What is Rapid Prototyping?
Rapid prototyping is the fast fabrication of a physical part, model, or assembly using 3D computer-aided design (CAD). The creation of the part, model, or assembly is usually completed using additive manufacturing, more commonly known as 3D printing.
Rapid prototyping is the process of creating something that can be used to quickly evaluate a product. Within engineering, a prototype is an early version of a product. Rapid prototyping allows companies to test and analyze the technology.
When the design closely matches the proposed final product, it is said to be a high-fidelity prototype, as opposed to a low-fidelity prototype where there is a distinct difference between the prototype and the final product.
In other words, rapid prototyping is a test method. You can analyze the future of a product and its success with customers. As a result, the analysis will tell you whether it will work well. Companies use this process in every phase of product development.
Efficiency makes the process cheaper and faster. This allows more room for flexibility and error when creating a product. In the long run, this is more beneficial than other methods.
MORE: What is 3D Printing?
There are three main steps in rapid prototyping. The first is to create the prototype. They do this by developing a solution for the company to test.
The next step is reviewing. Many companies do this by sharing the prototype with their users and stakeholders. This allows them to get feedback so they can fix the product and improve it for their customers.
The last step is refining. Based on the feedback the company receives, they can either repair or change the product. This will also help them improve future designs.
How Does Rapid Prototyping Work?
Rapid Prototyping, also known as 3D printing, is an additive manufacturing technology. The process begins with taking a virtual design from modeling or computer-aided design (CAD) software. The 3D printing machine reads the data from the CAD drawing and lays down successive layers of liquid, powder, or sheet material building up the physical model from a series of cross-sections.
These layers, which correspond to the virtual cross-section from the CAD model, are automatically joined together to create the final shape.
Rapid Prototyping uses a standard data interface, implemented as the STL file format, to translate from the CAD software to the 3D prototyping machine. The STL file approximates the shape of a part or assembly using triangular facets.
Typically, Rapid Prototyping systems can produce 3D models within a few hours. Yet, this can vary widely, depending on the type of machine being used and the size and number of models being produced.
While additive manufacturing is the most common rapid prototyping process, other more conventional methods can be used to create prototypes.
MORE: What is Additive Manufacturing?
These processes include:
- Subtractive – Where carving through a block of material to create the desired shape by milling, grinding or turning.
- Compressive – Being pressed into the desired shape by a semi-solid or liquid material before solidification, for example by casting, compressive sintering or molding.
Different Types of Rapid Prototyping
Types of rapid prototyping techniques:
- Stereolithography (SLA)
- Selective laser sintering (SLS)
- Direct metal laser sintering(DMLS)
- Fused Deposition Modelling (FDM)
- Binder jetting
- Poly jetting
There are dozens of ways prototypes can be made. As prototyping processes continue to evolve, product designers are constantly trying to determine which method or technology is best for their unique application.
1. Stereolithography (SLA) or Vat Photopolymerization
This fast and inexpensive technique was the first successful method of commercial 3D printing. A bath of photosensitive liquid is used which is solidified layer by layer using computer-controlled ultraviolet (UV) light.
SLA is an industrial 3D printing, or additive manufacturing, a process that builds parts in a pool of UV-curable photopolymer resin using a computer-controlled laser. The laser is used to trace out and cure a cross-section of the part design on the surface of the liquid resin.
The solidified layer is then lowered just below the surface of the liquid resin and the process is repeated. Each newly cured layer adheres to the layer below it. This process continues until the part is completed.
Pros: For concept models, cosmetic prototypes, and complex designs, SLA can produce parts with intricate geometries and excellent surface finishes as compared to other additive processes. Cost is competitive and the technology is available from several sources.
Cons: Prototype parts may not be as strong as those made from engineering-grade resins, so the parts made using SLA have limited use for functional testing. Additionally, while parts undergo a UV cycle to solidify the outer surface of the part, built-in SLA should be used with minimal UV and humidity exposure so they don’t degrade.
2. Selective Laser Sintering (SLS)
Used for both metal and plastic prototyping, SLS uses a powder bed to create a prototype layer by layer with a laser to heat and sinter the powdered material. However, the strength of the parts is not as good as SLA, while the surface of the finished product is usually rough and secondary work may be required to complete it.
During the SLS process, a computer-controlled CO2 laser draws onto a hotbed of nylon-based powder from the bottom up, where it lightly sinters (fuses) the powder into a solid. After each layer, a roller lays a fresh layer of powder on top of the bed, and the process repeats.
SLS uses either rigid nylon or elastomeric TPU powders similar to actual engineering thermoplastics, so parts exhibit greater toughness and are accurate, but have a rough surface and lack fine details. SLS offers a large build volume, can produce parts with highly complex geometries, and create durable prototypes.
Pros: SLS parts tend to be more accurate and durable than SLA parts. The process can make durable parts with complex geometries and is suitable for some functional testing.
Cons: The parts have a grainy or sandy texture and the process has a limited resin choice.
3. Direct metal laser sintering(DMLS)
DMLS is an additive manufacturing technology that produces metal prototypes and functional, end-use parts. DMLS uses a laser system that draws onto a surface of atomized metal powder. Where it draws, it welds the powder into a solid.
After each layer, a blade adds a fresh layer of powder and repeats the process. DMLS can use most alloys, allowing prototypes to be full-strength, functional hardware made out of the same material as production components.
It also has the potential, if designed with manufacturability in mind, to transition into metal injection molding when increased production if needed
Pros: DMLS produces strong (typically, 97 percent dense) prototypes from a variety of metals that can be used for functional testing. Since the components are built layer by layer, it is possible to design internal features and passages that could not be cast or otherwise machined. Mechanical properties parts are equal to conventionally formed parts.
Cons: If producing more than a few DMLS parts, costs can rise. Due to the powdered metal origin of the direct metal process, the surface finish of these parts is slightly rough. The process itself is relatively slow and also usually requires expensive post-processing.
4. Fused Deposition Modelling (FDM) or Material Jetting
This inexpensive, easy-to-use process can be found in most non-industrial desktop 3D printers. A spool of thermoplastic filament is used which is melted in a pressure nozzle housing before the resulting liquid plastic is deposited layer by layer according to a computer deposition program.
While the early results generally had poor resolution and were poor, this process improves quickly and is quick and cheap, making it ideal for product development.
FDM uses an extrusion method that melts and re-solidifies thermoplastic resin (ABS, polycarbonate, or ABS/polycarbonate blend) in layers to form a finished prototype. Because it uses real thermoplastic resins, it is stronger than binder jetting and may be of limited use for functional testing.
Pros: FDM parts are moderately priced relatively strong, and can be good for some functional testing. The process can make parts with complex geometries.
Cons: The parts have a poor surface finish, with a pronounced rippled effect. It is also a slower additive process than SLA or SLS and has limited suitability for functional testing.
6. Injection Molding
Rapid injection molding works by injecting thermoplastic resins into a mold, just as in production injection molding. What makes the process “rapid” is the technology used to produce the mold, which is often made from aluminum instead of the traditional steel used in production molds.
Molded parts are strong and have excellent finishes. It is also the industry standard production process for plastic parts, so there are inherent advantages to prototyping in the same process if the situation allows.
Almost any engineering-grade plastic or liquid silicone rubber (LSR) can be used, so the designer is not constrained by the material limitations of the prototyping process.
Pros: Molded parts are made from an array of engineering-grade materials, have an excellent surface finish, and are an excellent predictor of manufacturability during the production phase.
Cons: There is an initial tooling cost associated with rapid injection molding that does not occur with any of the additive processes or with CNC machining. So, in most cases, it makes sense to do one or two rounds of rapid prototypes (subtractive or additive) to check fit and function before moving to injection molding.
7. Binder Jetting
This technique allows one or more parts to be printed at once, although the parts made are not as strong as those made with SLS. Binder jetting uses a powder bed onto which nozzles spray microfine droplets of liquid to bind the powder particles together and form a layer of the part.
Each layer can then be compacted by a roller before the next layer of powder is applied and the process begins again. When the part is complete, it can be cured in an oven to burn off the binder and fuse the powder into an integral part.
8. Polyjet
Polyjet uses a print head to spray layers of photopolymer resin that are cured, one after another, using ultraviolet light. The layers are very thin allowing quality resolution. The material is supported by a gel matrix that is removed after the completion of the part. Elastomeric parts are possible with Polyjet.
Pros: This process is moderately priced, can prototype over-molded parts with flexible and rigid materials, can produce parts in multiple color options, and easily duplicates complex geometries.
Cons: Polyjet parts have limited strength (comparable to SLA) and are not suitable for functional testing. While PolyJet can make parts with complex geometries, it gives no insight into the eventual manufacturability of the design. Also, colors can be yellow when exposed to light over time.
Comparing Prototyping Processes
| PROCESS | DESCRIPTION | STRENGTH | FINISH | EXAMPLE MATERIALS |
| Stereolithography | Laser-cured photopolymer | 2,500-10,000 (psi) 17.2-68.9 (mpa) | Additive layers of 0.002-0.006 in. (0.051-0.152mm) typical | Thermoplastic-like photopolymers |
| Selective Laser Sintering | Laser-sintered powder | 5,300-11,300 (psi) 36.5-77.9 (mpa) | Additive layers of 0.004 in. (0.102mm) typical | Nylon, TPU |
| Direct Metal Laser Sintering | Laser-sintered metal powder | 37,700-190,000 (psi) | Additive layers of 0.0008-0.0012 in. (0.020-0.030mm) typical | Stainless steel, titanium, chrome, aluminum, Inconel |
| Fused Deposition Modeling | Fused extrusions | 5,200-9,800 (psi) 35.9-67.6 (mpa) | Additive layers of 0.005-0.013 in. (0.127-0.330mm) typical | ABS, PC, PC/ABS, PPSU |
| Multi Jet Fusion | Inkjet array selectively fusing across a bed of nylon powder | 6,960 (psi) 48 (mpa) | Additive layers of 0.0035-0.008 in. (0.089-0.203mm) typical | Black Nylon 12 |
| PolyJet | UV-cured jetted photopolymer | 7,200-8,750 (psi) 49.6-60.3 (mpa) | Additive layers of 0.0006-0.0012 in. (0.015-0.030mm) typical | Acrylic-based photopolymers, elastomeric photopolymers |
| Computer Numerically Controlled Machining | Machined using CNC mills and lathes | 3,000-20,000 (psi) 20.7-137.9 (mpa) | Subtractive machined (smooth) | Most commodity and engineering-grade thermoplastics and metals |
| Injection Molding | Injection-molded using aluminum tooling | 3,100-20,000 (psi) 21.4-137.9 (mpa) | Molded smooth (or with selected texture) | Most commodity and engineering-grade thermoplastics, metal, and liquid silicone rubber |
Why is rapid prototyping important?
In this fast-paced modern consumer market, companies need to develop and launch new products faster to stay competitive. Since faster product development and technological innovation are the keys to a company’s success, rapid prototyping becomes the most important element in new product development. The following goals are achieved through rapid prototyping.
- Faster new product development- Prototyping plays a vital role in the process of creating successful products because it speeds up the new product development process
- Early stage design/concept validation of form, fit, and function of the design
- Final stage product verification against the technical requirement and business objectives
- It allows functionality testing to test the objectives of the concept and to finalise the specification
- Prototype gives the end user, client, customer, user participants hands-on user experience to get feedback
Applications
Product designers use this process for the rapid manufacturing of representative prototype parts. This can aid in the visualization, design, and development of the manufacturing process before mass production.
Originally, rapid prototyping was used to create parts and scale models for the automotive industry, although it has since been adopted by a wide variety of applications in various industries such as medical and aerospace.
Rapid Tooling is another application of RP where part from an injection molded plug or an ultrasonic sensor wedge is made and used as a tool in another process.
Advantages of rapid prototyping
- Reduced design & development time
- Reduced overall product development cost
- Elimination or reduction of risk
- Allows functionality testing
- Improved and increased user involvement
- Ability to evaluate human factors and ergonomics
Disadvantages of rapid prototyping
- Lack of accuracy
- Added initial costs
- Some rapid prototyping processes are still expensive and not economical
- Material properties like surface finish and strength cannot be matched
- Requires skilled labor
- The range of materials that can be used is limited
- Overlooking some key features because they cannot be prototyped
- End-user confusion, customers mistaking it for the finished project/developer misunderstanding of user objectives