Honing common problems and solutions

 

Honing is to use several oil stones installed on the circumference of the honing head, and the oil stones are radially expanded by the expansion mechanism, so that the oil stones are pressed against the hole wall of the workpiece to generate a certain pressure and contact area, and the honing head (or workpiece) rotates and reciprocates The workpiece is ground at low speed during motion, as shown in Figure 1. In order to reduce the influence of the different axis between the machine tool spindle and the workpiece center and the rotation accuracy of the machine tool spindle on the machining accuracy of the workpiece, the connection between the honing head and the machine tool spindle adopts a floating connection, guided by the workpiece hole. During honing, the overlapping contact points between the oilstone and the hole wall interfere with each other and are trimmed each other, so that the hole surface presents a crossed helical cutting track during the honing motion. Since the motion trajectory is not repeated, the chances of interference points are almost equal, the cutting effect is continuously weakened, the roundness and cylindricity of the hole and the oilstone surface are continuously improved, and the surface roughness value of the hole wall will be continuously reduced, and the required dimensional accuracy is achieved. After that, the honing process is completed.

During the honing process, the machining accuracy (size and shape), machining efficiency and machining surface quality of the workpiece all depend on the reasonable structure of the honing head, and also depend on the feeding method of the machine tool, the characteristics of the oilstone and the workpiece fixture. The structure of the honing head is good, the expansion and contraction of the oil stone are uniform, the cutting fluid is easy to inject, and the chips and abrasive particles are easy to remove after falling off. The dressing and positioning of the oil stone are accurate and easy to manufacture, which will directly affect the honing effect.

In the process of machining parts, a variety of processes are used, among which honing is a processing method for finishing holes. This kind of processing can get more accurate hole diameter, which is of great help to improve the precision of parts.

Honing processing has the following characteristics:

(1) Wide range of processing. It is mainly used for finishing holes, such as cylindrical holes, stepped holes, blind holes and tapered holes. It can also be used on flat, spherical and forming surfaces and external circular surfaces. The honing hole diameter is 1-1200mm or larger, and the hole length can reach 12000mm. Almost all workpiece materials can be honed.

(2) The processed surface quality is good. The surface after honing is cross-textured, which is beneficial to the storage of lubricating oil and the maintenance of lubricating film, wear resistance and long service life. Also because the honing speed is several tenths of the general grinding speed, the grinding force and heat are very small, and the surface of the workpiece does not produce burns, cracks, deterioration and hard layers.

(3) High processing precision. When honing is used to process the inner hole, the roundness and cylindricity can reach 0.005-0.01mm, and the surface roughness value Ra can reach 0.05-0.2μm, but the position accuracy cannot be improved, and it can replace part of the grinding process. The processing efficiency and grinding quite.

(4) Low requirements for machine tool precision. In addition to the special honing machine, honing can also be carried out on lathes, boring machines and drilling machines.

There are also some problems in the honing process. Moresuperhard makes the following solutions for different problems:

The dimensional accuracy of the hole is low and the dimension is unstable

1. The heat of honing is high, and the size becomes smaller after cooling

(1) The honing allowance is large and the time is long

(2) The speed of the honing head is high and the reciprocating speed is low

(3) Whetstone clogged, self-sharpening is not good

(4) The honing feed is too fast and the pressure is too high

(5) Improper selection of oilstone abrasives, particle size, and organization

(6) The workpiece material has high strength (hard, tough, sticky)

(7) Insufficient honing fluid or poor cooling performance

2. The process system is unstable, and the size varies from time to time

(1) The pre-processing quality of the hole is low, and the honing allowance changes greatly

(2) The hardness of the oil stone is uneven, and the cutting performance is unstable

(3) The processed surface of the hole has a cold work hardened layer or a rough surface

(4) The timing honing method cannot obtain accurate honing aperture

(5) The air measuring nozzle on the honing head is worn, and the gap is too large

(6) The magnification of the automatic measuring instrument is low, and it is inconvenient to adjust and control

(7) The information feedback system of the automatic measuring instrument is insensitive and unreliable

(8) The air pressure is unstable, the air source is not filtered, and the honing fluid is too dirty

Solutions:

1. Control the honing allowance and time, select the appropriate amount of honing and the performance of the oilstone, and use low-viscosity, large-volume, low-temperature honing fluid to reduce honing heat.

2. To improve the processing quality of honing holes, select oil stones with uniform hardness and structure, and timely detect and replace automatic measuring systems and tools.

Shape error and roundness out of tolerance

(1) The centering error between the honing spindle (or guide sleeve) and the workpiece hole is too large

(2) The clamping force of the fixture is too large or the clamping position is improper

(3) The hole wall is uneven, the honing temperature is high or the honing pressure is too large

(4) The hardness or material of the inner hole of the workpiece is uneven

(5) Too little or uneven supply of honing fluid, resulting in uneven heating and cooling of the inner surface

(6) The roundness error is large after hole preprocessing, or the machining allowance is too small

(7) The floating connection of the honing head is too loose, the speed is high, and the swing inertia is large

(8) The floating connecting rod of the honing head is not flexible, or the rigid connecting rod is bent, and the swing difference is large, etc.

(9) The reciprocating speed is too high, and the mutual dressing between the oil stone and the hole is not enough

Solution:

Correctly install and adjust the honing head, improve the quality of blanks and honing holes, supply sufficient honing fluid evenly, and pay attention to the capacity and flow of the pump

The straightness of the hole is out of tolerance

1. The cylindricity is out of tolerance

(1) The overrun of the honing oil stone at the upper and lower ends of the hole is too large, and a bell mouth appears (both ends are large); the overrun is too small, and a drum shape appears;

(2) The workpiece is clamped and deformed, or the upper and lower wall thicknesses are inconsistent, and the material and hardness are inconsistent

(3) The cylindricity error after hole preprocessing is large, or the honing allowance is too small

(4) Improper selection of the length of the whetstone

(5) The hardness of the oilstone is inconsistent, the durability is low (soft), and the wear is uneven (up and down eccentric wear)

(6) The reciprocating speed of the honing spindle is inconsistent

(7) The axial position change of the oilstone on the honing head

(8) The reciprocating stroke position accuracy of the honing machine is low

Solution:

Carefully adjust the overtravel length of the oil stone at the upper and lower ends of the hole; correctly select the length of the oil stone, and the hardness should not be too soft; reduce the clamping force and change the clamping position accordingly; control the roundness error after the pre-processing of the hole to not exceed 1/ of the honing allowance 5~1/4; adjust or repair the machine tool, or add a limit mechanism

2. The straightness of the hole is out of tolerance

(1) The honing stone is too short, or the honing head is short and unguided

(2) The oil stone is too soft, wears quickly, and has poor formability

(3) Out-of-tolerance straightness after hole preprocessing

(4) The floating joint of the honing head is not flexible, which affects the guidance of the honing head

(5) Clamping deformation

(6) Honing reciprocating speed or uneven supply of honing fluid

(7) The alignment between the fixture and the spindle or guide sleeve is not good

Solution:

Correctly select the length of the oilstone according to the length of the hole, and lengthen the guide; replace the oilstone in time to improve durability; adjust or clean the lubricated floating joint to make the floating flexible and without gaps; increase the reciprocating speed or increase the honing fluid; clamping force.

The axis of the hole is not perpendicular to the end face

(1) The positioning surface of the fixture is not perpendicular to the honing spindle or the positioning surface is excessively worn

(2) The verticality error after hole preprocessing is large

(3) The honing head without rigid connection is used for short hole honing

(4) The bottom surface of the workpiece is not clean, and the positioning surface is inclined

(5) The clamping force is uneven, so that one side of the workpiece is lifted

(6) The clamping force is too small to loosen the workpiece and leave the positioning surface

(7) When the clamping force is too large, when short hole honing or stacked honing, the workpiece with uneven end surface will be completely fitted and deformed

(8) The alignment between the main shaft of the honing machine and the workpiece hole is not good

Solution:

Adjust the fixture, clamp the workpiece correctly, check and improve the pre-machining accuracy of the hole

Surface defects

Honing Surface Scratches

(1) The oil stone is too hard, the structure is uneven, iron filings accumulate after the surface is clogged, and the surface is scratched

(2) The gap of the honing head in the hole is too small, and occasionally the machined iron filings are not easy to discharge and scratch the surface

(3) The honing pressure is too small, and the oilstone is squeezed and scratched

(4) The coolant is not filtered well, and the flow and pressure are small

(5) The whetstone is not retracted first when the honing head exits

(6) The guide sleeve and the workpiece hole are centered, and the tail end is deflected when the honing head withdraws

(7) The whetstone is too wide, iron filings are not easy to remove and fall off, and accumulate on the surface of the whetstone to form hard spots

Solutions:

Reduce the pressure, increase the strength and width of the honing stone or groove in the middle, remove the hard spots on the honing stone, choose soft, loose and uniform tissue, and have better self-sharpening; properly reduce the diameter of the honing head to ensure the radial clearance, make the coolant flow.

How to choose a high-quality and suitable dicing blade for wafer dicing?

 The wafer dicing blade is made of synthetic resin, copper, tin, nickel, etc. as a bonding agent and synthetic diamond. It can be divided into a hub-type diamond dicing blade and hubless diamond blade, which can be used to process chips of different materials and semiconductor-related materials. Therefore, how to choose a suitable scribing blade mainly depends on these factors, such as the particle size and concentration of the diamond, the strength of the blade bond, the length and thickness of the blade, etc.

Moresuperhard can provide:

* Resin diamond dicing blade（Suited for dicing hard and brittle materials,such as QFN, sapphire, quartz and glass, etc）

* Metal diamond dicing blade （ used for cutting and slotting varieties of hard or fragile materials. Such as silicon slices,glass,ferrite,quartz crystals,piezoelectric ceramics,optical glass,  FR4, BGA and QFN packages, BGA, magnetic heads, optical sensors , communication, MEC, QFN, etc）

* Electroformed hub dicing blade （ used for cutting Silicon Wafers, copper wafer, IC/LED Packages, Compound Semiconductor Wafers (GaAs, Gap),Oxide Wafers (LiTaO3), Optical Glass）

The effect of diamond particle size on dicing:

1) Large particles: First, the dicing blade edge is large, the removal of debris is large, and the product is not easy to accumulate and precipitate silicon powder; second, the contact surface with the binder is large, it can withstand large resistance, the processing efficiency is high, and it is not easy to wear; the third is with The product contact range is large, the debris and chipping produced are large, and the cutting quality is poor.

2) Small particles: First, the contact range with the product is small, and the debris and cracks produced are small or even no cracks; second, the blade edge is small, the debris removed is small, and the product is easy to deposit silicon powder,the third is the bond with the binder. The contact surface is small, the withstand resistance is small, the processing efficiency is low, and it is easy to wear.

Effect of Diamond Concentration on Dicing Blade

The higher the diamond concentration, the longer the service life of the dicing blade, and the better the chipping angle on the surface, but the worsening the chipping angle on the back side, so the most suitable diamond concentration should be selected according to the demand.

Influence of dicing blade bond strength

1) High-strength binder: first, strong toughness, not easy to break the blade, and high utilization rate; second, strong wear resistance, weak blade regeneration ability, and poor product quality; third, high resistance, slow feed speed, and low efficiency.

2) Low-strength binder: first, small resistance, fast feed speed, and high efficiency. Second, easy to wear, strong blade regeneration ability, and good product quality; third, weak toughness, easy to break the blade, and low utilization rate.

The nickel-based scribing blade for semiconductor cutting uses electroformed nickel-based binder, combined with coarse-grained diamond, to achieve ultra-long life scribing.

4. The effect of particle concentration

1) High concentration: First, there are many cutting edges, more debris removed, and the product is not easy to residue silicon powder; second, the diamond particle load is small, the cutting resistance is small, the progress speed is fast, and the efficiency is high; the third is the small cutting edge of the product, resulting in The debris is small, easy to wash, and the quality is guaranteed; the fourth is less binder, low toughness of the blade, easy to break the blade, and the risk of scratching the product.

2) Low concentration: First, there are more binders, high toughness of the blade, and it is not easy to break the blade; second, there are few cutting edges, less debris removed, and easy silicon powder residue; third, the diamond particle load is large, the cutting resistance is large, and the progress speed Slow and inefficient.

CHICO wafer dicing blade expands the selection range of concentration, which can more accurately meet the various processing needs of users. It can shorten the pre-cutting time and reduce backside cracking.

5. The influence of blade thickness

1) Thickness of the blade: First, the vibration of the blade is small, and the product quality is guaranteed; second, the blade is strong and not easy to break; third, the cutting contact area is large, the resistance is large, the debris generated is large, the feeding speed is slow, and it is easy to pollute.

2) Thin blade: First, the cutting contact area is small, the resistance is small, and the feed speed is fast; second, the blade vibration is small, and the product quality is guaranteed; third, the blade is weak and easy to break.

6. The influence of blade length

1) Long blade: first, long service life; second, weak blade, slow feed speed, easy to break; third, large vibration, prone to deflection, and serpentine cutting.

2) The blade is short: one is the service life

7. The influence of grinding and scribing blade

The purpose of grinding the scribing blade is to expose the diamond on the surface of the blade, and to correct the eccentricity of the blade, hub and flange. When a new blade is installed on the main shaft and the flange, although the blade is in direct contact with the top of the main shaft, there is still a gap between the two. The blade is "concentric" with the holder. If the blade is used in an "off-center" condition, only a part of the blade will work, and the load will be too large, which will easily cause reverse blade and overload, which will affect the product quality.

Application of PCD countersink drill

 Compared with other materials, composite materials have the characteristics of light weight, high strength, high temperature resistance, and corrosion resistance. Whether it is in the automotive field or the aerospace field, composite materials are ideal materials for the aerospace field.

With the gradual increase in the proportion of carbon fiber composite materials used in aircraft, the size of carbon fiber composite material accessories also increases. How to correctly select and rationally use cutting tools for high-efficiency and high-quality cutting is a very important issue.

PCD countersink drill is suitable for processing CFRP, GFRP, titanium alloy and ceramic materials. The PCD cutting edge is sharper, the service life is long and the surface roughness is kept the best.

At present, the composite materials widely used in the aerospace field mainly include resin matrix composites, metal matrix composites, carbon matrix composites and ceramic matrix composites. For different composite material processing workpieces, the tool configuration solutions provided by Moresuperhard for customers are also Constantly update and improve to help customers improve the economic benefits of processing more effectively.

Difficulties in processing composite materials?

A: The material is highly abrasive, which causes a high wear rate of the tool;

The material is anisotropic, and the interlayer strength is low. Defects such as delamination and tearing are prone to occur under the action of cutting force during cutting, especially when drilling;

Due to the high cutting temperature, the thermal expansion coefficient difference between the reinforcing fiber and the matrix resin is too large, the dimensional accuracy and surface roughness of the machined surface are not easy to meet the requirements, and residual stress is easy to occur.

Processing carbon fiber materials with polycrystalline diamond pcd tools can greatly improve the surface quality of carbon fiber composite materials and improve production efficiency. It is an ideal tool.

PCD tool processing features:

PCD tools have sharp and wear-resistant cutting edges, which are very effective in processing composite materials such as carbon fiber reinforced materials (CFRP), glass fiber reinforced materials (GFRP) and aluminum-based silicon carbide (SiCp/AI), which are widely used in the aerospace field. Solve the defects of material delamination, tearing, burr and so on in the process of composite material processing

While obtaining precise and smooth cutting effect, it makes the processing efficiency higher, the wear resistance is better, and the tool life is longer. For example, drilling, hole processing is a common and important process in the processing of composite materials, especially carbon fiber, while carbon fiber parts used in aerospace can use PCD countersink drilling to process the edges of holes such as countersink holes, rivet holes and bolt holes. Using diamond PCD countersink drill, the sharp edge can ensure the good quality of the hole, smooth and burr-free.

What is spot facing? What kinds of countersinks are commonly used?

The surface of the orifice is processed with a countersinking method to process a flat-bottomed or tapered countersunk hole, which is called a countersink, and the countersink works as shown in the figure.

Countersinks are divided into cylindrical countersinks, tapered countersinks, and end countersinks：

1. Cylindrical countersinking is used for countersinking cylindrical countersinks.

The main cutting function of the cylindrical countersink is the end face blade, and the oblique angle of the spiral groove is its rake angle. There is a guide post at the front end of the countersink drill, and the diameter of the guide post is closely matched with the existing hole of the workpiece to ensure good centering and guidance. This guide post is detachable, and the guide post and countersink can also be integrated into one. (Generally, it is a countersunk knife, stepping on a cylindrical countersunk).

2. Tapered countersink is used for countersinking tapered holes.

The taper angle of the tapered countersink is different according to the requirements of the tapered countersink of the workpiece, including 60°, 75°, 82°, 90°, 100°, 120°, etc. Among them, 90° is used the most.

3. The end face countersinking drill is specially used for countersinking the end face of the hole.

Countersinking on the end face can ensure the perpendicularity of the end face of the hole to the center line of the hole. When the diameter of the machined hole is small, in order to maintain a certain strength of the tool bar, a section of the diameter of the tool bar head can be matched with the machined hole as a gap to ensure a good guiding effect.

What is reverse spot facing?

In the processing of some parts, it is necessary to spot-face the oblique or curved surface of the part to install bolts in the subsequent assembly, but due to the structural limitations of the parts, some spot-sinks cannot be spot-spotted from the front, and need to be reverse-sinked through the mounting holes of the bolts out, we call it reverse spot facing.

The role of countersinking?

Countersinking is the processing of planes, cylinders, tapers and other surfaces on the end face of the hole. Countersinking is used when machining cylindrical countersinks, tapered countersinks and end bosses on the machined holes.

Flat-bottom counterbore (English name Counterbore), its circumference and end face each have 3~4 cutter teeth, insert guide post into the processed hole, its function is to control the coaxiality error between the counterbore and the original hole . The guide post is generally made detachable, so as to facilitate the manufacture of the face teeth of the countersink drill and the sharpening of the countersink drill.

Flat-bottomed countersinking drill has 3~4 cutter teeth on its circumference and end face respectively, inserting a guide post into the processed hole, its function is to control the coaxiality error between the countersinked hole and the original hole. The guide post is generally made detachable, so as to facilitate the manufacture of the face teeth of the countersink drill and the sharpening of the countersink drill.

Compared with other materials, composite materials have the characteristics of light weight, high strength, high temperature resistance, corrosion resistance, etc., and become ideal materials in the aerospace field. With the wide application of aerospace composite materials, how to correctly select and rationally use cutting tools for efficient and high-quality cutting is a very important issue. At present, the tool materials widely used in the aerospace manufacturing industry mainly include cemented carbide, superhard tool materials and ceramics, among which cemented carbide and superhard tool materials account for the largest proportion. The leading tool in the development of aerospace industry tools has a wide range of applications.

Moresuperhard PCD superhard material cutting tools and carbide cutting tools have been maturely used in the field of aerospace manufacturing and processing. PCD tools and cemented carbide tools have finely ground sharp cutting edges, which are widely used in the aerospace field for composite materials such as carbon fiber reinforced materials (CFRP), glass fiber reinforced materials (GFRP) and aluminum-based silicon carbide (SiCp/AI) The effect is excellent, which effectively solves the defects of material delamination, tearing, burrs and so on in the process of composite material processing. While obtaining precise and smooth cutting effect, it makes the processing efficiency higher, the wear resistance better and the tool life longer. longer.

Hole machining and edge milling of parts are difficult points in the machining of aerospace composite materials. Therefore, Moresuperhard has developed high-performance hole machining tools and milling cutters made of PCD and cemented carbide, which are now mature. It is widely used in the processing of aerospace composite materials.

Drilling is a common and important process in the processing of composite materials, especially carbon fiber. Hole machining in composite materials is extremely prone to defects such as material burns, poor hole machining surface quality, delamination, tearing and collapse. The 8-edge twist drill in the Moresuperhard hole processing tool, the 8-edge design, reduces the cutting force when the drill is pulled away from the material, and avoids delamination; the tapered drill has a special drill tip shape, and the drilling axial force is small and the edge is small. The sharp edge ensures the good quality of the hole; PCD countersink drill, PCD cutting edge has high durability, good surface roughness index retention, precision grade 2A thread and taper surface fit, ensuring high precision, quick and easy replacement of the drill bit, 100° and The metric and American standard tools with 130° countersinking angle are supplied in full specifications; the drill-reamer-sinking integrated tool can complete drilling and countersinking at one time, omitting the need for retracting, changing and cutting tools when machining with conventional drills and reamers Indexing can greatly shorten the processing time, and the polishing margin can squeeze the hole wall.

Case of turning Aircraft carbon fiber skin with PCD countersink drill

For carbon fiber skins, the rivet holes require high precision and are difficult to process, so PCD countersinking is generally used for processing.

Aircraft skin refers to the three-dimensional component that surrounds the frame structure of the aircraft and is fixed on the frame with adhesives or rivets to form the aerodynamic shape of the aircraft. The skin structure composed of aircraft skin and skeleton has a large bearing capacity and rigidity, but its own weight is very light, and it plays the role of bearing and transmitting aerodynamic loads. After the skin is subjected to aerodynamic action, the force is transmitted to the connected fuselage and wing frame. The force is complex, and the skin is in direct contact with the outside world. Therefore, not only the skin material is required to have high strength and good plasticity, but also a smooth surface. It has high corrosion resistance.

 

The key points and difficulties in the preparation of silicon carbide substrates

 Semiconductor Materials and Processes

The silicon carbide production process includes the preparation of material end substrates and epitaxy, the design and manufacture of subsequent chips, and then the packaging of devices, and finally flows to the downstream application market. Among them, the substrate material is the most challenging link in the silicon carbide industry. The silicon carbide substrate is hard and brittle, and it is very difficult to cut, grind, and polish, which makes it easier to produce waste products and reduce the yield rate during processing. At present, most international silicon carbide manufacturers are planning to change silicon carbide wafers from 6 inches to 8 inches.

Silicon carbide substrate The core material of the industrial chain, the preparation is difficult

The preparation of silicon carbide substrates mainly includes raw material synthesis, silicon carbide crystal growth, ingot processing, ingot cutting, wafer grinding, wafer polishing, and polishing pad cleaning. The link is the focus and difficulty in the entire substrate production link, and has become a bottleneck that limits the yield and production capacity of silicon carbide.

Crystal growth

Crystal growth difficulties:

● Crystal growth is slow. The growth rate of silicon carbide is only 0.3-0.5mm/h, and the maximum crystal length can only reach 2-5cm, which is quite different from silicon-based substrates. And as the size of silicon carbide crystals expands, the difficulty of its growth process increases geometrically.

● The yield rate of black box operation is low. The core parameters of silicon carbide substrates include micropipe density, dislocation density, resistivity, warpage, surface roughness, etc. The production process is completely completed in a high-temperature sealed graphite cavity. It is necessary to arrange the atoms in the closed high-temperature cavity in an orderly manner to complete the crystal growth and control the parameter indicators at the same time. It is very dependent on the manufacturer's process experience and is prone to various defects and other problems. The crystal growth process is difficult, the yield rate is low, and the output is small.

● There are many types of silicon carbide crystal structures, but only a few of them are required materials. It is difficult to control impurities, and polymorphic inclusions are likely to occur, which reduces product yield.

Cutting, Grinding and Polishing

After the silicon carbide crystal is prepared, it needs to be cut into thin slices with a thickness of no more than 1mm along a certain direction, and ground with diamond abrasive fluids of different particle sizes to remove knife marks and metamorphic layers and control the thickness before CMP After polishing to achieve global planarization, it enters the final cleaning process.

Difficulties in cutting, grinding and polishing: Since silicon carbide is a brittle material with high hardness, it has serious problems such as warping and cracking during processing, and the loss is huge. Under the traditional reciprocating diamond-bonded abrasive multi-wire cutting method, the overall material The utilization rate is only 50%. After polishing and grinding, the cutting loss ratio is as high as 75%, and the usable part ratio is relatively low.

 

Slicing of SiC single crystal

As the first process in the silicon carbide single crystal processing process, the performance of the slice determines the processing level of subsequent thinning and polishing. Slicing is easy to produce cracks on the surface and sub-surface of the wafer, which increases the chip fragmentation rate and manufacturing cost. Therefore, controlling the crack damage on the surface of the wafer is of great significance to promote the development of silicon carbide device manufacturing technology.

Main Influencing Factors and Optimizing Measures of Slicing Quality

Surface crack damage is closely related to slice quality. The epitaxial growth on the silicon carbide substrate material, the device manufacturing process and the device performance are all related to the crystal orientation. In order to avoid brittle cracks in wafers caused by orientation sensitivity during slicing, crystal orientation detection is required before slicing silicon carbide ingots. Silicon carbide ingots are generally grown on the SiC { 0001} plane, and cutting along the SiC crystal plane parallel to the growth direction of the ingot can effectively reduce the through-thread dislocation density on the slice surface and improve the slice quality.

Thinning of silicon carbide wafers

2.1 The thinning of silicon carbide slices is mainly achieved by grinding and grinding.

Grinding

The most representative form of wafer grinding is self-rotation grinding. While the wafer is self-rotating, the spindle mechanism drives the grinding wheel to rotate, and at the same time the grinding wheel is fed downwards, thereby realizing the thinning process. Although self-rotating grinding can effectively improve processing efficiency, the grinding wheel is prone to passivation with the increase of processing time, the service life is short, and the wafer is prone to surface and sub-surface damage. The existence of processing defects seriously restricts the processing accuracy and efficiency. In order to solve these problems, researchers have developed different auxiliary technologies, such as online dressing of grinding wheels, or the development of new soft abrasive grinding wheels. At present, the main technologies include ultrasonic vibration assisted grinding and online grinding. Electrolytic dressing assisted grinding.

Ultrasonic assisted grinding is a method of reducing grinding force and grinding wheel wear through ultrasonic vibration, and improving processing quality. Many studies have shown that under certain process conditions, ultrasonic-assisted grinding is more suitable for thinning of hard and brittle materials than ordinary grinding.

Under the action of electrolysis during online electrolytic dressing assisted grinding, an insulating oxide film is formed on the surface of the grinding wheel, which can slow down the loss of the grinding wheel, and at the same time support a large number of electrolytically shed abrasive particles, which is similar to the grinding effect of free abrasive particles, which is conducive to improving the quality of the grinding surface.

Lapping

The lapping process can be divided into single-side and double-side grinding, and single-side and double-side grinding technologies for small-sized silicon carbide wafers have been developed one after another. When grinding the surface of silicon carbide slices, the abrasive used is usually boron carbide or diamond, which can be divided into rough grinding and fine grinding. Coarse grinding is mainly to remove the knife marks caused by slicing and the metamorphic layer caused by slicing, and the abrasive grains with larger particle sizes are used. The purpose of fine grinding is to remove the surface damage layer left by coarse grinding, improve the surface roughness, and use finer abrasive grains.

 

2.2 The main factors affecting the thinning effect

The study found that the wafer material removal rate in the thinning process is closely related to abrasive particle size, density, grinding disc rotation speed, grinding pressure and other factors. The higher the hardness of the abrasive grains in the slurry, the larger the grain size, and the greater the surface roughness of the processed wafer. Too hard grinding discs will damage and pollute the surface of the workpiece, soft grinding discs can allow more sliding movement of the abrasive, and the surface finish after processing is high, but the flatness is low.

Polishing of silicon carbide wafers

3.1 Research status of polishing technology

The polishing process of silicon carbide wafers can be divided into rough polishing and fine polishing. Mainly include electrochemistry, magnetorheology, plasma, photocatalysis, etc., and mechanical synergistic methods mainly include ultrasonic assistance, mixed abrasive grain and consolidated abrasive grain polishing, etc.

3.2 Key factors and development trends affecting CMP

Polishing results are optimized when the mechanical and chemical effects of CMP are balanced. The polishing effect of CMP is mainly affected by three parameters: process parameters, polishing liquid, and polishing pad. Polishing fluid and polishing pads are the main consumables in CMP, and controlling and optimizing their properties to ensure repeatable polishing efficiency is critical for process stability. Improving the polishing solution and developing a polishing pad with self-catalysis is the research direction of CMP consumables in the future.

Cylindrical grinding method and the choice of grinding allowance

 

2022-11-16 

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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.

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

2022-11-21 

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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.

 

Application hybrid CBN grinding wheel for medical stainless cutting tools

 

New requirements for precision tools in the medical industry
Difficult-to-machine materials, complex workpiece shapes and frequent small-batch production place high demands on the tools used to process medical materials. The precision tools produced by Walter enjoy a high reputation in this field.
Medical materials, such as implant products and prosthetics, play an important role in successful surgical procedures, helping surgeons achieve optimal medical outcomes. Cutting tools for processing medical materials determine the quality of medical materials to a large extent. The use of cutting tools in the manufacture of medical materials is diverse and extensive. It can process relatively simple workpieces such as large-scale equipment (such as computerized tomography cameras), while the production of implanted products or workpieces used to repair the skull or treat fractures. more challenging.

Precision – the most basic requirement
Tolerances in the micron range are common in the medical industry, and selecting the correct tool requires insight and experience. On the one hand, even drilling small holes requires the use of lubricants to reduce friction, reliably dissipate heat and dispose of fine iron filings at the cutting edge; cutting tools for high-quality surfaces. Commonly used cutting tools are high-speed steel drills or solid carbide drills. Walter Titex (Walter Titex) drill bit of Walter Group in Germany is used for processing difficult-to-machine materials such as titanium, stainless steel, precious metals and even composite materials. The diameter of the drill bit can reach 0.75mm.
Milling and Drilling – Dental Restoration
In the material selection of orthopedic cutting tools , stainless steel cutting tools occupy a large part. The grinding problem of stainless steel cutting tools is placed in front of the processor. The slotting of the cutting tools is the process with the largest machining allowance and the most time-consuming. For this application, we have developed a grinding wheel specially for stainless steel tool grooving, and conducted a series of experimental tests. The specific test results are as follows:

Test purpose	Test hybrid CBN grinding wheel for fluting stainless cutting tools
Test equipment	DjtolS500   Spindle power:6KW
Size of grinding wheel	3A1 100X31.75X10X3
Grinding wheel formula	B107 hybrid-A
Workpiece material	30Cr13 stainless,Heat treatment hardness-52
Workpiece parameters	Diameter4mm，4×27，twirl angle-40°rake-5°
Grinding process	linear velocity：30m/s cutting depth:0.6mm+0.5mm The cutting speed setting value is 600, and the grinding wheel is not sharpened
Grinding effect	Sharpness: the grinding power is about 150 watts after the grinding is stable Durability: 70 pieces of bar (equivalent to the machining allowance of 200 pieces of cutting tools from the customer) after slotting, measure the radius of the grinding wheel from R0.05mm to R0.10mm

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