How does diamond grinding wheel wear?

 Under the condition of low grinding force and grinding speed, after the operation of diamond grinding wheel, the surface of the diamond abrasive is scattered with many edges clearly reflecting the small wear plane of diamond abrasive. This is because the mechanical wear caused by the mechanical conflict between diamond abrasive particles and superhard data is gradually carried out, and the wear amount of abrasive particles is directly proportional to the grinding stroke length.

According to the properties of diamond, the degree of graphitization depends on the crystal integrity of diamond abrasives, and the degree of graphitization is related to the crystal orientation. Diamond abrasives with good crystal integrity have a low degree of graphitization loss.

On the surface of diamond grinding wheel, some diamond abrasive grains crack and break, causing the whole grain to fall off. Because crystal cleavage is the plane rupture caused by the type strength and distribution of chemical bond of crystal structure element 7, it often occurs along the directional plane at the end of the strength of chemical bond.

The fracture formed by the breakage is that in the irregular grinding process, the abrasive rises to high temperature instantaneously, and then cools rapidly under the effect of grinding fluid, which is repeated repeatedly, forming a great thermal stress on the surface of the abrasive, which makes the surface of the abrasive crack, the thermal stress, the fracture wear and the defect distribution and oxidation of the diamond abrasive Graphitization has a close contact, so, first of all, some thermal stress occurs at the surface shortcomings of the abrasive crystal, causing multiple cracks to occur and expand under the effect of grinding force, some of the weakest strength of the crushing and falling abrasive is the result of grinding force and grinding heat together.

Reasonable selection of diamond abrasive and bond:

Selection of abrasive particle size

The selection of abrasive particle size of diamond grinding wheel directly affects the surface quality and processing power of superhard data grinding. On the premise that the processing quality requirements can be satisfied, the coarser particle size should be selected as far as possible to improve the processing power Abrasive with 120-150# particle size can be selected for coarse grinding, abrasive with 180-240# particle size can be selected for fine grinding, and micro-powder abrasive with W40-W7 particle size can be selected for superfine grinding

Selection of abrasive concentration

The concentration of abrasive in diamond grinding wheel has certain influence on the grinding effect of superhard data, too high or too low concentration will cause the premature drop of abrasive, so that the grinding wheel loss cost addition test results show that in coarse grinding, a higher concentration can be selected to add the number of useful abrasive particles per unit area, and in improving the processing power + fine grinding, a lower concentration should be selected Under normal conditions, abrasive concentration can be selected 100-150% when coarse grinding, abrasive concentration can be selected 75-100% when fine grinding.

Selection of binding agent

Metal bonds with excellent thermal conductivity (mainly bronze grinding wheels) have a larger binding force on abrasive grains, which is suitable for diamond abrasives with intact crystal shape and relatively high grinding ratio. Resin bond is suitable for diamond abrasives with high brittleness and low strength because of its weak adhesion to abrasive particles. The function of ceramic bond is between the above two. The binding force of cast iron short fiber bond on abrasive particles is as high as 50-100kg/mm2, and the tensile strength is as high as 15-30kg/mm2, which is much superior to the function of common metal bonds. The grinding ratio of the diamond grinding wheel made of the diamond grinding wheel is about 4-5 times that of the resin bond grinding wheel, which is suitable for the manufacture of diamond grinding wheel with intact crystal shape.

Under the condition of low grinding force and grinding speed, mechanical conflict wear occurs mainly in diamond abrasive particles. Under the condition of high temperature in the grinding zone, the diamond particles oxidize and graphitize. The cleavage and crushing of abrasive particles are the result of the combined effect of grinding force and grinding heat. When the mechanical force on the grinding grains exceeds the binding force of the grinding wheel bond, the whole grains fall off.

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The importance of the joint of the sanding belt

 The sanding belt is connected together by a joint, forming a ring belt, suitable for various belt grinding machines.

The most critical part is that joint, because it is an artificial intersection and must be done in the most careful and efficient way, ensuring high resistance and promoting smooth motion without vibration.

Type of joint
There are two main distinguishable joints: overlap and butt.

Overlapping

This type of joint was most common during the first few years of industrial use of the belt. Although it is still in use today, the overlaid back base that must be dealt with can cause all kinds of inconvenience during rolling.

This joint method is most suitable for paper bases because of its very small thickness and because it does not have the wire weaving that occurs in textile supports, it can be mitered without the risk of compromising its resistance. In addition, the paper itself has excellent bonding ability, forming a stable and strong bonding.

This overlap joint is also the main reason for the arrowhead printed on the back of the flexible abrasive indicating the direction of movement in which the sand belt must be mounted on the machine.

Because, if the belt is used in the opposite direction, the overlap of the abrasive portion may be elevated by the constant friction it exerts on the workpiece to be polished, thus breaking the joint and with it the belt.

The fabrication of overlapping joints requires extensive experience and expertise, as the flexible nature of the bracket does not help to make its behavior stable during the bewel process and can be easily automated. If done precisely, overlapping joints are likely to be most effective.

Butt

Butt splicing is done by connecting the ends of the sanding belt face to face, without overlapping, and securing the connection with tape specially designed for this purpose, which sticks to the backs of the ends and joins them very effectively.

This type of joint and its variants are the most widely used today because it does not require such a precise miter operation, its automation is simple and versatile, and the connecting tape or film has very low thickness and strong tensile strength.

Another great advantage is its symmetry. There is no overlap in this oriented structure, so the belt can cycle the joint dip Angle in both directions without problem.

 

Angle of joint

Whether overlapping or butt splicing, joints rarely form right angles. If this is the case, the joint area will strike the workpiece uniformly across the entire workpiece surface, resulting in continuous strikes that produce noise and high vibration, which can rapidly impair the strength of the joint.

In addition to providing a larger anchoring surface, which will enhance its drag, the slight Angle will always help the belt cycle smoothly, avoiding premature wear the smaller the Angle relative to the direction of movement of the sand belt, or the further away it is from the right Angle, the better its drag and dynamic performance.

However, very small angles can create very sharp edges at the ends and become weak areas that are very easy to break or separate, especially when using small pulleys or curvatures.

 The most common Angle is usually 45° to 70°

Special joint

Most applications can fit perfectly with the above criteria, whether overlapping or butt splicing, with dimensional tolerances low enough to allow traditional sanding processes to be used without marks or scratches, and with high enough tensile strength.

However, there are some particularly demanding applications where special joints must be used for high resistance flexibility or smoothness.

There are many types of tape used to make joints, and their width, thickness, resistance and flexibility may be large or small, depending on the resistance of the process to the sensitivity of the trace support or the size of the abrasive particles used.

These adhesive strips or films can resist working stresses greater than 60Kg/cm. If greater resistance is required, special tapes of greater thickness and width can be used, or other thinner strips More flexible tape for very flexible straps or very fine grits.

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Hydraulic industry hole honing solution

 In order to solve the problems of low precision and short life of hole processing in hydraulic industry,Moresuperhard diamond honing reamer, with honing machine, machining center and drilling press for grinding, the superhard energy of diamond abrasive can ensure the high precision and high efficiency of hydraulic parts aperture.

(1) Electroplating process

Diamond reamer construction

(1) fixed: good rigidity of the tool body, easy to grind, the size of the machining hole is stable, the tool life is slightly lower

(2) Adjustable: processing size adjustable, long life

Diamond/CBN honing reamer advantage

(1) Coating adhesion, diamond bond fastness, uniform diamond particle distribution, high appearance quality.

(2) The external roundness and cylindricity of the front and rear guides of the diamond reamer are 0.005mm and 0.005mm, respectively. The external circular roughness of the front guide and the rear guide are RA0.63um and Ra0.16um, respectively. The coaxiality between the tool handle and the front and rear guides is 0.015mm.

(3) The cylindricity of the reamed workpiece is less than 0.003, and the roughness can reach Ra0.4-0.2, with high precision, high efficiency and long service life.

(4) Tailored service, standardized process, create value for customer service beyond contract.

Diamond honing reamer application pass
(1) Through hole, blind hole, step hole, etc.

Instructions for diamond honing reamer

(1) Correct selection of reamer
Diamond reamer is suitable for reaming cast iron, steel, aluminum and other non-ferrous and non-metallic materials.
In the reamer structure selection, there are two kinds of fixed diamond reamer and adjustable diamond reamer. In use, in order to prolong the life of the reamer, the reamer of the above two structures can be combined, coarse hinge, half fine hinge with adjustable diamond reamer, fine hinge with fixed diamond reamer.
(2) Select a reasonable processing allowance
Generally should not exceed the abrasive itself particle size of 1/3- 1/4, otherwise it will be too much chip and diamond reamer stuck in the workpiece hole, will reduce the life of the tool.
Particle size 80/100-100/120 diamond reamer, processing allowance is controlled in 0.02mm-0.04mm.
Particle size 170/200-230/270 diamond reamer, processing allowance is controlled in 0.015mm-0.025mm.
Fine-grained 325/400 diamond reamer, machining allowance is controlled in 0.005mm-0.01mm.
(3) Reamer in the hole reciprocating times should not be too much
In general, the next reciprocating stroke can be. At present, many operators use this diamond reamer as grinding rod, because increasing the reciprocating times too much, will reduce the life of diamond reamer.
(4) Select a reasonable cutting fluid

For hinged cast iron holes, a mixture of 80% kerosene and 20% vulcanized or mechanical oil can be used as cutting fluid, or all kerosene can also be used.
When processing steel parts, 70% kerosene and 30% vulcanized oil can be used.
(5) Fair use
In order to improve the life of diamond reamer, the new reamer can be used for rough hinge, generally 5000 ~ 6000 reams.

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What is the sapphire window and what is it used for?

 Sapphire has high hardness and is a hard and brittle material at room temperature, which is difficult to process and has a low yield. Especially in the process of precision and ultra-precision processing, sapphire sheets often have cracks, scratches, edge breakage and other defects.

Sapphire material is anisotropic material, and the periodicity and density of atomic arrangement are different in different crystal direction, which leads to different mechanical properties, optical properties and electrical properties. People take advantage of this directional difference and choose products with different crystal orientation in different applications. For example, gallium nitride epitaxy usually uses C-plane, SOS usually uses R-plane, and mobile phone screen usually uses A-side sapphire wafer. In the aspect of application, the crystal direction of sapphire should be taken into account. In the process of processing, different hardness of different crystal direction can also be used to choose different processing directions, so as to improve the processing efficiency and improve the yield.

Sapphire window is a kind of parallel plane version, double plane round sapphire glass, usually used as the protection window of electronic sensors and detectors, the window piece will not change the magnification of the system, widely used in high energy detection and high power laser important window materials, such as aerospace applications.

 

Features of sapphire window:

Sapphire has the characteristics of high temperature resistance, good thermal conductivity, high hardness, infrared penetration, good chemical stability, good light transmission, corrosion resistance and so on.

The role of sapphire window:

Sapphire protective window is a window piece product used to protect the user or the contents of the container by using sapphire’s characteristics of pressure resistance, scratch resistance and high temperature resistance. Due to the high hardness of sapphire, it has stronger compression and scratch resistance than other glass products. Protective window pieces processed with sapphire are often used in deep water, oil fields, inflammable and explosive occasions, high pressure containers, vacuum containers and other fields.Sapphire can withstand up to 2030 degrees Celsius and is often used in high temperature containers.

In addition to its good hardness, sapphire window piece also has good electrical and dielectric characteristics, and has chemical corrosion resistance, high temperature resistance, good thermal conductivity, good chemical stability and other characteristics.So it can be used to make optical components, night vision cameras and other instruments.

The processing sequence of sapphire window pieces is usually first processed into sapphire crystal blocks, sliced before edge processing, namely chamfering and chamfering. In the process of chip or chip cutting, edge breakage is easy to occur at the edges and corners. In addition, the processing time is long because of the large amount of removal required for the edge of wafer.

The process is divided into six steps:

(I) crystal orientation

(2) Crystal square root

(3) Flat grinding chamfer

(4) Directional section

(5) Edge processing

(6) Grinding and polishing

The specific steps are as follows:

First, X-ray diffractometer is used to find planes A, C and M on the ingot surface.

The ingot is then cut into sapphire hexahedra.

The surface of the sapphire crystal block was smoothed with A grinder, and the 4 edges perpendicular to the A-side were pre-chamfered.

Use A multi-line cutter to cut the sapphire blocks into A – directional wafers.

The edge of the wafer is chamfered with an engraving or chamfering machine.

The wafer is processed into the final product by means of mechanical grinding and chemical mechanical polishing.

Diamond grinding wheel is the most widely used in the processing of sapphire silicon wafer and other hard and brittle materials. Different kinds of diamond grinding wheels are used in the processing of crystal rod, rough machining of wafer and then fine machining. They are respectively crystal rod roller grinding wheel and face grinding wheel The diamond size ranges from 100# to 8000#. The matrix materials include metal bond, resin bond and ceramic bond.

 

  

A large number of diamond grinding wheels are also used in sapphire processing, for example, the outer diameter grinding crystallization flattening, mainly using resin bonded diamond grinding wheels, coarse grinding particle size of about 100#, about 200# fine grinding, resin bond has a certain elasticity, play a polishing role, the processed workpiece quality is good.

Chamfered edging grinding wheel is metal bonded diamond grinding wheel, common size :1FF1V/9 202*20*30*2.5, metal bonding has higher toughness and strength, high groove precision, long service life, sapphire window rough grinding using ceramic diamond grinding disc processing, compared with cast iron disc processing, has high processing efficiency, high precision, Good grinding quality, long service life and so on. In addition, backside thinning grinding wheel, diamond abrasive liquid and other products are also widely used, which have great market value.

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How does diamond grinding wheel wear?

 Under the condition of low grinding force and grinding speed, after the operation of diamond grinding wheel, the surface of the diamond abrasive is scattered with many edges clearly reflecting the small wear plane of diamond abrasive. This is because the mechanical wear caused by the mechanical conflict between diamond abrasive particles and superhard data is gradually carried out, and the wear amount of abrasive particles is directly proportional to the grinding stroke length.

According to the properties of diamond, the degree of graphitization depends on the crystal integrity of diamond abrasives, and the degree of graphitization is related to the crystal orientation. Diamond abrasives with good crystal integrity have a low degree of graphitization loss.

On the surface of diamond grinding wheel, some diamond abrasive grains crack and break, causing the whole grain to fall off. Because crystal cleavage is the plane rupture caused by the type strength and distribution of chemical bond of crystal structure element 7, it often occurs along the directional plane at the end of the strength of chemical bond.

The fracture formed by the breakage is that in the irregular grinding process, the abrasive rises to high temperature instantaneously, and then cools rapidly under the effect of grinding fluid, which is repeated repeatedly, forming a great thermal stress on the surface of the abrasive, which makes the surface of the abrasive crack, the thermal stress, the fracture wear and the defect distribution and oxidation of the diamond abrasive Graphitization has a close contact, so, first of all, some thermal stress occurs at the surface shortcomings of the abrasive crystal, causing multiple cracks to occur and expand under the effect of grinding force, some of the weakest strength of the crushing and falling abrasive is the result of grinding force and grinding heat together.

Reasonable selection of diamond abrasive and bond:

Selection of abrasive particle size

The selection of abrasive particle size of diamond grinding wheel directly affects the surface quality and processing power of superhard data grinding. On the premise that the processing quality requirements can be satisfied, the coarser particle size should be selected as far as possible to improve the processing power Abrasive with 120-150# particle size can be selected for coarse grinding, abrasive with 180-240# particle size can be selected for fine grinding, and micro-powder abrasive with W40-W7 particle size can be selected for superfine grinding

Selection of abrasive concentration

The concentration of abrasive in diamond grinding wheel has certain influence on the grinding effect of superhard data, too high or too low concentration will cause the premature drop of abrasive, so that the grinding wheel loss cost addition test results show that in coarse grinding, a higher concentration can be selected to add the number of useful abrasive particles per unit area, and in improving the processing power + fine grinding, a lower concentration should be selected Under normal conditions, abrasive concentration can be selected 100-150% when coarse grinding, abrasive concentration can be selected 75-100% when fine grinding.

Selection of binding agent

Metal bonds with excellent thermal conductivity (mainly bronze grinding wheels) have a larger binding force on abrasive grains, which is suitable for diamond abrasives with intact crystal shape and relatively high grinding ratio. Resin bond is suitable for diamond abrasives with high brittleness and low strength because of its weak adhesion to abrasive particles. The function of ceramic bond is between the above two. The binding force of cast iron short fiber bond on abrasive particles is as high as 50-100kg/mm2, and the tensile strength is as high as 15-30kg/mm2, which is much superior to the function of common metal bonds. The grinding ratio of the diamond grinding wheel made of the diamond grinding wheel is about 4-5 times that of the resin bond grinding wheel, which is suitable for the manufacture of diamond grinding wheel with intact crystal shape.

Under the condition of low grinding force and grinding speed, mechanical conflict wear occurs mainly in diamond abrasive particles. Under the condition of high temperature in the grinding zone, the diamond particles oxidize and graphitize. The cleavage and crushing of abrasive particles are the result of the combined effect of grinding force and grinding heat. When the mechanical force on the grinding grains exceeds the binding force of the grinding wheel bond, the whole grains fall off.

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How to ultra precision processing bearing ?

 What is ultra-precision grinding?

Ultra-precision grinding is a kind of feed movement to achieve a micro grinding of a finishing process.The surface before ultra-finish machining is generally precision turning and grinding.

Specifically refers to in good lubrication and cooling conditions, with fine-grained abrasive (whet) to exert a small pressure on the workpiece, and in the direction of vertical dry workpiece rotation, rotation at a certain speed of the workpiece for fast and short reciprocating oscillation movement of a finishing processing method.

Ultra-precision grinding is a traditional machining process of grinding by high-frequency small oscillations of whetstone, aiming at improving the surface quality of the workpiece. It is widely used in many industries such as bearings, automobiles, hydraulics and pneumatics, especially in the bearing industry. At present, it is the main final machining process of the inner working surface of bearings.

  

What is bearing ultra-precision machining?

Bearing super finishing, also known as super finishing, is a micro-grinding process. For high-precision bearings, usually the ring rolling surface and the working surface of the rolling body need to be ultra-finished.
Ultra-finish machining has different processing equipment, processing principles are not the same, in order to achieve the geometric accuracy requirements, surface quality requirements, it is necessary to consider the equipment, tooling, whetstone, grinding fluid, and even the grinding process bearing parts of the state.

 

 

 

 

 

 

 

 

Moresuperhard offers a complete range of grinding wheels for ID, OD, centerless grinding, superfinishing and lapping as well as diamond and CBN dressing tools for grinding bearing rings and profiling wheels.

What is the role of bearing ultra-precision machining?

In rolling bearing manufacturing process, ultra precision bearing ring processing is at the end of the process, to reduce or eliminate grinding legacy of circular deviation, repair the shape of the channel error, refining its surface roughness, improve physical and mechanical properties, surface reduce the vibration and noise of bearing, improve the service life of bearing, plays an important role, specific as follows:
1. Can effectively reduce the ripple degree.
In the process of super finishing, in order to ensure that the whetstone always acts on the peak and does not contact with the trough, the arc of the contact between the whetstone and the workpiece is ≥ the wavelength of the surface corrugations of the workpiece. In this way, the contact pressure of the peak is larger, and the convex peak is removed, thus reducing the corrugations.
2.Improve the groove shape error of ball bearing raceway.
Super precision can effectively improve the groove shape error of about 30% raceway.
3. It can produce compressive stress on the superrefined surface.
In the process of super finishing, the main cold plastic deformation occurs, so that the residual compressive stress is formed on the surface of the workpiece after super finishing.

4. It can increase the contact area of the working surface of the ring.

After super precision grinding， he contact support area of the working surface of the bearing ring can be increased from 15%- 40% to 80% - 95% after grinding.

  

Analysis of bearing ultra-precision machining process

Bearing ultra-precision machining can generally be divided into three stages:

1. Cutting 

 When the surface of the whetstone and the rough convex peak of the raceway surface contact, due to the small contact area, the force on the unit area is large, under a certain pressure, the whetstone is first subjected to the "reverse cutting" effect of the bearing workpiece, so that part of the whetstone surface abrasive off and broken, exposing some new sharp abrasive and edge. At the same time, the convex peak of the surface of the bearing workpiece is subjected to rapid cutting, and the convex peak and grinding deterioration layer on the surface of the bearing workpiece are removed by the action of cutting and reverse cutting. This stage is known as the cutting stage, in which most of the metal allowance is removed.

2. The bearing half cutting stage

As the processing continues, the surface of the bearing workpiece is gradually ground flat.

At this time, the contact area between the whetstone and the workpiece surface increases, the pressure per unit area decreases, the cutting depth decreases, and the cutting ability weakens.

At the same time, the pores on the surface of the whetstone are blocked, and the whetstone is in a semi-cutting state. This stage is known as the half-cutting stage of bearing finishing, in which the cutting traces on the surface of the bearing workpiece become shallower and darker luster appears.

3. Finishing bearing
This stage can be divided into two steps: one is the grinding transition stage; The second is the grinding after stopping cutting.

Grinding transition stage:

abrasive particles from reduced, abrasive edge is ground, chip oxide began to embed in the gap of whetstone, abrasive powder blocked whetstone pores, so that the abrasive particles can only be weak cutting, accompanied by extrusion and polishing, then the workpiece surface roughness is quickly reduced, the surface of the whetstone has black chip oxide attachment.

Stop cutting grinding:

When the oil stone and workpiece friction has been very smooth, contact area greatly increased, pressure decreased, the abrasive has been unable to penetrate the oil film and the workpiece contact, when the supporting surface oil film pressure and the pressure of the whetstone is balanced, the whetstone is floating. During the formation of oil film, at this time has no cutting effect. This stage is unique to ultra-finishing.

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Cylindrical grinding method and the choice of grinding allowance

Many shapes, sizes and types of bearings exist including: ball bearings, roller bearings, needle bearings, and tapered roller bearings 

 

OUTER RING

The outer part of a bearing that fi ts into the housing and contains the internal raceway for the rolling elements.

INNER RING

The inner part of a bearing that fi ts on a shaft and contains the external raceway for the rolling elements.

RACEWAY

The ball or roller path, profi led in the inner and outer rings in which the balls or rollers ride. Also called: guide path, race, ball path, roller path.

EXTERNAL RACEWAY

The ball or roller path on an inner ring. Also called: inner race, inner ring race.

INTERNAL RACEWAY

The ball or roller path on the bore of the outer ring. Also called: outer ring race, outer race.

BALL

A spherical rolling element.

ROLLER

Cylindrical or conical rolling element of slightly greater length than diameter.

Cylindrical grinding and the step face.

2. The grinding method of the cylinder and the step surface

1. The method of cylindrical grinding

(1) Longitudinal grinding method

Longitudinal grinding method is the most commonly used grinding method. During grinding, the table is used for longitudinal reciprocating feed, and the grinding wheel is used for periodic transverse feed. The grinding allowance of the workpiece should be ground in multiple reciprocating trips.

 

Characteristics of longitudinal grinding method (referred to as longitudinal method) :

1) In the whole width of the grinding wheel, the abrasive works differently. The sharp Angle of the left (or right) end face of the grinding wheel mainly plays the cutting role. Part of the grinding allowance of the workpiece is removed by the abrasive particles at the sharp Angle of the grinding wheel, while most of the abrasive particles at the width of the grinding wheel play the role of reducing the surface roughness of the workpiece. The longitudinal grinding method has low grinding force, good heat dissipation condition, and can obtain higher machining accuracy and smaller surface roughness.

2) Low labor productivity.

3) Low grinding force, suitable for grinding slender, precision or thin wall workpiece.

 

(2)Plunge grinding method

The length of the cylinder of the grinding workpiece shall be less than the width of the grinding wheel, and the grinding wheel shall make continuous or intermittent transverse feed movement until all the allowance is removed. There is no longitudinal feed movement of the grinding wheel. Higher cutting speed can be used in coarse grinding; In fine grinding, the cutting speed is low to prevent the workpiece from burning and heating deformation.

The characteristics of cutting in grinding method (referred to as cutting in method) :

1) The working condition of the grains on the whole width of the grinding wheel is the same, giving full play to the grinding effect of all the grains. At the same time, because of the continuous transverse feed, the basic grinding time is shortened, so the production efficiency is very high.

2) The radial grinding force is large, the workpiece is easy to produce bending deformation, generally not suitable for grinding fine workpiece.

3) Large grinding heat is generated during grinding, and the workpiece is easy to burn and heat deformation.

4) The shape of the grinding wheel surface (dressing traces) will be copied to the workpiece surface and affect the surface roughness of the workpiece. In order to eliminate the above defects, small longitudinal movement can be made at the end of the cutting method.

5) Due to the limitation of the width of the grinding wheel, the cutting method is only suitable for grinding the outer circular surface with short length.

(3) Step grinding method
Subsection grinding method is also called comprehensive grinding method. It is the comprehensive application of the cutting method and the longitudinal method, that is, the first use the cutting method to coarse grinding workpiece segments, leaving 0.03~0.04mm allowance, and finally use the longitudinal method to fine grinding to size. This grinding method not only takes advantage of the high efficiency of the cutting method, but also has the advantage of the high precision of the longitudinal method. In segmental grinding, there should be 5~10mm overlap between two adjacent sections. This grinding method is suitable for grinding the workpiece with good allowance and rigidity, and the length of the workpiece should be appropriate. Considering the grinding efficiency, wider grinding wheels should be used to reduce the number of segments. When the length of the machined surface is about 2~3 times of the width of the grinding wheel, it is the best condition.

(4) Deep grinding method
This is a more commonly used grinding method, which uses a large back bite to grind all the grinding allowance of the workpiece in a single longitudinal feed. Because the basic grinding time is shortened, the labor productivity is high.
Characteristics of deep grinding method:
1) Suitable for grinding rigid workpiece
2) Grinder should have high power and stiffness

2. Grinding method of step surface
The step surface of the workpiece can be ground out by the end face of the grinding wheel by moving the table by hand after grinding the outer circle. During grinding, the grinding wheel should be slightly removed laterally and the work table should be manually operated until the grinding wheel is in contact with the end face of the workpiece, and the grinding wheel should be fed intermittently. Pay attention to pouring sufficient cutting fluid to avoid burning the workpiece. Usually, the end face of the grinding wheel can be shaped into a concave shape to reduce the contact area between the grinding wheel and the workpiece and improve the grinding quality.
When grinding the step surface, the grinding wheel is under great lateral pressure. Therefore, it is necessary to move the table carefully during operation. When the end face of the workpiece contacts with the grinding wheel, the longitudinal feed handwheel can be gently tapped by hand to achieve small and uniform feed.

3. Selection of outer round grinding wheel

1. Principle of reasonable selection of grinding wheel
The choice of grinding wheel not only affects the machining accuracy and surface quality of the workpiece, but also affects the loss, service life, production efficiency and production cost of the grinding wheel. To achieve the purpose of reasonable selection of grinding wheel, the following basic principles should be observed:
(1) The abrasive particles shall have good grinding performance.
(2) The grinding wheel should have proper "self-sharpening" during grinding.
(3) The grinding wheel should not be blunt and has a long service life.
(4) Small grinding force is generated during grinding.
(5) Small grinding heat is generated during grinding.
(6) can achieve high machining accuracy (dimensional accuracy, shape accuracy, position accuracy).
(7) Small surface roughness can be achieved.
(8) The workpiece surface does not produce burns and cracks.