Abstract: The grinding wheel is a particularly important tool in the grinding process for the roll grinder, and it is a part directly in contact with the roll body. The quality of the grinding wheel, the selection and correct use of the grinding wheel, the dressing of the grinding wheel before grinding and the operator's familiarity with the characteristics of the grinding wheel directly determine the surface quality of the roll and whether it can meet the process requirements. Therefore, the selection of grinding wheel is mainly based on the requirements of the material, hardness and surface roughness of the roll, and the selection of abrasive, particle size, hardness, bond and organization of the grinding wheel. At the same time, according to the requirements of aluminum processing products and the characteristics of CNC roll grinding machine and grinding technology, the comprehensive analysis and use are carried out.
There are three principles for selecting a grinding wheel. 1) Good cutting performance and high metal removal rate during rough grinding. 2) When grinding, the grinding wheel has good contour and micro-edge, and the grinding heat is small. 3) Economical and reasonable use. As an excellent CNC roll technician must understand the manufacturing and selection of grinding wheel in detail, the use of the process, to master the characteristics of grinding wheel and the difference between domestic and foreign grinding wheel is particularly important to improve the skills of operating roll grinding machine.
1 Shaping of grinding wheel
In addition to the static balance before the use of the grinding wheel, in the grinding process, the grinding wheel often appears cutting effort, abrasive can not fall off in time, passivation and other phenomena, so that the surface of the grinding roll appears burned, vibration, serious will cause resonance phenomenon of the machine tool, which requires the operator to re-trim the grinding wheel to maintain the sharpness of the grinding wheel and the correct shape, and remove the excess passivation layer. Maintain an even contour edge. If necessary, the end face of the grinding wheel should be trimmed, as shown in Figure 1.
It is necessary to choose a reasonable dressing process, generally choose a single diamond pen, CNC grinding machine has a special dressing equipment, using the grinding wheel speed of 18 m/s, the drag plate speed of 200 mm/min, the cutting amount of 0.02 mm each time. Run back and forth 6 times, you can restore its cutting performance, if the drag plate speed is more than 500mm/min, the dressed wheel marks are too heavy, will be back printed on the roll surface. It will increase the grinding times and affect the efficiency of the roller. If the speed of the drag plate is less than 100 mm/min, the drag plate will crawl, so that the dressing surface is too fine, affecting the normal grinding, so it is necessary to choose the dressing process reasonably and economically according to the hardness of the grinding wheel. After finishing the dressing, the washing of grinding fluid should be increased to remove excess grinding wheel particles [1].
2 Reasonable choice of grinding wheel hardness is the key
When selecting the hardness of the grinding wheel, as the operator, you want the grinding wheel to stay sharp at all times, not easy to passivate, reduce the number of dressing times during grinding and reduce the processing time. In fine grinding, it is required that the degree of falling off is small, the amount of feed compensation is reduced, the hardness of the roll and the hardness of the grinding wheel are reasonable, and the grinding efficiency is high and stable.
When selecting the hardness of the grinding wheel, the most important thing is to match the hardness of the roll, the equipment characteristics of the grinding machine, the grinding process used, the grinding fluid used and the surface requirements of the aluminum plate. In order to maintain good cutting, it is soft with hard, hard with soft. The spindle accuracy of the grinding machine will affect the grinding wheel. If the grinding wheel is too hard, the grinding wheel speed can be reduced to 12m/s~5m/s, and the final grinding is carried out. The concentration ratio of grinding fluid should be less than 3%, and the high concentration and viscosity will easily block the grinding wheel, which will cause the grinding wheel to be hard and cause vibration. Matching the roughness of the roll processing, too soft grinding wheel will make the surface uniformity of the roll inconsistent.
For the selection of grinding wheels, the following six situations should generally be considered.
2.1 Grinding wheel and contact surface
When the contact area between the grinding wheel and the workpiece is large, the hardness of the grinding wheel should be selected lower, so as to avoid excessive heating of the roll and affecting the grinding quality.
2.2 Requirements for grinding and casting rolls
A hard grinding wheel should be selected; When heavy load grinding turned casting rolls, also should choose a hard grade grinding wheel, so as not to wear the grinding wheel too fast. Grade J is generally chosen.
2.3 Selection of heavy grinding machine
Because of their small vibration during grinding, the abrasive particles are not easy to be destroyed, so a wheel with lower hardness can be used. Generally choose H class, G class.
2.4 Low surface roughness requirements
When the roughness value of the machining surface is smaller and the size of the workpiece is more accurate, the grinding wheel with lower hardness should be selected to avoid excessive grinding heat and bad surface tissue of the workpiece. Generally, grade F is selected.
2.5 Scratches on the surface of the workpiece
The scratches on the surface of the workpiece are often related to the improper selection of the hardness of the grinding wheel. When the hardness of the grinding wheel is too low, the abrasive particles are easy to fall off. Due to the action of extrusion or friction, the abrasive particles will scratch the surface of the workpiece, so the hardness of the grinding wheel should be properly increased at this time. Generally, grade H is selected.
2.6 Grinding requires high cutting
The following processes can be used: the grinding wheel speed is 30 m/s, the drag plate speed is 2500 mm/min, and the cutting capacity is 0.15 mm each time. Roll speed 25 r/min for fast and efficient roughing.
3. Influence of grinding wheel on workpiece surface quality
From the grinding performance point of view, white corundum, single crystal grinding wheel is better. From the point of view of grinding surface roughness, the finer the grinding grain of the grinding wheel, the smaller the residual area on the surface of the grinding workpiece and the lower the surface roughness. From the point of view of reducing hair and scratches, the grinding wheel can not be too soft, and the grinding wheel that is too soft can easily fall off and cause small scratches. However, it can not be too hard or too hard after the grinding wheel is blunted, the abrasive particles are not easy to fall off and will cause burns on the surface of the workpiece, so H grade grinding wheel is generally used. From the point of view of the binder, the elasticity of the resin binder is good, and it is suitable for low roughness surface grinding. The ceramic binder is brittle, poor elasticity, can not stand the side twisting pressure, but its organization porosity is good, resistance to water, oil and ordinary acid and alkali erosion, suitable for general grinding.
The author believes that if you want to process a high-quality roll, the surface of the roll can not have spiral lines (knife lines), vibration lines, mesh lines, small scratches (drop sand marks), water ripples, twill and color difference, and the roughness of the surface of the roll surface is basically uniform, and the surface of the roll can not be very bright, the more white the fog the better, in order to achieve this requirement, The accuracy of all aspects of the machine tool should meet the requirements of the equipment, the selection of the grinding wheel should match the hardness of the roll, and the performance should be excellent regardless of cutting or polishing.
The excellent grinding process is the embodiment of the operator's skills. These aspects complement each other, and no matter which aspect has a problem, the surface quality of the roll processing may not reach the ideal state. But this is not absolute, for example, the machine has a problem unstable, can also be compensated by grinding process. For example, if there is a problem with the grinding process, it can also be made up by the selection of grinding wheels. For example, the machine tool is very good, other factors are poor, but also can process a qualified roll, so a good machine tool and excellent grinder is the main factor, of which the grinding wheel is the key factor, so the quality of the grinding wheel will directly determine the surface quality of the roll.
4 Aluminum foil roll selection as an example
Aluminum foil roller surface roughness is generally 0.2μm~0.04μm commonly used resin grinding wheel, because the grinding amount of its own roll is very small, generally less than 0.05mm, only the geometric accuracy of the roll shape, surface quality, roll hardness Shore 95~105, roll diameter 260 mm, The length is 1 600 mm~2 200 mm, and the material is 9cr2m, mc3, mc3t, etc., which requires the roll toughness, rigidity, and uniform hardness, etc., which has further requirements for the grinding wheel.
4.1 The grinding wheel must have certain cutting performance
The so-called cutting performance refers to the grinding process, the grinding ammeter should be able to reflect, accurate to 0.2A ~ 1A. If the grinding wheel is too soft, falls off seriously, and the current monitoring is not good, then the shape and roughness of the processed rolls are difficult to ensure uniformity. If the grinding wheel is too hard, the cutting current is there, the grinding wheel does not fall off and there is vibration, and the surface finish is high, that is, the roll will shine, then the roll surface defect is easy to see, and reflected to the aluminum foil surface, if the fall off is too serious, sometimes the grinding wheel will sand out, and extrusion to the roll surface, resulting in small scratches and small scratches. Therefore, the hardness of the grinding wheel should be matched with the hardness of the roll, which should not only meet the self-sharpness, but also take into account the cutting and marking, and have enough polishing performance.
4.2 Material selection of grinding wheel
Aluminum foil processing tends to be mostly white corundum, there are also many abrasive mills in the material selection of mixed abrasive, taking into account cutting performance. The author thinks that the choice of single crystal corundum material is far better than white corundum.
4.3 Selection of organization number of grinding wheel
It is recommended that the aluminum foil industry choose No. 7 to 9, because the grinding amount is small, the grinding load is also small, and the large porosity wheel is sometimes used in the plate processing to increase the grinding load.
In the selection of aluminum foil grinding wheel, according to the roughness of the appropriate granularity of the grinding wheel, such as 0.25μm roughness of 150 granularity.
0.15μm ~ 0.2μm Select 180 particle size
0.10μm to 0.15μm Select 220 particle size
0.08μm ~ 0.07μm Select 280 particle size
0.07μm ~ 0.05μm Select 320 particle size
Select 500~1 000 particle size for mirror polishing
According to the requirements of aluminum foil roll surface processing, the grinding wheel selection is as follows:
Roll material 9cr2m, hardness Shore (HS)105, roll 260 mm×1 600 mm, roughness requirements of 0.15 μm, SA180J9B(single crystal corundum 180 particle size, hardness soft 1 tissue No. 9, resin binder).
The roughness requirement is 0.08μm, and SA280H9B(single crystal corundum 280 grains, hardness soft 2 tissue No. 9, resin binder) is selected.
The roughness requirement is 0.05μm, and WA320J7B(white corundum 320 particle size hardness soft 1 tissue No. 7, resin binder) is selected.
If the roller hardness is higher, the grinding wheel hardness can be selected to F level.
4.4 Grinding wheel for cold rolling
The thickness of aluminum plate rolling is generally 0.18mm ~ 0.4mm, including decorative plate, air conditioning foil, ginning plate, evaporator, capacitor, PS plate, aluminum foil blank and can material, etc., choose white corundum, single crystal corundum mostly, hardness is J, H, GH, G, pores are mostly micro pores, but also useful large pores. Generally, when the particle size exceeds 120, the micro-pores are mostly used, and the ceramic bond is used, the grinding wheel must first have cutting force, and the self-sharpening of the grinding wheel is better. According to the experience, WA120G7V grinding wheel can meet the rolling requirements of grinding cold rolling work rolls.
With the continuous maturity of aluminum processing technology, customers have higher and higher requirements for the surface of aluminum foil, and more and more stringent requirements for the grinding of rolls. In addition to uniform surface roughness, it is also necessary to observe the roll surface without sensory defects affecting the aluminum surface with strong light flashlight. The machine tool and operating skills also need to keep pace with The Times. Selection and use also have the corresponding requirements, many grinding wheel selection requires white corundum and single crystal corundum for mixing selection, such as a country imported grinding wheel model 40A120-1H7V6200, not only has good self-sharpness, but also a wide processing surface, no grinding scratches, normal use does not need dressing. Economical and reliable, it can be popularized in roll grinding machines.
5 Conclusion
Whether it is a technician or an operator, can choose a suitable grinding wheel for grinding, to improve the grinding process, grinding efficiency, roller working pressure and machine tool accuracy is crucial, which requires users in the grinding work through continuous summary, continuous learning, master the selection of grinding wheels, according to the grinding requirements of reasonable economic use. In order to maximize the characteristics of the grinding wheel, grinding out high-quality rolls.
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