In today’s fast-paced industrial world, how do we ensure the precision and consistency of manufactured products? The answer lies in CNC manufacturing standards. What are these standards? And why are they so crucial? Let’s embark on a journey to uncover the significance and details of CNC manufacturing standards.
CNC Manufacturing Standards
CNC manufacturing standards are significant specifications that ensure the accuracy and consistency of CNC machining China, covering various aspects.
Contents of CNC Machining Standards
1. Processing Technology Standards
The processing technology standards mainly cover the design requirements of the workpiece, process routes, tool selection, cutting parameters, fixture design, and other contents.
2. Processing Quality Standards
The processing quality standards include accuracy, surface roughness, workpiece size deviation, and efficiency.
3. Programming Requirements
The programming basis includes CNC machining orders, mold materials, processing requirements, processing sequence, machine tool parameters, tool parameters, cutting data, EDM data, etc. The programming process requires careful analysis of the mold structure and product.
4. Standards for Electrode Dismantling
For the production of electrode dismantling, there are standards such as being able to combine but not separate, translation rather than rotation, avoiding wire cutting as much as possible if it can be avoided, and fully considering the effect of tool CNC turning and milling.
Work Requirements for Process Engineers
When the process engineer compiles the process card, the processing allowance, orientation, roughness requirements, and precautions should be detailedly noted, following the principle of giving priority to the use of high-efficiency equipment under the premise of ensuring accuracy and quality.
Processing Allowance and Accuracy Requirements
1. Processing Allowance
Different allowance standards for workpieces require heat treatment processing, the rough machining parts of mold core inserts, the rough milling of the shape by bench workers and milling machines, workpieces that require grinding machine processing after wire cutting, CNC finishing, and electrical pulse, etc.
2. Accuracy Requirements
The processing accuracy requires that the manufacturing accuracy of the mold size be within the range of 0.005 to 0.02mm, and there are also corresponding standards for perpendicularity, coaxiality, and the parallelism of the parting surfaces of the movable and fixed molds.
If abnormal situations occur during production, they should be inspected and handled promptly to ensure processing quality. Different industries and application scenarios may have different focuses and specific requirements for CNC manufacturing standards.
CNC Machining Process Standards
CNC machining process standards cover multiple aspects from machine tool selection, tool selection, and processing sequence to processing parameter setting. In terms of machine tool selection, an appropriate type of CNC machine tool, such as a milling machine or machining center, should be chosen based on the characteristics and processing requirements of the workpiece. The selection of tools needs to consider factors such as workpiece material, processing accuracy, and surface quality requirements. Here are some key standards and precautions:
1. Tool Use and Safety:
At the beginning of each program execution, it is necessary to check whether the tool used is consistent with the one in the programming guidebook.
When starting the processing, adjust the feed rate to the minimum, execute the single section, concentrate, and keep your hand on the stop button. Stop immediately if there is any problem, and pay attention to observing the movement direction of the tool to ensure safe tool entry.
Use coolant or cold air to cool the tool and the workpiece to reduce the influence of heat on the workpiece.
2. Process Flow:
After roughing processing, recalibration and touching numbers should be carried out to ensure that the workpiece is not loose.
After the workpiece is processed, its main dimension values should be measured to see if they are consistent with the requirements of the drawing. If there is any problem, immediately notify the relevant personnel to check and solve it.
3. CNC Machining Principles:
For the parts that require roughing by CNC, a unilateral allowance of 0.2mm should be reserved.
For the workpieces that require CNC finishing after heat treatment, if the appearance of the product allows, CNC processing should be preferred; otherwise, electrodes should be made for electrical pulse processing.
CNC Machining Quality Standards
The CNC machining quality standards mainly include aspects such as dimensional accuracy, geometric tolerances, and surface quality. The dimensional accuracy requires that the deviation of the actual size of the workpiece from the designed size is within the prescribed tolerance range. Geometric tolerances such as straightness, flatness, roundness, etc., also have strict requirements to ensure the accurate geometric shape of the workpiece. In terms of surface quality, it is required that the surface has no cracks, sand holes, pores, burrs, and other defects, and the surface roughness reaches the prescribed value. To achieve these quality standards, it is necessary to control factors such as machine tool accuracy, tool wear, and processing technology during the CNC production machining process.
Inspection of Finished Parts
1. Consistency Inspection
The appearance, color, and surface finish of the incoming materials of the same batch must be consistent. The incoming materials of different batches used in the same machine need to be consistent with the previous batches of incoming materials and other parts of the entire machine, and there is no obvious difference in chromaticity and finish from the sample.
2. Appearance Inspection
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The part surface is smooth, flat, and clean, without burrs, deformation, rust, cracks, etc.; the thread has no defects or corrosion; there should be no processing residue;
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Blunting of sharp edges (corners) of parts: The blunting value is not inspected under normal circumstances. In case of disputes, it is inspected according to the following principles:
When the shortest straight wall is greater than 2mm, chamfer or fillet less than 0.5mm, not scratchy;
When the shortest straight wall is less than or equal to 2mm, chamfer or fillet not more than 0.2 times the straight wall, not scratchy;
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Thread chamfer: The internal thread chamfers to the major diameter, and the external thread chamfers to the minor diameter. Requirements for appearance defects are as follows:
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Appearance Defect Type Allowable Range |
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Class A |
Class B |
Class C |
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Substrate Speckle |
Not allowed |
Not allowed |
S total ≤ 5% of the measured area |
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Shallow Scratch |
Not allowed |
L ≤ 50 × 0.4, P ≤ 2 |
L ≤ 50 × 0.4, P ≤ 5 |
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Deep Scratch |
Not allowed |
Not allowed |
Not allowed |
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Pit |
Not allowed |
Diameter ≤ 0.5 |
P ≤ 2, Unlimited |
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Pore, Bubble |
Not allowed |
Diameter ≤ 0.5, P ≤ 2 |
Diameter ≤ 0.5, P ≤ 5 |
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Polishing Area |
Not allowed |
Not allowed |
S total ≤ 5% of the measured area |
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* Note: S is the area of a single defect (mm2), P is the number of defects (pcs), and L is the length or spacing of the defect (mm). |
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3. Inspection of Dimensions, Geometric Tolerances, Roughness, and Center Holes
The process is as the same as that of in-process inspection.
4. Thread Inspection
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If the thread tolerance grade is marked on the drawing, inspect according to the drawing requirements; if it is not marked on the drawing, follow the following principles:
Default tolerance grade of common thread: 6H for internal thread, 6g for external thread;
Default tolerance grade of unified thread: 2B for internal thread, 2A for external thread.
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Inspection of common coarse thread:
Method 1: Inspect with a calibrated and qualified thread plug gauge or ring gauge. The go gauge should pass and the no-go gauge should not pass;
Method 2: Test assemble with a screw or nut that has passed the inspection of the thread plug gauge or ring gauge. It is qualified if it can pass smoothly and the thread limit size complies with relevant national standards.
Under normal circumstances, either of the methods 1 and 2 can be used for inspection and be qualified. However, when the parts inspected by method 2 have problems during assembly, method 1 must be used to inspect this part subsequently.
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Fine thread is inspected with a calibrated and qualified thread plug gauge or ring gauge. The go gauge should pass and the no-go gauge should not pass.
CNC Programming Basis and Process
The basis for CNC programming mainly includes three-dimensional models, engineering drawings, and part manufacturing instructions. In terms of the programming process, first, determine the programming basis and analyze the structure and process of the part. Then establish a process model, including trimming the model and establishing reference planes. Next, define machining operations, generate tool path trajectories, and conduct machining trajectory simulation verification. After that, perform post-processing to generate machining programs specific to a particular numerical control system.
Steps such as simulation verification and proofreading inspection of the numerical control machining program are also needed to ensure the correctness of the program. For example, when determining the programming basis, carefully analyze the complex shape and accuracy requirements of the part and select an appropriate programming method and tool path.
Programming Preparation Work
1. After receiving the entity, understand the mold structure first.
2. Understand the mating relationship of the product and reserve allowance at the mating positions (such as spigots and holes).
3. Determine the machining coordinate system. Generally, the mold center is the machining coordinate system. The mold base surface or parting surface is the Z zero surface. Pay attention to the height difference between the mold base surface and the parting surface.
4. Determine the rapid positioning lift height.
Determine the Machining Process (Based on the Principle of Improving Efficiency and Machining Quality)
1. Numerical control machining processes are generally divided into roughing – corner cleaning – semi-finishing – finishing.
2. Try to use large tools for roughing and small tools for corner cleaning. The tool diameter for roughing should be larger than that for corner cleaning.
3. For large-area platforms, always use flat-bottomed cutters for milling. It is prohibited to use ball cutters for overall processing for convenience.
4. The machining step distance should be flexibly adjusted. Generally, the upper mold should be smoother and the lower mold can be rougher.
5. During roughing, the cutting depth per layer is about 0.8 – 1.2mm. After roughing, the machining allowance is 0.5 – 1.0mm.
6. Machining step distance: The finishing step distance for cavity machining is 0.3mm, for core machining is 0.4mm, for parting surface is 0.3 – 0.4mm, for the rough electrode is 0.3mm, and for the fine electrode is 0.2mm. (The machining step distance can be appropriately adjusted according to the tool diameter.)
Problems to be Noted in the Programming Process
1. Try to use rounded-edge cutters for roughing to reduce tool insert wear.
2. Fully consider tool rigidity and try to control the length-to-diameter ratio to be less than 5. When using extended tools for machining, sharp-cornered cutters can be used to reduce the milling contact area and avoid tool deflection.
Machining Methods and Tool Selection
1. Try to use large tools for roughing and then small tools for corner cleaning. Moreover, large-diameter tools have good rigidity, and the cutting depth and feed rate are significantly greater than those of small-diameter tools.
2. Try to use rounded-edge cutters for roughing and flat-bottomed cutters for corner cleaning. Because the tool inserts of rounded-edge cutters are better stressed and can be used for multiple corner turns, while square inserts can only be used twice more.
3. Generally, ball cutters should not be used for machining flat surfaces. Instead, flat-bottomed cutters should be used. It is best to leave 0.2mm for a final finishing pass.
4. For straight-wall groove machining, finish machining the bottom surface of the workpiece first and then the side surfaces. For side surfaces with a height less than 50mm, try to avoid using carbide insert tools for a large number of reciprocating machining. Instead, use straight-shank integral tools for contour machining. (The cutting depth per pass is approximately the radius of the tool.)
5. Appropriate use of formed tools for machining workpieces with regular shapes to improve efficiency. For example, taper cutters for milling inclined surfaces, finger cutters for milling ribs, and rounded-edge cutters (R0.3 – R1) for cleaning small rounded corners.
6. To ensure a constant cutting load on the tool, try to use a layer-by-layer circumferential machining method for tool movement and avoid up-down tool movement machining.
7. The rigidity of the tool used should be sufficient. Generally, the length-to-diameter ratio (measured by the ratio of tool length to diameter) should not exceed 5. For example, for a tool with a diameter of 16mm, the extended length should not be greater than 80mm. The tool should also have a clamping length of 25 – 45mm. This is to prevent tool deflection and overcutting due to insufficient rigidity during machining.
CNC Electrode Dismantling Production Standards
The CNC electrode dismantling production standards include electrode material selection, electrode combination principles, etc. The electrode material usually requires good electrical conductivity, such as copper, graphite, etc.
When combining electrodes, factors such as processing efficiency, convenience for subsequent processing, and avoiding wire cutting should be considered. For example, for electrodes that can be combined but not separated, they should be of appropriate size, height, and thickness; for electrodes that translate but do not rotate, subsequent processing efficiency and integration of data should be fully considered; for electrodes that can avoid wire cutting, wire cutting should be avoided as much as possible, and at the same time, the effect of CNC machining by tools should be fully considered.
CNC Machining Accuracy Requirements
The accuracy requirements of CNC machining mainly include dimensional accuracy, surface roughness, parallelism, and perpendicularity.
Dimensional accuracy: CNC machining can achieve very high dimensional accuracy, usually meeting tolerance requirements of ±0.01mm or smaller. This means that the size of the processed part should be very close to the size on the design drawing to meet the accuracy requirements of precision hardware parts.
Surface roughness: CNC machining should be able to control the surface roughness of parts to meet specific requirements. The surface roughness can reach Ra 0.8μm or smaller, and sometimes even below Ra 0.4μm to ensure the smoothness and quality of the part surface.
Parallelism and perpendicularity: CNC machining needs to ensure the parallelism and perpendicularity of parts to ensure that the relationship between the various surfaces of the part meets the requirements. This usually requires parallelism and perpendicularity requirements within 0.02mm to ensure the geometric accuracy and assembly performance of the part.
In addition, CNC machining also needs to pay attention to other technical requirements, such as selecting appropriate processing equipment and processing technologies, strictly monitoring and controlling the processing process, and avoiding the generation of processing errors to ensure that the processed parts meet the accuracy requirements.
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Are you in need of CNC manufacturing China? In the actual CNC manufacturing process, strictly following these standards mentioned above can ensure processing quality and efficiency and improve the competitiveness of products. If you want to meet CNC manufacturing needs, especially for small and medium-sized enterprises, it may require a lot of resources and professional knowledge in machining parts and obtaining CNC certification. Then you can cooperate with professional CNC processing suppliers such as Richconn.
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FAQ
1.How to avoid and solve the problem of chatter marks in CNC manufacturing?
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Select an appropriate tool: Choose an appropriate tool tip radius and ensure that the tool is firmly clamped.
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Control cutting parameters: Select an appropriate cutting speed.
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Consider tool paths: Adopt an appropriate tool path.
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Ensure that the workpiece is firmly clamped: Use an appropriate fixture to ensure that the workpiece does not move or vibrate during processing.
2.How to improve the efficiency of batch parts in CNC machining?
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Optimization of clamping scheme: Design fast and reliable tooling fixtures to reduce clamping time and improve clamping accuracy.
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Use automated clamping equipment such as pneumatic or hydraulic fixtures to improve clamping efficiency and consistency.
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Reduce the number of times of repeated clamping of workpieces.
3.Some precautions for CNC machining of complex parts?
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Ensure the accuracy and completeness of the drawing, and clearly mark requirements such as dimensions, tolerances, and surface roughness.
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Understand the cutting performance of materials, such as hardness and toughness, and adjust cutting parameters.
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Select a stable and reliable clamping scheme to avoid displacement or deformation of parts during processing.
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Operators should have rich processing experience and programming skills and be able to adjust process parameters in time according to the actual processing situation.