Introduction of Boring Cutters

The boring cutters is a kind of boring cutters, which is generally round shank, and there are also larger workpieces that use a square shank. The most commonly used occasions are inner hole processing, reaming, profiling, etc. A tool with one or two cutting sections dedicated to roughing, semi-finishing or finishing an existing hole. Boring tools can be used on boring machines, lathes or milling machines.
Due to different clamping methods, there are various forms such as square shank, Morse taper shank and 7:24 taper shank. The double-edged boring cutters has two teeth distributed on both sides of the center for simultaneous cutting. Since the radial forces generated during cutting are balanced with each other, the cutting amount can be increased and the production efficiency is high. Double-edged boring cutters are divided into floating boring cutters and fixed boring tools according to whether the blade floats on the boring bar or not. Floating boring cutters are suitable for finishing holes. It is actually equivalent to a reamer, which can bore holes with high dimensional accuracy and smooth surface, but cannot correct the linearity deviation of the holes. In order to increase the number of regrinds, floating boring cutters are often made into adjustable structures.
In order to meet the needs of various hole diameters and hole depths and reduce the variety and specifications of boring cutters, people design boring bars and cutter heads into serialized basic parts-modules. In use, appropriate modules can be selected according to the requirements of the workpiece, and various boring cutters can be assembled, thereby simplifying the design and manufacture of the tool.
Advantage
The technical improvement of the boring tool is mainly in the following four aspects.
Since the advent of numerical control (NC) technology, digital display technology has been widely used in CNC machine tools and coordinate measuring machines.
In addition, digital measuring tools such as digital micrometers and digital calipers have also been widely used. However, the application of digital display technology in precision boring tools has been developing slowly, and the constraints are mainly the coolant used in boring machining and the high-speed rotation of the boring head.
In the past, great care had to be taken when boring on machining centers to avoid splashing coolant into the electronics of the boring head digital readout. Today, new boring tools with internal cooling design can better solve this problem.

Since the coolant can directly reach the cutting part through the channel inside the tool, the coolant is completely isolated from the digital display device of the boring head. In addition, the exterior of the new CNC boring cutters is well sealed, which can effectively prevent the coolant from contacting the electronic components in the digital display device.
In high-speed boring processing, the high-speed rotation of the boring head, centrifugal force and the unbalance of the boring head itself may cause large vibrations, thereby damaging the sensitive digital display device.
The new boring head reduces or eliminates harmful vibrations during high-speed boring by using a built-in balancing mechanism. The precision boring head with digital display reading screen can be used for high-speed boring processing with a speed of 16000r/min.
The digital display of the new boring head can directly display the displacement of the boring tool slider without having to determine the displacement through the rotation of the adjusting screw. Since the boring bar is directly installed on the boring tool slide, the digital reading value of the boring head can truly reflect the displacement of the boring tool without being affected by the screw idle error. This feature of the digital boring head makes it possible to adjust the diameter of the boring hole more quickly and precisely, and to realize error compensation for machining deviation or tool wear.
Most boring cutters require a cut-and-measure operation to determine their set size, that is, a small part of the machined hole is first cut and bored, and then the machined hole diameter is measured. Usually, this means removing the boring tool from the machine and installing it on a tool setter to fine-tune the boring tool size to get the correct hole size. This presetting operation is necessary because reading and presetting the vernier dial of a common boring head directly on the machine is quite difficult, however, this method of operation may result in out-of-tolerance boring or damage to the workpiece.
Since it is difficult to predict the nose deviation of a boring cutters when installing it on a machine tool, a trial cut-measure operation is required to pre-set the tool. With the new easy-to-read digital boring tools, it is possible to fine-tune the tool bore diameter directly on the machine spindle. Even if the boring tool must be removed from the machine tool for hole size adjustment due to the feed limitation of the machine tool spindle, the tool adjustment process of the new digital boring tool is faster and more accurate.
Related methods
Design method
1. Tool design ideas and characteristics
The machine-clamped indexable turning tool is a finished indexable insert with reasonable geometry and cutting edge assembled on the tool holder by mechanical clamping. When a cutting edge is worn and can no longer be used, it can be quickly replaced by indexing New cutting edge. Machining with machine-clamped indexable turning tools has the following characteristics:
The tool geometric parameters and cutting performance are stable, and the positioning accuracy and repeatability are high, which can ensure the change of the tool tip position within the allowable range of workpiece accuracy and the consistency of machining accuracy.
The blade is clamped reliably, and it is not easy to loosen under the impact of cutting force, vibration and cutting heat. The tool life is long, no sharpening is required, the operation is simple, and the auxiliary man-hours such as downtime for tool change can be shortened.
The tool holder can be easily and quickly indexed, and can be used repeatedly, with a long service life, which can reduce inventory and simplify tool management.
The design of the machine clip indexable turning tool rake angle g=-4°, the edge inclination angle l=-4°, the cutting edge has sufficient strength, can withstand the impact of large cutting force, and avoid the edge of the cutting edge.
The indexable turning insert adopts the diamond-shaped national standard general insert, which can ensure the smoothness of automatic chip rolling and curve processing during the cutting process, and is easy to realize the standardization and serialization of tools, which is suitable for profiling turning in automated production.
The tool adopts a screw pin pressing structure, and the screw clamps the insert through the insert counterbore. The structure is simple, the parts are few, the positioning accuracy is high, the cutting edge indexing repeatability is high, and the chip space is large.
According to the characteristics of the material to be processed, and considering the wear of the blade during the cutting process, the TiC+Al2O3+TiN composite coating blade is used. This insert can reduce the friction between the chip and the tool, maintain high hardness and good oxidation resistance at high cutting temperatures, thereby increasing the service life of the insert and reducing the surface roughness of the part.
2. Tool design method
The inner spherical dimensions of the differential housing to be processed are respectively S=f138.5mm, f124mm, and f161mm. Workpiece material: ductile iron GH45-33-15 (core hardness HB150～190). Machining accuracy requirements: the positional tolerance relative to the reference is f0.03mm, and the surface roughness is Ra1.6µm. Cutting amount: cutting speed vc=2m/s, feed rate f=0.4mm/r, cutting depth ap=3mm. Processing machine tool: S1-325 CNC machine tool.
The tool design steps are as follows:
According to the material and processing requirements of the parts to be processed, the blade material is a new type of composite coating (TiC+Al2O3+TiN) blade with YG6 cemented carbide substrate. According to the characteristics of the parts to be processed and cutting parameters, the fastening form of the insert is designed as a screw pin pressing hole structure. The indexable insert type adopts the diamond-shaped national standard general-purpose insert, the tool tip angle is 55°, the normal clearance angle is 7°, there is a V-shaped chip breaker on one side, the insert thickness S=3.97, and the corner radius re=0.4± 0.1mm; according to the requirements of machining accuracy, the blade accuracy is M grade. Make sure the indexable insert model is DCMT11T304-V1. ;
Insert cutting edge length Sa=ap/sinkrcosl=3/sin62.5°cos-4°=3.39mm; cutting edge length L≥1.5Sa=5.086mm when rough turning, the main cutting edge length L of the selected insert ≈11.6mm, which can meet the cutting requirements.
Determine the connection method between the indexable turning tool holder and the tool holder: according to the machine model and center height, in order to increase the strength of the tool holder, the cross-sectional dimension of the tool holder is designed to be an unequal section, and the tool holder and the tool holder are self-locking through the wedge surface. , which can make the tool loading and unloading quick, accurate and reliable.
3. The designed machine clip can index the turning tool head
After the machine-clamp indexable turning method is adopted to replace the original spherical countersinking method, there is no need to manufacture a special fixture, and the processing of the spherical surface of the differential housing can be completed in one clamping on the CNC machine tool. Due to the reduction of auxiliary man-hours such as tool change, the processing efficiency of CNC machine tools is improved, the tool does not need to be sharpened, the durability is improved, the production efficiency is increased by 2 times, and the tool cost is reduced by 75%. Since the machining error caused by the tool regrinding of the original machining method is avoided, the product quality is also effectively guaranteed.
Quality analysis
The commonly used cemented carbide adjustable floating boring tool is mainly characterized by cutting and wide cutting edge extrusion, and the surface of the hole after boring is tight and smooth. Since the boring tool is in a floating state in the hole, the cylindricity and coaxiality of the bottom hole are required to be high. The use of floating boring tools requires high technical requirements, often causing problems such as unstable hole size and chatter lines.
1. The influence of the machining error of the tool hole on the boring bar on the quality of the boring hole.
There is a deviation between the center plane of the tool hole size 12F7 and the rotation center of the machine tool, because ① the machining of the tool hole is deviated from the center of the tool holder; There is a deviation between the plane and the center of rotation. When the main shaft rotates, a radial component force that changes in direction with the change of the rotation angle is generated, so that the hole diameter of the boring will be larger than the size of the floating tool.
The two sides of the knife hole size 25F7 are not perpendicular to the rotation center. If the two sides of the hole size 25F7 are not perpendicular to the center of the tool holder, the floating boring tool will be inclined in the hole, so that the hole diameter will be smaller, and there will be obvious tool marks. Manufacturing error of hole size. The boring tool and the tool hole are in clearance fit. If the clearance is too large, jitter will occur during boring, which will make the machined hole size unstable and generate vibration lines.
2. Influence of semi-fine boring quality on floating pins
The quality of semi-fine boring directly affects the quality of floating boring. Before floating boring, semi-fine boring must meet the requirements of cylindricity and coaxiality, and the surface roughness should be lower than Ra3.2. In addition, the allowance after semi-fine boring should not be too large, generally 0.06-0.12 smaller than the size of the boring tool.
3. The influence of the amount of boring on the quality of floating boring
It is also very important to choose the appropriate amount of boring. If the boring speed and feed amount are too large or too small, it will affect the aperture size and finish. The reasonable amount of cutting is: casting Vc=12m/min, f=1-2mm/ r; steel Vc=10m/min, f=0.5-1mm/r.
4. How to improve the boring quality
From the above analysis, the key to affecting the quality of floating boring is the machining accuracy of the tool hole, while the traditional tool hole can only be processed by plunge cutting, which cannot guarantee high geometric tolerance, dimensional tolerance and smoothness.
When boring a deep inner hole, because the rigidity of the boring bar is limited, vibration is easily generated during boring, which reduces the dimensional accuracy and smoothness of the floating boring. By changing to the form shown in Figure 4, the stability of boring will be greatly enhanced due to the support of the “O” ring. For inner holes of different sizes, it is more convenient to replace the piston of the corresponding size. From the perspective of use effect, the quality problem caused by processing deep holes is basically solved.
In addition, diesel cooling and lubrication should be added during floating boring, and the leading angle of the floating knife should be moved into the hole before boring.
installation steps
1. Connect the tool bridge to the tool handle with bolt 1;
2. Install the fine boring tool holder on the tool bridge;
3. Install the counterweight on the sliding body;
4. Tool adjustment:
1) Loosen the locking screw;
2) Roughly adjust the tool holder according to the scale line, and the size of the tool tip is about 0.5mm smaller than the size to be processed;
5. Adjust the counterweight in the same way to adjust the dynamic balance;
6. Tighten the locking screw, test boring, measure the size of the machined hole and compare it with the required size, and calculate the small value;
7. Loosen the locking screw and turn the dial (each turn of the dial represents a change of 0.01mm in diameter and depth of cut) to make the movement amount to the calculated small value;
8. Tighten the screw and process the workpiece to size.
Matters needing attention: Pay attention to the adjustment of the fine boring head, do not use excessive force (do not rotate the dial out of range); do not disassemble the place blocked with red paint, otherwise the fine-tuning device will be damaged; regular maintenance, add lubricating oil.
Instructions
When installing the tool, pay special attention to cleaning. Whether the boring tool is roughing or finishing, attention must be paid to cleanliness in all aspects of installation and assembly. The assembly of the tool holder and the machine tool, the replacement of the blade, etc., must be wiped clean, and then installed or assembled, and must not be done carelessly.
The tool is pre-adjusted, and its dimensional accuracy and perfect condition must meet the requirements. Indexable boring tools, except for single-edged boring tools, generally do not use manual trial cutting methods, so pre-adjustment before processing is very important. The pre-adjusted size must be accurate, adjusted to the middle and lower limits of the tolerance, and corrected and compensated considering the temperature factor. Tool presetting can be carried out on a special presetter, on-machine tool setter or other measuring instruments.
The dynamic runout check is performed after the tool is installed. The dynamic runout inspection is a comprehensive index, which reflects the accuracy of the machine tool spindle, tool accuracy and the connection accuracy between the tool and the machine tool. If the accuracy exceeds 1/2 or 2/3 of the required accuracy of the machined hole, the machining cannot be performed. It is necessary to find out the reason and eliminate it before proceeding. The operator must keep this in mind and strictly implement it. Otherwise, the machined holes cannot meet the requirements.
The life of each part of the tool should be determined by statistical or testing methods to ensure the reliability of machining accuracy. For single-edge boring tools, this requirement can be lower, but for multi-edge boring tools, it is particularly important. The processing characteristics of indexable boring tools are: pre-adjusting the tool, one-time processing to meet the requirements, must ensure that the tool is not damaged, otherwise it will cause unnecessary accidents