Rapid Prototyping

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Abstract

Rapid Prototyping is a relatively new and developing set of technologies. A variety of different techniques used in the design of products and prototypes are presented in this article. The enablers and limitations for certain materials, such as plastics, to construct models and components are considered. Although some materials limit the applicability for these techniques as a viable method for constructing prototypes, rapid prototyping with metallic materials provide a profound breakthrough and enabling effect on product design and manufacturing.

Background

For most of history, the construction and machining of prototypes or products has involved processes such as milling, lathing, or drilling. All of these processes are considered subtractive, which means that the finished product is created by subtracting material from a larger block to shape it as desired (i.e. sawing or drilling into wood) (Kochan, Kai & Zhaohui, 1999). However, in the past 30 or so years, new technologies have begun to emerge (Noorani, 2006).  Known as Rapid Prototyping, these technologies are additive instead of subtractive. They consist of techniques that progressively add material to a product as it is constructed (Gebhardt, 2003). To the general public, this is commonly known as 3D Printing since certain rapid prototyping processes are analogous to regular printing. In such processes, models are created on a computer and from these models a 3D printer deposits material in layers to create an object.

Rapid Prototyping Techniques

While the term 3D Printing evokes images of a large inkjet printer spitting out heated material that hardens to create an object, this is not the only technique that has been developed in the field of rapid prototyping. In fact, the first technique developed used a process called stereo lithography (Noorani, 2006). This process involved solidifying liquid polymers by shining ultraviolet light on them to create each individual layer of the object (Noorani, 2006). Another process that was later developed is Selective Laser Sintering, which uses a special powder as its base material (Noorani, 2006). The powder is heated by a laser to sinter and then fuse the powder to create the final product (Noorani, 2006). In addition to these techniques, there are several other additional techniques that will not be described here.

Overall, the three techniques listed above demonstrate that the field of rapid prototyping is not simply limited to 3D printing. There are a variety of methods and each has its own merits. Nevertheless, there is a common thread to all of these techniques. They all seek to improve the quality of manufacturing and prototyping using the advances in digital computers that have occurred in the last 40 years. Through use of 3D modeling software, all of these rapid prototyping techniques have the precision and versatility to create many different models to a high degree of accuracy.

Figure 1

A rapid prototyping machine that uses sugar to create shapes. The sugar is heated using a jet of hot air to fuse it together. Photo by author Oskay at Wikipedia

Applications of Rapid Prototyping

In the context of product development, Rapid Prototyping can be an invaluable tool. The Product Design process generally consists of stages where prototypes are created and tested to verify and improve designs (Ulrich & Eppinger, 2011). This is typically an iterative process to ensure that any flaws in the design are detected before a final product is ready to be manufactured and shipped (Ulrich & Eppinger, 2011). Given that rapid prototyping technology is very versatile in the shapes and objects it can create compared to standard manufacturing techniques that require specialized tools to create each different prototype, it is perfect for this part of the design phase.

In the absence of rapid prototyping, the creation of a complex component can require injection molding or the use of a variety of tools such as lathes or drills. Molds themselves need to be manufactured and the use of tools can become difficult and time consuming. Furthermore, if the component needs to be redesigned to correct a mistake, any previous molds will become useless. All of this can be avoided by creating prototypes using rapid prototyping techniques. The machinery does not need to be modified to create new parts. Instead the only changes that need to be made are to the 3D model that the printer uses to create the prototype. As a result, rapid prototyping can provide a cost-saving and time-efficient way to generate multiple prototypes.

In cases where a company is trying to make the design process more efficient, rapid prototyping can be useful in a few ways. In a situation where it may be infeasible or too costly to create prototypes using older methods, rapid prototyping may be able to manufacture the desired object. This means that the prototype is available to engineers so that they can analyze it visually and by actually holding and touching the prototype which is a key part of discovering any flaws (Gebhardt, 2003). While computers can analyze 3D models using software, that type of analysis still cannot compare to actually having a person hold and examine a physical prototype (Gebhardt, 2003). In addition, other crucial tests can be conducted on these prototypes such as whether or not separate components fit together and if a prototype made up of several components functions as it was intended after it is assembled (Gebhardt, 2003).

Beyond just prototype construction, rapid prototyping technology can also be applied to other parts of the manufacturing process or to other fields. One example is rapid tooling, which is very similar to rapid prototyping. In rapid tooling, tools for the manufacture of a product such as molds are created using rapid prototyping technology (Gebhardt, 2003). This allows high quality molds that must be very accurate to be constructed using precise machines to ensure that they are within the required tolerances.

Additionally, rapid prototyping technology can potentially be extended not just to creating prototypes for testing, but also to generating final manufactured products in a process called rapid manufacturing (Gebhardt, 2003). Rapid Manufacturing is naturally limited to products that are made from the materials currently used in rapid prototyping technologies. Lastly, rapid prototyping also has potential outside of just product design and manufacturing. In some cases, it has been suggested as a tool in the field of architectural design (Sass & Oxman, 2006). Similar to product design, the use of rapid prototyping has the ability to assist architects in the design phase of a structure or building (Sass & Oxman, 2006). Having an actual 3D model of the proposed structure can help an architect visualize, test, and analyze innovative designs (Sass & Oxman, 2006)

Case Study

One real world instance of the benefits of rapid prototyping is the design of an intake manifold of a four-cylinder engine. To optimize this component, it is not enough to simply run numerical 3D calculations using software (Noorani, 2006). Rather, insight gained from tests on a physical model can result in improvements that would be difficult to achieve if software alone were to be used (Noorani, 2006). This is where rapid prototyping becomes a valuable tool in the design process. After a 3D model has been created, rapid prototyping technology can be used right away to generate a physical model (Noorani, 2006).  As soon as the model has been constructed, it can be tested and the original 3D model can be altered for further improvements (Noorani, 2006). In addition, the software used to analyze the 3D models can be improved to suggest optimizations that it originally missed, but were implemented after testing the prototype (Noorani, 2006).

Overall, the previous real world example illustrates how the speed and versatility of rapid prototyping is the key to its usefulness. In terms of speed, in the case of the intake manifold, the model can be created immediately after a 3D model has been finalized. Whereas the alternative is designing and creating molds just to generate one prototype. In terms of time, effort, and cost rapid prototyping has a clear advantage over older prototyping methods. Next, in terms of generating newer prototypes after changes have been made, rapid prototyping technologies are versatile enough that the technology does not need to be altered to create a slightly or even vastly different model. One just has to change the 3D model and then feed that 3D model to the rapid prototyping device to create the latest prototype. On the other hand, for older methods using molds, the mold used to create the previous prototype is useless for creating a newer prototype that may only be slightly different from its predecessor. This means that for every iteration, a new mold would have to be designed and created. Once again, rapid prototyping proves to be the more convenient option because of the time and cost it saves over a long product design phase.

Video 1

3D Printing-PolyJet-Additive Technologies: A video about 3D printing and its use in creating models and parts. Source: Additive Technologies Channel on YouTube.com.

Application to Senior Project

Currently, the materials used in rapid prototyping technologies to create models are usually some kind of polymer or plastic (Kochan, Kai & Zhaohui, 1999). However, this means that rapid prototyping is not necessarily applicable to the design of every product since plastic cannot be used to create every single component that is designed in the world. For instance, some components such as various car parts must be constructed using metal. Consequently, the future of rapid prototyping lies in adapting the technology to create models and components using metals (Kochan, Kai & Zhaohui, 1999). Such a breakthrough would have tremendous benefits. Not only would it allow for metal prototypes to be created, but it could also potentially open the door for rapid manufacturing. This technology would then allow for the construction of many different components and products using a single type of machine without having to create molds or use machining equipment (Kochan, Kai & Zhaohui, 1999).

To further the use of metal in rapid prototyping, the Infrared Team senior project team has attempted to develop a 3D printer that builds using metal. Their main concept is to use a welder as a “print head” to liquefy metal and deposit it to create simple shapes. The movement of the welder and how much metal it deposits will naturally have to be controlled by some circuitry that can accept and respond to simple movement commands. While the end result will not be anywhere near as sophisticated or as precise as current 3D printing technology that uses plastic, a working prototype that can make basic shapes would still be considered a success. Any sort of working prototype could then be used as a platform to create more advanced metal 3D printers in the future.

Cited References

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