Casting – is more than 6,000 years old and is still widely used. Advances in the technology of this process have made it possible to cast high-quality parts with tight tolerances. CNC machining is also ubiquitous, but much newer. Have you ever thought about machining your regular castings? Or are you wondering what method to choose to complete your project? In this article, we will introduce two manufacturing processes and discuss the advantages and disadvantages of each. Stainless steel, malleable iron, and other material have specific properties in the workpiece. How do you implement the advantages of insert geometry? Is casting or stainless steel machining better? What are the associated advantages and disadvantages? We write about it below!
What is casting?
Casting is an ancient craft that is still used in many molds. There are many types of casting, but they all use molds. Molten metal is then poured or placed in such a die, where it cools and hardens into its final form. Cores or inserts can create complex internal geometries. Once hardened, the part is cleaned and subjected to a course of heat treatment to the desired surface finish. Sometimes this additional operation includes CNC machining to achieve tighter tolerances. Examples of such castings include train wheels, bus pedals, turbine blades, and engine blocks. They are used in almost every industry, including automotive, aerospace, consumer products, and medical devices. Casting is used for isothermally hardened ductile iron.
What are CNC machining and turning?
CNC machining, or CNC turning, is part of a manufacturing technology called subtractive machining, which means the cutting tool removes material to achieve the desired geometry. A computer program using code tells the machine where to move and how to cut. Such a process can produce very precise parts that are used virtually everywhere. Metal cases for laptops, small parts inside cell phones, aerospace and automotive components, as well as hardware and instruments, are produced by CNC machining.
Choosing a manufacturing method based on geometry
When designing a part, one usually starts with a manufacturing method so that realistic, achievable features can be planned that are well suited to the way the part works. On the other hand, a part’s function may require a specific size, shape, or geometry, which in turn may even dictate a specific manufacturing process. CNC machining and casting are tailored to specific specifications. For example, some designs require significant material removal from the initial metal block. This would take a long time and lead to excessive waste of plastic, so such a case may be a good candidate for casting. Hollow parts with thin walls and large cavities are good examples. Complex figures are also good candidates for casting because they require complexity and long machining times. Casting is a great process for simplifying the design of a single part or an entire assembly. Instead of machining many small parts and then assembling them, you can cast the whole thing at once and avoid many assembly steps. However, some features are more difficult to achieve by choosing this method. Undercuts or internal components will be complex and require complicated molds with cores and inserts. Castings also oblige all parts to have a spiral angle. Large or unusually thick-walled parts are better suited for CNC machining. When casting, these geometries are difficult to fill and cool evenly. CNC cutting is ideal for thick parts that require high precision. Keep in mind, however, that cutting can create cutting resistance that makes cutting difficult. CNC uses carbide inserts that work in the cutting zone.
Advantages and disadvantages
In addition to differences in geometry, casting and machining processes have their own advantages and disadvantages.
Casting – advantages, and disadvantages
- Casting reduces material waste. The process uses only the plastics needed for the final section, with little metal flowing through the gates, rails, and guides. Excess material can be easily removed and re-melted for use once again in another section.
- It is also a quick process once the mold is ready. This makes it suitable for producing high-volume parts. Disposable molds are used for some types of solutions. However, in die casting using a permanent mold, the time and cost per part decrease as the volume increases.
- It can also be a fast, repeatable process. Repeatability is important in manufacturing, and casting produces very close parts. Once a mold is selected and machined, each part can be made exactly the same.
During aluminum die casting, tolerances can be held to +/- 0.25 mm by up to 25.4 mm and 0.05 for precision casting (0.01″ by up to 1″ for standard and 0.002″ for precision). This will vary depending on the material. Aluminum has a higher melting point than, for example, zinc, so it requires higher injection pressure and a generally more aggressive process. As a result, even tighter tolerances can sometimes be maintained when casting zinc.
CNC machining advantages and disadvantages
On the other hand, CNC machining provides a faster turnaround with fewer parts. You don’t have to wait for molds to be produced. All you need is a CAD model, a CAM program, and a CNC machine.
Design changes are easier with CNC cutting. When a concept is constantly changing, all you have to do is remodel the solution and rework the CAM program instead of rebuilding or creating it from scratch. CNC machining is also a highly repeatable process. For standard metal cutting, 0.025 mm (0.001 inches) is a reasonably expected tolerance.
Casting or machining?
Knowing the above facts, would you choose to cast over machining or vice versa? A few key things to consider are the stage of development, the number of parts required, the variability of requirements, and the part geometry discussed earlier. The stage of development is related to the degree to which the design of parts is constantly evolving. This can be repeated many times at the beginning of the design process. In this case, CNC machining would be a better choice because of the relative efficiency of changes in this process. The number of parts required is also important. Earlier in the prototyping process, you may not need many parts, so CNC machining may make more sense. Another thing to consider is the variability of your needs. How often do you actually need the parts? If demand fluctuates, CNC machining may be a better option. CNC machined parts are available more quickly, especially as the digital transformation continues. This can be a good option from an economic standpoint because you can order them as needed, rather than trying to anticipate what you will need and end up with excess inventory. You may be forced to have more parts after the project is completed and in production. At this point, casting is a good choice because it is more suitable for producing thousands or more parts. Finally, quality matters. CNC machining is able to maintain tighter tolerances on parts, making it a more precise process. Precision CNC machining can produce them to a tolerance of +/- 0.0002 inches, while precision aluminum castings are more like 0.002 inches. If this level of accuracy is extremely important to your application, CNC machining may be a better choice for you. The manufacturing process always depends on the specific demand. You may find yourself with a unique combination of requirements that forces you to be creative and find innovative solutions. CNC machining has become a very common craft, but there is still a place for casting! Each manufacturing method has its advantages. Instead of doing business, as usual, try re-evaluating your project to see if it is better suited for casting or CNC machining based on attributes such as part geometry, quantity, quality needs, and schedule.
The advantage of machining stainless steel using CNC
Currently, there is austenitic stainless steel and martensitic stainless steel. The difference between the two is the corrosion resistance. Austenitic steel has excellent corrosion resistance. Factors that make CNC machining better than stainless steel casting.
Here are some examples of stainless steel CNC machining operations that make it a better alternative to stainless steel casting.
- No mold costs: unlike casting, CNC machining process does not require molds. CNC machines for shaping products use various cutting tools controlled by digital computer code. Therefore, it saves tooling costs.
- One-stop production: CNC machining stainless steel can be used for small and complex part production. However, casting has limitations that are not suitable for manufacturing complex parts. Using casting for complex products can lead to dimensional errors and rough surfaces.
- CNC machining is done with constant feed rates, proper tooling, and low-tolerance dimensional coding so that when using stainless steel products, it can be efficiently implemented for complex but precise production.
- Faster production cycle: CNC machining of stainless steel is a faster production process compared to casting this material. Die alignment is a time-consuming operation followed by melting and cooling the metal and casting the final product. CNC machining, on the other hand, involves computer code generation, workpiece alignment, and post-production ejection of stainless steel parts.
- Dimensional accuracy and stability: CNC operations are managed by computer, reducing the risk of human error in dimensional accuracy. Stainless steel casting may require extreme heating and cooling, which can alter the dimensional accuracy of the final product.
In contrast, CNC machining can be done with low dimensional tolerances. Additionally, it does not require extreme heating or cooling of the stainless steel sheet. Therefore, CNC processes exclude dimensional changes caused by temperature fluctuations.
Due to the aforementioned advantages of CNC machining of stainless steel, stainless steel castings have been quickly replaced by it and have proven useful in many applications.
In general, CNC milling is an alternative to stainless steel casting (regardless stainless steel types etc.: austenitic stainless steels,martensitic stainless steels, duplex stainless steel) because it provides fast product creation, maintains a glossy surface finish, and provides high strength and durability to products made from this material. However, different technologies such as CNC, turning, drilling, etc. can also be used for different parts.