Metal casting is a manufacturing process that dates back to ancient times.
It involves pouring molten metal into a mold to create a desired shape.
Today, metal casting is used in a variety of industries, from automotive to jewelry making.
A complete guide to metal casting is an essential resource for anyone interested in learning about the process.
This guide covers everything from the basics of metal casting to the different types of casting processes, including sand casting, lost wax casting, and die casting.
It also includes information on the metallurgy of different metals and techniques for designing and creating molds.
Whether you are a hobbyist or a professional, a complete guide to metal casting can help you improve your skills and create high-quality castings.
With the right knowledge and tools, you can produce complex metal parts and objects that are both functional and beautiful.
The investment casting process
Investment casting is a process that involves several steps, including metal die construction, wax pattern production, ceramic mold creation, pouring, solidification, shakeout, and cleanup.
1. Metal die construction
In investment casting, the wax pattern and ceramic mold used in the process are eliminated, requiring a new wax pattern for each casting.
This makes a mold or dies necessary to manufacture the wax patterns, except when producing a small volume of artistic work or original jewelry.
The careful calculation is required to determine the size of the master die, taking into account the anticipated shrinkage of the wax pattern, the ceramic material invested in it, and the metal casting itself.
2. Wax pattern production
For each casting, a new wax pattern is required, resulting in the same number of wax patterns as castings to be produced.
Hot wax is injected into the mold or die and left to solidify. Cores may be necessary to form any internal features.
The outcome is a precise replica of the part to be created, resembling the die-casting process, but using wax rather than molten metal.
3. Mold creation
The wax mold is equipped with a gating system, including sprue, runner bars, and risers.
In the case of smaller castings, multiple wax patterns are joined to form a tree-like structure with a central wax gating system.
A pouring cup is typically attached to the end of the runner bars to facilitate the introduction of molten metal into the mold.
Next, the assembled “pattern tree” is immersed in a slurry made of fine-grained silica, and it is repeatedly dipped in the slurry until the ceramic coating reaches the desired thickness.
The thickness of the ceramic shell is determined by the size and weight of the part being cast, as well as the pouring temperature of the metal being cast.
The average wall thickness is around 0.375 inches (9.525 mm). After the ceramic coating is dried and hardened, it forms a shell around the patterns and gating system.
To eliminate the wax pattern, the solidified ceramic mold is inverted and placed in an oven.
The mold is heated until the wax melts and flows away, resulting in a hollow ceramic shell.
4. Pouring
The ceramic mold is subjected to high temperatures ranging from 1000°F to 2000°F (550°C to 1100°C) in order to further reinforce its strength, eliminate any remaining wax or impurities, and evaporate moisture from the mold material.
Once the mold is properly heated, molten metal is poured into it while it’s still hot.
The liquid metal enters the pouring cup and flows through the central gating system, filling each mold cavity on the pattern tree.
The pre-heated mold allows for an easy flow of metal through even thin and detailed sections, resulting in improved dimensional accuracy.
Cooling and shrinking of the mold and casting occur simultaneously, producing a high-quality casting.
5. Cooling
The cooling and solidification of the metal occur after the mold has been filled.
The duration required for the mold to cool and solidify depends on the type of material that has been cast and the thickness of the casting.
6. Shakeout
After the metal casting has solidified, the ceramic molds are destroyed to extract the castings.
This can be done either manually or with water jets.
The individual castings are then separated from their gating system tree using methods such as manual impact, sawing, cutting, burning, or by using liquid nitrogen to cold break them.
7. Finishing
To ensure a smooth finish and eliminate any imperfections, finishing operations such as grinding or sandblasting are often used on the castings, especially at the gates.
Heat treatment may also be applied to harden the final part, depending on the metal used for casting.
When to use investment casting
Investment casting is a costly process due to its complexity and labor requirements, but it offers several benefits.
It can be used with almost any metal and is suitable for producing small to medium-sized parts weighing up to 75 lbs.
The investment casting process allows for the creation of complex parts with excellent surface finishes.
Additionally, it eliminates the need for taper, making it possible to produce parts with 90-degree angles without shrinkage allowances or additional machining.
Investment casting delivers parts with superior dimensional accuracy, and net-shape parts can be produced without secondary machining.
However, each unique casting run requires a new die to produce wax patterns, and tooling costs can range from $1000 to $10,000, depending on the complexity.
For high-volume orders, the time and labor saved by eliminating secondary machining justify the cost of new tooling.
However, for smaller casting runs, investment casting may not be cost-effective, typically requiring a run of 25 parts or more.
The investment casting process takes about seven days to go from a fresh wax pattern to complete casting.
Most of the time is taken up by creating and drying the ceramic shell mold. Some foundries have quick-dry capabilities to produce castings more quickly.
However, the time-intensive nature of investment casting not only affects cost but also leads to longer lead times due to limited equipment and production capacity in foundries.
Custom casting services
Casting services are available for a wide range of applications and industries, from small, one-of-a-kind pieces to large-scale production runs.
Custom casting services allow customers to order parts that are designed to their specific needs, with unique features and finishes.
Common types of custom casting services include investment casting, sand casting, and die casting.
Investment casting, also known as lost wax casting, is often used to produce complex parts with superior dimensional accuracy and excellent surface finishes.
Sand casting is ideal for larger parts and short production runs, while die casting is often used for the mass production of small, intricate parts.
Custom casting services can work with a variety of materials, including aluminum, brass, bronze, steel, and iron.
Additional services, such as heat treating and finishing operations, are also commonly available.
When working with a custom casting service, it is important to consider factors such as lead time, production capacity, and tooling costs.
Depending on the complexity of the part and the production volume, some casting processes may be more cost-effective than others.
Overall, custom casting services offer a wide range of options for producing high-quality parts to meet specific design requirements.
Foundry King: www.foundryking.com
Foundry King collaborates with clients to develop customized casting patterns and molding methods.
Contact us for a quote and learn how our casting services can meet your project needs.