Spincasting (or centrifugal casting) is a method of using centrifugal force to produce castings from in a silicone mould. In other words, a silicone mould is spun around really quickly, and the force of this spinning movement forces liquid metal to fill the cavities in the mould.
Let’s break down this process, step-by-step:
Step 1: Creating a prototype
If we’ve made this product before, we skip this step as we will have the masters stored in our library. We’ll pull out the masters, and ensure they are ready to go into the mould.
If it’s a new development, the first step is to create the prototype. How we do this will vary project-by-project, but it will often begin with artwork. From artwork we’ll have a plastic prototype cut, and then build on to it by hand. Once we’re happy with the prototype, it will be sent to moulding.
Step 2: Making a mould
We use silicone moulds for casting. When we receive the moulds, the silicone is soft and putty-like. We push the prototype (or masters) into one side of the mould, and then place the other half of the mould on top. We then vulcanise (using heat and pressure) the moulds to cure the silicone. After the curing process, the silicone is harder and more rubber-like.
Once it’s been vulcanised, we remove the prototype (or masters), leaving a negative impression of the prototype (or masters) behind. Then we cut channels leading to each impression, and vents. It is along these channels that the molten zinc will flow, once we start casting.
Depending on the types of products being made, we’ll use a different thickness of mould. We can also combine multiple types of products in one mould, which allows us to run smaller order quantities.
Step 3: Casting the mould
We now have our mould – a round disc of silicone, consisting of a top and bottom half, which has impressions of what we want to make. This mould is placed into the spincasting machine. It lies upon a plate, which will spin around very quickly.
In a furnace near the spincasting machine we have our molten zinc. This is spooned into an opening at the top of the casting machine, and will flow down into the centre of the mould. The centrifugal force created by spinning the plate (and therefore the mould) forces molten zinc to flow through the channels and fill the impressions in the moulds.
Once it’s finished spinning, the mould is removed from the machine and opened. The metal impressions are removed, and the mould is left to cool before it’s used again. Moulds have a lifespan of about 80 – 140 spins, depending on the type of products being made. If a mould is overused it will result in a poor quality casting.
Step 4: Smoothing the edges
Once the products have been separated after casting, we need to smooth the edges. Where we break off the product from the channel (through which the zinc flows) there will be a rough edge.
For smoothing (or deburring) we have a few options. One is tumbling, another is machine grinding.
Tumbling is a mechanical process whereby the products are mixed around with small stones (or ‘media’). Water and cleaning products are added, and this mixing causes the media to rub against the product, smoothing off the edges.
Machine grinding is done by hand. Rough areas will be identified, and then held against a grinding wheel to grind off the sharp edges.
Step 5: Assembly of additional components
Depending on type of product, we made need to assemble another component before we electroplate.
For example, if we’re making buckles then we will need to assemble the prong. If we’re making badges, then we’ll need to spin rivet on the brooch pin.
Step 6: Electroplating
Now it’s time to add some colour! We have an in-house electroplating line, and offer a wide variety of nickel and nickel-free finishes. Electroplating is a process of depositing metal on the surface of a component. An electrical current is used to attach dissolved metal as a coating on a product.
Step 7: Final Assembly
Depending on the product, there may be need for some final assembly post-electroplating. For example we may be adding paint, or assembling diamantes. All of these final processes are done by hand.
Step 8: Quality Control & Packing
Once production is complete it’s time for a final quality check, and packaging.