Programming Overview
A comprehensive guide to the fundamental concepts, methods, and procedures involved in creating precise instructions for computer numerical control (CNC) machines, essential knowledge for successful cnc machining jobs.
2.1.1 Basic Concepts of Programming
Before CNC programming, it is necessary to analyze the technical requirements, geometric shapes, machining content, and machining accuracy specified on the part drawing. Based on this analysis, the machining plan, processing route, tool setting point, cutting tools, and cutting parameters are determined, followed by necessary coordinate calculations. These foundational steps are critical for anyone pursuing cnc machining jobs.
Following the process analysis and coordinate calculations, machining information such as the part processing sequence, relative movement trajectory and direction between the part and the tool, dimensional data, process parameters (F, S, T), and auxiliary actions (speed change, tool change, coolant pump on/off, workpiece clamping and releasing, etc.) are compiled into a processing program list using codes and formats consisting of letters, numbers, and symbols specified by the CNC machine tool manufacturer.
This program list information is then input into the CNC device through various methods such as manual input (MDI), RS232C interface, USB interface, DNC interface, or network communication, enabling automatic machining by the CNC device. This sequence of CNC machining instructions, prepared according to the drawings of the part to be processed, its technical and process requirements, and in accordance with the instructions and format specified by the CNC device, constitutes the CNC machining program. The process of obtaining this CNC machining program is known as CNC programming, which is an extremely important task in CNC machining, especially for those engaged in cnc machining jobs.
It should be noted that there are many brands and types of CNC devices, each with different rules and formats for the CNC program language used. When preparing a machining program for a specific CNC machine tool, strict adherence to the provisions in the machine tool programming manual is essential. This book primarily introduces the programming methods based on ISO (International Organization for Standardization) standards, providing valuable knowledge for individuals seeking cnc machining jobs.
CNC Programming Interface
Modern CNC control systems display both the program code and a visual simulation of the machining process, improving efficiency and reducing errors in cnc machining jobs.
2.1.2 Basic Methods of Programming
The basic methods of CNC programming can be divided into manual programming and automatic programming. Each method has its advantages and applications in various cnc machining jobs, depending on the complexity of the part and production requirements.
Manual Programming
In manual programming, the entire process is completed manually. This requires programmers to not only be familiar with CNC codes and programming rules but also to master knowledge of mechanical processing technology and possess numerical calculation capabilities – essential skills for anyone performing cnc machining jobs that involve manual programming.
Manual programming is particularly suitable for simple parts with straightforward geometries, where the programming process can be completed efficiently without advanced software assistance. It remains a valuable skill in many cnc machining jobs, especially in small-batch production environments.
Automatic Programming
In automatic programming, the programmer inputs the part processing information into a computer according to the specifications of a specific automatic programming system, based on the requirements of the part drawing. The computer then automatically generates the program, and the programming system can automatically print out the program list – a technology that has revolutionized many cnc machining jobs.
Automatic programming not only reduces labor intensity and shortens programming time but also minimizes errors, making the programming process more efficient and reliable. This method is particularly advantageous for complex parts and is widely used in modern cnc machining jobs that require high precision and intricate geometries.
This chapter focuses on the relevant content in manual programming and will briefly introduce automatic programming, providing a balanced foundation for understanding both approaches used in contemporary cnc machining jobs. The ability to understand and apply both methods is increasingly valuable in the manufacturing industry, as different cnc machining jobs may require different approaches based on complexity, production volume, and specific technical requirements.
A comparison of manual and automatic programming workflows, highlighting the different steps and tools involved in each approach to cnc machining jobs
2.1.3 Steps and Content of Manual Programming
The steps of manual programming are a systematic process that ensures the accurate translation of part specifications into machine-executable code. Mastering these steps is fundamental for anyone involved in cnc machining jobs that require manual programming expertise.
Figure 2-1: Steps in Manual Programming
The sequential process that transforms a part design into a machined component through manual programming techniques, essential knowledge for cnc machining jobs.
Analyze the Part Drawing and Determine the Process
This step is a necessary prerequisite for part processing and forms the foundation of successful cnc machining jobs. The main content includes: based on the process analysis of the part drawing, selecting the machine tool, cutting tools, and fixtures; determining the part processing route, sequence of worksteps, and cutting parameters such as cutting speed, feed rate, and depth of cut.
Thorough analysis at this stage prevents costly mistakes later in the manufacturing process and is therefore a critical skill for professionals in cnc machining jobs. It involves understanding material properties, tolerance requirements, surface finishes, and any special processing considerations that might affect the programming approach.
Calculate Motion Trajectories
According to the dimensions on the part drawing and the requirements of the processing route, calculate the coordinate values of each point (such as starting point, end point, center, intersection point, tangent point) on the part contour and tool motion trajectory within the selected coordinate system (such as the workpiece coordinate system). This calculation step is particularly demanding in complex cnc machining jobs that involve intricate part geometries.
Sometimes it is only necessary to calculate the trajectory of the tool relative to the part contour, but in other cases, it is necessary to further convert to obtain the tool center motion trajectory. Additionally, the coordinates of each point must be converted into corresponding digital quantities according to the programming unit (pulse equivalent) specified by the CNC machine tool.
This step is also known as geometric calculation or numerical calculation and requires a strong mathematical foundation, making it one of the more challenging aspects of manual programming in cnc machining jobs. Accuracy here is paramount, as even minor calculation errors can lead to significant dimensional inaccuracies in the final part.
Prepare the Processing Program and Perform Initial Verification
Based on the established processing route, cutting parameters, tool numbers, tool compensation methods, auxiliary actions, and tool motion trajectories, prepare the part processing program in accordance with the instruction codes and program format specified by the machine tool's CNC system. This step requires meticulous attention to detail, a key attribute for success in cnc machining jobs.
The program must then be checked for errors, with necessary modifications made followed by further verification. This verification process is crucial in cnc machining jobs to ensure that the program will produce the desired part geometry without collisions between the tool and workpiece or machine components.
Input to the CNC System
The information from the processing program list is input into the CNC device through various methods such as MDI, RS232C interface, USB interface, DNC interface, or network communication. For simpler programs, direct input via the keyboard is also possible. Proficiency with these input methods is essential for efficient workflow in cnc machining jobs, as it ensures that the correct program is accurately transferred to the machine control system.
Program Verification and Test Cutting
After the program is input into the CNC device, it must undergo further verification and test cutting before being used for formal production. This quality control step is vital in cnc machining jobs to prevent material waste and ensure product quality.
A common practice is to perform an empty run or test cut on the machine tool for the input program. For planar contour parts, an empty run can be performed on the machine using a pen instead of a tool and graph paper instead of the workpiece, allowing for visualization of the tool path without consuming materials – a cost-effective verification method in cnc machining jobs.
For spatial curved surface parts, test cutting can be performed using wax blocks, plastic, wood, or low-cost materials to check the correctness of the program. This approach provides a practical validation of the program while minimizing material costs, an important consideration in many cnc machining jobs.
On machines with graphic display capabilities, static display (machine does not move) or dynamic display (simulating the workpiece processing process) methods are more convenient. However, these methods can only check the correctness of the motion trajectory and cannot determine the machining accuracy of the workpiece.
The method of first article test cutting (when conditions permit) can not only detect whether the input program contains errors but also determine whether the machining accuracy meets the requirements. When errors are found, the nature of the error should be analyzed, and the program list should be modified or the tool compensation dimensions adjusted until the workpiece meets the accuracy requirements specified in the part drawing – a final quality assurance step that distinguishes professional cnc machining jobs from amateur attempts.
Program Verification Methods in CNC Machining
Dry run verification using pen and paper for simple parts in cnc machining jobs
Computer simulation for complex geometries common in advanced cnc machining jobs
Test cutting with inexpensive materials to verify program accuracy in cnc machining jobs