Process and Programming in the Training of CNC Lathes

CNC Lathe

When beginners in numerical control technology, especially students from higher vocational colleges, practice on CNC machine tools, they often face challenges despite having studied related technical courses. The lack of real-world production experience makes it difficult for them to fully grasp how to apply their knowledge effectively. As a result, even after learning, they may struggle to produce parts that meet the intended specifications. To address this, training examples are used to guide students through the process of analyzing and discussing both the machining procedures and programming aspects.

1. Training Conditions

(1) Equipment: "GTC2E" CNC lathe from Shenzhen.

(2) Software: "SANYING" CNC lathe simulation system.

(3) Practical Example: Boring tool handle.

(4) Blank: φ26mm round wood.

(5) Part Drawing: The boring tool handle is shown in the drawing.

2. Process Planning

(1) Start by carefully studying the part drawing. Identify the shape, which consists of a truncated cone, a cylinder, and three arc-connected surfaces. Determine the workpiece coordinate origin and calculate the coordinates of each vertex and the connection points of the curves. Refer to the notes on the drawing for details.

(2) Tool selection is critical. Ensure the tool’s structure and size do not interfere with the already machined areas. If the cutting point deviates from the tool tip, overcutting may occur. For smaller profile curves, consider using shaped tools. For the handle, which has a complex non-uniform profile made up of three arcs, choose an external turning tool with a main inclination angle of 90° and an auxiliary angle of 15°, as this helps avoid interference with the contour.

(3) Based on the selected tools, plan the machining sequence. Use the right-hand right-handed tool for most operations, aiming to complete as much material removal as possible before changing tools. This reduces the number of tool changes and saves time.

(4) Consider roughing and finishing steps. While using a full contour cycle simplifies programming, it can lead to excessive idle movements, reducing efficiency. Therefore, use the cone-cutting method for the R8mm ball end first, then apply a roughing cycle for the R30mm concave arc. After rough machining, perform a final pass to ensure accuracy and surface finish.

(5) Select cutting parameters wisely. Prioritize processing quality and tool life while maximizing machine and tool performance to achieve high efficiency and low cost. During roughing, use lower speeds, larger depths, and higher feed rates. For finishing, increase speed and reduce feed rate.

CNC Lathe

3. Programming and Training Considerations

(1) Programming should follow the process plan. Define the workpiece origin at the center of the right end of the handle. Calculate the coordinates of all key points and curve connections. See the notes on the drawing. Set the correct starting position for each operation, such as N00040, N00110, N00210, and N00300. The starting point directly affects the contour accuracy.

(2) Divide the program into roughing, finishing, and special operations like tapering and cutting. For example, the roughing program runs from N00040 to N00200, removing most of the material. Finishing uses N00210 to N00280 with T01 (external right-handed tool). Tapering and cutting are handled by T02 (4mm cutting knife). Pay attention to the actual tool nose and its width when programming.

(3) Avoid using G00 to move directly to the workpiece surface. Instead, use G01 for controlled movement to prevent collisions. For instance, in N00140, N00220, N00270, and N00310, G01 ensures safe tool movement.

(4) Accurate tool setting is essential. Programming is based on the tool tip's position relative to the part. Before training, set the tool so its tip aligns with the workpiece origin. This ensures accurate contouring after programming.

(5) Use simulation to check the tool path. Even if the simulation looks correct, it might not show all potential overcuts or interferences. Simulation confirms programming correctness but doesn’t guarantee flawless results during actual machining.

4. Example Programming

The following is the program for the boring tool handle on the "GTC2E" CNC lathe:

N00010 M03 S600

N00020 G00 X60 Z20

N00030 T1 (external right-handed tool, 15° side angle)

N00040 G00 X16 Z2

N00050 G24 X36 W-10 F50

N00060 U-5

N00070 U-5

N00120 G00 X37 Z2

N00130 G22 L2

N00140 C00 U-31

N00150 G01 W-2 F60

N00160 G03 U15.2 W-5.5 R8

N00170 G03 U4.4 W-46.9 R85

N00180 G02 U2.4 W-17.6 R30

N00185 G01 U4

N00190 G00 W72

N00200 G80

N00210 G00 X0 S1000

N00220 G01 Z0 F40

N00230 G03 X15.2 Z-5.5 R8

N00240 G03 X19.6 Z-52.4 R85

N00250 G02 X22 Z-70 R30

N00260 G01 Z-95

N00270 G01 X26

N00280 G00 X60 Z20 S500

N00290 T2 (cutting tool, 4mm wide)

N00300 G00 X24 Z-84

N00310 G01 X17 F30

N00320 G01 X16 Z-94

N00330 G01 X0

N00340 G00 X60 Z20

N00350 M05

N00360 M02

5. Conclusion

In summary, the numerical control training process includes several key steps: analyzing the part drawing, developing a process plan, programming, tool setup, simulation, and finally machining the part. In the initial stages, it's better to focus on simple features rather than complex contours. Don’t try to implement every step at once—start with a few representative surfaces and build up from there. Through practical examples, students can develop a clear process plan, select the right tools, and create programs that match the part design, leading to better understanding and improved skills. This approach not only enhances learning efficiency but also helps students gain confidence in real-world applications.

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