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Rapid Prototyping Techniques for Plastic Parts

Rapid prototyping are various techniques to manufacture parts quickly. Initial verification and validation testing can be done on prototype samples.  Therefore product development time is reduced. This article covers various rapid prototyping techniques for plastic parts.

Factors affecting the Selection of Plastic Prototyping Technique
  1. Product Functional and Aesthetic Requirements
  2. Cost Limitations
  3. Lead Time
  4. Required Volumes
Plastic Rapid Prototyping Techniques

Following techniques are uses for plastic prototypes.

  • Additive Manufacturing / 3D Printing
  • CNC Machining
  • Vacuum Casting
  • Rapid Tooling

Additive Manufacturing / 3D Printing

This is fastest way to create plastic prototypes. In 3D printing, parts are created by 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. Each technique has their own strength and weakness. 

  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 & Electron Beam Melting)

Material Options

3D printing materials are available in various grades similar to commercial grade plastic. Even metals like aluminum can also be 3D printed.

Engineering Tolerance

Depending on 3D printer and material used tolerance in the range of 50 to 150 microns can be achieved.

Cost  and Lead time

Cost and lead time for 3D printed prototypes is less. You can get the prototypes within hours. 

Part Quality 

Very good quality prototypes can be manufactured with 3D printing. But the cost will be higher.

Ideal Quantities

1 to 20 Units

Advantages Of 3D printed Prototypes
  • Metal parts can be also 3D printed.
  • Parts with deep undercuts can be printed.
  • Specialized tooling is not required.
  • Fast turnaround.
Limitations of 3D printed Prototypes
  • Moderate manufacturing Cost and accuracy.
  • Critical features are very difficult to manufacture.
  • Limited Material options.

CNC Machining

CNC machining is a subtractive manufacturing process. In this process, material is removed from solid block with a variety of precision cutting tools to achieve final product.

Post processing operations such as buffing, sand blasting, plating, painting or screen printing are required to achieve good aesthetic finish.

Material Options

ABS, PC, ABS+PC, HDPE, Nylon and Hard PVC etc. sheets are available for plastic part prototyping.

Engineering Tolerances

General tolerances ” ISO-2768 m can be applicable for cnc machined plastic prototypes.

Part Quality 

CNC machined prototypes are functional and identical to injection molded parts. Various validation tests can be performed on CNC machined plastic prototypes.

Cost

CNC prototypes manufacturing cost is very high. Therefore they are recommended for small quantities.

Ideal Quantities

1 to 20 units

Advantages Of CNC Prototypes
  • Highly accurate and repeatable
  • Various material options are available
  • Customized tooling is not required
  • Fast turnaround
Limitations of CNC Prototypes
  • High manufacturing Cost
  • Critical features are added manually

Vacuum Casting / Silicon Rubber Mold

Polyurethane vacuum casting is used for making high quality and low volumes prototypes using silicone molds. Master piece (generally 3D printed part) is required for the manufacturing of Silicone Mould.

Silicone mold is filled with two part polyurethane resin inside vacuum chamber and then processed in a heat chamber at controlled temperature.

Material Options

Materials equivalent to commercial injection molding thermoplastics are available.

Engineering Tolerances

Tight tolerance are very difficult to achieve with vacuum casting parts . Depending on feature complexity. Tolerance in the range of 100 to 150 microns can be achieved.

Part Quality 

Silicon molded plastic prototypes are functionally and aesthetically identical to injection molded parts. Very few finish operations are required on vacuum casting parts.

Cost

Silicon molding is economical if manufactured quantities are more than 10. 

Ideal Quantities

10 to 100 units

Advantages Of Vacuum Casting
  • Low cost
  • Various material options are available
  • Fast turnaround.
  • Manufactured parts are similar to injection molded parts
  • Optically Clear prototypes can be manufactured
  • Overmolding and insert molding is possible
Limitations of Vacuum Casting
  • Manufactured part accuracy is not good
  • Slow Process

Rapid Tooling

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

Following technologies are used for rapid tooling:

  1. 3D Printed Plastic injection molding tools.
  2. Aluminum injection molding tool. 
  3. 3D printed metal injection tools.
Material Options

Almost all thermoplastic materials can be used.

Engineering Tolerances 

Tight tolerances can be achieved using rapid tooling. 

Part Quality

Rapid tooling prototypes are identical to injection molded parts. The only difference between rapid tool and final tool is the material used for tooling. 

Cost and Lead Time

Initial Investment cost for rapid tools is very high compared to silicon molding tool. Rapid tooling lead time is approximate 2 to 3 weeks.

Ideal Quantities

100 to 5000 units

Advantages Of Rapid Tooling
  • Low Cost
  • Quick Turnaround time
  • Manufactured prototypes are functionally equivalent to molded parts.
  • Over-molding and insert molding is feasible
Limitations of Rapid Tooling
  • High Tooling Cost
  • Recommended for moderate quantities.

Summery

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 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 summery table for comparison between various technologies.

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