Metal casting can not offer 100% accurate results. To meet the required specifications, foundries must do additional finishing tasks. Casting machining helps in this case. As you know, casting parts may come in various shapes and sizes. Multiple types of casting machining methods arise to accommodate these shapes.
There are many types of casting processes. Sand casting uses sand to create molds, and then you can pour molten metal into it. It is a simple method, but you will need more machining services. The die-casting method injects molten metal into the mold. The high pressure creates finer casting parts. For this method, you may need less casting machining process.
You may observe situations similar to other types of casting methods. However, whatever the type of casting method is, you must need casting machining. In these ways, you can achieve the desired specs. Note that you can achieve tolerances up to ±0.0001 mm. So, these casting machining methods are crucial for metal parts.
This article presents the fundamentals of casting machining. You will learn what they are, how they work, and their types. In addition, we will explore the benefits and limitations of each type. Ultimately, you will have a comprehensive understanding of casting machines. This knowledge helps a lot when choosing a suitable foundry.
What is Casting Machining?
Casting machining refers to the machining services performed on cast metal parts. After a metal part is cast, it typically needs further refinement. Various casting machining removes excess materials and shapes the parts to the exact dimensions.
How does casting machining work? Casting machining may vary depending on the customer’s needs. Usually, there are three types of casting machining: cutting, abrasive, and advanced. Whatever the type, the raw cast part is secured in a machining tool. Then, various cutting tools remove material from the part.
Every process ensures the part meets the exact specifications. It mainly improves surface finish and accuracy. CNC machining can achieve up to ±0.01 mm, while EDM can achieve up to ±0.0001 mm. Standard tools for CNC machining are lathes, milling, and drilling.
Machining Casting: Cutting
These casting machining methods remove excess material from the raw cast parts. Various cutting methods are turning, drilling, milling, or sawing. The turning method is suitable for cylindrical parts. The milling method is ideal for face and peripheral cutting. Drilling creates holes and sawing cuts parts to size.
Machining Casting: Advanced Method
Advanced methods are typically not traditional ones. Their precision is much higher. EDM and laser cutting/engraving are two popular advanced methods. These two casting machining techniques are widely used in casting foundries. Using this tech, you can achieve tolerances up to ±0.0001 mm. More information is available in the later sections.
Machining Casting: Abrasive Machining
Abrasive machining in casting uses grinding wheels and abrasive materials. It mainly fine-tunes the cast parts to get the smoothest surface. Some standard methods used in this case are grinding, honing, and lapping. These processes create high-quality finishes in metal casting components.
What is the Difference Between Casting And Machining Processes?
Casting is an additive process in which molten metal is poured into a mold to create various shapes. This method is suitable for metals only. Standard methods are sand, die, and investment casting. It’s ideal for making complex shapes in large quantities.
Machining, on the other hand, is a subtractive method. As mentioned, it removes material from parts to achieve precise shapes and finishes. Let’s check the differences between casting and machining.
Casting and Machining: Material Choice
Casting is limited to metals only. You can use aluminum, iron, steel, and many other metal alloys. These metals are ideal for creating complex shapes and large parts.
Machining supports various materials, including metals, plastics, and solid materials. Casting machining is prevalent to create a perfect finish on cast parts.
Casting and Machining: Production Speed
Casting is generally faster for large quantities once molds are made. It is perfectly suitable for high-volume orders.
Machining, on the other hand, is slower for high-volume orders. But it is an accurate and precise method. Because of this, casting machining is widely used by casting companies.
Casting and Machining: Dimension Tolerances
As you know, shrinkage and vibration occur during casting, which usually provides lower tolerances. Therefore, every casting part needs an additional machining process to achieve the best quality. Although casting can handle complex designs, it can not give accurate results.
Machining usually offers higher tolerances. There are many types of machining processes. CNC machining can achieve up to ±0.01mm. Conversely, EDM can achieve up to ±0.0001mm. They are both perfect for parts that need tight accuracy.
Casting and Machining: Prototyping
Casting is sometimes used to create prototypes, but it requires machining services. As you know, casting takes time and costs more to make molds, although it’s better for large-scale orders.
In contrast, machining is highly suitable for prototyping. It is fast and accurate, and it costs less than metal casting. Although sand casting is cheap, casting machining is still famous for its best results.
The Benefits of Machined Castings
Machined castings are the metal parts made after casting machining. They offer various features and benefits. In short, they feature high precision, smooth surface finish, and no defects. Because of this, machined castings are always preferred.
High Precision
Machined castings typically offer improved precision with high tolerances. Casting machining improves the tolerance by refining the dimensions of the cast parts. As a result, you can get exact specifications. CNC machining can achieve up to ±0.01 mm, while advanced machining can achieve up to ±0.0001mm.
Improved Surface Finish
Machined castings usually come with an improved surface finish. Grinding and polishing typically create such a smooth surface.
Machined casting part surfaces are much smoother and more refined than cast-only surfaces. This level of improvement typically reduces the need for additional finishing touches.
No Defects and Flaws
Casting machining can help you identify and correct casting defects. It can remove defects like porosity and inclusions. In this case, drilling, milling, and grinding are most typical. These processes generally eliminate the weak spots in the materials. Overall, your metal part gets enhanced structural quality.
Material Efficiency
Another significant benefit is material efficiency. Casting machining typically minimizes material waste by accurately removing material. So, it creates optimal material usage and reduces excess scrap.
Better Performance
These metal parts can perform best since machined castings offer the above four benefits. This feature is particularly crucial for machines and vehicles. For instance, perfect engine components can give the best run on the road. In addition, improved performance also leads to longer-lasting parts. So, it means you don’t frequently need to replace and repair them.
Preparing for Electro Coating
Machined castings come with an excellent surface finish. It is particularly suitable for various surface treatments. Popular surface treatment methods are anodizing, e-coating, painting, or plating. Casting machining prepares the cast part surfaces for these surface treatment methods. As a result, you can get a long-lasting and effective result on every cast part.
7 Common Casting Machining Process
After coming out of the mold, every casting part usually has excess material. You must remove these redundant sections because they can disrupt the original part’s function. Also, the casting part has rough surfaces.
Can the machine you are using to smooth the surface of the casting part remove unnecessary parts? Or can you do smooth work with a cutter? So you can realize that there are many types of casting machining. In the following, we will highlight seven standard casting machining processes. Each casting machine has a unique purpose and job to accomplish.
#1 CNC Machining
CNC stands for Computer Numerical Control. CNC machining is typically subtractive, creating various shapes by removing materials. It is also an automated process. Once you have inserted the code, the machine automatically makes the shape.
A CNC machine typically has a controller, servo motors, and multiple axes. In general, you can find three-axis CNC machines everywhere. For more complex cases, 4-12 axes CNC machines are used.
CNC machining is widely used in many industries. From aerospace to automotive, every industry involving metal needs this. Engine parts, brackets, and surgical instruments are some everyday products.
Features & Benefits
· Incredibly fast and accurate, you can achieve tolerances up to ±0.01mm.
· CNC machine is safe to operate.
· No need for labor costs.
· The best benefit of CNC machining is that it can deal with complex shapes.
Limitations
· High Initial Cost
· Need experts for accurate programming.
#2 Turning
Turning is a widely used method in every metalworking workshop or factory. In this method, the object is connected to the spindle horizontally. (Horizontal Machining)
The object typically spins, and the cutting tool gradually removes the material. It continues to do so until the object gets the desired shape. The tool generally moves linearly.
CNC turning is suitable for cylindrical casting parts. Shafts and pulleys are some famous examples.
Features & Benefits
· Turning offers highly accurate results.
· It creates a smooth surface finish.
· The method is typically suitable for a wide range of materials.
· Turning is usually efficient for cylindrical parts.
· This method is versatile and can be used with different lathe types.
Limitations
· Turning is only limited to cylindrical shapes
· Initial setup time can be high.
· Manual lathe needs skilled operations.
#3 Milling
Milling is also a machining process in which the object remains stationary while the cutting tool spins and shapes it. This process creates more complex designs than cylindrical objects.
Milling machines can typically be of two types. Vertical milling has a vertical spindle, hence the name. This spindle holds the cutting tool and can move up and down. Conversely, horizontal milling has a horizontal spindle, thus the name. This spindle moves from side to side.
Milling is a prevalent machining casting method in foundries. It is widely used to make molds for die casting, aluminum casting machining, and various metal parts.
Features & Benefits
· It can handle various materials and shapes.
· Milling produces accurate and detailed parts.
· This casting machining offers high-speed operations.
Limitations
· Cutting tools may wear out quickly.
· Initial setup can be expensive.
#4 Drilling
Drilling is another casting machining type that only creates holes. It is commonly used in many applications, especially in manufacturing and construction. Casting drilling is widely used in foundries to make molds and finish the cast parts.
The drilling machine has a rotating cutting tool called a drill bit. The object remains stationary. The cutting tool gradually removes the material and creates a hole. The machine presses the drill but against the material. As it rotates, it cuts away the material to form a hole.
Features & Benefits
· Drilling is suitable for all solid materials.
· It is a cost-effective method.
· This method offers high accuracy (up to ±0.01 mm).
· There is a wide range of drill bit options.
Limitations
· Drilling can create heat, which can deform thinner materials.
· The hole depth depends on the size of the drill bits.
#5 Grinding
Grinding is a very famous casting machining process, especially in casting foundries. It typically uses an abrasive wheel to remove material from the workpiece’s surface. This casting machining is prevalent for the smoothening of casting parts.
You can generally find four types of grinding machines. Surface grinders are suitable for flat surfaces. On the other hand, cylindrical grinders are for cylindrical parts. Centerless grinders are prevalent for parts without centers. Finally, internal grinders are used for internal surfaces. Although there are many grinders, these four are the most common.
Features & Benefits
· Grinding makes the surface of your metal parts smooth and shiny.
· It can achieve high precision and surface finish.
· Suitable for both hard and brittle materials.
· It improves the accuracy of the cast parts.
Limitations
· Slow process
· Needs labor
#6 EDM: Electrical Discharge Machining
As the name suggests, this casting machining method uses electrical discharges to shape metal. It is especially suitable for ultra-complex metal parts.
EDM removes material using controlled electrical sparks. This technology is widely used in casting foundries. In this method, a dielectric fluid separates the workpiece and the electrode. Sparks generally erode the metal and create the desired shape.
This method is used in casting foundries to make molds and dies. Later, casting foundries use these molds to create unique metal parts. EDM is also prevalent when making fine-tuned and finished cast parts.
Features & Benefits
· EDM casting machining can achieve extremely high tolerances. Experts said you can achieve tolerances up to ±0.0001 mm.
· You can create a wide range of complex shapes and intricate designs.
· This method creates no mechanical force.
· EDM offers a smooth and fine surface finish.
Limitations
· EDM is a slow process.
· Only works with conductive materials
#7 Laser Cutting/Engraving
Laser engraving is another popular casting machining method in metal casting foundries. It uses a high-powered laser beam to cut/engrave materials and engrave marks or etch the surface. Both processes are precise, and computer software allows you to control them.
In casting machining, a laser machine cuts through metal. The laser melts, burns, or vaporizes the material. In this way, you can remove unnecessary metal parts from the original. For engraving, you can mark text, logos, or product numbers using laser tech.
Features & Benefits
· Laser cutting offers high precision.
· You can use a laser cutting machine to cut many materials.
· It creates less waste.
· It is a non-conductive process, so the method is safe.
· Fully automated.
Limitations
· Laser cutting/engraving is relatively more expensive than other methods.
· You can not work with thicker materials. The denser the metal is, the more laser power is necessary.
· Reflective materials can cause issues.
Introducing Aluminum Casting Machining
Aluminum casting machining is typically the finishing formalities of aluminum cast parts. It mainly combines two processes: casting and machining. The die-casting method is often preferred for aluminum casting.
First, we insert the raw aluminum into the heating chamber. Then, this chamber automatically delivers the molten metal into the injection chamber. The injection chamber then pushes the molten metal into the die at an appropriate pressure. The high pressure allows the liquid metal to reach every design corner. HPDC, LPDC, gravity, and vacuum casting are standard die-casting methods. In these ways, precise aluminum cast parts are made.
After the metal casting parts are ready, they need some finishing touches. Usually, we use different types of casting machining to improve these parts even more. To get rid of the extra stuff, we use cutting tools. To smooth a cast part’s surface, we often grind, clean, or blast it. Next, we clean the surface in several different ways. If needed, we can add anodizing, e-coating, or plating later.
Aluminum casting machining is widely popular in many industries. Automotive, aerospace, medical, electronics, and consumer goods are common. However, we can use various aluminum alloys to make many aluminum parts for these industries.
For instance, an aluminum-silicone alloy is perfect for strength and wear resistance. On the other hand, aluminum-magnesium alloy offers excellent corrosion resistance. Moreover, aluminum-zinc alloy is suitable for machineability. So, the choice mainly depends on the product’s type.
Things You Must Consider When Aluminum Casting Machining
Several factors must be considered when aluminum casting machining. These factors usually ensure the final part’s quality, efficiency, and precision. Each aspect below plays a crucial role in achieving the best results.
#1 Material Condition
Before machining, the condition of the aluminum cast part must be checked. Do you see any warpage or flash? Warpage means any distortion or deformation of an aluminum cast part. In the factory, we first clean the aluminum cast part if there are any issues.
The next thing you must consider is the type of aluminum. Is it not heat-treated or heat-treated aluminum? Note that non-heat-treated aluminum is usually soft, while heat-treated ones are stronger. So, this factor plays a crucial role when selecting the cutting tool.
#2 Cooling
Coolant is a big deal here. It has three main jobs. (1) it prolongs the machine’s life. (2) it maintains the quality of the machined castings. (3) it ensures the safety of the operator.
You may wonder how to choose the correct coolant for your project. As you know, there are three types of coolant. Testing all of them can cost money and time. However, we always recommend using a micro-emulsion coolant.
#3 Cutting Tools
The cutting tool must be carefully chosen for the specific aluminum alloy. We usually select high-shear cutting tools.
You can either use solid carbide end mills or PCD. Note that PCD is relatively costlier than solid carbide tools. However, you can get better results and work for a long time.
#4 Cutting Geometry
Three cutting geometries are essential: rake angle, clearance angle, and chip formation. A positive rake angle is suitable for soft and malleable metals like aluminum. Proper clearance angle typically prevents tool rubbing. Finally, perfect design helps in efficient chip removal. These factors are essential for cutting efficiency and smooth surface finish.
#5 Feed and Speed
Cycle time is a crucial aspect to consider here. We always focus on reducing it. We use CAD/CAM programs for accurate machining simulations to do this. Besides, modern technology can improve consistency and efficiency.
#6 Fixtures
Choosing the right fixture becomes an issue when dealing with complex designs. In this case, we professionally assess how to hold and clamp each aluminum part. Our experts typically find the best solution for each part. In this case, spring-loaded supports help a lot.
Frequently Asked Questions
Why is machining always required when a component is cast?
Machining is typically needed after casting to achieve accurate dimensions. As you know, cast components often have rough surfaces and must meet the exact specs. Casting machining removes excess material and gives a smooth surface finish.
What is cast aluminum vs. CNC aluminum?
Cast aluminum is typically formed by pouring molten aluminum into a mold. After solidifying, the molten metal creates complex shapes. CNC aluminum is generally machined from a solid aluminum block using CNC technology. One is an additive process, while the other is a subtractive process.
Is casting cheaper than machining?
It depends. For large production orders, casting is generally cheaper than machining. In casting, making the dies can be expensive. However, you can create hundreds and thousands of cast parts once dies are made. So, considering the overall cost, casting is cheaper. However, for small-scale production, machining is the more affordable option.
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