Fabricating parts or objects from raw materials is a difficult task if done manually. However, with the CNC machining process, the task becomes simple. To fabricate parts from raw materials, CNC machining uses computer-controlled and automated machine tools. CNC and machining may also be used in numerous industries, such as automotive, medicine, and aerospace. Designing objects will be done faster with CNC machining. 

CNC Machining: Definition

CNC stands for Computer Numerical Control. It is a process that uses computer-based programs to remove materials from an item until a desired shape is attained.  

With CNC machining, the digital model of a part is broken down into numerical instructions that enable the cutting tools to produce the desired results. This process works on a wide range of materials, including wood, stone, metal alloys, metals and others. The size of the machine tool may vary depending on the exact item being manufactured. 

Since CNC machining is computer-controlled, it offers greater efficiency, precision and adaptability than other typical production technologies. All these attributes make CNC machining a preferred production choice across diverse industries and applications. 

What is the Mechanism of CNC Machining?

With the help of computer software, CNC machining empowers machine tools to design processes. Since users cannot connect with the machine tools directly, Computer-Aided Design (CAD) software is used. 

The components that CNC machining produces, CAD software generates two and three-dimensional models of those components. With these models, the machine understands what the finished product will look like. To make sure the workpiece looks like the final item designed in CAD software to eliminate the materials, the computerized controls do the necessary calculations. 

There are numerous operations that take place during CNC machining in different stages; let’s have a look. 

First Stage: Creating the Computer-Aided Design Model

As CNC machining begins, the final model should be represented in a 2D or 3D model. These models should be built using CAD software. You can find different free and premium CAD software online. 

Designing a CAD model is not complex; rather, it is much more straightforward and easy to learn. However, there are some complicated sections that require advanced CAD knowledge. In that case, professional designers can be recruited. 

Second Stage: CAD File to CNC Model Conversion

It is difficult for CNC machining to comprehend CAD files directly. The process only recognizes movements using coordinates. To make CNC machines understand the CAD document, CAD models shall be converted into a G code file. 

There are numerous CAD software that can write output files directly in G Code. All a person needs to do is select the appropriate option before saving it. In other circumstances, transforming CAD models to G code requires using specialized software known as CAM or Computer-Aided Manufacturing. This is a highly useful tool for automating machine processes. 

Stage 3: Setting Up the CNC Equipment

The CNC must be appropriately configured before initiating the manufacturing process. It is just like setting up a printer before printing something. In order to print something, a person needs to put pages in the printer and check particular settings. That’s similar to how a CNC machine works. 

There are some configuration steps that need to be done before you begin the machining part. For instance, you need to ensure the workpiece has been placed properly on the machine. In addition, the molds and other position settings must be proper. 

Stage 4: Executing Machining Operation

Once the configuration part is done, the machine may start to operate. On the CNC machine’s display screen, you can execute the program. Depending on what you create, you have to go through different program prompts to select other kinds of features and settings. 

Once the CNC program is executed, the machine will continue to run until the program is completed. If only the operator is turned off or hits a power loss or an unforeseen fault, the machining process will stop. 

Types of CNC Machining system:

The two main types of CNC machining systems are milling and turning. Due to the characteristics of each machine type, milling and turning are each uniquely ideal for manufacturing different geometrics.

1. CNC Milling: 

CNC milling is the most common type of CNC machining. In fact, the term CNC milling is usually used to describe CNC machining. CNC milling machines use rotational cutting tools to remove material from a part mounted on the machine bed. Most CNC milling machines have 3 linear degrees of freedom like X, Y & Z axes.

2. CNC Turning:

CNC turning machines use stationary cutting tools to remove material from a part, which is mounted on a rotating chuck. This is an ideal way to manufacture parts with symmetry along with centre axis. Turned parts are typically produced faster and at a lower cost than milled parts. Typically, CNC turning systems are also known as lathes and are used to create cylindrical parts. 

Benefits and Limitations of CNC machining:

Benefits:

1. High accurate parts with tight tolerances:

CNC machining offers superior dimensional accuracy compared to many other manufacturing methods. In the final finishing steps, material can be precisely removed from the workpiece, achieving extremely tight tolerances. The standard tolerance for any dimension in CNC machining is ± 0.125 mm. However, it is possible to achieve tighter tolerances down to  ± 0.050 mm, and even tolerances of ± 0.025 mm are feasible.

2. Excellent material properties:

CNC machined parts possess excellent physical properties that are identical to the bulk material, making them perfect for high-performance applications. Furthermore, merely any common material with sufficient hardness can be CNC machined, providing engineers with the flexibility to choose a material that best suits their specific application needs.

3. Quick Turnaround time: 

Advances in modern CNC systems, CAM software, and digital supply chains have significantly accelerated production times. Now, CNC machined parts are usually ready for delivery within just 5 days, comparable to the turnaround time of industrial 3D printing processes like SLS.

4. One off custom parts and prototypes:

Unlike formative technologies like injection molding, CNC machining does not require tooling. This makes on-demand production of custom one-off parts and prototypes economically viable. This is particularly true for custom metal parts and prototypes, where CNC machining offers the most cost-effective solution.

Limitations:

1. High Set up cost:

In CNC machining, start-up costs are primarily associated with process planning, which demands expert manual input, making these costs relatively high compared to the highly automated process planning in 3D printing. It is important to note that start-up costs are fixed. 

2. Tool access and workholding restrictions:

For CNC machining, a cutting tool with the right geometry is essential to remove material from solid blocks. The tool must access all necessary surfaces, which makes machining internal geometries or steep undercuts difficult. Securely holding the workplace is crucial to avoid vibrations that reduce dimensional accuracy.

Application of CNC machining:

1. Space:

CNC machining is among the select manufacturing processes ideal for producing parts for space applications. This is due to the exceptional accuracy and material properties of CNC parts, as well as the variety of surface treatments that can be applied post-machining.

2. Aerospace:

The aerospace industry was among the pioneers in adopting CNC machining, thanks to its capability to produce lightweight components with superior physical properties and extremely tight tolerances. It is utilised not only for manufacturing aircraft parts but also during the development phases. 

3. Automotive:

CNC machining has applications in the automotive industry when manufacturing of high-performance custom parts is required. 

4. Product Design & Development:

The capacity to rapidly produce metal parts with high dimensional accuracy makes CNC machining an ideal choice for creating functional prototypes. This is crucial during the advanced stages of design and development.

5. Electronic Manufacturing: 

CNC machining serves numerous applications in the electrical and electronic manufacturing industry, including the prototyping of PCBs and the production of enclosures.

Material for CNC machining:

1. Metal:

CNC machining is primarily used with metals and metal alloys. Metal can be used for both the manufacturing of custom one-off parts and prototypes and for low-to-medium batch production. Aluminums 6061 is by far the most used material in CNC machining. Metal like Stainless steel, alloy steel, mild steel, brass, etc.

2. Plastics:

Plastics, valued for their diverse physical properties, are lightweight materials frequently chosen for their chemical resilience and electrical insulating qualities. They are commonly subjected to CNC machining during prototyping stages before undergoing injection molding. Plastic like ABS, Polycarbonate, Nylon etc.

Surface Finishes:

1. As-machined:  

As-machined parts feature the tightest tolerances since no additional operations are conducted on them. They display visible marks aligned with the cutting tool's path. The typical surface roughness of as-machined parts is 3.2 μm (125 μin), which can be further reduced to as low as 0.4 μm (16 μin) through subsequent operations.

2. Bead blasting:

Bead blasting is employed to achieve a consistent matte or satin finish on machined parts by eliminating tool marks. It is primarily utilized for aesthetic enhancement, although the resulting surface texture may vary. Certain critical areas or features, such as holes, can be shielded to prevent alterations in dimensions.

3. Anodizing:

Anodizing enhances aluminum parts by creating a thin, durable ceramic coating that boosts their resistance to corrosion and wear. Masking critical areas preserves their precise tolerances, while dyed anodized parts achieve a sleek, visually appealing finish.

4. Hardcoat anodizing:

Hardcoat anodizing creates a robust ceramic coating that is thicker and denser, offering superior corrosion and wear resistance. This process is ideal for functional purposes, with a typical coating thickness of 50 μm, often applied without color. Areas requiring precise tolerances can be masked to maintain their critical dimensions.

5. Powder coating:

Powder coating applies a durable, corrosion-resistant polymer paint layer thinly onto part surfaces. It's suitable for parts of any material and comes in a wide range of colors.

6. Silk Screening:

Silk screening offers a cost-effective method to apply text or logos onto the surface of CNC machined parts purely for aesthetic enhancement. This method complements other finishes, such as anodizing, and is specifically applied to the external surfaces of the part.

Conclusion

CNC machining is essential when it comes to modern manufacturing needs. The process of CNC involves fabricating the most basic raw materials and shaping them into anything the mind wishes. For prototype requirements and small-scale or large-scale productions, CNC machining can be your go-to option. Mech Power is offering CNC machining service and now you can also take the benefit of it by visiting our website.