Plastic Prototyping Techniques : 3D Printing Silicon Molding

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Various plastic prototyping techniques are available to manufacture plastic parts quickly. Plastic prototypes are required for Initial product design verification and validation. Prototyping helps in reducing overall product development time and launch products faster in the market. This article covers various plastic prototyping techniques their advantages, applications and limitations.

Factors affecting the Selection of Plastic Prototyping Technique

Following factors affect the selection of best plastic prototyping technique for required application. 

  1. Product Functional and Aesthetic Requirements
  2. Cost Constraints
  3. Lead Time
  4. Required Quantities
Plastic Rapid Prototyping Techniques

Various plastic prototyping techniques are available to manufacture plastic parts quickly. Each process has their own advantage and limitations

    Additive Manufacturing / 3D Printing

    Additive manufacturing / 3D printing is one of the fastest way of plastic prototyping. In 3D printing, plastic prototypes are created by adding successive layers of material. Each of these layers can be seen as a thinly sliced horizontal cross-section of the final part.

    Following 3D printing technologies are available for plastic prototyping. 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)
    ParameterDescription
    Material Options3D printing materials are available in various grades that are similar to commercial grade plastic. Even metals such as 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 prototypes very less compared to cnc machining prototypes. You can get the 3D printed prototypes within hours.
    Part QualityVery good quality prototypes can be manufactured. But manufacturing cost is very high.
    Ideal Quantities1 to 20 Units
    Advantages
    • Metal parts can be also 3D printed.
    • Parts with deep undercuts can be printed.
    • Specialized tooling is not required.
    • Fast turnaround time.
    Limitations
    • Moderate manufacturing Cost and accuracy.
    • Critical features are very difficult to manufacture.
    • Limited Material options.

    CNC Machining

    CNC machining is the best way to create functional functional plastic prototypes. It is a subtractive manufacturing process, where material is removed from solid block by using a variety of precision cutting tools.

    Post processing operations such as buffing, sand blasting, plating, painting or screen printing are required to achieve required part finish on plastic prototypes.

    ParameterDescription
    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. Various validation tests can be performed on CNC machined plastic prototypes.
    Ideal Quantities1 to 20 Units
    Advantages
    • Highly accurate and repeatable.
    • Various material options are available.
    • Customized tooling is not required.
    • Fast turnaround time.
    Limitations
    • High manufacturing Cost.
    • Critical features are added manually

    Vacuum Casting / Silicon Rubber Mold

    Polyurethane vacuum casting is used for manufacturing high quality and low volumes prototypes using silicone molds. Masterpiece (generally 3D printed part) is required to develop Silicone Mould.

    For plastic prototyping, silicone mold is filled with two part polyurethane resin inside vacuum chamber and then processed in a heat chamber at controlled temperature.

    ParameterDescription
    Material OptionsCommercial grade injection molding thermoplastics equivalent materials are available.
    Engineering ToleranceTight tolerance are very difficult to achieve in vacuum casting prototypes. Depending on feature complexity, 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 parts.
    Ideal Quantities10 to 100 Units
    Advantages
    • Low cost
    • Various material options are available.
    • Manufactured parts are closer to injection molded parts.
    • Optically Clear prototypes can also be manufactured.
    • Overmolding and insert molding is also possible.
    Limitations
    • Manufactured part accuracy is not good.
    • Slow Process : Long Lead time

    Rapid Tooling

    Quick turn injection molds is a good choice for moderate prototype quantities. Sometimes they are also known as intermediate tools.

    Following technologies are used for rapid tooling:

    1. 3D Printed Plastic injection molds.
    2. Machined Aluminum injection molds. 
    3. 3D printed metal injection molds.
    ParameterDescription
    Material OptionsAlmost all thermoplastic materials can be used.
    Engineering ToleranceTight tolerances can be achieved using rapid tooling.
    Cost  and Lead timeCompared to silicon molding tool, 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)
    Advantages
    • Low Cost
    • Quick Turnaround time compared to final tools
    • Manufactured prototypes are functionally equivalent to injection molded parts.
    • Over-molding and insert molding is feasible
    Limitations
    • High Tooling Cost.
    • Recommended for moderate quantities.

    Summary

    Properties 3D Printing CNC Machining Vacuum Casting Rapid Tooling
    Tooling Cost NA NA Very Low High
    Unit Part Cost Moderate Very High High Low
    Form and Fit Moderate Good Good (not better than CNC) Excellent
    Functional Moderate Good Good Excellent
    Aesthetics Moderate Good Good Excellent
    Lead Time Low (hours to days) Moderate (3 to 7 days) High (min 7 days) Very high
    Quantities 1 to 50 1 to 10 10 to 100 100 to 2000

    Conclusion

    To sum up, Rapid prototyping is one of the best way to ensure designed product is meeting required expectations. Various prototyping techniques are available. But FDM 3D printing is extensively used. FDM printers starts from $300. Refer summary table for comparison between various technologies. We suggest you to read this article to know the factors affecting injection mold cost.

    Got Questions?  We will be happy to help.

    If you think we missed Something?  You can add to this article by sending message in the comment box. We will do our best to add it in this post.


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