0102030405
12 CNC machining experience summaries
2025-07-31
Cnc Machining, also known as numerical control machining, refers to machining performed using numerically controlled tools. BecauseCNC machining is computer-controlled after programming, it offers advantages such as stable machining quality, high precision, high repeatability, the ability to machine complex surfaces, and high efficiency. However, in actual machining, human factors and operator experience significantly impact the final machining quality. Below, we summarize twelve valuable experiences...
1.How to divide Cnc Machining Processes?
The division of CNC machining processes can generally be carried out in the following ways:
（1）The centralized tool sequencing method divides the process by tool used, using the same tool to complete all possible CNC machining areas on the part. A second and third tool are then used to complete the remaining areas that can be completed by them. This reduces the number of tool changes, shortens idle time, and minimizes unnecessary positioning errors.
（2）For parts with a lot of CNC machining content, the machining area can be divided into several parts according to their structural characteristics, such as internal shape, external shape, curved surface or plane. Generally, planes and positioning surfaces are machined first, and holes are machined later; simple geometric shapes are machined first, and then complex geometric shapes; parts with lower precision are machined first, and then parts with higher precision requirements.
（3）For parts prone to CNC machining deformation, the potential for deformation after rough machining requires correction. Therefore, generally speaking, all rough and fine machining processes must be separated. In summary, when dividing the processes, it is important to flexibly consider the part's structure and manufacturability, the machine tool's capabilities, the amount of CNC machining required, the number of installations, and the company's production organization. Whether to adopt a centralized or decentralized process principle should be determined based on actual conditions, but always strive for rationality.
2. What principles should be followed in arranging the CNC machining sequence?
The arrangement of the processing sequence should be based on the structure of the parts and the condition of the blank, as well as the need for positioning and clamping. The focus is on not destroying the rigidity of the workpiece. The sequence should generally be carried out according to the following principles:
（1）The CNC machining of the previous process cannot affect the positioning and clamping of the next process, and the general machine tool processing processes in the middle must also be considered comprehensively.
（2） Carry out the inner shape and inner cavity processing process first, and then carry out the outer shape processing process.
（3）It is best to carry out CNC machining processes with the same positioning, clamping method or the same tool in succession to reduce the number of repeated positioning, tool changes and platen movements.
（4）When multiple processes are carried out in the same installation, the process that causes the least damage to the rigidity of the workpiece should be arranged first.
3. What aspects should be paid attention to when determining the workpiece clamping method?
The following three points should be noted when determining the positioning reference and clamping scheme:
（1） Strive to unify the standards of design, technology, and programming calculations.
（2） Minimize the number of clamping times and ensure that all surfaces to be processed can be CNC machined after one positioning.
（3） Avoid using manual adjustment solutions that require the machine to be occupied.
（4） The fixture should be open, and its positioning and clamping mechanism should not affect the tool movement during CNC machining (such as collision). When encountering such a situation, you can use a vise or add a bottom plate to clamp it.
4. How to determine the most reasonable tool setting point? What is the relationship between the workpiece coordinate system and the programming coordinate system? （1）The tool setting point can be set on the workpiece being processed, but please note that the tool setting point must be the reference position or the part that has been finely processed. Sometimes the tool setting point is destroyed by Cnc Processing(https://www.xmrex-tech.com/customized-cnc-machined-plastic-and-metal-parts-product/) after the first process, which will make it impossible to find the tool setting point in the second process and later processes. Therefore, when setting the tool in the first process, pay attention to setting a relative tool setting position at a place with a relatively fixed size relationship with the positioning reference, so that the original tool setting point can be found based on the relative position relationship between them. This relative tool setting position is usually set on the machine tool workbench or fixture. The selection principles are as follows:
a,It is easy to find the alignment.
b, Easy to program.
c, Small tool setting error.
d,It is convenient and traceable to check during processing.
（2）The origin of the workpiece coordinate system is set by the operator. It is determined by tool setting after the workpiece is clamped. It reflects the distance and position relationship between the workpiece and the machine tool zero point. Once the workpiece coordinate system is fixed, it is generally not changed. The workpiece coordinate system and the programming coordinate system must be unified. That is, during machining, the workpiece coordinate system and the programming coordinate system are consistent.
5. How to choose the cutting route?
The tool path refers to the trajectory and direction of the tool relative to the workpiece during CNC machining. The proper selection of the machining path is very important because it is closely related to the CNC machining accuracy and surface quality of the part. The following points are mainly considered when determining the tool path:
（1）Ensure the machining accuracy requirements of parts.
（2） Facilitate numerical calculations and reduce programming workload.
（3） Seek the shortest CNC processing route and reduce idle time to improve CNC processing efficiency.
（4） Minimize the number of program segments.
（5）To ensure the roughness requirements of the workpiece contour surface after CNC machining, the final contour should be arranged to be processed continuously in the last pass.
（6）The tool's entry and exit (cutting in and out) routes must also be carefully considered to minimize tool marks caused by stopping at the contour (elastic deformation caused by sudden changes in cutting force), and to avoid scratching the workpiece by cutting vertically on the contour surface.
6. How to monitor and adjust during CNC machining?
After the workpiece is aligned and the program is debugged, it can enter the automatic processing stage. During the automatic processing, the operator must monitor the cutting process to prevent abnormal cutting that may cause workpiece quality problems and other accidents.
The following aspects are mainly considered when monitoring the cutting process:
（1）Process Monitoring: Rough machining primarily focuses on the rapid removal of excess material from the workpiece surface. During automatic machining, the tool automatically cuts along a predetermined cutting path based on the set cutting parameters. The operator should monitor the cutting load during automatic machining using the cutting load meter. Adjust the cutting parameters based on the tool's tolerances to maximize machine efficiency.
（2）Monitoring cutting sound during the cutting process:During the automatic cutting process, at the beginning of the cutting process, the sound of the tool cutting the workpiece is generally steady, continuous, and brisk, and the machine tool is moving smoothly. As the cutting process progresses, if there are hard spots on the workpiece, the tool is worn, or the tool is clamped, the cutting process may become unstable. This instability is manifested by changes in the cutting sound, the sound of collision between the tool and the workpiece, and vibration of the machine tool. At this time, the cutting amount and cutting conditions should be adjusted promptly. If the adjustment effect is not obvious, the machine tool should be paused to check the condition of the tool and workpiece.
（3） Monitoring the finishing process: Finishing is mainly to ensure the machining size and surface quality of the workpiece, with high cutting speed and large feed rate. At this time, attention should be paid to the impact of built-up edge on the machined surface. For cavity machining, attention should also be paid to overcutting and tool letting at corners. To solve the above problems, one is to pay attention to adjusting the spray position of the cutting fluid to keep the machined surface in a cooling condition at all times; the second is to pay attention to observing the quality of the machined surface of the workpiece and avoid quality changes as much as possible by adjusting the cutting amount. If the adjustment still has no obvious effect, the machine should be stopped to check whether the original program is reasonable. In particular, pay attention to the position of the tool when pausing for inspection or stopping for inspection. If the tool stops during the cutting process and the spindle stops suddenly, tool marks will be left on the workpiece surface. Generally, consider stopping the machine when the tool leaves the cutting state.
（4）Tool Monitoring: Tool quality largely determines workpiece machining quality. During automated cutting, methods such as sound monitoring, cutting time control, pause inspections during cutting, and workpiece surface analysis should be used to determine normal tool wear and abnormal tool damage. Tools should be promptly processed according to machining requirements to prevent machining quality issues caused by untimely tool processing.
7. How to choose machining tools properly? What are the major factors in cutting parameters? What materials are there for cutting tools? How to determine the tool speed, cutting speed, and cutting width?
（1）For plane milling, use a carbide end mill or end mill that has not been reground. For general milling, use two passes whenever possible. The first pass is best done with an end mill for roughing, making continuous passes along the workpiece surface. The recommended width for each pass is 60%-75% of the tool diameter.
（2） End mills and end mills with carbide inserts are mainly used for processing bosses, grooves and box surfaces.
（3） Ball cutters and circular cutters (also known as round nose cutters) are commonly used for machining curved surfaces and variable angle contours. Ball cutters are primarily used for semi-finishing and finishing. Circular cutters with carbide inserts are primarily used for roughing.
8. What is the function of a processing procedure sheet? What should be included in a processing procedure sheet?
（1） The machining procedure sheet is one of the contents of CNC machining process design. It is also a procedure that the operator needs to follow and execute. It is a specific description of the machining procedure. The purpose is to let the operator know the content of the program, the clamping and positioning method, the tools selected for each machining procedure, and the issues that should be paid attention to.
（2） The machining program sheet should include: drawing and programming file names, workpiece name, clamping sketch, program name, tool used in each program, maximum cutting depth, machining nature (such as rough machining or finishing), theoretical machining time, etc.
9. What preparations should be made before CNC programming?
After determining the processing technology, before programming, you need to understand:
（1） Workpiece clamping method;
（2） The size of the workpiece blank - to determine the processing range or whether multiple clamping is required;
（3）The material of the workpiece - in order to select the tool to be used for processing;
（4） What tools are in stock? This can help you avoid having to modify the program during processing due to the lack of such tools. If you must use such tools, you can prepare them in advance.
10. What are the principles for setting safety height in programming?
The principle of setting the safety height is generally higher than the highest surface of the island. Or set the programming zero point at the highest surface, which can also minimize the risk of tool collision.
11. Why do we need to perform post-processing after the tool path is compiled?
Because different machine tools can recognize different address codes and NC program formats, it is necessary to select the correct post-processing format for the machine tool used to ensure that the compiled program can run.
12. What is DNC communication?
Program transmission methods can be categorized as CNC and DNC. CNC involves transferring programs to the machine tool's memory via a media medium (such as a floppy disk, tape reader, or communication line) for storage. During machining, the program is retrieved from memory. Because memory capacity is limited, DNC processing is often used for large programs. During DNC processing, the machine tool reads the program directly from the control computer (i.e., processes the program as it is being transferred), so it's not subject to memory capacity limitations.
（1）There are three major factors in cutting parameters: cutting depth, spindle speed and feed speed. The general principle for selecting cutting parameters is: less cutting, faster feed (i.e. smaller cutting depth, faster feed speed).
（2）According to material classification, cutting tools are generally divided into ordinary hard white steel knives (made of high-speed steel), coated cutting tools (such as titanium-plated tools, etc.), and alloy cutting tools (such as tungsten steel, boron nitride cutting tools, etc.).