Rapid Prototyping For Plastic Parts : Advantages Limitation and Selection

Rapid prototyping for plastic parts is used to develop plastic parts quickly for Initial design verification and validation. Waiting for injection molded parts to verify part functional and aesthetic design can delay product design and can cause high tool modification costs. Therefore it is always recommended to rapid prototype plastic parts before manufacturing final tooling. In this article we will discuss various plastic rapid prototyping techniques, their advantages, applications and limitations.

Advantages of Rapid Prototyping Plastic Parts

Rapid Prototyping plastic parts before final production has following advantages:

  • Verification of product aesthetics and function before final tooling.
  • Reduces overall product development time and cost.
  • Early user feedback.
  • Tool modification costs are reduced.
  • Products are launched faster in the market.
Disadvantages of Rapid Prototyping

Along with so many advantages rapid prototyping has following limitations as well.

  • Can not rely 100% on test results done on rapid prototype parts.
  • Low Accuracy.
  • Design features such as Plastic snap or fits can not be simulated.
  • Good quality prototypes such as cnc machining cost is very high.
  • Limited material options are available.
  • Structural strength of prototype parts is not similar to injection molded parts.

Selection of Best Rapid Prototyping Process For Plastics

Various plastic prototyping techniques available in the market have its own advantages and limitations. Here are the points you should consider before the selection of the plastic prototyping process.

  1. Product Functional and Aesthetic Requirements
  2. Prototyping Cost
  3. Lead Time
  4. Number of Prototypes Required

Plastic Rapid Prototyping Techniques

Following plastic prototyping methods are widely used to manufacture plastic parts quickly. Each process has its own advantages and limitations.

  1. Additive Manufacturing.
  2. CNC Machined Plastic Parts.
  3. Vacuum Casting
  4. Rapid Injection Mold Tooling.
Properties3D PrintingCNC MachiningVacuum CastingRapid Tooling
Tooling CostNot ApplicableVery LowHigh
Unit Part CostModerateVery HighHighLow
Form and FitGoodGood (not better than CNC)Excellent
Lead TimeLow (hours to days)Moderate (3 to 7 days)High (min 7 days)Very high
Quantities1 to 501 to 1010 to 100100 to 2000
1. Additive Manufacturing (3D Printing)

Additive manufacturing or 3D printing is one of the fastest methods to manufacture plastic prototypes quickly. In 3D printing, plastic prototypes are manufactured by adding successive layers of material. Each of these layers can be seen as a thinly sliced horizontal cross-section of the final part. Click this link!! to know the best available 3D printers.

Following 3D printing technologies are widely used for prototyping plastic parts. Each technique has their own strengths and weaknesses.

  1. FDM (Fused Deposition Modelling)
  2. SLA (Stereolithographiy)
  3. DLP (Digital Light Processing)
  4. (SLS) Selective Laser Sintering 
  5. Material Jetting (PolyJet and MultiJet Printing)
  6. Metal Printing (Selective Laser Melting and Electron Beam Melting)
Advantages of Plastic Prototyping using 3D Printing

Following are the advantages of manufacturing rapid prototypes using 3D Printing: 

  • Various metals can also be 3D printed by utilizing metal 3D printing technologies.
  • Parts with deep undercuts can be 3D printed.
  • Specialized tooling is not required.
  • Fast turnaround time.
Disadvantages of Plastic Prototyping using 3D Printing

Following are the disadvantages of manufacturing rapid prototypes using additive manufacturing.

  • Moderate manufacturing cost and accuracy.
  • Critical features are very difficult to manufacture.
  • Limited Material options.
  • Aesthetics are not good.
Key Features for Prototyping Plastic Parts using 3D Printing
Material Options3D printing materials are also available in commercial grade plastic. Using metal 3D Printing even metals like aluminum can also be 3D printed.
Engineering ToleranceDepending on 3D printer, part geometry and material. Tolerance in the range of 50 to 150 microns can be achieved.
Cost and Lead timeCost and lead time for 3D printed plastic prototypes very less compared to cnc machining prototypes.
Part QualityGood Surface finish and strength can be achieved in 3D printed plastic prototypes.
Ideal Quantities1 to 20 Units
2. CNC Machined Plastic Prototypes

CNC machining is a subtractive method to manufacture Rapid plastic prototypes. During CNC machining, material is removed from the solid block by using precision cutting tools. Post processing operations such as buffing, sand blasting, plating, painting or screen printing are required to achieve required part finish on CNC machined plastic prototypes.

CNC Machining
Advantages of Prototyping Plastic Parts using CNC Machining

Here are the advantages of rapid prototyping using CNC machining.

  • Highly accurate and repeatable.
  • Various material options are available.
  • Customized tooling is not required.
  • Fast turnaround time.
  • Various functional testing can be done on rapid plastic prototypes.
  • Very good aesthetic finish similar to molded parts can be achieved using powder coating.
Disadvantages of plastic part Prototyping using CNC Machining

Following are the limitations of rapid prototyping using CNC machining

  • Not a good choice for large numbers because of high manufacturing costs.
  • Critical features are added manually.
  • Over molding or Insert molding is not feasible.
Key Features of Plastic Prototyping using CNC Machining
Material OptionsABS, PC, ABS+PC, HDPE, Nylon and Hard PVC etc. solid blocks are available for plastic part prototyping.
Engineering ToleranceGeneral tolerances " ISO-2768 m" is applicable for cnc machined plastic prototypes.
Cost  and Lead timeManufacturing cost is very high. Therefore they are recommended for small quantities.
Part QualityCNC machined prototypes are functional and identical to injection molded parts. Validation tests can be done on CNC machined plastic prototypes.
Ideal Quantities1 to 20 Units
3. Vacuum Casting / Silicone Rubber Mold

Polyurethane vacuum casting is used for manufacturing good quality and low volume prototypes using silicone molds. Masterpiece (generally 3D printed part) is required to develop the silicone mold. For vacuum casting, silicone mold is filled with two part polyurethane resin inside the vacuum chamber and then processed in a heat chamber at controlled temperature.

Advantages of Manufacturing Plastic Parts using Silicon Molding

Following are the advantages of rapid prototyping plastic parts using Silicone molding.

  • Low unit part manufacturing cost.
  • Various material options are available.
  • Manufactured parts are closer to injection molded parts.
  • Optically Clear prototypes can also be manufactured.
  • Over molding and insert molding of plastic parts is also possible.
Limitations of Manufacturing Plastic Parts using Silicon Molding

Following are the limitations of rapid prototyping plastic parts using vacuum casting.

  • Manufactured part accuracy is not good.
  • Slow Process : Long Lead time.
Vacuum Casting Features
Material OptionsCommercial grade injection molding thermoplastics equivalent materials are available.
Engineering ToleranceTight tolerance are very difficult to achieve in vacuum casting plastic prototypes. Depending on part feature, tolerance in the range of 100 to 150 microns can be achieved.
Cost and Lead timeSilicon molding is more economical if manufactured in the multiples of 10 to 15.
Part QualitySilicon molded plastic prototypes are functionally and aesthetically more close to injection molded plastic parts.
Ideal Quantities10 to 100 Units
4. Rapid Tooling For Plastic Parts

Quick turn injection molds is a good choice for moderate prototype quantities. Sometimes they are also known as intermediate tools. Following technologies are used to manufacture a rapid tool.

  1. 3D Printed Plastic injection molds.
  2. Machined Aluminum injection molds. 
  3. 3D printed metal injection molds.
Advantages of Manufacturing Plastic Prototypes using Rapid Tooling

Following are the advantages of rapid prototyping plastic parts using rapid tooling.

  • Low Part Manufacturing Cost.
  • Quick Turnaround time compared to final tooling.
  • Manufactured prototypes are functionally equivalent to injection molded parts.
  • Over-molding and insert molding is feasible.
Limitations of Manufacturing Plastic Prototypes using Rapid Tooling

Following are the limitations of rapid prototyping plastic parts using rapid tooling.

  • High lead time compared to 3D printing and cnc machining.
  • High Tooling Cost.
  • Recommended for moderate quantities only.
Features of Rapid Plastic Tooling
Material OptionsMost of thermoplastic materials can be injection molded.
Engineering ToleranceTight tolerances can be achieved using rapid tooling.
Cost and Lead timeCompared to silicone molding, initial Investment cost for rapid tools is very high. Rapid tooling lead time is approximate 2 to 3 weeks.
Part QualityRapid tooling prototypes are identical to injection molded parts. The only difference between rapid tool and final tool is the material used for tooling.
Ideal Quantities100 to 5000 Units (Depends on Material Used)

We will keep adding more information on various plastic prototyping techniques. Please add your suggestions, comments or questions on rapid plastic prototyping techniques in the comment box.

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