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Rapid Prototyping (RP) - Rapid Tooling (RT) - Composite Tooling / Epoxy Tooling

 

 

Rapid Tooling Techniques

Composite Tooling (Epoxy Tooling)

Epoxy Mold Composite/Epoxy tooling is a rapid tooling technique that fills the void between current prototype processes. For plastic parts, the two most common tooling processes are RTV molding and soft tooling (machined aluminum). Composite tooling bridges this gap by offering advantages of both processes: 1) The quicker time and smaller expense associated with RTV Molding and 2) The capability of soft tooling to use production materials (thermoset plastics) for prototyping injection molded parts.

In general, composite tooling generates injection molded parts in 2 to 6 weeks (including SLA pattern generation) at a cost reduction of 50% to 70% versus aluminum tools. Although suitable for simple designs, cost and lead - time advantages are enhanced as the design increases in complexity.

The ideal application of composite tooling blends all of the following factors:

  1. Production material is required.
  2. Available lead time is limited.
  3. Strong cost considerations.
  4. A small prototype lot is required (50 - 500 pieces).
  5. The design is of moderate to high complexity.


PROCESS DESCRIPTION

Epoxy molds or aluminum epoxy molds are reasonably fast in comparison to machined molds and are a relatively inexpensive way to create prototype and production tooling. New epoxy products offer a much higher compression strength and heat resistance. If the molds are designed properly they can withstand injection and compression pressures with the use of aluminum standoffs or mold boxes.

A high strength mold can be achieved within a few weeks with a master pattern or rapid prototype. The process begins by creating a pattern; as with castable silicones, these epoxy resins will reproduce surface detail and textures exactly. Therefore, the pattern is finished to the desired quality before making the mold. Typically an interim RTV mold will be made in order to create a urethane reproduction for the epoxy process. This is done because the master is usually destroyed in the epoxy molding process.

The parting lines are established in much the same way we would make a RTV tool. The epoxy is applied to one part of the mold at a time and then goes through a multilevel post curing process. The post curing is where the high strength is achieved. At this time, the mold is machined to hold square and any gates and vents that could not be molded in are applied. Often, intricate core detail will be added in with a machined aluminum or steel insert.

Curing time is dependent on the product and curing agent. Times range from 30 minutes to over 40 hours. Adding heat will speed up the curing process significantly. Aging the mold at room temperature for up to 72 hours, if possible, will increase the productive life of the mold.

Properties of epoxy such as compression strength and hardness vary considerably from product to product. Choosing the proper epoxy for a particular design is based on experience and manufacturers recommendations. The most important consideration is the intended production material.

Epoxy tools are constructed of a rigid material to allow for injection molding. This rigidity does not allow for shortcuts common to RTV molding. With RTV molds, the flexibility of the tool allows it to be "peeled" away from the part. Therefore, draft and small undercuts are not considerations. With a composite tool, the pattern must be drafted. Also, the manufacturability of a part design must be reviewed to ensure that an undercut or backdrafted feature will not prevent part ejection.


Specifications

Time:

Composite tooling generates injection molded parts in 2 to 6 weeks.

Production Rate:

The molding process will have a cycle time of 5 to 15 minutes.

Composite Tool Life Expectancies
Thermoplastic
Tool Life (# shots)
ABS
50 - 3000
Acetal
100 - 1000
Nylon
250 - 3000
Nylon (Glass filled)
50 - 200
PBT
100 - 500
PC/ABS blends
100 - 1000
Polycarbonate
100 - 1000
Polyethylene
500 - 5000
Polypropylene
500 - 5000
Polystyrene
500 - 5000
Investment Casting Wax
1000 -10000
 

Accuracy

Accuracy is dependent on the SLA model. Typically about +/-0.005" to +/-0.015".
 
Cost

Dependent upon the cost of the master pattern, and overall size of the part. A SLA master pattern can cost between $300 to $1000, on average, and the epoxy tool is typically between $800 and $1000.

 

 


 

 




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