In metal turning, the setting of cutting parameters is critical to ensure machining quality, improve productivity, and extend tool life. Whether using traditional lathes or modern CNC machines, proper selection of cutting parameters is the foundation for efficient machining. This article will focus on the setting of cutting parameters in a metal woodturning machine (non-CNC), emphasizing how to select cutting speed, feed rate, cutting depth, and other key parameters. Specific examples will be provided to illustrate these concepts.

1. Basic Structure and Working Principle of a Metal Woodturning Machine

A metal woodturning machine differs significantly from a traditional wood lathe. Metal lathes generally use harder materials for cutting tools and are capable of higher spindle speeds and more precise feed controls. In non-CNC lathes, the operator manually adjusts the machine to control the cutting process, using the handwheels and controls to set and adjust cutting parameters.

The basic components of a metal lathe include:

1. Spindle: Drives the workpiece to rotate.

2. Tool Post: Holds the cutting tool and allows it to move along the workpiece.

3. Bed and Tailstock: Provide support for the machine's components, ensuring accuracy.

4. Feed System: Controls the movement of the cutting tool in various directions.

2. Importance of Cutting Parameters

Cutting parameters are crucial factors that influence the machining process. Different settings can directly affect the results, including tool life, surface finish, and cutting forces. The primary cutting parameters include:

1. Cutting Speed (V): The relative speed between the tool and the workpiece, typically measured in meters per minute (m/min).

2. Feed Rate (f): The distance the tool moves along the workpiece per revolution or per minute, measured in millimeters per revolution (mm/rev) or millimeters per minute (mm/min).

3. Cutting Depth (ap): The maximum depth to which the tool cuts into the workpiece, typically measured in millimeters (mm).

4. Cutting Width (ae): The width of the tool's contact with the workpiece, often considered alongside cutting depth.

Proper selection of these parameters is essential for achieving high-quality machining results. Improper settings can lead to excessive tool wear, rough surfaces, and increased cutting forces.

3. Selection of Cutting Parameters in Metal Turning

1. Cutting Speed (V)

Cutting speed refers to the relative velocity between the tool and the workpiece. It directly affects the amount of heat generated during cutting, the rate of tool wear, and the surface quality of the workpiece. The choice of cutting speed depends on the material being machined, the tool material, and the machining conditions.

Formula for calculating cutting speed:

$$V = \pi \cdot D \cdot n$$

Where $V$ is cutting speed (m/min), $D$ is the workpiece diameter (mm), and $n$ is spindle speed (rpm).

Cutting speed varies widely depending on the material. For example:

• Aluminum alloys: High cutting speeds, generally around 150-200 m/min.

• Steel: Generally around 100-150 m/min.

• Stainless steel: Lower cutting speeds, typically around 50-100 m/min.

On a non-CNC lathe, the operator adjusts the spindle speed to control the cutting speed. It is essential to select the appropriate cutting speed based on the material's hardness and the desired machining outcome to optimize tool life and cutting efficiency.

2. Feed Rate (f)

The feed rate refers to the speed at which the cutting tool moves relative to the workpiece. It is typically measured as the distance moved per revolution (mm/rev) or per minute (mm/min). The feed rate affects both the machining efficiency and the surface finish.

• High feed rate: Results in faster cutting but may lead to rougher surfaces and increased tool wear.

• Low feed rate: Results in better surface finish but can reduce machining efficiency.

For example, in machining aluminum, the feed rate can be set higher (0.2-0.3 mm/rev) since aluminum is easier to cut. For harder materials like steel or stainless steel, the feed rate should be lower (0.05-0.1 mm/rev) to prevent excessive tool wear.

3. Cutting Depth (ap)

Cutting depth is the maximum depth at which the tool engages the workpiece. It plays a significant role in machining efficiency and tool life. The selection of cutting depth depends on the workpiece geometry, tool durability, and the desired material removal rate.

• Smaller cutting depth (e.g., 0.5-2 mm) is used for finishing or machining thin-walled parts.

• Larger cutting depth (e.g., 3-5 mm or more) is used for rough cutting, optimizing material removal rate.

A deeper cutting depth generates higher cutting forces, so it may be suitable for roughing but could lead to poor surface finish or tool wear in finishing operations.

4. Cutting Width (ae)

Cutting width refers to the lateral width of the contact area between the tool and the workpiece. It is typically considered alongside cutting depth in operations where the tool engages more of the workpiece surface. The appropriate selection of cutting width helps control the machining forces and tool wear.

For precision work, cutting width is usually kept smaller to improve surface quality, while for roughing operations, cutting width may be larger to increase material removal rates.

4. Example of Setting Cutting Parameters

Let's assume we are using a non-CNC metal lathe to machine a steel workpiece with a diameter of 50mm. The following steps can be followed to set the cutting parameters:

1. Select Cutting Speed: Steel typically has a cutting speed range of 100-150 m/min. For this example, we choose 100 m/min.

   $$n = \frac{V}{\pi \cdot D} = \frac{100}{\pi \cdot 50} \approx 63.66 \, \text{rpm}$$

   So, the spindle speed should be set to approximately 64 rpm.

2. Set Feed Rate: Based on the material and the machining task, we can select a feed rate of 0.1 mm/rev, which balances machining efficiency with surface quality.

3. Select Cutting Depth: Since this is roughing, a cutting depth of 3 mm is suitable to maximize material removal rate.

4. Set Cutting Width: For rough cutting, a cutting width of 2 mm is selected to optimize material removal.

Thus, the cutting parameters for this operation would be:

• Cutting speed: 100 m/min

• Spindle speed: 64 rpm

• Feed rate: 0.1 mm/rev

• Cutting depth: 3 mm

• Cutting width: 2 mm

5. Conclusion

In a non-CNC metal woodturning machine, proper setting of cutting parameters is crucial for improving machining efficiency, ensuring high-quality results, and extending tool life. By selecting appropriate cutting speed, feed rate, cutting depth, and cutting width, the operator can control the machining process effectively, preventing issues like excessive tool wear and poor surface finish. The choice of cutting parameters should always be based on the material being machined, the type of operation (roughing or finishing), and the desired quality of the workpiece. Through experience, operators can fine-tune these parameters for optimal performance in specific machining tasks.