Split Mould

 

What is a Split Mould?


A split mould is a great way to cast complex shape of small to medium size quickly and effectively. This method is virtually identical to the one part open mould making technique, being that it is essentially a one-part mould with strategic splits cut through it. These splits allow for greater complexity of shape to be used because the rubber (usually silicone) mould can be stretched open along the splits to extract the master and the subsequent castings from the mould. This method is commonly used when casting figurines and action figure prototypes.


This technique sometimes requires the use of air vents to assist in evacuating the air pockets that are caused and trapped by certain shapes. Although initially more difficult and longer to prepare, moulds with air-vents are likely to produce higher quality castings than plain split moulds.

How do I make a Split mould?



To highlight the process and help you understand this technique I have documented a real example below.


1.Construction of a container or vessel for your master is the first step when making this type of mould, stick the master to a rigid base (MDF) using hot glue or other suitable adhesives like double-sided tape.


2.In this case, a miniature model of a gorilla is being moulded, as with any shape similar to this (legs that raise a body and head above the floor) split mould is the easiest and quickest method for reproduction. Select the very lowest points such as the chin and belly that are not directly attached to an evacuation route (arms and legs). Remember your master will be cast in an inverted position (upside down) so low points of the master will be high points in the casting acting as air traps. Once you have selected these low points cut down matchsticks, nylon rods or toothpicks to fit between the master and the base. Use hot glue to fix these in place at these locations.


3.The vessel walls can then be constructed out of thin metal sheet, clay, MDF, or anything else that will hold the weight of the silicone to be poured.



Tip: when your vessel is complete and before measuring out your mould making material it is helpful to pour water into the vessel first to work out how much you will need bring the mould to the required level (usually 10-15mm covering above your object).


Remember to place the master in the vessel with the water in order to displace the excess water, we then carefully pour out and measure the volume of water remaining. This is a good way to ensure only minimal wastage occurs. Of course this method is only possible if both object and vessel are compatible with water, so check with your technician first.



  1. 4.Next, mix as much silicone as you have estimated will be needed to fill the vessel, keeping in

    mind that we will need 10-15mm extra above the height of the master.



  1. 5.When pouring the silicone always pour into the lowest point of the vessel containing the

    master. This will force out air as the level rises.



6.Once the silicone is set, remove the vessel walls and pull the silicone from the board (this takes a bit of strength sometimes). Now, using a fresh scalpel blade, cut the splits into the mould in strategic place such as along the inside of an arm or leg to minimise how visible these lines will be on the castings. You will also have to cut out the air vents to remove the vent rods, so bare this in mind as you are cutting. This process can be a little tricky sometimes so, as always, ask your technician to help you if you are unsure. When the master and the vent rods are removed you are ready to begin casting.

   

Silicone split mould

   

   

Silicone split mould

Silicone split mould with Polyurethane rubber casting