32 Cavity Cap Mould
This project was built for an injection molding company in the capping industry. The main concerns with parts like these are cycle time and the ability to produce an extremely high volume of parts consistently and reliably. Being able to do this comes down to intelligent tool design and a quality build.
Getting into high volume applications like this, requires additional considerations in the design process. For example, using a cold runner system to feed 32 cavities is not economical as it can add injection time, increase plastic pressures, add to take out time, increase the overall size of the mold, and the list goes on. For this part, there were several advantages to utilizing a 32 drop valve gated hot runner system.
The next design consideration is optimizing cooling channels to remove heat as quickly and efficiently as possible. There is several factors that can dramatically effect the ability to remove heat from the plastic with the largest one bring wall thickness. For high volume applications the goal is to have as thin of a wall section as possible, without effecting the part functionality and moldability. Using tools such as Moldflow, we can consider the part design's influence on the process.
Beyond wall thickness, designing effective cooling and material selection can have a large impact on cooling time. In the image below you can see one cavity and the path of the cooling system. Water enters from one side of the core insert, travels up a large channel directed by a baffle, back down the same channel, and then out and around. For reference, the water flow is drawn in 3D. The blue colored area represents the first half and the red colored area represents the second half. Each cavity is fed by a series of water lines machined into various plates of the mold.
Cycle time is such a major factor in the molding operation, making sure the parts eject off quickly and easily is critical. The pictures below (drawing simplified) shows how the ejection system works. Use of a stripper ring system creates a balanced and even mechanism for removing the part, while also helping to remove an under cut feature in the plastic part.