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Since investment casting involves a complex process, there is no shortage of opportunities for error. When certain undesirable irregularities in the metal casting process cause defects, the fabricator can decide whether these defects are tolerable, repairable or need to be eliminated entirely. However, the nature of the defect must be clearly understood before making a decision. In addition, the location, appearance, size and shape of the defect must also be considered. These investment casting defects fall into the following categories:
Hot tear or shrinkage crack
Hot tear defects can occur when the ceramic shell mold restricts the shrinkage of the molten metal during solidification or cooling. This usually looks like a jagged crack with an irregular path. Manufacturers often modify investment casting designs to address this issue.
Inclusions
These are classified as negative defects and appear as small, round, angular or irregular pits and are usually due to foreign non-metallic particles within the casting. They can also be surface cavities or depressions of various shapes and sizes with traces of refractory material. One possible cause of inclusions could be cracks in the wax pattern allowing ceramic fragments to enter the cavity.
Misrun
Poor pouring is a negative defect that can occur when the mold cavity is not completely filled with molten metal. This usually happens when the shell is too cold, the metal is too cold, or the filling rate is too slow.
porosity or gas
This can manifest itself as air pockets forming within the investment casting during cooling. Since liquid materials tend to contain large amounts of dissolved gas, these materials outgas as they solidify.
Cast aluminum is something you've probably heard of before. But do you really know what this metal alloy is actually made of? In this article, we'll learn about cast aluminum alloys, explaining exactly what it is, why it's used, and other important information. You'll never wonder what cast aluminum is again.
This type of die-cast aluminum is commonly used to produce many types of automotive parts. Additionally, it is used to create many other products that people use every day. Even furniture can be crafted using this special type of metal! Cookware is also commonly made of cast aluminum because it is so strong, and patio furniture is another place where cast aluminum is easy to find. It is a special type of metal alloy that must be so-called cast before it can be used. This process increases the durability and strength of the material, and makes it more efficient to use. Casting can be done in several different ways, including through sand casting, die casting, and mold casting. Die casting is generally the most popular casting method.
When this die-cast material is used in vehicle interiors, it is also used with many other components to enable specific operations. Using this material type, torque converter stators, stator plate thrust washers, radiator tanks and many other components important to vehicle operation can be manufactured. The boat also contains components made of cast aluminum material.
Why Cast Aluminum?
Cast Aluminum Radiators As you can see, cast aluminum is used in many different items that most of us use on a daily basis. Why is it so popular and why are so many people using it? It's popular for a reason.
As mentioned, it's very strong and durable. It may not be as strong as cast iron, however, it comes very close and is certainly one metal you can rely on when you need it most. This is one of the reasons people choose this alloy, but they also like the cost. It is very cost effective compared to other metals. Its purchase cost is about half that of other types of metals and aluminum alloys.
This alloy metal has many different uses in our everyday life. It is a very strong metal and has many advantages over other metals in the market. Definitely worth a look when you're in need of good value for your money. This is especially true when it comes to the parts inside the car. You want your car to always perform at its best and last for as many years as possible. When working with die castings, you can be sure that this will happen. Die casting parts will never let you down, fully meet your project needs.
Sand casting remains one of the most cost-effective, widely used and efficient casting solutions, helping to reduce lead times and costs.
What is sand casting?
Sand casting is a metal casting manufacturing technique that involves using sand to create molds. This process is used to manufacture metal products of various shapes and sizes.
How does sand casting work?
The sand casting molding process consists of several steps. The sand casting process begins with the creation of a mold pattern and gating system. Each pattern requires a new mold designed to match the exact size and shape of the target part. The setup also requires a two-part casting flask called the cap and drag.
The mold model is placed in the sand and the gating system is provided with a series of tunnels and a pouring cup. After the sand is filled around the model, the model is removed, leaving the mold cavity.
The metal is then heated to high temperatures, turning the metal into a liquid state. The temperature required to melt the metal depends on the alloy. Some metals take longer to heat up.
The molten metal is poured into the mold cavity. After the metal is poured into the mold, the metal begins to cool and solidify. To remove the part, the sand mold is separated along the parting line. During this process, the mold cavity is destroyed. However, mold models are usually reusable.
History of Sand Casting
Casting metal from sand is the oldest method of metal casting and one of the most versatile. The earliest recorded use of sand casting is around 1540.
It wasn't until the high demand for cars and machines that the sand casting process became fully automated. Increased demand has also led to advancements in sand casting technology, including increased molding speeds and increased mold strength.
The following materials can be used in sand castings:
Stainless Steel/Duplex 2205, 2507 and Zeron
alloy steel
Gray Iron, Ductile Iron and White Iron
aluminum
Brass, Bronze and Copper
magnesium
Stainless steel investment casting, also known as stainless steel lost wax casting, is a precision casting process for stainless steel alloys (304, 316, 17-4PH, 2205, etc.), which can produce stainless steel castings with high precision and complex details and similar manufacturing processes such as stainless steel sand casting compared to.
In stainless steel investment casting, the wax pattern is injected and coated by dipping in a refractory slurry. Once the refractory coating has hardened, this dipping process is repeated several times to increase the coating thickness and its strength. Once the final coating has hardened, the wax is melted and the molten stainless steel is poured into the cavity formed by the wax pattern. Once the stainless steel has solidified within the mold, the stainless steel casting is removed by breaking the refractory mold.
The difference between stainless steel investment casting and stainless steel sand casting
Stainless steel investment casting and stainless steel sand casting are two different casting methods for making stainless steel parts by pouring liquid metal into molds. Because both stainless steel investment casting and stainless steel sand casting have their own advantages, we can't say which one is better, just for different applications.
Cost: Due to the complexity and preparation work required, the stainless steel investment casting process is always more expensive than stainless steel sand casting.
Weight: Stainless steel investment casting can make castings less than 0.5kg, while stainless steel sand casting cannot always produce small and complex parts like investment casting. Stainless steel investment casting also has limitations on the size and weight of sand casting. The mold handling equipment in the foundry can affect the weight of the product.
Surface Finish: Surface finish is another big difference between stainless steel investment casting and stainless steel sand casting. Stainless steel investment casting produces finished parts with smooth surfaces and close tolerances. After degating and shot blasting, the billet can be turned directly into net shape. For stainless steel sand casting, the mold must be disassembled to remove the final product. As a result, the parting line will remain outside the finished part. And because the sand is rough, the surface of the finished casting will be equally rough. Therefore, additional cost and time are required in secondary processing to remove parting lines and smoother surfaces.
The investment casting process is generally superior to other types of stainless steel castings, especially when it comes to surface finish.
Lost wax casting is a technique for manufacturing simple to complex objects from various metals such as gold, silver, brass or bronze by casting an original model or pattern.
It is one of the oldest known metal forming techniques, dating back 6,000 years, but is still widely used in the production of jewelry, dentistry and art. Its industrial form, investment casting, is a common method of making precision metal parts in engineering and manufacturing.
While traditionally associated with manual craftsmanship, creators can now transform the lost-wax casting process through digital design and 3D printing to streamline workflows, save time, reduce costs and reinvent craftsmanship for the 21st century.
The lost-wax casting process may vary by industry and application, but generally includes the following steps. Castings can be made from the wax pattern itself, known as the direct method, or from a replica of the original wax pattern, known as the indirect method. The direct method skips directly from the first step to the fourth step.
Model making: The artist sculpts the design in wax. The size and complexity of the wax model are limited by the skill of the wax carver and the capabilities of the casting equipment.
Create the mold: The caster then casts the model and polishes the cast to produce the "master" pattern. The master model is used to create a wax pattern out of rubber, which is heated and "vulcanized" around the master casting to make a flexible wax pattern.
Make a Wax Model: Molten wax is injected or sometimes poured into a rubber mold. This can be done over and over to make copies of the original design.
Assembling the wax pattern: Sprues are added to the wax pattern and they connect to form a tree-like structure that provides paths for the molten wax to flow out and for the molten metal to later fill the cavity.
Apply investment material: Dip the wax tree in a silica slurry, or place in a flask and surround with liquid investment plaster.
Burnout: After the investment material has dried, the flask is placed upside down in a kiln where the wax melts, leaving the cavity in the shape of the original model.
Pouring: The investment pattern is further heated in a kiln to reduce the temperature difference with the molten metal. The metal is melted and poured, using gravity or vacuum pressure to pull the metal into the cavity.
Demolding: Once the molten metal has cooled slightly, the investment pattern is quenched in water to dissolve the refractory plaster and release the rough casting. . The sprue is cut and recycled, while the casting is cleaned to remove traces of the casting process.
Finishing: Filing, grinding, machining or blasting of cast parts to achieve final geometry and surface finish. When necessary, the castings are also heat treated to enhance the mechanical properties of the material.
A Short Summary of the Long History of Lost Wax Casting
It is no exaggeration to say that lost wax casting is as old as civilization itself. Artifacts such as scepters, sculptures and furniture made by lost-wax casting have been found as far away as Israel, Vietnam, Nigeria, Nicaragua and the Indus Valley. The oldest known lost-wax cast objects are amulets created by Indus Valley societies over 6,000 years ago.
After being used for centuries in the production of sculptural ornaments and textile reliefs, lost-wax casting began to be replaced by block molding in Europe in the 18th century. Part of the process was adapted to investment casting to meet the needs of industrial development in the 19th century.
In dentistry, the lost wax method is widely used to create gold crowns, inlays and onlays. Thus, the legacy of lost-wax casting is still evident today.
In fact, nothing can be made without heat treatment, the process of heating and cooling metals under tight control to improve their properties, performance and durability.
Heat treatment softens the metal and improves formability. It hardens the part for strength. It can place a hard surface on a relatively soft part for added wear resistance. It forms a corrosion-resistant skin to protect components that would otherwise corrode. Also, it can harden brittle products.
Heat treating parts is critical to the operation of automobiles, aircraft, spacecraft, computers and a variety of heavy equipment. Saws, shafts, cutting tools, bearings, gears, shafts, fasteners, camshafts and crankshafts all rely on heat treating.
Basic knowledge of heat treatment
Although steel accounts for the vast majority of heat-treated materials, alloys of aluminum, copper, magnesium, nickel, and titanium can also be heat-treated.
The heat treatment process requires three basic steps:
heated to the specified temperature
Hold at that temperature for an appropriate time
Lower the temperature according to the prescribed method
Temperatures may range up to 2400°F and times at temperature may vary from a few seconds to as many as 60 hours or more.
Some materials cool slowly in the furnace, but others must be cooled or quenched quickly. Certain cryogenic processes require processing at -120°F or lower. Quenching media include water, brine, oil, polymer solutions, molten salts, molten metals and gases. Each has specific properties that make it ideal for certain applications. However, 90% of parts are quenched in water, oil, gas or polymers.
The value of heat treatment Heat treatment
Adding an estimated $15 billion in value to metal products annually by giving components the specific properties they need to operate successfully.
It is closely related to the manufacture of steel products: about 80% of heat-treated parts are made of steel. These include bars and tubes output from steel mills, and parts that have been cast, forged, welded, machined, rolled, stamped, drawn or extruded.
It is also a crucial step in the manufacture of non-ferrous metal products. For example, aluminum alloy automotive castings are heat-treated to increase hardness and strength; brass and bronze items are heat-treated to increase strength and prevent cracking; and titanium alloy structures are heat-treated to increase strength at high temperatures.
Silica Sol Castingis a form of investment casting. The process is very similar, except that the investment is made from silica sol zircon sand mixed with refractory powder. The silica sol zircon grit is very fine (10-20 microns) and can be mixed into a very low viscosity slurry when making molds. The result is a casting method that provides dimensionally accurate castings and an excellent as-cast surface finish. Crucially, silica sol zircon molds can withstand temperatures up to 2000°C, making them useful when casting superalloyed and stainless steels.
Advantages of silica sol investment casting:
Versatile; suitable for casting most metals.
Will allow the production of very complex castings with thin walls.
A smooth surface finish can be achieved without parting lines, so machining and finishing can be reduced or eliminated.
Allows precision casting of unmachinable parts.
Excellent dimensional accuracy
Silica Sol Process
Make a metal mold with the same impressions that will be required for the final mold.
Molten wax is injected into a metal mold to form a pattern, allowed to solidify and then removed. Some intricate wax patterns are made by using adhesive to join several individual patterns together.
The wax is then assembled on the wax tree, many parts can be placed on the tree depending on the size, the weight of the assembly is usually between 0.1 kg and 50 kg.
The tree is then dipped into a silica sol zircon slurry to coat the wax, which is very fine and low viscosity, resulting in an excellent as-cast surface finish. The slurry is coated with a refractory material, and the process is repeated several times until a shell forms around the wax mold.
The drying process is crucial. The shell must be allowed to dry naturally at a constant temperature to bond the silica sol gel and refractory particles, resulting in a strong, high-quality shell mold. Place the wax tree in an oven at about 200 degrees to melt the wax.
After all the wax is removed, the trees are heated to over 1000 degrees in preparation for casting.
The metal is then poured into a hot mold, allowing the alloy to reach the thinnest part of the mold before solidifying.
Die casting is an automated casting process in which a liquid melt is forced into a mold under high pressure (150 to 1200 bar) and high filling speed (up to 540 km/h).
Die casting is an automated casting process in which a liquid melt is forced into a mold under high pressure (150 to 1200 bar) and high filling speed (up to 540 km/h).
(Source: Messe Nuremberg/EUROGUSS)
Die casting is one of the most economical and fastest forming processes. The advantage of this production process is that hundreds of thousands of castings can be produced relatively quickly using only one mold. All components produced are of uniform quality and relatively low unit cost.
Application areas of die casting
Die casting is mainly used for mass production, i.e. for casting many parts of the same type. High casting quality is achieved despite the high pressure used in the manufacturing process. The die casting process is particularly suitable for the production of very thin (up to 1 mm) (light weight) parts.
Most commonly, die-cast components such as wheels, cylinder blocks, cylinder heads, valve bodies and manifolds are manufactured for the automotive industry. The sector accounts for about 84% of the castings produced by German foundries. 3 The use of aluminum components can reduce the weight of the vehicle, thereby reducing fuel consumption. In addition, there are other industries that use die castings:
aerospace
household appliances
furniture
electrical tools
electronic product
mechanical
lighting technology
In the future, foundries will be interested in other industries such as electric vehicles. This offers great potential for light metal castings.
So how does sand casting work? Sand casting, also known as sand casting, is a very popular alternative to die casting and investment casting.
This type of metal casting process is performed when molten metal is poured into a sand mold cavity.
Sand casting has many advantages as a low-volume manufacturing option. These advantages include the ability to cast large parts, complex geometries or parts that require a core.
This metal casting process also has faster lead times and faster turnaround times compared to other casting methods. Finally, when using sand as a tool, companies can save a lot on tool costs.
What are the steps involved in sand casting?
Sand casting is a simple process that can quickly produce parts in small batches. Here's a simple breakdown of how sand-casting works.
step 1. Master Pattern Design
Step 2. Create Matching Platforms and Tools
Step 3. Forming the mold
Step 4. Pouring the metal
Step 5. break out
Step 6. Parts cleaning
Step 7. Additional machining if necessary