Large-size optical mold material for aspheric glass lens molding and preparation method thereof

Abstract

The present invention provides a large-scale optical mold material for molding aspheric glass lenses, a preparation method thereof, and a large-scale optical mold for molding aspheric glass lenses made from the large-scale optical mold material. The large-scale optical mold material is formed by SPS sintering of tungsten carbide and a sintering inhibitor, has a diameter of 100-200 mm and a height of 10-100 mm; the fracture toughness of the large-scale optical mold material is 7.4-7.5 MPa·m 1 / 2 The content of the sintering inhibitor is 0.1 wt.% to 2 wt.%. The large-size optical mold material has high density, high hardness, and a suitable thermal expansion coefficient. It also has good processing performance and excellent surface finish, and has uniform radial hardness. It is suitable for processing large-size optical molds for molding aspheric glass lenses.

Description

Technical Field

[0001] The present invention belongs to the technical field of powder metallurgy, and in particular relates to a large-size optical mold material for molding aspheric glass lenses and a preparation method thereof. Background Art

[0002] Optical glass precision molding technology utilizes high-precision molds and specialized molding equipment to mold optical glass from its transition point to its softening point into the desired optical component in a single operation. This technology offers advantages such as low cost, high efficiency, near-net-shape formation, and environmental friendliness. It is widely used in aspheric optical components, optical diffraction elements, optical array elements, gratings, and more. WC-based cemented carbide, with its excellent properties such as high hardness, high strength, high wear resistance, good corrosion resistance, high surface finish, and excellent electrical machining, is widely used as a mold material in the molding process of aspheric glass lenses.

[0003] Currently, the highest-quality optical mold material in the industry is the M78 product from Japan's NJS manufacturer, which is prepared using spark plasma sintering technology. Its maximum specification is 100mm in diameter and 55mm in height. This size severely limits the material's utilization efficiency and the current mold manufacturers' demand for cost reduction. Therefore, there is an urgent need to improve the large-scale preparation technology of high-quality optical mold materials to promote the rapid development of the aspheric glass lens molding industry. Summary of the Invention

[0004] Technical issues

[0005] In response to the above problems, the present invention proposes a large-size optical mold material for molding aspheric glass lenses and a preparation method thereof. While meeting the requirements of optical mold materials for density, hardness, and smoothness, this product can effectively improve material utilization and reduce production costs.

[0006] Technical Solution

[0007] The present invention provides a method for preparing a large-size optical mold material for molding aspheric glass lenses, and the large-size optical mold material prepared by the method.

[0008] According to a first aspect of the present invention, a large-scale optical mold material for molding aspheric glass lenses is provided. The large-scale optical mold material is formed by SPS sintering a composite powder of tungsten carbide powder and sintering inhibitor powder. The large-scale optical mold material has a diameter of 100-200 mm and a height of 10-100 mm. The large-scale optical mold material has a fracture toughness of 7.4-7.5 MPa·m 1 / 2The content of the sintering inhibitor powder is 0.1 wt.%~2 wt.%, preferably 0.5 wt.%~1.8 wt.%, for example, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, 1.0 wt.%, 1.1 wt.%, 1.2 wt.%, 1.3 wt.%, 1.4 wt.%, 1.5 wt.%, 1.6 wt.%, 1.7 wt.%.

[0009] Preferably, the sintering inhibitor powder is one or more selected from Cr3C2 powder, VC powder, TaC powder and NbC powder.

[0010] Preferably, the thermal expansion coefficient of the large-size optical mold material at 800°C is 4.8~5.1×10 -6 / K, more preferably 4.9~5.0×10 -6 / K.

[0011] Preferably, the density of the large-size optical mold material is 15.45-15.55 g / cm 3 .

[0012] Preferably, the hardness of the large-size optical mold material is 2550~2700 HV30.

[0013] According to a second aspect of the present invention, there is provided a method for preparing a large-sized optical mold material for molding an aspherical glass lens according to the present invention, comprising the following steps:

[0014] Step 1) Mixing and drying raw powders: tungsten carbide powder and sintering inhibitor powder are mixed in a mixing device under an inert atmosphere to obtain a composite powder. The composite powder is dried, sieved, and stored in an inert atmosphere. The total amount of sintering inhibitor powder added is 0.1 wt.% to 2 wt.%, preferably 0.5 wt.% to 1.8 wt.%, relative to the total mass of the composite powder, for example, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, 1.0 wt.%, 1.1 wt.%, 1.2 wt.%, 1.3 wt.%, 1.4 wt.%, 1.5 wt.%, 1.6 wt.%, and 1.7 wt.%.

[0015] Step 2) Mold loading: Place the composite powder into a graphite female mold and pre-press using a hydraulic press at a pressure of 10-20 MPa. After pre-pressing, adjust the height of the upper and lower press heads so that they are at the same height when exposed to the female mold.

[0016] Step 3) Remove the covers on the upper and lower water cooling plates in the spark plasma sintering system so that the graphite pads can directly contact the water cooling plates;

[0017] Step 4) Sintering: Place the assembled graphite mold in a spark plasma sintering system with an initial axial pressure of 5-10 MPa. Evacuate to below 10 Pa and start sintering with electricity. Adjust the heating rate by current to achieve gradient sintering. The maximum sintering temperature is 1600°C-2000°C, the holding time is 20-40 minutes, and the maximum sintering pressure is 40-100 MPa. After the holding period is completed, cut off the current and cool the mold with water through the cooling system until the mold temperature is less than 100°C before removing from the furnace.

[0018] Step 5) Sampling: The sample is taken out using a hydraulic press and the graphite on the sample surface is treated by sandblasting;

[0019] Step 6) Post-processing: The processed large-size optical mold material is subjected to a cryogenic cycle treatment, with the cycle temperature ranging from room temperature to -160°C to -200°C, and the number of cycles is 10 to 20 times.

[0020] Preferably, the raw material powder consists of tungsten carbide powder and sintering inhibitor powder.

[0021] Preferably, the WC powder has a particle size of 0.1 to 1 micron and a purity of 99.9 wt.% to 99.99 wt.%.

[0022] Preferably, the sintering inhibitor powder is one or more selected from Cr3C2 powder, VC powder, TaC powder and NbC powder.

[0023] Preferably, the composite powder does not contain a binder, that is, does not contain any of cobalt, nickel and iron.

[0024] Preferably, the sintering inhibitor powder has an average particle size of 1 to 2 microns and a purity greater than 99%.

[0025] Preferably, the mixing device is a planetary ball mill, a drum wet mill or a tilting wet mill, as well as other commonly used mixing methods in the industry.

[0026] Preferably, the inner wall of the material barrel of the mixing device is made of cemented carbide, the ball-to-material ratio is 3-5:1, the grinding balls are cemented carbide balls, the ball milling speed is 30-200 r / min, and the ball milling time is 12-48 h.

[0027] Preferably, the composite powder is dried, sieved and stored under a nitrogen atmosphere with a nitrogen purity greater than 99.999%.

[0028] Preferably, during the sintering process, a gradient temperature increase method is adopted, from room temperature to 800°C, the heating rate is 30~50°C / min; from temperature greater than 800°C to 1000°C, the heating rate is 25~35°C / min; from temperature greater than 1000°C to 1400°C, the heating rate is 20~30°C / min; and from temperature greater than 1400°C, the heating rate is 5~15°C / min.

[0029] Preferably, during the sintering process, a gradient pressurization method is used for sintering. When the temperature reaches above 800°C, the sintering pressure is increased to 20-25 MPa. When the temperature reaches above 1400°C, the sintering pressure is increased to 40-100 MPa.

[0030] Preferably, after the insulation is completed, the sintering pressure remains unchanged at the maximum pressure.

[0031] Preferably, the cryogenic treatment equipment is a liquid nitrogen cryogenic device.

[0032] Preferably, the cryogenic treatment procedure is a cycle temperature from room temperature to -160°C to -200°C, with a cycle number of 10 to 20 times, without heat preservation, and a heating time and a cooling time of 60 minutes.

[0033] According to a third aspect of the present invention, a large-sized optical mold for molding aspheric glass lenses is provided, which is prepared from the large-sized optical mold material for molding aspheric glass lenses according to the present invention.

[0034] Beneficial effects

[0035] In the present invention, the large-size optical mold material prepared by spark plasma sintering equipment has high density, high hardness and a suitable thermal expansion coefficient, as well as good processing performance and excellent surface finish, and the radial hardness is uniform and consistent. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a graph showing the radial hardness distribution results of the optical mold material with a diameter of 120 mm and a height of 57 mm prepared according to Example 1. DETAILED DESCRIPTION

[0037] The embodiments of the present invention are presented for purposes of illustration and description and are not intended to be exhaustive or to limit the invention to the disclosed forms. Many modifications and variations will be apparent to those skilled in the art. The embodiments are chosen and described in order to better illustrate the principles of the invention and its practical application and to enable those skilled in the art to understand the invention and design various embodiments with various modifications as suited for specific applications.

[0038] First, graphite paper is cut to size according to the graphite die and placed on the inner wall of the die, ensuring it fits snugly. Next, the lower punch is placed into the die, along with two layers of graphite paper of the same diameter as the punch, ensuring it fits snugly. A properly mixed and dried composite powder is then loaded into the die. Finally, two layers of graphite paper and the upper punch are added, followed by a hydraulic press to apply preload and maintain pressure. Once this is complete, the die is wrapped with high-temperature graphite felt. The size of the graphite die and punch is determined by the desired sample size.

[0039] The particle size of WC powder is 0.1 to 1 micron, and the purity is 99.9 to 99.99 wt.%.

[0040] The average particle size of the sintering inhibitor powder is 1 to 2 microns, and the purity is greater than 99%.

[0041] The spark plasma sintering systems used in the following examples are from SINTER LAND, Japan, and include models LABOX-350 and LABOX-6020, as well as continuous production lines. It should be noted that the preparation of cemented carbide blocks using the methods described herein using equipment from other manufacturers and models falls within the scope of this invention. Spark plasma sintering includes pulsed current pressure sintering, electric field-assisted sintering, and pulsed current rapid sintering.

[0042] The density results in the following examples were measured using the Archimedes displacement method;

[0043] The hardness test was obtained using a Vickers hardness tester under a load of 30 kg and holding for 15 s;

[0044] The fracture toughness test complies with the international standard ISO 28079-2009 "Hardmetals-Palmqvist toughnesstest". The total length of the four cracks at the indentation tip is measured and calculated, and the fracture toughness KIC is calculated in combination with the Vickers hardness value of the sample under the indentation.

[0045] Thermal expansion coefficient test method: According to the national standard GB / T 4339-2008 "Determination of characteristic parameters of thermal expansion of metallic materials", the thermal expansion coefficient of the test sample is within the specified range.

[0046] Example 1

[0047] An optical mold material with a size of φ120 mm×57 mm was prepared, wherein the mass ratio of WC to sintering inhibitor in the composite powder was 99:1, and the composition and mass ratio of the sintering inhibitor powder were a mixed powder of Cr3C2:VC=6:4.

[0048] 1. Powder Mixing: 30 kg of the powders weighed according to the above mass ratio were placed in a tilting wet mill and wet-milled under a nitrogen atmosphere. Carbide balls were used as the abrasive, with a ball-to-powder ratio of 3.5:1. The milling speed was 45 rpm, and the milling time was 24 hours. The milled powders were dried and sieved at 100°C and stored under a nitrogen atmosphere.

[0049] 2. Mold filling: Take 10 kg of the dried composite powder and put it into a graphite female mold, and use a hydraulic press to pre-press it with a pre-pressing pressure of 15 MPa.

[0050] 3. Remove the covers on the upper and lower water cooling plates in the spark plasma sintering system so that the graphite pads can directly contact the water cooling plates.

[0051] 4. Sintering: Place the assembled graphite mold in a spark plasma sintering system, set the initial axial pressure to 10 MPa, evacuate to below 10 Pa, and start sintering with power on; during the sintering process, a gradient temperature increase method is used for sintering. When the temperature is from room temperature to 800°C, the heating rate is 40°C / min; when the temperature is greater than 800°C to 1000°C, the heating rate is 30°C / min; when the temperature is greater than 1000°C to 1400°C, the heating rate is 25°C / min; when the temperature is greater than 1400°C, the heating rate is 10°C / min.

[0052] The sintering is carried out by gradient pressure. When the temperature reaches above 800℃, the sintering pressure increases to 25MPa. When the temperature reaches above 1400℃, the sintering pressure increases to 60MPa.

[0053] The highest sintering temperature is 1680℃, and the sintering is completed after holding for 30 minutes. After the holding is completed, the sintering pressure is maintained at 60MPa, and the temperature is cooled down by the water cooling system until it is below 100℃ and taken out.

[0054] 5. Sampling: Use a hydraulic press to take out the sample and use sandblasting to remove the graphite on the sample surface.

[0055] 6. The processed large-size optical mold material is subjected to deep cold cycle treatment, with the cycle temperature ranging from room temperature to -180°C without heat preservation. The cooling time and heating time are both 60 minutes, and the number of cycles is 20 times.

[0056] The optical mold product can be obtained. After finishing, the surface has no white spots and edge collapse defects, the hardness is 2620HV30, there is no hole defect, and the fracture toughness is greater than 7.4 MPa·m 1 / 2 , the thermal expansion coefficient is 4.9×10 -6 / K (800℃), density is 15.48g / cm 3 .

[0057] The optical mold product was cut transversely and the hardness in the radial direction was measured. The results are shown in Figure 1 In. Figure 1 As shown, the radial hardness of the optical mold product is uniform.

[0058] Example 2

[0059] An optical mold material with a size of φ100 mm×40 mm was prepared, wherein the mass ratio of WC to sintering inhibitor in the composite powder was 99:1, and the composition and mass ratio of the sintering inhibitor powder were a mixed powder of Cr3C2:NbC=95:5.

[0060] 1. Powder Mixing: 20 kg of the powders weighed according to the above mass ratio were placed in a tilting wet mill and wet-milled under a nitrogen atmosphere. Carbide balls were used as the abrasive, with a ball-to-powder ratio of 3.5:1. The milling speed was 45 rpm, and the milling time was 24 hours. The milled powders were dried and sieved at 100°C and stored under a nitrogen atmosphere.

[0061] 2. Mold loading: Take 5 kg of the dried composite powder and put it into a graphite female mold, and use a hydraulic press to pre-press it with a pre-pressing pressure of 15 MPa.

[0062] 3. Remove the covers on the upper and lower water cooling plates in the spark plasma sintering system so that the graphite pads can directly contact the water cooling plates.

[0063] 4. Sintering: Place the assembled graphite mold in a spark plasma sintering system, set the initial axial pressure to 10 MPa, evacuate to below 10 Pa, and start sintering with power on; during the sintering process, adopt a gradient temperature increase method, from room temperature to 800 ° C, the heating rate is 40 ° C / min; from greater than 800 ° C to 1000 ° C, the heating rate is 30 ° C / min; from greater than 1000 ° C to 1400 ° C, the heating rate is 25 ° C / min; when the temperature is greater than 1400 ° C, the heating rate is 8 ° C / min.

[0064] The sintering is carried out by gradient pressure. When the temperature reaches above 800℃, the sintering pressure increases to 25MPa. When the temperature reaches above 1400℃, the sintering pressure increases to 50MPa.

[0065] The maximum sintering temperature is 1750°C, and the sintering is completed after holding for 20 minutes. After the holding is completed, the sintering pressure is maintained at 50 MPa, and the sample is cooled down by the water cooling system until it is below 100°C and taken out.

[0066] 4. Sampling: Use a hydraulic press to take out the sample and use sandblasting to remove the graphite on the sample surface.

[0067] 5. The processed large-size optical mold material is subjected to deep cold cycle treatment, with the cycle temperature ranging from room temperature to -180°C without heat preservation. The cooling time and heating time are both 60 minutes, and the number of cycles is 15.

[0068] The optical mold product can be obtained. After finishing, the surface has no defects such as white spots and edge collapse, the hardness is 2625HV30, there is no hole defect, and the fracture toughness is greater than 7.4 MPa·m 1 / 2 , the thermal expansion coefficient is 4.9×10 -6 / K (800℃), density is 15.45g / cm 3 .

[0069] Example 3

[0070] An optical mold material with a size of φ140 mm×21 mm was prepared, wherein the mass ratio of WC to sintering inhibitor in the composite powder was 99.2:0.8, and the sintering inhibitor powder was TaC powder.

[0071] 1. Powder Mixing: 30 kg of the powders weighed according to the above mass ratio were placed in a tilting wet mill and wet-milled under a nitrogen atmosphere. Carbide balls were used as the abrasive, with a ball-to-powder ratio of 3.5:1. The milling speed was 45 rpm, and the milling time was 24 hours. The milled powders were dried and sieved at 100°C and stored under a nitrogen atmosphere.

[0072] 2. Mold filling: Take 5.1 kg of the dried composite powder and put it into a graphite female mold, and use a hydraulic press to pre-press it with a pre-pressing pressure of 20 MPa.

[0073] 3. Remove the covers on the upper and lower water cooling plates in the spark plasma sintering system so that the graphite pads can directly contact the water cooling plates.

[0074] 4. Sintering: Place the assembled graphite mold in the spark plasma sintering system, set the initial axial pressure to 5MPa, evacuate to below 10Pa, and start sintering with power on; during the sintering process, adopt a gradient temperature increase method, from room temperature to 800℃, the heating rate is 30℃ / min; from greater than 800℃ to 1000℃, the heating rate is 25℃ / min; from greater than 1000℃ to 1400℃, the heating rate is 20℃ / min; when the temperature is greater than 1400℃, the heating rate is 5℃ / min.

[0075] The sintering is carried out by gradient pressure. When the temperature reaches 800℃, the sintering pressure increases to 30MPa. When the temperature reaches above 1400℃, the sintering pressure increases to 60MPa.

[0076] The maximum sintering temperature is 1750°C, and the sintering is completed after holding for 35 minutes. After the holding is completed, the sintering pressure is maintained at 60MPa, and the temperature is cooled down by the water cooling system until it is below 100°C and taken out.

[0077] 5. Sampling: Use a hydraulic press to take out the sample and use sandblasting to remove the graphite on the sample surface.

[0078] 6. The processed large-size optical mold material is subjected to deep cold cycle treatment, with the cycle temperature ranging from room temperature to -180°C without heat preservation. The cooling time and heating time are both 60 minutes, and the number of cycles is 20 times.

[0079] The optical mold product can be obtained. After finishing, the surface has no defects such as white spots and edge collapse, the hardness is 2580HV30, there is no hole defect, and the fracture toughness is greater than 7.4 MPa·m 1 / 2 , the thermal expansion coefficient is 4.9×10 -6 / K (800℃), density is 15.53g / cm 3 .

[0080] Example 4

[0081] An optical mold material with a size of φ200 mm×30 mm was prepared, wherein the mass ratio of WC to sintering inhibitor in the composite powder was 99:1, and the sintering inhibitor powder was Cr3C2 powder.

[0082] 1. Powder Mixing: 30 kg of the powders weighed according to the above mass ratio were placed in a tilting wet mill and wet-milled under a nitrogen atmosphere. Carbide balls were used as the abrasive, with a ball-to-powder ratio of 3.5:1. The milling speed was 45 rpm, and the milling time was 24 hours. The milled powders were dried and sieved at 100°C and stored under a nitrogen atmosphere.

[0083] 2. Mold filling: Take 14.7 kg of the dried composite powder and put it into a graphite female mold, and use a hydraulic press to pre-press it with a pre-pressing pressure of 20 MPa.

[0084] 3. Remove the covers on the upper and lower water cooling plates in the spark plasma sintering system so that the graphite pads can directly contact the water cooling plates.

[0085] 4. Sintering: Place the assembled graphite mold in the spark plasma sintering system, set the initial axial pressure to 10MPa, evacuate to below 10Pa, and start sintering with power on; during the sintering process, adopt a gradient temperature increase method, from room temperature to 800℃, the heating rate is 30℃ / min; from greater than 800℃ to 1000℃, the heating rate is 25℃ / min; from greater than 1000℃ to 1400℃, the heating rate is 20℃ / min; the temperature is greater than 1400℃, the heating rate is 5℃ / min.

[0086] The sintering is carried out by gradient pressure. When the temperature reaches 800℃, the sintering pressure increases to 25MPa. When the temperature reaches above 1400℃, the sintering pressure increases to 60MPa.

[0087] The maximum sintering temperature is 1650 ℃, and the sintering is completed after holding for 40 minutes. After the holding is completed, the sintering pressure is maintained at 50 MPa, and the temperature is cooled down by the water cooling system until it is below 100 ℃ and taken out.

[0088] 5. Sampling: Use a hydraulic press to take out the sample and use sandblasting to remove the graphite on the sample surface.

[0089] 6. The processed large-size optical mold material is subjected to deep cold cycle treatment, with the cycle temperature ranging from room temperature to -196°C without heat preservation. The cooling time and heating time are both 60 minutes, and the number of cycles is 20.

[0090] The optical mold product can be obtained. After finishing, the surface has no white spots and edge collapse defects, the hardness is 2560HV30, there is no hole defect, and the fracture toughness is greater than 7.4 MPa·m 1 / 2 , the thermal expansion coefficient is 4.9×10 -6 / K (800℃), density is 15.50g / cm 3 .

[0091] Example 5

[0092] An optical mold material of φ120mm×57mm was prepared, wherein the mass ratio of WC to sintering inhibitor in the composite powder was 98.5:1.5, and the composition and mass ratio of the sintering inhibitor powder were a mixed powder of Cr3C2:VC:TaC:NbC=2:1:1:1.

[0093] 1. Powder Mixing: 30 kg of the powders weighed according to the above mass ratio were placed in a tilting wet mill and wet-milled under a nitrogen atmosphere. Carbide balls were used as the abrasive, with a ball-to-powder ratio of 3.5:1, a speed of 40 rpm, and a milling time of 48 h. The milled powders were dried and sieved at 100°C and stored under a nitrogen atmosphere.

[0094] 2. Mold filling: Take 10 kg of the dried composite powder and put it into a graphite female mold, and use a hydraulic press to pre-press it with a pre-pressing pressure of 15 MPa.

[0095] 3. Remove the covers on the upper and lower water cooling plates in the spark plasma sintering system so that the graphite pads can directly contact the water cooling plates.

[0096] 4. Sintering: Place the assembled graphite mold in a spark plasma sintering system, set the initial axial pressure to 10 MPa, evacuate to below 10 Pa, and start sintering with power on; during the sintering process, adopt a gradient temperature increase method, from room temperature to 800 ° C, the heating rate is 40 ° C / min; from greater than 800 ° C to 1000 ° C, the heating rate is 30 ° C / min; from greater than 1000 ° C to 1400 ° C, the heating rate is 25 ° C / min; the temperature is greater than 1400 ° C, the heating rate is 10 ° C / min.

[0097] The sintering is carried out by gradient pressure. When the temperature reaches above 800℃, the sintering pressure increases to 25MPa. When the temperature reaches above 1400℃, the sintering pressure increases to 60MPa.

[0098] The maximum sintering temperature is 1750°C, and the sintering is completed after holding for 25 minutes. After the holding is completed, the sintering pressure is maintained at 60MPa, and the temperature is cooled down by the water cooling system until it is below 100°C and taken out.

[0099] 5. Sampling: Use a hydraulic press to take out the sample and use sandblasting to remove the graphite on the sample surface.

[0100] 6. The processed large-size optical mold material is subjected to deep cold cycle treatment, with the cycle temperature ranging from room temperature to -196°C without heat preservation. The cooling time and heating time are both 60 minutes, and the number of cycles is 20.

[0101] The optical mold product can be obtained. After finishing, the surface has no defects such as white spots and edge collapse, the hardness is 2580HV30, there is no hole defect, and the fracture toughness is greater than 7.4 MPa·m 1 / 2 , the thermal expansion coefficient is 4.9×10 -6 / K (800℃), density is 15.45g / cm 3 .

[0102] Comparative Example 1

[0103] An optical mold material with a size of φ120 mm×57 mm was prepared, wherein the mass ratio of WC to sintering inhibitor in the composite powder was 99:1, and the composition and mass ratio of the sintering inhibitor powder were a mixed powder of Cr3C2:VC=6:4.

[0104] 1. Powder Mixing: 30 kg of the powders weighed according to the above mass ratio were placed in a tilting wet mill and wet-milled under a nitrogen atmosphere. Carbide balls were used as the abrasive, with a ball-to-powder ratio of 3.5:1. The milling speed was 45 rpm, and the milling time was 24 hours. The milled powders were dried and sieved at 100°C and stored under a nitrogen atmosphere.

[0105] 2. Mold filling: Take 10 kg of the dried composite powder and put it into a graphite female mold, and use a hydraulic press to pre-press it with a pre-pressing pressure of 15 MPa.

[0106] 3. Remove the covers on the upper and lower water cooling plates in the spark plasma sintering system so that the graphite pads can directly contact the water cooling plates.

[0107] 4. Sintering: Place the assembled graphite mold in the spark plasma sintering system, set the initial axial pressure to 10MPa, evacuate to below 10Pa, and start sintering with power on; during the sintering process, adopt a gradient temperature increase method. When the temperature is from room temperature to 800℃, the heating rate is 40℃ / min; when the temperature is greater than 800℃ to 1000℃, the heating rate is 30℃ / min; when the temperature is greater than 1000℃ to 1400℃, the heating rate is 25℃ / min; when the temperature is greater than 1400℃, the heating rate is 10℃ / min.

[0108] The sintering is carried out by gradient pressure. When the temperature reaches above 800℃, the sintering pressure increases to 25MPa. When the temperature reaches above 1400℃, the sintering pressure increases to 60MPa.

[0109] The highest sintering temperature is 1680℃, and the sintering is completed after holding for 30 minutes. After the holding is completed, the sintering pressure is maintained at 60MPa, and the temperature is cooled down by the water cooling system until it is below 100℃ and taken out.

[0110] 5. Sampling: Use a hydraulic press to take out the sample and use sandblasting to remove the graphite on the sample surface.

[0111] 6. The processed products are not cryogenically treated.

[0112] The optical mold product obtained has a hardness of 2620 HV30 and a density of 15.48g / cm 3 However, the indentation is incomplete and has no hole defects. The thermal expansion coefficient is 4.9×10 -6 / K (800℃), but the fracture toughness is less than 7.4 MPa·m 1 / 2 During the finishing process, cracking, edge collapse, corner collapse and particle shedding are likely to occur, which cannot meet the molding technology requirements of aspherical glass lenses.

[0113] Comparative Example 2

[0114] An optical mold material with a size of φ120 mm×57 mm was prepared, wherein the mass ratio of WC to sintering inhibitor in the composite powder was 99:1, and the composition and mass ratio of the sintering inhibitor powder were a mixed powder of Cr3C2:VC=6:4.

[0115] 1. Powder Mixing: 30 kg of the powders weighed according to the above mass ratio were placed in a tilting wet mill and wet-milled under a nitrogen atmosphere. Carbide balls were used as the abrasive, with a ball-to-powder ratio of 3.5:1. The milling speed was 45 rpm, and the milling time was 24 hours. The milled powders were dried and sieved at 100°C and stored under a nitrogen atmosphere.

[0116] 2. Mold filling: Take 10 kg of the dried composite powder and put it into a graphite female mold, and use a hydraulic press to pre-press it with a pre-pressing pressure of 15 MPa.

[0117] 3. Do not remove the covers on the upper and lower water cooling plates in the spark plasma sintering system, so that the graphite pads can be directly placed on the covers.

[0118] 4. Sintering: Place the assembled graphite mold in the spark plasma sintering system, set the initial axial pressure to 10MPa, evacuate to below 10Pa, and start sintering with power on; during the sintering process, adopt a gradient temperature increase method, from room temperature to 800℃, the heating rate is 40℃ / min; from greater than 800℃ to 1000℃, the heating rate is 30℃ / min; from greater than 1000℃ to 1400℃, the heating rate is 25℃ / min, and when the temperature is greater than 1400℃, the heating rate is 10℃ / min.

[0119] The sintering is carried out by gradient pressure. When the temperature reaches above 800℃, the sintering pressure increases to 25MPa. When the temperature reaches above 1400℃, the sintering pressure increases to 60MPa.

[0120] The maximum sintering temperature is 1500°C, and the sintering is completed after holding for 0 minutes. After the holding is completed, the sintering pressure is maintained at 60MPa, and the temperature is cooled down by the water cooling system until it is below 100°C and taken out.

[0121] 5. Sampling: Use a hydraulic press to take out the sample and use sandblasting to remove the graphite on the sample surface.

[0122] 6. The processed large-size optical mold material is subjected to deep cold cycle treatment, with the cycle temperature ranging from room temperature to -180°C without heat preservation. The cooling time and heating time are both 60 minutes, and the number of cycles is 20 times.

[0123] The optical mold product can be obtained, the hardness of the product is lower than 2385HV30 and the density is 15.33g / cm 3 The core grain size is too large, and the hardness is lower than that of the edge, resulting in radial unevenness and cracking during processing. The surface quality requirements of the optical mold are not met.

[0124] It can be seen from the above embodiments and comparative examples that the large-size optical mold material prepared by the spark plasma sintering equipment using this method has high density, high hardness and a suitable thermal expansion coefficient, as well as good processing performance and excellent surface finish, and is radially uniform.

[0125] Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field and related fields without making any creative work should fall within the scope of protection of the present invention.

Claims

1. A large-size optical mold material for molding aspheric glass lenses, characterized in that: The large-size optical mold material is formed by SPS sintering a composite powder of tungsten carbide powder and sintering inhibitor powder. The diameter of the large-size optical mold material is 100-200 mm and the height is 10-100 mm. The fracture toughness of the large-size optical mold material is 7.4-7.5 MPa·m 1 / 2 The content of the sintering inhibitor is 0.1wt.%~2wt.%, and the thermal expansion coefficient of the large-size optical mold material at 800°C is 4.9~5.0×10 -6 / K; the sintering inhibitor powder is one or more selected from Cr3C2 powder, VC powder, TaC powder and NbC powder; The large-size optical mold material for molding the aspherical glass lens is prepared by a method comprising the following steps: Step 1) Mixing and drying raw material powders: tungsten carbide powder and sintering inhibitor powder are mixed in a mixing device under an inert atmosphere to obtain a composite powder, which is then dried, sieved, and stored in an inert atmosphere. Step 2) Mold loading: Place the composite powder into a graphite female mold and pre-press using a hydraulic press at a pressure of 10-20 MPa. After pre-pressing, adjust the height of the upper and lower press heads so that they are at the same height when exposed to the female mold. Step 3) Remove the covers on the upper and lower water cooling plates in the spark plasma sintering system so that the graphite pads can directly contact the water cooling plates; Step 4) Sintering: Place the assembled graphite mold in a spark plasma sintering system with an initial axial pressure of 5-10 MPa, evacuate to below 10 Pa, and start sintering by power on; adjust the heating rate by current to achieve gradient temperature rise sintering, with the maximum sintering temperature being 1600-2000°C, the holding time being 20-40 minutes, and the maximum sintering pressure being 40-100 MPa. After the holding period is completed, cut off the current, cool the mold by water cooling through the cooling system until the mold temperature is less than 100°C, and then take it out of the furnace; during the sintering process, sintering is carried out by gradient temperature rise, from room temperature to 800°C, the heating rate is 30-50°C / min; from temperature greater than 800°C to 1000°C, the heating rate is 25-35°C / min; from temperature greater than 1000°C to 1400°C, the heating rate is 20-30°C / min; and from temperature greater than 1400°C, the heating rate is 5-15°C / min; Step 5) Sampling: The sample is taken out using a hydraulic press and the graphite on the sample surface is treated by sandblasting; Step 6) Post-processing: The processed large-size optical mold material is subjected to deep cold cycle treatment, with the cycle temperature ranging from room temperature to -160℃~-200℃, and the number of cycles is 10~20 times. Among them, the cryogenic treatment procedure is a cycle temperature from room temperature to -160℃~-200℃, the number of cycles is 10~20 times, no insulation, and the cooling and heating time are both 60 minutes.

2. The large-size optical mold material for molding aspherical glass lenses according to claim 1, characterized in that: The density of the large-size optical mold material is 15.45-15.55 g / cm 3 and / or The hardness of the large-size optical mold material is 2550~2700 HV30.

3. A method for preparing a large-size optical mold material for molding aspherical glass lenses according to claim 1 or 2, characterized in that: It includes the following steps: Step 1) Mixing and drying raw powders: tungsten carbide powder and sintering inhibitor powder are mixed in a mixing device under an inert atmosphere to obtain a composite powder. After drying and sieving, the composite powder is stored in an inert atmosphere. The total amount of sintering inhibitor powder added is 0.1 wt.% to 2 wt.% relative to the total mass of the composite powder. Step 2) Mold loading: Place the composite powder into a graphite female mold and pre-press using a hydraulic press at a pressure of 10-20 MPa. After pre-pressing, adjust the height of the upper and lower press heads so that they are at the same height when exposed to the female mold. Step 3) Remove the covers on the upper and lower water cooling plates in the spark plasma sintering system so that the graphite pads can directly contact the water cooling plates; Step 4) Sintering: Place the assembled graphite mold in a spark plasma sintering system with an initial axial pressure of 5-10 MPa, evacuate to below 10 Pa, and start sintering by power on; adjust the heating rate by current to achieve gradient temperature rise sintering, with the maximum sintering temperature being 1600-2000°C, the holding time being 20-40 minutes, and the maximum sintering pressure being 40-100 MPa. After the holding period is completed, cut off the current, cool the mold by water cooling through the cooling system until the mold temperature is less than 100°C, and then take it out of the furnace; during the sintering process, sintering is carried out by gradient temperature rise, from room temperature to 800°C, the heating rate is 30-50°C / min; from temperature greater than 800°C to 1000°C, the heating rate is 25-35°C / min; from temperature greater than 1000°C to 1400°C, the heating rate is 20-30°C / min; and from temperature greater than 1400°C, the heating rate is 5-15°C / min; Step 5) Sampling: The sample is taken out using a hydraulic press and the graphite on the sample surface is treated by sandblasting; Step 6) Post-processing: The processed large-size optical mold material is subjected to deep cold cycle treatment, with the cycle temperature ranging from room temperature to -160℃~-200℃, and the number of cycles is 10~20 times. Among them, the cryogenic treatment procedure is a cycle temperature from room temperature to -160℃~-200℃, the number of cycles is 10~20 times, no insulation, and the cooling and heating time are both 60 minutes.

4. The method for preparing a large-sized optical mold material for molding aspherical glass lenses according to claim 3, wherein: WC powder particle size is 0.1 to 1.0 micron, purity is 99.9 wt.% to 99.99 wt.%; and / or The sintering inhibitor powder is one or more selected from Cr3C2 powder, VC powder, TaC powder and NbC powder; and / or The total addition amount of the sintering inhibitor powder is 0.5wt.%~1.8wt.%.

5. The method for preparing a large-sized optical mold material for molding aspherical glass lenses according to claim 3 or 4, characterized in that: The composite powder does not contain any of cobalt, nickel and iron; and / or The sintering inhibitor powder has an average particle size of 1.0 to 2.0 microns and a purity greater than 99.0%.

6. The method for preparing a large-sized optical mold material for molding aspherical glass lenses according to claim 3 or 4, characterized in that: The mixing device is a planetary ball mill, a drum wet mill or a tiltable wet mill; and / or The inner wall of the material barrel of the mixing device is made of cemented carbide, the ball-to-material ratio is 3-5:1, the grinding balls are cemented carbide balls, the ball milling speed is 30-200 r / min, and the ball milling time is 12-48h; and / or The composite powder is dried, sieved and stored under a nitrogen atmosphere with a nitrogen purity greater than 99.999%.

7. The method for preparing a large-sized optical mold material for molding aspherical glass lenses according to claim 3 or 4, characterized in that: During the sintering process, a gradient pressure is used. When the temperature reaches above 800°C, the sintering pressure is increased to 20-25 MPa. When the temperature reaches above 1400°C, the sintering pressure is increased to 40-100 MPa. And / or After the insulation is completed, the sintering pressure remains unchanged at the maximum pressure.

8. The method for preparing a large-size optical mold material for molding aspherical glass lenses according to claim 3 or 4, characterized in that: The cryogenic treatment equipment is a liquid nitrogen cryogenic device.

9. A large-size optical mold for molding aspheric glass lenses, characterized in that: The optical mold is prepared from the large-size optical mold material for molding aspherical glass lenses according to claim 1 or 2.

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