Which CNC Milling Gives Better Surface Finish
Surface finish is a critical factor in any manufacturing process, particularly machining, known for its excellent surface finishing. It refers to the texture and smoothness of the machined part’s exterior. The surface finish influences the part’s appearance and functionality. Therefore, manufacturers and machinists must take note of the surface properties of the parts they machine.
The type of CNC milling process may contribute to the quality of the surface finish. Therefore, machinists must select the best device or method for their fabrication’s surface finishing requirements.
This article focuses on different CNC milling operations and examines their surface finish quality. We will discuss the factors that influence the surface finishing of CNC machined parts.
Factors Influencing the Surface Finish on CNC Milled Parts
Generally, CNC milling creates parts with high-quality surface finish, such that some parts may even be left as machined, requiring no additional post-processing. However, the surface finish achieved may vary depending on various factors, some of which include:
Material Properties
The material you are machining plays a major role in determining the surface finish of the CNC-milled part. Different materials possess unique properties that affect the final finish after machining. Materials like aluminum with excellent machinability can achieve fine finishes with less effort, while tougher materials may require special tools to achieve a high-quality surface finish.
For example, hard materials like titanium will likely produce a rougher finish, unlike aluminum, which is likely to produce a smooth finish. The difficulty of machining and cutting the material increases the surface roughness.
Cutting Tool
There is a direct relationship between the cutting tool and the parts surface quality of the machined product. CNC machining is a contact process, with the cutting teeth pressed against friction as you attempt to cut it. In addition, several other factors, such as the tool geometry, the tool material, the condition of the tool, and the tool finishing, may influence the surface finish of the machined part.
The type and condition of the milling tool significantly affect the surface finish of the material. For example, sharp tools will result in a faster and more perfect cut than an old blunt tool, which will most likely leave a smear and result in a rough finish.
Feed Rate, Spindle Feed, and Chip Load
Besides the cutting tool, machining parameters, including the feed rate, spindle speed, and chip load, are all essential factors influencing a machine’s surface finish. The feed rate is how fast the cutting tools move across the material, while the spindle feed is how fast the cutting tool rotates around the material. On the other hand, chip load refers to the amount of materials the cutting tool removes per revolution.
Finding the optimal balance between these cutting parameters is essential to achieving a fine finish. Generally, using a higher spindle speed with a lower feed rate will result in a smoother finish. The chip load also requires optimization, as too much load may cause deflection in the tool, leading to rough surfaces of the machined part. It’s also important to note that too little chip load can cause friction during machining, reducing surface quality.
Depth of Cut
The depth of the cut during machining influences the surface finish and the tool used in the process. Generally, shallower cuts result in smoother finishes because less material is removed. In contrast, excessively deep cuts may increase the forces acting on the cutting tools, leading to tool wear and tear and a rougher surface. Therefore, when making deep cuts, machinists often produce a light finishing pass on the material after making an initial rough cut. This finishing pass helps to smoothen the roughness from deeper rough cuts.
Machine Stability and Rigidity
The CNC machine’s stability and rigidity are essential factors in ensuring a high-quality surface finish. A rigid machine reduces vibrations during the machining process and ensures smoother cuts. When the machine is stable, the cutters engage the workpiece with minimal vibration, resulting in smoother cuts. In contrast, when there’s looseness or instability in a machine, there’s more vibration during the machining process, leading to chatter marks, uneven surfaces, or compromised dimension accuracy. Therefore, controlling or minimizing vibration in the machine is essential for a better surface finish.
Coolants and Cutting Fluids
Coolants and cutting fluids play an essential role in CNC milling. They help to minimize friction, preventing excessive heat build-up in the machine. Coolant helps to avoid machine overheating, reducing the risk of material deformation or degradation, which reduces surface finish. Therefore, manufacturers and machinists should ensure the proper use of coolants and cutting fluid to improve the surface finish of the material and flush away chips from the cutting zones to avoid recutting.
Choice of CNC Milling Machine
The type of CNC milling device you use in machining also influences the surface finish of the workpiece. The precision and dimensional accuracy of the machine determines the surface quality it achieves. Therefore, using machines with higher precision and accuracy standards will provide a better finish than most traditional milling machines.
Which CNC Milling Gives Better Surface Finish
Machinists use different CNC milling techniques depending on the surface finish requirement of the project they are handling. Below, we examine the common CNC milling techniques and their surface finish quality.
5-Axis CNC Milling
5-axis CNC milling is often used for fabrications with complex geometries and demanding parts with high precision and tight tolerance specifications. This machine allows movement along five axes simultaneously, reducing the need to reposition material parts.
Therefore, the device reduces the risk of surface irregularities from adjusting workpiece positions. This feature makes it deliver smoother cuts on the materials. While there are even more sophisticated multi-axis milling devices, 5-axis CNC seems the most practical, as the extra cutting axes often result in more complexities.
High-Speed CNC Milling
High-speed CNC milling is another type of CNC milling technique for producing excellent surface finishes. As the name indicates, this milling method involves operating the machine at high speeds. However, the machinist must set the device at a lower feed rate to allow the cutting tool to operate at high precision, achieving significant dimensional accuracy. This method also produces a smaller chip load, which reduces the stress on the machine part and helps achieve a fine finish.
Precision CNC Milling
Precision CNC milling machines are designed for high accuracy and tight tolerances, which directly impact the material’s surface finish. These machines often come with advanced features like automatic tool changers, high-precision spindles, and superior rigidity to reduce tool vibrations. All these features also contribute to improved surface cleaning.
Ultrasonic CNC Milling
Ultrasonic CNC milling is another high-precision type with a better surface finish. It uses ultrasonic vibrations to enhance the cutting process. The ultrasonic vibration reduces the force needed to cut through the material, resulting in reduced deformation. It is mainly used for hard materials like ceramics or titanium, where achieving precision and a good finish might be difficult.
Conclusion
While CNC milling services generally result in excellent surface finishes, the machinist or operator must still optimize the process. They must also ensure that they work around the different factors that may influence the surface property of the machined part. Knowledge of how these factors – the machine and material type, machining parameters, coolants and cutting fluids, etc.- are vital for achieving a high surface finish is critical.
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