In general, the gate is placed at the thickest cross-section to allow the material to flow from thick to thin cross-sections. Additionally, the location of the gate(s) should be placed to allow uniform filling of the mold cavity.
The following characteristics are typical for an edge gate:
- Gates are typically removed manually and are not suited for high annual volume applications as they require removal by manual or automated means. Regardless, the removal process is an additional process step and cost
- Suited for low to medium annual volume applications
- Recessed gates are preferred to minimize vestige above functional component surfaces.
- Normally located along the parting line
The following characteristics are for a submarine, or sub-gate:
- The gate automatically shears off from the part during the part ejection portion of the molding process.
- Suited for low to high annual volume applications
- Leaves minimal gate vestige or breaks off below the surrounding component surface
- Sub-gates should be placed on a recessed surface to minimize vestige above functional component surfaces
The following characteristics are for a submarine or sub-gate to a removable post:
- The gate automatically shears off from the post during the part ejection portion of the molding process
- The post is removed after the part is out of the mold, and this removal process is not typically automated
- The post is preferably located in a recessed pocket on the MIM component so the post can be broken off below the component surface
- Suited for low to medium annual volumes
- The post and related recess or pocket should be located on a non-cosmetic surface
Other gating techniques can also be applied to MIM parts including three-plate molds with direct gating and hot-runner systems for direct gating.