Technology Information

Metal Casting

Metal Casting is an ancient method of creating statues and sculptures that has been in practice in Meso-America, China, and Ancient Egypt since 2000 BC. The Greeks practiced it, so did the Romans, and pretty much any civilization with a strong interest in art.

Weapons and Sculptures have been made using bronze since the begining of its discovery by man. Bronze is able to fill in the fine detail of molds making it very desirable to artists. When art casting, bronze is the alloy of choice since it is both beautiful and easy to work with. There are few examples of bronze statues left from antiquity since the alloy became scarce and many of the statues were melted down for weapons and other sculptures usually for new emperors or victors.

The Lost Wax Casting process is the preferred method used when art casting. This process was used in ancient times to create bronze items. Small foundries like the type found in backyards, personnel workshops, and garages are able to use the Lost Wax Casting process with a certain amount of professionalism. Commercial foundries and professional art companies use the Lost Wax Casting process as well to create custom items and monuments. The process remains, essentially, the same since the ancient craftsmen who first pioneered the method. Lost wax casting also gets another name when it is used in the commercial manufacturing business or when its just to make jewelry and that name is Investment Casting.

Metal Casting is one of the more enjoyable reasons to fire up the furnace and get into metal casting. While most think metal casting to be strictly limited to hobbyist and historical re-enactors, casting is a popular skill and craft used by a wide range of people for varying reasons. Artists see the need to have metal casting skills as it allows the artists to have direct control over the process instead of out sourcing it to a commercial foundry. Commercial foundries that specialize in custom pieces will often charge outrageous prices for their services. Metal Casting on your own is often times economical and just smart.

The Lost Wax Casting process is rather simple when compared to other casting methods but it can be time consuming and attention to detail is important. The artists will start with an original piece sculpted from wax. The original can be made of other substances like clay or even metal but wax seems to be the easiest to work with. The original will be used to make the mold. If the piece to be cast is large, multiple molds will be needed. This is common in art casting and completely possible with the use of shims and keys that will allow placing the pieces together after the casting process easier. Most molds will be made out of latex or other materials to help transfer the fine detail into the mold cavity.

The original is often destroyed during the mold making process upon removal. Molten wax is poured into the mold until the desired thickness is achieved.  When dry, this wax copy is removed and chased which rids the piece of imperfections and is used to combine the pieces.  You will place paths for the molten metal on the wax copy.  You will also place a cup or funnel at the top of the copy. This process is called spruing and is done in wax.

A ceramic shell is placed around the copy. The shell isn’t really ceramic but a sand and liquid silica combination.  You will repeat this step until the shell is thick enough for the piece. You will then heat the item which will melt the wax inside. The wax runs out of the shell through the paths placed during spruing. 

Then comes the part for the molten bronze. The bronze is poured into the top of the hollow shell. When cool you are going to remove the shell carefully to reveal the finished product. The bronze sculpture is chased, painted, and finished up however the artists choose.

Art casting can be done with any metal or alloy. If you are going to use the Lost Wax Casting process then you do not have to stick with bronze. Sometimes it is a good idea to try a few other metals until you get the exact look that you are searching for.

 
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Metal Casting

Aluminum is the most common alloy used in metal casting. There are several reasons for this, but the main one seems to be availability and quality. Many metal casters have access to a large amount of aluminum with soda and beer cans that they crush and melt down. Aluminum has several desirable properties for the metal caster no matter if they are a hobbyist, artist, or are casting needed parts for home repairs. Many who cast aluminum also love the alloy since it can be used in all of the varying casting processes giving it a wide range of possibilities. Aluminum is often used as a practice alloy for the first time metal caster or for casters who are trying out new methods and ideas.

DIY Home foundries usually will not have a problem at all getting hot enought to melt aluminum. It may even be possible to use charcoal though many just use propane since they have it on hand for other alloys. For your first run at casting, charcoal should be fine.

Soda cans is a great way to find cheap aluminum, but remember you will need quite a few cans to cast just one medium sized object. Make sure to crush the cans as much as possible before placing in the crucible or other area that will be used to melt the alloy.

Since any Aluminum Casting process can be used with aluminum the choice will rest with you. There are three casting methods out of the numerous methods available for aluminum that seems to be preferred by small time metal casters. These methods are sand casting, lost foam casting, and investment casting.

Remember, though, aluminum can be used with any metal casting process so do not be afraid to experiment.

Sand Casting

Sand casting aluminum is very common and is a popular way to break in a new furnace. Casters use sand mixed with a bonding agent to create a mold around the item to be cast. The item, or pattern, is removed very carefully revealing the mold. If there will be any empty spaces in the finished product then a core is added to the mold. The core can be made of sand and is placed so that the molten metal fills the area of the mold around it. So, say you’re making a picture frame you will place a cone where the glass will go so the molten aluminum will not fill that area.

Many choose not to use sand casting since it does not allow for fine detail whereas other casting does, but it is inexpensive.

Lost Foam Casting

Lost foam casting which is sometimes called evaporative casting. The lost foam casting is a form of sand casting. The entire process is relatively cheap and when used with old soda cans casting aluminum this way is great on the budget. A foam copy of what you want to cast is created and surrounded by a ceramic shell. Loose sand is where you will want to place the copy so that you can help to hold the shape during the pour. The molten aluminum is poured into a cup that in inserted into the copy. The foam vaporizes and the aluminum replaces it filling the area in the ceramic shell. Removing the shell will reveal the Metal Casting . This method is great for fine details but the copy is lost to the ages. Luckily, foam is not all that expensive.

Investment Casting

Investment casting is commonly used by jewelers as it allows precise castings with full detail. This form of casting has been around since ancient times under the name of lost wax casting. Investment casting involves creating a wax copy which is then covered in slurry creating a shell, much like the kind of shell in lost foam casting. The molten aluminum replaces the wax which melts out of the shell and can be collected for reuse. Artists and casters that need high precision parts favor this technique.

Given the number of options that aluminum presents to the caster finding the right casting method will involve some time. To help decide which Metal Casting process is best consider factors like quality and cost.

Many metal casters use aluminum far more then they use other alloys like brass, bronze, or iron.
 
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Metal Casting

There are various casting processes being implemented now days. The oldest amongst them is sand casting. Spin Casting is also widely used. They can be described as follows:

Sand Casting: Sand Casting involves formation of mold from a mixture of sand and to pour a casting liquid, most probably, a molten metal into mold. To remove the mold, you must wait a little while for the metal to solidify. There are two methods or types of sand molding and those are the green sand method and the air set method. The first one consists of mixture of clay, moisture, silica, and many other additives. The second one consists of mixture of dry sand and other materials, not moist clay. They are mixed with the help of a quick curing adhesive. The collective use of these materials is called ‘air set’.

At times, there is temporary plug placed to pour the fluid which is to be molded. Air-set molds usually form molds consisting of two parts-the bottom and the top. After the mix of sand gets added, it also gets tamped down. It does not generate any by-product. After the solidification and cooling of metal, the mold gets usually destroyed. This is because its removal involves a lot of breaking and cracking. The casting accuracy depends a great deal on the sand and the process of molding used. Castings composed of green sand result into formation of rough texture on casting surface, and this characteristic makes them easily recognizable. In reality, studies show that molds that are air-set produce the smoothest castings.

Many a times, the casting process results in losing of components of sand mixture. It is possible to reuse green sand by the way of adjusting the composition to get the lost additives and moisture replenished. The entire pattern itself is eligible to be reused for producing novel sand molds. The method of reuse can be continued for an indefinite period. In 1950, casting process got automated partially. They have been in great demand for developing production lines since then. 

Spin Casting: Spin Casting is better known as Centrifugal Rubber Mold Casting (CRMC). It implies utilization of centrifugal force for producing castings out of rubber mold. As a customary practice, a mold having shape of a disc gets spun through its ‘central axis’ at a pre-decided speed. The material used for casting is usually thermoset plastic in the liquid form or a molten metal. It gets poured into the mold through the opening at its centre. Corresponding to the solidification of metal, or the setting of thermoset plastic, the spinning of the filled mold takes place.

Normally, organic rubber or vulcanized silicone is used as a mold-making substrate in spin casting. Vulcanization takes place in the middle of process of mold-making. After the successful completion of vulcanization process, venting and gating must be undergone by the mold. This implies carving of channels for ensuring proper material flow and air during the course of casting. Your best bet for preforming the proccessed is to either use a scalpel or knife. The mold complexity is directly proportional to the time required in implementation of venting and gating.  

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