Rapid Prototyping / History / Prototyping Technologies

History of Rapid Prototyping

Rapid prototyping is quite a recent invention. The first machine of rapid prototyping hit the markets in the late 1980s. The early rapid prototyping process derived its name from the activities and the purpose for which the earlier machines were utilized.

What is Rapid Prototyping?

Rapid prototyping refers to physical objects that are automatically constructed with the aid of additive manufacturing technology.

Rapid prototyping in its earlier days was applied to production of models and prototype parts. But nowadays with the advancement in technology, rapid prototyping is used widely for many applications that include manufacturing production-quality parts. The manufacturing of these quality parts however are very small in numbers. Apart from industrial applications, rapid prototyping is also used in sculpting. The application of rapid prototyping in sculpting is to generate fine arts exhibitions.

Rapid prototyping as mentioned earlier, involves the use of additive manufacturing technology which actually takes the virtual designs from computer aided design (CAD) or animation modeling software (AMS).

These designs are further transformed into thin, virtual, horizontal cross sections and then the process of creating successive layers continues till the model in complete. On completion of the model, one may find that the virtual model is almost same as the physical model. Over here a process called WYSIWYG (What You See Is What You Get) takes place wherein the final product is same as the image created. Once the layers which correspond to the virtual cross section from CAD are formed, they are either joined or fused automatically to yield the final shape. Additive fabrication has the benefit of creating any shape or geometric feature.

Working of Rapid Prototyping Machines

CAD software and the rapid prototyping machine are connected with a data interface that is called as the STL file format.

This STL file format enables the approximation of a shape of a part or the entire assembly using triangular facets. Smaller the facet, higher is the quality surface. One should consider the meaning of the word rapid as ‘relative’, as the construction process of a model with the contemporary methods can take up a long time which can be several hours to several days. It actually depends upon the complexity and size of the model. The method used over here also plays an important role. Sometimes the type of machine being used also influences the time taken for the creation of a new model though the additive systems are applied. Even here the size and the number of models to be created play an equally important role.

There are some other techniques that are used in the construction of parts. The technique used in solid free-form fabrication involves the use of two materials in the construction of parts. One of it is the building material of that part and the other is the support material. The use of support material is to provide support to the projecting features during construction.

In case of manufacturing polymer products in higher quantities, a process called traditional injection molding is more feasible in terms of cost, but when it comes to manufacturing parts in smaller volumes, the application of additive fabrication is recommended more and is cost effective.

Prototyping Technologies

Some of the prototyping technologies used in various rapid prototyping machines are as follows:

Selective Laser Sintering (SLS):

This technology involves the use of high power laser for the fusion of tiny particles of plastic, metal etc, into a mass that represents a desired 3D object, through the help of a SLS machine. This is an additive manufacturing technique. Materials used in this technique are metal powders and thermoplastics.

Fused Deposition Modeling (FDM):

This additive manufacturing technology was invented in the late 1980s by S. Scott Crump and is used for applications like modeling, prototyping and production. This technology involves the use of eutectic metals and thermoplastics.

Stereo lithography (SLA):

This also is an additive manufacturing technology and is used for production of models, patterns etc through the Stereo lithography machine. Photo-polymer is the principle material used in this technique.

Laminated object manufacturing (LOM):

Paper material is the base material used in this technology. In this method layers of adhesive-coated plastic, paper or metal laminates are fused together and cut into shape with the aid of a knife or a laser cutter.

3D Printing:

This too is an additive manufacturing technology and involves the use of various materials. In this technology successive layers of material create a 3D object. 3D printing technology actually is said to be more affordable, easy to use and speedy than the additive manufacturing technologies. Though production applications are actually dominated by the additive manufacturing technologies, 3D has a great potential to prove useful in the production applications.

Rapid prototyping, is now entering into rapid manufacturing which is more advanced as compared to rapid prototyping machines as it can be used for large products. This is an additive fabrication technique, that would be applied to the manufacturing of solid objects. This process involves the sequential delivery of energy, material (material sometimes may not be used) to the specified points in space, in order to produce a particular part. Rapid manufacturing is an advanced form of this technology.

Introduction To Additive Fabrication

Additive fabrication refers to a class of manufacturing processes, in which a part is built by adding layers of material upon one another. These processes are inherently different from subtractive processes or consolidation processes. Subtractive processes, such as milling, turning, or drilling, use carefully planned tool movements to cut away material from a work piece to form the desired part. Consolidation processes, such as casting or molding, use custom designed tooling to solidify material into the desired shape. Additive processes, on the other hand, do not require custom tooling or planned tool movements. Instead, the part is constructed directly from a digital 3-D model created through Computer Aided Design (CAD) software. The 3-D CAD model is converted into many thin layers and the manufacturing equipment uses this geometric data to build each layer sequentially until the part is completed. Due to this approach, additive fabrication is often referred to as layered manufacturing, direct digital manufacturing, or solid freeform fabrication.

The most common term for additive fabrication is rapid prototyping. The term “rapid” is used because additive processes are performed much faster than conventional manufacturing processes. The fabrication of a single part may only take a couple hours, or can take a few days depending on the part size and the process. However, processes that require custom tooling, such as a mold, to be designed and built may require several weeks. Subtractive processes, such as machining, can offer more comparable production times, but those times can increase substantially for highly complex parts. The term “prototyping” is used because these additive processes were initially used solely to fabricate prototypes. However, with the improvement of additive technologies, these processes are becoming increasingly capable of high-volume production manufacturing, as will be explored in the section on applications.

Additive fabrication offers several advantages, listed below.

• Speed – As described above, these “rapid” processes have short build times. Also, because no custom tooling must be developed, the lead time in receiving parts is greatly reduced.

• Part complexity – Because no tooling is required, complex surfaces and internal features can be created directly when building the part. Also, the complexity of a part has little effect on build times, as opposed to other manufacturing processes. In molding and casting processes, part complexity may not affect the cycle times, but can require several weeks to be spent on creating the mold. In machining, complex features directly affect the cycle time and may even require more expensive equipment or fixtures.

• Material types – Additive fabrication processes are able to produce parts in plastics, metals, ceramics, composites, and even paper with properties similar to wood. Furthermore, some processes can build parts from multiple materials and distribute the material based on the location in the part.

• Low-volume production – Other more conventional processes are not very cost effective for low-volume productions because of high initial costs due to custom tooling and lengthy setup times. Additive fabrication requires minimal setup and builds a part directly from the CAD model, allowing for low per-part costs for low-volume productions.

With all of these advantages, additive fabrication will still not replace more conventional manufacturing processes for every application. Processes such as machining, molding, and casting are still preferred in specific instances, such as the following:

• Large parts – Additive processes are best suited for relatively small parts because build times are largely dependent upon part size. A larger part in the X-Y plane will require more time to build each layer and a taller part (in the Z direction) will require more layers to be built. This limitation on part size is not shared by some of the more common manufacturing methods. The cycle times in molding and casting processes are typically controlled by the part thickness, and machining times are dependent upon the material and part complexity. Manufacturing large parts with additive processes is also not ideal due to the current high prices of material for these processes.

• High accuracy and surface finish – Currently, additive fabrication processes can not match the precision and finishes offered by machining. As a result, parts produced through additive fabrication may require secondary operations depending on their intended use.

• High-volume production – While the production capabilities of additive processes are improving with technology, molding and casting are still preferred for high-volume production. At very large quantities, the per-part cost of tooling is insignificant and the cycle times remain shorter than those for additive fabrication.

• Material properties – While additive fabrication can utilize various material types, individual material options are somewhat limited. As a result, materials that offer certain desirable properties may not be available. Also, due to the fabrication methods, the properties of the final part may not meet certain design requirements. Lastly, the current prices for materials used in additive processes are far greater than more commonly used materials for other processes.

Applications:

Additive fabrication processes initially yielded parts with few applications due to limited material options and mechanical properties. However, improvements to the processing technologies and material options have expanded the possibilities for these layered parts. Now, additive fabrication is used in a variety of industries, including the aerospace, architectural, automotive, consumer product, medical product, and military industries. The application of parts in these industries is quite vast. For example, some parts are merely aesthetic such as jewelry, sculptures, or 3D architectural models. Others are customized to meet the user’s personal needs such as specially fitted sports equipment, dental implants, or prosthetic devices. The following three categories are often used to describe the different application of additive fabrication and may be applied to all of the above industries.

• Rapid prototyping – Prototypes for visualization, form/fit testing, and functional testing

• Rapid tooling – Molds and dies fabricated using additive processes

• Rapid manufacturing – Medium-to-high volume production runs of end-use parts

AUTOCAD basic

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Computer Aided Design (CAD) is a form of design in which people work with computers to create ideas, models, and prototypes. CAD was originally developed to assist people with technical drawing and drafting, but it has expanded to include numerous other potential uses. A variety of software products designed for CAD can be found on the market, with many being targeted to a specific application or industry.

Drafting and technical drawing can be very painstaking, and they require some special skills. Using CAD for drafting still requires many of the same skills, but by working with a computer instead of on paper, people can be much more efficient. They can also play around with ideas much more easily, moving design elements around and running the design through software programs which can determine whether or not the design is structurally viable. For example, an architect working on a bridge can test the design in simulations to see if it will withstand the load it will need to carry.

CAD can be used to design structures, mechanical components, and molecules, among other things. One advantage of using CAD is that people don’t have to make prototypes to demonstrate a project and its potential, as they can use a three dimensional modeling program to show people how something might look. CAD also allows for endless variations and experiments to show how the look and feel of something can be altered, and these can be done at the click of a button, rather than with painstaking drafting work.

Casual users sometimes like to play with CAD for things like deciding how to organize their furniture, or lay out a garden. They can drag and drop elements and play with the space in a variety of ways, and generate a configuration which will be suitable and aesthetically pleasing. CAD is used by professionals in a number of industries across the manufacturing sector, and it can also appear in some surprising places, like forensics labs, where researchers recreate crime scenes on a computer to explore scenarios.

  

Advanced CAD programs usually require extensive training from their users, as they can be very complex and challenging to work with. More casual programs can be learned in shorter periods of time, with some designed to allow people to work within the program immediately, learning as they go. Simple programs can also sometimes have their functionality increased with expansion packs which are designed to provide additional features, so that people can work within a program they are familiar with when they want to develop more complex designs.

CAD

Computer-aided design (CAD) is a process that allows computer users to design a variety of products and geometric shapes on-screen, rather than building them by hand. Using CAD software, one can create and modify an object to determine how it will appear and function after it is built. CAD drawings often include a computer-generated image of the design, as well as its dimensions, processes, and materials. CAD drawings may be either two dimensional (2D) or three-dimensional (3D). When an object is drawn in 3D using CAD, the process is often referred to as rendering or modeling, while 2D design is often called “drafting.”

CAD drawings are used in a large number number of industrial and manufacturing applications. This technology is widely utilized in art and graphic design, and gives these artists a greater level of design flexibility than that of other mediums. CAD drawings are also used in automotive and aerospace design, as well as in the development of industrial products and equipment. Many special effects used in films and television rely on computer animation generated with CAD software. Finally, CAD drawings are a critical component of the construction and engineering trades.

Before the invention of CAD, products and building plans were drawn by hand. This was a laborious and time-intensive process that required a high number of draftsmen, as well as frequent revisions. With the introduction of CAD software, engineers and designers were able to quickly and easily generate and modify drawings. Design firms could hire fewer staff, and both design and product development cycles were greatly reduced. CAD software also allowed engineers and designers to generate their own drawings, rather than to attempt to explain them to a draftsman, resulting in more accurate design.

Though CAD drawings have been in use since the 1960s, it wasn’t until the late 1980s and early 1990s that CAD software became a cost-effective option for many industries. Early versions of the software relied on 2D vector design, while modern CAD drawings include 3D modeling capabilities. Today’s modeling software allows designers to not only draw an object, but to rotate it on an axis, and to see through the object’s walls from the inside. This modeling capability is particularly useful in construction and engineering, allowing designers to virtually “walk-through” a structure and explore different angles.

Most CAD software is designed only for Windows or Linux operating systems. Complex CAD drawings may require advanced graphics cards and high levels of random access memory (RAM), but simpler drawings can be done on almost any basic computer. CAD software is operated using a traditional mouse, though some professional designers may supplement this operation using a digital pen or drawing tablet.