Method for the preparation of a mold or core by additive manufacturing synchronized with the brushing of a foundry coating

Abstract

The present application relates to a casting mold or core preparation method for additive manufacturing synchronous brush coating of foundry coating, and belongs to the technical field of additive manufacturing. The complex casting mold or core is layered and extrusion formed in the additive manufacturing process, and synchronous brush coating of foundry coating is implemented. According to the complex structure of the casting mold or core, a micro brush head with adjustable coating flow and working angle is used for synchronous brush coating of foundry coating. The synchronous brush coating of foundry coating is implemented on the printed 2-5 layers, until the last printing of the casting mold or core is completed. The present application effectively solves the problem of rough surface of the layered extrusion formed additive manufacturing casting mold or core. After the brush coating of foundry coating, the surface roughness Ra of the casting mold or core is in the range of 10-25 μm. It is a kind of efficient high-surface-precision casting mold or core additive manufacturing technology, and is suitable for small batch, multi-variety, large, medium and small complex structure casting mold or core short process rapid manufacturing.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, and more specifically, to a method for preparing molds or cores by simultaneously applying casting coatings in additive manufacturing, and particularly to a method for printing molds or cores with high surface precision by simultaneously applying casting coatings through layered extrusion molding. Background Technology

[0002] Layered extrusion additive manufacturing technology is a novel rapid prototyping method based on slurry extrusion. Compared with commonly used rapid prototyping technologies such as selective laser sintering and micro-jet bonding, layered extrusion ceramic cores can form three-dimensional ceramic samples at room temperature without laser radiation. It boasts significant advantages such as low equipment cost and environmentally friendly material systems, broadening the application of rapid prototyping technology in the casting field and representing a highly promising method for preparing complex cores. Molds and cores are crucial components of casting and are widely used in the casting of various parts.

[0003] Layered extrusion molding technology can effectively improve the efficiency of mold and core preparation, especially suitable for small-batch, multi-variety, rapid, short-process casting. However, molds and cores directly formed by layered extrusion have the following problems: insufficient surface precision, large interfacial reaction thickness, and limited application temperature range. Furthermore, it is difficult to apply coatings to the complex internal cavities of molds after printing. Even for simple molds and cores, although coating is possible, it reduces manufacturing efficiency and increases time costs. Additionally, since the mold and core are already dry and cured before applying casting coatings, the penetration efficiency of the casting coatings is also weakened.

[0004] Based on this, existing technologies have studied layered extrusion additive manufacturing to address the typical problems of poor surface finish and low forming efficiency in molds and cores. A method of simultaneously applying casting coating to directly form molds and cores with complex structures and high surface finish is disclosed. The coating simultaneously fills the interlayer steps formed during printing and the rough surfaces formed by coarse (core) sand, improving the surface finish of the mold and core cavities to Ra 10-25μm, approaching the surface finish of precision casting. This technology solves the typical problems of interlayer steps and rough surfaces formed by coarse (core) sand during the printing process of layered extrusion additive manufacturing, improves the surface finish of layered extrusion additive manufacturing products, reduces post-processing costs, and increases production efficiency. It can be used for short-process rapid manufacturing of complex structure molds and cores with high surface finish. Summary of the Invention

[0005] In response to the problems existing in the prior art and the development needs of casting technology, this invention provides a method for forming high-precision molds or cores by simultaneous brushing of casting coatings during layered extrusion molding. The purpose is to solve the typical problems of interlayer steps and rough surfaces formed by coarse (core) sand during the printing process of layered extrusion additive manufacturing technology, and to achieve the goal of manufacturing high-precision molds and cores using layered extrusion additive manufacturing technology.

[0006] To achieve the above-mentioned objective, a method for preparing a mold or core with improved surface precision through simultaneous brushing of casting coating during layered extrusion additive manufacturing is provided, comprising the following steps:

[0007] (1) Prepare printing paste and brush coating paste, wherein the particle size of ceramic powder in the printing paste is 10-150 μm and the particle size of ceramic powder in the brush coating paste is less than 10 μm;

[0008] (2) Based on the three-dimensional model data of the mold or core to be printed, set the printing parameters and brushing parameters; first, use the printing paste prepared in step (1) to print at least one layer of the cross-section of the mold or core, and then use the brushing paste prepared in step (1) to brush the surface of the mold or core to be printed, and print at the same time until the printing is completed first, and then the brushing of the surface of the part to be printed is completed.

[0009] (3) Dry the mold obtained in step (2), or dry the core obtained in step (2) and then sinter it to obtain a mold or core with improved surface precision.

[0010] Preferably, in step (2), after printing 2-5 layers of the cross-section of the mold or core, the surface of the mold or core is then brushed.

[0011] Preferably, the coating thickness is 0.1 to 0.2 mm.

[0012] Preferably, in step (2), after the surface of the printed part is coated, the cross section of the last printed part is coated to improve the accuracy of the printed surface.

[0013] Preferably, the ceramic powder in the printing paste and the ceramic powder in the brush coating paste are each independently selected from silicon oxide, aluminum oxide, or yttrium oxide.

[0014] Preferably, the binder in the printing paste and the binder in the brushing paste are each independently selected from silica sol, ethyl silicate, yttrium sol, or polyvinylpyrrolidone.

[0015] Preferably, the mold is a shell.

[0016] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0017] (1) This invention proposes a method for layered extrusion additive manufacturing of high-precision molds and cores for complex structures by simultaneously applying casting coatings. The matrix material of the molds and cores uses silica powder with different particle sizes, which is beneficial for forming molds and cores with high strength and good porosity. The casting coating process is simultaneously applied during the layered extrusion printing process, allowing the molds and cores to be formed in one step, enhancing the penetration and uniformity of the casting coating, improving forming efficiency, and reducing time costs. During the sintering process, the molds and cores are embedded in refractory powder, and a reasonable sintering process curve is designed to effectively prevent deformation and cracking of the molds and cores. Finally, the molds and cores are polished. The surface roughness of the final molds and cores can reach Ra 10-25μm, which is better than the surface precision of molds and cores formed by direct layered extrusion.

[0018] (2) Preferably, in this invention, the printing surface of the part to be printed is coated after the surface of the part to be printed is coated, thereby improving the accuracy of the printing surface. Experimental verification shows that after the coating is applied, the surface roughness of the mold surface is reduced from Ra~70μm to Ra~20μm, indicating that the surface accuracy is greatly improved and the coating has a significant effect. At the same time, since the coating and printing are carried out simultaneously, the time for mold forming and processing is shortened by about 40%, which greatly improves the efficiency of mold forming. Attached Figure Description

[0019] Figure 1 A schematic diagram illustrating the simultaneous brushing of casting coatings to print high-surface-quality molds and cores for layered extrusion additive manufacturing.

[0020] Figure 2 The surface microstructure of the mold formed by simultaneous brushing of casting coating and layered extrusion in Example 1 is shown.

[0021] Figure 3 The surface microstructure of the mold formed by layering and extrusion without simultaneous brushing of casting coating in Comparative Example 1. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0023] Figure 1 A schematic diagram illustrating the simultaneous brushing of casting coatings to print high-surface-quality molds, shells, and cores for layered extrusion additive manufacturing.

[0024] This invention discloses a method for layered extrusion additive manufacturing of simultaneously brush-coated casting coatings for printing high-precision molds, shells, and cores. The forming method includes the following steps:

[0025] Step 1: Raw material preparation, the preparation process includes:

[0026] S1: Select molding (core) sand (silica, alumina, yttrium oxide, etc.) of appropriate particle size and organic binder, mix them evenly in a mass ratio of (80-85):(20-15) to make a slurry. The particle size selected according to the casting requirements is 10-150μm. The binder is a mixture of silica sol, ethyl silicate or yttrium sol, polyvinylpyrrolidone, and deionized water (anhydrous ethanol) in a mass ratio of (9-15):(91-85).

[0027] S2: Add an appropriate amount of defoamer to the well-stirred slurry and stir evenly. The mass of the defoamer is 0.1-0.3% of the total mass of the slurry. The defoamer is a n-butanol solution.

[0028] S3: Mix ceramic powder, binder, defoamer, etc. evenly to make printing paste;

[0029] S4: Select fine powder of molding (core) sand (silicon oxide, aluminum oxide, yttrium oxide, etc.), ethanol, silica sol, polyvinyl butyral (PVB), n-butanol, fatty alcohol polyoxyethylene ether (JFC) etc. according to the surface precision requirements of the casting, and mix them evenly in an appropriate proportion as casting coating.

[0030] Step 2: Printing preparation, the preparation process includes:

[0031] S1: Fill the slurry into the feed cylinder, put in the feed cylinder cap, and tighten the connection port;

[0032] S2: Load the casting coating into the coating hopper and tighten the connection;

[0033] S3: Turn on the drive switch and adjust the drive force so that the slurry and casting coating can be smoothly extruded at the required flow rate;

[0034] S4: Connect to the computer, import the 3D model data of the mold, shell and core to be printed, and set the printing parameters and brushing parameters (including paint flow rate, brushing path and brushing speed, etc.) accordingly.

[0035] S5: Adjust the height and angle of the slurry printing needle and the paint brush head, as well as the starting printing position; the paint brush head and the printing needle are simultaneously controlled by the stepping system;

[0036] Step 3: Printing process, which includes:

[0037] S1: Cleaning. The purpose of this cleaning process is to ensure a pollution-free printing environment.

[0038] S2: Zeroing, the purpose of which is to adjust the device to the starting point of the program, so that the needle can start printing the mold, shell and core from the starting printing position, and the zeroing position of the brush head does not interfere with the needle.

[0039] S3: Printing. At the start of the printing process, the needle squeezes out slurry from the needle opening and deposits it onto the printing platform layer by layer according to the preset path of the program; each layer printed by the printing needle has an interlayer groove on the side (i.e. the surface of the workpiece to be printed).

[0040] S4: Coating. The coating process begins after printing has progressed to a certain extent. At this time, the mold, shell, or core has completed 2-5 layers of printing, or after surface finishing by other methods, the brush head coats the surface according to the preset coating path, filling the grooves formed by coarse sand on the surface and covering it with a fine surface layer composed of fine sand, which significantly improves the surface accuracy.

[0041] The hopper and brush head move synchronously with the printing needle, but do not interfere with each other.

[0042] The brush head is used to coat the surfaces of molds, shells, and cores with grooves, or the surfaces that have been finished and are composed of larger-particle (core) sand.

[0043] S5: Return stroke, which includes needle return stroke and brush head return stroke. The needle return stroke is when the needle returns to the starting printing position after printing each layer. The needle return stroke and the brush head return stroke do not interfere with each other. The brush head return stroke is when the brush head returns to the starting position after completing the coating. The brush head return stroke and the needle return stroke do not interfere with each other.

[0044] S6: Layer-by-layer printing, wherein the needle and brush head repeatedly complete the process of S3-S5 until the mold, shell or core is printed.

[0045] S7: Mold, shell or core treatment, clean the burrs on the surface of the mold, shell or core with a brush;

[0046] Step 4: Sintering process, the sintering process includes:

[0047] S1: After letting the shell or core obtained in step 3 stand for a period of time, put it in an oven and dry it at 50°C. Take it out after the billet is dry; the mold does not need to be sintered.

[0048] S2: The dried blank obtained in S1 is embedded in refractory material and placed in a sintering furnace. A suitable sintering curve is selected for sintering. After sintering is completed and cooled to room temperature, the shell or core is removed.

[0049] In some embodiments, the mass ratio of molding (core) sand (silicon oxide, alumina, yttrium oxide, etc.) to binder used in preparing the slurry is (80-85):(20-15), and the selected molding material has a particle size of 10-150 μm as required.

[0050] In some embodiments, molding (core) sand, ethanol, binder (silica sol, ethyl silicate or yttrium sol, etc.), polyvinyl butyral (PVB), n-butanol, fatty alcohol polyoxyethylene ether (JFC) and other components are mixed in a certain proportion.

[0051] In some embodiments, the defoamer is a n-butanol solution, and the added mass of the defoamer is 0.1-0.3% of the slurry mass.

[0052] In some embodiments, the casting paint hopper is placed above the brush head, with a pipe and switch in the middle, allowing for real-time control of the flow rate and volume of paint entering the brush head.

[0053] In some embodiments, a casting coating is applied to the printed mold, shell, or core blank so that the casting coating evenly covers the surface of the mold, shell, and core, and the thickness of the casting coating is 0.1 to 0.2 mm.

[0054] In this invention, the brushing parameters are paint flow rate, brushing path, and brushing speed.

[0055] In this invention, the printing parameters are printing speed, extrusion speed, and layer thickness.

[0056] The surface roughness inspection of this invention is carried out using any flat surface coated with casting paint.

[0057] Example 1

[0058] A layered extrusion additive manufacturing method for simultaneously brushing casting coatings to form complex structures with high surface precision molds, shells, and cores, the forming method comprising the following steps:

[0059] Step 1: Select 82g each of 300-mesh and 1000-mesh silica powder, 36g of binder, and 0.4g of n-butanol defoamer, and mix thoroughly to form a slurry. The binder is a mixture of polyvinylpyrrolidone and anhydrous ethanol in a mass ratio of 10:90. Select 100g of zirconium oxide powder, 100g of ethanol, 25g of silica sol, 4g of polyvinyl butyral (PVB), 0.2g of n-butanol, and 0.5g of fatty alcohol polyoxyethylene ether (JFC) and mix thoroughly to form a casting coating.

[0060] Step 2: Fill the barrel with slurry, put in the barrel cap, tighten the connection, turn on the drive switch, and adjust the drive force so that the slurry can be smoothly extruded at the required flow rate;

[0061] Step 3: Fill the casting coating hopper with casting coating. Turn on the drive switch and adjust the drive force so that the casting coating can wet the brush at the required flow rate;

[0062] Step 4: Connect to the computer, import the 3D model data of the mold, shell and core to be printed, and set the printing parameters and brushing parameters accordingly. Adjust the height of the needle and brush head and the starting printing position. The brush head and printing needle are controlled by the stepper system.

[0063] Step 5: The printing device is set to zero, and the needle extrudes the slurry from the needle tip according to the preset path of the program and deposits it onto the printing platform to print layer by layer;

[0064] Step 6: After 2-5 layers have been printed and a certain strength has been achieved, the brush head fills the micro-grooves on the printed surface according to the preset milling and brushing path.

[0065] Step 6: After completing one mold, shell and core shaping, the brush head returns and the needle continues to print to prepare for the next brush head shaping. Repeat the printing-painting process until the mold, shell and core are formed.

[0066] Step 7: Clean the surface of the printed and cured mold, shell and core with a brush to remove any burrs;

[0067] Step 8: The solidified mold, shell, and core are placed in a drying oven to dry, and then placed in a sintering furnace for sintering. After sintering is completed and cooled to room temperature, the mold, shell, and core are removed. The sintering process includes heating to 200℃ and holding for 1 hour, then heating to 400℃ and holding for 1 hour, then heating to 600℃ and holding for 1 hour, then heating to 900℃ and holding for 1 hour, and finally heating to 1150℃ and holding for 2 hours.

[0068] Figure 2 The surface microstructure of the mold formed by simultaneous brushing and layering of casting coating in Example 1 is shown. Figure 2 As can be seen, the surface after coating is relatively smooth and flat, without obvious grooves.

[0069] Results analysis: The surfaces of the printed mold, shell and core were observed using a metallographic microscope. The surface roughness of the mold, shell and core was Ra 10-25μm, as shown by the roughness tester.

[0070] Comparative Example 1

[0071] A layered extrusion additive manufacturing method for simultaneously brushing casting coatings to form complex structures with high surface precision molds, shells, and cores, the forming method comprising the following steps:

[0072] Step 1: Select 82g each of 300-mesh and 1000-mesh silica powder, 36g of binder and 0.4g of n-butanol defoamer, and mix them thoroughly to form a slurry. The binder is a mixture of polyvinylpyrrolidone and anhydrous ethanol in a mass ratio of 10:90.

[0073] Step 2: Fill the barrel with slurry, put in the barrel cap, tighten the connection, turn on the drive switch, and adjust the drive force so that the slurry can be smoothly extruded at the required flow rate;

[0074] Step 3: Connect to the computer, import the 3D model data of the mold, shell and core to be printed, and set the printing parameters accordingly, adjust the needle height and the starting printing position; the printing needle is controlled by the stepper system;

[0075] Step 4: Set the printing device to zero, and the needle will squeeze the paste from the needle tip and deposit it onto the printing platform layer by layer according to the preset path of the program until the printing is completed and the program stops;

[0076] Step 5: Clean the surface of the printed and cured mold, shell and core with a brush to remove any burrs.

[0077] Figure 3 The microstructure of the surface of the mold formed by layered extrusion of casting coating without simultaneous brushing in Comparative Example 1 is shown. Figure 3 It can be seen that the unpainted mold surface has many grooves and protrusions, and the surface is rough and uneven to the naked eye.

[0078] Results analysis: The surfaces of the printed mold, shell and core were observed using a metallographic microscope. The surface roughness of the mold, shell and core was Ra 40-80μm, as shown by the roughness tester.

[0079] Table 1. Surface roughness test results for experimental examples and comparative examples.

[0080]

[0081] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a mold or core with improved surface precision through simultaneous brushing of casting coating during layered extrusion additive manufacturing, characterized in that, Includes the following steps: (1) Prepare printing paste and brush coating paste, wherein the particle size of ceramic powder in the printing paste is 10-150 μm and the particle size of ceramic powder in the brush coating paste is less than 10 μm; (2) Based on the three-dimensional model data of the mold or core to be printed, set the printing parameters and brushing parameters; first, use the printing paste prepared in step (1) to print at least one layer of the cross-section of the mold or core, and then use the brushing paste prepared in step (1) to brush the surface of the mold or core to be printed, and print at the same time until the printing is completed first, and then the brushing of the surface of the part to be printed is completed. (3) Dry the mold obtained in step (2), or dry the core obtained in step (2) and then sinter it to obtain a mold or core with improved surface precision.

2. The method for preparing a mold or core with improved surface precision through simultaneous brushing of casting coating during layered extrusion additive manufacturing as described in claim 1, characterized in that... In step (2), after printing 2-5 layers of the cross-section of the mold or core, the surface of the mold or core is then brushed.

3. The method for preparing a mold or core with improved surface precision through simultaneous brushing of casting coating during layered extrusion additive manufacturing as described in claim 1 or 2, characterized in that... The coating thickness is 0.1 to 0.2 mm.

4. The method for preparing a mold or core with improved surface precision through simultaneous brushing of casting coating during layered extrusion additive manufacturing as described in claim 1 or 2, characterized in that... In step (2), after the surface of the printed part is coated, the cross section of the last printed part is coated to improve the accuracy of the printed surface.

5. The method for preparing a mold or core with improved surface precision through simultaneous brushing of casting coating during layered extrusion additive manufacturing as described in claim 1, characterized in that... The ceramic powder in the printing slurry and the ceramic powder in the brush coating slurry are each independently selected from silicon oxide, aluminum oxide, or yttrium oxide.

6. The method for preparing a mold or core with improved surface precision through simultaneous brushing of casting coating during layered extrusion additive manufacturing as described in claim 1, characterized in that... The binder in the printing paste and the binder in the brushing paste are each independently selected from silica sol, ethyl silicate, yttrium sol, or polyvinylpyrrolidone.

7. The method for preparing a mold or core with improved surface precision through simultaneous brushing of casting coating during layered extrusion additive manufacturing as described in claim 1, characterized in that... The mold is a shell.

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