Manufacturers usually maintain high machining accuracy for high-precision hole parts, strictly controlling the diameter, depth, shape, location, and other parameters.
The level of machining accuracy directly affects the performance and service life of the parts. CNC milling machine as a modern manufacturing industry, one of the important equipment, its machining accuracy and efficiency directly affect the quality of products and market competitiveness.
Therefore, the application range of CNC machine tools is expanding. Explore the method of CNC milling processing high-precision hole parts has important practical significance.
High precision hole parts processing method
High-precision hole parts generally use reaming and boring processing methods, they differ in processing range, accuracy, economy and applicable scenes.
Reaming is more suitable for processing smaller holes, and precision and surface quality requirements are higher; and boring is more suitable for processing larger holes, or the need to expand the hole diameter, improve precision and reduce surface roughness.
In practice, according to specific processing needs and workpiece characteristics to choose the appropriate processing method.
Tool selection
In CNC milling of high-precision hole parts, operators should choose the appropriate tool based on the material properties, hole diameter, depth, and other factors.
Operators commonly use tools such as center drills, twist drills, reamers, and boring tools. They generally clamp hole tools using a self-tightening drill chuck (as shown in Figure 1).
To avoid damaging the chuck’s accuracy, operators should tighten it by hand instead of using wrenches. During drilling, the cutting force and spindle rotation act in opposite directions, causing the tool to tighten further and preventing it from falling out.
Boring tool has a special shank for clamping, general boring tool is a complete set, according to the size of the hole diameter, choose different boring tool shank and insert.
Requirements for higher precision holes, generally the first center drill centering, and then use the appropriate drill bit drilling, and finally according to the requirements of the use of the hole reamer reaming or boring tool boring.
Reaming process control
Reaming is a reamer from the workpiece hole wall to excise trace metal layer, in order to improve its dimensional accuracy and hole surface quality method, it is one of the hole finishing methods, widely used in production.
For smaller holes, reaming is a more economical and practical processing method compared to internal grinding and boring. The size of the molding reamer limits the processing range of reaming.
Reaming process
1. Reamer preparation
According to the processing needs to choose the appropriate reamer, common including straight shank reamer shown in Figure 2 and taper shank reamer shown in Figure 3.
2. Accuracy grade
There are three kinds of reamers: H7, H8 and H9, so choose the right reamer according to the machining accuracy requirements.
3. Preparation before reaming
(1) Before reaming, it is usually necessary to center drill and then drill with twist drill to ensure that the initial size and shape of the hole meets the reaming requirements.
(2) Install the selected drill and reamer on the spindle of the CNC milling machine, rotate it, and carry out the centering operation to prevent the drill and reamer from swinging.
4. Reaming operation process
(1) Drill Bit Selection and Sharpening
When drilling, choose a drill bit 0.3mm smaller than the reamer diameter. Sharpen and check the drill bit before use.
You should center the cross-cutting edge. Both sides of the main cutting edge should be equal in length. The outer edges at the turning point should be equal in height.
The outer edge of the turning point should be higher than its root. Poor sharpening can result in oversized holes, which affect reaming.
This is especially important for new drill bits. Rotate the drill left and right to inspect carefully.
After the operator qualifies the drill, you can first drill a depth of about 4mm and then use the reamer to try first, the hole size is not a problem and then continue to drill to the specified depth.
(2) Cutting Parameters and Reaming Guidelines
set the amount of cutting, according to the processing material to choose the appropriate amount of cutting.
If the material is 45# steel and you need to process a 10mm pin hole, use a 9.7mm drill bit to drill the hole.
First, check if the drill bit is qualified, as sometimes a 9.7mm drill bit can create a hole larger than 10mm.
Once the drill bit is qualified, drill about 4mm deep, then use a 10mm reamer to check the hole. If the reamer doesn’t fit, continue drilling.
This method ensures the most security.
After drilling, use Φ10H7 reamer to ream the holes, when reaming the holes, the speed of the reamer should not be too fast, generally the speed is about 120r/min, and the feed speed is 80mm/min.
For holes with high precision requirements, it may be necessary to carry out rough reaming first, and then carry out fine reaming.
In general, the larger the diameter of the tool, the slower the speed, the smaller the diameter of the tool the faster the speed.
(3) Select cutting fluid
To reduce the cutting temperature and extend the life of the tool, you need to choose the right cutting fluid.
Reaming toughness of the material, you can use emulsion or extreme pressure emulsion; reaming cast iron and other brittle materials, you can use kerosene or kerosene and mineral oil mixture.
Reaming notes
(1) reamer exit: reamer exit workpiece can not stop, to wait for the reamer completely out of the workpiece and then stop, in order to prevent the reamer reversal caused by the expansion of the hole diameter.
(2) axis coaxial: reamer axis and drilling, expanding the hole axis coaxial, the best drilling, expanding, reaming continuously to ensure the accuracy of the hole.
(3) prevent bumping: in the process of use to prevent bumping the cutting edge, so as not to damage the accuracy of reaming.
Quality inspection
(1) Aperture detection: the use of appropriate measuring tools to detect the aperture to meet the requirements, such as pin holes, you can take the standard pin detection.
(2) Surface quality: observe the surface quality of the hole to ensure smooth, no burrs, no defects.
(3) follow-up: according to the need for follow-up treatment of holes, such as cleaning, rust, etc..
Boring process control
Boring processes forged, cast, or drilled holes for further processing.
It can expand the hole diameter, improve accuracy, reduce surface roughness, and better correct the original hole axis skew.
You can divide boring into rough boring, semi-fine boring, and fine boring.
Among them, fine boring hole size accuracy up to IT8 ~ IT7, surface roughness Ra value of 1.6 ~ 0.8μm.
Boring process
1. Workpiece clamping
Fix the workpiece onto the CNC milling machine table to ensure stability and prevent movement or shaking.
2. Boring tool selection
According to the material, size and processing requirements of the workpiece, select the appropriate boring tool or other cutting tools, other cutting tools, including center drills, drills, milling cutters, etc., the choice of tool directly affects the quality and efficiency of processing.
The boring tool is a widely used hole processing tool. Boring tools come in various types, including single-edged, double-edged, and fine-tuning boring tools.
Choose the right type based on processing needs. The general CNC milling machine uses a fine-tuning boring tool, as shown in Figure 5.
The micro-adjustable boring tool has a fine adjustment device that allows for fine-tuning the cutting diameter, making it suitable for processing tasks with higher precision requirements.
3. Preparation before boring
Boring, to the boring tool should not be too large, the general diameter of the hole to stay about 1mm can be. In the boring before, with a drill first for drilling, and then milling with a milling cutter for milling, the purpose is to pre-form the base shape of the hole in the workpiece, in order to facilitate the subsequent boring operation. The following are the general steps and points of the boring process.
(1) Determine the processing requirements:
clear hole size, accuracy, surface roughness and other requirements, according to the workpiece material and processing requirements to select the appropriate tool and cutting parameters.
(2) workpiece preparation:
the clamped workpiece for the tool operation, the general programming zero point set in the center of the hole, that is, X, Y-axis tool to take the center of the circle, to facilitate the boring program. Check whether the surface of the workpiece is flat, to ensure the accuracy of the machining datum, the surface of the workpiece for the Z-axis zero point.
(3) tool installation:
select the appropriate milling cutter, ensure that the shank extends the length of moderate, leakage part to be longer than the depth of the hole, but also do not leave too long, affecting the rigidity of the tool processing.
4. Programming processing
(1) processing parameter setting: the use of CNC programming software or manual programming, according to the shape of the workpiece and processing requirements for the preparation of processing programs.
If it involves multiple holes or deeper holes, you can use a fixed cycle of instructions to simplify programming, such as drilling cycle G81, G73, boring cycle G85, G76.
After the program is written, verify and simulate the run to ensure the correctness and feasibility of the program.
In programming, according to the workpiece material and processing requirements, set the appropriate processing parameters.
These parameters include spindle speed, feed speed, depth of cut, machining radius and so on.
Ensure that these parameters are set correctly to ensure machining accuracy and quality.
(2) monitoring and adjustment: CNC milling machine boring process should strictly abide by the operating procedures and safety standards to ensure the personal safety of the operator and the safe operation of the equipment.
In the processing process, pay close attention to the operating status of the CNC milling machine and processing quality.
If necessary, according to the processing situation to make appropriate adjustments, such as changing the spindle speed, feed rate, etc., in order to obtain the best processing results.
5. Boring operation process
(1) First of all, rough milling of the round hole, remove most of the residual amount, the formation of the basic shape of the hole. In the rough milling based on fine milling, to further improve the accuracy and surface quality of the hole.
Namely, to bore a round hole of R30, as shown in Fig. 6, first use Φ18 drill bit to drill in the center of the circle, and then use Φ16 alloy milling cutter to mill the hole to R29.5.
To summarize, the milling process before boring is an important preparatory stage, which directly affects the quality and efficiency of the subsequent boring process.
Therefore, in practice, should be strictly in accordance with the technical requirements for processing, to ensure that each step to achieve the intended quality objectives.
(2) boring tool boring, boring is divided into rough boring and fine boring, you need to first touch the tip of the boring tool round the inner wall, the boring tool lifted, then fine-tune the boring tool dial, adjust the amount of cutting 0.3mm, fine-tune the boring tool on the dial to adjust the size refers to the diameter.
Cutting off 0.3mm after using the internal diameter gauge as shown in Figure 7 for measurement, the remaining size in two boring, each boring needs to be measured with the internal diameter gauge, to ensure the accuracy of the size of the bore.
6. The use of internal diameter gauge
(1) I.D. gauge specifications 18 ~ 35mm, 35 ~ 50mm, 50 ~ 160mm, etc., in accordance with the size of the hole to choose different specifications of the I.D. gauge, I.D. gauge is a complete set of screws with different diameters, according to the size of the hole to be measured by selecting the corresponding screws and screwed in the table on the rod, while the percentage of the meter is installed to the table on the rod.
(2) According to the measured size tolerance, first choose a micrometer, such as R30 round hole, diameter of 60mm, you can choose 50 ~ 75mm micrometer, micrometer adjusted to 60mm and lock.
(3) one hand to hold the inner diameter of the meter, one hand to hold the micrometer, the table will be placed in the micrometer probe for calibration, pay attention to make the meter rod as perpendicular to the micrometer.
(4) adjust the meter so that the amount of pressure gauge in 0.2 ~ 0.3mm, and set the needle at zero.
(5) After boring, the internal diameter gauge into the hole to be measured, up and down, left and right slightly swing, see the needle changes, measured the maximum diameter of the hole value.
When the needle points to zero, just the micrometer calibration size, that is, the diameter of 60mm, if not to zero, according to the actual situation continue to bore, until the size requirements.
Boring notes
(1) in the adjustment of the boring tool cutting amount, if the wrench screwed over the need to reach the scale, to more back some, re-screwed to the need for the scale position, the reason is to adjust the clearance excluded.
(2) To control the cutting speed and feed, to avoid too fast lead to tool damage or deformation of the workpiece.
(3) Maintain a full supply of cutting fluid to reduce the cutting temperature, improve tool life and processing quality.
Regularly check the tool wear in the boring process, timely replacement of badly worn tools and inserts.
(4) the use of internal diameter gauge to measure the diameter of the processed hole, first check whether the meter is intact, you can use your finger to touch the meter probe to see whether the needle can return to the initial position, if it fails to return to the initial position, it is necessary to replace the meter.
(5) when the completion of the last boring, in order to ensure the quality of the surface of the bore, the boring tool in the hole first do not lift out, so that the spindle rotation stops, adjust the dial so that the boring tool to leave the wall of the hole, and then lift the spindle, to avoid scratching the bore, which is manually let the boring tool to exit, but also in the programming of the use of the boring cycle instruction G76 to achieve.
(6) according to the needs of the hole for subsequent processing, such as chamfering, deburring and so on.
High-precision hole parts processing future development trend
(1) Emerging Advanced Processing Technologies
With the continuous progress of science and technology, new advanced processing technology such as laser processing technology, electron beam processing technology, microfabrication technology, etc. will continue to emerge, and in high-precision holes in the processing of parts widely used.
(2)Integration of Artificial Intelligence in High-Precision Machining
The continuous progress of science and technology drives innovation., intelligent technology in high-precision hole parts processing will be more and more widely used.
Intelligent technology will be integrated with more advanced technologies (such as the Internet of Things, blockchain, etc.) to promote the continuous innovation and upgrading of high-precision hole parts processing technology.
For example, multiple sensors are arranged on the machining equipment, and through real-time monitoring of various parameters in the machining process (such as cutting force, vibration, temperature, etc.), adaptive control algorithms are used to dynamically adjust the machining parameters in order to cope with the uncertainties in the machining process, and improve the machining accuracy and stability.
(3) Big Data Analytics for Smart Manufacturing
Using big data analysis technology to process and analyze the data collected by the sensors in real time, identify potential problems and abnormalities, and issue early warning signals in advance to avoid mistakes and losses in the processing.
Conclusion
CNC milling processing of high-precision hole parts requires comprehensive consideration of factors such as tool selection, machining programming and techniques, and machining process control.
Through reasonable selection and configuration of these elements, can ensure that the processing quality and accuracy to meet the requirements.
In the future, with the continuous development of manufacturing technology, the method of CNC milling high-precision hole parts will be further improved and optimized.