The Difference Between CNC Milling And CNC Turning

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CNC (Computer Numerical Control) machining is a manufacturing process that creates exact and complex parts. Two of the most common CNC machining methods are milling and turning. Despite being similar in many ways, there are some key differences between these two machining methods. 

In this blog, we will explore the differences between CNC turning and CNC milling, the types of parts each machine is best suited for, and the advantages and disadvantages of each machining method.

What is CNC milling?

CNC milling is a machining process that uses computerized numerical control (CNC) to control the movement and operation of cutting tools to remove material from a workpiece. The process involves a rotating cutting tool that “mills” away unwanted material, creating the desired shape and size of the part. 

The machine is programmed with a set of instructions that dictate the tool path and the depth and speed of the cutting process, resulting in a high level of precision and accuracy.

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What is CNC turning?

CNC turning is a computerized process of manufacturing that creates cylindrical parts by removing material from a rotating workpiece. The process uses CNC machines to precisely and automatically control the cutting tools. 

The machine rotates the workpiece while the cutting tools move along a predetermined path to remove the material and create the desired shape gradually.

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Differences between CNC milling and CNC turning

Operation principle

Milling

The operating principle of CNC milling is based on using a computer-controlled cutting tool to remove material from a workpiece to create a desired shape or design. Here are the main steps involved in a CNC milling operation. 

Workpiece Setup: Secure clamps or vises onto the worktable.

Tool Setup: The cutting tool is selected based on the machined material, and the desired surface finish. Then load the tool into the tool holder on the spindle.

Program Generation: Generate a digital program using CAD/CAM software. The program includes the cut’s dimensions, shape, and sequence required to produce the desired part.

Program Transfer: The program is transferred to the machine control unit through a direct connection or a remote network.

Machine Setup: The milling machine is set up to operate. It includes setting the speed and feed rate for the cutting tool and positioning the workpiece.

Cutting Process: The machine uses a digital program to control the movement of the cutting tool. The cutting tool moves along the X, Y, and Z axes to produce the desired shape.

Finishing: After completing the cutting process, we should inspect the part and carry out any necessary finishing operations, such as deburring or polishing.

Turning

The operating principle of CNC turning is based on using a computer-controlled cutting tool to remove material from a rotating workpiece to create a desired shape or design. Here are the main steps involved in a CNC turning operation:

Workpiece Setup: Clamp the workpiece onto the chuck or collet and spin at a controlled speed.

Tool Setup: The cutting tool is selected based on the machined material, and the desired surface finish. The tool is then loaded into the tool holder on the turret.

Program Generation:  Generate a digital program using CAD/CAM software. The program includes the cut’s dimensions, shape, and sequence required to produce the desired part.

Program Transfer: The program is transferred to the machine control unit through a direct connection or a remote network.

Machine Setup: The turning machine is set up to operate, including setting the speed and feed rate for the cutting tool and positioning the workpiece.

Cutting Process: The machine uses a digital program to control the movement of the cutting tool. The cutting tool moves along the X and Z axes to produce the desired shape.

Finishing: After completing the cutting process, we should inspect the part and carry out any necessary finishing operations, such as deburring or polishing.

Types of machines

Milling machines

Milling machines are computer-controlled or manually operated. There are several types of milling machines:

Vertical Milling Machines: They have a vertical spindle axis and a worktable that can move horizontally and vertically.

Horizontal Milling Machines: They have a horizontal spindle axis and a worktable that can move horizontally.

Types of milling machines

Turret Milling Machines: They have a stationary spindle and a turret that can hold multiple cutting tools, allowing for quick tool changes.

Bed Milling Machines: They have a bed that supports the workpiece and a spindle that can move horizontally and vertically.

Turning machines

Turning machines are also computer-controlled or manually operated. There are several types of turning machines:

Engine Lathes: They are manually operated and rotate the material on the spindle while a cutting tool moves along the length of the workpiece.

Turret Lathes: They have a stationary spindle and a turret that can hold multiple cutting tools, allowing for quick tool changes.

Automatic Lathes: They are automated and can perform multiple operations without human intervention.

CNC Lathes: They use CNC to automate the turning operation and produce precise and complex parts with high repeatability.

Workpiece shapes

Milling

The shapes of workpieces produced by CNC milling machines are virtually limitless due to the machine’s versatility and accuracy. Here are some of the most common workpiece shapes that are produced with CNC milling:

Flat surfaces: CNC milling can create flat workpieces with high precision and accuracy, which helps create flat parts for machines, tools, and equipment.

Contoured surfaces: A CNC milling machine can create complex contoured shapes with great accuracy and speed. It gives businesses more control over the final product’s shape and design.

Cylinders: CNC milling machines can accurately create cylindrical shapes, which help create parts like shafts, pistons, and gears.

Conical shapes: CNC milling can create tapered shapes like cones, ordinary in parts like drill bits, reamers, and tapered rollers.

Cubes and blocks: CNC milling can easily create rectangular, square, or triangular shapes for various applications.

Curved shapes: CNC milling can create complex curved shapes like curves, arcs, and ellipses, which help create curved parts like gears and cams.

Turning

Here are some of the most common workpiece shapes created with CNC turning:

Shafts: CNC turning can create long, straight shafts with high precision, accuracy, and surface finish, which are helpful for parts like axles, drive shafts, and crankshafts.

Tubes: CNC turning can create tubular shapes with various diameters and thicknesses, which help create parts like pipes, fittings, and hydraulic cylinders.

Flanges: CNC turning effectively creates circular flanges for pipe connections and other applications.

Rods: CNC turning can create rods, which are suitable for a wide range of applications, including fasteners, hinges, and handles.

Cones: CNC turning can produce conical shapes, such as drill bits, reamers, and cones for tanks or hoppers.

Spheres: CNC turning can create spherical shapes, such as bearings, rollers, and valves.

Tool functions

Milling

Here are some of the most common tool functions of CNC milling:

End mills: These are the most common tool used in CNC milling. They have a flat or ball end with varying diameters and lengths to cut a wide range of materials.

End mills

Drills: Used for creating holes in materials, drills have a sharp point at the end and are available in different sizes and shapes.

Fly cutters: Used to create a flat surface on a workpiece, fly cutters have a single blade that spins rapidly to skim the material.

Thread mills: Used to create threads, thread mills can create a range of thread sizes and pitches.

Chamfer mills: These create beveled edges on parts with precise angles.

Face mills: Used to create flat surfaces with a wide range of sizes, face mills have multiple cutting teeth that remove material from the surface of the workpiece.

Reamers: Used to finish drilled holes, reamers smooth and refine the inner surface of the hole.

Ball mills: These cutters have a rounded shape at the end to create curved and contoured surfaces.

Turning

Here are some of the most common tool functions of CNC turning:

Turning tools: These are the most common tools used in CNC turning. They cut and remove material from the workpiece while it rotates in the lathe to create cylindrical or conical shapes. 

Turning tools

Boring tools: Used to enlarge or refine the inner diameter of a hole, boring tools are available in different shapes and sizes to match specific design requirements.

Threading tools: Used to create threads on the surface of the workpiece in a range of thread sizes and pitches.

Parting tools: Used to cut a workpiece and separate it from the rest of the material being turned.

Knurling tools: These tools are used to create a pattern of raised lines or ridges on the surface of the workpiece for increased grip.

Drill bits: To create holes in the workpiece, drill bits with different sizes and shapes can be utilized for specific hole types.

Gouging tools: These tools remove excess material from the workpiece, typically used to create concave or curved features.

Material removal rate 

CNC milling machines generally have a higher MRR than CNC turning machines, as they can remove more material simultaneously due to multiple cutting edges in contact with the workpiece. CNC milling machines are also capable of removing material from multiple axes simultaneously.

However, CNC turning machines may still offer a higher overall MRR when producing high volumes of simple parts. Ultimately, the decision between CNC milling and turning should be made based on the specific part requirements, precision, production volume, and machining material.

Advantages and disadvantages of CNC milling and CNC turning

Advantages of CNC milling

CNC milling offers numerous advantages for manufacturing and engineering applications. Here are some of the main advantages of CNC milling:

Increased accuracy and precision: CNC milling machines can achieve high precision and accuracy, which is essential for manufacturing parts.

Increased repeatability and reliability: CNC milling can produce high repeatability and accuracy parts, reducing the likelihood of defects and inconsistencies in the final product.

Greater flexibility and customization: CNC milling machines can quickly switch between different tasks, allowing an operator to create custom parts with high complexity and design flexibility.

Reduced labor costs: CNC milling machines can run continuously for hours without requiring a human operator. It reduces labor costs and increases overall efficiency.

Improved safety: CNC milling machines offer enhanced safety features, such as automatic tool changers and safety curtains, further reducing the chance of operator injury.

Consistent quality: Because CNC milling machines use computer programs to control the milling process, the final product’s quality is consistent, ensuring the products are consistently high quality.

Disadvantages of CNC milling

While CNC milling offers numerous advantages for manufacturing and engineering, it’s not without disadvantages. Here are some of the main disadvantages of CNC milling:

High initial cost: CNC milling machines can be expensive, making it challenging for small businesses or hobbyists to afford them.

Maintenance and repair cost: CNC milling machines require regular maintenance to keep running smoothly, and repairs can be costly.

Required skillset: CNC milling operators require specialized skills, training, and experience to the program, maintain and operate CNC machines effectively.

Limited flexibility: While CNC milling machines offer a high degree of flexibility in design options, they are still limited by the machine’s size and capabilities.

Limitations with certain materials: CNC milling machines can struggle with specific materials prone to deflection, such as thin-walled parts, making it challenging to achieve accurate cuts.

Risk of errors: Mistakes in programming or machine operation can lead to errors that can compromise the product’s quality and increase costs.

Advantages of CNC turning

Here are some of the primary advantages of CNC turning:

High accuracy and precision: CNC turning machines offer exceptional accuracy and precise tolerances. They provide excellent control over the quality and consistency of the parts produced.

High-quality surface finish: CNC turning machines can produce parts with a smooth and uniform surface finish. They also improve the final product’s aesthetic appeal and functionality.

Excellent repeatability: CNC turning machines can produce parts consistently with minimal variability from one product to another, providing excellent reliability.

Shorter lead times: CNC turning is a fast process of manufacturing that can produce high-quality parts quickly and efficiently, which can reduce lead times.

Reduced labor costs: CNC turning machines can run automatically for long hours and do not require direct operator involvement, reducing labor costs while increasing production efficiency.

Greater design flexibility: CNC turning machines offer a high degree of design flexibility, making it possible to create complex parts with intricate shapes and contours.

Multiple materials: CNC turning can work with various materials, including metals, plastics, and composites.

Disadvantages of CNC turning

Here are some of the primary disadvantages of CNC turning:

High initial cost: CNC turning machines can be expensive and challenging for small businesses or individuals to afford.

Required skillset: CNC turning operators require specialized training and experience to operate these machines effectively and program them for different production needs.

Limitations on part geometry: CNC turning machines are limited in the shapes and designs of parts they can produce due to the turning process’s constraints.

Material limitations: Certain materials, such as materials prone to warping or deformation, are challenging for CNC turning machines to work with.

Maintenance and repair costs: CNC turning machines require regular maintenance and repairs to keep running optimally, which can be expensive.

Additional setup time: Setting up CNC turning machines can take longer than other manufacturing processes, reducing efficiency and increasing costs.

Applications Of CNC Milling And Turning

CNC milling and turning are versatile machining methods that find applications across various industries. 

CNC milling is ideal for producing complex, intricate parts. It is widely used in aerospace, automotive, medical, and other industries where precision is critical. 

Swiss machining parts

On the other hand, CNC turning is commonly suitable for parts such as shafts, bushings, and bearings, especially in manufacturing hydraulic and pneumatic systems. CNC turning is also suitable in high-volume production runs where speed and efficiency are critical. 

CNC turning parts

CNC milling and turning are used in producing custom parts, prototypes, and small to large-scale production runs.

Materials Of CNC Milling And Turning

CNC milling and turning can process various materials, including metals and plastics. 

Metals such as aluminum, brass, copper, steel, and titanium can be easily machined using both methods. Plastics such as acrylic, polycarbonate, and nylon can also be machined with CNC milling and turning. 

CNC milling and turning allow manufacturers to work with various materials with high accuracy and precision, often impossible with manual machining methods. 

CNC machines can effectively cut through various materials while maintaining precision and surface finish by selecting the right cutting tools, feeds, and speeds.

When to consider CNC milling instead of CNC turning

Consider CNC milling instead of turning your parts when they have the following characteristics:

Requires complex shapes or intricate features. 

Produce in a low volume or small batch. 

It involves exotic materials that are difficult to turn on a lathe. 

Requires tight tolerances for dimensions or surface finish. 

Requires a high degree of precision in multiple axes.

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Conclusion

In summary, CNC turning and milling are two distinct methods of CNC machining.

CNC milling is ideal for creating intricate shapes, while CNC turning is more efficient for creating simple cylindrical parts. The choice between the two depends on the specific manufacturing and project requirements. 

Both methods are critical for modern industries, and their advantages and disadvantages make them suitable for different applications.