Abstract With the wide application of superhard material tools such as PCD and CBN in automobiles, motorcycles, air conditioner compressors, wood processing and other industries, the market demand for such tools is increasing. At present, about 20 companies in China have been engaged in the development, processing and sharpening of superhard tools, but among them...
With the widespread use of PCD, CBN and other superhard material tools in the automotive, motorcycle, air conditioning compressor, wood processing industries, the market demand for such tools is increasing. At present, about 20 companies in China have been engaged in the development, processing and sharpening of superhard tools, but most of them are limited to the processing of low-end products (such as blade-mounted super-hard tools with low precision requirements). This has led to fierce competition in such products. In order to reduce production costs, enterprises are eager to achieve localized processing and sharpening of such tools. 1. High-precision welding type PCD tool technical requirements
High-precision welding PCD tools have high technical requirements. The tool holder adopts HSK adapter or straight shank installed in HSK hydraulic chuck; PCD tool length is less than 150mm, diameter is less than 50mm, blade diameter tolerance is 0.003mm, accuracy grade is IT2~IT3, and the coaxiality tolerance of IT3 precision is 0.003mm.
The coaxiality error between the cutting edge of the welded PCD tool and the tool holder is a combination of grinding machining error and tool mounting error. It is quite difficult to control it within the range of 0.003 mm. In order to guarantee a tool outer diameter tolerance of 0.003 mm, high precision is also required for the machining accuracy of the machining machine and the grinding process. In addition, in order to achieve accurate measurement of high-precision welded PCD tools, the comprehensive measurement accuracy of the measuring instrument is required to reach the micron level, and the measuring force acting on the cutting edge of the tool should be controlled within 150 mN.
2. High precision PCD tool grinding machine
Taking the FC-500D PCD&CBN tool grinding machine produced by Yuanshan Machinery Co., Ltd. as an example, the structural characteristics and processing performance of high-precision PCD tool grinding machine are briefly introduced.
(1) Machine tool features
The grinding wheel travel of the FC-500D PCD & CBN tool grinding machine is 500mm, which can meet the grinding stroke requirements of the 150mm tool. With the rotary table of the machine tool and its corner display function, the reverse taper grinding requirement of the cutting edge of the tool 1:1000~1:1500 can be realized. Both the wheel base and the table rail are Swiss SchneeBerger high-precision roller linear guides. The table feed mode is pneumatic flexible feed, and the feed amount per handle is 1 μm (display display). The contact pressure between the grinding wheel and the tool is adjustable during sharpening. The height of the grinding head is adjustable to grind large diameter PCD saw blade milling cutters. The grinding machine is equipped with a high-precision camera system (CCD), which can clearly display the tool sharpening process (magnification 15~120 times) through the screen. At the same time, the tool edge arc can be detected through the display screen (the minimum arc R0 can be measured. 05mm).
(2) Indexing work head
In order to achieve precise sharpening of high-precision PCD tools, the grinding machine is designed with an indexing work head that can be fine-tuned. The working head adopts the spindle fine adjustment mechanism of the SK40 spindle inner hole and the worm gear. When the worm is disengaged from the worm wheel, the spindle can be rotated quickly. The 24 aliquots of the indexing plate and the spindle can be empty or interlocked. The pin fixed on the clip can be inserted into the gap of the indexing plate, so that the indexing plate and the main shaft are positioned and fixed on the circumference (the indexing plate and the main shaft are interlocked at this time). The 24 equalizing indexing plate is suitable for machining 2, 3, 4, 6, and 8 equal parts. If you need to machine 5 or 7 equal parts, you need to use 20 equal parts or 28 equal parts.
(3) Reducer sleeve
Since the indexing work head adopts the inner hole of the SK40 spindle, when machining the tool of the HSK handle, the reducer sleeve must be used to fix the tool in the inner hole of the working spindle. When machining the straight shank tool, the tool can also be installed first. The hydraulic shank clamp of the HSK handle is then inserted into the bore of the main shaft of the working head through a variable diameter). Since there are coaxiality errors in the inner bore of the spindle and the reducer sleeve, in order to meet the coaxiality requirement of the tool processing (0?003mm), a new technology of adjustable center reducer sleeve developed abroad is adopted. The reducer sleeve structure consists of two parts, the SK40 part on the left side, which can be installed in the inner hole of the indexing work head spindle; the HSK part on the right side can be connected with the HSK handle of the tool. The shaft and the hole are positioned and connected between the left and right parts, and are fixed by four hexagon socket screws. The gap between the shaft and the hole is a clearance fit, and the fit clearance is the center adjustment range. There are four facets on the shaft. The coaxiality deviation of the left and right axes is adjusted by the hexagonal set screws facing the facets, and the parallelism of the axes is adjusted by the set screws. After the adjustment sleeve is adjusted, mark the circumference of the inner hole of the SK40 handle and the indexing work head SK40 with which it is matched to determine the installation position of the reducer sleeve, and avoid repeating the adjustment of the coaxiality when reinstalling the reducer sleeve. .
(4) Tool online measuring device
The high-precision PCD tool online measuring device developed by the author and the relevant unit is installed on the side of the machine table and can be moved along with the table. It is kept in the same position as the tool mounted on the work table. The column of the measuring device can be moved up and down to adjust the measuring head component to the same height as the tool center. The column can also be rotated 180° to keep the measuring head components away from the tool when the measuring device is not working. The top of the column is equipped with a cross-drag. When measuring different lengths of the tool, the longitudinal small carriage can move along the tool axis (stroke up to 150mm); the horizontal small carriage can move radially along the tool (stroke up to 50mm). When measuring tools of different diameters, the radial position of the measuring head components is adjustable. The measuring arm is mounted on a cross-drag and the measuring head assembly is mounted on the measuring arm. When measuring the tool diameter, the axis of the measuring head component must be perpendicular to the tool axis, otherwise the measurement result will be larger than the actual diameter of the tool. For this purpose, a fine adjustment device that can be rotated along the vertical axis is mounted above the measuring head component to ensure the measuring head. The axis is perpendicular to the tool axis.
The measuring head assembly consists of a bracket, a bow arm, a fixed measuring head, a grating scale and a moving measuring head. The fixed measuring head is mounted on the bow arm, the moving measuring head is mounted on the scale, and the scale can be moved on the bracket. The fixed measuring head and the moving measuring head adopt a measuring grating with a stroke of 3 to 5 mm, the measuring stroke of the grating ruler is 50 mm, and the grating measuring accuracy is 1 μm.
The measuring device measures the diameter and circular runout of the PCD tool with a measuring force of less than 150 mN. When measuring, first move the scale to make the moving measuring head contact the fixed measuring head and set it to zero, then open the moving measuring head (subject to the non-contact tool); turn the indexing working head to make the cutting edge slightly lower than the horizontal plane, adjust the shaft To the small carriage, the measured blade edge is placed between the two measuring heads, and the axial small carriage is locked; the radial small carriage is adjusted to make the fixed measuring head and the tool contact about 1 mm (can be observed through the display); The ruler makes the moving measuring head contact the tool, locks the small radial sliding plate, adjusts the fine adjustment mechanism until the display shows the smallest diameter (ie the measuring head axis is perpendicular to the tool axis); the tool is slowly rotated to make the cutting edge contact with the fixed measuring head. When the measuring head touches the tool chip pocket, the maximum value recorded by the measuring device is the tool diameter dimension. At this time, the display shows the tool diameter value and the maximum reading value of the fixed measuring head. Then the tool is rotated through 180°, and then measured again in the same way (the moving measuring head can be exited at this time), and the fixed measuring head can measure a maximum value. The difference between the two measured values ​​is the tool edge rounding momentum. When measuring the edge of the tool edge, the entire measurement system should not be displaced or vibrated during the two measurements, otherwise the accuracy of the measurement results will be affected. If the measurement system is not stiff enough and the measured value fluctuates greatly, another method can be used to measure the circular runout, that is, the measuring head is fixed on the magnetic table, and the magnetic table is mounted on the machine bed to measure the two cutting edges of the tool. It is also possible to measure the round runout of the tool.
3. Precision sharpening process of PCD cutter
Foreign research literature points out that the sharpening of high-precision PCD tools cannot be performed by the traditional sharpening method of grinding the outer circle and grinding the back angle, because the sharpening method is easy to cause the cutting edge of the cutting edge and the machining coaxiality is difficult. Guarantee. For small-diameter PCD tools, the center hole of the toolholder has been destroyed when machining the insert pocket of the PCD insert, so the outer circle cannot be sharpened by conventional methods. In order to ensure the machining accuracy of the outer circle and coaxiality of the PCD tool, it is necessary to use a one-side trimming method for sharpening. Taking the processing of tappet hole cutter 78-33C-205026 as an example, the process steps of high-precision PCD tool grinding machine sharpening are explained. The tool to be machined is loaded into the reducer sleeve and then loaded into the indexing head with a fine-tunable angle. Note: The shank, the reducer sleeve and the inner hole of the indexing work head must be wiped clean, otherwise it is difficult to ensure the coaxiality of the installation.
(2) Adjust the installation coaxiality
Place the dial gauge on the adjustment rings A and B of the tool, adjust the set screw so that the tool axis is parallel to the spindle axis of the work head; adjust the set screw so that the tool axis coincides with the spindle axis of the work head. The adjusted installation coaxiality error should be less than 1μm.
(3) Adjust the cutting edge position of the tool
Rotate the tool so that the cutting edge is on a level surface (slightly lower than the horizontal plane), adjust the rear corner of the grinding wheel, and grind the cutting edge at the back corners of the two cutting edges of the tool. The two measuring heads of the measuring device are in contact with the back of the tool, and then the tool is moved slowly so that the cutting edge of the tool contacts the measuring head. When the displayed measured data is at the maximum value, the tool position has a rake angle of 0°. Insert the indexing work head pin into the aliquot notch and interlock the bisector with the working head spindle.
(4) Sharpening the rear corner of the end face
Disengage the measuring device, turn the rotary table through 90°, adjust the grinding wheel to the rear corner of the end face, and sharpen the two cutting edges; then remove the tool from the reducer sleeve and measure the cutting edge with an optical tool Contour and 180° apex angle, and adjusted by the rotary table until the processing requirements are met; then the distance from the HSK reference surface to the cutting edge is measured, and the size requirement of 112±0.03mm is achieved by sharpening (if it is a step tool, Then the step length and the step angle are ground according to the drawing).
(5) Sharpening tool circumference edge
Rotate the rotary table clockwise through 90.086°. After adjustment, the sharpened knife has an inverted cone of 1.5×10-3; adjust the angle of the grinding wheel to the rear corner of the tool, and sharpen the two cutting edges respectively. angle.
The tool diameter D and the circle runout δ are measured according to the aforementioned measurement method, and the radius of the two cutting edges is discriminated. Let the radius of the large side of the tool be R2 and the radius of the small side be R1, then D=R1+R2, δ=R2-R1; R2=(D+δ)/2, R1=(D-δ)/2. If the tool nominal radius is R0, the large side grinding allowance is R2-R0, and the small side grinding allowance is R1-R0. According to the measurement calculation results, the edge of both cutting edges is measured until the diameter and coaxiality of the tool meet the processing requirements.
4. Cutting edge processing of PCD tool
The wear process of the new tool in the cutting process can be divided into three stages: the initial wear stage, the dimensional stability stage and the sharp wear stage. In the sharpening of PCD tools, edge processing is important to improve tool life. Taking the PCD tool for machining the valve hole of the engine as an example, the normal service life of the imported tool is 30,000 pieces, but the self-made tool without the edge treatment only processes 300 pieces, and the part size is too small, the main reason is the initial tool. The wear amount in the wear stage exceeds the tool tolerance. When the tool wears into the dimensional stability stage, the size of the machined part is out of tolerance. Although the tool edge is in good condition, it has to be scrapped. The purpose of the edge treatment is to reserve the initial wear amount during sharpening. When the tool wears into the dimensional stability stage, the machining size is within the tolerance range to extend the tool life.
The specific method of tool edge treatment can be determined according to the processing conditions. The tool edge can be used to passivate the cutting edge and remove the burr and front edge. The first back angle of 1° can be sharpened on the original back angle. The corner edge width is 0.08 to 0.10 mm. When cutting the edge, the grinding wheel of the grinding machine should be replaced with a super-fine grinding wheel with finer grain size. If the second back angle of the PCD tool is 18°, the margin of the cutting edge should be 14~18μm.
5. The dynamic balance of the PCD tool
Superhard tools are usually used for high-speed cutting, and the cutting speed is 5 to 10 times that of ordinary cutting, so the new tool must be dynamically balanced. The tool should be mounted on the knife aid to balance it. According to the requirements of ISO1940/4, the allowable dynamic balance U (gmm) of the tool is: U=9549GW/n, where G is the dynamic balance level, for the tool, G=2.5; W is the weight of the tool plus the tool aid (kg); n is the speed (r/min) at the time of tool machining. If the test indicates that the dynamic balance is out of tolerance, you can drill holes in the tool or knife aid to remove the unbalance. The specific operation can be performed on the tool balancing machine.
6. Processing environment requirements
The sharpening of high-precision PCD tools places high demands on the machining environment. When installing the machine, the shock absorber groove should be set to reduce the influence of external vibration on the machining accuracy of the machine. There should be constant temperature equipment in the workshop to maintain the processing environment temperature of 20 ~ 25 °C (consistent with the ambient temperature of the high-precision PCD tool) to reduce the temperature error of the tool size. When clamping the tool, use a special tool to carefully wipe the contact surface between the tool and the reducer sleeve, the reducer sleeve and the work head. Otherwise, the dust between them (although the particle size is only a few microns) may cause the tool to be coaxial. Degree is too bad. In addition, dust and high humidity tend to cause the measuring device to malfunction. Therefore, when the measuring device is not in use, the bag should be covered with dustproof, and the bag should be damp-proof to prevent moisture.
Since the high-precision PCD tool sharpening machine tool is manually operated, the operator's processing technology and experience are the key factors to ensure the machining accuracy. The technical training for the operator is also an important part of the high-precision PCD tool sharpening processing technology.
Cnc Part,Cnc Machine Parts,Cnc Components,Cnc Spare Parts
Taizhou TS HARDWARE Co., Ltd , https://www.shuwengroup.com