What is the hardness of grinding wheel?

 What is the hardness of grinding wheel?

The hardness of grinding wheel refers to the adhesive strength of the bond to the abrasive(how easy it is for the abrasive to detach from the grinding wheel). The hardness of the grinding wheel is determined by the bonding strength of the binder, not by the hardness of the abrasive. Under the same conditions and certain external force, if the abrasive particles are very easy to fall off from the grinding wheel, the hardness of the grinding wheel will be relatively low (or soft). On the contrary, the hardness of the grinding wheel is relatively high (or hard).

What is self-sharpening of grinding wheel?

After the abrasive particles on the grinding wheel are passivated, the grinding force acting on the abrasive particles increases, which makes the surface abrasive particles of the grinding wheel fall off automatically, and the sharp cutting edge of the new abrasive particles in the inner layer is put into cutting, and the grinding wheel recovers its original cutting performance. This ability of grinding wheel is called "self-sharpening".

Whether the grinding wheel hardness is reasonable or not has great influence on the grinding quality and productivity. Generally speaking, the harder the component material, the softer the grinding wheel should be. This is because the hardness of the parts is high and the abrasive wear is fast. Choosing a softer grinding wheel is conducive to the "self-sharpening" of the grinding wheel. However, if the hardness is too low, the grinding wheel will wear quickly and it is difficult to ensure the correct sand profile. If the hardness of the grinding wheel is too high, it is difficult to realize the self-sharpening of the grinding wheel, which is not only low productivity, but also easy to produce high temperature burns on the surface of parts.

If the grinding wheel is soft, it is easy to dressing, but the retention of shape and contour is usually not ideal. In order to improve the surface roughness of the workpiece, the hardness of the grinding wheel is too high will occur heat and shake, resulting in the problem of poor surface roughness.

  Importance of cutting force

If the forming wheel to maintain the force, the best way is increasing the hardness of the wheel. However, it is easy to occur the problem of cutting force, if the grinding wheel cutting force is good, grinding resistance is small, in addition to the speed of feeding can be accelerated, the heat will be less, the grinding wheel cooling and heat change degree is small, the grinding wheel consumption will be less. If only hardness is required, the grinding temperature may rise even higher and the grinding wheel consumption may even speed up.

Enhancement of bond

The choice of abrasive particle size is mainly related to the surface roughness and productivity.

Bond is the key to the self-sharpening of grinding wheel and the main determinant of the hardness of grinding wheel.
In terms of forming grinding, the requirements of bond, in addition to balance cutting force and shape holding force, if the heat dissipation and grinding ratio can be further improved, the grinding efficiency will be greatly improved.
In addition to the significant improvement of the grinding ratio, the reduced binder also means that the space of the pores is made available, the space for heat dissipation is increased and the chance of blockage is reduced.

Bond	Characteristics
Ceramic bond	Good chemical stability, heat resistance, corrosion resistance, cheap, accounting for 90%, but brittle, should not be made into thin sections, should not be high-speed, linear speed is generally 35m/s
Resin bond	High strength, good elasticity, impact resistance, suitable for high-speed grinding or cutting grooves and other work, but poor corrosion resistance and heat resistance (300℃), good self-sharpening.
Metal bond	Bronze, nickel, etc., high strength and toughness, good formability, but poor self-sharpening, suitable for diamond, cubic borax nitride wheel.

Coarse grinding

During coarse grinding, the grinding allowance is large, the required surface roughness value is large, should choose a coarser abrasive. Because of coarse abrasive particles, large pores and large grinding depth, the grinding wheel is not easy to block and heat.

Fine grinding

In fine grinding, the allowance is small and the required roughness value is low, so fine grinding particles can be selected. Generally speaking, the finer the abrasive particles, the better the grinding surface roughness. Granularity is not the only factor that plays a decisive role. I have seen mirrors made with 80K grinding wheels. See Table 3 for the application of grinding wheels with different grain sizes.

Not "hard" is suitable
In the selection of forming grinding wheel, the most important thing is to avoid the blind spot of grinding wheel hardness. In fact, more attention should be paid to the basic performance of grinding wheel such as cutting force, organization uniformity and heat dissipation, so as to select the most suitable product.

The hardness of grinding wheel:

Hardness
Workpiece	Grinding wheel
HRC＜45	M
HRC＜45-55	L
HRC＜50-60	K
HRC＜58-62	J
HRC＜60-65	H

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Application of diamond abrasive belt for thermal spray coating

 Grinding characteristics of diamond sanding belt

The hardness of high-hardness thermal spray coatings such as superalloys and special ceramics is generally above 1000HV0.2, the coating thickness is mostly between 0.1mm and 0.5mm, and the thermal spray coating is hard and thin. In the grinding process, due to the high hardness of the thermal spray coating, diamond grinding tools are often used. However, due to the use of diamond consolidation grinding - grinding wheel grinding not only has high power consumption, high grinding temperature, easy to burn the workpiece, affecting the surface and internal quality of the workpiece. Moreover, the grinding wheel needs to be trimmed frequently, which is labor-consuming. However, the use of ordinary abrasive grinding wheels and abrasive belts for grinding has lower cutting efficiency or difficulty in grinding due to its low hardness (see Table 1, Mohs hardness table of various substances for details).

  

Diamond Mohs hardness is 10, the hardest material ever found. It is especially suitable for machining hard-to-machine non-metal and non-ferrous metals with high hardness and brittleness. The diamond abrasive belt made by electroplating process has high bonding strength between diamond and base cloth, and adopts the arrangement of grinding units with gaps (see Figure 1, the arrangement of several diamond abrasive belt surface grinding units). It has better chip removal and lower grinding temperature, which can not only ensure the surface quality of the workpiece, but also the internal quality of the workpiece, thereby improving the fatigue strength of the parts, prolonging the service life and improving production efficiency. The grinding process of diamond abrasive belt also has the characteristics of less dust, low noise and low energy consumption, which is in line with my country's policy of energy conservation and environmental protection.

The surface quality of diamond abrasive belt grinding workpiece is high, which is mainly manifested in small surface roughness value, good residual stress state, and no microscopic cracks or changes in metallographic structure on the surface. From the surface roughness point of view, abrasive belt grinding can reach Ra0.01mm at present, achieving the effect of mirror grinding, and for the case where the roughness value is above Ra0.1mm, it is very easy to achieve. The test shows that under certain other conditions, when the linear speed of the abrasive belt increases from 35m/s to 100m/s, the grinding surface roughness decreases from Ra2.0µm to Ra1.5µm, and the precision reaches the effect that ordinary abrasive tools cannot achieve. . Therefore, diamond abrasive belts and their derivatives are the best products for grinding high-hardness thermal spray coatings.

Diamond abrasive belt grinding

 

The diamond abrasive belt is mainly used for the processing of rollers and shafts, and the diamond abrasive disc and the diamond impeller are mainly used for the grinding and polishing of plane, curved and complex surfaces.

Grinding process of ceramic piston rod with diameter of 540mm× length of 15m

Workpiece	540mm× length ceramic piston rod
Speed of sand belt	16m/s (1500rpm)
Sand belt specification	60mm×1950mm
Abrasive belt contact mode	soft contact (non-contact wheel grinding)
Workpiece specification	Diameter 540mm× length 15m
Workpiece speed:	30rpm
Grinding head cutting speed:	Rough grinding: 60#, 200#, 2mm-3mm/r;
	Fine grinding:  800#, 0.5mm - 1mm/r
cooling liquid	Water
Workpiece spraying material	ceramic coating
Spray coating thickness:	60μm
Initial roughness of sprayed coating	RA0.4mm -- 0.6mm
Spraying coating processing allowance	25μm
Coating thickness after processing	35μ

 

Characteristics of diamond abrasive belt grinding process

Advantages:
(1) The equipment is simple, easy to operate, and no expensive special grinder is needed. It can be stuck on the lathe tool rest of common specifications to carry out work.
(2) High grinding speed, high efficiency, good grinding effect.
(3) Because of the special orderly arrangement design of diamond particles on the surface of diamond sand belt, the grinding is sharp, the chip removal is good, and there is no need for dressing. The processing requirements can be achieved by replacing the sand belts with different grain sizes.

Disadvantages:

This kind of non-contact wheel grinding processing accuracy is slightly lower (cylindricity), if the use of contact wheel grinding (contact wheel hardness 90) can greatly shorten the processing time and can achieve the workpiece processing accuracy requirements.

Grinding scheme of plane and surface thermal spraying coating
For the grinding of some plane and surface after thermal spraying, such as automobile stamping die, steam turbine blade and aviation parts, the most advanced grinding method is to adopt:
Diamond impeller grinding plane and surface: installed in pneumatic and electric grinding machine, speed 10000 ~ 20000rpm, high grinding efficiency, good effect, flexible and convenient operation.
Grinding process of diamond disc: installed in pneumatic and electric Angle grinder, grinding speed is fast, good smoothness.
Diamond lapping disc :

Diameter 2 inch, grit 200#, 400# mounted on high speed pneumatic tools, tools, has the characteristics of compact, flexible operation, fast loading and unloading.

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Attribute composition of grinding tools and matters needing attention in grinding

 Grinding is a machining method for machining parts with high dimensional tolerances, which cannot be achieved by turning and milling methods.

Grinding is preferred for：

• Hard materials with good machining properties.
• High dimensional accuracy and high shape accuracy (IT5~IT6).
• Very small surface waviness and roughness (Rz= 1~3um).

 Abrasive tool

The rotating abrasive tool consists of abrasive particles, adhesive and closed pores. Most of the different shapes and positions of abrasive particles constitute negative cutting angles, and the cutting thickness of each abrasive particle is not always the same. Grinding is cutting with cutting edges of uncertain geometry.

 

Abrasive 
Most grinding wheels contain abrasive particles composed of either natural corundum (white, pink) or silicon carbide (green, black). The toughness of abrasive decreases with the increase of abrasive hardness. The brittle and hard abrasive particles have self-sharpening property due to the fragmentation of the abrasive particles when the abrasive load is small (fine grinding). Sufficient toughness can prevent premature fragmentation of the abrasive particles under heavy load (coarse grinding). The abrasive particles should have high hardness and sufficient particle toughness and heat resistance.

  

Abrasive wear

When the cutting force is high, the abrasive particles are broken and come out of the binder. When the cutting force is small, the abrasive load increases with the increase of friction and wear on the cutting edge, and finally the abrasive particles break into particles. A new cutting edge is formed by the fragmentation of the abrasive particles and the breaking out of the binder, and the grinding tool is self-sharpened by this process.

 

Abrasive types
Sharp abrasive particles are suitable for long chip materials. When grinding brittle materials, square grits have more wear resistance, and single grain grits (single grain crystals) have very high grain strength, so they are especially suitable for grinding glass and ceramics. Many fine cutting edge particles are formed due to small fragmentation before the polycrystalline particles break out from the binder during grinding. Therefore, the abrasive particles can be better utilized in hard metal grinding.

Particle size
The particle size is equivalent to the number of meshes that can be passed through exactly one inch of the screen before the next screen, which is more densely meshed. Very fine particles can be separated by panning. The grain size of diamond and boron nitride is equivalent to the width of UM mesh. The grain size of the D150 (diamond abrasive) or B150 polycrystalline cubic boron nitride (CBN) abrasive ranges from 125 to 150/um. The higher the required surface roughness of the workpiece, the sharper the edge of the grinding profile, and the finer the abrasive particle size must be.

Bond

The purpose of the bond is to hold the individual abrasive particles together for a long time until they are blunt. The grinding wheel with ceramic bond has pore space, so it has good dressing ability. Artificial resin bond can bond particles more firmly and therefore can withstand greater grinding forces. However, the arbitrary arrangement of the grain tips can produce a lower temperature grinding.

Hardness of abrasive tools
The hardness of grinding wheel should not be understood as the hardness of abrasive particles, but as the resistance of adhesive to prevent abrasive particles from disengagement. In the grinding of hard materials, jimi rub wear is large and grinding load is small, so only the soft grinding wheel can produce "self-sharpening effect". When grinding soft materials, thicker chips require larger grain retention, so a harder wheel is required. A soft grinding wheel is always uneconomical from the point of view of processing cost due to its high wear: the abrasive particles detach from the grinding wheel disc before the wear surface is formed, and the grinding wheel quickly loses its shape (contour), that is, the grinding wheel "collapses". On the contrary, a hard grinding wheel keeps the grain too long, and the grinding wheel "lubricates" and grinds. At the same time, the grinding pressure and temperature in the contact area between the grinding wheel and the parts also rise. The effective hardness of grinding wheel depends not only on the hardness of abrasive material, but also on the particle size, pore volume and chip thickness before leaving the workpiece.

For hard workpiece materials, a soft grinding wheel should be selected, and for soft workpiece materials, a hard grinding wheel should be selected. For thin chip cutting with fine abrasive particles, a softer grinding wheel should be used because the abrasive particles of this grinding wheel are easier to detach due to the greater effective hardness.

Balance of grinding wheel

The uneven distribution of abrasive particles and adhesives will lead to centrifugal force due to the unbalance of the grinding wheel disk.

Therefore, for large and wide grinding wheels, especially those with high circumferential speed, the balance of grinding wheel disc is particularly important.

For static balancing, place the grinding wheel on a balance scale or balance rolling frame.

Dressing of grinding wheel

• Trim the shape
Make the grinding wheel disk contour, radius and size are kept within the tolerance range. The radial and axial runout performance of the newly clamped grinding wheel must be improved.

• Sharpening
The volume of the chip storage chamber is expanded by grinding the binder, and the cutting performance of the grinding tool is improved. The natural corundum grinding wheel and silicon carbide grinding wheel can achieve sufficient sharpness after shaping and dressing of diamond or steel dressing grinding wheel. While diamond grinding wheel or polycrystalline cubic boron nitride (CBN) grinding wheel must be shaped by silicon carbide dressing wheel or diamond dressing grinding wheel. When sharpening, the natural corundum grindstone shall be used to remove the bonding agent until the outstanding state of the abrasive particle reaches 1/3 of its particle size.

Safety precautions for grinding
The grinding wheel disc using ceramic binder is a type of easily cracked grinding wheel. If the grinding wheel is cracked due to hairlike cracks or incorrect fastening, when the circumferal speed of the grinding wheel reaches 80m/s (equivalent to 288km/h), there is a risk that the grinding wheel fragments will fly out and cause death. Only on the premise of strictly obeying the safety rules, grinding is a safe machining method.

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Centerless grinding principle

 

Working principle of centerless grinding
The grinding wheel rotates at a high speed, while the regulating wheel rotates in the same direction at a slow speed, thus driving the workpiece to rotate and make circular feed. The axial feed can be realized by adjusting the inclination Angle of the regulating wheel axis during through-grinding, and the radial feed can be realized by moving the regulating wheel frame or grinding wheel frame during entry grinding.

In centerless grinding, the center of the workpiece must be higher than the center line of the grinding wheel and the regulating wheel, so that the contact point between the workpiece and the grinding wheel and the regulating wheel is impossible to be symmetric, so that some convex surfaces on the workpiece can be gradually rounded in multiple rotation. If the top surface of the bracket is horizontal, and the center of the adjusted piece is at the same height with the center of the grinding wheel and the regulating wheel, when there is a raised point on the workpiece and the regulating wheel contact, the opposite side of the raised point is ground into a pit, and its depth is not affected by the height of the raised point. After the workpiece turns 180 degrees, the raised point contacts with the grinding wheel. At this time, the pit is just at the Angle of contact with the regulating wheel, and the raised point cannot be ground flat. At this time, the outer circular surface of the workpiece is an edge circle with the same diameter.

The grinding wheel, regulating wheel, and workpiece actually rotate in the same direction at different speeds.
The grinding wheel rotates at high speed, and the linear speed of the grinding wheel is very high, generally around 35m/s
The slow rotation of the regulating wheel plays a guiding drive role. The linear speed of the regulating wheel is 10-50m /min. The speed of the regulating wheel determines the rotation speed of the workpiece, and the linear speed of the workpiece is basically equal to that of the regulating wheel.
In order to avoid grinding out the rounded workpiece, the center of the workpiece must be higher than the center line between the grinding wheel and the regulating wheel (higher than 15% ~ 25% of the workpiece diameter), so that the contact point between the workpiece and the grinding wheel and the regulating wheel is not on the same diameter line, so that the workpiece can be gradually rounded during multiple rotation.

  

Centerless grinding is suitable for grinding slender shaft and shaft, sleeve, pin and other small parts without center hole in mass production. In fact, no grinding application industry is very wide:

- Aerospace

- Agriculture

- Automotive

- Defense

- Medical

- Military

- Motorsport

- Power generation

- Research and development

- Sub-sea oil and gas

-White goods

Centerless grinding grinding method

 Infeed grinding/plunge grinding

The supporting plate is equipped with axial positioning fulcrum, and the workpiece is supported at a certain position on the supporting plate, and grinding is carried out by grinding wheel or regulating wheel. It is used for grinding workpiece with shaft shoulder or boss as well as cone, sphere or other rotating body workpiece.

Thru-feed grinding

The workpiece is fed along the axis of the grinding wheel for grinding, and the small dip Angle of the regulating wheel axis is adjusted to realize the axial feed of the workpiece. It is suitable for grinding thin cylindrical workpiece, short shaft and sleeve workpiece without center hole.

Thru-feed and Infeed grinding

Thru-feed and Infeed grinding is a combination of the above two kinds. In addition, there are tangent feed grinding and step workpiece in the axial forward and backward face feed grinding.

The maximum machining diameter of centerless grinding is 500, which is quite unexpected. The previous found that the diameter of the products that can be grinded by centerless grinding ranges from 1.2mm to 300mm. It is rare to see such a large diameter of 500. With the development of grinder and market demand, it should not be a problem.

Many of the common types of grinding wheels used for centerless cylindrical grinding machines in China have been replaced by resin and ceramic superhard diamond wheels. The most common specifications for resin and ceramic centerless grinding wheels:

D250-T125-H75-X10

D300*T50/T100*H127-X10

D350-T100/T125-H127-X10

D400-T100/T150-H203-X10

D500-T150-H305-X10

D600-T200-H305-X10

The following are common centerless grinding wheel sizes
1. Resin centerless grinding wheel

Diameter(mm)	Thickness(mm)	Diamond layer(mm)
300	50	5,10
	100
	150
350	100
	125
	150
400	100
	150
	205
450	100
	150
	205
500	150
	200
	250

2.Abrasive selection

A: Grinding of ordinary carbon steel bearings and bearing inner and outer rings

WA: Precision grinding of alloy steel bearings and bearing inner and outer rings

GC: Micro motor shaft grinding

A/WA: Grinding of bearing steel, bearing raceway and inner hole

Particle size to choose

According to the different machining roughness requirements, the size selection range is generally 60#-180#

Hardness to choose

J. K. L. M. N

Linear velocity standard

The working line speed of centerless grinding wheel is 35M/S. The order of 60M/S high speed grinding wheel is also accepted.

Grinding machine type	Grinding wheel size (mm)
M1020	P300*100*127
AMG1020	PSA300*100*127
MT1040	PSA350*125*127
AM1050	P400*150*203
AMG1050	P500*150*305
AM1080	P600*200*305
MGT1050	P450*150*250
C-12	PSA305*150*120
C-18	PSA455*205*228.6
C-18A	PSA455*255*228.6
C-18B	PSA455*305*228.6
C-20	PSA510*205*254

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What is honing?

 Honing is a method of finishing workpiece surface at low cutting speed. It is a special form of grinding and an efficient machining method in finishing. This process can not only remove large machining allowance, but also improve dimensional accuracy. Geometric precision and effective machining methods to reduce surface roughness are widely used in automobile parts manufacturing。

High machining accuracy

Honing can improve the shape accuracy of the workpiece, especially for some small and medium-sized through holes, the cylindricity of which can be up to 0.001mm. For some parts with uneven wall thickness, such as connecting rod, the roundness of which can be up to 0.002mm. If there is no ring groove or radial hole, the straightness of honing is less than 0.01mm/1m, and the precision of honing is higher than that of grinding. During grinding, the bearing supporting the grinding wheel is located outside the grinding hole, which will cause deviation, especially for small hole machining.

Good surface quality

The surface is cross mesh, which is conducive to the storage of lubricating oil and the maintenance of oil film has a high surface support rate (the ratio of the actual contact area between the hole and the shaft and the matching area between the two), so it can bear large load and wear resistance, thus improving the service life of the product. Due to the low honing speed and the surface contact between the honing stone and the hole, The average grinding pressure of each abrasive particle is small, so the heat of the workpiece is small, the temperature of the cutting area can be maintained at 50-150, the surface of the workpiece almost no thermal damage and metamorphism layer, small deformation.

Wide processing range

Main processing of a variety of cylindrical holes: through holes, axial and radial discontinuous holes, such as radial holes or slots, keyway holes, spline holes, blind holes, In addition, the special honing head can also be used to process conical holes, oval holes, etc., but because of the complex structure of the honing head, the cylindrical body can be honed without the outer round honing tool, but the margin removed is far less than that of the inner round honing

Small cutting allowance

Honing is the one that removes the least amount of margin among all machining methods. In honing, the honing tool takes the workpiece as the guide to remove the excess amount of the workpiece and achieve the required precision of the workpiece

Strong ability to correct holes

Shortcomings due to other processing technology, the machining process will appear the following defects: such as round, bell, corrugated hole, small size, drum-shaped, taper, boring cutter, hole deviation and surface roughness, the honing process can remove the minimum machining allowance and greatly improve the hole and the size precision of cylindrical, roundness, Straightness, cylindricity and surface roughness.

Diamond/CBN honing reamer

More Superhard provides precision bore honing finishing solution, the honing tools include
- Diamond honing stone, cbn honing stick
- Single pass diamond honing tools
- Cylinder honing tools
- Diamond honing head
- Diamond cylinder hone
Honing Machine: Sunnen, Nagel, Gehring, Nissin, Engis, Fuji, Mas and other honing machines.

Diamond honing reamer have fixed and adjustable diamond honing honing reamer reamer, and contains ladder diamond honing reamer, from literal meaning can also see, fixed electroplating diamond reamer is a fixed size, guide, before the blade, the guidance as a whole, while the adjustable electroplating diamond reamer is adjustable reamer size, after the reamer body wear, can be in bushing vertebral body The upper trace movement can compensate the wear size, so that the cutter body can be reused, thus extending the service life. The fixed electroplated diamond reamer is more used in the blind hole, and the adjustable diamond honing reamer is more used in the through hole.

  

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The difference between diamond grinding wheel and ordinary grinding wheel and how to dressing diamond grinding wheel?

 How to dress diamond grinding wheel?

In the dressing process, the ordinary abrasive grinding wheel is aligned with the diamond grinding wheel, and the diamond grinding wheel rotates, while the ordinary abrasive grinding wheel carries out feed movement while rotating Under the action of friction, the grinding particles on the surface of the diamond grinding wheel begin to rotate slowly, which produces certain extrusion pressure on the metal adhesive while rotating, leading to cracks in the adhesive. With the continuous action of friction, cracks in the adhesive are further expanded Finally, the adhesive breaks, making the blunt diamond particles fall off the surface of the grinding wheel and exposing the sharp diamond particles for the purpose of repair.

 

Q: What material is suitable for grinding artificial diamond wheel?

A: synthetic diamond grinding wheel is suitable for grinding high hardness inorganic materials Cemented carbide materials and high hardness of metal materials Diamond grinding wheel for grinding glass ceramic ferrite and semiconductor materials and other hard brittle materials and metal materials, and carbide materials Synthetic diamond grinding wheel is grinding carbide optical glass ceramic gem stone high hardness The best grinding tool for brittle non-metallic materials.

Q: What material is suitable for grinding artificial diamond wheel?

A: Diamond grinding wheel, with diamond abrasive as raw material, made of metal powder resin powder ceramics and electroplating metal circular through hole consolidation abrasive called diamond grinding wheel (alloy grinding wheel).

Diamond grinding wheel belongs to superhard grinding wheel. Compared with ordinary grinding wheel, diamond grinding wheel has very obvious characteristics and advantages:

1. The hardness of diamond abrasive determines the main characteristics of diamond grinding wheel: it can effectively grind hard alloy glass ceramics and other difficult materials, grinding tools have the longest service life.

2 Diamond has higher wear resistance, the less wear of grinding wheel, the longer the use time. In the grinding process, the size, shape and shape of diamond grinding particles change little, more suitable for high-precision machining, high production efficiency diamond wheel is a kind of tool that can meet the requirements of efficient and precision machining at the same time.

3. The repaired diamond grinding wheel can maintain the micro-blades of particles for a long time, and the good cutting performance ensures the small grinding force in the grinding process, thus reducing the grinding power and saving energy.

4. Diamond has good thermal conductivity, conducive to heat dissipation, avoid the phenomenon of workpiece burns, cracking and falling off, greatly improve the quality of workpiece surface processing.

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High precision gear machining for new energy vehicles

 1. Hard surface gear

The hard tooth surface processing technology is mainly applied to the gear finishing whose tooth surface hardness is higher than 45 HRC after heat treatment. The purpose is to improve the efficiency and quality of the gear finishing and reduce the processing cost. The main processing methods are for the hard tooth surface shaving fine rolling (scraping) tooth grinding and honing, etc. Compared with the traditional processing technology, the hard tooth surface processing method can improve the tool materials and coatings of machine tools tool technology and other higher requirements.

Hard gear surface machining technology is mainly applied to gear finishing whose tooth surface hardness is higher than 45 HRC after heat treatment, aiming to improve the efficiency and quality of gear finishing and reduce the processing cost. The main processing methods are for hard tooth surface shaving, fine rolling (scraping), grinding and honing, etc. Compared with traditional processing technology, The machining method of hard tooth surface puts forward higher requirements for machine tool, tool material and coating, tool technology and so on.

Gear honing and grinding can use electroplating or sintering grinding tools of CBN or diamond superhard abrasive. The forming grinding tools of CBN grinding wheel are shown in Figure 3, and the rough-finishing cutting tools are designed into combined cutting tools during tool design. The number of working procedures can be reduced by using coated HSS or cemented carbide cutting tools for tooth shaving and fine rolling on the hard tooth surface.

Compared with the traditional technology, the superhard tool material grinding wheel can significantly reduce the surface roughness, improve the surface quality, and improve the accuracy of 1~2 degrees. The processing efficiency is more than 25 times of the conventional tooth surface grinding. In order to adapt to the requirements of the hard tooth surface gear processing, the machining machine pays more attention to the CNC technology, high-speed machining and multi-function.

2. Strong precision honing

 

Due to the limitation of the gear hobbing and shaving heat treatment grinding process commonly used in gear processing in high precision automotive transmission gear processing, it is difficult to meet the technical requirements of gear to grind the hard tooth surface after heat treatment, and then adopt the honing method to improve the quality and the processing cost is high However, it is an efficient method for high precision gear machining to use strong gear honing directly on the hard tooth surface.

When the manufacturing cost is close to the traditional process, higher machining precision and surface quality and machining efficiency can be obtained, showing good economic benefits. The tooth shape and direction correction of strong gear honing can be greater than 0.05 mm, can correct the heat treatment deformation and micro-defects, surface roughness can reach Ra0.2μm below, after heat treatment using strong gear honing process, can reduce the surface wear caused by grinding teeth, avoid the resonance and noise generated in the transmission gear meshing process.

The tooth surface has a large residual compressive stress, which significantly increases the strength, wear resistance and pitting corrosion resistance of gear. In the process of strong gear honing, the tool slides relative to the tooth surface and removes the workpiece material at the same time. The cutting speed is low, which avoids the tooth surface burn caused by high-speed grinding in the process of gear grinding.

Compared with gear grinding, gear honing can process the gear with shoulder. Although the precision is slightly lower than that of gear grinding, the cost and comprehensive efficiency of strong gear honing are obviously better than that of gear grinding process. Gear honing costs about 50% of the shaving cost and 20% of the grinding cost.

Therefore, the application of strong gear honing process in high-precision gear machining of automobile transmission has great advantages, and improves the reliability and stability of transmission operation, extends the overhaul cycle, and reduces the problem of automobile noise. The process route of high-precision gear machining of automobile transmission can be simplified into rolling, shaving, honing, and even the strong gear honing can be carried out directly after hobbing.

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Using diamond band saw blade for high precision dicing

 Diamond band saw blade is a straight line curve cutting tool of brittle materials. It is a composite steel strip with diamond embedded in a high-quality spring steel matrix. It can cut any non-metallic, super hard, brittle materials (such as marble, agate, hard alloy, glass, magnetic alloy) with energy saving, raw materials saving, good cutting quality (smooth and smooth), high cutting efficiency. Good formability, not easy to crack four advantages.

 

When cutting carbide speed can reach 300mm/min, cutting marble can reach 100mm/min, cutting granite can reach 40mm/min, is the traditional reciprocating saw or line cutting efficiency of dozens of times, its narrow incision (only 1.2mm) It can efficiently cut monocrystalline silicon, polysilicon, graphite, jade products, fiberglass, quartz, sapphire, zircon, marble, ceramics and other metallic materials.

Diamond band saw blade blade can efficiently cut monocrystalline silicon, polysilicon, graphite, jade products, fiberglass, quartz, sapphire, zircon, marble, ceramics and other metallic materials.

 Advantage for diamond band saw blade :

1. Diamond sand and coating combined firmly, sand, wear-resistant.

2. The diamond particles on the surface of the band saw have regular crystal shape, sharp edges and moderate chip space.

3. The cutting edge is sharp, the cutting speed is stable, the dimensional precision of the product after cutting is high, the cutting surface is smooth and smooth, and the damage is small.

4. The matrix of the band saw is made of high quality steel, both rigid and flexible, the welding is firm and smooth, not easy to break, and the service life is long.

Process selection of diamond band saw blade 

1. Selection of diamond particle size

When the diamond particle size is coarse and single, the blade head is sharp and the cutting efficiency is high, but the bending strength of diamond agglomeration decreases. When the diamond particle size is fine or mixed, the saw blade head has high durability but low efficiency. Considering the above factors, 50/60 mesh diamond size is selected as the most suitable diamond size. When the diamond particle size is coarse and single, the saw blade head is sharp and the cutting efficiency is high, but the bending strength of diamond agglomeration decreases. When the diamond particle size is fine or mixed, the saw blade head has high durability but low efficiency. Taking the above factors into consideration, 50/60 mesh diamond size is more appropriate.

2. Selection of diamond distribution concentration

In a certain range, when the diamond concentration changes from low to high, the sharpness and cutting efficiency of the saw blade gradually decrease, but the service life is gradually extended. But the concentration is too high, the saw blade will become dull and use low concentration coarse particle size, efficiency will improve the use of the different parts of the tool head in the sawing cutting, using different concentrations (that is, in the three or more layers of the structure of the middle layer can use a lower concentration), the process of the saw head work on the formation of the middle groove, is conducive to prevent the saw blade swing, so as to improve the quality of stone processing.

3. Selection of diamond strength

The strength of diamond is an important index to ensure the cutting performance. If the strength is too high, the crystal will not be broken easily, and the abrasive particles will be polished during use, and the sharpness will decrease, leading to the deterioration of tool performance. When the strength of diamond is not enough, it is easy to break after impact, and it is difficult to bear the cutting load. Therefore, the strength of diamond should be selected in the range of 130~140N.

4. Selection of bond 

The performance of the saw blade is not only dependent on diamond, but depends on the diamond and binder properly matched to the tool head of the overall performance of this composite material for marble and other soft stone, the mechanical properties of the tool head is relatively low, can choose copper based binder but copper based binder sintering temperature is low, strength hardness is low, toughness is high, and diamond combination strength is low When WC is added, WC or W2C is used as the skeleton metal, and appropriate amount of cobalt is added to improve the strength and hardness and bonding characteristics. A small amount of Cu, Sn, Zn and other metals with low melting point and hardness are added as the bonding phase. The particle size of the main additive component should be finer than 200 mesh, and the particle size of the additive component should be finer than 300 mesh 5. Choice of sintering process

With the increase of temperature, the densification degree of the tire body increases, so does the bending strength. With the extension of holding time, the bending strength of the blank tire body and diamond caked first increases and then decreases. The sintering process of 120s at 800 ℃ can be selected to meet the performance requirements

The diamond particles on the surface of the band saw have regular crystal shape, sharp edges and corners, moderate chip space, sharp cutting edge, stable cutting speed, high dimensional accuracy of the product after cutting, smooth and smooth cutting surface, and small damage. The matrix of the band saw is made of high quality steel, both rigid and flexible, the welding is firm and smooth, not easy to break, and the service life is long.

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