Aluminum is one of the most common materials used in product development. It is lightweight, strong, and has good corrosion resistance properties. Of the various techniques one can use to fabricate aluminum metal, CNC machining and sheet metal fabrication stand out. CNC machining is suitable for complex geometries with tight tolerance and sheet metal fabrication is cost-effective for large production runs.
While both have their capabilities and limitations, choosing the best depends on many factors such as cost, part aesthetics, and speed. This article will cover everything on CNC vs sheet metal fabrication. It will explain what CNC machining and sheet metal fabrication are, their advantages and disadvantages, and situations when one technique is better than the other.
What is CNC Machining
CNC machining is a subtractive technique that creates accurate and precise aluminum components. It uses pre preprogrammed software to control the movement of tools and machinery including mills, lathes, and grinders. As these tools engage and disengage with the workpiece, they remove excess material to get the final product.
The process of CNC machining begins with creating a digital 3D model which is a representation of the final part. You then convert this model to a CNC-compatible format in the form of programming languages. These languages including G-code and M-code tell the cutting tools how and where to move. The final step in CNC machining involves executing the operation and manufacturing the part.
Based on the sophistication level of the machine you are using, CNC machining can either be 3-axis or 5-axis. 3-axis CNC is the simplest multi-axis machining. The cutting tools move in linear directions which makes it ideal when working with simple shapes and designs. On the other hand, 5-axis CNC allows you to machine workpieces in five different directions. This feature makes it possible to create complex parts with a high-quality finish.
Pros and Cons of CNC Machining
CNC machining is becoming the mainstay technology in manufacturing. It is used when producing parts that we see everyday including electronic housing, automotive engine components, and medical devices. Let’s look at some advantages of CNC machining.
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Accuracy and Precision
CNC machining produces accurate and precise products. This process is fully automated and machine parts are exactly to specifications. The final parts closely resemble the initial design which makes CNC machining suitable for high-tolerance applications. Furthermore, the results of CNC machining are consistent and repeatable. Components within and across batches closely resemble one another provided that the CNC parameters remain constant.
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Speed
The speed of CNC machining is second to none. Once the setup is complete, CNC machining manufactures parts in a short time. You do not have to manually position the workpiece in an operation which makes this technique suitable for mass production. Furthermore, many machines come with automatic tool changers and can run uninterrupted for a long period. This further increases overall productivity.
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Versatility
CNC machining is a highly versatile process as you can modify it to meet the requirements of different projects. This technique is compatible with various aluminum alloys including 6061 and 7075. Additionally, it can perform multiple operations such as milling, drilling, turning, and grinding. All you have to do is adjust the spindle speed and feed rate to get the best results.
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Surface Finish
The surface finish of CNC machined parts is one of the selling points of this process. This is especially true for 5-axis CNC machining. The simultaneous movement of the tools along different directions in a single setup minimizes human errors and produces a better finish. Furthermore, you can use shorter and more rigid tools with this machine. The tools are closer to the workpiece and do not vibrate excessively. Hence, there is less incidence of tool marks and chatter.
Despite the many benefits of CNC machining, it has the following disadvantages
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Cost
The cost of carrying out a CNC machining operation is on the high side. The machines may be expensive for small and medium-scale businesses. Note that the cost of the machine depends on the model and capacity. Additionally, the CAM and CAD software CNC machining use are pricey.
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High Skill Level
CNC machining comes with high skill requirements. You must be experienced to be able to carry out the process efficiently. It is compulsory to have IT and mathematical skills so you can interpret drawings and models. Having problem-solving skills and the ability to pay close attention to detail is an added advantage.
What is Sheet Metal Fabrication
Sheet metal fabrication is another technique you can use to produce aluminum parts. It involves everything from cutting and forming to joining and assembly that creates useful components from sheets of aluminum metal. The process of sheet metal fabrication is used for aluminum sheets with thickness ranging from 0.005 to 0.25 inches. Working with metal sheets above this thickness level will require specialized equipment and machinery. The techniques under sheet metal fabrication can be grouped into three main categories; cutting, forming, and joining.
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Cutting Sheet Metal
Cutting is usually the first step in aluminum sheet metal fabrication. It involves removing excess material to get the final part. Cutting can be with or without shearing. Cutting with shearing covers techniques such as sawing, punching, and blanking. Conversely, waterjet cutting, laser cutting, and plasma cutting fall under cutting without shearing.
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Forming Sheet Metal
In aluminum sheet metal forming, you do not cut or join any material. What you do is manipulate the metal sheet in its solid state. Bending is the most common technique under sheet metal forming. It involves using force to turn the metal sheets into curved or angle shapes. Other forming sheet metal operations include hemming, stamping, and rolling.
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Joining Sheet Metal
After individual fabrication of parts, there may be a need to join them to make a whole. The two major joining techniques are fastening and welding. Fastening is a temporary process that uses screws, bolts, and nuts to secure a part. On the other hand, welding is a permanent operation that is suitable for many types of aluminum alloys. Examples of welding techniques you can use are laser welding, MIG welding, and TIG welding.
Pros and Cons of Sheet Metal Fabrication
Sheet metal fabrication is a popular choice in many manufacturing industries. This section explains the benefits and limitations of aluminum sheet metal fabrication
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Cost-effective
Aluminum sheet metal fabrication comes at a low cost especially for medium to large scale production runs. The machines are easy to set up and install. This technique generates low waste which lowers the unit cost per part. Furthermore, you need a minimal skill level to carry out the fabrication techniques. Hence, the labor costs are low
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Lightweight
The final parts of aluminum sheet metal fabrication have a high strength-to-weight ratio. Aluminum is lightweight and using it in the form of sheet metals makes it easier to handle. This feature is particularly important in automotive and aerospace applications. Lightweight aluminum sheet metal parts increase fuel and energy efficiency.
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Versatility in Design
Aluminum sheet metal fabrication allows for the creation of complex parts with intricate features. It brings out the creativity in you as there is no limit to the designs one can create. Sheet metal fabrication makes it possible to make customized and one-off components. Furthermore, the final parts support various finishing options including plating and powder coating.
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Fast Turnaround
Sheet metal fabrication is a fast process and gets your products to market in time. You can use it for rapid prototyping as you get feedback and refine designs without wasting time. Some of the techniques under sheet metal fabrication are automated and computer-controlled. They allow for easy scalability from prototyping to mass production.
The following are some shortcomings of aluminum sheet metal fabrication
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Surface Finish
Aluminum sheet metal fabrication comes with some limitations in aesthetic finishes. However, this depends on the particular technique you are using. Cutting with shearing can leave tool marks and scratches. Additionally, laser-welded parts may have discoloration or rough spots if the process is not properly controlled.
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Thickness Limitations
There is a limit to the metal sheet thickness one can process. This is a disadvantage for applications requiring structural and heavy components. Fabricating very thick metal sheets makes them prone to warping and distortion. Furthermore, you may find it difficult to work on very thin metals. Metal sheets thinner than 0.005 inches are challenging to weld and assemble.
Table 1: Differences between CNC machining and sheet metal fabrication
| Parameters | CNC Machining | Sheet Metal Fabrication |
| Ptocess Overview | A subtractive manufacturing technique that removes excess material to create the final part. | It involves cutting, bending, rolling, and joining aluminum metal. |
| Starting material | Solid blocks. | Thin sheets of metal. |
| Part Complexity | Complex 3D shapes with detailed features. | Simple 2D or 3D parts. |
| Accuracy and Precision | High. | Limited |
| Speed | High. | Depends on the particular technique. |
| Cost | Less cost-effective. | More cost-effective. |
| Surface Finish | High quality and smooth. | Limited and may require further finishing. |
| Applications | Engine components, medical implants, and mold making. | Panels and electrical enclosures. |
CNC Machining vs Sheet Metal Fabrication: Which One is Better for Aluminum Parts
When comparing CNC machining and sheet metal fabrication, none is considered better. Your choice depends on the project requirements, starting material, cost, and desired surface finish.
When to Choose CNC Machining
CNC machining is the go-to method if you are starting from solid blocks of aluminum metal and you want to create complex shapes out of it. If the applications come with high tolerance requirements and the project is time-sensitive. You should also consider the smoothness of the surface finish you want to achieve and your budget.
When to Choose Sheet Metal Fabrication
You should use sheet metal fabrication for thin sheets of metal when producing simple 2D parts with straightforward designs. This technique is ideal for components that permit low accuracy and precision. Sheet metal fabrication is perfect for large-volume production and when you do not mind carrying out further processing to improve surface quality.
Conclusion
While CNC machining and sheet metal fabrication are two techniques one can use to manufacture aluminum components, they have distinct capabilities and are suitable for different applications. CNC machining is an automated process that produces parts with high-quality finish. However, it may be expensive, especially for low-volume production. Conversely, metal fabrication produces lightweight components that can come in varying designs. The limitation of sheet metal fabrication is the limited quality of the final part’s finish.