CNC Knowledge: Analysis of typical examples of CNC LATHE machining and programming

Unlocking the Power of CNC Machining: A Comprehensive Guide to Programming Methodologies and Best Practices

As the demand for precise and complex parts continues to grow, CNC (Computer Numerical Control) machining has become an indispensable technology in various industries. While CNC machining offers numerous advantages, programming these systems can be a daunting task, especially for those new to the field. In this article, we’ll delve into the different programming methods, steps, and best practices to help you unlock the full potential of CNC machining.

Programming Methodologies: Manual vs. Automatic

When it comes to CNC programming, there are two primary methods: manual and automatic. Manual programming involves creating a program manually, which is suitable for simple parts with fewer geometric complexities. In contrast, automatic programming uses computer-aided design (CAD) software and machine-specific software to create the program, making it ideal for complex parts with numerous geometric features.

While manual programming is suitable for straightforward tasks, it can be time-consuming and prone to errors. Automatic programming, on the other hand, ensures precision and efficiency, as it eliminates the risk of human error. However, it’s essential to note that manual programming is the foundation for automatic programming, and a thorough understanding of the latter is contingent upon a comprehensive grasp of the former.

Programming Steps

The programming process involves several critical steps, which are outlined below:

1. Analysis of Part Drawings: Upon receiving a part drawing, the first step is to analyze the part’s geometry, determine the processing method, and identify the necessary tools, lines, and functions required to manufacture the part.
2. Digital Calculations: Digital calculations are performed to determine the optimal processing parameters, including tool selection, feed rates, cutting speeds, and cutting depths. Most CNC systems have built-in toolpath generation capabilities, which simplify the process.
3. Tool Selection and Positioning: Based on the calculated parameters, the program generates a movement trajectory for the tool, considering factors such as feed rates, acceleration, and deceleration.
4. Programming: The generated toolpath and processing parameters are combined to create the part processing program. This program is then loaded into the CNC machine’s memory for execution.

Typical Examples and Best Practices

CNC machines specialize in treating various materials, including rotational parts, which are often categorized as follows:

• External Cylinders
• External Cones
• Wires
• Arc Surfaces
• Grooves

For example, a manual programming approach is often employed for parts with simple geometric shapes, such as the one depicted in Figure 1. In contrast, automatic programming is more suitable for complex parts with intricate features.

Case Study: Siemens 802S CNC System

To illustrate the programming process, let’s consider a Siemens 802S CNC system, which requires a multi-step approach:

1. Determine the Treatment Route: Define the processing sequence, starting with the roughing operation, followed by finishing, then removing the groove, and finally dealing with the thread.
2. Selecting and Assembling the Tool Point: Utilize an eccentric mandrel with three ingots and select the tool point at the intersection of the right-hand end of the room and the rotation axis.
3. Selecting the Tool: Choose different tools depending on the processing requirements: No. 1 for rough external turning, No. 2 for finished external circular turning, No. 3 for groove cutting, and No. 4 for thread cutting.
4. Determining the Cutting Use: For instance, the exterior circle of the car is treated with a cutting speed of 500 revolutions per minute, a feed rate of 0.3 mm per revolution, a spindle speed of 800 revolutions per minute, and a feed rate of 0.08 mm per revolution.
5. Programming: Establish the programming origin at the intersection point between the axis line and the center of the ball head, and define the part processing procedure.

Main Program

JXCP1.MPF
N05 G90 G95 G00 X80 Z100 (tool change point)
N10 T1D1 M03 S500 M08 (External tool Round Rough Turning)
-CName = "L01"
R105 = 1 R106 = 0.25 R108 = 1.5 (define the parameters of the white cutting cycle)
R109 = 7 R110 = 2 R111 = 0.3 R112 = 0.08
N15 LCYC95 (calling on the Rugueux treatment cycle)
N20 G00 X80 Z100 M05 M09
N25 m00
N30 T2D1 M03 S800 M08 (External precision turn)
R105 = 5 (define the parameters of the empty cutting cycle)
N40 LCYC95 (calling for the finish of the empty cutting cycle)
N45 G00 X80 Z100 M05 M09
N50 m00
N55 T3D1 M03 S300 M08 (Groove cutting tool, 4 mm knife width)
N60 G00 x37 Z-23
N65 G01 X26 F0.1
N70 G01 X37
N75 G01 Z-22
N80 G01 X25.8
N85 G01 Z-23
N90 G01 X37
N95 G00 X80 Z100 M05 M09
N100 m00
N105 T4D1 M03 S300 M08 (triangular turn tool)
R100 = 29.8 R101 = -3 R102 = 29.8 (define the parameters of the wire cutting cycle)
R103 = -18 R104 = 2 R105 = 1 R106 = 0.1
R109 = 4 R110 = 2 R111 = 1.24 R112 = 0
R113 = 5 R114 = 1
N110 LCYC97 (Call wire cutting cycle)
N115 G00x80 Z100 M05 M09
N120 m00
N125 T3D1 M03 S300 M08 (cutting rotation tool, 4 mm knife width)
N130 G00 X45 Z-60
N135 G01 X0 F0.1
N140 G00 x80 Z100 M05 M09
N145 m02
Sub-program
L01.SPF
N05 G01X0 Z12
N10 G03 x24 Z0 CR = 12
N15 G01 Z-3
N20 G01 X25.8
N25 G01 X29.8 Z-5
N30 G01 Z-23
N35 G01 X33

By understanding the programming methodologies, steps, and best practices outlined in this article, you’ll be well-equipped to unlock the full potential of CNC machining. Whether you’re a seasoned expert or just starting out, this comprehensive guide will help you navigate the world of CNC programming with confidence.