High-precision welding double-edged PCD tool sharpening technology (2)

(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.

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