Honing technology is a special form of grinding, and also an efficient method of finish processing. This process can improve the dimensional accuracy, geometric accuracy and surface roughness of parts. It is widely used in the manufacture of automobile parts.
The Principle of Honing Technology
Honing is to use one or more honing stick (stones) installed on the honing head around, stick (stones) along the radial direction open by expanding mechanism(rotation and pull type), put the pressure to the workpiece hole wall, resulting in certain surface contact. Honing head rotates and reciprocates without moving parts, or the honing head only rotates and the workpiece moves back and forth, finishing the honing process.
In most cases, the structure between the honing head and the honing machine spindle is floating, and structure between the honing head and the workpiece fixture is also floating. In this way, the honing head is guided by the whole wall of the workpiece. Therefore, the accuracy of the machine has little influence on the processing accuracy and forms a unique processing surface.
The reciprocating motion makes the processing surface form a cross and spiral cutting track. Since the turning number of honing head in each reciprocating motion is not round number, the track of each abrasive grain on the hole wall is not repeat during the two motions. In addition, when the honing head rotates, there is an overlap in the axes between the honing stones and previous track, making the connection between the front and backtracks smoother and more uniform. Then, every point of hole wall and the honing surface has almost the same opportunities to interfere with each other during the whole honing process. Therefore, with the honing process going, interference points are constantly generated, and they are continuously polished off, then new interference points are generated again, the honing process will constantly recycle. With the increase of contact area between holes and the surface of honing stones, the degree of interference and cutting effect are weakened, improve the roundness and cylindricity of hole and surface of honing stones. Finally, finish the process of hole surface. In order to get cylindricity better, change the position of the honing head and the axial workpiece under the conditions permit.
It should be noted that if diamond or CBN honing stick (stone) is used, owing to small wear of superhard abrasive in the process, that is honing stick (stone) is dressed small by workpiece, therefore, the accuracy of the hole depends on the original accuracy of honing stone on the honing head to a certain extent. Before using the diamond and CBN honing stone, the honing stone should be well dressed.
Cutting and Grinding Process of Honing
1. Constant pressure feed honing
The feed mechanism presses the hole wall with constant pressure in the process of constant pressure feed. There are 3 stages.
The first stage is shedding cutting. At the beginning of honing, the hole wall is rough, the contact area od honing stone and the hole wall is small, and the contact pressure is large, and the protruding part of the hole wall is quickly worn off. Owing to the large contact pressure of the honing stone surface and the wear of chips for the bond, the bonding strength between abrasive grains and the bond decreases. Therefore, some abrasive grains will fall off and expose new ones.
The second stage is crushing cutting. With the honing process going, the surface of hole wall is more and more smooth, and the contact area with honing stone is larger, and contact pressure per unit area decreases and the cutting efficiency is also decreased. At the same time, the chips cut off are small and fine, and the wear of these chips for the bond is also small. Therefore, the abrasive grains of honing stone fall off very little, and grinding dose depend on new abrasive grains, is the tips of abrasive grains for cutting. So, the abrasive grain tips load is very large, and the abrasive grains are easy to break off and form new cutting edges.
The third stage is blocking cutting. When honing continues, the contact area between the honing stone and hole surface is larger and larger. Fine chips between the honing stone and hole wall are not easy to discharge, making the honing stone block and smooth. At this time, the cutting ability of hone stone is very low and is for polishing. If honing continues, the honing stone is blocked serious and cohesive blockage occurs, and the honing stones will lose cutting ability and heat seriously, and it will affect the hole accuracy and surface roughness. So, honing should be finished as soon as possible.
2. Quantitative feed honing technology
The feed mechanism expands the feed at a constant speed to force the abrasive grains into the workpiece when quantitative feed honing. Therefore, there are only shedding cutting and crushing cutting in the honing process, not blocking cutting occurs. When the cutting force decreases, the feed is larger than the actual grinding amount, and then the honing pressure increases, so that the abrasive grains fall off, break off, and the cutting effect is enhanced. Non-feed honing can be used finally in order to improve the hole accuracy and surface roughness.
3. Constant pressure-quantitative feed honing technology
Starting with constant pressure feed honing, when the honing stone enters the blocking cutting stage, convert to quantitative feed honing to improve the efficiency. Non-feed honing can be used finally in order to improve the hole accuracy and surface roughness.
The Features of Honing Technology
1.High machining accuracy
There are some small and medium-sized through holes, their cylindricity is within 0.001 mm. The roundness of some parts with uneven wall thickness is 0.002 mm, such as connecting rods. The roundness can also reach 0.005 mm for large holes (aperture is over 200mm). It is possible that the straightness can reach within 0.01 mm/1 M if there are not ring grooves or radial holes.
The accuracy of honing is higher than that of grinding. Because the bearing supporting the grinding wheel is located outside the honed hole when grinding, it results in deviation. The grinding accuracy is worse for small hole processing. Generally, honing can only improve the shape accuracy of the workpiece. If want to improve the position accuracy of the workpiece, take some necessary measures.
2.Good surface quality
It is good for storage of lubricating oil and the maintenance of oil film for cross mesh surface. There is a higher surface support rate（the ratio of actual contact area and a matching area between the hole and the shaft）, and it can bear the larger load and has good wear resistance, improving the product service life. Honing speed is low( dozens of the grinding speed), and the surface of honing stone is in contact with the hole, so the average grinding pressure of each abrasive grain is small, and the heat of the workpiece is very small. There is no thermal damage and metamorphic for the workpiece and the deformation is small. There are almost no sanding and extrusion hard layer on the honing surface.
3.Wide processing range
Mainly process various cylindrical holes: through holes, discontinuity hole on axial and radial, such as radial holes or slotted holes, keyway holes, spline holes, blind holes, multi-step holes, etc. In addition, a special honing head can also process conical holes, elliptical holes, and etc. Cylindrical honing tools can hone the cylinder, but the removal margin is far less than that of inner cylindrical honing. Honing can process almost any material, especially the diamond and CBN abrasives used, which further expands the applications of honing and greatly improves the honing efficiency.
Honing is one of the least removal margin processing method in order to achieve the required accuracy of drawings. In the honing process, honing tools takes the workpiece as the guide to cut the surplus allowance of the workpiece and achieve the required accuracy of the workpiece. When honing, honing tools first hone the parts of the workpiece with much allowance, then gradually hone the parts of the workpiece with less allowance.
5.Strong ability of holes rectification
Due to the shortcomings of process methods in technology, some processing defects will appear in the process, such as out-of-round, mouth of a born, turbo hole, small size, drum shape, taper, boring tool grain, reamer grain, rainbow shape, hole deviation, surface roughness, etc. Honing can greatly improve the dimensional accuracy, roundness, straightness, cylindricity and surface roughness of holes by removing the least machining allowance.
Applications of Honing Technology in Automobile Manufacturing
Advanced precision hole processing technology is widely used in automobile and parts manufacturing industry. Typical applications include engine cylinder block, cylinder sleeve,
connecting rod, gear, oil pump nozzle, brake pump, brake drum, hydraulic cylinder, steering gear, supercharger, and etc.
Applications of Honing in Oil Pump Nozzle Industry
SUNNEN KGM-5000 series honing machine is a high-precision honing machine developed for plungers in the oil pump nozzle industry. Its removal rate is 0.01mm, total processing period is 30s, roundness is 0.0005mm, straightness is 0.0007mm, the surface roughness is Ra0.06. It has achieved the goal of honing completely replace of grinding, thus greatly improving the performance and prolonging the life of oil pump nozzle.
Applications of Honing in Gear Inner Bore
Nowadays, honing technology is widely used in automobile gears, such as planetary gear, sun gear, double gear, etc.
Applications of Honing in Supercharger Parts
According to the material of the medium shell and the special structure of the inner hole of the supercharger, the electroplated diamond abrasive sleeve can be used as honing tools with the muti-vertical axis structure, complete a series of process, such as rough process, semi-finish process, finish the process and deburring in a cycle. The Multi-station turntable can realize the automation of process and improve work efficiency.