CN116475508A - A kind of processing method of metal large-diameter thin plate parts - Google Patents

Abstract

The invention discloses a processing method of a metal large-diameter sheet part, which relates to the technical field of grinding and polishing. Then, performing surface shape error control by a chemical mechanical polishing method with surface shape prediction capability to reduce the surface shape error of the thin plate, avoid excessive processing and save resources; furthermore, only a general single-sided lapping polisher is required and the working disk diameter d ₁ Diameter d of sheet ₂ Satisfy d ₂ <d ₁ ≤2d ₂ The large-diameter thin plate part can obtain micron-sized surface shape precision, and the equipment cost is reduced. Finally, the electrochemical mechanical polishing is used for realizing the high-surface-quality processing of the thin plate, and the processing surface quality is greatly improved on the basis of no obvious deterioration of the surface shape precision. The invention solves the problem that the metal large-diameter thin plate is sensitive to force and heat load, and realizes the processing of the metal large-diameter thin plate with high surface shape precision and high surface quality.

Description

A kind of processing method of metal large-diameter thin plate parts

technical field

The invention relates to the technical field of grinding and polishing, in particular to a method for processing metal large-diameter thin plate parts with high surface shape precision and high surface quality.

Background technique

As a common engineering product, sheet metal parts are widely used in the fields of electronic information, aerospace, national defense, energy transportation, and material engineering. Faced with the demand for the service performance of thin plate parts in related fields, it is often necessary to perform precision or ultra-precision machining to achieve the required processing quality. Some precision physical experiments such as detonation wave collision experiment and fly layer impact experiment require metal thin plates to meet the high requirements of diameter Φ100～Φ200mm, thickness 2.2～3mm, flatness PV≤2μm, and surface roughness R _a ≤5nm. However, when machining thin plate parts of different materials, the processing method of the parts and the non-uniformity of material removal on the surface of the parts will affect the processing quality of the parts. In addition, the metal thin plate parts generally have poor rigidity. Due to the influence of various factors such as the internal stress of the blank, the clamping force of the tooling, the cutting force and cutting heat during processing, and the residual stress on the processing surface, the thin plate parts often appear in the form of warping, bending and twisting. The processing deformation is complex and diverse, which seriously affects the processing accuracy of the parts. Therefore, in the field of mechanical manufacturing, it is always a difficult problem to process thin plate parts with high surface accuracy and high surface quality.

At present, the processing of high surface shape precision and high surface quality of metal sheets mainly adopts mechanical processing methods, and its processing route mainly adopts cutting technology, such as turning, ultra-precision fly cutting and other processes. However, due to the weak rigidity of the thin plate structure, the thin plate parts are extremely sensitive to force. After the thin plate parts are processed by the above-mentioned traditional machining methods, the workpiece is prone to deformation such as warping and edge collapse, and it is difficult to ensure the surface shape accuracy. Pure copper sheet is processed by mechanical grinding, grinding and other mechanical processing methods. The grinding tool is easily blocked by chips and abrasive particles, resulting in unstable processing status of the grinding tool, and it is difficult to maintain a constant material removal rate (MRR). Moreover, as the processing time goes on, the clogging degree of the abrasive becomes more and more serious, causing the MRR to gradually decrease, and finally leading to the failure of the abrasive.

Other special compound processing technologies based on chemical, electrochemical and other multi-field effects, such as chemical mechanical polishing, electrochemical polishing, electrochemical polishing, and electrochemical mechanical polishing, can greatly weaken or suppress the negative impact of force during processing due to the synergistic effect of chemistry, electrochemistry, and machinery. However, due to the bottleneck of the process itself, it is difficult to achieve high surface accuracy and high surface quality indicators at the same time. Chemical mechanical polishing, through the chemical reaction on the surface of the workpiece to generate easy-to-remove substances, and then wipe the substances with polishing pads or abrasive grains, can make the surface of pure copper obtain sub-nanometer roughness, but due to the deformation of the polishing pad during the material removal process, it may cause the surface shape error of pure copper sheets to increase. Electrochemical polishing can make pure copper obtain nano-scale roughness, and has the advantage of stress-free processing, but it is easy to increase the surface shape error due to stray current corrosion. Electrochemical polishing has a higher etchant concentration due to the local high points on the processing surface of metal parts, and the removal rate of electrochemical polishing is higher, which realizes the stress-free preferential removal of local high points of the workpiece, and then realizes the smoothing of the processed surface, but the MRR is limited. During static processing of pure copper sheets (the workpiece is stationary relative to the electrode), MRR=0.107μm/h, and during dynamic processing (the workpiece rotates relative to the electrode) MRR=0.618～0.756μm/h. Electrochemical mechanical polishing forms a passivation film on the surface of metal parts through electrochemical reaction to inhibit electrolysis, and then uses the friction of the abrasive tool to erase the high points of the passivation film to avoid direct contact between the surface of the workpiece and the abrasive grains. However, the current high polishing pressure P≥0.8psi may introduce stress when the abrasive grains scratch the thin-walled metal surface, causing an increase in the surface shape error and making it difficult to meet the processing quality requirements.

In summary, the current research on high surface precision and high surface quality machining of metal large-diameter thin plate parts still has the following problems:

1. The metal large-diameter thin plate is sensitive to force due to the structure of the thin plate, and it is easy to induce deformation due to stress introduced into the surface of the thin plate by mechanical processing technology, which increases the surface shape error.

2. The existing special processing technology is difficult to directly meet the processing quality requirements of metal large-diameter thin plates.

Contents of the invention

In view of this, the present invention provides a processing technology for metal large-diameter thin plate parts. Through the compound processing of chemical/electrochemical and mechanical action, the process realizes high-efficiency and low-stress thinning, surface shape error control, and surface quality improvement of large-diameter metal thin plates in three stages. It provides a new technology for high surface precision and high surface quality machining of large diameter thin plates.

For this reason, the invention provides the following technical solutions:

The invention provides a method for processing metal large-diameter thin-plate parts. The method comprises: performing electrochemical grinding on the metal plate to be processed according to the processing parameters of high-potential, low-pressure, and strong electrochemical grinding, so as to obtain a metal large-diameter thin-plate workpiece after thinning and surface shape transformation;

The chemical mechanical grinding method based on pressure and speed regulation controls the surface shape error of the workpiece, and adjusts the distribution of surface material removal in a targeted manner;

Low-pressure high-strength electrochemical-mechanical polishing is performed on the metal large-diameter thin plate after surface shape error control.

Further, electrochemical grinding is performed on the metal plate to be processed according to the processing parameters of high potential, low pressure and strong electrochemical grinding, including:

The hydroxyethylidene diphosphonic acid-based electrolyte is used to form a corrosion-inhibiting film to replace the passivation film to protect the metal surface under the flat-order potential of the limiting current higher than the passivation zone, and coupled with the abrasive friction of the diamond-bonded abrasive pad, electrochemical grinding is carried out under low grinding pressure.

Further, the components of the hydroxyethylidene diphosphonic acid-based electrolyte include: hydroxyethylidene diphosphonic acid with a mass fraction of 5-10 wt%, 0.1-0.5 wt% tolylbenzotriazole, 1-5 wt% ammonium citrate, 3-6 wt% potassium hydroxide and deionized water; the pH of the hydroxyethylidene diphosphonic acid-based electrolyte is 8-9.

Further, the chemical mechanical polishing method based on pressure and speed regulation controls the surface error of the workpiece, including:

Processing the initial surface shape of the workpiece to obtain a centrally symmetrical convex surface or a centrally symmetrical concave surface;

Aiming at the workpiece shape after processing, a large-diameter thin plate surface shape prediction model considering the influence of pressure and velocity distribution on the material removal amount is established;

Determine the chemical mechanical grinding motion parameters, the motion parameters include: eccentricity, workpiece rotation speed and grinding pad revolution speed; when facing the convex surface shape, adjust the eccentricity to e>r ₁ -r ₂ range for chemical mechanical grinding; when facing the concave surface shape, adjust the eccentricity to e<r ₂ range for chemical mechanical grinding, when e is lower than the workpiece radius r ₂ and approaching zero, the edge relative speed of the metal sheet is higher than the center so that the edge material removal is higher than the center material removal; Wherein, e represents Eccentricity, r ₁ represents the radius of the grinding pad, r ₂ represents the radius of the workpiece;

Based on the surface shape prediction model and the motion parameters, the relationship between the predicted surface shape error and the processing time is obtained, and the processing time of the workpiece is determined based on the relationship between the predicted surface shape error and the processing time;

The workpiece is processed according to the motion parameters and the processing time.

Further, the initial surface shape of the workpiece is processed to obtain a centrally symmetrical convex surface or a centrally symmetrical concave surface, including:

If the initial surface shape of the workpiece is a centrally symmetrical convex or concave surface shape, no processing is performed;

If the initial surface shape of the workpiece is a non-centrosymmetric surface shape, the chemical mechanical grinding motion parameters are selected according to the overall unevenness of the surface shape. For workpieces with a convex overall surface shape _, use e>r ₁ -r ₂ for chemical mechanical grinding to convert it into a centrally symmetrical concave surface shape;

Further, a large-diameter thin plate surface shape prediction model considering the influence of pressure and velocity distribution on material removal is established, including:

The material removal amount at any place on the processing surface is obtained by the product of the material removal rate and the processing time T, and the material removal rate is the product of the Preston coefficient k, the pressure P between the workpiece and the grinding tool, and the absolute value of the relative speed V;

Through the pressure distribution of the entire area between the workpiece and the grinding tool, the absolute value of the relative velocity V distribution, the product of the Preston coefficient k and the processing time T, the distribution of material removal in the entire area is obtained;

Calculate the pressure distribution in the whole area between the workpiece and the grinding tool;

Calculate the absolute value of the relative velocity at any point in the contact area between the workpiece and the grinding pad, and obtain the absolute value distribution of the relative velocity in the entire area between the workpiece and the grinding tool;

Assuming that the Preston coefficient k is a constant value, the instantaneous material removal distribution is obtained, and then combined with the actual surface shape results in the calibration test, the Preston coefficient k is calibrated by one-dimensional search and trial method;

After the instantaneous material removal amount distribution of the workpiece is obtained by multiplying the Preston coefficient k, the pressure distribution of the entire area between the workpiece and the grinding tool, and the absolute value distribution of the entire area between the workpiece and the grinding tool, the material removal amount of the entire area within the rotation period of the workpiece is obtained according to the rotation speed of the workpiece;

The predicted surface shape of the workpiece is obtained by subtracting the total area material removal amount from the initial surface shape of the workpiece.

Further, low-pressure electrochemical mechanical polishing is performed on the large-diameter thin metal plate after surface shape error control, including:

Select the electrolyte according to the initial surface roughness. For the processed surface with a roughness R _a >350nm, the thin plate parts are first electrochemically polished with a thiosalicylic acid-based electrolyte at a working pressure P≤0.3psi, and the processing parameters are selected by the variation coefficient method to reduce the workpiece roughness to R _a ≤30nm. , to reduce the roughness R _a ≤ 5nm; for the processed surface with roughness R _a ≤ 350nm, it is directly polished with glycine-phenylacrylic triazole-based electrolyte;

The composition of the thiosalicylic acid-based electrolyte includes: 1-10wt% glycine, 1.1-1.5wt% thiosalicylic acid, 1-5wt% polyethylene glycol, 1-9wt% silica sol, 1-5wt% potassium hydroxide and deionization, and the pH of the thiosalicylic acid-based electrolyte is 8.5;

The components of the glycine-phenylacryltriazole-based electrolyte include: 3.5-4wt% glycine, 1-1.5wt% benzotriazole, 2-2.5wt% potassium hydroxide, 2-3wt% silica sol with a particle size of 50nm and deionized water, and the pH of the glycine-phenylacryltriazole-based electrolyte is 8.5.

Further, under e>r ₁ -r ₂ , the characteristic of the pressure distribution between the workpiece and the grinding tool is that the entire area is linearly distributed along the edge-out direction of the workpiece, and the slope of the pressure distribution function increases as the edge-out distance increases.

Further, the grinding pad is a fixed abrasive pad, and the grinding liquid is an acidic grinding liquid based on persulfate.

Further, the large-diameter thin plate parts have a diameter of Φ50-Φ220 mm, a thickness of 1.5-4 mm, and an aspect ratio of ≥20.

Advantage and positive effect of the present invention:

1. Realize the high surface precision and high surface quality processing of metal large-diameter thin plates, and overcome the problem of sensitivity of planar weak rigid components to force and thermal load.

2. Under the flat-order potential of the limiting current higher than the potential of the passivation zone, electrochemical grinding can thin the workpiece with a higher material removal rate, reduce roughness, and improve processing efficiency.

3. In electrochemical grinding, the edge of the workpiece is at a high potential due to the effect of the sharp point, and the removal rate is higher than other parts. In addition, the negative correlation between the distance between the workpiece and the counter electrode and the material removal rate can make the irregular surface of the workpiece into a centrally symmetrical surface. In addition, if the initial surface shape of the workpiece is center-symmetrical, the surface accuracy of the workpiece will not deteriorate significantly during the thinning process.

4. Reduce the cost of equipment. The chemical mechanical grinding method in the present invention does not require the diameter of the working disc of the grinding and polishing machine to be greater than or equal to 2 times the diameter of the thin plate, and does not need to be equipped with a high-precision grinding machine. It only needs a general single-sided grinding machine to make the large-diameter thin plate parts reach micron-level surface shape accuracy, which greatly reduces equipment costs.

5. Strong guidance in the process of surface shape error control, which is conducive to improving processing efficiency. After inputting the initial surface shape data of the workpiece, the relationship between the surface shape error of the workpiece and the processing time can be obtained within 5 minutes, and the optimal processing time corresponding to the lowest surface shape error can be obtained to avoid over-processing and save resources.

6. In the electrochemical mechanical polishing process, the surface quality is greatly improved on the basis of no obvious deterioration of the surface shape accuracy.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the accompanying drawings that are required in the description of the embodiments or prior art. Obviously, the accompanying drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other accompanying drawings can also be obtained according to these drawings without paying creative labor.

Fig. 1 is the schematic diagram of electrochemical grinding/electrochemical mechanical polishing in the embodiment of the present invention;

Fig. 2 is a diagram of a surface error control strategy based on chemical mechanical polishing for centrosymmetric convex and concave surface shapes in an embodiment of the present invention;

Fig. 3 is the calculation principle diagram of surface shape prediction model in the embodiment of the present invention;

Fig. 4 is the schematic diagram of calculating the pressure distribution between the edge workpiece and the grinding pad in the embodiment of the present invention;

Among them, O ₁ , the center of the grinding pad; O ₂ , the center of the workpiece; C, the coincidence point of the edge of the grinding pad and the surface of the workpiece; A, C, the intersection point of the workpiece edge along the negative direction of the _x1 axis; B, the intersection point of AC and the _y2 axis; D, C, the intersection point of the workpiece edge along the positive direction of _{the x1 axis; w 1 , the} revolution speed of the grinding pad;

Fig. 5 is the calculation flowchart of surface shape prediction model in the embodiment of the present invention;

Fig. 6 is a flow chart of surface error control in an embodiment of the present invention;

Fig. 7 is the flow chart of the method for processing metal large-diameter thin plate parts in the embodiment of the present invention;

Fig. 8 is a schematic diagram of R _a 607.0nm before electrochemical polishing in the embodiment of the present invention;

Fig. 9 is a schematic diagram of R _a 162.4nm after electrochemical polishing for 10 minutes in the embodiment of the present invention;

Fig. 10 is a schematic diagram of the relationship between workpiece flatness and electrochemical grinding processing time in the embodiment of the present invention;

Figure 11 is a schematic diagram of the initial PV49.6μm in the embodiment of the present invention;

Figure 12 is a schematic diagram of PV49.2 μm after 90 minutes of electrochemical polishing in the embodiment of the present invention;

Figure 13 is a schematic diagram of PV48.5 μm after 150 minutes of electrochemical polishing in the embodiment of the present invention;

Fig. 14 is a schematic diagram of the process of changing the radial profile of the workpiece surface with the processing order in the embodiment of the present invention;

Fig. 15 is a schematic diagram of the relationship between the predicted flatness of the first chemical mechanical polishing and the processing time in the embodiment of the present invention (Φ100mm×3mm, r ₁ =110mm, e=70mm, w ₁ =30rpm, _w2 =39rpm);

Fig. 16 is a schematic diagram of PV3 3.9 μm after the first chemical mechanical polishing prediction processing for 180 minutes in the embodiment of the present invention;

Fig. 17 is a schematic diagram of PV30.9 μm after the first chemical mechanical polishing measurement of 180 minutes in the embodiment of the present invention;

Fig. 18 is a schematic diagram of the comparison of the predicted/measured radial profile of the surface of the first chemical mechanical grinding workpiece in the embodiment of the present invention;

Figure 19 is a schematic diagram of the initial PV12.9 μm of the fourth chemical mechanical polishing in the embodiment of the present invention;

Fig. 20 is a schematic diagram of the relationship between predicted flatness and processing time in the embodiment of the present invention (Φ100mm×3mm, r ₁ =110mm, e=70mm, w ₁ =30rpm, w ₂ =39rpm);

Fig. 21 is a schematic diagram of PV8.3 μm after the fourth chemical mechanical polishing prediction processing for 60 minutes in the embodiment of the present invention;

Fig. 22 is a schematic diagram of PV8.5 μm after 60 minutes of the fourth chemical mechanical polishing in the embodiment of the present invention;

Fig. 23 is a schematic diagram of the comparison of the predicted/measured radial profile of the fourth chemical mechanical grinding workpiece surface in the embodiment of the present invention;

Figure 24 is a schematic diagram of the initial PV4.2 μm of the seventh chemical mechanical polishing in the embodiment of the present invention;

Figure 25 is a schematic diagram of the relationship between the predicted flatness of the seventh chemical mechanical polishing and the processing time in the embodiment of the present invention (Φ100mm×3mm, r ₁ =110mm, e=70mm, w ₁ =30rpm, _w2 =39rpm);

Fig. 26 is a schematic diagram of PV 2.1 μm after the seventh chemical mechanical polishing prediction processing for 30 minutes in the embodiment of the present invention;

Fig. 27 is a schematic diagram of PV 2.0 μm after 30 minutes of the 7th chemical mechanical polishing measurement in the embodiment of the present invention;

Fig. 28 is a schematic diagram of the comparison of the predicted/measured radial profile of the surface of the 7th chemical mechanical grinding workpiece in the embodiment of the present invention;

Fig. 29 is a schematic diagram of the profile PV = 2.0 μm before low pressure electrochemical mechanical polishing in the embodiment of the present invention;

Fig. 30 is a schematic diagram of roughness R _a 339.4nm before low pressure electrochemical mechanical polishing in the embodiment of the present invention;

Fig. 31 is a schematic diagram of the profile PV=2.4 μm after low pressure electrochemical mechanical polishing for 1 hour in the embodiment of the present invention;

Fig. 32 is a schematic diagram of roughness R _a 177.8nm after low pressure electrochemical mechanical polishing for 1 hour in the embodiment of the present invention;

Fig. 33 is a schematic diagram of PV = 2.0 μm after 2 hours of low pressure electrochemical mechanical polishing in the embodiment of the present invention;

Fig. 34 is a schematic diagram of the roughness R _a 4.2nm after 2 hours of low pressure electrochemical mechanical polishing in the embodiment of the present invention.

Detailed ways

In order to enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

It should be noted that the terms "first" and "second" in the description and claims of the present invention and the above drawings are used to distinguish similar objects, but not necessarily used to describe a specific sequence or sequence. It is to be understood that the data so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein can be practiced in sequences other than those illustrated or described herein. Furthermore, the terms "comprising" and "having", and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device comprising a series of steps or elements is not necessarily limited to those steps or elements explicitly listed, but may include other steps or elements not expressly listed or inherent to the process, method, product or device.

Aiming at the processing requirements of large-diameter metal thin plates in physical experiments and the problems existing in the existing processing technology, the present invention proposes a processing technology for large-diameter metal thin plates with high surface shape precision and high surface quality. First, the high-potential, low-pressure, and high-strength electrochemical polishing method is used to achieve efficient and low-stress thinning of the metal sheet; then, the chemical mechanical polishing method based on pressure and speed control is used to effectively reduce the surface shape error of the pure copper sheet; finally, the low-pressure, high-pressure electrochemical mechanical polishing method is used to obtain a high-quality metal sheet while ensuring surface shape accuracy.

For ease of understanding, the electrochemical polishing method, the chemical mechanical polishing method and the electrochemical mechanical polishing method are described in detail below.

(1) High-potential, low-voltage, and high-strength electrochemical grinding method, using hydroxyethylidene diphosphonic acid (HEDP)-based electrolyte at a level potential higher than the limiting current of the passivation zone, to generate a corrosion-inhibiting film instead of a passivation film to protect the metal processing surface at a potential higher than the passivation zone, and coupled with the friction of diamond abrasive pads, the roughness of the processed surface can be quickly reduced under low grinding pressure (P=0.27psi), and the residual stress on the surface can be reduced; The removal rate is high, coupled with the negative correlation between the distance between the workpiece and the counter electrode and the material removal rate, the irregular surface shape of the workpiece can be transformed into a centrally symmetrical surface shape.

The composition of the HEDP-based electrolyte is: HEDP with a mass fraction of 5-10wt%, 0.1-0.5wt% methylbenzotriazole, 1-5wt% ammonium citrate, 3-6wt% potassium hydroxide and deionized water; the pH of the HEDP-based electrolyte is 8-9.

(2) The chemical mechanical grinding method based on pressure and speed control is used to control the surface error of large-diameter thin plate parts. The specific steps are: first, select the processing method according to the initial surface shape of the workpiece; face the centrally symmetrical convex or concave surface shape, and directly enter the next step; face the non-centrosymmetric surface shape, first select the chemical mechanical grinding motion parameters according to the overall concave-convex situation of the surface shape.₁-r₂Carry out chemical mechanical grinding to transform it into a centrally symmetrical concave surface shape; for workpieces whose overall surface shape is a concave surface shape, the eccentricity e<r₂Carry out chemical mechanical grinding to transform it into a centrosymmetric concave surface shape; then, according to the post-processing profile of the workpiece, that is, the centrally symmetrical convex profile or the centrally symmetrical concave profile, a large-diameter thin plate surface profile prediction model is established considering the influence of pressure and velocity distribution on the material removal amount, and the chemical mechanical grinding motion parameters are selected to determine the relationship between the predicted profile error of the workpiece and the processing time.

Among them, the eccentricity is e, the radius of the grinding pad is _r1 , and the radius of the workpiece is _r2 ; when facing a convex surface, adjust the eccentricity to the range of e> _r1 - _r2 for chemical mechanical polishing; Carry out chemical mechanical grinding from heart distance to e<r ₂ range. When the eccentricity e is lower than the workpiece radius _r2 and approaches zero, the relative speed of the edge of the pure copper sheet is higher than that of the center, so that the material removal amount at the edge is higher than that at the center. The radial distribution of the material removal amount in the entire area of the workpiece is characterized by a distribution that is approximately parabolic. The center is low and the edge is high, thereby reducing the surface error of the workpiece.

Motion parameters include eccentricity, workpiece rotation speed, and grinding pad revolution speed.

The predicted surface shape is obtained by subtracting the material removal amount in the entire area from the initial surface shape of the workpiece. The calculation of the material removal amount at any point on the machined surface is based on the Preston equation, and is obtained by the product of the MRR and the processing time T, and the MRR is the product of the Preston coefficient k, the pressure P between the workpiece and the abrasive tool, and the absolute value of the relative velocity V.

Under the condition of eccentricity e>r ₁ -r ₂ , the characteristic of the pressure distribution between the workpiece and the grinding tool is that the whole area is linearly distributed along the edge-out direction of the workpiece, and the slope of the pressure distribution function increases with the distance from the edge out.

The grinding pad is a fixed abrasive pad, and the grinding liquid is an acidic grinding liquid based on persulfate.

Large-diameter thin plate parts, the diameter of the part is Φ50~Φ220mm, the thickness is 1.5~4mm, and the ratio of diameter to thickness is ≥20.

The above-mentioned chemical mechanical polishing method has the ability to predict the surface shape, and the pressure and relative velocity absolute value distribution are the decisive factors for the material removal distribution. Therefore, the pressure distribution and relative velocity absolute value distribution of the workpiece should be determined first.

Under the condition of eccentricity e>r ₁ -r ₂ , the present invention calculates the pressure distribution of the circular workpiece when the arc boundary is out of the edge state, as shown in FIG. 4 . The main parameters in Fig. 4 are as follows: O ₁ C=r ₁ , the radius of the grinding pad; O ₂ D=r ₂ , the _radius of the workpiece; O ₂ B=y, the ordinate of the edge-out range on the workpiece _; CD=l, the edge-out distance; AD= _s , the total length of _the beam; Workpiece rotation speed.

Assuming that the junction of any beam AD along the x ₁ direction on the workpiece and the edge is C, the relationship between the edge distance l and the eccentricity e, the radius r ₁ of the polishing pad, and the radius r ₂ of the workpiece is:

The relationship between the total length s of the beam, the radius r ₂ of the workpiece, and the vertical coordinate y of the beam is as follows:

According to the above inference, when the centroids of all protruding beams in the workpiece do not exceed the support edge, there is no shear force and bending moment between the protruding beams without the exposed edge and the protruding beams with the exposed edge, that is, when the polishing pad is not exposed along the diameter of _O2B on the workpiece, there is no shear force and bending moment between any two beams along the _x1 direction on the workpiece. If all the diameters along the O ₂ B are located on the grinding pad, the intersection point (e, r ₂ ) of the workpiece and the diameter of O ₂ B must be located on the grinding pad, and the eccentricity e, the radius r ₁ of the grinding pad, and the radius r ₂ of the workpiece must satisfy:

Let m be the mass of the workpiece, and g be the acceleration of gravity. If the eccentricity e, the radius r ₁ of the polishing pad, and the radius r ₂ of the workpiece satisfy the conditions of formula (3), the pressure distribution function f(x) is calculated based on the linear model.

Through the formula (4), the pressure distribution in the whole area between the workpiece and the grinding tool can be obtained under the eccentricity e>r ₁ -r ₂ . Under the condition of eccentricity e<r ₂ , the pressure distribution between the workpiece and the grinding tool in the whole area is obtained from formula (4) as a uniform distribution. Since the workpiece is completely located on the grinding pad at this time, it conforms to the assumption of an approximate uniform distribution.

Then calculate the absolute value distribution of the relative velocity between the workpiece and the grinding pad. Taking point C in Figure 4 as an example, set the coordinates of point C as (x, y), set the velocity V ₁ at the coincidence point on the polishing pad with point C, and the velocity V ₂ at point C on the workpiece. Then the decomposition velocity of V ₁ along the _x1 axis is:

V _1x = -w ₁ ·y (5)

V ₁ breaks down the velocity along the y ₁ axis as:

V _1y =w ₁ ·x (6)

Similarly, the decomposition velocity of V ₂ along the x ₁ axis is:

V _2x = -w ₂ ·y (7)

_V2 breaks down the velocity along the _y1 axis as:

V _2y =w ₂ ·(xe) (8)

Combining formula (5) to formula (8), the absolute value of relative velocity at point C can be obtained as:

Right now:

By analogy, the absolute value of the relative velocity at any point in the contact area between the workpiece and the polishing pad can be obtained by formula (10), and the absolute value of the relative velocity under the eccentricity e>r ₁ -r ₂ and e<r ₂ is consistent with formula (10). The instantaneous material removal is then calculated. However, the Preston coefficient k has not yet been calibrated. It can be calculated by setting k as a constant value first to check whether the distribution trend of the workpiece material removal is in line with expectations. In the later stage, combined with the actual surface shape results in the calibration test, the instantaneous material removal distribution of the workpiece is obtained through calculation, and the material removal distribution within the rotation cycle of the workpiece can be obtained according to the rotation speed of the workpiece. Afterwards, the predicted surface shape can be obtained by subtracting the material removal amount in the whole area from the initial surface shape of the workpiece, and then the relationship between the predicted surface shape error of the workpiece and the processing time can be obtained, and finally the surface shape error control of the workpiece can be obtained.

The calculation process of the surface shape prediction model is shown in Figure 5. First, the initial surface shape of the workpiece is imported into the surface shape prediction model, and then according to the initial surface shape of the workpiece, motion parameters are selected to adjust the material removal distribution on the surface of the copper plate.

The surface shape error control is based on the surface shape prediction model, and its processing flow is shown in Figure 6. First, measure the surface shape of the workpiece to be processed and import it into the surface shape prediction model, and then select the processing parameters (select the motion parameters, calculate the relationship between the flatness and the processing time, according to the above variation relationship, before the flatness drops to the lowest point, and combine the actual working conditions to select the effective time to reduce the flatness).

(3) Electrochemical mechanical polishing method, select the electrolyte according to the initial surface roughness, for the processed surface with roughness _Ra > 350nm, first use thiosalicylic acid-based electrolyte to perform electrochemical mechanical polishing on the thin plate parts under the working pressure (P≤0.3psi), select the processing parameters by the variation coefficient method, reduce the roughness of the workpiece to _Ra≤30nm , and then use glycine-phenylacrylic triazole-based electrolyte to polish the thin plate under low polishing pressure (P≤0.3psi) Electrochemical mechanical polishing is performed on the parts, and the processing parameters are selected by the coefficient of variation method to reduce the roughness to _Ra ≤ 5nm. For the processed surface with roughness R _a ≤ 350nm, the glycine-phenylacryltriazole-based electrolyte is directly used for polishing.

The thiosalicylic acid-based electrolyte consists of 1-10wt% glycine, 1.1-1.5wt% thiosalicylic acid, 1-5wt% polyethylene glycol, 1-9wt% silica sol, 1-5wt% potassium hydroxide (KOH) and deionized water, and the pH is 8.5.

The glycine-phenylacryltriazole-based electrolyte solution comprises 3.5-4wt% glycine, 1-1.5wt% phenylacryltriazole, 2-2.5wt% KOH, 2-3wt% silica sol with a particle size of 50nm and deionized water, pH=8.5.

In the following, a specific example of processing a large-diameter pure copper thin-plate part will be used to describe in detail the above-mentioned processing method for a large-diameter thin-plate metal part with high surface accuracy and high surface quality. As shown in Figure 7, the processing method includes three stages of electrochemical grinding (thinning and surface shape transformation), surface shape error control and electrochemical mechanical polishing (surface quality improvement).

In the electrochemical grinding stage, the pure copper sheet (Φ100mm×3mm) was processed for 10 minutes according to the high-potential, low-pressure, high-strength electrochemical grinding processing parameters, and the roughness was detected by the Taylor profiler. The surface roughness before and after processing is shown in Figure 8 and Figure 9. After electrochemical grinding, the surface roughness of the copper sheet decreased from R _a 607.0nm to R _a 162.4nm, a decrease of 73.2%.

Then, in order to test the ability of the high-potential, low-voltage, strong electrochemical grinding method to maintain the flatness of the pure copper sheet, the pure copper sheet Φ100mm×3mm was processed for 5 consecutive processing times, each time for 30 minutes.

The results show that after 5 times of high-potential, low-pressure, and high-strength electrochemical polishing, the flatness of the pure copper sheet remains at about PV49.0 μm, without further increase, as shown in Figure 10. After processing, the surface shape of the pure copper sheet still maintains a centrally symmetrical convex surface shape, as shown in Figures 11-13, which is conducive to reducing its surface shape error in the next stage through the chemical mechanical polishing method based on pressure and speed control. The MRR calculated by weighing method is about 1 μm/min, which is in line with expectations. To sum up, high-potential low-pressure high-strength electrochemical polishing can obtain MRR≈1μm/min at 0.27psi, so that the surface roughness of pure copper sheet processing can be about R _a 150nm and avoid the obvious increase of surface error.

Next, surface shape error control was carried out on the pure copper sheet (Φ100mm×3mm). The processing parameters and surface shape error results used in the surface shape error control process are shown in Table 1. The radial profile of the workpiece surface changes with the processing sequence as shown in Figure 14. The results show that the surface error of the workpiece decreases effectively with the processing order, and the radial profile of the workpiece surface tends to be flat.

Table 1

In the first processing, as shown in Figure 13, after thinning, the surface shape of the pure copper sheet presents a centrally symmetrical convex surface shape (PV=48.5 μm). Since the surface shape has no obvious step convexity, the edge distance should be no greater than 20% of the workpiece radius. Therefore, the eccentricity e=70mm, revolution speed w ₁ =30rpm, and rotation speed w ₂ =39rpm are selected to import the surface shape prediction model (radius r ₁ =110mm of the polishing pad). Through calculation, the relationship between the predicted flatness (PV) and processing time is obtained, as shown in Figure 15, the flatness shows a linear downward trend with the passage of processing time. However, the hydrophilic diamond bonded abrasive pad needs to be cleaned and repaired regularly, so the processing time should not be too long, and the processing time t=180min should be selected first. According to prediction, after 180min processing of pure copper sheet, the flatness will be reduced from PV48.5μm to PV33.9μm, and the surface shape of the workpiece is still a centrally symmetrical convex surface shape, as shown in Figure 16.

The pure copper sheet is chemically mechanically ground with e=70mm, w ₁ =30rpm, w ₂ =39rpm, T=180min. After processing, the surface shape of the workpiece is measured by a flatness meter. The measured flatness of the workpiece is PV30.9μm, as shown in Figure 17, and the flatness prediction error rate is lower than 10%. The predicted and measured surface radial profiles are basically similar, as shown in Figure 18.

In the fourth processing, the initial surface shape of the workpiece is PV12.9 μm, as shown in Figure 19. Since the initial surface shape of the workpiece is a centrally symmetrical convex surface shape without obvious steps, the first motion parameters (eccentricity e=70mm, revolution speed w ₁ =30rpm, rotation speed w ₂ =39rpm) are used. Import the motion parameters into the surface shape prediction model, and calculate the relationship between the predicted flatness and processing time. As shown in Figure 20, the flatness first decreases with the processing time, but there will be a hysteresis after 100 minutes, and the flatness increases with the processing time after 140 minutes. Since it is predicted that the flatness of the pure copper sheet will rise after 120 minutes of processing, the processing time should satisfy T≤120 minutes. Select the processing time t=60min, according to the prediction, after 60min processing, the predicted flatness of the pure copper sheet will drop from PV12.9μm to PV8.3μm, and it will still be a centrally symmetrical convex surface, as shown in Figure 21.

After processing the pure copper sheet with e=70mm, w ₁ =30rpm, w ₂ =39rpm, T=60min, the workpiece is measured by the FlatMaster200 flatness meter. The measured flatness of the workpiece is PV8.5μm, as shown in Figure 22, and the flatness prediction error rate is lower than 10%. The predicted and measured surface radial profiles are in good agreement, as shown in Figure 23.

In the seventh processing, as shown in Figure 24. Although the initial flatness of the workpiece is lower than PV5μm, but there are obvious steps within Φ80mm, the eccentricity e=70mm should be used to concentrate the material removal in the area within Φ80mm, and the parameter combination of revolution speed w ₁ =30rpm and rotation speed w ₂ =39rpm should be used to import the surface shape prediction model. Through calculation, the relationship between the predicted flatness (PV) and processing time is obtained. As shown in Figure 25, the flatness first decreases with the processing time, and then increases with the processing time after 30 minutes. Therefore, the processing time t=30min is selected. According to the prediction, after 30 minutes of processing the pure copper sheet, the flatness will decrease from PV4.2μm to PV2.1μm, and it will still be a centrally symmetrical convex surface, as shown in Figure 26.

Carry out chemical mechanical grinding on the pure copper sheet with e=70mm, w ₁ =30rpm, w ₂ =39rpm, T=30min. After processing, measure the surface shape of the workpiece with a flatness meter. The measured flatness of the workpiece is PV2.0μm, as shown in Figure 27. Flatness prediction error rate is less than 10%. The predicted surface radial profile is basically consistent with the measured surface radial profile. In summary, after seven times of chemical mechanical polishing based on pressure and speed control, the flatness of the pure copper sheet was reduced from PV48.5 μm to PV2.0 μm, and the flatness prediction error rate was lower than 10%. The radial profile of the predicted surface was basically consistent with the radial profile of the measured surface, effectively reducing the surface error of the pure copper sheet, as shown in Figure 28.

After surface shape error control, the present invention uses _B2 electrolytic solution to carry out low-pressure high-pressure electrochemical-mechanical polishing to pure copper thin plate, and processing parameter is polishing pressure P=0.27psi, and polishing pad revolution speed is _w1 =40rpm, workpiece autorotation speed _w2 =45rpm, and electrolyte flow rate is 25ml/min. The flatness and roughness of the pure copper sheet before polishing are shown in Figure 29 and Figure 30. The flatness is PV2.0μm, the roughness is R _a 339.4nm, and the roughness measurement range is (0.36mm×0.27mm). In order to improve the surface quality, after electrochemical mechanical polishing of the pure copper sheet for 1 hour, the flatness of the pure copper sheet increased to PV2.4μm, and the roughness decreased to R _a 177.8nm, which was significantly improved compared with before polishing, and the number of surface scratches was significantly reduced, as shown in Figure 31 and Figure 32. This result preliminarily proves that B ₂ electrolyte can improve the surface quality of pure copper sheet under low polishing pressure.

After another 1 hour of electrochemical mechanical polishing, the flatness of the pure copper sheet decreased to PV2μm; the roughness decreased to _Ra 4.2nm, which was significantly improved compared with before polishing, and the surface was uniform, as shown in Figure 33 and Figure 34. In summary, the pure copper thin plate (Φ100mm×3mm) is processed according to the high surface precision and high quality processing plan of the pure copper large diameter thin plate. After thinning, surface shape error control and surface quality improvement, the pure copper thin plate finally reaches the flatness PV ≤ 2μm, and the roughness Ra _≤ 5nm.

In the processing method in the above embodiment, the thin plate is electrochemically polished to achieve high-efficiency and low-stress thinning, then the chemical mechanical grinding with surface shape prediction capability is used to reduce the surface shape error of the thin plate, and finally the high surface quality processing of the thin plate is realized by electrochemical mechanical polishing. Under the flat-order potential of the limiting current higher than the potential of the passivation zone, electrochemical polishing can thin the workpiece with a higher material removal rate, reduce roughness, and improve processing efficiency. By virtue of the edge effect of the workpiece and the negative correlation between the electrode spacing and the material removal rate, the irregular surface shape of the workpiece is transformed into a centrally symmetrical surface shape. In the process of surface shape error control, it is only necessary to provide the initial surface shape data of the workpiece to the surface shape prediction model, and the predicted surface shape _of the workpiece corresponding to the selected processing parameters can be obtained within 5 minutes after inputting. After the initial _surface shape data _of the workpiece is input, _the relationship between the surface shape error of the workpiece and the processing time can be obtained within 5 minutes, and the optimal processing time corresponding to the lowest surface shape error can be obtained to avoid over-processing and save _resources ; Large-diameter thin-plate parts obtain micron-level surface accuracy, reducing equipment costs. In the electrochemical mechanical polishing process, the surface quality can be greatly improved on the basis of no obvious deterioration of the surface shape accuracy. The invention overcomes the problem that the metal large-diameter thin plate is sensitive to force and heat load, and realizes the processing of the metal large-diameter thin plate with high surface shape precision and high surface quality.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. A method for processing metal large-diameter thin plate parts, characterized in that, the method comprises: Perform electrochemical grinding on the metal plate to be processed according to the high-potential, low-pressure, high-strength electrochemical grinding processing parameters to obtain a metal large-diameter thin plate workpiece after thinning and surface shape transformation; The chemical mechanical grinding method based on pressure and speed regulation controls the surface error of the workpiece, and adjusts the distribution of surface material removal in a targeted manner; Low-pressure high-strength electrochemical mechanical polishing is performed on the large-diameter thin metal plate after surface shape error control. 2. A kind of metal large-diameter sheet parts processing method according to claim 1, is characterized in that, carries out electrochemical grinding according to high-potential low-voltage strong electrochemical grinding processing parameters of the metal plate to be processed, comprising: The hydroxyethylidene diphosphonic acid-based electrolyte is used to form a corrosion-inhibiting film to replace the passivation film to protect the metal surface under the flat-order potential of the limiting current higher than the passivation zone, and coupled with the abrasive friction of the diamond-bonded abrasive pad, electrochemical grinding is carried out under low grinding pressure. 3. A method for processing metal large-diameter thin plate parts according to claim 2, wherein the composition of the hydroxyethylidene diphosphonic acid-based electrolyte comprises: hydroxyethylidene diphosphonic acid with a mass fraction of 5-10 wt%, 0.1-0.5 wt% tolylbenzotriazole, 1-5 wt% ammonium citrate, 3-6 wt% potassium hydroxide and deionized water; the pH of the hydroxyethylidene diphosphonic acid-based electrolyte is 8-9. 4. A method for processing metal large-diameter thin plate parts according to claim 1, wherein the method of chemical mechanical grinding based on pressure and speed regulation controls the surface error of the workpiece, including: Processing the initial surface shape of the workpiece to obtain a centrally symmetrical convex surface or a centrally symmetrical concave surface; Aiming at the workpiece shape after processing, a large-diameter thin plate surface shape prediction model considering the influence of pressure and velocity distribution on the material removal amount is established; Determine the chemical mechanical grinding motion parameters, the motion parameters include: eccentricity, workpiece rotation speed and grinding pad revolution speed; when facing the convex surface shape, adjust the eccentricity to e>r ₁ -r ₂ range for chemical mechanical grinding; when facing the concave surface shape, adjust the eccentricity to e<r ₂ range for chemical mechanical grinding, when e is lower than the workpiece radius r ₂ and approaching zero, the edge relative speed of the metal sheet is higher than the center so that the edge material removal is higher than the center material removal; Wherein, e represents Eccentricity, r ₁ represents the radius of the grinding pad, r ₂ represents the radius of the workpiece; Based on the surface shape prediction model and the motion parameters, the relationship between the predicted surface shape error and the processing time is obtained, and the processing time of the workpiece is determined based on the relationship between the predicted surface shape error and the processing time; The workpiece is processed according to the processing time, the motion parameters and the processing time. 5. A method for processing metal large-diameter thin plate parts according to claim 4, wherein the initial surface shape of the workpiece is processed to obtain a centrally symmetrical convex surface or a centrally symmetrical concave surface, including: If the initial surface shape of the workpiece is a centrally symmetrical convex or concave surface shape, no processing is performed; If the initial surface shape of the workpiece is a non-centrosymmetric surface shape, the chemical mechanical grinding motion parameters are selected according to the overall unevenness of the surface shape. For a workpiece with a convex overall surface shape _, use e>r ₁ -r ₂ to perform chemical mechanical grinding to convert it into a centrally symmetrical concave surface shape; 6. A method for processing metal large-diameter thin-plate parts according to claim 1, wherein a large-diameter thin-plate surface shape prediction model considering the influence of pressure and velocity distribution on material removal is established, including: The material removal amount at any place on the processing surface is obtained by the product of the material removal rate and the processing time T, and the material removal rate is the product of the Preston coefficient k, the pressure P between the workpiece and the grinding tool, and the absolute value of the relative speed V; Through the pressure distribution of the entire area between the workpiece and the grinding tool, the absolute value of the relative velocity V distribution, the product of the Preston coefficient k and the processing time T, the distribution of material removal in the entire area is obtained; Calculate the pressure distribution in the whole area between the workpiece and the grinding tool; Calculate the absolute value of the relative velocity at any point in the contact area between the workpiece and the grinding pad, and obtain the absolute value distribution of the relative velocity in the entire area between the workpiece and the grinding tool; Assuming that the Preston coefficient k is a constant value, the instantaneous material removal distribution is obtained, and then combined with the actual surface shape results in the calibration test, the Preston coefficient k is calibrated by one-dimensional search and trial method; After the instantaneous material removal amount distribution of the workpiece is obtained by multiplying the Preston coefficient k, the pressure distribution of the entire area between the workpiece and the grinding tool, and the absolute value distribution of the entire area between the workpiece and the grinding tool, the material removal amount of the entire area within the rotation period of the workpiece is obtained according to the rotation speed of the workpiece; The predicted surface shape of the workpiece is obtained by subtracting the total area material removal amount from the initial surface shape of the workpiece. 7. A method for processing metal large-diameter thin-plate parts according to claim 1, wherein the low-pressure electrochemical-mechanical polishing of the large-diameter metal plate after surface shape error control comprises: Select the electrolyte according to the initial surface roughness. For the processed surface with a roughness R _a >350nm, the thin plate parts are firstly electrochemically polished with a thiosalicylic acid-based electrolyte at a working pressure P≤0.3psi, and the processing parameters are selected using the variation coefficient method to reduce the workpiece roughness to R _a ≤30nm. , to reduce the roughness to Ra _≤ 5nm; for the processed surface with roughness Ra _≤ 350nm, it is directly polished with glycine-phenylacrylic triazole-based electrolyte; The composition of the thiosalicylic acid-based electrolyte includes: 1-10wt% glycine, 1.1-1.5wt% thiosalicylic acid, 1-5wt% polyethylene glycol, 1-9wt% silica sol, 1-5wt% potassium hydroxide and deionized water, and the pH of the thiosalicylic acid-based electrolyte is 8.5; The components of the glycine-phenylacryltriazole-based electrolyte include: 3.5-4 wt% glycine, 1-1.5 wt% benzotriazole, 2-2.5 wt% potassium hydroxide, 2-3 wt% silica sol with a particle size of 50nm and deionized water, and the pH of the glycine-phenylacrylic triazole-based electrolyte is 8.5. 8. A method for processing metal large-diameter thin plate parts according to claim 4, characterized in that: under e> _r1 - _r2 , the pressure distribution between the workpiece and the grinding tool is characterized in that the entire area is linearly distributed along the edge-out direction of the workpiece, and the slope of the pressure distribution function increases with the increase in the edge-out distance. 9. A method for processing metal large-diameter thin plate parts according to claim 4, wherein the grinding pad is a consolidated abrasive pad, and the grinding liquid is an acidic grinding liquid based on persulfate. 10. A method for processing metal large-diameter thin-plate parts according to any one of claims 1-9, characterized in that: the diameter of the large-diameter thin-plate parts is Φ50-Φ220 mm, the thickness is 1.5-4 mm, and the diameter-thickness ratio is ≥ 20.