The metal casting process is one of the essential technology in this manufacturing world. Metal casting builds most of the metal structures of the machines and equipment.
What is Metal Casting
Metal casting is a contemporary technique with a long history. The metal casting process creates metal parts by pouring molten metal into a mold cavity, where it cools before we retrieve it from the mold. Metal casting is one of history’s oldest and most impactful industrial processes.
Many metal items we use every day show how metal casting works. Examples include car parts, railway wheels, lamp poles, and school bus pedals. Metal casting foundries also recycle metal. This saves money on raw materials and reduces scrap metal in landfills.
Metal Casting Terminology
The term “metal casting” is often used in metal shops and industries. You can better understand the metal casting process if you realize the common language utilized in this method. It would help if you first mastered all this terminology to grasp metal casting better.
Casting Molding
A mold is a cavity in a material that accepts liquid metal and generates a cooled product in that cavity’s structure. Molds don’t have to be complex. Manufacturers make metal ingots like loaf pans by putting the metal within and allowing it to cool.
Cope and drag
The cope is the upper half of the mold in horizontal molding, while the drag is the bottom half.
Swing Ram
The swing is the top half of the mold in vertical molding, whereas the ram is the back half.
Molding Cores
Typical construction of a core is essential when you require a mold to have interior voids or holes. The inside space formation is like these cores. The cores are easy to maintain when they extend beyond the casting. You hold them in place with core prints, like a bridge, by suspending the core between two banks.
Dimensional Tolerance
Dimensional tolerance is a key consideration when selecting a casting procedure. It refers to the amount of variance in the finished product’s size that is permitted.
Surface Finishing
Surface finishing is another factor to consider. How granular, bumpy, or rough may the casting’s surface be?
It would be best if you did not make a wedding ring of the same material as a cast-iron pan. In this case, you use the machine to achieve very smooth metal surfaces, which adds cost. If you need a glossy and smooth finish, choosing a casting process with a more refined finish may minimize machining expenses.
Types of Metal Casting Methods
There are thousands of metal shapers available in the world. The metal casting method is a key part of manufacturing. It depends on how complex the metal structures and designs are. In the following, we will discuss different types of metal casting methods.
Reusable molds
A reusable metal mold is the most typical method of filling the mold via gravity, but you can also use gas pressure or a vacuum. Hollow castings are applicable for using a version of the gravity casting method known as slush casting.
Aluminum alloys, magnesium, and copper alloys are common casting metals. Tin, lead, and zinc alloys and iron and steel alloys are also suitable for graphite molds.
When the metal injection starts, the gravity process kicks in. First, heat the mold to 150–200 °C (300–400 °F). This helps smooth the metal flow and protects the casting from thermal damage.
The reusable Mould Method uses six techniques based on mold types and casting methods.
Permanent molds
Permanent mold composition has various excellent melting points compared to the metal used to fill them. Pouring metal in a fluid state with no external pressure is the primary step in this casting process. Workers must design permanent cores to be simple enough for removal from the completed casting and reuse.
The molding process sometimes uses these molds for casting iron and low-temperature alloys. The most frequent industrial workflow uses turntables rather than assembly lines.
Each mold moves to the next station. Here are the steps involved:
Coat the mold.
Install the cores.
Close the mold.
Pour the material.
Open the mold.
Eject the casting.
Semi-permanent molds
Semi-permanent mold casting and permanent mold casting differ mainly in their use of cores. In semi-permanent mold casting, the cores can be replaceable sand cores. Sand cores enable more complicated core forms because they do not require recovery intact from the final casting.
If a hole is left in the casting to extract the cores, they can be “shaken out” on a vibrating table and drained like sand through an hourglass. Only the part cast against the metal mold has the tolerance, density, and aesthetic benefits of permanent mold casting.
Slush casting
This casting process creates hollow pieces by covering the mold’s inside with metal. This forms a metal “skin” and eliminates the need for cores. Depending on how rapidly the metal or other material sets, there are several approaches to slush casting.
One approach involves pouring tiny volumes of liquid into a mold and rotating it to coat the interior with metal. In another, the founder can fill the mold and then pour the surplus material out when a set amount of time has passed. Metals such as zinc, aluminum, and pewter are routinely slush cast.
Centrifugal casting
This casting process uses a water-cooled mold. It spins quickly around its central axis while liquid metal is poured in. This method is known as centrifugal casting. The liquid metal is pulled in an equal layer across the mold’s surface by centrifugal force. The final casting must have even geometries around the spin axis for this approach to operate. As a result, this casting method is suitable for molds that are generally cylindrical or circular, such as tubes or rings.
Pressure casting
Other than gravity, pressure casting technologies regulate the flow of metal into a permanent mold. In pressure casting, air or gas, vacuum, mechanical, or centrifugal forces are all employed. These techniques help foundries control how fast a mold fills. Gravity pulls with the same strength, but other forces can change.
Die casting
Die casting machines consist of three main parts: a basin for molten metal, a two-plate mold, and an injection system. The injection system pulls the material and pushes it into the mold under pressure.
It uses an open mold to start the die casting process. Nozzles spray a lubricant into the mold to keep the item from sticking. This process seals the mold’s two sides together and injects the closed mold with a pressure nozzle. Before the die opens, it gives the fresh casting a chance to cool. The new casting is pushed out of the die by ejector pins, and the process begins all over again.
Expendable molds
When it comes to casting ferrous metals, disposable mold technologies are the apparent victors. They are less expensive since they do not need to withstand high temperatures.
Sand casting
The most prevalent process for metal casting is sand casting. It’s a three-thousand-year-old process. The earliest proof of clay casting appears in China during the Shang Dynasty (c. 1600 to 1046 BC).
This method is still popular for good reasons: sand is cheap, easy to find, flexible, and can withstand heat.
This process shakes out the sand cores, which are easy to remove because a vibrating table can remove them. Runners and gates, which guide the metal into the mold cavity, are either hand-cut by an expert molder or included in the design.
Shell molding
Shell molding is a sand casting technique that allows for tighter dimensional tolerances. It’s comparable to sand molding, with the exception that it blends the sand with a resin.
Over each side of the hot metal molding pattern, it pours a combination of sand and resin. This mixture melts into a shell and cools. It joins the mold’s “shells” together and is frequently held by a flask of sand.
These shells produce a highly accurate mold because the resin provides extra support to the inner surfaces.
Investment casting (lost-wax)
Sand casting is by far the most popular method of metal casting, but it has one drawback that makes it unsuitable for some applications.
In this process, you must remove the sand casting patterns from the molds they generate, which may be time-consuming.
Pattern makers need to assess the pattern’s requirements at every step of casting. This includes checking draft needs, parting line positions, gates, risers, and cores.
The lost wax, investment, or precision-casting technique offers a sand-casting alternative. It works with many metals, including high-melting-point ferrous alloys. This method also helps avoid some pattern-making problems found in sand casting.
Full mold or foam
This casting process uses a mixture of sand and investment cast methods in the whole mold or foam casting process. However, it makes use of foamed polystyrene in the design.
This process can make the foamed pattern complete with a gate and runner system and the elimination of draft allowances.
It may remove the design before filling. But for some foams, you can leave part of the design in the mold. This helps it vaporize quickly when hot metal is added.
Metal Casting Process
Patternmaking – A pattern is a scale model of the casting’s exterior. Wood, metal, plastic, and plaster are common materials for designs. Patternmaking is key to making industrial parts. Accurate calculations are essential for ensuring that pieces fit together and function correctly.
Core making
If casting is hollow, it uses an extra piece of sand or metal (referred to as a core) to sculpt the internal form. Cores are generally robust but collapsible, allowing them to be removed from the final casting with ease.
Molding
Imagine yourself going on the beach toward the water to envision the metal casting process thus far. Examine a footprint you’ve left in the moist sand.
The core would be your foot, and the sand imprint would be a cast of your foot. Molding is a multi-step procedure that uses molding sand to create a cast around the design.
A flask is a frame that holds a mold during casting. Greensand, also popular as molding sand, not around the design in the flask. Metal sand casting is the term for this process. It may erase the design after compacting the sand tightly, but the cast will remain.
It also creates a two-piece, non-destructible metal mold. This mold can repeatedly cast identical parts for industrial use.
Melting and pouring molten metal
After it heats the metal, they pour it into the mold hole and allow it to harden. And, after the casting has formed, the shakeout process occurs. At this moment, the mold vibration occurs to remove sand from the casting.
Our Two-Mass Shakeouts operate with precision and effectiveness. This helps to keep manufacturing output high in industrial settings.
Typically, it collects the removed sand, cools, and recycles it for use in subsequent castings. The VIBRA-DRUM® Sand Casting Conditioner improves sand separation from castings. It chills sand and castings, drains moisture, and keeps castings safe from damage. The result is a clean metal casting and sand that is ready for restoration.
Cleaning
This stage takes the cast metal piece from the mold and fettles it in this final stage. After that, it cleans the object of any molding material and eliminates the rough edges during the fettling.
Comparing casting processes
It is beneficial to consult with manufacturers to determine the most cost-effective manner to cast a project. It usually casts ferrous metals with disposable molds. Non-ferrous metals have more options, but there are exceptions to this rule.
Understanding the project’s needs will help you choose the best casting method. Is it necessary for the design to be exact in size? How thin should the walls be? What size and weight will the finished casting be? What about the finish of the surface?
Knowing the answers to these questions can help a smart designer. It lets them understand and guide their product during the casting process. This way, they can choose the best and most cost-effective method for the job.
Summery
Most mechanical equipment we use today, like vehicles and washing machines, relies on metal casting for its metal parts.
Metal casting technology today achieves high accuracy and tight tolerances. This is thanks to computerized design and modern methods for making complex cores and molds. As a result, today’s cast metal products are very different from those made 100 years ago. Metal casting in the modern era is an example of innovation at work.
As a result, we believe that this article will serve as the most comprehensive reference on metal casting methods for you.