Casting Production: Process Flow, Equipment, Principle and Characteristics

Casting production process

Casting production process

Casting production is a sophisticated multi-step process that encompasses the following critical stages:

1. Process Planning and Documentation: This initial phase involves creating a comprehensive production process plan and associated technical documents. Engineers develop detailed casting process drawings based on part specifications, production volume requirements, and target delivery dates. This stage is crucial for optimizing workflow efficiency and ensuring quality outcomes.

2. Material Preparation: This stage involves the meticulous selection and preparation of materials for various sub-processes:

• Melting: Carefully calculated quantities of base metals, alloying elements, and recycled materials are prepared.
• Molding: Sand mixtures with specific grain sizes, binders, and additives are formulated to achieve the desired mold properties.
• Core Making: Specialized sand mixtures and binders for cores are prepared.
• Equipment Readiness: Core boxes, sand boxes, patterns, and other tooling are inspected, cleaned, and prepared for use.

3. Molding and Core Making:

• Molds are created using advanced techniques such as green sand molding, no-bake molding, or investment casting, depending on the part complexity and production volume.
• Cores, when required, are manufactured using processes like cold box or hot box core making to create internal cavities or complex geometries in the casting.

4. Melting and Pouring:

• Metal is melted in furnaces (e.g., induction, cupola, or electric arc) under precisely controlled temperatures and compositions.
• Molten metal undergoes treatments such as degassing, modification, or inoculation to enhance its properties.
• The prepared melt is poured into molds using methods like gravity pouring, low-pressure casting, or centrifugal casting, depending on the alloy and part requirements.

5. Post-Casting Operations:

• Sand Disposal and Reclamation: Used sand is cooled, screened, and reconditioned for reuse, minimizing waste and environmental impact.
• Casting Inspection: Rigorous quality control measures are implemented, including visual inspection, dimensional verification, and non-destructive testing (e.g., X-ray, ultrasonic) to ensure castings meet specified standards.

See also:

• 14 Different Types of Casting Process

Casting manufacturing process

The casting process is a foundational metalworking technique that involves melting metal or alloy and pouring it into a mold for cooling and solidification. This versatile method enables the production of complex geometries and is widely used in various industries, from automotive to aerospace.

The production of high-quality castings is a multifaceted process that encompasses several critical steps:

1. Material preparation and selection
2. Mold and core fabrication
3. Melting and alloying
4. Pouring and solidification
5. Post-casting operations

Each stage requires precise control and expertise to ensure the final product meets stringent quality standards. Let’s examine these steps in detail:

1. Preparation of molding and core sand

The quality of molding sand is paramount, as it directly influences the casting’s surface finish, dimensional accuracy, and overall integrity. Modern foundries employ sophisticated sand preparation systems that precisely control moisture content, grain size distribution, and additives. For example, green sand molding typically uses a mixture of silica sand, bentonite clay, and water, while chemically bonded sand systems utilize synthetic resins for enhanced strength and thermal stability.

2. Modeling and mold making

Mold creation is a critical step that determines the casting’s final shape and surface quality. Advanced techniques such as 3D printing of sand molds and lost foam casting have revolutionized this process, allowing for greater design freedom and reduced lead times. For complex internal geometries, core making is essential. Cores are typically made from specially formulated sands that can withstand the heat of molten metal while maintaining dimensional stability.

3. Melting and alloying

The melting process is where metallurgical control begins. Modern foundries use various furnace types, including induction furnaces for precise temperature control and rapid melting of smaller batches, and cupola furnaces for high-volume cast iron production. Advanced spectrometric analysis ensures the molten metal meets exact compositional requirements. For cast iron platforms and machine tool castings, cupola furnaces remain popular due to their efficiency in handling large volumes and ability to maintain consistent iron chemistry.

4. Mold preparation and pouring

For large or high-precision castings like machine tool beds or workbenches, dry sand casting is often employed. This method involves drying the mold to remove moisture, enhancing dimensional stability and surface finish. The pouring process is critical and often automated in modern foundries to ensure consistent fill rates and minimize turbulence. Innovations like bottom-pouring ladles and computer-controlled pouring systems have significantly improved casting quality and reduced defects.

5. Cooling and solidification

Controlled cooling is essential for achieving desired microstructures and minimizing internal stresses. Techniques such as directional solidification and the use of chills can enhance mechanical properties in critical areas of the casting.

6. Cleaning and finishing

Post-casting operations include sand removal, cutting of risers and gates, and surface finishing. Advanced techniques like high-pressure water jetting and robotic grinding have improved efficiency and consistency in this stage. For machine tool castings, precision surface grinding is often required to achieve the necessary flatness and parallelism.

7. Heat treatment

Heat treatment is crucial for optimizing the casting’s mechanical properties and dimensional stability. For cast iron platforms and machine tool components, stress relief annealing is commonly performed to minimize distortion during subsequent machining operations. More complex heat treatments, such as normalizing or quench and temper processes, may be applied to achieve specific strength and toughness requirements.

The casting manufacturing process continues to evolve with advancements in simulation software, allowing for virtual optimization of gating and risering systems, prediction of solidification behavior, and identification of potential defects before physical production begins. This integration of digital tools with traditional foundry practices is key to producing high-quality, cost-effective castings for demanding applications in the machine tool industry and beyond.

Forming principle

Casting production is a metal forming technique that involves heating the metal to bring it to a fluid state and pouring it into a mold with a desired shape. The metal fills the mold cavity under the influence of gravity or external forces such as pressure, centrifugal force, or electromagnetic force, and then cools and solidifies into a casting or part.

 Fig. 1 casting process

The casting process usually involves turning a blank into a part.

However, some castings meet the necessary design accuracy and surface roughness requirements without the need for further cutting and can be used as parts directly.

Properties and composition of molding sand

1. Properties of molding sand

The key performance criteria for molding sand (including core sand) include strength, permeability, fire resistance, yield, fluidity, compactness, and the ability to resist collapse.

2. Composition of molding sand

Molding sand is made up of raw sand, binder, and additives.

The raw sand used in casting should be sea sand, river sand, or mountain sand with low mud content, uniform particle size, and a mixture of rounded and polygonal shapes.

Adhesives used in casting include clay (such as ordinary clay and bentonite), water glass sand, resin, synthetic oil, and vegetable oil, which are referred to as clay sand, water glass sand, resin sand, synthetic oil sand, and vegetable oil sand, respectively.

To enhance specific properties of the mold (core) sand, additives such as coal, sawdust, and pulp are sometimes added to the mold (core) sand.

The structure of molding sand is illustrated in Figure 2.

Fig. 2 Schematic diagram of molding sand structure

Casting process characteristics

Casting remains a fundamental method for producing component blanks, particularly for parts made from brittle metals or alloys (such as various cast irons and non-ferrous alloys) where it often represents the sole viable manufacturing process.

Compared to alternative manufacturing methods, casting offers several distinctive characteristics:

Versatility in material, size, and weight:

The casting process accommodates a diverse range of materials, including ferrous metals (cast iron, cast steel) and non-ferrous alloys (aluminum, copper, magnesium, titanium, zinc, and various specialty alloys).

Castings can span from miniature components weighing just a few grams to massive structures exceeding hundreds of tons.

Wall thicknesses in castings can range from as thin as 0.5 mm to approximately 1 meter, allowing for both intricate details and robust structures.

Casting lengths can vary from mere millimeters to upwards of ten meters, catering to a wide array of applications.

Ability to produce complex geometries:

Casting excels in creating parts with intricate shapes and internal cavities, such as engine blocks, pump housings, turbine blades, and complex impellers, which would be challenging or impossible to manufacture through other methods.

Near-net shape capabilities:

Modern casting techniques can produce parts very close to their final dimensions and geometry, significantly reducing material waste and subsequent machining operations. This near-net shape capability is particularly advantageous for complex or large components.

Raw material accessibility and cost-effectiveness:

Casting utilizes readily available raw materials, often including recycled metals, contributing to its cost-effectiveness. The relatively low tooling costs for many casting processes further enhance its economic viability, especially for low to medium production volumes.

Flexibility and high productivity:

Casting processes can be tailored to various production scales, from manual methods for small batches or prototypes to fully automated, high-volume production lines.

Advanced casting technologies, such as automated molding lines and robotic pouring systems, enable high productivity rates, making casting suitable for mass production of complex parts.

Furthermore, casting allows for the integration of multiple components into a single cast part, reducing assembly time and improving structural integrity. This consolidation of parts can lead to significant cost savings and performance improvements in the final product.

Analysis of common defects in casting

The casting process is complex and the quality of castings can be impacted by a multitude of factors.

Frequent occurrences of casting defects result from poor control of raw materials, inadequate process planning, improper production operations, and insufficient management systems.

The following is a list of common casting defects, along with their names, characteristics, and causes.

Defect name	features	Main causes
Stoma	There are smooth holes of different sizes inside or on the surface of the casting.	① The furnace charge is not dry or contains many oxides and impurities; ② Pouring tools or additives in front of the furnace are not dried; ③ Too much water is contained in the molding sand or too much water is brushed during mold lifting and trimming; ④ Insufficient core drying or blocked core vent; ⑤ The spring sand is too tight and the air permeability of molding sand is poor; ⑥ The pouring temperature is too low or the pouring speed is too fast.
Shrinkage cavity and porosity	The shrinkage holes are mostly distributed at the thick section of the casting, with irregular shape and rough inside.	① The structural design of the casting is unreasonable, for example, the wall thickness difference is too large, and no riser or cold iron is placed at the thick wall; ② The position of pouring system and riser is wrong; ③ Pouring temperature is too high; ④ The chemical composition of the alloy is unqualified, the shrinkage rate is too large, and the riser is too small or too few.
Sand holes	There are holes filled with molding sand inside or on the surface of the casting.	① The strength of the molding sand is too low or the compactness of the sand mold and the core is not enough, so the molding sand is flushed into the mold cavity by the molten metal; ② The sand mold is partially damaged when the box is closed; ③ The pouring system is unreasonable, the direction of the ingate is wrong, and the sand mold is damaged by the molten metal; ④ The loose sand in the mold cavity or gate is not cleaned up when the box is closed.
Sticky sand	The surface of the casting is rough with a layer of sand.	① The fire resistance of raw sand is low or the particle size is too large; ② The fire resistance of molding sand decreases when the mud content is too high; ③ Pouring temperature is too high; ④ The content of pulverized coal in the molding sand is too small in the process of green casting; ⑤ The dry type is not painted obliquely or the coating is too thin.
Sand inclusion	A layer of molding sand is sandwiched between the metal sheet protrusion and the coupling part.	① The hot wet tensile strength of the molding sand is low, and the surface of the mold cavity is heated and baked to expand and crack; ② The local compactness of the sand mold is too high, the water is too much, and the surface of the mold cavity is cracked after the water is dried ten times; ③ Improper selection of pouring position causes the cavity surface to expand and crack due to high temperature molten iron baking for a long time; ④ The pouring temperature is too high and the pouring speed is too slow.
Wrong type	The casting has relative displacement along the parting surface.	① The upper mold half and the lower mold half of the pattern are not aligned; ② When the box is closed, the upper and lower sand boxes are misaligned; ③ The upper and lower sand boxes are not clamped or the upper box is not sufficiently pressed, and the wrong box is generated during pouring.
Cold barrier	There are gaps or pits on the casting where the cards are completely fused, and the joints are smooth.	① The pouring temperature is too low and the alloy fluidity is poor; ② The pouring speed is too slow or the flow is interrupted during pouring; ③ The position of the pouring system is improper or the cross-sectional area of the ingate is too small; ④ The casting wall is too thin; ⑤ The height of sprue (including sprue cup) is insufficient; ⑥ When pouring, the amount of metal is insufficient and the cavity is not full.
Insufficient pouring	The casting is not fully filled.
Crackle	The casting is cracked and there is oxide film on the metal surface at the crack.	① The casting structure design is unreasonable, the wall thickness difference is too large, and the cooling is uneven; ② The retreat of sand mold and core is poor, or the spring sand is too tight; ③ Premature sand falling; ④ Improper gate position leads to uneven shrinkage of all parts of the casting.

Common casting defects and their preventive measures

Casting – Pouring of Molten Metal

In production casting, adhering to the principle of high-temperature tapping and low-temperature pouring is crucial for achieving optimal results.

Elevating the tapping temperature of molten metal facilitates complete dissolution of inclusions and promotes slag flotation, enhancing the effectiveness of cleaning and degassing processes. This approach significantly reduces the probability of slag inclusions and porosity defects in the final castings.

Conversely, maintaining a lower pouring temperature offers several advantages:

1. Decreased gas solubility in the melt
2. Reduced liquid shrinkage
3. Minimized surface reactions between high-temperature molten metal and the mold cavity

These benefits help prevent defects such as porosity, sand adhesion, and shrinkage cavities.

Therefore, the optimal strategy is to maintain the lowest possible pouring temperature that still ensures complete mold cavity filling.

The pouring process involves transferring molten metal from the ladle into the mold. Improper execution can lead to various casting defects, including:

• Incomplete filling
• Cold shuts
• Gas porosity
• Shrinkage cavities
• Slag inclusions

Moreover, inadequate safety measures during pouring can pose significant risks of personal injury.

To ensure high-quality castings, enhance productivity, and maintain safe operations, strictly adhere to the following guidelines during the pouring process:

1. Thoroughly dry all equipment before use, including:

• Ladles
• Pouring tools
• Inoculants
• Spheroidizing agents used in furnace pretreatment

2. Enforce proper personal protective equipment (PPE) for pouring personnel:

• Appropriate work clothing
• Protective eyewear
  Ensure the working area is free from obstacles.

3. Avoid overfilling the pouring ladle to prevent spillage and potential injuries during transport and pouring operations.

4. Optimize pouring speed using the “slow-fast-slow” principle:

• Begin slowly to align the gate and reduce molten metal impact on the sand mold
• Increase speed to prevent cold shuts
• Reduce speed again towards the end of the pour
  This approach facilitates proper gas evacuation and ensures consistent filling.

5. For components prone to high liquid and solidification shrinkage (e.g., medium and large steel parts), implement secondary feeding through the gate or riser after initial pouring is complete.

6. Ignite any gases emitted from the casting mold during pouring to:

• Prevent gas porosity defects
• Minimize health hazards and air pollution caused by incomplete gas combustion

8 basic steps of sand casting

Sand casting technology is a method of casting that uses sand as the primary material for mold preparation.

Sand casting is a tried and true casting method that has been used for centuries.

Despite its age, sand casting remains the most widely used casting method, particularly for single pieces or small batches, due to its versatility in accommodating a wide range of shapes, sizes, complexities, and alloys, as well as its short production cycle and low cost.

The traditional sand casting process consists of the following steps: preparing the sand, mold making, core making, molding, pouring, removing the sand, grinding, and inspection.

1. Sand mixing stage

The molding sand and core sand are prepared for the molding process.

Typically, a sand mixer is utilized to mix the used sand with the proper amount of clay.

2. Mold making stage

Molds and core boxes are created based on the part drawings. Single pieces are typically made using wooden molds, while mass production may utilize plastic or metal molds, also known as iron or steel molds.

For high volume production, molds can be made using templates.

With the use of engraving machines, the mold-making process has become much quicker, reducing the production cycle to 2 to 10 days.

3. Molding (core making) stage

The molding process involves forming the mold cavity of the casting using molding sand. Core making involves creating the internal shape of the casting, and mold matching involves placing the core into the mold cavity and sealing it with the upper and lower sand boxes.

Molding is a crucial step in the casting process.

4. Melting stage

To produce the desired metal composition, the chemical composition is carefully prepared. An appropriate melting furnace is selected to melt the alloy materials and produce a qualified liquid metal with the correct composition and temperature.

Traditionally, smelting was performed using a cupola furnace, but due to environmental concerns, this method has largely been replaced by the use of electric furnaces.

5. Pouring stage

The molten metal produced in the electric furnace is transferred to the mold using a ladle.

It is important to control the pouring speed to ensure that the entire mold cavity is filled with the molten metal.

Please note that pouring molten metal can be hazardous, and proper safety precautions should always be taken.

6. Cleaning stage

Once the molten metal has solidified after pouring, the gate is removed using a hammer and the sand is shaken off the casting. The casting is then sandblasted using a sand blasting machine to achieve a clean surface.

Casting blanks with less stringent requirements can typically be delivered after inspection.

7. Casting processing

Some castings with special requirements or those that do not meet the required specifications may require additional processing.

This is typically performed using a grinding wheel or grinder to remove any burrs and achieve a smoother surface on the casting.

8. Casting inspection

Inspections are usually conducted during the cleaning or processing stage and any unqualified castings are identified at this time.

However, some castings may have specific requirements and require additional inspection. For example, a casting may need to be tested by inserting a 5cm shaft into its central hole to ensure it meets the required specifications.

Conclusion:

After completing the above 8 steps, the casting process is essentially complete. However, for castings that require high precision, additional machining may be necessary.

Note that machining is outside the scope of this description.

As casting technology continues to advance, traditional sand casting is being improved or replaced by other methods.

Innovation is an eternal theme and a fundamental quality that a foundry must possess in order to succeed.

What equipment is needed for sand casting?

Sand casting is the most common and traditional casting method used in the foundry industry, and is often the preferred choice for small foundry manufacturers when starting out.

What are the basic equipment and tools required for the sand casting process?

The sand casting process requires the following equipment and tools, in accordance with the production process sequence: sand mixing equipment, mold making equipment, core making equipment, molding equipment, melting equipment, pouring equipment, cleaning equipment, and casting processing equipment.

1. Sand mixing equipment

The equipment required for this step is a sand mixer, and the tools required are a shovel and a sieve.

Sand mold casting is dependent on sand, which serves as a special molding material.

The molding sand can be recycled, but it must be sieved before reuse.

The sand must be fine and evenly mixed using a sand mixer.

A small sand mixer can cost as little as 2,000 units.

2. Mold manufacturing equipment

Equipment needed: Engraving machine.

Materials required: Wood mold, Plastic mold (special plastic plate), Metal mold (metal block).

The mold should be created based on the customer’s provided samples or drawings.

The quality of the mold directly impacts the precision of the cast’s shape.

Previously, wood molds were typically crafted by carpenters. However, with the advancement of engraving machines, they are now used to create wood, plastic, and metal molds.

A basic engraving machine that can engrave both wood and plastic molds can be purchased for a few thousand yuan. However, for metal engraving, you may need an engraving machine that costs tens of thousands to hundreds of thousands of yuan.

The price of the engraving machine is primarily determined by its material capabilities, accuracy, and level of automation.

3. Core making equipment

Equipment required: Oven. Materials required: Coated sand and thick gloves.

The process of creating internal cavities in castings often involves making a core, and there are several methods for doing so.

The two most common methods are:

• First, the mold is made (usually together with the core mold in the first step) and then manually filled with a mixture of molding soil and sand (referred to as core beating).
• Second, the aluminum core box is filled with coated sand and fired in an oven. The oven can be either a dedicated casting oven or a self-made one, which can be constructed by welding an iron sheet and baking it on a furnace.

Note that the core box becomes very hot during the firing process, so it’s important to wear gloves for protection.

I recommend the second method, as the core baked with coated sand does not require firing during pouring and results in a relatively clean inner surface of the casting.

4. Modeling equipment

Equipment Required: Molding Machine Tools Needed: Sandbox, Bottom Plate, Scraper, Shovel, Dip Pen, V-Shaped Iron Sheet for Gate Opening, Brush, Air Hole Needle, etc.

Molding is the most demanding and crucial step in sand casting, possessing the most distinctive industrial characteristics. In the past, molding was performed entirely by hand, but today, most molding workers use molding machines, significantly reducing the labor intensity.

There are various tools utilized in molding, including a sandbox for expansion, a bottom plate, scraper, shovel, dip pen, a V-shaped iron sheet for gate opening, brush, air hole needle, among others. These tools are mostly small and customized by the molding workers to suit their personal preferences.

In conclusion, producing a high-quality mold is the key to success in this process.

5. Melting equipment

Equipment Required: Electric Furnace and Transformer Materials Needed: Iron, Aluminum, Copper, and other Raw Materials, Tin, and Iron (Batching).

The primary goal of this step is to melt iron into molten iron. The challenge lies in mixing and controlling the temperature of the molten iron.

Due to the ban on cupola, most large and small factories now use electric furnaces as their melting equipment. Electric furnaces come in various sizes and have a wide price range. The smaller ones, with a capacity of 200 kg, cost between 10,000 to 20,000, while the larger ones can reach hundreds of thousands to millions.

In addition to the electric furnace, a special transformer is also required and must be purchased separately. The use of the transformer must be approved by the local power bureau, and the application costs vary.

Setting up a small foundry can cost several hundred thousand at minimum, with half of the cost being attributed to the application fee.

6. Pouring equipment

Equipment Required: Molten Iron Ladle and Aerial Crane

The molten iron produced in the electric furnace can be divided into large and small quantities. It is first poured into a large container and then transferred to smaller containers for easier handling.

Workers carry the small containers and pour the molten iron into the completed mold. This step involves high risks, and workers must take necessary protective measures.

In large factories, large castings are poured using large equipment such as aerial cranes. This helps to ensure safety and efficiency in the casting process.

7. Cleaning equipment

Equipment Required: Sand Blasting Machine

After the casting has cooled following the pouring process, workers remove it from the mold. They remove most of the soil from the surface and break off the gate using a hammer.

The next step is to place the casting into a sand blasting machine for sand blasting. This process helps to clean and smooth the surface of the casting.

8. Casting processing

Common Equipment: Grinding Wheel, Polishing Machine, Cutting Machine, and Lathe.

Casting processing falls under the category of machining. Most general machining equipment can be used, but it goes beyond the scope of casting.

Typically, foundries possess the essential tools such as grinding wheels, polishing machines, cutting machines, and it is advantageous to have a lathe as well. These tools are sufficient for basic casting processing.

Summary

All work must be coordinated with each other. Small foundries that are just starting out may not have all the casting processes and may not have the capability to produce and process their own molds.

To compensate for this, they can collaborate with specialized mold makers and machinists and only be responsible for casting the blanks.

Casting is a traditional and admirable industry. Despite facing bans due to environmental protection, many small traditional foundries have been engaged in casting their entire lives and have either been unemployed or continued their work as professionals.

I would like to give a salute to the older generation of foundry workers!