Metals are one of the most important engineering materials that are used in todays technologies ranging from customer products to aerospace… everywhere. Important thing is, giving the reqired shape and properties to metals that they will be used in such engineering applications. One of these metal shaping processes is casting. Casting is very prominent and very important process to obtain required shape of materials, not only metals. But in this extent, we will assess the topics about metal casting;
- Properties of metal casting processes,
- Advantages and disadvantages of metal casting processes,
- Classification of metal casting processes according to different aspects,
- General aspects of metal casting processes.
What Is Metal Casting?
As we stated just above, casting is the process of giving a shape to a metal, by liquify them with heating. Then pouring them into prepared molds that has intended shape in cavity. So, design of mold for casting of metals is very important thing. Casting of metals generally has two categories; ingot casting and shape casting.
Ingot casting of materials can be explained like this: Metals are cast in the form of bulk or simple shape. Before casting these metals, required adjustments are generally done in the way of obtaining ingots. Such as addition of alloying elements to obtain required material characteristics or mechanical characteristics. Metallurgy techniques are very important in this step of casting the metals. These bulk of metal ingots are used in further shaping operations such as forging, rolling etc.
As you understand from its name that shape casting is the casting processes of metals to obtain required shape of metal. In this process, metallurgy techniques can be used, but in general design of required mold cavity is more prominent. Ingots or other scrap metals can be used as liquid metal to pour them.
Some Terminology And Classifications Of Metal Casting Processes
If there is a constant metal casting processes in a place, this place is called as foundry and the workforce is called in foundry is foundrymen
In shape casting processes of metals, mold design and mold cavity design is very important thing. Engineering level aproach must be adopted. In mold design, the most important parameter is shrinkage. Every materials and metal shrinks upon solidification. This shrinkage must be considered, in the phase of mold design.
The cavity of the mold is generally designed oversize, according to the produced product’s shape. This oversized design of mold is done according to calculations of shrinkage.
Types of molds also another important parameters in the phase of metal casting mold design. There are generally two types of molds; open mold and closed mold.
Open molds are the type of molds that the metal is directly cast from the open side of mold that is opem the atmosphere. Designing this type of mold is much more easy compared with closed mold one. There is no complex ventilating systems and gating systems to achieve a good molding process of metals. Ingots can be cast in open molds.
Closed molds are generally most used one to obtain more complex metal parts. The casting of liquid metal is done by gating system that has a pouring cup. The metal is poured into this pouring cup of closed mold, and downsprue and runner systems transmit the poured metal into closed mold cavity. Risers, pouring cups and runners, mold cavity, core and the placement of molding cavity according to the parting line are veyr important parameters in terms of design of mold.
So, closed mold design is very complex and has engineering level design characteristics. An engineer must design closed mold in detail to obtain flawless geometry from it.
Molds that are used in metals casting are also classified according to their use. Some of molds are used only one time and some of others are used in lots of processes. Because of this difference, the types of molds are; permanent molds and expendable molds.
Permanent molds are the kinds of mold that can be used lots of time without crashing it. Lots of products can be produced from permanent molds. So, the material that is used in the production of permanent molds must be a refractory material, and must withstand cycling heat loads. In general, permanent molds has collapsible system to take the molded material from it after solidification.
Expendable molds are generally used only for one time. Because, they are demolished generally to extract the molded material after solidification. Various kinds of refractory and cheap materials are used for it such as ceramics. With expendable molds, more intricate metal parts can be produced.
What Are The Advantages And Disadvantages Of Metal Casting?
- Very large metal parts up to 100 tons can be produced with metal casting processes.
- If a material has ability of being liquid upon melting such as metals, casting of this material is generally possible.
- Very complex internal and external shapes from metals can be produced with metal casting methods.
- Mass production with casting methods can sound impossible slightly but the situation is not like that. Certain metal casting methods are avaliable for mass production.
- Net shaped final metal products can be established with only one casting process. But sometimes, the surface characteristics can not be sufficient. In these situations, some polishing and some machining processes can be applied. In this case, product that is produced with metal casting methods is called as near-net shaped product.
Disadvantages of metal casting methods;
- Environmental problems are the most serious downside of metal casting methods. Because of the very high temperatures, lots of energy to melt tons of metals are consumed. Also very hazardous gases are released to atmosphere because of molten metals. These conditions are generally harmful for workforce.
- In some metal casting processes, poor surface characteristics are achieved. After that, some machining operations can be required to obtain optimum surface characteristics.
- Mechanical properties of produced product from metal casting methods can be affected in bad wayi because of possible porosity formation during the solidification.
These are the general properties of metal casting methods. Do not forget to leave your comments and questions about metal casting methods and their characteristics below.
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