Prototyping 101

17 October 2007

As product development is not an exact science, every contingency cannot be foreseen and therefore prototyping is a crucial part of developing any new product.
Prototyping both develops as well as validates ideas before products go into production and much larger investment is incurred.
Reasons and types of prototypes can vary depending on each product and project. They can range from form studies that show the styling of a design all the way to near production-ready, mechanically accurate parts suitable for regulatory compliance. Therefore it is essential that the correct prototype process is chosen to ensure the best end result.
We have compiled a ‘Prototyping 101 - Key Stats’ summary of some of the most common rapid prototyping techniques to help demystify this process (at least a little) for the un-initiated.

Common Starting Point
A common feature to most modern prototyping techniques is the use of 3D virtual models as the starting point for a prototype to be constructed.  These models are real as far as a computer is concerned and are created using specialised CAD (computer aided design) software. Rapid prototyping (as the processes are collectively known) is also sometimes called 3D printing in that the concept is the same; printing a physical ‘document’ that previously only existed within a computer file.  In spite of claims by CAD retailers, these processes put the power of the design firmly in the hands (and talents) of the designer or design engineer whose ideas are exactly re-created with no room for interpretation or error.  Compared to now ‘traditional’ techniques, today’s prototypes are also incredible accurate as well fast and inexpensive to make.

 

Prototyping 101 - Key Stats
What is it? Stereolithography (SLA)

SLA
How does it work? A computer controlled laser beam is fired into liquid epoxy resin causing the liquid to form a solid. The laser creates a thin slice of the CAD modelled part. Each new pass of the laser building the on top of the last layer to build up the overall part geometry. The part is then placed into a UV oven to fully cure and harden prior to finishing and use.
What are the parts made from? There are a range of epoxy resins to choose from. Materials are available in both translucent/clear and opaque/white versions. There is also a range of mechanical properties available which allow materials to roughly mimic a range of production plastics.  
Advantages
  • Suited for styling/aesthetic applications due to :
    • Higher resolution of fine detail
    • Ability to be finished to a very high level suitable for polishing and painting
  • Excellent dimensional accuracy
  • Some materials are roughly representative of production plastics and allow evaluation of flex and part rigidity
  • Fast turnaround times
  • Also good for use as master parts for other processes such as cast PU
Disadvantages
  • Not as suited to mechanical applications as material can be brittle
  • Lower mechanical strength compared to other processes
  • Materials are sensitive to exposure to heat and water
What else could i use? 3D Printing, CNC Machining

What is it? 3D Printing

3d Printing
How does it work? Similar to your standard inkjet printer; a print head deposits material creating a thin slice of the part with each pass, building the geometry similarly to the SLA process
What are the parts made from?
  • Plaster based materials
  • A range of photopolymers are available in both translucent, opaque and colours, with properties that mimic a limited range of production plastics including soft rubber.
Advantages
  • Quick turn around times
    Plaster variants can have dyes added during printing to create multicoloured parts.
    Excellent dimensional accuracy possible
  • Able to achieve high level of finish for aesthetic review.
Disadvantages
  • Not as suited to mechanical applications as material can be brittle and has low mechanical strength
  • Materials are sensitive to exposure to heat and water
What else could i use? SLS, SLA, CNC Machining
What is it? Selective Laser Sintering (SLS)

SLS
How does it work? Again similar to SLA, but instead of using a liquid base, the SLS process uses fine, dry nylon powder with the laser melting (sintering) layers together to build the part geometry
What are the parts made from?
  • Rigid nylon
  • Rigid Glass filled nylon
  • Metal and green sand are also possible (but much less common)
Advantages

Excellent for mechanical evaluation (especially if the parts are to be nylon or a similar engineering plastic in production) due to :

  • Very good impact strength
    Ability to replicate snap fits and mechanical moulding geometries
    Heat resistant
  • Good mechanical strength
Disadvantages

Not as suited to styling/aesthetic applications due to:

  • Lower level surface finish (especially in glass filled versions)
    Material difficult to hand finish to level suitable for painting
  • Lower resolution of fine details
What else could i use? CNC Machining, FDM (Fused deposition modeling)
What is it? CNC Machining

CNC
How does it work? A computer controlled mill machines parts directly from CAD data in a wide variety of machineable materials
What are the parts made from?
  • Range of cast/extruded production plastics and metals
    PU and chemical wood
  • Polystyrene foam
Advantages
  • Ability to create parts in similar material (if not same) as production allowing very accurate evaluation of mechanical properties
    High precision and excellent dimensional accuracy possible
  • Ability to achieve high level of finish for aesthetic review
Disadvantages
  • Often more expensive to other techniques due to higher manual processes
    Can have longer lead times
  • Some limitations to possible geometries due to machining process
What else could i use? SLS, SLA, 3D Printing
What is it?

Cast PU (Polyurethane)
Also known as Vacuum cast parts, silicon moulded parts

PU
How does it work?

This is somewhat different to the other (rapid prototyping) processes, in that cast PU parts allows parts already prototyped to be replicated in limited numbers without production tooling.

Flexible silicone tools are cast from master models created via other processes. Liquid PU is injected into the tools (usually in a vacuum chamber) to create replicas of the original part.
What are the parts made from?

There are a range of versions of the PU materials that can replicate production materials from glass filled nylon through to soft rubbers.

Material can also be coloured to match production colours
Advantages

Ability to easily create multiple sets of parts, usually up to 15-20 parts per cavity.
Especially good for pre-production evaluation and testing, as parts are difficult to discern from production units
Ability to create parts which closely mimic production materials allowing a very accurate mechanical evaluation.
Over moulding process are also able to be replicated
Able to achieve high level of finish for aesthetic review.

Provides multiple parts much quicker lead times than production tooling
Disadvantages Has higher set up costs which usually mean the technique is not economical if less than 3-5 replica parts are required.
What else could i use? SLS, SLA, 3D Printing, CNC Machining

In addition to these processes there are a range of more specialised techniques, and follow-on processes that can be used. If you would like more information regarding specific prototyping processes to suit your projects please contact CobaltNiche.

Photos courtesy of ARRK Australia
prototyping