CNC milling operation
Milling is the subtractive manufacturing approach, which removes the material from the workpiece to convert it into a desirable shape. It is accomplished by continuous feeding of the workpiece into a rotating tool.
Typically, the milling cutting tool’s rotation is unidirectional- clockwise! However, feeding can be done either clockwise or anti-clockwise. Based on the motion of the workpiece, there are two milling approaches; Climb milling and Conventional milling. Climb milling involves feeding the workpiece along the same direction of tool motion, while conventional refers to providing against the tool direction.
This article will discuss convention & climb milling, their advantages & disadvantages, and comparative scenario in different aspects.
The Conventional Milling Process
The cutting tool rotates against the feed in the conventional milling process. So the chip thickness starts with zero at the initial position and continuously increases to exit a cutter point. Both manual and CNC machines can perform conventional milling, which is ideal for bulk milling.
Schematic diagram of up-milling
Conventional milling is also known as Up Milling since its starts with the bottom of the cut. When the workpiece first comes into contact with the cutting teeth, the tool is rubbed forcefully, leading to rapid wear and tear. The Cutter’s teeth hit the material and pushed against the motion, throwing away the chips in front of the Cutter. It can cause the chips to be re-cutting and increase surface roughness.
Advantages of Conventional Milling
1. Minimum backlash
The space created by movement during axis reversals is backlash. The motion of the rotating tool and workpiece does not generate any backlash during conventional milling. Backlash affects the milling accuracy, but don’t worry; conventional milling prevents backlash.
2. Stability
The gradual increase of chip thickness and width has one significant advantage, it keeps the workpiece stable and creates less vibration. The stability of the workpiece during the milling produces very accurate parts.
3. Low chance of undesirable cuts
The feed’s opposite motion causes the tool’s deflection away, which minimizes the likelihood of unwanted cuts. Furthermore, if it does, the cutting depth will be minimal.
Disadvantages of Conventional Milling
1. Generation of heat
The against-rotation of the workpiece involves high friction with the milling tool at the initial point, which generates heat. In addition, the width and thickness of chips continuously increase from point zero to the exit position, indicating that the tool is absorbing heat. It shortens the cutting tool’s lifespan and reduces the quality of the machined part.
Related: the impact of tool wear on CNC Machining Defects
2. Surface roughness
The continuous increase of cutting force from the initial to the exit position might cause deflection between the workpiece and the cutting tool. The deflection creates a comparatively rough surface. In addition, the chip re-cutting phenomena also contribute to the rough surface finish.
Related: How to avoid roughness on a CNC milling machine?
3. Lower tool life
Generation of excessive heat, continuous incensement of cutting force, and friction with the workpiece are all reasons for wear and tear. It affects the precision of milling and tool life.
All materials, including metals, alloys, polymers, and ceramics, can be machined using conventional milling. It produces a poor surface finish, making it more suitable for primary cutting or parts that involve post-processing.
The Climb Milling Process
Schematic diagram of climb milling
In the climb milling process, the feeding is carried out in the same direction as the cutting tool. The uni-direction of the Cutter and feed direction removes the maximum material while the Cutter touches the workpiece at the initial position. Therefore the chip thickness starts at maximum at the initial work and will become zero at the exit point of the Cutter.
The milling tool leaves the chips behind the Cutter, which minimize the risk of re-cutting. The friction between the workpiece and cutting tool is less than the conventional milling, so it lowers the wear and tear of the cutting tool.
Advantages of Climb Milling
1. Smooth surface finishing
The gradual decrease of chip size from the initial cutting point to the exit point decreases the cutting force proportionally. This behavior of climb-milling creates a smoother surface finish. In addition, climb milling prevents the re-cutting of chips, contributing to achieving a finer surface.
2. Low heat generation
Heat storage in the workpiece and chips is more than the tool as the size of the cut steadily decreases. Additionally, the downward cutting lowers the required holding force and reduces friction.
3. Better tool life
The low-heat production and lower friction contribute to better tool life. In climb milling, the workpiece has limited deflection, which limits the tool’s exposure to excessive stress. Therefore, low friction, heat, deflection, and stress help to enhance the durability of the tool.
Disadvantages of Climb Milling
1. Backlash
The cutting-edge force into the workpiece pulls the table against the backside of the lead screw thread (Climb Milling vs Conventional Milling, 2019). It creates a backlash because of the effect on flute engagement.
Backlash might cause injuries to the workpiece and operator. It is considered to use climb milling with old milling machines because flying shrapnel can cause physical harm to the operator. A backlash eliminator is an additional set-up to the climb milling process, which prevent the backlash problem.
2. Harder material
Climb milling is unsuitable for more rigid materials, including carbon steel, cast iron, and carbide-based alloys. The cutting force is maximum at the initial contact position of the workpiece and cutter teeth, which creates a high impact force in the teeth and can damage the tool.
3. Safety attention
Feeding in the same direction as the tool’s rotation causes the cut to approach the tool, which means it needs to pull. The pulling of the workpiece requires more attention for safety.
4. Vibration
The high fast feeding of the workpiece in climb milling creates a vibration, which can trigger the deflection of the tool. Even a slight deviation can have a significant impact on accuracy.
What is the difference between climb milling and conventional milling
Climb milling and conventional milling are two types of milling that differ in the direction of the cutting tool’s rotation relative to the direction of the workpiece’s movement.
In climb milling, the cutting tool rotates in the same direction as the workpiece’s movement, which allows the chips to be lifted away from the workpiece and results in a smoother surface finish. Climb milling also generates less heat and results in longer tool life. However, climb milling can result in more cutting forces and has a higher tendency for tool deflection.
In conventional milling, the cutting tool rotates in the opposite direction of the workpiece’s movement, resulting in a tendency for the chips to be pushed into the workpiece and resulting in a rougher surface finish. Conventional milling generates more heat and results in shorter tool life, but it has a lower tendency for tool deflection and produces fewer cutting forces.
Comparison of Conventional and Climb Milling Processes
Let’s compare the conventional and climb milling processes in different aspects, such as their capacity, cutting tool, surface finish, and many more.
| Criteria for Comparison | Description |
| Cutting force | In Conventional milling, cutting force gradually increases from the initial contact of the Cutter and workpiece to the exit point. While it gradually decreases in the case of climb milling. In addition, Climb milling requires less cutting force than conventional. |
| Chip thickness | Conventional milling involves a progressive rise in chip thickness from the initial contact between the Cutter and the workpiece to the exit point. While in the case of climb milling, it gradually decreases. |
| Chip-direction | Conventional milling involves leaving the chip in front of the tool. Climb milling leaves in the cutter path. |
| Drag | In climb milling, the workpiece is dragged in the cutter direction due to feeding in the same order. On the other hand, conventional milling pushes the workpiece away. |
| Friction & Heat | Conventional milling produces greater friction due to its high cutting force than climb milling. Heat generation occurs similarly because friction and heat generation are proportional. |
| Tool life | Excessive heat, vibration, and high cutting force of conventional milling cause more wear and tear on the Cutter than climb milling. Therefore, the tool has more life with climb milling. |
| Tool deflection | Tool deflects parallel with cut in conventional milling & perpendicular in climb mill. The parallel deflection implies a low risk of undesirable cuts. |
| Surface finish | Climb milling offers smoother as-machine surface finishing. The re-cutting of chips and high cutting force results in a poor finish with conventional milling. |
How to Choose the Right Milling Approach?
Selecting one milling approach from conventional & Climb is a complicated phenomenon. It needs to consider various factors, such as material type, required specification, accuracy, etc.
| Requirements and scenarios | Selection |
| Facing | The facing demands a burr-free, smooth surface finish. Therefore, it is recommended to utilize climb milling. Climb milling includes forcing the chips onto the center. |
| High accuracy | Conventional milling is suitable for accurate milling. The deflection occurs parallel to the feed, which causes the minimum impact on accuracy. In addition, it also gives more control over possible errors. |
| Smooth finish | Climb milling is preferable. It prevents the re-cutting, and the lower cutting force offers a more smooth finish. |
| Hard material | Conventional milling is an accurate option for hard material, and climb milling can affect the tool while working with hard material. |
| Size of workpiece | Large workpieces, blocks, and bars are better suited for conventional milling. At the same time, climb milling is the best option for small parts that require a high-quality finish. |
Conclusion
CNC machining is capable of performing both conventional and climb milling. The best approach depends on the requirement of machining and material type. Both conventional and climb milling have advantages and drawbacks. Whether you utilize Climb or conventional milling, the quality of the results depends on the selection of the right tool, milling parameters, operator expertise, and the capacity of the CNC machine.
Prolean Hub offers professional CNC milling services for more than 50 materials. We have cutting-edge CNC technology with expert engineers and operators with a decade of industry experience. If you need any CNC machining service, we can be your partner to convert any design into functional par, exactly as you need, please feel free to contact us.
FAQ’s
What does it mean by Climb and conventional milling?
Climb and conventional milling are two types of milling processes distinguished by the direction of feed with respect to tool rotation. The same feeding direction refers to climb milling, while the opposite direction occurs in conventional milling.
What are the advantages of conventional milling?
The advantages of conventional milling include no backlash effect, higher stability & control, accuracy, and a low chance of undesirable cuts.
What are the advantages of climb milling?
Climb milling provides a more smooth surface finish, less heat generation, low friction, lower tool deflection, better tool life, and many other advantages.
When to choose conventional milling?
Conventional milling is appropriate for large workpieces, such as blocks. It is also compatible with hard materials. It is recommended in those applications where a high-quality surface finish is not an issue.
When to choose climb milling?
Climb milling is appropriate for small workpieces of comparatively low-hardness material. Where a flawless surface finish is crucial, it is perfect.
Bibliography
- (2019). Climb Milling vs Conventional Milling. Sherline Products from https://www.sherline.com/wp-content.
- Ofir Galiki. (2021). Climb vs Conventional Milling: The Differences. All3DP, from https://all3dp.com/.
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