up of heat, so that when the laser energy is removed, the molten material rapidly solidifies again.
- 11. Printing Technologies Ink-jet or droplet printing technology has rapidly developed in recent years. Improvements in resolution and reduction in costs has meant that high-resolution printing, often with multiple colors, is available as part of our everyday lives. Such improvement in resolution has also been supported by improvement in material handling capacity and reliability. Initially, colored inks were low in viscosity and fed into the print heads at ambient temperatures. Now it is possible to generate much higher pressures within the droplet formation chamber so that materials with much higher viscosity and even molten materials can be printed. This means that droplet deposition can now be used to print photocurable and molten resins as well as binders for powder systems.
- 12. Programmable Logic Controllers The input CAD models for AM are large data files generated using standard computer technology. Once they are on the AM machine, however, these files are reduced to a series of process stages that require sensor input and signaling of actuators. This is process and machine control that often is best carried out using microcontroller systems rather than microprocessor systems. Industrial microcontroller systems form the basis of Programmable Logic Controllers (PLCs), which are used to reliably control industrial processes. Designing and building industrial machinery, like AM machines, is much easier using building blocks based around modern PLCs for coordinating and controlling the various steps in the machine process.
- 13. Materials Earlier AM technologies were built around materials that were already available and that had been developed to suit other processes. However, the AM processes are somewhat unique and these original materials were far from ideal for these new applications. For example, the early photocurable resins resulted in models that were brittle and that warped easily. Powders used in laser-based powder bed fusion processes degraded quickly within the machine and many of the materials used resulted in parts that were quite weak. As we came to understand the technology better, materials were developed specifically to suit AM processes. Materials have been tuned to suit more closely the operating parameters of the different processes and to provide better output parts. As a result, parts are now much more accurate, stronger, and longer lasting
- 14. Computer Numerically Controlled Machining One of the reasons AM technology was originally developed was because CNC technology was not able to produce satisfactory output within the required time frames. CNC machining was slow, cumbersome, and difficult to operate. AM technology on the other hand was quite easy to set up with quick results, but had poor accuracy and limited material capability. As improvements in AM technologies came about, vendors of CNC machining technology realized that there was now growing competition. CNC machining has dramatically improved, just as AM technologies have matured. AM can be used to more quickly and economically produce the part than when using CNC.
- 15. Metal Systems One of the most important recent developments in AM has been the proliferation of direct metal processes. Machines like the EOSint-M and Laser-Engineered Net Shaping (LENS) have been around for a number of years. Recent additions from other companies and improvements in laser technology, machine accuracy, speed, and cost have opened up this market. Most direct metal systems work using a point-wise method and nearly all of them utilize metal powders as input. The main exception to this approach is the sheet lamination processes, particularly the Ultrasonic Consolidation process from the Solidica, USA, which uses sheet metal laminates that are ultrasonically welded together.
- 16. Metal Systems Of the powder systems, almost every newer machine uses a powder spreading approach similar to the SLS process, followed by melting using an energy beam. This energy is normally a high-power laser, except in the case of the Electron Beam Melting (EBM) process by the Swedish company Arcam. Another approach is the LENS powder delivery system used by Optomec. This machine employs powder delivery through a nozzle placed above the part. The powder is melted where the material converges with the laser and the substrate. This approach allows the process to be used to add material to an existing part, which means it can be used for repair of expensive metal components that may have been damaged, like chipped turbine blades and injection mold tool inserts.
- 17. Hybrid Systems Some of the machines described above are, in fact, hybrid additive/subtractive processes rather than purely additive. Including a subtractive component can assist in making the process more precise. An example is the use of planar milling at the end of each additive layer in the Sanders and Objet machines. This stage makes for a smooth planar surface onto which the next layer can be added, negating cumulative effects from errors in droplet deposition height. It should be noted that when subtractive methods are used, waste will be generated. Machining processes require removal of material that in general cannot easily be recycled. Similarly, many additive processes require the use of support structures and these too must be removed or “subtracted.”
- 18. Hybrid Systems It can be said that with the Object process, for instance, the additive element is dominant and that the subtractive component is important but relatively insignificant. There have been a number of attempts to merge subtractive and additive technologies together where the subtractive component is the dominant element. An excellent example of this is the Stratoconception approach, where the original CAD models are divided into thick machinable layers. Once these layers are machined, they are bonded together to form the complete solid part. This approach works very well for very large parts that may have features that would be difficult to machine using a multi-axis machining center due to the accessibility of the tool.
- 19. Hybrid Systems A lower cost solution that works in a similar way is Subtractive RP (SRP) from Roland, who is also famous for plotter technology. SRP makes use of Roland desktop milling machines to machine sheets of material that can be sandwiched together, similar to Stratoconception. The key is to use the exterior material as a frame that can be used to register each slice to others and to hold the part in place. With this method not all the material is machined away and a web of connecting spars are used to maintain this registration.
- 20. The Eight Steps in Additive Manufacture The sequence of steps is generally appropriate to all AM technologies. There will be some variations dependent on which technology is being used and also on the design of the particular part. Some steps can be quite involved for some machines but may be trivial for others. The eight key steps in the process sequence are: Conceptualization and CAD Conversion to STL/AMF Transfer and manipulation of STL/AMF file on AM machine Machine setup Build Part removal and cleanup Post-processing of part Application
- 21. The Eight Steps in Additive Manufacture There are other ways to breakdown this process flow, depending on your perspective and equipment familiarity. For example, if you are a designer, you may see more stages in the early product design aspects. Model makers may see more steps in the post-build part of the process. Different AM technologies handle this process sequence differently.
- 23. Step 1: Conceptualization and CAD The first step in any product development process is to come up with an idea for how the product will look and function. Conceptualization can take many forms, from textual and narrative descriptions to sketches and representative models. If AM is to be used, the product description must be in a digital form that allows a physical model to be made. It may be that AM technology will be used to prototype and not build the final product, but in either case, there are many stages in a product development process where digital models are required.
- 24. Step 1: Conceptualization and CAD The generic AM process must therefore start with 3D CAD information. There may be a variety of ways for how the 3D source data can be created. This model description could be generated by a design expert via a user interface, by software as part of an automated optimization algorithm, by 3D scanning of an existing physical part, or some combination of all of these. Most 3D CAD systems are solid modeling systems with surface modeling components; solid models are often constructed by combining surfaces together or by adding thickness to a surface. In the past, 3D CAD modeling software had difficulty creating fully enclosed solid models, and often models would appear to the casual observer to be enclosed but in fact were not mathematically closed. Such models could result in unpredictable output from AM machines, with different AM technologies treating gaps in different ways. Most modern solid modeling CAD tools can now create files without gaps (e.g.,“water tight”), resulting in geometrically unambiguous representations of a part.
- 25. Step 2: Conversion to STL/AMF Nearly every AM technology uses the STL file format. The term STL was derived from STereoLithograhy, which was the first commercial AM technology from 3D Systems in the 1990s. STL is a simple way of describing a CAD model in terms of its geometry alone. It works by removing any construction data, modeling history, etc., and approximating the surfaces of the model with a series of triangular facets. The minimum size of these triangles can be set within most CAD software and the objective is to ensure the models created do not show any obvious triangles on the surface.
- 26. Step 2: Conversion to STL/AMF The triangle size is in fact calculated in terms of the minimum distance between the plane represented by the triangle and the surface it is supposed to represent. In other words, a basic rule of thumb is to ensure that the minimum triangle offset is smaller than the resolution of the AM machine. The process of converting to STL is automatic within most CAD systems, but there is a possibility of errors occurring during this phase. There have therefore been a number of software tools developed to detect such errors and to rectify them if possible.
- 27. Step 2: Conversion to STL/AMF STL files are an unordered collection of triangle vertices and surface normal vectors. As such, an STL file has no units, color, material, or other feature information. These limitations of an STL file have led to the recent adoption of a new “AMF” file format. This format is now an international ASTM/ISO standard format which extends the STL format to include dimensions, color, material, and many other useful features. STL file repair software, like the MAGICS software from the Belgian company Materialize, is used when there are problems with the STL file that may prevent the part from being built correctly.
- 28. Step 3: Transfer to AM Machine and STL File Manipulation Once the STL file has been created and repaired, it can be sent directly to the target AM machine. Ideally, it should be possible to press a “print” button and the machine should build the part straight away. This is not usually the case however and there may be a number of actions required prior to building the part. The first task would be to verify that the part is correct. AM system software normally has a visualization tool that allows the user to view and manipulate the part. The user may wish to reposition the part or even change the orientation to allow it to be built at a specific location within the machine.
- 29. Step3: Transfer to AM Machine and STL File Manipulation It is quite common to build more than one part in an AM machine at a time. This may be multiples of the same part (thus requiring a copy function) or completely different STL files. STL files can be linearly scaled quite easily. Some applications may require the AM part to be slightly larger or slightly smaller than the original to account for process shrinkage or coatings; and so scaling may be required prior to building.
- 30. Step3: Transfer to AM Machine and STL File Manipulation Applications may also require that the part be identified in some way and some software tools have been developed to add text and simple features to STL formatted data for this purpose. This would be done in the form of adding 3D embossed characters. More unusual cases may even require segmentation of STL files (e.g., for parts that may be too large) or even merging of multiple STL files.
- 31. Step 4: Machine Setup All AM machines will have at least some setup parameters that are specific to that machine or process. Some machines are only designed to run a few specific materials and give the user few options to vary layer thickness or other build parameters. These types of machines will have very few setup changes to make from build to build. Other machines are designed to run with a variety of materials and may also have some parameters that require optimization to suit the type of part that is to be built, or permit parts to be built quicker but with poorer resolution. Such machines can have numerous setup options available.
- 32. Step 4: Machine Setup It is common in the more complex cases to have default settings or save files from previously defined setups to help speed up the machine setup process and to prevent mistakes being made. Normally, an incorrect setup procedure will still result in a part being built. The final quality of that part may, however, be unacceptable. In addition to setting up machine software parameters, most machines must be physically prepared for a build. The operator must check to make sure sufficient build material is loaded into the machine to complete the build.
- 33. Step 5: Build Although benefitting from the assistance of computers, the first few stages of the AM process are semi- automated tasks that may require considerable manual control, interaction, and decision making. Once these steps are completed, the process switches to the computer controlled building phase. This is where the previously mentioned layer-based manufacturing takes place.
- 34. Step 5: Build All AM machines will have a similar sequence of layering, including a height adjustable platform or deposition head, material deposition or spreading mechanisms, and layer cross-section formation. As long as no errors are detected during the build, AM machines will repeat the layering process until the build is complete.
- 35. Step 6: Removal and Cleanup Ideally, the output from the AM machine should be ready for use with minimal manual intervention. While sometimes this may be the case, more often than not, parts will require a significant amount of post-processing before they are ready for use. In all cases, the part must be either separated from a build platform on which the part was produced or removed from excess build material surrounding the part. Some AM processes use additional material other than that used to make the part itself (secondary support materials)
- 36. Step 6: Removal and Cleanup Some processes have been developed to produce easy-to- remove supports, there is often a significant amount of manual work required at this stage. For metal supports, a wire EDM machine, bandsaw, and/or milling equipment may be required to remove the part from the baseplate and the supports from the part. There is a degree of operator skill required in part removal, since mishandling of parts and poor technique can result in damage to the part.
- 37. Step 6: Removal and Cleanup Different AM parts have different cleanup requirements, but suffice it to say that all processes have some requirement at this stage. The cleanup stage may also be considered as the initial part of the post-processing stage
- 38. Step 7: Post-Processing Post-processing refers to the (usually manual) stages of finishing the parts for application purposes. This may involve abrasive finishing, like polishing and sandpapering, or application of coatings. This stage in the process is very application specific. Some applications may only require a minimum of post- processing. Some post-processing may involve chemical or thermal treatment of the part to achieve final part properties. Different AM processes have different results in terms of accuracy, and thus machining to final dimensions may be required.
- 39. Step 8: Application Following post-processing, parts are ready for use. It should be noted that, although parts may be made from similar materials to those available from other manufacturing processes (like molding and casting), parts may not behave according to standard material specifications. Some AM processes inherently create parts with small voids trapped inside them, which could be the source for part failure under mechanical stress. In almost every case, the properties are anisotropic (different properties in different direction).
- 40. Step 8: Application For most metal AM processes, rapid cooling results in different microstructures than those from conventional manufacturing. As a result, AM produced parts behave differently than parts made using a more conventional manufacturing approach. This behavior may be better or worse for a particular application, and thus a designer should be aware of these differences and take them into account during the design stage