Optical mold surface polishing device and method

Abstract

The invention discloses an optical mold surface polishing device and method.The optical mold surface polishing device comprises a mold fixing table used for clamping and driving an optical mold to conduct multi-degree-of-freedom pose adjustment; the polishing assembly is arranged opposite to the mold fixing table and comprises a polishing main shaft used for providing rotation driving force and multi-shaft linkage feeding and a polishing tool arranged at the tail end of the polishing main shaft, and the polishing tool makes contact with the surface of the optical mold during polishing; the electrochemical auxiliary assembly comprises a power supply and a liquid supply part, the positive electrode of the power supply is connected with the optical mold, the negative electrode is connected with the polishing tool to form an electrolysis loop, and the liquid supply part is used for supplying conducting media to the polishing area. The device generates a soft conversion layer on the surface of the hard and brittle material to be polished in real time through electrochemical action, so that a main object for mechanical polishing is changed into a low-hardness softening layer from a high-hardness matrix, and the polishing efficiency is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ultra-precision polishing, in particular to an optical mold surface polishing device and method. BACKGROUND

[0002] Small aperture optical aspheric elements with variable curvature radius have been widely used in high-end fields such as consumer electronics, space optics, precision optoelectronic instruments and defense systems, due to their significant advantages in aberration correction, system miniaturization and imaging quality improvement. With the continuous improvement of the performance requirements of optical systems, such elements are developing towards higher surface accuracy (PV < 0.1 μm) and lower surface roughness (Ra < 3 nm).

[0003] To achieve efficient and consistent batch production of such elements, precision glass molding technology has become the mainstream manufacturing process, the core of which is high-precision optical mold. The precision of the mold is directly copied to the final optical element, so the mold itself must meet the stringent requirements of nanoscale surface quality and sub-micron surface accuracy. Currently, hard and brittle materials (such as tungsten carbide) with high hardness and high wear resistance are widely selected as the substrate of such molds due to their excellent mechanical and thermal stability.

[0004] However, such materials are typical high-hardness, high-brittle difficult-to-machine materials. After ultra-precision grinding, the mold surface still has sub-micron surface error and surface / subsurface damage, which must be corrected by subsequent polishing process. Especially for small aperture (usually less than 20 mm) optical molds with sharp curvature changes, the current general method is to use pure mechanical polishing for polishing treatment, but for high-hardness optical molds, only using pure mechanical polishing will result in low removal efficiency and easy surface damage.

[0005] Therefore, developing a polishing technology that can efficiently remove material, achieve nanoscale ultra-smooth surface, and be suitable for small aperture complex curved mold, has become a key problem that the industry urgently needs to break through. SUMMARY

[0007] In view of the above problems, the present application is proposed in order to provide an optical mold surface polishing device and method which overcomes the above problems or at least partially solves the above problems.

[0008] According to one aspect of the present application, there is provided an optical mold surface polishing device, comprising: a mold fixing table for clamping and driving an optical mold to perform multi-degree-of-freedom pose adjustment; a polishing assembly arranged opposite to the mold fixing table, comprising a polishing spindle for providing rotary driving force and multi-axis linkage feeding, and a polishing tool arranged at the end of the polishing spindle, the polishing tool being in contact with the surface of the optical mold during polishing; and an electrochemical auxiliary assembly comprising a power supply and a liquid supply, the positive electrode of the power supply being connected to the optical mold, and the negative electrode being connected to the polishing tool to form an electrolytic loop, and the liquid supply being used to supply conductive medium to the polishing area.

[0009] Optionally, in the device according to the present application, the polishing tool comprises a conductive rigid base and a flexible porous layer covering the surface of the rigid base, and the flexible porous layer is used to adsorb the conductive medium.

[0010] Optionally, in the device according to the present application, the mold fixing table comprises a workpiece spindle and a workpiece clamp, the workpiece clamp being fixedly connected to the workpiece spindle and used to clamp the optical mold to be polished; and the workpiece spindle is configured to be rotatable about its axis and swingable along the B-axis, and is used to control the spatial pose of the optical mold during polishing.

[0011] Optionally, in the device according to the present application, the liquid supply comprises a liquid storage tank, a liquid supply pump, a liquid supply nozzle and a liquid delivery pipe; the liquid storage tank is used to store the conductive medium; the liquid supply pump is used to pump the conductive medium from the liquid storage tank to the liquid supply nozzle; the liquid supply nozzle is used to direct the conductive medium to the polishing contact area; and the liquid delivery pipe is used to connect the liquid storage tank, the liquid supply pump and the liquid supply nozzle.

[0012] Optionally, in the device according to the present application, the rigid base is a metal ball head, and the flexible porous layer is polyurethane or damping cloth.

[0013] Optionally, in the device according to the present application, the thickness of the flexible porous layer in the unloaded state is 0.2mm to 0.3mm.

[0014] Optionally, in the device according to the present application, the conductive medium comprises abrasive particles, deionized water and electrolyte solution.

[0015] Optionally, in the device according to the present application, the liquid supply pump is a peristaltic pump.

[0016] Optionally, in the device according to the present application, it further comprises a waste liquid collection tray arranged below the mold fixing table.

[0017] According to another aspect of the present application, there is provided a method for polishing the surface of an optical mold, using the polishing device described above, the method comprising: clamping the optical mold to be polished on the mold fixing table; controlling the polishing tool to contact the surface of the optical mold and apply a normal load; supplying the conductive medium between the polishing tool and the optical mold through the liquid supply member, and connecting the power supply to form an electrolytic loop between the surface of the optical mold and the polishing tool, so as to induce an electrochemical oxidation reaction in the contact area of the optical mold to generate a softened layer; and driving the polishing spindle and the mold fixing table to move, so that the polishing tool mechanically grinds and removes the softened layer.

[0018] According to the scheme of the present application, a soft transformed layer is generated on the surface of the hard and brittle material to be polished in real time through electrochemical action, so that the main object of mechanical polishing is changed from the high-hardness substrate to the low-hardness softened layer, thereby greatly improving the polishing efficiency. More importantly, the electrochemical transformation and mechanical removal are dynamically and synchronously performed in the same area, which not only avoids the reaction inhibition caused by the over-thick softened layer, but also maintains the high-speed electrochemical reaction by continuously exposing the fresh surface, so as to realize the synergistic effect of the two processes and improve the comprehensive material removal efficiency.

[0019] The above description is only a summary of the technical scheme of the present application, in order to more clearly understand the technical means of the present application, and to be implemented according to the content of the specification, and in order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0020] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are included to provide a description of the preferred embodiments and are not meant to limit the present application. Furthermore, the same reference numerals are used throughout the several drawings to refer to the same or like parts. In the drawings: Figure 1 FIG. 1 shows a structural schematic diagram of an optical mold surface polishing device 1000 according to an embodiment of the present application; Figure 2 FIG. 3 shows a flowchart of an optical mold surface polishing method 3000 according to an embodiment of the present application. DETAILED DESCRIPTION

[0021] Exemplary embodiments of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the present disclosure are shown. It is to be understood that the present disclosure can be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art.

[0022] For high-hardness molds with small diameters (typically less than 20 mm) and large curvature variations, existing mainstream polishing technologies are mainly divided into two categories: one is advanced energy field-assisted polishing technologies such as airbag polishing and magnetorheological polishing; the other is traditional small-tool mechanical polishing. However, both have limitations: 1. Advanced energy field-assisted polishing technology – limited by physical accessibility and economic factors These technologies (such as airbag polishing and magnetorheological polishing) use a special medium to form a flexible polishing head for processing. However, their polishing heads have a minimum size limit, and when processing small-diameter, deep-curvature, or concave surfaces, physical interference can easily create "processing dead zones," making it impossible to achieve full-surface precision polishing. Another type of high-precision technology (such as ion beam polishing) can achieve atomic-level removal, but it relies on a high-vacuum environment and expensive equipment, resulting in complex processes and lower efficiency, making it difficult to meet the cost and capacity requirements of large-scale manufacturing.

[0023] 2. Traditional small-tool mechanical polishing technology – facing the fundamental contradiction between "efficiency" and "quality". This method uses small polishing tools (usually consisting of a metal ball head covered with polishing cloth) to remove material through the purely mechanical micro-cutting action of abrasive grains. Its limitation does not stem from the equipment, but from the process principle: to ensure the nanoscale surface quality required for optical molds, fine abrasive grains and low loads in the "plastic domain" polishing must be used, but this results in extremely low material removal rates and long processing cycles; if the load is increased or coarse abrasive grains are selected to improve efficiency, brittle fracture is easily triggered, resulting in scratches, pits, and subsurface damage on the surface, which cannot meet the integrity requirements of high-precision molds.

[0024] It is evident that neither of the existing technologies can meet the comprehensive polishing requirements of small-diameter complex curved surface molds for high precision, high efficiency, low damage, and low cost.

[0025] To address the problems existing in the prior art, the present invention provides a solution. This application proposes an optical mold surface polishing device that generates a soft conversion layer in real time on the surface of the hard and brittle material to be polished through electrochemical action. This transforms the primary target of mechanical polishing from a high-hardness substrate to a low-hardness softened layer, thereby significantly improving polishing efficiency. More importantly, the electrochemical conversion and mechanical removal occur simultaneously and dynamically in the same area. This avoids reaction inhibition caused by an excessively thick softened layer and maintains a high-speed electrochemical reaction by continuously exposing a fresh surface, achieving synergistic effects between the two processes and resulting in an order-of-magnitude improvement in overall material removal efficiency.

[0026] Figure 1 A schematic diagram of the structure of an optical mold surface polishing apparatus 1000 according to an embodiment of the present invention is shown.

[0027] like Figure 1As shown, the device 1000 includes a mold fixing platform 1100, a polishing assembly 1200, an electrochemical auxiliary assembly 1300, and a waste liquid collection tray 1400.

[0028] The mold fixing table 1100 includes a workpiece spindle 1110 and a workpiece clamp 1120, wherein the workpiece clamp 1120 is fixedly installed at the output end of the workpiece spindle 1110 and is used to clamp and position the optical mold 2000 to be polished.

[0029] As the core driving component of the mold fixing stage 1100, the workpiece spindle 1110 directly determines the accuracy and stability of the pose control of the optical mold 2000 during the polishing process. The workpiece spindle 1110 has the function of continuous rotation around its axis (usually defined as the C-axis) and a swing degree of freedom (usually defined as the B-axis) to achieve precise adjustment of the spatial posture of the optical mold 2000.

[0030] For example, the workpiece spindle 1110 may be a high-precision air-bearing electric spindle, a hydrostatic spindle, or a direct-drive torque motor spindle.

[0031] The high-precision air-bearing electric spindle uses compressed air to form a uniform air film at the journal, achieving contactless support. This results in advantages such as extremely low friction, high motion accuracy, no wear, and minimal thermal deformation. For example, the model suitable for this device (model 1000) features 360° continuous C-axis rotation (adjustable speed range 0-500 rpm, radial runout less than 0.1 micrometers) and a B-axis oscillation mechanism integrated into the spindle head (oscillation range ±30°, resolution better than 1 arcsecond). Its housing is typically designed with a standard flange interface for easy installation of workpiece fixtures (model 1120).

[0032] The hydrostatic spindle utilizes high-pressure oil film support, exhibiting extremely high rigidity, load-bearing capacity, and smooth motion, making it particularly suitable for applications requiring extremely high motion smoothness and low-speed performance. Suitable hydrostatic spindles can also integrate rotation and oscillation functions, achieving nanometer-level rotational accuracy. Since the hydrostatic system itself requires an oil circuit, special attention must be paid to the sealing design of the oil circuit and the isolation of the electrochemical polishing area when used in this device 1000 to prevent contamination. Conductivity is typically achieved through a specially designed precision conductive ring isolated from the hydrostatic oil circuit.

[0033] Direct-drive torque motor spindles (DD motors) integrate the torque motor directly into the rotating components, eliminating traditional mechanical transmission mechanisms (such as worm gears). They offer advantages such as compact structure, fast response speed, no backlash, and simple maintenance. A typical application is to use a direct-drive motor as the C-axis drive, combined with a high-precision direct-drive oscillating table to form the B-axis. This combination provides extremely high angular accuracy and dynamic response. To achieve conductivity, a high-current-capacity conductive slip ring assembly can be placed between the stator and rotor of the DD motor.

[0034] All three spindle technologies can integrate precise rotation and oscillation functions and necessary conductive interfaces, reliably meeting the dual requirements of the device 1000 of this invention for the workpiece spindle 1110 of "multi-degree-of-freedom posture adjustment" and "stable conductivity". The specific selection can be weighed according to the size, weight, accuracy requirements and cost budget of the workpiece, and this embodiment does not limit it.

[0035] The workpiece fixture 1120 can be configured to achieve stable, precise and electrically conductive clamping by adopting appropriate fixture forms according to the specific shape, size and material of the optical mold 2000.

[0036] For example, the vacuum chuck clamp is suitable for optical molds 2000 with a large, flat bottom surface or precision-ground surfaces. For instance, for a flat-bottomed tungsten carbide aspherical mold, a ceramic or metal vacuum chuck with evenly distributed vacuum orifices can be used. After the mold is placed on the chuck surface, the vacuum pump is activated, using negative pressure to firmly adhere and fix it. The advantage of this method is the absence of mechanical clamping stress and the ease of electrical connection to the positive terminal of a power source via the chuck body or an integrated conductive ring.

[0037] Precision three-jaw chucks or collets are suitable for molds with cylindrical shanks or requiring external circumferential positioning. For example, high-precision spring collets can be used for molds with standard cylindrical shanks. The mold shank is inserted into the collet's inner hole, and tightening the nut causes the collet to contract, thus evenly clamping the mold. The chuck or collet body is typically made of metal and can be directly connected to the spindle as a conductive component.

[0038] Specialized modular tooling can be designed with specialized fixtures for irregularly shaped or particularly fragile molds. For example, for an irregularly shaped micro-mold, a cavity seat (material can be conductive engineering plastic or metal) that complements its bottom surface can be machined. The mold is embedded in the cavity seat for positioning and then secured with a top cover or side locking screws. Conductivity can be achieved by embedding electrode contacts within the cavity seat or by using conductive material throughout.

[0039] These fixtures are all securely mounted on the workpiece spindle 1110, thereby accurately transmitting the multi-degree-of-freedom motion, such as rotation (C-axis) and oscillation (B-axis) provided by the spindle, to the clamped optical mold 2000.

[0040] The polishing assembly 1200 is arranged opposite to the mold fixing table 1100, and includes a polishing spindle 1210 and a polishing tool 1220.

[0041] The polishing spindle 1210 is the core of power and motion execution in the polishing process. It is typically integrated into a high-precision multi-axis motion platform.

[0042] On the one hand, the polishing spindle 1210 can provide rotational driving force. The polishing spindle 1210 body (i.e., electric spindle or pneumatic spindle) provides high-speed, smooth rotation around its own axis (usually defined as the S-axis), with a speed range typically from 0 to several thousand revolutions per minute (RPM) and can be precisely controlled. This is the direct power source for driving the polishing tool 1220 to perform mechanical grinding.

[0043] On the other hand, the polishing spindle 1210 can also provide multi-axis linkage feed force. The polishing spindle 1210 is mounted as a whole on a multi-degree-of-freedom motion mechanism. For example, it can be fixed on the Z-axis slide of a three-axis (X, Y, Z) linear motion platform. Through the linear interpolation motion of the X, Y, and Z axes, combined with the C-axis rotation and B-axis oscillation of the workpiece spindle 1110, the "linkage feed" of the polishing tool 1220 relative to the three-dimensional trajectory of the optical mold 2000 surface can be realized.

[0044] In a specific example, the polishing spindle 1210 can also be fixed to a precision linear module, an air-bearing platform, or a hydraulic servo drive platform. The positioning accuracy and repeatability of these motion platforms are typically required to reach the micrometer (μm) or even sub-micrometer level to ensure the precision of the polishing path and the accuracy of surface shape control.

[0045] The polishing spindle 1210 often uses a high-precision electric spindle because of its fast start-stop, stable speed, and low vibration. The front end of the spindle needs to have a standard tool interface (such as HSK-E, Capto, etc. quick-change interface) and integrate a rotary conductive connector (such as a conductive slip ring) to reliably transmit the negative current of the power supply to the high-speed rotating polishing tool 1220.

[0046] The polishing tool 1220 is a functional component that interacts directly with the surface of the optical mold 2000 and is mounted on the end interface of the polishing spindle 1210. It is a composite structure, typically consisting of an inner rigid substrate 1221 and an outer flexible porous layer 1222. It is often a metal (such as stainless steel) ball head or a mandrel of a specific shape, and its main functions are to provide defined geometric support, transmit the normal pressure applied by the spindle, and act as a cathode conductor in the electrochemical circuit.

[0047] A flexible porous layer 1222 is wrapped around a rigid substrate 1221 and is typically made of polishing cloth (such as a polyurethane pad or damping cloth) or a special fiber fabric. This layer is soft, loosely porous, and its main function is to adsorb and store conductive polishing slurry, and to undergo elastic deformation under pressure to conform to the curved surface of the mold. In some embodiments, the thickness of the flexible porous layer 1222 under no-load conditions is 0.2 mm to 0.3 mm.

[0048] During the polishing process, the flexible porous layer 1222, which adsorbs the slurry, comes into contact with and is moderately compressed on the surface of the optical mold 2000 under pressure. On the one hand, it mechanically rubs the surface of the optical mold 2000 through abrasive particles provided by the conductive medium; on the other hand, the compressed liquid-containing flexible porous layer 1222 forms a low-resistance channel for current to flow from the cathode (rigid substrate 1221) to the anode (optical mold 2000), thereby achieving electrochemical-mechanical coupling at the micro-contact point.

[0049] The polishing assembly 1200 provides precise spatial movement and rotation through a high-precision polishing spindle 1210, and then couples mechanical energy and electrochemical energy onto the surface of the optical mold 2000 through a specially designed polishing tool 1220. It is the key execution module for realizing the efficient and high-precision polishing process of this invention.

[0050] The electrochemical auxiliary component 1300 is a core support system that provides the necessary electrochemical reaction conditions and material delivery for the entire polishing process. By establishing a controllable electrolytic environment and continuously supplying the reaction medium, it enables electrochemical-mechanical coupling polishing.

[0051] The electrochemical auxiliary component 1300 mainly consists of the following two parts working together: The power supply 1310 is the core of energy control for the entire electrochemical polishing process. Its core task is to establish a stable and controllable DC electric field. A DC regulated power supply is typically selected, capable of providing a continuously adjustable DC voltage within a wide range of 0-30V or more, and offering constant voltage or constant current operating modes. Precise and stable voltage control directly determines the rate and uniformity of the oxidation reaction on the mold surface. For example, when processing tungsten carbide molds, a typical set voltage might be between 15-25V.

[0052] The positive terminal of the power supply 1310 is connected to the optical mold 2000 via a wire. Since the optical mold 2000 rotates or oscillates during the polishing process, this connection usually needs to be achieved through a conductive slip ring or brush to ensure that the current can still be transmitted continuously and stably in motion.

[0053] The negative terminal of the power supply 1310 is connected to the rigid base 1221 (such as a metal ball head) of the polishing tool 1220 via a wire.

[0054] When the circuit is connected, and the current flows through the contact area between the polishing tool 1220, which is wetted with a conductive medium, and the optical mold 2000, a precise and controllable electrochemical oxidation reaction is induced on the surface (anode) of the optical mold 2000, generating a softening film that is easy to remove. This is the basis for achieving efficient polishing.

[0055] The liquid supply unit 1320 is responsible for stably and continuously delivering the prepared conductive medium (usually a water-based slurry containing abrasive particles and electrolytes) to the contact area between the polishing tool and the mold.

[0056] Liquid supply unit 1320 includes the following components: The storage tank 1321 is used to store and mix the prepared conductive polishing slurry, and is usually equipped with a stirring device to prevent solid particles from settling.

[0057] The transfer pump 1322, which is the power source for the liquid supply unit 1320, is responsible for pumping the slurry from the storage tank. To precisely control the minute flow rate and avoid slurry contamination of the pump body, a peristaltic pump is a common choice. It delivers liquid by squeezing the tubing with rollers, and the flow rate is precisely adjustable and easy to clean.

[0058] Infusion tubing 1323 consists of pipes that connect various parts, typically using chemically inert tubing (such as silicone tubing).

[0059] The slurry nozzle 1324 is installed near the polishing contact point. Its function is to apply the slurry in a directional and stable manner to the surface of the polishing tool 1220 or to drip it directly into the vicinity of the contact area, so as to ensure that the flexible porous layer 1222 can continuously absorb fresh slurry.

[0060] The liquid supply unit 1320 provides a continuous supply of conductive slurry, ensuring the necessary ionic and liquid environments for the electrochemical reaction. Simultaneously, it continuously delivers abrasive particles, the primary component for mechanical removal, to the processing interface. The flowing liquid helps remove reaction products and frictional heat, maintaining the stability and cleanliness of the processing area.

[0061] In some embodiments, the conductive medium includes abrasive particles, deionized water, and electrolyte solution.

[0062] In a specific example, when tungsten carbide (WC) is used as the optical mold 2000, the conductive medium can be a water-based electrochemical polishing slurry. This slurry serves as a common carrier for both electrochemical reaction and mechanical removal, and its components, by weight percentage (wt%), include: Abrasive particles (0.5 wt%-5.0 wt%): serving as the main component for mechanical removal. Diamond micron powder (single crystal) is preferred due to its significantly higher hardness compared to tungsten oxide layers, enabling highly efficient removal; silicon oxide (SiO2), cerium oxide (CeO2), or aluminum oxide (Al2O3) can also be used. A particle size of 0.1-1.0 μm is preferred to ensure nanoscale surface roughness. It is worth noting that a content below 0.5% results in excessively low removal efficiency, while a content above 5% easily leads to agglomeration, scratching the surface and excessive cost.

[0063] Electrolyte salts (1.0 wt%-15.0 wt%): Used to provide conductive ions in the solution and reduce contact resistance. Neutral or weakly alkaline inorganic salts are selected, such as sodium chloride (NaCl), potassium chloride (KCl), or sodium nitrate (NaNO3).

[0064] It should be noted that too low a concentration will result in insufficient current density and a slow oxidation rate; too high a concentration will easily lead to salt crystallization, clogging of the fabric or corrosion of the equipment. In this example, a concentration of 5.0 wt% - 10.0 wt% is preferred.

[0065] An appropriate amount of pH adjuster (to adjust the pH value to 7.0-10.0) is used to regulate the electrochemical reaction environment. Dilute solutions of sodium hydroxide (NaOH), potassium hydroxide (KOH), or sodium carbonate (Na₂CO₃) can be used. In this example, oxidation can be achieved under neutral conditions (pH=7) by applying an external voltage, or the reaction can be further assisted by adjusting to a weakly alkaline environment (pH 8-9).

[0066] Dispersants and stabilizers (0.1 wt% - 2.0 wt%) are used to prevent abrasive particle agglomeration and precipitation. Common surfactants such as sodium hexametaphosphate (SHMP), polyethylene glycol (PEG), or sodium dodecyl sulfate (SDS) are selected.

[0067] And the remaining deionized water.

[0068] The electrochemical auxiliary component 1300 establishes and controls the electric field driving the chemical reaction through the power supply 1310, and ensures that the reaction interface always has suitable chemical and material conditions through the liquid supply component 1320. Both are indispensable and together provide a fundamental guarantee for the synchronous coupling of "electrochemical softening" and "mechanical removal", which is the key auxiliary system for realizing the efficient and high-quality polishing of this invention.

[0069] The waste liquid collection tray 1400 is located below the mold fixing platform 1100 and the optical mold 2000 it holds. It is used to receive the liquid that drips and splashes during polishing and electrochemical reaction to prevent waste liquid from contaminating the equipment base and working environment, and to facilitate centralized cleaning.

[0070] In a specific example, the implementation process is explained in detail by taking the processing of a 15mm diameter binder-free tungsten carbide (WC) aspherical mold.

[0071] 1. Experimental preparation and apparatus connection Equipment modification: Install a DC regulated power supply 1310 on the existing five-axis small tool polishing machine. Connect the negative terminal of the power supply 1310 to the shank of the stainless steel ball tool, and connect the positive terminal of the power supply 1310 to the tungsten carbide surface through a conductive carbon brush.

[0072] The polishing tool 1220 uses a stainless steel ball head with a radius of 1.5mm, and the surface is covered with a polyurethane polishing cloth with a thickness of 0.25mm.

[0073] Connect the liquid supply unit 1320 to the peristaltic pump and set the flow rate to 5 mL / min.

[0074] 2. Preparation of conductive polishing slurry Base solution: Deionized water.

[0075] Electrolyte: 5 wt% sodium chloride (NaCl) is added as a conductive medium. Compared with strong alkaline solutions, neutral salt solutions do not corrode machine tools.

[0076] Abrasive particles: 2 wt% diamond micro powder with a particle size of 1 μm is added. Adjustment: Stir thoroughly and disperse using ultrasound, and measure the pH of the solution to approximately 7.0 (neutral).

[0077] 3. Electrochemical reaction mechanism (principle explanation) Under energized conditions, the following main oxidation reactions occur on the surface of the tungsten carbide mold (anode): WC + 5H2O → WO3 + CO2 + 10H + +10 e -1 The generated WO3 oxide film has a loose structure and a Mohs hardness of only about 1-2, which is much lower than that of the WC matrix (Mohs hardness of about 9).

[0078] 4. Implementation Steps 1) Tool setting and loading: Control the machine tool to make the polishing tool 1220 contact the apex of the tungsten carbide mold, and set the downward pressure to 20μm. At this time, the cloth in the contact area is compressed, forming an effective conductive path.

[0079] 2) Parameter settings: Turn on the DC power supply and set the voltage to 24V (according to experiments, 24V can induce significant oxidation under neutral conditions).

[0080] Polishing spindle 1210 speed: 180 rpm.

[0081] Workpiece spindle 1110 speed: 150 rpm.

[0082] 3) Processing procedure: First, a peristaltic pump continuously drips slurry into the polishing area.

[0083] Then, under the action of the electric field, a thin oxide layer is instantly generated on the WC surface in the contact area.

[0084] Then, the high-speed rotating polishing cloth carries the diamond particles, quickly removing the softened layer.

[0085] Finally, the machine tool controls the polishing tool 1220 to perform scanning motion along the aspherical trajectory according to the preset dwell time path.

[0086] 4) Cleaning and Inspection: After processing, turn off the power supply 1310 and rinse the surface of the tungsten carbide mold with deionized water. White light interferometer testing showed that the surface roughness of the tungsten carbide mold rapidly decreased from Ra 10 nm after grinding to Ra 2 nm, with no obvious scratches. Compared to pure mechanical polishing without power, the processing time was reduced by more than three times.

[0087] The device 1000 provided by this invention has the following significant advantages compared to the prior art: 1. Significantly improves material removal efficiency: Device 1000 utilizes an electrochemical reaction to transform extremely difficult-to-machine hard metals (with extremely high hardness, such as WC) into a soft oxide film (with a hardness approximately 1 / 10 that of the substrate). Abrasive cutting of the soft oxide layer is far more efficient than direct cutting of the hard substrate.

[0088] The advantage of "simultaneous processing": Compared with the step-by-step method (oxidation followed by polishing), this invention adopts a dynamic mode of "oxidation and removal simultaneously". This avoids the problem of increased resistance and obstruction of subsequent electrochemical reactions (passivation inhibition) caused by an excessively thick oxide layer; at the same time, mechanical removal promptly exposes a highly active fresh surface, maintaining the highest electrochemical reaction rate and achieving a synergistic effect of 1+1>2.

[0089] 2. Significantly improves surface quality, achieving non-destructive polishing: Since the object to be removed is transformed into a soft oxide layer, the required polishing load can be significantly reduced. Under low load, abrasive grains are less likely to cause deep scratches, pits, or subsurface cracks (SSD) in the substrate due to brittle fracture, making it easier to obtain sub-nanometer-scale ultra-smooth surfaces (Ra < 1 nm).

[0090] 3. Precise and controllable local removal function: Utilizing the principle of the "path of least resistance" for electric current, the current is primarily concentrated in the area where the polishing cloth is compressed to its thinnest and most tightly contacted region (i.e., the center of the polishing spot). This means that the oxidation reaction is highly concentrated at the contact point of the polishing head, with almost no reaction occurring in non-contact areas. This characteristic enables this method not only to achieve uniform polishing but also to possess extremely strong surface shaping capabilities (Curing / Figuring), making it suitable for point-to-point correction of surface shape errors in aspherical molds.

[0091] 4. High process adaptability and low cost: This invention breaks through the limitation that hard optical molds typically require a strong alkaline or acidic environment. Under the condition of applying an external electric field (tens of volts of DC current), efficient oxidation can be achieved using a neutral salt solution (such as NaCl or KCl), which not only reduces the corrosion requirements on equipment but is also safer for operators and more environmentally friendly.

[0092] This can be achieved by modifying existing small-tool polishing machines, without the need for expensive and complex vacuum or ion beam equipment.

[0093] Figure 2 A flowchart of an optical mold surface polishing method 3000 according to an embodiment of the present invention is shown. Method 3000 is adapted to use the above-described apparatus 1000.

[0094] like Figure 2 As shown, the purpose of method 3000 is to achieve a method that generates a soft conversion layer on the surface of a hard and brittle material to be polished in real time through electrochemical action, so that the main object of mechanical polishing changes from a high-hardness substrate to a low-hardness softened layer, thereby greatly improving polishing efficiency.

[0095] Method 3000 begins with step 3100, in which the optical mold to be polished is clamped on the mold fixing table.

[0096] Subsequently, in step 3200, the polishing tool 1220 is controlled to contact the surface of the optical mold 2000 and a normal load is applied.

[0097] Subsequently, in step 3300, a conductive medium is supplied between the polishing tool 1200 and the optical mold 2000 through the liquid supply component 1320, and the power supply 1310 is turned on to form an electrolytic circuit between the surface of the optical mold 2000 and the polishing tool 1200, so as to induce an electrochemical oxidation reaction in the contact area of ​​the optical mold 2000 to generate a softening layer.

[0098] Finally, in step 3400, the polishing spindle 1210 and the mold fixing table 1100 are driven to move, so that the polishing tool 1220 mechanically grinds and removes the softened layer.

[0099] It should be noted that the working principle and process of the method 3000 provided in this embodiment are similar to those of the above-mentioned device 1000. For relevant details, please refer to the description of the above-mentioned device 1000. It will not be repeated here.

[0100] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0101] As used herein, unless otherwise specified, the use of ordinal numbers such as “first,” “second,” “third,” etc., to describe ordinary objects merely indicates different instances of similar objects and is not intended to imply that the objects being described must have a given order in time, space, ordering, or any other manner.

[0102] Although the invention has been described with reference to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of interpreting or limiting the subject matter of the invention. Therefore, many modifications and alterations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims.

Claims

1. An optical mold surface polishing apparatus, comprising: a mold fixture for clamping and driving an optical mold to adjust its pose in multiple degrees of freedom; a polishing assembly disposed opposite to the mold fixture, comprising a polishing spindle for providing rotational driving force and multi-axis linkage feed, and a polishing tool disposed at the end of the polishing spindle, the polishing tool being in contact with the surface of the optical mold during polishing; an electrochemical auxiliary assembly comprising a power supply and a liquid supply, the positive electrode of the power supply being connected to the optical mold, and the negative electrode being connected to the polishing tool to form an electrolytic loop, and the liquid supply being used to supply a conductive medium to the polishing area.

2. The apparatus of claim 1, wherein: the polishing tool comprises a conductive rigid substrate and a flexible porous layer covering the surface of the rigid substrate, the flexible porous layer being used to adsorb the conductive medium.

3. The apparatus of claim 1, wherein: the mold fixture comprises a workpiece spindle and a workpiece clamp, the workpiece clamp being fixedly connected to the workpiece spindle and used to clamp the optical mold to be polished; the workpiece spindle is configured to be rotatable about its axis and swingable along the B-axis, for controlling the spatial pose of the optical mold during polishing.

4. The apparatus of claim 1, wherein: the liquid supply comprises a liquid storage tank, a liquid supply pump, a liquid supply nozzle, and a liquid delivery pipe; the liquid storage tank is used to store the conductive medium; the liquid supply pump is used to pump the conductive medium from the liquid storage tank to the liquid supply nozzle; the liquid supply nozzle is used to direct the conductive medium to the polishing contact area; the liquid delivery pipe is used to connect the liquid storage tank, the liquid supply pump, and the liquid supply nozzle.

5. The apparatus of claim 2, wherein, the rigid substrate is a metal ball head, and the flexible porous layer is polyurethane or damping cloth.

6. The apparatus of claim 2 or 5, wherein, the thickness of the flexible porous layer in the unloaded state is 0.2-0.3 mm.

7. The apparatus of claim 1, wherein, the conductive medium comprises abrasive particles, deionized water, and electrolyte solution.

8. The apparatus of claim 4, wherein, the liquid supply pump is a peristaltic pump.

9. The apparatus of claim 1, wherein, a waste liquid collection tray is further disposed below the mold fixture.

10. An optical mold surface polishing method using the polishing apparatus of any one of claims 1-9, the method comprising: clamping the optical mold to be polished on the mold fixture; controlling the polishing tool to contact the surface of the optical mold and apply a normal load; supplying the conductive medium between the polishing tool and the optical mold through the liquid supply, and connecting the power supply, to form an electrolytic loop between the surface of the optical mold and the polishing tool, so as to induce electrochemical oxidation reaction in the contact area of the optical mold to generate a softened layer; driving the polishing spindle and the mold fixture to move, so that the polishing tool mechanically removes the softened layer.

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