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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