Purpose of this Chapter: Key points for discussion (mold review) after injection mold design and before production.

An injection mold review (mold review) involves a mechanical engineer reviewing mold design and structure, providing modification suggestions from a product design perspective.
A good mechanical engineer should be familiar with injection molds and understand how mold structure affects product strength, function, and appearance. They should also be able to make accurate judgments regarding design of parting surfaces, gates, ejector pins, and other components within mold structure.
Generally speaking, before formal injection mold production begins, mold supplier should provide mold design drawings, including parting surface, gate, ejector pin, and other designs, along with a mold flow analysis report. If mold design issues affect part strength, function, or appearance, mechanical engineer should request that mold supplier modify mold design. Otherwise, discovering problems after mold production is complete will lead to costly and time-consuming modifications.
Note that mold design is closely linked to part quality. While structural design engineers aren't required to be proficient in mold design, they should at least be aware of discussion points outlined above.

Review general chapter to determine which stage mold discussion is in. Determine timing of mold discussion.
Plastic Mold Process B: Mold Design Phase (Mold Maker)

 

As shown in figure above, mold discussion stage generally occurs after mold design and mold flow analysis are completed, but before official mold opening. More formal suppliers will provide a mold flow analysis report and 3D mold drawings, allowing designer and manufacturer to sit down and discuss mold opening confirmation. Mold opening is time-consuming and expensive, especially for hard molds. Resolving any issues during mold discussion stage is much more effective than making changes later.

Discussions regarding injection molds generally focus on four key points: design of parting surface, gate, and ejector pins, and mold flow analysis report. A good mold flow analysis report can provide insights into design of parting surface, gate, and ejector pins. Of course, it's best to request 3D mold drawings from supplier.

Parting surface is dividing line between punch and die of an injection mold. Following points should generally be considered when selecting a parting surface:
1) It must not be located in a prominent position that would affect product's appearance quality;
2) It must minimize undercuts, simplify mold structure, and reduce mold costs;
3) It must facilitate part demolding. Generally, part should remain on punch side after mold opening, as it is easier to install a demolding mechanism on punch side;
4) Parting surface should facilitate meeting certain dimensional accuracy requirements for plastic parts, such as concentricity, coaxiality, and parallelism, especially when product design requires these dimensional accuracies;
5) For features with high height and low draft angles, parting surface can be positioned in the middle;
6) It must be located in an area that facilitates mold processing and product post-processing;
7) It must facilitate texturing and polishing of part.

Gate, also known as feed gate, is passage from runner to mold cavity. It is the smallest and shortest section in gating system.
1) Gate should be located in the thickest part to ensure smooth and complete mold filling.
2) Gate should be placed at point where plastic filling process is shortest to minimize pressure loss and facilitate mold venting.
3) Location of gate determines location of weld marks. Mold flow analysis or experience can be used to determine whether weld marks caused by gate location affect product's appearance and function. Cold slug wells can be added to address this.
4) Avoid placing gates near slender cores to prevent molten plastic from directly impacting core, causing deformation, misalignment, or bending.
5) For large or flat products, multi-point gating is recommended to prevent warping and material shortages.
6) Try to place gate where it does not affect product's appearance and function, such as at the edge or bottom. For transparent plastic parts, special attention should be paid to concealing gate location, as otherwise it will seriously affect product's appearance.
7) Gate size is determined by product size, geometry, and plastic type. A small size can be used initially and then adjusted based on mold test results.
8) When molding multiple cavities in a mold, use a symmetrical gating method for same product. When molding different products in same mold, prioritize placing the largest product near main runner.

1) To prevent part deformation due to ejection, ejector mechanism should be located in locations with high part strength, such as ribs or part edges.
2) Ejector force and position should be balanced to ensure that product does not deform or crack.
3) Ejector mechanism must be located where it does not affect product's appearance and functionality. For transparent plastic parts, particular attention should be paid to selection of ejector mechanism and its location.
4) Use standard parts whenever possible for safety, reliability, and ease of manufacturing and replacement.

A good mold flow analysis report can comprehensively evaluate quality of an injection mold design. This includes basic information such as injection time, locations of maximum stress, shrinkage points, and weld mark locations. It also includes information on mold materials, injection parameters, and other aspects. This assumes that company has clear requirements for mold flow analysis report during initial communication with suppliers. In real-world mold development, it's common to start a mold without a mold flow analysis report. From my perspective, I don't approve of this mold development process.

Also called Mold Discussion and Review Form, as shown below, it's used in same way as DFMA form.
Injection Mold Discussion and Review Form