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Proof-of-Principle Prototypes

Proof-of-Principle (PoP) Prototypes are a cornerstone of engineering design. PoP, also referred to as Proof-of-Concept, prototyping is an effective way to rapidly take ideas from intangible designs to tangible, working models. Developing these prototypes enables you as an inventor or designer to demonstrate the fundamental technology used in your product to be fabricated. They also allow you to test your solution to ensure that it functions as you intended or envisioned. Being able to create fabricate prototypes from a CAD model gives product developers a competitive edge by reducing design iteration times and associated costs. This article from ASTCAD describes methods, advantages, and disadvantages of the most essential rapid prototyping processes that are used in the industry by product design engineers to meet development milestones. Taking your design from a CAD model to a proof-of-principle prototype will accelerate your design and allow you to bring new products to market more efficiently. Using the right process, your CAD model can quickly be transformed into a working prototype.

PoP Prototype Advantages

Advantages of PoP Prototyping include:

  • Reduces product development time.
  • Reduces product development costs.
  • Makes design flaws apparent.
  • Provides a demonstration tool for obtaining user feedback.
  • Results in higher quality end products.
  • Makes potential future system enhancements apparent to engineers and inventors.

PoP Prototype Disadvantages

Disadvantages of PoP Prototyping include:

  • May not include all of the features of a more complex complete system.
  • Cannot be used in place of rigorous system analysis.
  • May not be representative of the full functionality of the end product.
  • Can lead to over-confidence in solution.

Proof-of-Principle Prototyping Methods and Processes

There are several ways to prototype your design. Typically referred to as Rapid Prototyping, these methods provide an initial fabrication of your design. The processes used to create these prototypes include Additive Processes, where the part is built in subsequent layers, Subtractive, where the material is removed to create the final product, Injection Molding, where thermoplastics are injected into negative moulds, and Casting, which uses urethanes thermoset resins.

  • Additive Processes build plastic parts layer by layer directly from a 3D CAD model. Recently, 3D printers have been developed for most additive processes and have gained tremendous acclaim.
  • Stereolithography (SLA) uses lasers to cure thin layers of liquid UV-sensitive photopolymer. SLA is cost-effective, can be used to produce intricate parts, and has the look and feel of a finished product after sanding. However, it tends to produce parts that are relatively weak and have little UV stability as a result of the UV curing process.
  • Fused Deposition Modeling (FDM) is similar to SLA but uses the addition of layers of extruded thermoplastic to create the part. This method provides complex parts that are structurally sound and can be used for limited mechanical and functional testing. However, the surface finish is typically poor compared to other methods.
  • Selective Laser Sintering (SLS) creates parts by adhering layers of polymer powder that is cured using a laser. SLS prototypes can be made with more complexity than parts made with SLA. However, the parts tend to have a rough texture and have poor mechanical properties.
  • Direct Metal Laser Sintering (DMLS) uses laser-generated heat to sinter thin layers of metal powders, including steel, stainless steel, cobalt-chromium, and titanium, to generate prototypes. DMLS parts provide highly realistic parts but are less cost-effective than their plastic counterparts, which often leads designers to either produce cheaper plastic prototypes or have the product fully machined.
  • The Polyjet process utilizes jetting heads and UV curing bulbs to apply consecutive layers of material in multiple colours and durometer in a single build. This method provides a representation of multi-material parts with excellent surface finish quality. However, mechanical properties are lacking using the Polyjet process.
  • Subtractive Processes begin with raw material and machine away excess volume to produce a final part.
  • CNC Machining (CNC) is the most common example. Using CNC machining, a part can be produced from almost any variety of material, including both plastics and metal. The advantages of CNC machined parts are that they are highly accurate, can be made with the mechanical properties of the final product, and can have a highly polished and professional finish. Limitations include less complex geometries due to the nature of the tooling and significantly higher costs.
  • Injection Molding is a very popular prototyping process that cures thermoplastics into a mould that is machined from soft metal. The process is highly cost and time effective and is one of the only methods that are representative of volume production fabrication. A wide range of resins with different properties is available for this method, allowing the parts to match the properties of the final product. The final cost per unit is typically very inexpensive, even after factoring in the cost of the mould, but the initial non-recurring engineering cost of the mould requires a significant up-front investment.
  • Casting is in some ways similar to injection moulding but uses a master model that has been fabricated using another method, such as SLA, to create a silicone rubber mould. Liquid urethane thermoset resin is then used to generate the prototype. The urethane can be made to match almost any colour or texture. These parts are highly cost-effective but have limited use in functional testing.

Whatever your proof-of-principle prototype needs might be, there is a suitable rapid prototype method that exists that requires only a CAD model and material/finish selection. It is always important to consider the method, time to fabricate, cost of the prototype part, and the manufacturer, as the quality of a part varies rapidly between one fabricator and the next.

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