Additive manufacturing of high precision fugitive ceramic shells

Abstract

The application provides a kind of high-precision easy-to-collapse ceramic shell for additive manufacturing, belonging to investment precision casting technical field, comprising slurry, the slurry includes ceramic matrix powder, photocuring resin, dispersing agent and suspending agent, the matrix powder includes EC95 powder, high-purity alumina powder, bauxite powder, micro-fine silicon nitride powder, the mass percentage of each material in the matrix powder is: EC95 powder is 60-80wt%, high-purity alumina powder is 10-20wt%, bauxite powder is 8-15wt%, micro-fine silicon nitride powder is 2-5wt%, after the slurry is prepared, the shell wet blank is prepared by using photocuring 3D printing equipment, then the ceramic shell is formed by using step oxygen supplement process for debinding and baking. The application can reduce the shell making cycle, improve the shell making efficiency, on the basis of ensuring the high-temperature strength of the ceramic shell, improve the size accuracy of the shell and the collapsibility after pouring.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of investment precision casting, in particular to a high-precision and easily collapsible ceramic mold shell prepared by additive manufacturing. BACKGROUND

[0002] Ceramic mold shell preparation is a key process in investment precision casting, which is a process of obtaining a mold shell with certain strength through dewaxing and baking after repeatedly implementing multiple times of "coating-sand scattering-drying" process on the assembled wax mold module. The performance and quality of the mold shell are one of the important guarantees for obtaining qualified size-precision castings. During dewaxing, the mold shell will be subjected to the pressure of wax volume expansion; during baking and pouring, the parts of the mold shell will be mutually restrained to produce uneven expansion and contraction, resulting in stress in the mold shell; during pouring, the mold shell will be subjected to the impact, pressure and thermal shock of high-temperature metal liquid. After pouring, the mold shell is required to have certain collapsibility and be easy to be stripped. The ceramic mold shell obtained by the traditional multiple coating method has long shell preparation period and low efficiency, and the performance of the mold shell is greatly affected by the environment temperature and humidity. At the same time, the performance of the mold shell is subject to the coating quality, and the mold shell is prone to defects such as material leakage, sand accumulation, layering, cracking, uneven thickness, inconsistent quality, insufficient strength, and poor collapsibility, which further affect the metallurgical quality and size precision of the castings.

[0003] Therefore, how to reduce the shell preparation period and improve the shell preparation efficiency, and improve the size precision of the mold shell and the collapsibility after pouring on the basis of ensuring the high-temperature strength of the ceramic mold shell, is an urgent problem to be solved in the industry.

[0004] Therefore, how to reduce the shell preparation period and improve the shell preparation efficiency, and improve the size precision of the mold shell and the collapsibility after pouring on the basis of ensuring the high-temperature strength of the ceramic mold shell, is an urgent problem to be solved in the industry. SUMMARY

[0005] One of the main purposes of the present application is to overcome at least one of the defects of the prior art, and to provide an additive manufacturing high-precision and easily collapsible ceramic mold shell which can reduce the shell preparation period, improve the shell preparation efficiency, and improve the size precision of the mold shell and the collapsibility after pouring on the basis of ensuring the high-temperature strength of the ceramic mold shell.

[0006] To achieve the above-mentioned application purposes, the present application adopts the following technical solutions:

[0007] According to one aspect of the present application, a high-precision collapsible ceramic shell is provided, which is prepared by additive manufacturing, and comprises a slurry, the slurry comprising a ceramic base powder, a photocuring resin, a dispersant and a suspending agent, the base powder comprising EC95 powder, high-purity alumina powder, bauxite powder and micro-fine silicon nitride powder, the mass percentage of each material in the base powder being 60-80wt% for EC95 powder, 10-20wt% for high-purity alumina powder, 8-15wt% for bauxite powder and 2-5wt% for micro-fine silicon nitride powder, the slurry being prepared by using a photocuring 3D printing device to prepare a shell wet blank, and then using a step oxygen supplementing process to perform debinding and sintering to form a ceramic shell.

[0008] According to one specific embodiment of the present application, the ceramic base powder accounts for 44-70% of the volume of the slurry, the photocuring resin accounts for 28-50% of the volume of the slurry, the dispersant accounts for 1-3% of the volume of the slurry, and the suspending agent accounts for 1-3% of the volume of the slurry.

[0009] According to one specific embodiment of the present application, in the EC95 powder of the base powder, the Al2O3 content is 95±2wt%, and d50=15-20μm; in the high-purity alumina powder, the Al2O3 content is ≥99.9wt%, and d50=3-8μm; in the bauxite powder, the Al2O3 content is ≥80wt%, and d50=20-28μm; and in the micro-fine silicon nitride powder, the Si3N4 content is ≥99.9wt%, and the α phase content is ≥90wt%, and d50=3-8μm.

[0010] According to one specific embodiment of the present application, the dispersant is a mixture of polyvinylpyrrolidone and polyvinyl alcohol, the volume ratio of the polyvinylpyrrolidone to the polyvinyl alcohol being 1:2-3; the polyvinylpyrrolidone is of type K30, and the average molecular weight is 40000±10%; and the polyvinyl alcohol is of type 17-92, i.e. PVA17-92, and the average molecular weight is 80000±10%.

[0011] According to one specific embodiment of the present application, the suspending agent is a mixture of magnesium aluminum silicate and organic bentonite, the mass ratio of the magnesium aluminum silicate to the organic bentonite being 1:1; the magnesium aluminum silicate has a particle size of 325 mesh, and the dry sieve residue is ≤3%; and the organic bentonite has a particle size of 220 mesh, and the dry sieve residue is ≤5%.

[0012] According to one specific embodiment of the present application, the photocuring resin contains a photosensitive resin and a photocuring aid, the photosensitive resin being a mixture of acrylic resins, accounting for 75-85% of the volume percentage of the photocuring resin, and the photocuring aid being a mixture of dipropylene glycol diacrylate and dipropylene glycol diacrylate, accounting for 15-25% of the volume percentage of the photocuring resin.

[0013] According to one specific embodiment of the present application, the preparation of the slurry comprises the following steps:

[0014] Step one, proportionally weigh each material in the ceramic matrix powder, add to the mixer and mix uniformly to obtain the ceramic matrix powder;

[0015] Step two, mix the photosensitive resin and photocuring auxiliary agent in the stirrer with cooling system uniformly, and the stirring time is greater than or equal to 20 minutes;

[0016] Step three, add the uniformly mixed photocuring resin and dispersing agent into the planetary mixer barrel with vacuum function, continuously add the ceramic matrix powder into the barrel, mix for 2-4 hours, then proportionally add the suspending agent, continue to mix the ceramic slurry for at least 4 hours, and then vacuum for 5-10 minutes to obtain the required ceramic slurry;

[0017] Step four, add the slurry into the photocuring 3D printing equipment and print the mold shell according to the model.

[0018] According to one specific embodiment of the present application, the debinding and sintering of the ceramic mold shell is carried out in a gas furnace with oxygen supplement function, first heat the gas furnace to 550℃, then open the oxygen supplement when the temperature is stable, open the furnace door to put the wet blank into the furnace and close the furnace door, maintain the oxygen supplement state and burn for 10-30 minutes, then heat to 1200-1250℃ at a heating rate of 300℃ / h, and then heat preservation for 2-4 hours to obtain the high-precision and easy-to-collapse ceramic mold shell.

[0019] From the above technical solution, the advantages and positive effects of the additive manufacturing high-precision and easy-to-collapse ceramic mold shell of the present application are that:

[0020] The present application can reduce the shell making period and improve the shell making efficiency, and on the basis of ensuring the high temperature strength of the ceramic mold shell, improve the dimensional accuracy of the mold shell and the collapsibility after pouring. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is the implementation flowchart of one specific embodiment of the additive manufacturing high-precision and easy-to-collapse ceramic mold shell of the present application. DETAILED DESCRIPTION

[0022] Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments, however, can be implemented in many different forms and should not be construed as limited to the implementations set forth in this disclosure; rather, these implementations are provided so that this disclosure will be thorough and complete, and will fully convey the inventive concept of example embodiments to those skilled in the art. Like reference numerals refer to like elements throughout the figures, and thus a detailed description of them will not be repeated.

[0023] According to one aspect of the present application, a high-precision collapsible ceramic shell is provided, which is prepared by additive manufacturing, and comprises a slurry, the slurry comprising a ceramic base powder, a photocuring resin, a dispersant and a suspending agent, the base powder comprising EC95 powder, high-purity alumina powder, bauxite powder and micro-fine silicon nitride powder, the mass percentage of each material in the base powder being 60-80wt% for EC95 powder, 10-20wt% for high-purity alumina powder, 8-15wt% for bauxite powder and 2-5wt% for micro-fine silicon nitride powder, the slurry being prepared by using a photocuring 3D printing device to prepare a shell wet blank, and then using a step oxygen supplementing process to perform debinding and sintering to form a ceramic shell.

[0024] According to one specific embodiment of the present application, the ceramic base powder accounts for 44-70% of the volume of the slurry, the photocuring resin accounts for 28-50% of the volume of the slurry, the dispersant accounts for 1-3% of the volume of the slurry, and the suspending agent accounts for 1-3% of the volume of the slurry.

[0025] According to one specific embodiment of the present application, in the EC95 powder of the base powder, the Al2O3 content is 95±2wt%, and d50=15-20μm; in the high-purity alumina powder, the Al2O3 content is ≥99.9wt%, and d50=3-8μm; in the bauxite powder, the Al2O3 content is ≥80wt%, and d50=20-28μm; and in the micro-fine silicon nitride powder, the Si3N4 content is ≥99.9wt%, and the α phase content is ≥90wt%, and d50=3-8μm.

[0026] According to one specific embodiment of the present application, the dispersant is a mixture of polyvinylpyrrolidone and polyvinyl alcohol, the volume ratio of the polyvinylpyrrolidone to the polyvinyl alcohol being 1:2-3; the polyvinylpyrrolidone is of type K30, and the average molecular weight is 40000±10%; and the polyvinyl alcohol is of type 17-92, i.e. PVA17-92, and the average molecular weight is 80000±10%.

[0027] According to one specific embodiment of the present application, the suspending agent is a mixture of magnesium aluminum silicate and organic bentonite, the mass ratio of the magnesium aluminum silicate to the organic bentonite being 1:1; the magnesium aluminum silicate has a particle size of 325 mesh, and the dry sieve residue is ≤3%; and the organic bentonite has a particle size of 220 mesh, and the dry sieve residue is ≤5%.

[0028] According to one specific embodiment of the present application, the photocuring resin contains a photosensitive resin and a photocuring aid, the photosensitive resin being a mixture of acrylic resins, accounting for 75-85% of the volume percentage of the photocuring resin, and the photocuring aid being a mixture of dipropylene glycol diacrylate and dipropylene glycol diacrylate, accounting for 15-25% of the volume percentage of the photocuring resin.

[0029] According to one specific embodiment of the present application, the preparation of the slurry comprises the following steps:

[0030] Step one, proportionally weigh each material in the ceramic matrix powder, add into the mixer and mix uniformly to obtain the ceramic matrix powder;

[0031] Step two, mix the photosensitive resin and photocuring auxiliary agent in the stirrer with cooling system uniformly, and the stirring time is greater than or equal to 20 minutes;

[0032] Step three, add the mixed photosensitive resin and dispersant into the planetary mixer barrel with vacuum function, continuously add the ceramic matrix powder into the barrel, mix for 2-4 hours, then proportionally add the suspending agent, continue to mix the ceramic slurry for at least 4 hours, then vacuum for 5-10 minutes to obtain the required ceramic slurry;

[0033] Step four, add the slurry into the photocuring 3D printing equipment and print the mold shell according to the model.

[0034] According to one specific embodiment of the present application, the debinding and baking of the ceramic mold shell is carried out in the gas furnace with oxygen supplement function, first heat the gas furnace to 550℃, then open the oxygen supplement when the temperature is stable, open the furnace door to put the wet blank into the furnace and close the furnace door, keep the oxygen supplement state and burn for 10-30 minutes, then heat to 1200-1250℃ at the heating rate of 300℃ / h, and keep the temperature for 2-4 hours to obtain the high-precision and easy-to-collapse ceramic mold shell.

[0035] From the above technical solution, the advantages and positive effects of the additive manufacturing high-precision and easy-to-collapse ceramic mold shell of the present application are that:

[0036] The present application can reduce the shell making period and improve the shell making efficiency, on the basis of ensuring the high temperature strength of the ceramic mold shell, improve the size precision of the mold shell and the collapsibility after pouring.

[0037] The beneficial effects also include:

[0038] EC95 powder is selected as the base powder because its high temperature refractoriness is above 1800℃, which can resist the pouring temperature of conventional nickel-based, cobalt-based, iron-based high-temperature alloy and maintain stable crystal phase structure, dimensional stability and high temperature strength. Because the refractoriness of EC95 powder is high, it is difficult to sinter at medium temperature, and other sintering active materials need to be added to reduce the sintering temperature. The addition of active materials is on the premise of not sacrificing the high temperature performance of EC95 powder. Alumina powder and high alumina bauxite powder are selected as active materials because they belong to the same aluminum-based material as EC95, have good compatibility with the matrix, and have similar thermal expansion performance at high temperature, so that cracks will not be generated due to the difference in expansion caused by heating. The high-purity alumina powder has a d50 of 3-8 μm, and the fine powder is beneficial to promote the solid phase sintering of the matrix. The main petrographic phase of high alumina bauxite is γ-alumina, which is more active and beneficial to sintering; the Al2O3 content of high alumina bauxite powder is ≥80wt%, and the rest is SiO2 and trace impurities. High alumina bauxite can also promote the liquid phase sintering of the matrix due to the presence of the above elements. The purpose of adding fine silicon nitride powder is to improve the fluidity of the slurry. Silicon nitride has lubricity and can improve the uniformity of the refractory material, thereby improving the formability of the slurry. At the same time, the thermal expansion coefficient of silicon nitride is much smaller than that of aluminum-based materials. A small amount (2-5wt%) of fine (d50=3-8 μm) petrographic stable (α phase content ≥90wt%) silicon nitride powder is added to evenly cut the matrix into thermal expansion islands, thereby reducing cracks and micro-cracks caused by the structure, thickness, and thermal expansion of the material itself, and improving the overall strength and dimensional stability of the shell. Considering the sedimentation problem of the slurry, aluminum magnesium silicate and organic bentonite are added as suspending agents, which can not only reduce the sedimentation of the slurry, but also promote the sintering of the matrix. At the same time, organic bentonite also plays a positive role in the collapse of the shell.

[0039] Figure 1 is the implementation flowchart of a specific embodiment of the additive manufacturing high-precision easy-to-collapse ceramic shell of the present application. As shown in Figure 1 , a specific embodiment of the present application is described as follows.

[0040] First, according to the casting design paper, the three-dimensional drawing of the ceramic shell of the casting is designed, the reasonable pouring system is calculated through machine learning, and the support and compensation structure is designed to form the whole shell three-dimensional drawing. The EC95 powder, high-purity alumina powder, bauxite powder and silicon nitride mixed material are weighed according to the proportion, and the mass percentage of each refractory material is 70% of EC95 powder, 15wt% of high-purity alumina powder, 12wt% of bauxite powder and 3wt% of silicon nitride. The mixture is mixed uniformly in the mixer to obtain the ceramic matrix powder. The 2L acrylic resin photocuring resin, 0.5L mixture of tripropylene glycol diacrylate and dipropylene glycol diacrylate, and 0.1L dispersant are put into the stirrer with cooling system and stirred for 20min, then the mixed liquid is added into the planetary mixer with vacuum function, and 2.35L ceramic matrix powder is continuously added into the cylinder, mixed for 4h, then 0.05L suspending agent is added, and mixed for another 4h, then vacuumized for 5min, and the required ceramic slurry is prepared. The ceramic slurry is added into the photocuring 3D printing equipment, and the shell wet blank is printed according to the input three-dimensional drawing of the shell. After the shell wet blank is printed, the inner surface is washed with cleaning agent, and then placed in a constant temperature and humidity chamber for air drying. After the shell wet blank is dried, the gas furnace with oxygen supplement function is heated to 550℃, and after the temperature is reached, the oxygen supplement is opened, and after the temperature is stabilized, the furnace door is opened and the shell wet blank is put into the furnace and the furnace door is quickly closed, and the oxygen supplement state is maintained for 10min, then the temperature is raised to 1000℃ at a rate of 300℃ / h, and then the temperature is kept for 3h, and the high-precision easy-to-collapse ceramic shell is obtained. The performance of the ceramic shell is measured according to HB 5352, the baking strength of the shell is 15.14MPa, the high temperature strength at 1500℃ is 17.56MPa, and the permeability of the shell at 1500℃ is 8.62cm 4 / (g•min)。

[0041] Those skilled in the art to which the present application pertains will understand that the specific structures and processes shown in the above detailed description part are only exemplary and not limiting. Moreover, those skilled in the art to which the present application pertains can combine the various technical features shown above in various possible ways to form new technical solutions, or make other modifications, which all belong to the scope of the present application.

Claims

1. A high-precision additively manufactured easily collapsible ceramic shell, characterized in that, The slurry includes ceramic matrix powder, photocurable resin, dispersant, and suspending agent. The matrix powder includes EC95 powder, high-purity alumina powder, high-alumina bauxite powder, and fine silicon nitride powder. The mass percentage of each material in the matrix powder is as follows: EC95 powder 60-80 wt%, high-purity alumina powder 10-20 wt%, high-alumina bauxite powder 8-15 wt%, and fine silicon nitride powder 2-5 wt%. After the slurry is prepared, a wet shell blank is prepared using a photocurable 3D printing device, and then a stepped oxygen supplementation process is used for debinding and calcination to form a ceramic shell. The ceramic matrix powder accounts for 44-70% of the slurry volume, the photocurable resin accounts for 28-50% of the slurry volume, the dispersant accounts for 1-3% of the slurry volume, and the suspending agent accounts for 1-3% of the slurry volume. The EC95 matrix powder contains 95±2wt% Al2O3 and d50=15-20μm; the high-purity alumina powder contains ≥99.9wt% Al2O3 and d50=3-8μm; the high-alumina bauxite powder contains ≥80wt% Al2O3 and d50=20-28μm; the fine silicon nitride powder contains ≥99.9wt% Si3N4, ≥90wt% α-phase content, and d50=3-8μm. The dispersant is a mixture of polyvinylpyrrolidone and polyvinyl alcohol, with a volume ratio of 1:2-3 between the polyvinylpyrrolidone and the polyvinyl alcohol; the polyvinylpyrrolidone is selected as K30, with an average molecular weight of 40,000 ± 10%; the polyvinyl alcohol is selected as 17-92, i.e., PVA17-92, with an average molecular weight of 80,000 ± 10%.

2. The additive manufacturing high-precision easily collapsible ceramic shell according to claim 1, characterized in that: The suspending agent is a mixture of magnesium aluminum silicate and organobentonite, with a mass ratio of magnesium aluminum silicate to organobentonite of 1:1; the magnesium aluminum silicate has a particle size of 325 mesh and a dry sieve residue of ≤3%; the organobentonite has a particle size of 220 mesh and a dry sieve residue of ≤5%.

3. The additive manufacturing high-precision easily collapsible ceramic shell according to claim 1, characterized in that: The photocurable resin contains a photosensitive resin and a photocuring additive. The photosensitive resin is a mixture of acrylic resins, accounting for 75-85% of the volume percentage of the photocurable resin. The photocuring additive is a mixture of tripropylene glycol diacrylate and dipropylene glycol diacrylate, accounting for 15-25% of the volume percentage of the photocurable resin.

4. The additive manufacturing high-precision easily collapsible ceramic shell according to claim 3, characterized in that: The preparation of the slurry includes the following steps: Step 1: Weigh each material in the ceramic matrix powder according to the proportion, add them to the mixer and mix evenly to obtain the ceramic matrix powder; Step 2: Add the photosensitive resin and photocuring additive to a mixer equipped with a cooling system and mix thoroughly for ≥20 minutes. Step 3: Add the uniformly mixed light-curing resin and dispersant to the cylinder of a planetary mixer with vacuum function. Continuously add the ceramic matrix powder to the cylinder and mix for 2-4 hours. Then add the suspending agent in proportion and continue mixing the ceramic slurry for at least 4 hours. Finally, vacuum for 5-10 minutes to obtain the desired ceramic slurry. Step 4: Add the slurry to the photopolymer 3D printing equipment and print the shell according to the model.

5. The additive manufacturing high-precision easily collapsible ceramic shell according to any one of claims 1-4, characterized in that: The degreasing and firing of the ceramic shell is carried out in a gas furnace with oxygen supply function. First, the gas furnace is heated to 550°C. After reaching the temperature, the oxygen supply is turned on. After the furnace temperature stabilizes, the furnace door is opened, the wet blank is put into the furnace, and the furnace door is closed. The furnace is kept in oxygen supply state for 10-30 minutes. Then, the temperature is raised to 1200-1250°C at a heating rate of 300°C / h and held for 2-4 hours to obtain a high-precision, easily collapsible ceramic shell.

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