editor's note
Deep hole boring processing has always been a difficult problem in mechanical and mold processing. Before, a colleague encountered a 48×215mm deep hole processing problem on a rubber hose mold. Now share the pits he stepped on with everyone, hoping to provide some help and reference.
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Part drawing analysis and process planning
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1. Analysis of parts drawings
The hose mold part is shown in Figure 1, and there are four holes with a diameter of 48×215mm that need to be processed. The overall size is 420×270×250mm, there are 4 grooves on the top, bottom, left, and right sides, there are steps on the hole surface, and slopes on both sides are row matching surfaces.
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Figure 1 Hose mold parts
The technological requirements of this part are that the conicity of the hole cannot exceed 0.1mm, the surface roughness value is Ra3.2μm, the hole distance dimension tolerance cannot exceed 0.03mm, and the verticality is 0.03mm. The product of this mold is a glass rubber tube, and its wall thickness It is only 0.8mm, and the customer requests that the thickness exceeds 0.8mm not to be accepted. It can be said that the thinner the better, it is to save costs.
At that time, I really had no idea about such a difficult part. Although the author's unit was only responsible for processing deep cavity borings, customers could cooperate in other aspects of processing. After many attempts, a simple and reasonable processing scheme was finally developed.
2. Process planning
(1) Simple processing sequence before part boring
After the fine material comes back, the milling machine first processes the grooves on both sides. As shown in Figure 1, the positions B and E are first rough and then refined, and the number is processed.
The steps on the front of the machine are roughened, leaving a margin of 0.5mm on one side, as shown in Figure 1 at A and F.
The step of the processed bottom surface is roughened, and a margin of 0.5mm is left on one side, as shown in C and D in Figure 1.
Then re-clamp and adjust the meter, divide the four sides, and center the center for drilling and positioning. It is processed step by step by drills with a diameter of 10mm, 24mm and 35mm, and finally drilled through with a drill with a diameter of 44mm.
After the completion, go to the large water mill to process the surface and bottom, as shown in Figure 2, and grind to the number to ensure that the parallelism is 0.03mm.
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Figure 2 Dimensions of parts
As shown in Figure 1, a 0.3mm finishing allowance is reserved for side grinding of B and E.
(2) Clamping and positioning datum of parts
The workpiece is directly clamped on the CNC workbench, and the 4 mold feet are separately coded, and the calibration is divided into centers, and the error is controlled within 0.03mm.
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CNC machining of parts
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1. Analysis of parts drawings
Self-made boring tool: first make a boring tool holder as shown in Figure 3, the material is 837H, rough turning first, reserve 0.5mm margin, and process it with an external cylindrical grinder after heat treatment, the focus is to ensure the coaxiality. The small knife holder with the insert blade is purchased as a standard piece of 10×10mm, which is convenient for replacing the blade and guarantees the size.
The inclination angle of the built-in small knife holder is 20°, wire cutting processing, slightly tight fit. The boring tool holder is equipped with M6mm inner hexagon screws, and the small tool holder is locked with the inner hexagon screws. Carbide inserts are installed in the standard small tool holder, the main deflection angle is 30°, the clearance angle of the flank face is 15°, and the sharp corner of the insert has an angle of R0.3~R0.4mm to minimize the contact surface to prevent vibration.
2. Determination of processing plan
(1) Hole processing scheme 1 adopts fast wire cutting processing. This method is the most direct and simple, and does not need to be roughed. However, due to the deep size of 215mm, it is difficult to solve cooling and flushing during processing, and it is easy to break the wire and the surface is rough. value does not meet the requirements.
(2) Hole processing plan 2 adopts slow wire-cutting processing, and the wire is easy to break due to the depth of the hole, but the processing fee for each hole is about 1,945 yuan, and the total cost of wire cutting for the mold is nearly 7,700 yuan, which is far beyond the customer's cost calculation .
(3) Hole processing scheme 3 CNC shape milling processing, using an extended handle to install round or rhombic alloy blades, and deep layered processing. Due to the large contact area, the sound is very loud and harsh when the tool enters and exits each time. , the processed surface roughness value and dimensional accuracy are very poor, and there are undercut grooves in the middle from time to time, the roughness alone cannot be controlled, and it is far from reaching the standard.
(4) Hole processing plan 4 CNC boring processing, the model used is 850B type, which can be used for general machine tools. The Z-axis height of this model is 500mm, which can meet the processing requirements of boring tool holder 230 and workpiece hole depth 250mm , and the processing time is only 2 hours per hole, the processing accuracy is high, and the surface roughness value and dimensional accuracy all meet the requirements of the drawing.
Through the comparison of cost, processing accuracy and processing difficulty, the hole processing plan of plan 4 is selected.
3. CNC boring process
(1) Clamp and align the workpiece on the machine tool, tighten the position of the 4 corners, and level the parallel position and level of the workpiece. If it exceeds 0.03mm, the upper and lower sides of the workpiece must be reground, otherwise it is difficult to ensure the verticality of the hole . The calibration tolerance is controlled within 0.02mm. Among the 4 surfaces, the second step surface is used as the 0 surface of the Z-axis for processing, and there is enough space for lifting the tool as much as possible.
(2) Install the boring tool holder For the first rough machining, measure the size of the boring blade higher than the large tool holder with a table card, and reserve about 0.5mm on one side for rough machining, which is convenient for semi-finishing. The leading deflection angle of the boring insert is 30°, the clearance angle of the flank is 15°, and the rounded corner of the tool tip is R0.3~R0.4mm, so as to minimize the contact surface and force to prevent undercutting caused by vibration. The surface of the boring tool against the workpiece is 0.
(3) The command format of the boring program is G76X_Y_Z_R_Q_P_F_;, G76 is the fine boring command, X/Y/Z coordinate position of the hole, P means there is a pause at the bottom of the hole, Q means that the tool is paused and offset after machining, and it is scratch-resistant when lifting the tool The wound has been machined on the side.
(4) Rough machining parameter setting The speed S is 120 rpm, the feed F is 80 mm/min, the cutting amount is 1.0 mm, the cutting oil is the cooling liquid, the fluidity of the oil needs to be good, and the cooling is in place.
(5) Semi-finishing parameters are set. After the roughing is completed, the card number and inspection are carried out. The size of the deep inner hole can be measured by the inner hole gauge, which usually has a certain taper. The speed S is 110 rpm, and the feed F is 70mm. /min, the cutting amount is 0.6mm, the cutting oil is the coolant, the fluidity of the oil needs to be good, and the cooling is in place to ensure the roughness of the finishing.
(6) Finishing parameter setting Each hole is processed with a new blade, the speed S is 100 rpm, the feed F is 60mm/min, the position of the blade is measured with a micrometer card, and the small tool holder is locked for processing. Test hole processing first, because there is a 15mm step on the top surface of the workpiece, until the size meets the drawing requirements.
