Design Guidelines
If your part is relatively simple and already designed in 3D CAD–ready to prototype or produce, then we can quickly and cost effectively provide you with injection molded plastic parts using your CAD model. We can also model your part in 3D and provide images, drawings, and CAD files.
In order to maintain quality products, competitive pricing, and fast delivery, we suggest using the following parameters and materials in the design of your product. We can offer you a variety of other materials, however any adjustments to the following guidelines may affect a product’s price and lead time.
Parameters
- Size – In house molding is up to 16 ounces in part volume.
- Design should be provided as a complete 3D CAD model. Note: If you do not have a 3D CAD model we can model your part- all we need is sketch, drawing, or sample.
- Part should have no undercuts. Undercuts will add significant cost.
- Mold cavity will be CNC machined in aluminum (See What is a Simple Part?)
- Ejector Pins
- Minimum size is .047 inches
- May add bulge to ribs if the rib is smaller than the ejector pin
- Flat–may indent or bulge if on slanted areas of part
- We generally leave pins a few thousandths long on flat surfaces. This will produce a slight indentation which is usually more desirable than a raised area. We can give you ejector pin locations in advance if requested.
- Mold inserts belong to you and can be returned with your parts unless you desire that we keep them for future orders
Materials
- ABS – Very good for many applications
- Polypropylene – Strong and flexible
- Polyethylene – More flexible than polypropylene
- High impact polystyrene (HIPS) – Good for many applications
- Vinyl – Flexible PVC – Inexpensive material for soft, flexible parts
- Nylon – Very strong but more expensive
- Polycarbonate – “Lexan” – Very strong – more rigid than nylon
- TPE (Synthetic rubber) – Sarlink, Santoprene, etc.
- Acrylic – Very clear- more expensive
- Colors – Natural, black, white, and custom colors. Clear available in ABS, PC, styrene, and acrylic
What is a “Simple” Part
A simple part is a part that can be injection molded from a mold that:
- Has no undercuts, eliminating the need for slides or pulls. We do make molds with these features, but additional costs are incurred.
- Can be CNC Machined using cutters from .0625 in diameter whose length is no longer than 3-6 times the diameter (see table)
- Does not require EDM processes because of small details or sharp inside corners in mold. Note: If your part has sharp outside corners we can still make it, but corners will have a radius. We can EDM features as necessary, but for additional cost.
| Cutter Size | Maximum Length |
|---|---|
| 0.062″ | 0.180″ |
| 0.078 | 0.350 |
| 0.093 | 0.375 |
| 0.125 | 0.500 |
| 0.1875 | 0.625 |
| 0.250 | 1.250 |
| 0.3125 | 1.625 |
| 0.500 | 2.000 |
Many very complex parts can actually be simple by the above stated parameters.
Some Other Considerations
Shrinkage
The molding process involves injecting hot plastic into a mold cavity and allowing it to cool. As it cools, the plastic shrinks. While we can estimate shrinkage fairly well, different areas and/or materials may shrink a little differently. If you change materials, the size may vary slightly with the new material. If you anticipate several material types and size is critical, consideration should be given to what shrink factor to use. If your part involves very close tolerances, please so indicate when you supply us with a model.
Engraving
Simple engraving in which text, symbols, etc. stand up on the part, can usually be included at no extra cost. The engraving geometry must be supplied in the CAD file as curves on the surface of the part. Minimum cutter size for engraving is .031 diameter. This will provide very attractive results and is great for part identification, revision numbering, switch labels, web site, etc. Remember that the engraved features will be raised in the part. Make sure that there will be no interference issues when engraving is specified.