Exploring Advanced CNC Machining Procedures for Precision Manufacturing
Table of contents:
Chapter 1 : Basic principles of CNC machining procedures
Chapter 2: Processing part sequencing method
Chapter 3 : Tool centralized sequencing
Chapter 4 : Classification by processing part
Chapter 6: Precautions for process division
Chapter 7 : Example of process division
Chapter 8: Summary
Looking at CNC machining a part, it seems very simple. In fact, you may not know how complicated it is to process a CNC part. Different tools, different cutting methods, different parameter settings and other requirements will have different parameters and quality of the machined parts. In this way, the division of CNC machining procedures is very important. CNC machining procedures are the key links to ensure the machining accuracy, efficiency and economy of parts, and need to be considered comprehensively in combination with part structure, machining equipment characteristics, process requirements, etc. The division of CNC machining procedures can generally be carried out according to the following division principles, common methods, precautions and other aspects:
Chatper 1 : Basic principles of CNC machining procedures
Sequencing method based on rough and fine machining, For parts that are prone to machining deformation, due to the deformation that may occur after rough machining, correction is required. Therefore, generally speaking, all rough and fine machining procedures must be separated. In this way, machining accuracy can be guaranteed. Avoid mixing rough and fine machining to prevent the cutting force and thermal deformation during rough machining from affecting the precision of fine machining.
1.1 First machine the reference surface (such as plane, hole), and then use the reference surface to locate and machine other features.
1.2 Improve production efficiency
Reduce the number of clamping times to avoid repeated positioning errors (such as using one clamping to complete multi-faceted processing).
1.3 Concentrate similar processes (such as using the same tool to complete all similar hole processing) to reduce tool change time.
1.4 Simplify programming and process management
The process content should not be too complicated to facilitate program writing and debugging. Arrange the processes in the order of processing to avoid circuitous process routes.
Chapter 2: Processing part sequencing method
For parts with a lot of processing content, the processing of CNC parts 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 processed first, and then holes; simple geometric shapes are processed first, and then complex geometric shapes; parts with lower precision are processed first, and then parts with higher precision requirements. The common division methods of CNC processing processes are as follows:
2.1 Division by processing stage Rough processing process
Purpose: Quickly remove the blank allowance and form the basic shape of the part.
Features: Use large cutting amount (high feed, large cutting depth) to allow large processing errors.
Example: plane milling and rough boring of casting blanks.
2.2 Semi-finishing process
Purpose: reserve uniform allowance for finishing and correct roughing error.
Features: medium cutting amount, higher precision requirement than roughing.
Example: semi-finishing plane milling, semi-finishing boring.
2.3 Finishing process
Purpose: to achieve the final size, shape and surface roughness requirements of parts.
Features: use small cutting amount and strictly control errors.
Example: fine milling contour, fine grinding outer circle.
2.4 Finishing process
Purpose: to further improve surface quality (such as roughness Ra≤0.8μm).
Features: extremely small cutting amount, mostly using grinding, honing and other processes.
Chapter 3 : Tool centralized sequencing
Method is to divide the process according to the tool used, and use the same tool to process all the parts that can be completed on the part. Then use the second and third tools to complete the other parts that they can complete. This can reduce the number of tool changes, compress idle time, and reduce unnecessary positioning errors. Classification by processing tool
Advantages: Reduce the number of tool changes, improve efficiency, and avoid frequent loading and unloading of tools affecting accuracy.
Example:
Tool type Corresponding process
End mill Plane milling, groove processing
Drill Drilling, countersinking
Boring tool Boring, reaming
Thread cutter Tapping, thread turning
Forming tool Chamfering, arc groove processing
Chapter 4 : Classification by processing part
Grouping by geometric features:
Plane process: milling upper surface, step surface.
Hole system process: drilling, reaming, boring.
Contour process: outer contour milling, inner cavity processing.
Grouping by part relevance:
First process the reference surface (such as the bottom surface), and then use the reference surface to locate the processing side and hole.
Hole or plane in the same direction are processed together to reduce the movement of coordinate axis.
Chapter 5: Classification by installation times
Single clamping process: suitable for parts with simple structure that can be processed in one time.
Multiple clamping processes:
When flipping is required, divide the front and back processes (such as processing the front face first, and then flipping to process the back groove).
Note: The positioning reference must be clearly defined for each clamping to avoid cumulative errors.
Chapter 6: Precautions for process division
Consider the insertion of heat treatment processes
Arrange stress relief annealing after rough processing to avoid material deformation affecting subsequent processing.
Arrange finishing processes such as grinding after quenching to correct heat treatment deformation.
Reasonable arrangement of inspection processes
Set up inspections after key processes (such as size and shape tolerance detection) to prevent batch scrap.
Matching of equipment and process
Multi-axis linkage CNC machine tools are preferred for complex surface processing to simplify the process.
During mass production, consider special tooling and fixtures to reduce clamping time.
Avoid over-positioning and under-positioning
The clamping plan needs to match the process division to ensure positioning accuracy (such as the combination of three-jaw chuck and center).
Chapter 7 : Example of process division (taking box parts as an example)
Process 1: Rough milling of upper and lower surfaces
Equipment: vertical machining center, using face milling cutter.
Process 2: Fine milling of upper and lower surfaces (reference surface)
Reserve 0.5mm, surface roughness Ra≤3.2μm.
Process 3: Drilling (bottom surface mounting hole)
Use the bottom surface as the reference and use a drill.
Process 4: Boring (bearing hole)
Change the boring tool to ensure the hole accuracy H7.
Process 5: Milling side grooves
Flip over and clamp, and position with the bottom surface and the processed hole.
Chapter 8: Summary
In summary, it is understood that when dividing the process, it is necessary to flexibly grasp it according to the structure and processability of the parts, the function of the machine tool, the amount of CNC machining content of the parts, the number of installations and the production organization status of the unit. It is also recommended to adopt the principle of process concentration or the principle of process dispersion, which should be determined according to the actual situation, but it must be reasonable. The division of CNC machining processes should be based on "precision first, efficiency second" as the core, and the division method should be flexibly selected in combination with the characteristics of the parts. The typical process is: analyze the part drawing → determine the processing route → group by stage/tool/part → optimize the process sequence → verify the process feasibility. In actual production, the process can be simulated by process simulation software (such as UG, Mastercam) to further optimize the tool path and cutting parameters.
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