Mold Cavity and Layout
When we perform a mold design, the first thing we would consider is the manufacturing volume, which would directly determine our mold cavity and layout. For example, for a high volume mold(500,000~1,500,000), we will suggest to use at least 4 cavities or 8 cavities if possible. and a medium volume(50,000~100,000) mold would be designed as 2 cavities, however, for a low volume mold or prototype mold, we would like to suggest to use a single cavity only.
Once the mold cavity is defined, we would start to make a layout for the parts in the mold. During this stage, mold injection type, runners, parting line, ejection system, cooling system should also be considered.
Parting Line Design
A part line is a part separating line of mold cavity side and core side. a fantastic part line design is a comprehensive consideration of mold release, appearance, and part assembly. Our parting line design principal is to make the part appearance as better looking as possible while not affect part assembly and mold release. While mold making process, we require our mold makers to leave a part line as smaller as possible( 0.10 Max.).
In order to achieve as smaller parting line as possible, mold fitting and assembly are also very important process. Otherwise the parting line area will come out flash or overflowing parting line.
Injection Gate and Runner
Injection gate is the entrance point from mold runner to plastic part, where the injection material travels from injection machine to mold cavity.
There are many different types of injection molding gates(like bannar gate, point gate, direct gate, side gate, tab gate, fan gate, submarine gate, etc), different type of gates have its advantages and disadvantages. To determine which type of injection molding gate, we should consider injection molding balance, shrinkage, appearance, and dimension.
Slider and Lifter
Sliders and lifters are used to make some complex part structure that could not be directly obtained by the shape of mold cavity and core, as mold cavity and core are fastened into mold base and it could not move any more. However some holes, windows, snap-on features, or other special features must be produced by sliders or lifters. In this case, the sliders or lifters should move simultaneously outwards while mold tooling opens.
If some more complex parts, we might need to design more sliders or lifters for one feature, but most of products can be achieved by single slider or lifter.
Ejection system is a mechanism device to push injection molded part off from mold tooling, it consists of ejection foundamental plate, ejection spring(or pull bar), ejection pins(or ejection plate). The ejection system move forward to push molded parts off when mold opens, and it retracts again when mold tool closes.
Our design principle is to ensure injection molding part can be smoothly pushed out while not affect part appearance. However if any inappropriate ejection design, it could result in ejection defects or imperfection appearance.
Cooling system is the last step of a mold design, it seems not so important as it’s invisible from outside of mold tool, however it will actually affect product quality a lot. For instance, a mold tooling without proper cooling system could not be used for normal production indeed, and it could either result in serious shrinkage issue or burn out issue.
When we design a mold tool, a proper cooling channel is needed to travel as close to part as possible. A hard mold(HRC 48~52 Degree) should be processed cooling channel before heat treatment, otherwise it’s very hard to drill the cooling channels. But the cooling channel of normal mold can be manufactured whenever we needed.