 |
Depending on the geometry, size and production quantity of the component, a tool can have between 1 and 16 cavities. AMT warrants tool life to 500,000 shots and offers a number of flexible tooling options to meet the customer’s individual needs.
| Include |
Avoid |
| Plastic molding design rules |
Sharp fillets and edges if possible |
| Cores, holes and indents |
Placement of parting lines and weld lines in
functional locations |
| Draft or taper |
Dimensional tolerances tighter than ±0.5%
(more precise tolerances are costly) |
| Room for ejector pins and gating |
|
| Uniform cross-sections if possible |
|
| Flat surfaces |
|
| Coring and Holes |
Avoid material concentrations. Provide coring and holes to allow weight reduction and structural improvements as illustrated in diagrams (a) to (e).
[back to design selection] |
 |
| Uniform Wall Thickness |
Maintain uniform wall thickness as much as possible. Avoid abrupt changes in wall thickness which may result in distortions and stress concentrations.
[back to design selection] |
 |
| Cantilevered Section |
Design ribs across the cantilevered section to prevent slumping during sintering. Otherwise, subsequent straightening operations will be required and may add cost.
[back to design selection] |
 |
| Flats on Threads |
Molded parts may form flash along the parting line that can damage the thread accuracy. To eliminate such problems, design flats on external threads along the parting line surfaces.
[back to design selection] |
 |
| Intersections of Perpendicular Holes |
Holes are incorporated into PIM components through the use of shaft
(or pin) elements in the injection molding tool. The intersection of two holes becomes difficult because of the possibility of misalignment of the two shafts (or pins) creating the holes during injection. This can be alleviated by making one of the intersecting holes
a D-shape.
[back to design selection] |
 |
| Sharp Edges |
Cracks are easily formed at the intersection of sharp edges due to stress concentrations. Rounded corners and rounded intersecting surfaces are preferred.
[back to design selection] |
 |
| Aspect Ratio |
Components with an aspect ratio of less than 2 are recommended. Higher aspect ratio designs can be molded by incorporating ribs to strengthen the structure and thereby preventing distortion.
[back to design selection] |
 |
| Internal Holes |
Internal holes should be designed with tapers to enable efficient injection molding.
When assigning tolerances, give consideration to parting lines, gate locations, moving cores and slides, wall thickness variations, etc. For example, a gate will leave a mark on the finished part. Therefore, it is advisable to avoid placing the gate on a critical surface.
It is advisable to incorporate features that control the weight of the final PIM part to less than 250g (9oz). This can be done through holes, cores and other weight reduction methods.
|
 |
Avoid designing elongated features parallel to the gating direction in area where the material first enters the cavity during the injection molding cycle. Changing the direction of flow upon exit from the gate into the cavity eliminates jetting and insures laminar flow. Thus, optimal mold filling can be achieved.
The figure below shows the combination of parts for multi-functional applications. Such considerations contribute substantially towards cost reduction. [back to top]
 |
|
