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What is Rapid Prototyping? - Definition, Methods and Advantages

   

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, or more commonly known as 3D printing.

Rapid prototyping using selective laser meltingWhere the design closely matches the proposed finished product it is said to be a high fidelity prototype, as opposed to a low fidelity prototype, where there is a marked difference between the prototype and the final product.

How Does Rapid Prototyping Work?

Rapid prototyping (RP) includes a variety of manufacturing technologies, although most utilise layered additive manufacturing. However, other technologies used for RP include high-speed machining, casting, moulding and extruding.

While additive manufacturing is the most common RP process, other more conventional processes can also be used to create prototypes.

These processes include:

  • Subtractive - whereby a block of material is carved to produce the desired shape using milling, grinding or turning.
  • Compressive - whereby a semi-solid or liquid material is forced into the desired shape before being solidified, such as with casting, compressive sintering or moulding.

What are the Different Types of Rapid Prototyping?

Stereolithography (SLA) or Vat Photopolymerization

This fast and affordable technique was the first successful method of commercial 3D printing. It uses a bath of photosensitive liquid which is solidified layer-by-layer using a computer-controlled ultra violet (UV) light.

Selective Laser Sintering (SLS)

Used for both metal and plastic prototyping, SLS uses a powder bed to build a prototype one layer at a time using a laser to heat and sinter the powdered material. However, the strength of the parts is not as good as with SLA, while the surface of the finished product is usually rough and may require secondary work to finish it.

Fused Deposition Modelling (FDM) or Material Jetting

This inexpensive, easy-to-use process can be found in most non-industrial desktop 3D printers. It uses a spool of thermoplastic filament which is melted inside a printing nozzle barrel before the resulting liquid plastic is laid down layer-by-layer according to a computer deposition program. While the early results generally had poor resolution and were weak, this process is improving rapidly and is fast and cheap, making it ideal for product development.

Selective Laser Melting (SLM) or Powder Bed Fusion

Often known as powder bed fusion, this process is favoured for making high-strength, complex parts. Selective Laser Melting is frequently used by the aerospace, automotive, defence and medical industries. This powder bed based fusion process uses a fine metal powder which is melted in a layer by layer manner to build either prototype or production parts using a high-powered laser or electron beam. Common SLM materials used in RP include titanium, aluminium, stainless steel and cobalt chrome alloys.

Laminated Object Manufacturing (LOM) or Sheet Lamination

This inexpensive process is less sophisticated than SLM or SLS, but it does not require specially controlled conditions. LOM builds up a series of thin laminates that have been accurately cut with laser beams or another cutting device to create the CAD pattern design. Each layer is delivered and bonded on top of the previous one until the part is complete.

Digital Light Processing (DLP)

Similar to SLA, this technique also uses the polymerisation of resins which are cured using a more conventional light source than with SLA. While faster and cheaper than SLA, DLP often requires the use of support structures and post-build curing.

An alternative version of this is Continuous Liquid Interface Production (CLIP), whereby the part is continuously pulled from a vat, without the use of layers. As the part is pulled from the vat it crosses a light barrier that alters its configuration to create the desired cross-sectional pattern on the plastic.

Binder Jetting

This technique allows for one or many parts to be printed at one time, although the parts produced are not as strong as those created using SLS. Binder Jetting uses a powder bed onto which nozzles spray micro-fine droplets of a liquid to bond the powder particles together to form a layer of the part.

Each layer may then compacted by a roller before the next layer of powder is laid down and the process begins again. When complete the part may be cured in an oven to burn off the binding agent and fuse the powder into a coherent part.

Applications

Product designers use this process for rapid manufacturing of representative prototype parts. This can aid visualisation, design and development of the manufacturing process ahead of mass production.

Originally, rapid prototyping was used to create parts and scale models for the automotive industry although it has since been taken up by a wide range of applications, across multiple industries such as medical and aerospace.

Rapid tooling is another application of RP, whereby a part, such as an injection mould plug or ultrasound sensor wedge, is made and used as a tool in another process.

What are the Advantages?

There are a number of rapid prototyping advantages, such as being able to gain a more complete picture of how a product will look or perform in the early stage of the design and manufacturing cycle, allowing changes or improvements to be implemented earlier in the process. The time this takes can vary from a few days to a number of months, depending on the methods used.

RP is a very cost effective way to prototype products as it is an automated process, requiring less staff to operate. This process is also extremely precise, being able to use computer aided design (CAD) to help reduce the amount of material wastage and does not require special tools for prototyping each new product. Being able to act quickly and solve ay problems also reduces the risk of costly errors during the manufacturing stage.

Rapid Prototyping helps designers present new concepts to board members, clients or investors so that they can understand and approve a development or product. This visualisation can also allows designers to gain ready feedback from customers and clients based on an actual physical product rather than a concept. 

As rapid prototyping is an iterative process it allows customer requirements to be incorporated into designs cost-effectively. The process cuts out the need for customised products to be designed from scratch while providing greater choice and flexibility for customers.

 

How Much Does it Cost?

The cost depends on a number of factors, including volume or size of the part or parts being created, the surface finish, the materials used and how much post manufacture processing is required.

Rapid Prototyping Services

TWI has world leading experience and expertise in 3D printing technologies / additive manufacturing processes. We can also assist with rapid prototyping technology and manufacturing process development.

For more information please email:


contactus@twi.co.uk