Casting
Casting is the process of pouring hot molten metal into a mold to create a 3d object. This can either be a one-of-a-kind piece or repeated copies for semi-mass production. Here, we will explore the tools and techniques that will help you take your jewelry manufacturing to the next level.
Lost wax casting
This is the most popular method for replicating items in precious metals. This method can be used for a single item or large-scale mass production. However, the basic process remains much the same.
Making a wax model.
As the name "Lost Wax" suggests, the first stage is to create a wax model of the piece to be made. For unique items, you can carve the item directly from wax. As the wax is easy to bend, carve and stick together, it allows much more creativity and freedom to experiment with forms quickly and easily. Hence, it’s an ideal medium for creating original designs. Traditionally, this is done by using metal tools, which are warmed with an alcohol burner, to melt and carve the wax.
Ring model carved in blue wax
Pepetools TouchAmatic
Modern technology makes this much easier, thanks to the Pepetools TouchAmatic. This is an electrically heated pen. With just a simple touch on the barrel, the tip instantly heats up to a precise temperature, allowing you to melt, carve, and join wax. It's the perfect companion for working with wax.
Pepetools TouchAmatic, electronically heated wax pen.
Idela for making wax models and spruing.
Tip: The finished wax model can be invested and cast directly, but note that you will only get one shot, as the wax is lost in the process (hence the name). If you want more copies of the wax master, you can use a cold molding method, such as two-part silicone rubber, to make a mold and copy it.
Copying an existing item. Vulcanizing.
Alternatively, you can start with a pre-made item of jewelry or even a small 3D-printed item. But these need to be recreated in wax first. This is done by making a mold of the piece using vulcanizing rubber.
Tip: If you are aiming to copy a gem set item, you will need to remove the gems, or these will end up as solid metal in the final piece.
The piece is first placed into a small metal frame along with a small metal cone called a sprue former. And packed all around with special rubber.
Cones for making a perfect wax filling channel in the rubber molds
Pepetools supply a France of heavy duty vulcanizing molds.
It is then placed into a vulcanizing press, which produces heat and pressure, melting the rubber and squeezing it into all the tiny details of your piece. Once cooled, the rubber block can be cut open carefully and the pieces removed. The rubber will have made a mold of the piece, and where the sprue former was, a cone-shaped channel has been created at the end. The mold is reassembled and can now be filled with wax.
Vulcanizing press with heated jaws. Perfect for making high-quality rubber molds.
Note that the heat and pressure of the vulcanizing press means it cannot be used with a wax master, as it would simply melt. Hence, this process requires a metal master, such as a piece of jewelry.
The process of making a rubber vulcanized mold, using an original silver ring and brass sprue former, encased in black rubber. and vulcanized in a press, the rubber mould is then cut open, and the master is removed along with the sprue former. The mold can then be injected with wax.
Wax injection
The wax needs to be molten and injected into the mold with pressure to ensure it gets into all the details accurately. This is done by use of a wax injector. This is a special heating unit that melts the wax and injects it under pressure into the mold through a cone-shaped nozzle. ( Hence why the cone-shaped sprue former was used to create a corresponding hole in the rubber mold. This can be placed over the nozzle of the wax injector to ensure a quick and easy fill.)
Once cooled (almost instantly), the wax model can be carefully removed, and this can be repeated almost indefinitely, injecting wax to create multiple copies of the original.
The empty rubber mold is reassembled, and hot wax is injected into it. The wax copy is removed and cut from the wax sprue, you now have a wax copy of the silver ring.
Spuring
The wax models need to be sprued. This simply means adding them onto a wax tree; the branches or “sprues” will ultimately channel the molten metal to each piece. If you think of it as a tree, the base must be wider and tapered as this will create a wide opening in which to pour the metal. This can be done using built-up wax or pre-made wax cones. But in most cases, the base of the investment flask contains a small, raised dome on the base. This supports a central wax pillar and also creates the filling channel later.
One by one, the pieces are added to form a tree. Care should be taken that the tree will fit inside the casting flask, allowing space all around for the investment. Pieces are attached to branches using heated tools. The Pepetool Touchmatic is ideal for this, allowing you to simply touch and connect pieces quickly to the tree.
Several wax rings are attached to a wax sprue. Note the dimple in the base to create a filling channel later. The flask is placed over the wax tree and wrapped with plastic film or paper to seal the holes before filling it with investment.
Investing.
Investing is the process of creating the plaster mold, which will ultimately receive the molten metal. This is done using “investment”, which is a special kind of plaster. It comes as a dry powder which is mixed with water to produce a pourable plaster mix.
KAYACAST
No air bubbles must be in the mixture. To assist in this process, the KAYACAST system provides a vacuum chamber. The mixed plaster (in a bowl or jug) is placed under the sealed dome, and the machine creates a vacuum inside, which removes air bubbles from the plaster mixture. This helps to ensure a smooth, even pour. The investment mixture is then poured into the flask, surrounding the wax tree. The flask contains holes, which allow the vacuum to work in the casting stage, so this hole must be covered when filling with investment. Usually, a strip of plastic or paper is wrapped around the flask. This is simply removed once the investment has dried. It is vital that no air bubbles are created and that there are no voids in the investment. So, once again, the KAYACAST system is employed here. The filled flask is placed under the dome, and the vacuum is applied again. This will remove any air bubbles and assist in the investment filling every detail of the mould. It is also designed to allow the flask to be vibrated whilst under the vacuum, ensuring a complete fill. Note that the investment may need topping up again. Once the flask is filled, the plaster is allowed to dry and solidify before removing the paper or plastic film.
The Kaya cast desktop system. Note the vacuum dome on the left (for investing) and the vacuum casting chamber on the right. Also, a range of gasket rings and adapters to allow for different-sized flasks.
Pepetools also supply the larger XL version, supporting larger items and bigger flasks.
Burnout.
Once the investment is dry, we need to remove the wax without damaging the mold. This is done by “burnout” and uses a small kiln. The flask is placed on blocks upside down so that as the wax melts, it will run out of the flask (and burn off in the kiln), leaving a hollow void in the plaster. This takes time to completely remove every trace of the wax, typically several hours or even overnight. The use of a temperature-controlled kiln is essential for this process to maintain a constant temperature that will completely burn away all the wax without leaving any residue. Hence the term lost wax. It will also heat the flask and investment ready to accept the molten metal.
Note: After burnout, the flask is kept hot in the kiln and is only removed at the last second when the metal is ready to be cast. The metal is poured into a hot mold, which helps the metal to flow.
The flask is uncovered & base removed, then inverted in the kiln to burn out all the wax before finally filling with molten metal.
Melting the metal.
When burnout is complete, and the mold is still hot. The metal can be prepared. You will need enough metal to replicate the items and also to fill the branches of the wax tree and the sprue channel. A formula can be used to weigh the wax tree and calculate the weight of metal required to replicate it, but any surplus metal can simply be poured into an ingot mold for reuse later. (or kept hot in the crucible and multiple molds can be filled). The metal can be melted by use of an oxy-propane or acetylene torch, but this ties you up, and it is difficult to judge the specific casting temperature needed. Too cold, and it won't pour; too hot, and the metal may boil, creating bubbles and voids in the final cast piece.
Pepetools makes several electric melting furnaces in different sizes for this exact purpose. These allow larger volumes of metal to be melted quickly to a precisely controlled temperature. An electric furnace also allows you to work hands-free; simply fill the crucible and set it to temperature. No need to stand there holding a torch. Once the desired temperature is reached, the furnace will maintain the metal at that precise temperature, ready for casting.
Pepetool's range of Electric melting furnaces can melt metals quickly and easily.
Pouring the metal.
When molten metal pours into a mold, hot gas can expand, creating air pockets. The metal may also solidify before filling the mold. Again, the KAYACAST system is designed to overcome these problems. It also contains a vacuum casting section. The hot flask is placed into the casting chamber, and the KAYACAST creates a vacuum as the metal is poured. By removing the air from the flask, the metal is sucked into the mold, quickly filling every detail, without voids or bubbles. Remember, the flask should be filled, including the sprue hole.
Molten silver being poured into the flask of the Caya cast desktop machine.
Quenching
The whole flask is then removed (with tongs) and submerged in a bucket of water. This quenches the flask and washes out the investment, leaving a tree made of precious metal with the items attached to it. You now have a precious metal copy of the original wax tree.
De spruing.
The pieces now need to be cut from the metal tree (sprues). This can either be done with a jeweler's saw (using a larger blade such as No 8), Alternatively, thinner sprues can be cut with small bolt cutters. The metal sprues and trees can all be remelted for later use.
Removing the cast metal rings from the spue tree.
The pieces can now be cleaned and finished. Traces of investment can be washed and brushed off. For finely detailed pieces, an ultrasonic cleaner will remove every trace in a matter of seconds. Each piece will also have the remains of its sprue where the piece was attached to the tree. This is usually removed by grinding with a Flex shaft.
Finishing.
Magnetic polishers such as the Abre range are an ideal accompaniment to the KAYACAST system. These large polishers allow multiple items to be cleaned and polished effortlessly and quickly. Millions of tiny steel pins are swirled around at high speed in water and soap; this quickly cleans and burnishes the pieces, leaving a bright, slightly matte finish.
The pieces can now be finished as desired. Oxidized, gems set and final polishing with mops. As well as mops and polishers, Pepetools offers a whole range of tools and equipment to help get that perfect finish, from magnetic polishers and ultrasonic cleaners to buffing wheels and dust extraction.
See Pepetools for a wide range of polishing motors and accessories.
This may all sound complex, but with the correct tools, the process is effortless. Using the lost wax method, a single piece can be replicated in precious metal quickly and easily as many times as you need. The KAYACAST and other machines offer reliable and predictable results with minimal time and effort required. Take your jewelry manufacturing to the next level and begin mass production with the help of Pepetools.
See Pepetools for a full range of casting, investing, and polishing equipment. Plus, everything else for the jewelry maker.
