1、Honing features
Honing has the following characteristics:
(1) wide range of processing.It is mainly used for hole finishing, such as cylindrical hole, step hole, blind hole and cone hole.It can also be used for plane, sphere, forming surface and outer circle surface.The honing aperture is 1 ~ 1200mm or larger, and the hole length can reach 12000mm.Almost all workpiece materials can be honed.
(2) good surface quality.After honing, the surface is cross-reticulated, which is conducive to the storage of lubricating oil and the maintenance of lubricating film, abrasion resistance and long service life.Also because the honing speed is a tenth of the general grinding speed, grinding force and heat is very small, the workpiece surface does not produce burns, cracks, deterioration and hard layer.
(3) high machining accuracy.When honing the inner hole, the roundness and cylindricity can reach 0.005 ~ 0.01mm, and the surface roughness value Ra can reach 0.05 ~ 0.2m. However, it can not improve the position accuracy, and can replace part of the grinding. The machining efficiency is equal to that of grinding.
(4) low requirement for machine tool accuracy.Honing can be carried out on lathes, boring machines and drilling machines in addition to special honing machines.
02、Honing principle
Honing refers to low-speed grinding of the workpiece during the rotation and reciprocating movement of the honing head (or workpiece), as shown in FIG. 1.In order to reduce the machine tool spindle and the workpiece center is not coaxial and the impact of the machine tool spindle rotation accuracy on the workpiece processing accuracy, the connection between the honing head and the machine tool spindle adopts floating connection, with the workpiece hole as the guide.During honing, the overlapping contact points between the oil stone and the hole wall interfere and trim each other, so that the hole surface presents the intersecting spiral cutting trajectory during honing.Because the movement trajectory is not repeated, the opportunity of interference points is almost equal, the cutting effect is continuously reduced, the roundness and cylindricity of the hole and the surface of the oil stone are continuously improved, and the surface roughness of the hole wall will continuously decrease. After the required dimensional accuracy is achieved, honing processing will be completed.
03、The structure of the honing head
In the honing process, the machining accuracy (size and shape), machining efficiency and surface quality of the workpiece depend on the reasonable structure of the honing head, as well as the feeding mode of the machine tool, the characteristics of the oilstone and the workpiece fixture.The honing head has good structure, the honing stone expands and shrinks evenly, the cutting fluid is easy to be injected, the chip and abrasive particles are easy to be removed after falling off, the dressing, positioning and manufacturing of the honing stone are accurate and easy, which will directly affect the honing effect.
The honing head is composed of the honing head body, the oilstone base, the oilstone, the guide strip, the spring and the cone expanding core, as shown in figure 2.The structure and size of the honing head are designed and made according to the structure and size of the workpiece to be processed. The principle is the same.There are constant pressure expansion, step hole, manual expansion and contraction, universal and no universal, small holes, single stone and tile, blind hole and cone hole honing head.
04、The choice of whetstone
(1) selection of characteristics of oilstone.The abrasives of the whetstone are corundum, carbides, synthetic diamond and cubic boron nitride.In the past, the first two kinds of abrasives were mostly used.Because the hardness of the two abrasives is very high, is the first two abrasives hardness 3 ~ 4 times, wear resistance, long life, sharp cutting edge, good processing quality, relatively low cost.The binder of whetstone generally USES resin binder, the first two kinds of abrasives before the use of ceramic binder, for a few millimeters of small holes using metal (or electroplating) binder.The size of abrasive is selected according to the roughness value of the workpiece surface.Coarse particle size results in high machining efficiency and large surface roughness Ra.On the contrary, the machining efficiency of grain size is low and the surface roughness value Ra is small.When the abrasive particle size is F120 ~ F150, the surface roughness value Ra can reach 0.8 m.When the abrasive particle size is F150 ~ F240, the surface roughness value Ra can reach 0.4 m.When the abrasive particle size is F240 ~ W20, the surface roughness value Ra can reach 0.05 ~ 0.2 nm.For the hardness and structure of the whetstone, please refer to the selection principle for the characteristics of the grinding wheel.For ultra hard abrasives (synthetic diamond and cubic boron nitride), a reasonable concentration, i.e., the carat (ct) mass of ultra hard abrasives per cubic centimeter (1ct=0.2g), should also be selected, with 75% (313ct/cm3) and 100% (4.4ct/cm3) concentrations being preferred.The above options also apply to wheeled honing.
(2) selection of size of stone (honing wheel).When the workpiece material is hard, the whetstone should be narrow;When the workpiece material is soft, the whetstone should be wider.Processing brittle materials, whetstone should be wider;Processing plastic materials, whetstone should be narrow, for the removal of chips.The total width of the honing stone should be 15% ~ 28% of the circumference of the hole.About the length of the whetstone, for the general hole, the length of the whetstone is 1.0 ~ 1.5 times of the aperture;For small holes, the length of the stone is 1/2 to 2/3 of the length of the hole, but not too long. Too long will increase the quality of the honing head, but its orientation is good.If it is too short, it will affect the straightness (cylindricity) of the hole.The size of the honing wheel is usually 50 ~ 100mm in diameter and 25 ~ 35mm in width.
05、Honing the dosage
(1) vc of honing synthesis speed.It is composed of the circular velocity v of the honing head and the reciprocating velocity va. The movement track of the abrasive grains on the surface of the workpiece hole is two intersecting helices at a certain Angle. It is the result of countless abrasive grains cutting to form the intersecting mesh texture on the surface of the workpiece.The mesh texture cross Angle is called the cutting cross Angle, as shown in figure 3.The circumferential velocity v of different workpiece materials is also different. The circumferential velocity with high hardness is low, while the circumferential velocity with low hardness is relatively high. Generally, v=20 ~ 60m/min.The reciprocating velocity v a=18 ~ 25m/min, the cross Angle =40° ~ 90°, and the synthesis velocity vc=18 ~ 35m/min.
(2) working pressure of honing stone.It refers to the average pressure acting vertically on the unit area of the whetstone.The working pressure was 0.2 ~ 0.5mpa in rough honing and 0.05 ~ 0.1mpa in superfine honing.
(3) honing feed.The size of the feed depends on the hardness of the workpiece material, the size of the abrasive grains and the processing stage (coarse or fine machining).If the workpiece material hardness is large, in the finishing feed is small;The reverse should be larger.In general, the radial feed of honing is 1.8 ~ 3.2 m/r for rough honing and 0.1 ~ 1.5 m/r for fine honing.
(4) working stroke l and crossing stroke a of honing rod.It depends on the length of the oilstone, l1, and also affects the cylindricity of the hole after honing, as shown in figure 4.L = l +2a-l1 (l is the length of the workpiece).Generally, the cross distance of the stone is 1/5 ~ 1/3 of the length of l1.
(5) honing allowance.The size of honing allowance is related to the shape error and surface roughness value of the previous process, that is, the honing allowance must be greater than the total error of the two.Generally, 2 ~ 2.5 times of the total error of the previous process is taken, which is also related to the production batch size.The single production is 0.04 ~ 0.1mm, and the batch production is 0.02 ~ 0.06mm.
06、Honing liquid
Honing fluid with good cleaning, cooling and lubricating functions must be used.Steel processing, using 80% to 90% kerosene plus 10% to 20% of the oil 2 spindle, or 55% kerosene plus 40% oleic acid and 5% turpentine;When processing cast iron, kerosene, or kerosene plus 10% ~ 20% of the oil of the 2nd spindle;Kerosene is used in the processing of bronze or aluminum alloys.When honing fluid is used, it must be cleaned or filtered to avoid scratching the surface of the workpiece.The honing fluid is also suitable for honing of honing wheel.
07、Wheel honing
(1) principle of wheel honing.Wheel honing is a method of surface finishing of workpiece.Its principle and essence is to use fine - grained abrasive tools under elastic pressure for low - speed grinding of workpiece surface.There are single honing, double honing and multiple honing.Figure 5 shows the outer circle of the two-wheel honing shaft.The rotation of the workpiece drives the honing wheel to rotate passively. The axis of the honing wheel and the axis of the workpiece intersect in space 27° ~ 35°. Under the action of the spring, the honing wheel is pressed to the workpiece and fed along the axis of the workpiece to form a low-speed grinding movement and finish the honing process.Wheel-type honing is mainly used for finishing the inner and outer round surface of the workpiece, such as various types of shaft, roll, sleeve, cylinder, piston rod and large bearing inner and outer round raceways.The workpiece materials are steel, cast iron, hard alloy, quenched steel and hard brittle metal.
(2) characteristics of wheel honing.(1) lower roughness value of workpiece surface can be obtained.After a working procedure is processed, an additional working step can make the surface roughness value R a = 6.3 ~ 12.5 m, and reduce it to R a = 0.2 ~ 1.6 m through honing two or three times, which is very fast.Can improve the workpiece wear resistance, corrosion resistance and other performance.(3) to the pre-process processing requirements are not high, only to achieve the shape and position accuracy, according to the pre-process (step) processing conditions and workpiece requirements, leaving a margin of 0.03 ~ 0.1mm can, and can replace some difficult grinding workpiece grinding (such as slender shaft and rod, various long cylinder cylinder, box hole, etc.).The accuracy of the machine is not high, can be in the lathe, milling machine, boring machine and drilling machine.(5) large scope of application, for different hardness and material of the workpiece materials can be honing.
(3) wheeled honing tool (head).Wheeled honing tools, according to the batch of the workpiece and the size of the workpiece, there are many kinds of structure, its structure principle, function are the same.Double and multi-wheel honing head, mostly used for batch production of fixed size, high processing efficiency.However, a single round honing tool is commonly used, as shown in figure 6 and figure 7.Its applicable workpiece size range, simple structure, easy to manufacture, easy to operate, is widely used in production.The abrasive of the honing wheel is usually white corundum (WA) with particle size of F150 ~ F180 and F180 ~ F240.When honing hard alloys and ceramics, boron carbide, diamond and cubic boron nitride should be used.Binder for resin, generally for their own manufacturing.After the honing wheel is solidified, it must be positioned with the inner hole and turned with PCD tool to avoid run-out.The curved working face is self-shaped during honing process, and the honing effect is the best.After the arc surface is formed, its diameter varies greatly in width (a few millimeters), resulting in a difference in speed, which can achieve the purpose of low speed grinding after mutual interference.The axis of the honing wheel and the axis of the workpiece must intersect at 27° ~ 35° and be skewed to the right.If the cross Angle is too large, the honing may stop.If the cross Angle is too small, the processing efficiency is low.
(4) amount of wheel headway.(1) the workpiece or grinding head speed vc is generally 50 ~ 60m/min, if the honing wheel hole for rolling bearings, vc can reach 150m/min.Vc high processing efficiency is high.Feed is generally f=1 ~ 3mm/r, can not be too large, otherwise it will affect the surface quality of the workpiece.The honing allowance is generally 2ap=0.05 ~ 0.1mm.(4) the honing wheel and the workpiece contact pressure unit area is generally 50 ~ 200MPa, can not be large, otherwise it will cause the bearing heating.
(5) honing fluid and matters needing attention.The selection of honing fluid is the same as that of bar honing.If the honing fluid cannot be continuously poured, the grinding paste can be applied and a small amount of oleic acid can be added to improve work efficiency.If kerosene is not available, continuous pouring of emulsion can also be used instead.If the honing wheel does not make good contact with the surface of the workpiece, or if the honing time is too long and the surface of the workpiece produces ripples, one is to circle the honing wheel with the hole repair truck, and the other is to turn the honing wheel 180° and install it for reuse.
08、conclusion
Honing is one of the modern finishing methods, which has the advantages of simple tools and process and high machining efficiency.In the case that the surface roughness value of the workpiece is required to be R a < 1.6 mm, it can replace grinding and be widely used in production.