CN103331652A - Dynamic-pressure float-leaving polishing method - Google Patents

Abstract

The invention relates to a dynamic-pressure float-leaving polishing method. A basal disc stuck with a workpiece is made into a disc with a plurality of tilting planes along a peripheral direction; and when the disc rotates in liquid, hydrodynamic pressure is generated through a liquid wedge, the workpiece in a retaining ring float-leaves the surface of the disc, and the workpiece is polished through powder particles in a floating clearance. The dynamic-pressure float-leaving polishing method can reduce surface roughness, improve surface quality and can increase precision at the same time when the workpiece is processed.

Description

Dynamic pressure floating polishing method

Technical Field

The invention relates to the field of polishing, and provides a dynamic pressure floating polishing method.

Background

With the development of science and technology, various systems with crossed optical, mechanical and electronic disciplines are manufactured. In order to ensure the high quality and high performance of key elements in the system, the elements are required to have high processing precision, even have extremely high flatness and have no damage to the ultra-smooth surface, i.e. the workpieces are required to have no damage such as scratches, microcracks, pits, lattice distortion and the like. The processing of optical and semiconductor parts basically comprises 3 steps of milling, shaping, grinding and polishing, and the final surface quality is determined by polishing, so that polishing is the most important step. The polishing is usually carried out using fine abrasive grains of 1um or less, and the polishing disk is made of a soft metal or nonmetal material such as asphalt, paraffin, synthetic resin, artificial leather, tin, etc. to meet the technical requirements. However, in the investigation process, it is found that the domestic polishing equipment has low precision and many artificial factors of the polishing process at the present stage, which results in low product yield, poor precision, low working efficiency and the like.

And many research results of the current domestic and foreign research status of the ultra-smooth surface fluid polishing technology show that: the polishing pressure of the abrasive against the work surface is one of the important causes of polishing defects, the contact polishing surface has a roughness of about 1/5 the diameter of the polishing particle, the depth of the damaged layer of the sub-surface is about 1/2-1 times the depth diameter of the polishing particle, and the dislocation density is in the range of 5X 10⁹cm²—4×10¹⁰cm²The local strain value parallel to the polishing surface was 0.1%. Loose abrasive particles are mixed with fluid to form a liquid-solid two-phase or gas-solid two-phase abrasive particle flow, so that the quasi/non-contact polishing method represented by the abrasive particle flow is beneficial to reducing removal units, improving the contact condition of the abrasive particles and a workpiece and realizing less-damage and low-stress polishing more easily.

Therefore, in order to improve the surface quality and machining accuracy of a machined workpiece and to ensure the performance of various electronic and optical elements, it is increasingly important to develop a mirror surface ultra-precision machining method free from a machining-deteriorated layer and surface damage (not disturbing the atomic arrangement of crystals).

Disclosure of Invention

In order to overcome the defect that the traditional polishing method cannot give consideration to both the processing quality and the processing precision during processing a workpiece, the invention provides the dynamic pressure floating polishing method which can reduce the surface roughness and improve the surface quality and can improve the precision during processing the workpiece.

The technical scheme adopted by the invention for solving the technical problems is as follows:

a dynamic pressure floating polishing method features that when the base disk with workpiece adhered to it is made into several oblique planes along its circumference is rotated in liquid, the liquid wedge generates dynamic pressure to make the workpiece in holding ring float from the surface of disk, and the powder particles in floating gap are used to polish the workpiece.

Furthermore, the device for realizing the dynamic pressure floating polishing method comprises a frame, a capacitance ranging module, a dynamic pressure disc floating module, a micro-motion limiting module and a servo micro-feeding module; wherein,

the capacitive distance measurement module is realized by means of three capacitive sensors embedded on the main grinding disc. The capacitance sensor changes the capacitance of the capacitor by using the change of the displacement, thereby realizing signal conversion;

in the floating module of the movable pressure plate, the output shaft of the motor transmits power to the motor connecting shaft through a common flat key and then sequentially transmits the power to the limiting shaft sleeve, the main shaft connecting sleeve and the main shaft through the guide flat key. Under the specific processing technological condition, the dynamic pressure disc overcomes the gravity and the friction force to generate vertical upward micro displacement under the action of oil film buoyancy, so that springs with certain pretightening force are arranged between the extrusion sliding table and the polishing disc, between the limiting shaft sleeve and the locking nut, the floating energy of the polishing disc and the main shaft is absorbed, and the polishing disc and the main shaft are quickly restored to ideal working positions until dynamic pressure is balanced.

The micro-motion limiting module transmits micro-displacement to the thrust ball bearing and the limiting shaft sleeve through the micro-motion lifter and the limiting plate, so that the limiting shaft sleeve overcomes the matching friction between the limiting shaft sleeve and the motor connecting shaft, vertical downward micro-displacement is generated, the gap between the limiting shaft sleeve and the upper end of the main shaft is reduced, and the micro-motion limiting function is realized. The servo micro-feeding module drives the shaft coupling through the servo motor to enable the screw rod to rotate, the screw rod nut moves up and down, and therefore the sliding table is driven to move up and down, and micro-feeding is achieved.

The technical conception of the invention is as follows: the dynamic pressure floating polishing method mainly depends on the basic theory of fluid dynamic pressure lubrication:

three effects of the two-dimensional Reynolds equation: the starting point of research on hydrodynamic lubrication theory, Reynolds, is to solve how the lubricating oil between the surfaces of the moving pair generates dynamic pressure and the conditions under which it generates dynamic pressure. Analysis of the two-dimensional Reynolds equation: $\frac{\mathrm{\δ}}{\∂x}\left(\frac{h^2}{\mathrm{\η}}\frac{\∂P}{\∂x}\right)+\frac{\∂}{\∂y}\left(\frac{h^2}{\mathrm{\η}}\frac{\∂P}{\∂z}\right)=6\mathrm{\η}({\mathrm{\μ}}_1-{\mathrm{\μ}}_2)\frac{\∂h}{\∂x}+6h\frac{\mathrm{\δ}}{\∂x}({\mathrm{\μ}}_1+{\mathrm{\μ}}_2)+2\frac{\∂h}{\mathrm{\δt}}$

therefore, the following steps are carried out: the three terms on the right side of the equation represent the oil wedge effect, the surface stretching effect and the squeezing effect in the hydrodynamic lubrication process respectively.

Three cases of squeeze effect under hydrodynamic lubrication conditions:

(1) the effect of the squeezing effect is apparent in the event of a shock load or vibration to the shaft. At this time, not only the dynamic pressure of the oil film caused by the squeezing effect plays a leading role in oil film bearing, but also the damping film is a very favorable buffering damping film, but for a light-load high-speed shaft, attention should be paid to preventing oil film oscillation.

(2) When the shaft is subjected to a load direction change such as a rotating load, if the rotating speed u of the load is close to one half of the rotating speed of the shaft, the oil wedge effect does not work, and the oil film dynamic pressure caused by the squeezing effect is the key for ensuring that the system maintains dynamic pressure lubrication.

(3) When the shaft is subjected to a stable load and the size change is within a completely allowable range, the oil hydrodynamic pressure generated by the squeezing effect and the oil wedge effect is in the same order of magnitude. The dynamic pressure caused by the squeezing effect increases the load-bearing capacity of the oil film, and its effect should not be neglected.

In order to remove micro scratches, a non-contact polishing method, namely a dynamic pressure floating polishing method, is applied in the polishing process: when the base disc with the adhered workpiece is made into a disc with a plurality of inclined planes along the circumferential direction and rotates in liquid, liquid dynamic pressure (also called dynamic pressure thrust bearing working principle) is generated through a liquid wedge, so that the workpiece in a retaining ring floats from the surface of the disc, and the workpiece is polished through powder particles in a floating gap.

As shown in fig. 1 and 2, the substrate having the optimum tilt angle α and the ratio γ is found. The buoyancy F of the base plate can be calculated as follows:

$F=\frac{{6\mathrm{\ηULB}}^2}{h^2}K=\mathrm{PLB},\frac{\mathrm{dP}}{\mathrm{dx}}=\mathrm{\η}\frac{{\mathrm{dU}}^2}{{\mathrm{dy}}^2}---\left(1\right)$

wherein, $b=\frac{\mathrm{rB}\×\tan \mathrm{\α}}{h}---\left(2\right)$

$K=\frac{r^2\mathrm{In}(1+b)}{b^2}+\frac{{2r}^2}{b(b+2)}+\frac{\mathrm{br}(1-r)}{2(1-r){(b+1)}^2+r(b+2)}\&times;(\frac{r}{b+2}+\frac{1-r}{2})=\frac{h^2\mathrm{<figure-callout\; id="6"\; label="PLB"\; filenames="HDA00003362469700022.png"\; state="\{\{state\}\}">PLB</figure-callout>}}{6\mathrm{\&eta;}{B}^2\mathrm{LU}}=\frac{h^2}{6\mathrm{\&eta;B}}\&times;\frac{P}{U}---\left(3\right)$

in the formula:

u-relative velocity;

eta-fluid viscosity;

l is the dividing length of the base disc in the radius direction;

b is the dividing width of the circumference of the basal disc surface;

h-minimum gap;

k is a shape factor, which is a function of γ, α, B, h. The ratio of the width of the basal disc from the inner circle end to the outer circle end is gamma, and since gamma is a constant value, the relative speed U at different radiuses is different.

The invention has the following beneficial effects: 1. compared with the traditional contact type polishing, the processing precision is greatly improved, and the polishing efficiency is improved; 2. the invention can adjust the initial distance between the polishing disk and the grinding disk, and solves the problem that the polishing precision is influenced by the floating position change of the polishing disk in dynamic pressure floating polishing; 3. the invention adopts the dynamic pressure thrust bearing theory, designs the structure of the dynamic pressure floating polishing disk, and effectively reduces the roughness of the surface of the workpiece; 4. the invention has the effects of vibration reduction and noise reduction, reduces the vibration amplitude of the polishing disk, and can change the floating position of the polishing disk through the capacitive sensor.

Drawings

FIG. 1 is a sectional structure of a dynamic pressure floating polishing base plate.

FIG. 2 is a schematic plan view of a dynamic pressure floating polishing base.

Fig. 3 is a schematic diagram of a dynamic pressure floating machining prototype system.

FIG. 4 is a schematic diagram of the working principle of floating and micro-motion limiting of the movable platen.

Detailed Description

The invention is further described below with reference to the accompanying drawings.

Referring to fig. 1 to 4, in a dynamic pressure floating polishing method, when a base plate to which a workpiece is attached is rotated in a liquid as a disk having a plurality of inclined planes in a circumferential direction, a liquid wedge generates a dynamic pressure of the liquid to float the workpiece in a retainer ring from the surface of the disk, and the workpiece is polished by powder particles in a floating gap.

Furthermore, the device for realizing the dynamic pressure floating polishing method comprises a frame, a capacitance ranging module, a dynamic pressure disc floating module, a micro-motion limiting module and a servo micro-feeding module; wherein,

the capacitance distance measurement module is realized by three capacitance sensors embedded on the main grinding disc. The capacitance sensor changes the capacitance of the capacitor by using the change of the displacement, thereby realizing signal conversion.

In the floating module of the movable pressure plate, the output shaft of the motor transmits power to the motor connecting shaft through a common flat key and then sequentially transmits the power to the limiting shaft sleeve, the main shaft connecting sleeve and the main shaft through the guide flat key. Under the specific processing technological condition, the dynamic pressure disc overcomes the gravity and the friction force to generate vertical upward micro displacement under the action of oil film buoyancy, so that springs with certain pretightening force are arranged between the extrusion sliding table and the polishing disc, between the limiting shaft sleeve and the locking nut, the floating energy of the polishing disc and the main shaft is absorbed, and the polishing disc and the main shaft are quickly restored to ideal working positions until dynamic pressure is balanced.

The micro-motion limiting module transmits micro-displacement to the thrust ball bearing and the limiting shaft sleeve through the micro-motion lifter and the limiting plate, so that the limiting shaft sleeve overcomes the matching friction between the limiting shaft sleeve and the motor connecting shaft, vertical downward micro-displacement is generated, the gap between the limiting shaft sleeve and the upper end of the main shaft is reduced, and the micro-motion limiting function is realized.

The servo micro-feeding module drives the shaft coupling through the servo motor to enable the screw rod to rotate, the screw rod nut moves up and down, and therefore the sliding table is driven to move up and down, and micro-feeding is achieved.

Referring to fig. 3, the dynamic pressure floating polishing method mainly includes: the device comprises a frame 1, a capacitance distance measuring device 2, a dynamic pressure disc floating device 3, a micro-motion limiting device 4 and a servo micro-feeding device 5. The capacitance distance measuring device 2 is arranged in the frame, and the micro-motion limiting device 4 is connected with the dynamic pressure floating device 3. The servo micro-feeding device 5 can adjust the distance between the polishing disc and the grinding disc, and the micro-motion limiting device 4 can adjust the floating position of the polishing disc. The capacitance sensing device 2 changes capacitance along with the change of the floating position of the polishing disk, and the purpose of real-time detection is achieved.

Referring to fig. 4, firstly, the micro-elevator 11 is adjusted to move the driving limit plate 10 up and down, so as to sequentially push the thrust ball bearing 16 and the limit shaft sleeve 8 to move up and down, so that the spring generates different pre-tightening forces. And then the motor 6 is started, power is transmitted to the motor connecting shaft 7 in a common flat key and set screw mode, and then the power is transmitted to the limiting shaft sleeve 8, the main shaft connecting sleeve 9 and the main shaft 13 in sequence through the guide flat key, so that the polishing disc 12 is driven to rotate. When the polishing disk 12 and the grinding disk have enough relative speed in the liquid, the dynamic pressure of the liquid is generated, so that the workpiece in the retaining ring is floated off the surface of the grinding disk, and the workpiece is polished by the powder particles in the floating gap. The polishing disk 12 and the main shaft 13 are also impacted by the wedge-shaped liquid to float upwards, so that springs between the sliding table and the polishing disk 12, between the limiting shaft sleeve 8 and between the sliding table and the main shaft 13 and between the sliding table and the polishing disk 15 and between the sliding table and the main shaft 13 and between the sliding table and the polishing disk 12 and between the limiting shaft sleeve 8 and the locking nut 15 are pressed, the springs have certain pretightening force, a resisting effect is generated, the floating energy of the polishing disk 12 and the main shaft 13 is absorbed, the polishing disk 12 and the main shaft are quickly restored.

Claims (2)

1. A dynamic pressure floating polishing method is characterized in that: when the base plate with the adhered workpiece is made into a disc with a plurality of inclined planes along the circumferential direction and rotates in liquid, liquid dynamic pressure is generated through a liquid wedge, so that the workpiece in a retaining ring floats from the surface of the disc, and the workpiece is polished through powder particles in a floating gap.

2. The dynamic pressure floating polishing method according to claim 1, wherein: the device for realizing the dynamic pressure floating polishing method comprises a frame, a capacitance ranging module, a dynamic pressure disc floating module, a micro motion limiting module and a servo micro feed module; wherein,

the capacitive distance measurement module is realized by means of three capacitive sensors embedded on the main grinding disc. The capacitance sensor changes the capacitance of the capacitor by using the change of the displacement, thereby realizing signal conversion;

the floating polishing disk in the movable pressure disk floating module is driven by a rotating shaft arranged on the sliding table, springs with preset pretightening force are arranged at the bottoms of the polishing disk and the sliding table, the polishing disk and the rotating shaft are connected by a spline in clearance fit, and the functions of guiding and transmitting torque are achieved;

the micro-motion limiting module transmits micro-displacement to the thrust ball bearing and the limiting shaft sleeve through the micro-motion lifter and the limiting plate, so that the limiting shaft sleeve overcomes the matching friction between the limiting shaft sleeve and the motor connecting shaft, vertical downward micro-displacement is generated, the gap between the limiting shaft sleeve and the upper end of the main shaft is reduced, and the micro-motion limiting function is realized. The servo micro-feeding module drives the shaft coupling through the servo motor to enable the screw rod to rotate, the screw rod nut moves up and down, and therefore the sliding table is driven to move up and down, and micro-feeding is achieved.

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