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Introduction to rapid prototyping

Selecting the optimal shell and infill parameters for FDM 3D Printing

What is rapid prototyping?

Rapid prototyping uses 3D computer aided design (CAD) and manufacturing processes (typically additive manufacturing) to quickly develop 3D parts, models, or assemblies for research and development and/or product testing.

The use of rapid prototyping techniques allows design teams to develop multiple iterations of a design prototype without the added cost and time using traditional manufacturing and design techniques.

The parts of a speaker prototype, printed with FDM.

Different types of rapid prototyping

The fidelity of a prototype – or how closely the prototype matches the final product – varies for each project on a spectrum from lower fidelity to higher fidelity.

Lower fidelity

Prototype does not closely match the final product. The prototype may be used to test overall fit or function without optimizing the design for weight, manufacturability, or finish. The prototype may also be used to test the design only in key areas of concern to the design team, or to create a scaled down version of the final product.

Higher fidelity

Prototype closely matches the final product including geometry and material properties.

For a single prototype iteration, different attributes of the prototype such as geometry, material properties, fit-up, and finish may be considered at different levels of fidelity. This will impact the overall fidelity of the prototype.

The level of fidelity appropriate for a given design iteration will depend on overall project goals, the maturity of the design, and areas of interest for the design team. Determining the appropriate level of fidelity in rapid prototyping can save time in the design process and optimize design team resource allocation.

Common prototyping processes

Here is a high-level summary of common additive manufacturing techniques typically used in rapid prototyping processes.

In general, rapid prototyping typically uses additive manufacturing to create test parts, models or assemblies. However, other more conventional manufacturing processes such as milling, grinding, or casting may be used depending on the resources available and needs of the design team.

Common prototyping processes can be divided into six groups:


More information for each process is included below. For a general overview of these rapid prototyping processes, check out this article covering additive manufacturing technologies.

Vat photopolymerization

A solid part is created one layer at a time using light to convert a photopolymer resin to a solid.

  • Stereolithography (SLA) – SLA can produce parts with very high dimensional accuracy and intricate details but parts are generally brittle and mechanical properties may degrade over time – parts are typically not suitable for functional prototypes. This process is best suited for rapid prototyping of design geometry and proof of concept of part interfaces or details at the early stages of design and when mechanical properties are not the primary design focus.


  • DLP is similar to SLA and the main difference is level of detail and material properties. Parts produced using DLP will not have the same intricate details compared to SLA but will have similar dimensional accuracy and the part strength is considered equal to or greater than traditional injection molded parts. Therefore, DLP is best suited for rapid prototyping of design geometry and proof of concept when overall geometry and not specific details are the design focus or when mechanical properties are a design priority.


  • Continuous DLP (CDLP) – As with DLP, parts produced using CDLP will not have the same intricate details compared to SLA but will have similar dimensional accuracy and the part strength is considered equal to or greater than traditional injection molded parts. Therefore, CDLP is best suited for rapid prototyping of design geometry and proof of concept when overall geometry and not specific details are the design focus or when mechanical properties are a design priority.

Powder bed fusion

PBF technologies produce a solid part using a thermal source that induces fusion (sintering or melting) between the particles of a plastic or metal powder one layer at a time. The main variations in PBF processes come from the differing energy sources (for example lasers or electron beams) and the powders used in the process (plastics or metals).

Introduction to SLS 3D Printing
  • Selective Laser Sintering (SLS) – The materials used in SLS are thermoplastic polymers that come in a granular form. Since SLS parts are printed using many layers, small variations can occur between parts, therefore, SLS may be at a disadvantage for prototypes with intricate details or small tolerances. A smooth surface finish is also possible when post-processing is used. SLS is best suited for rapid prototyping when part geometry or overall fit and function are a design priority. SLS may also be advantageous for marketing or proof of concept prototypes if post-processing is feasible.


  • Selective Laser Melting (SLM) and Direct Metal Laser Sintering (DMLS) - SLM and DMLS processes can be used for a wide variety of metal materials and typically require post-processing for surface finish. Therefore, these processes are best suited for rapid prototyping when material properties are a design priority and can be cost effective when part finish is not a concern.


  • Electron Beam Melting (EBM) – As with SLM and DMLS, EBM is best suited for rapid prototyping when material properties are a design priority and can be cost effective when part finish is not a concern. The main difference is that EBM has limited material applications (titanium or chromium-cobalt alloys) but may be the most appropriate option for specialty industries that require these materials such as the aviation or medical industries.


  • Multi Jet Fusion (MJF) – MJF is very similar to SLS processes but with shorter cooling and post-processing times and greater accuracy and detailing. A more in-depth comparison of SLS and MJF processes can be found here. As with SLS, MJF is best suited for rapid prototyping when part geometry or overall fit and function are a design priority and can also be used to support higher level of details or tighter tolerances compared to SLS.

Material extrusion

Material extrusion technologies extrude a material through a nozzle and onto a build plate.

  • Fused Deposition Modeling (FDM) – FDM is a very versatile process for a wide range of thermoplastic materials with a short lead-time for production. One downside is that dimensional accuracy and resolution is lower compared to other additive manufacturing processes. FDM is best suited earlier in the prototyping phase when part geometry or overall fit and function are a design priority or when the material of the final part will be similar to the prototype but intricate details are not a concern such as functional or reliability testing.

Jetting

Jetting uses UV light or elevated temperatures to cure or harden materials such as photopolymers, metals, or wax and can be used for multi-material printing.

  • Material jetting – Material Jetting is considered one of the most accurate 3D printing technologies and can be used with a wide array of materials with varying colors and finishes. However, material properties are not suited for functional prototypes. Material Jetting can best be used for rapid prototyping when part geometry or fit is a design priority and part strength is not required or when material properties are not a concern such as proof of concept or marketing prototypes.


  • Nanoparticle Jetting (NJP) – The NJP process deposits a liquid, which contains metal nanoparticles or support nanoparticles onto the build tray in extremely thin layers of droplets. The build envelope is exposed to high temperatures which cause the liquid to evaporate leaving behind the metal part structure.


  • Drop-On-Demand (DOD) – DOD material jetting printers have two print jets: one to deposit the build materials (typically a wax-like liquid) and another for dissolvable support material. DOD printers deposit material in a pointwise path and employ a fly-cutter that trims the build area after each layer to prepare the surface for the next layer.

Binder Jetting

Part made withBinder Jetting have a high finish and form but are brittle. Binder Jetting is best suited for rapid prototyping when overall fit or part geometry are a design priority and material properties are not a concern such as proof of concept or marketing prototypes.

Advantages and disadvantages of rapid prototyping

Rapid prototyping uses modern manufacturing techniques to improve the design process – including overall cost and schedule – compared to traditional manufacturing and design techniques. But there are pitfalls to avoid when considering rapid prototyping – overuse, misuse, and misrepresentation.

Here’s an overview of the advantages and disadvantages below.

Advantages of rapid prototyping

Earlier 3D visualization and testing

Rapid prototyping allows for 3D visualization and testing earlier in the design process – which enhances functional design processes as well as marketing/investment activities.

More design iterations at a lower cost

Design team innovation and creativity may also be enhanced because rapid prototyping allows for increased design iterations without the negative impacts to overall cost or schedule that would apply with traditional manufacturing techniques. Multiple design alternatives can also be developed and compared early in the design process.

Cost effective tool for product design and R&D

Rapid prototyping offers a cost-effective tool to facilitate product design and research and development. By adjusting the prototype fidelity, rapid prototyping can be used by the design team to evaluate overall product functionality or focus on key areas of interest and design attributes in an efficient and cost-effective manner.

Disadvantages of rapid prototyping

Overuse may not have a positive impact on cost and time savings

While rapid prototyping can reduce cost and schedule, not every part requires rapid prototyping and an updated prototype may not need to be created after every design iteration. If rapid prototyping is overused then any cost and schedule savings of using this design tool may not be realized for the project as a whole.

Not beneficial to all stages of the prototyping process

Also, rapid prototyping is one tool in the designer’s “toolbox”; prototyping should be done at the correct time and for the correct reasons to support the overall design process. The fidelity of the prototype and maturity of the design should be kept in mind when evaluating a part, model, or assembly created using rapid prototyping techniques. It should be clearly understood by all parties involved what is being represented by the prototype and more importantly what is not (e.g., geometry, fit, material properties).

Applications in commercial industry

The applications of rapid prototyping for 3D design and manufacturing are limited only by the creativity of the designer and can be used throughout all stages of the design and manufacturing process. We’ve highlighted the most popular use cases below.



Proof of Concept (PoC)

One common application is proof of concept – 3D prototypes can be produced quickly and earlier in the design process to evaluate product viability, facilitate design team discussions, generate interest from key stakeholders such as marketing and investment, or compare different design alternatives. The primary advantage that rapid prototyping processes provide for proof of concept applications is reduced cost and schedule for 3D prototypes.



Design optimization

Rapid prototyping is also a cost-effective tool to accelerate design optimization, including product design and research and development. The design team can evaluate overall product functionality or focus on key attributes (e.g., geometry, fit, material properties, manufacturability) earlier in the design process without the costs associated with traditional manufacturing processes.



High fidelity prototypes

In addition, due to the versatility of additive manufacturing processes and materials, rapid prototyping can be used to create high fidelity prototypes that closely match the final product to demonstrate product functionality or perform reliability testing often at a lower cost or faster timeline compared to traditional manufacturing processes.