Metal Casting Process: the Complete Guide

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.  Thus, we brought you this guide to the metal casting process. We will explain each of the metal casting processes.

What is Metal Casting

Metal Casting
Metal Casting

Metal casting is a contemporary technique with a long history. The metal casting process makes the metal parts by pouring molten metal into a mold cavity, where it cools before being retrieved from the mold. Metal casting is one of history’s oldest and most impactful industrial processes.

Many metal things in our daily life are the perfect example of metal casting, including car parts, railway wheels, lamp poles, school bus pedals, and much more. Furthermore, metal casting foundries use metal recycling as a cost-effective supply of raw material, lowering the amount of scrap metal that ends up 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 of 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. Metal ingots are made similar to loaf pans, with the metal put within and allowed 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 maintainable when extending beyond the casting, and you keep it in place by core prints, suspending the core between two banks like a bridge.

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, an added cost. If a glossy and smooth finish is needed, choosing a casting process with a more refined finish may minimize machining expenses.

Types of Metal casting method

There are thousands of metal shapers available in this world. Depending on the complexity of the metal structures and design, the metal casting method comes to this manufacturing technology. In the following, we will discuss different types of metal casting methods.

Reusable molds

A reusable metal mold utilization is the most typical method of filling the mold via gravity; however, You can also utilize the 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 process goes into the mold cavity, the gravity process begins by preheating the mold to 150–200 °C (300–400 °F) to smooth the metal flow and prevent thermal damage to the casting.

The reusable Mould Method practices following six methods depending on different mold types and casting methods.  

Permanent molds

Permanent mold composition has various excellent melting points than the metal used to fill them. Pour metal in a fluid state with no external pressure is the primary step to this casting process. Permanent cores must be simple enough to be removed from the completed casting and reused.

The molding process occasionally employs these molds are in the casting of iron and lower-temperature alloys. The most frequent industrial workflow uses turntables rather than assembly lines. As each mold goes through the next station, individual procedures such as coating the mold, installing the cores, closing the mold, pouring, opening the mold, and ejecting the casting.

Semi-permanent molds

The main difference between semi-permanent mold casting and permanent mold casting is that the cores utilized in the casting process may be replaceable sand cores. Sand cores allow for more complicated core forms since they do not need to be recovered 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

By simply covering the inside of the mold with a bit of metal and forming a metal “skin,” this colorfully termed casting process makes hollow castings without 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 feeds a water-cooled mold that it rotates at high speed around its central axis as liquid metal into its inaccurate 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, vacuums, mechanical, or centrifugal forces are all employed. These techniques allow foundries to accurately regulate the pace at which a mold fills: gravity always exerts the same strength, but manufactured forces can vary.

Die casting

Die casting machines are made up of a basin containing molten metal, a two-plate metallic mold or die, and an injection system that draws the material and forces it into the die 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 industrial process: the first evidence of clay casting comes from China during the Shang Dynasty (c. 1600 to 1046 BC).

It’s no surprise that this method is still widely applicable: sand is inexpensive, abundant, malleable, and heat resistant.

This process shakes out the sand cores are simple to remove, as they may using a vibrating table. 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 joints the mold’s “shells” together and 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 must carefully evaluate the pattern’s demands at each stage of the casting process, including draft requirements, parting line locations, gates, risers, and cores.

The lost wax, investment, or precision-casting technique is a sand-casting alternative that can work with a wide range of metals, including high-melting-point ferrous alloys, while avoiding some of the patternmaking issues with 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 the design of foamed polystyrene.

This process can make the foamed pattern complete with a gate and runner system and the elimination of draft allowance.

And it sometimes removes the design before filling; however, with some foams, you can omit some of the design in situ in the mold to vaporize when it quickly puts in the hot metal.

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 critical in producing industrial parts, where accurate calculations are mandatory to ensure that pieces fit 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 it to remove them 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.

Alternatively, it makes a two-piece, non-destructible metal mold, which may cast identical components for industrial applications over and repeatedly

Melting and Pouring Molten Metal

After it heats the metal, they pour it into the mold hole and allowed it to harden. And, after the casting has formed, the shakeout process occurs. At this moment, the molds vibration occurs to remove sand from the casting.

Because of its efficient and smooth functioning, equipment like our Two-Mass Shakeouts maintains manufacturing output high in industrial applications.

Typically, it collects the removed sand, cooled, and recycled for use in subsequent castings. The VIBRA-DRUM® Sand Casting Conditioner helps to enhance the process of separating sand from castings by eliminating and chilling sand and castings, as well as draining moisture, all while preventing casting 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 fettled 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. In general, it casts the ferrous metals using disposable molds, whereas non-ferrous metals will have a larger selection of options, though even this simple rule has exceptions.

Going into the process with a comprehensive grasp of the project’s requirements will aid in selecting the optimal casting technique. 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 all of these questions ahead of time can aid a wise designer in better understanding and guiding their product through the casting process, allowing them to select the best and least-cost method for the task.

Summery

Almost every mechanical equipment we use today, from vehicles to washing machines, they all use metal casting process for metal pieces.

The metal casting technology can reach the accuracy and tolerances through the computerized automated design process and current means for making complex cores and molds distinguish today’s cast metal goods from those created even 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.

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