CBN grinding wheel for its excellent performance and the grinding surface quality in high-speed, ultra-high speed grinding, grinding difficult materials, high-performance, high-profile grinding and other processing areas has been applied widely. In the grinding process, because high grinding force and grinding area, adhesion and so on, the working surface of the abrasive grinding wheel gradually passivation; while the abrasive wheel working surface due to uneven wear and lose correct original geometry; addition, because high-speed grinding debris is very small, it is easy to plug the wheel working surface voids. To make CBN grinding wheel always maintain a good state, in the process of grinding wheel must be trimmed. CBN grinding wheel shaping dressing CBN grinding applications technology is a very important research topic.
CBN grinding wheel dressing shaping and sharpening can be divided into two steps. Shaping the macro by changing the shape of the grinding wheel, the grinding wheel to achieve the required accuracy of the geometry and dimensions, and to the fine broken grains to form a sharp edge sharpening; dressing the grinding wheel by removing the bond between abrasive agent, the abrasive binders convex surface to form the required chip space, the wheel having the best grinding ability. Depending on the circumstances, shaping and sharpening can be unified or simultaneously, can also be step by step.
2 CBN grinding wheel shaping method
CBN grinding wheel shaping methods are more commonly used method of turning shaping, rolling shaping method, grinding shaping method, EDM shaping method, etc., has emerged in recent years, laser shaping method.
2.1 Turning shaping method
Turning method is the use of a single particle diamond pen, pencil or powder metallurgy diamond films and other plastic diamond dressing tool turning wheel to achieve the shaping purposes.
A) single grain diamond pen plastic
Single particle diamond pen with high hardness and good wear resistance, so commonly used in vitrified or resin bonded CBN grinding wheel dressing. Diamond pen tip force due to the concentration of heat and continuous role in severe wear and tear, so trimming should be carried out through a rational supply coolant to cool sufficiently. Single grain diamond pen dressing vitrified CBN grinding wheels, grinding wheels grinding surface state is not easy to achieve the requirements of chip space is small, the cutting edge is wider, the grinding blade is not sharp, if directly used for grinding, grinding early force and the grinding temperature are larger, prone to grinding burn and chatter, it is necessary for oil stone grinding wheel trimmed rational surface dressing.
2) diamond dresser plastic sheet
Granular powder metallurgy method to diamond particles bonded to a cemented carbide substrate, into a sheet finisher. Dressing with a diamond dresser CBN grinding sheet has the advantage of lower cost, and the sheet after dresser wear little change in performance, can be used when a larger plastic dressing feed wheel without increasing the surface roughness of the trimmed degrees.
2.2 Rolling shaping method
Rolling shaping method is the use of rotating grinding wheel and the rolling wheel to scroll between the relative binding agent fracturing bridge, so that micro-abrasive surface chipping blade appears. Rolling wheels available carbide or hardened steel. Shaping method is characterized by rolling pressure dressing, finishing efficiency and low precision trimming, trimmed wheel surface damage layer deep, cutting edge low density abrasive sharper, easy to wear but clogging. To reduce the rolling force, to increase rolling stability, the rolling wheel surface or helical groove out of the chute. To avoid wheel surface to generate periodic ripples, must control wheel shaft and the roller shaft concentricity.
2.3 Grinding plastic Law
Grinding shaping method is to use ordinary abrasive grinding wheels, diamond grinding wheels, diamond and CBN grinding wheel roller mill and other plastic or mild steel with CBN grinding wheel for shaping.
A) ordinary plastic grinding wheel
Green silicon carbide or corundum ceramic bonded grinding wheel as plastic wheels, cylindrical grinding method using CBN grinding wheel for shaping. Shaft mounted in plastic wheel brakes, so shaping between the grinding wheel and CBN grinding wheel relative speed can improve the efficiency of plastic surgery, the greater the relative velocity, shaping the higher the efficiency. This method can also be used to repair sharp, but should use fine-grained (150 # to 220 #) wheel dressing. Braking shaping method is characterized by plastic pressure, high rigidity required for grinding the resin bonded grinding wheel prone to over-shaping.
2) low carbon steel grinding plastic
Plastic is the use of low-carbon steel grinding CBN grinding wheel is formed when low-carbon steel to scrape stream-like chip bonding agent, to shaping purposes. This method can be divided into single drum and double drum method. Method is the use of two double drum rollers for smooth shaping speed difference can improve the quality of plastic. Low carbon steel grinding shaping feature is dressing efficiency and low precision finishing, abrasive shedding more, shaping the quality of instability.
3) Plastic Cup Wheel
University of Tokyo Shoji g male developed Dresser cup feed into the dressing cut the feed to improve the precision trimming. Using cup-shaped grinding wheel CBN grinding wheel shaping ceramic, CBN grinding wheel grit produce tiny broken, with good flute and sharp cutting edge. CBN grinding cup wheel for shaping diamond wheel is better than using plastic effect.
4) diamond wheel shaping
Diamond wheel is the use of a plating method or a powder metallurgy method to diamond particles bonded to a metal substrate formed on the circumferential surface of the high forming dresser, which mechanism is through the diamond dressing wheel and CBN grinding wheel rotation motion relative movement between the realization wheel shaping. Feed ar dressing and dressing speed ratio q (q = vr / vs, vr as diamond wheel speed, vs the CBN wheel speed) right after finishing grinding performance of CBN grinding wheel has an important influence. Trimmed with a larger ratio q = trimmed CBN wheel grinding force smaller, but a larger surface roughness. Using a larger amount of feed ar dressing wheel trimmed relatively sharp. S.Malkin other people think, diamond dressing roller mechanism and shaping law trimmed wheel grinding performance mainly by the CBN grinding wheel with diamond abrasive grains track the trajectory of the angle between the (Interference Angle d) control, d greater , trimming force is smaller, but trimmed wheel surface is rough. The selection range of the ratio q = 0.4 ~ 0.7, precision grinding ratio should be selected q <-1.0, the specific values should be based on roughness and abrasive grinding characteristics are determined, for example, zirconium oxide grinding precision parts can be ratio q <-1.0 ceramic CBN grinding wheel dressing, this results in lower roughness (Ra = 0.06μm) and a higher roundness (0.6μm).
Diamond wheel shaped main advantage of simple structure, the roller durability, full width simultaneously on the wheel trim, trimming short time, trimming force is small, can copy specific wheel contour (especially for complex surface grinding wheel with a sharp Complex capacity), suitable for automated production. This method is a load or no load conditions can be used, make dressing time and other processing aids time cross coincide.
2.4 EDM shaping method
EDM shaping method can only be used for metal bonded grinding wheel, there are electrolysis, EDM method. Electrolysis for shaping the relatively difficult.
EDM shaping method is the use of rotary grinding wheel and the tool electrode spark discharge is generated between the electric pulses to erosion corrosion of the surface of the metal-bonded grinding wheel, in order to achieve the purpose shaping and sharpening. In the process of EDM shaping, the grinding wheel and the tool electrode spark discharge pulses generated between the surface of the wheel discharge pits, repeated discharge process, the discharge pit overlap, and gradually to the desired shape of the grinding wheel dressing. EDM machining force is characterized by trimming small, suitable for small diameter and thin wheel dressing; such as electrodes and with reasonable accuracy discharge parameters, can be easily molded wheel for fast, high-precision shaping.
3 CBN grinding wheel dressing method
CBN grinding wheel dressing commonly used methods are free abrasive sharpening method, consolidation sharpening tool sharpening method, EDM dressing method, laser dressing method.
3.1 Freedom abrasive sharpening France
1) Gas blast dressing
Silicon carbide, corundum or glass beads free abrasive media as dressing, dressing with compressed air injected into the rotating medium speed CBN grinding wheel surface to remove part of the binding agent to form a cutting edge, to achieve the purpose of sharpening wheel. Using a gas blast dressing method, the abrasive particle size should be the right choice, the injection pressure and dressing time. For example, with a particle size of 100 ~ 150μm glass beads to 60 ~ 70KPa pressure (or particle size of 50μm, WA to 100 ~ 140KPa pressure) of the CBN grinding wheel dressing blasting, just a few minutes to get satisfactory sharpening effect.
2) ultrasonic vibration dressing
Repair wheel is rotated at a constant speed, the ultrasonic vibration sharpening device to adjust to the resonant state, at a certain frequency and amplitude of longitudinal vibration for overclocking. The contaminated abrasive (20 # oil silicon carbide or corundum grains) injected into the sharps and wheel repair, between the use of energy transferred trim elements and active flutter, the free abrasive grinding wheel surface direct impact on the binding agent for cutting removed, the CBN abrasive wheel surface convex, to obtain better results dressing. Tests showed, CBN grinding wheel and dressing space reserved between the components of the free abrasive grains average size is less than 1/2, the gap size of the sharpening effect is not affected.
3) elastic dressing
The injection of contaminated abrasive CBN grinding and finishing element, driven by the rotation of the wheel through contaminated abrasive grinding wheel dressing device with a gap, free abrasive squeeze research on bond CBN grinding wheel dressing in order to achieve the purpose. When the free abrasive CBN grains hit hard spots, you can turn or retreat, specially cut and squeeze the soft particle research binder, while trimming the natural process of trimming element also enhances trimmed flutter effect. Elastic sharpening method can effectively dressing CBN wheel, without compromising the accuracy of the shape of the wheel, by selecting the average size of abrasive trimming, more accurate control of the projection height CBN grains. Elastic dressing method commonly used in resin bond CBN grinding wheel dressing.
4) free abrasive extrusion dressing
Using pressure (also available without pressure) will be injected into the silicon carbide or corundum abrasive CBN grinding wheel dressing and steel between the two gap should be smaller than the average diameter of the abrasive particles. CBN grinding wheel loose abrasives squeeze on research binder, so that protruding abrasive grinding wheel binder surface, to dressing purposes. Use this method sharpening resin bonded CBN grinding wheel, the initial wear large, grinding is relatively low.
5) Hydraulic blast dressing
This method is the use of high pressure fluid and abrasive wheel surface movement reached binder removal purposes. High-pressure pump with a pressure of about 15MPa and 20 l / min flow rate of the cooling fluid output, the cooling fluid into the vortex chamber a negative pressure, and the large amount of air sucked from the side hole and dressing media (free abrasive silicon carbide or corundum), and cooling after mixing, at a constant speed through the ceramic nozzle and a spray angle to the rotating surface of the CBN wheels.
CBN grinding wheels with diamond wheel right after the hydraulic blasting plastic dressing (Dressing time is 30 seconds), get a good sharpening results. If only shaping wheel, grinding wheel surface roughness of 10 ~ 15μm; when shaping the hydraulic blasting after dressing, the grinding wheel surface roughness can be increased to 30 ~ 35μm. Comparing the surface roughness after sharpening and CBN grains, the average diameter of the grinding wheel CBN shows binding agent between the grit removal about half the diameter of CBN grains. If a separate additional dressing time would lead to more binding agent is removed, easy to make the CBN grains fall off, thus sharpening time should not exceed the time limit dressing.
Hydraulic blast dressing is a highly effective method of dressing, in a short time to obtain satisfactory sharpening effect. With simultaneous shaping diamond wheel hydraulic blasting can reduce diamond sharpening wheel wear. In the grinding process at the same time increase the hydraulic blasting sharpening metal removal rate.
3.2 Consolidation Act sharpening tool sharpening
Silicon carbide or corundum sharpening sharpening block cut block in the radial direction to cut speed vfr pressure dressing to the CBN grinding wheel, sharpening abrasive hardness sufficient to block removal of CBN grains between the binding agent. When the CBN abrasive grains met with sharpening block, due to higher hardness CBN abrasive, abrasive sharpening block fragmentation will occur. Sharpening block fill the gap broken abrasive grains contribute to the binding agent for cutting, so that the CBN abrasive grinding wheel lighter off. Is the effective wheel dressing unit width roughness of corundum wear volume, and the cut-in speed vfr, the effective roughness trimmed wheel will eventually tends to a limit, the limit value with the increase vfr.
A) ordinary grinding wheel dressing
With dressing wheel (silicon carbide or corundum grinding wheel grinding wheel) for cylindrical plunge grinding, dressing CBN grinding wheel. Dressing wheel speed vr and CBN grinding wheel speed vs relationship should vr ≈ vs-1 (m / s).
2) Oil Dan Xiurui
Oil Shixiu Rui is the widely used method of dressing, it is mainly through the contact zone crushing squeeze research role abrasive CBN grinding wheel to remove the binding agent. Different particle size of abrasive grains after oil Dan Xiurui projection height were 6 ~ 10μm. Since oil Dan Xiurui unable to obtain a larger abrasive projection height, and therefore can not be used with large cutting grinding wheel dressing CBN. Dan Xiurui method using oil electroplated CBN grinding wheel can remove the coating surface micro-shaping high or unsound combination of CBN grains, thereby improving high abrasive resistance, reducing the size of electroplated grinding wheel type surface errors.
In addition to the dressing method, there are dressing stick, sharpening paste, wire brush, carbide blocks, low carbon steel grinding, sharpening method, magnetic abrasive sharpening method.
3.3 EDM dressing France
Commonly used method of processing power dressing with electrolytic dressing France Online (ELID), EDM dressing, electrolysis EDM composite dressing method. EDM efficient sharpening method, can be online, the reign of dressing.
Electrolysis online dressing (ELID) method can be realized on silicon, ceramic steel bonded carbide and other precision ultra-precision mirror grinding. Cylindrical grinding in bearing steel has also achieved good results. ELID grinding method for example cylindrical bearing steel, cast iron using 4000 # Bond CBN grinding wheel, the surface roughness of about Ra0.020μm, after grinding surface compressive stress is 150 ~ 400MPa.
EDM EDM sharpening methods include dressing method, contact discharge dressing (ECDD) method, it works the same as with the EDM shaping. ECDD abrasive sharpening technology enables the projection amount is constant, and can achieve high material removal rate. Application ECDD online dressing grinding, grinding force can be reduced, extended wheel life, improve the grinding quality.
3.4 new dressing method
1) laser dressing France
Irradiating a laser beam perpendicular to the wheel, and the heat generated by the laser wheel surface melt the binding moiety evaporate or vaporize, thus increasing the height of the grit wheel and the number of effective abrasive grains, to improve the chip space and high abrasive resistance. When scanning the energy density is constant, the laser pulse frequency and duty cycle on sharpening effect to some extent, the impact of the laser frequency which is more significant, the higher the frequency, the worse the dressing; increase the duty cycle will help to improve sharpening effect; increasing laser power helps to increase grain protrusion height.
2) high-pressure water jet sharpening France
The high pressure water jet perpendicular to the surface at the wheel, the use of high pressure water column wheel impact force to remove surface debris and part of the binding agent, thereby increasing the abrasive projection height, form a sufficient chip space. Reasonable control of the injection pressure and spray distance, get a good sharpening results. For example 325 # CBN grinding wheel Ti6Al4V alloys, a 107.1MPa injection pressure and spray distance of 20mm dressing, can significantly extend the trimming cycle and reduce the surface roughness, but the high injection pressure can cause wheel damage. High pressure water jet sharpening method is characterized by unnecessary to consider dressing tool wear, dressing device is simple, easy to control and operate.
4 Conclusion
CBN grinding wheel shaping many methods, in which the diamond wheel shaping method is better, in practice, may need to select a suitable shaping method. CBN grinding wheel dressing method is characterized by the CBN abrasive to avoid the role of binding agents directed against erosion, so in a variety CBN grinding wheel dressing method, the free abrasive sharpening method is better.
CBN grinding wheel dressing to improve technical level, should speed up the principle and application of new dressing technology. Trim system development should be given priority universal efficient trimming system design and application. At present, China is in progress at a university and intelligent ultra high speed grinding grinding technology research, associated trim trimming technology and intelligent systems research being conducted. (Full text)
