WO2019047926A1

WO2019047926A1 - Method for forming sand mold by means of self-adaptive gradient printing

Info

Publication number: WO2019047926A1
Application number: PCT/CN2018/104646
Authority: WO
Inventors: 刘丰; 单忠德; 赵蒙蒙
Original assignee: 北京机科国创轻量化科学研究院有限公司
Priority date: 2017-09-08
Filing date: 2018-09-07
Publication date: 2019-03-14
Also published as: CN107716855B; CN107716855A

Abstract

Disclosed is a method for forming a sand mold by means of self-adaptive gradient printing. The method comprises the following steps: firstly slicing and layering a three-dimensional CAD model of a sand mold, obtaining profile information about a section of each layer, and in conjunction with casting process requirements, such as the intensity and the air permeability of the sand mold, determining the resin content of different parts of the sand mold and obtaining grayscale value information about the section of each layer; premixing sand with a solidification agent, and feeding the mixture to a sanding hopper, and moving the sanding hopper to uniformly lay molding sand with a thickness of one layer; moving a printing device, and according to the profile information and grayscale information about the section of the current layer, carrying out printing with different grayscales for molding sand laid at each layer; and laying sand layer by layer, and carrying out grayscale printing layer by layer until a complete sand mold is finally formed by means of layer-by-layer staking and solidification.

Description

Sand type adaptive gradient printing forming method

Technical field

The invention belongs to the technical field of casting, and particularly relates to a rapid forming method of a moldless casting type.

Background technique

3D printing technology, also known as 3D printing technology, refers to the technology of manufacturing objects by using print heads, nozzles or other printing technologies. It belongs to an additive manufacturing technology and is an important research direction in the field of rapid prototyping. It refers to the transformation of a complex three-dimensional model of a desired shaped workpiece into a simple two-dimensional cross section. The material powder is printed layer by layer, stacked layer by layer, and a three-dimensional model with arbitrarily complex structure is formed from bottom to top.

Sand-type inkjet printing is a rapid prototyping technique based primarily on droplet spray forming. The sand-type printing technology based on the principle of droplet ejection mainly refers to the application of a print head to spray "ink", and the advanced forming technology for quickly forming a foundry sand type by bonding grit. The working principle is to convert the 3D model data into a two-dimensional section through the slice in the model processing stage, and then spray the adhesive onto the sand by the jet print head, and bond the sand together, and then directly produce through the layer stacking. The desired sand/core is required. The technology adopts a micro-drop array print head, has low cost, can manufacture a large-volume sand type, has high manufacturing speed and high precision, and has a good application prospect.

However, sand-type inkjet printing tends to have a lower sand strength than manual molding. In order to meet the demand for sand strength, the amount of resin adhesive is usually increased, and the sand type thus produced has increased gas generation and reduced gas permeability. Shortcomings such as poor collapsibility. The gas generation assembly causes pore defects in the casting and even makes the casting impossible. If the core has poor collapsibility, the casting will hinder the shrinkage of the casting during the cooling process, leaving internal stress and even cracking inside the casting.

Summary of the invention

In view of the comprehensive requirements of the sand type of the sand inkjet printing, such as strength, gas generation, gas permeability and the like, the present invention proposes a sand type adaptive gradient printing forming method.

To achieve the above object, the present invention adopts the following technical solutions:

A sanding adaptive gradient printing forming method includes the following steps:

Step 1: Convert the sand-type 3D CAD model into a file in the STL format for slice layering to obtain the contour information of each layer section;

Step 2: According to the casting process requirements including sand strength and gas permeability, determine the resin content of different parts of the sand type, and convert it into gray value to obtain the gray value information of each layer section;

Step 3: premixing the sand with the curing agent, and feeding the premixed molding sand into the sand hopper;

Step 4: Move the sanding hopper and evenly lay a layer of sand;

Step 5: moving the printing device, according to the contour information of the current layer section and the gray scale information, printing the sand of each layer on different gray scales;

Step 6: Repeat steps 4 to 5, layering the sand, and printing the layers in grayscale until the amount of sand in the sand hopper is insufficient to lay the next layer;

Step 7: Repeat steps 3 - 6 until the final layer-by-layer stack solidifies into a complete sand pattern.

Further, the gradation level described above refers to a resin in which the gradation level is divided according to the amount of resin ejection, the minimum level gradation ejection minimum volume resin, and the highest level gradation ejection maximum volume resin.

Further, the above-mentioned grayscale printing refers to determining the resin content of different parts of the sand type according to the casting process requirements of the strength and permeability of the sand type, and calculating the resin to be sprayed on different parts of each layer of sand according to the layer thickness of each layer of sand. The content is converted into gray value information of each layer of printed image, thereby guiding the nozzle to spray different gray scale resins in different portions of each layer of sand.

Further, the adaptive gradient printing described above refers to printing of different gray scales between the inner and outer contour regions of the sand mold and the regions between the different wall thicknesses.

Further, the above adaptive gradient printing means that the transition section of each region adopts a grayscale gradient transition to perform resin printing.

With the above technical solution, the following advantages are obtained:

1. In the process of inkjet printing, the amount of inkjet is controllable, and at the same time, the printing accuracy of the sand type can be ensured;

2, can be adaptive gradient printing according to the actual casting structure, casting precision and performance requirements, and then select different printing grayscale for different parts of the sand type, the printed sand type can meet the strength requirements, and the sand type has good hair. Gas volume and gas permeability.

DRAWINGS

The accompanying drawings, which are incorporated in the claims of the claims In the drawing:

Figure 1 is a three-dimensional model of a sand type;

2 is a flow chart of a method for forming a sand type adaptive gradient printing;

Figure 3 is a schematic view of gray scale printing of a sand wall with a smaller wall thickness;

Figure 4 is a schematic diagram of gradient transition printing of a larger sand wall thickness.

Detailed ways

The technical solutions in the embodiments of the present invention are clearly and completely described in the following with reference to the accompanying drawings in the embodiments of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, but not all embodiments. The following description of the at least one exemplary embodiment is merely illustrative and is in no way All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts are within the scope of the present invention.

As shown in Figure 1, a three-dimensional model of a sand type is taken as an example. The specific steps are as follows:

1. Convert the sand-type three-dimensional CAD model into a file in STL format for slice layering to obtain contour information of each layer section;

2. According to the requirements of casting process such as strength and permeability of different parts of the sand type, determine the amount of resin in different parts of the sand type, and convert it into gray value to obtain the gray value information of each layer section. As shown in Fig. 2 and Fig. 3, respectively, the gradient printing diagrams of the upper and lower wall thickness portions of the sand type are respectively required. Since the inner and outer surface contour portions of the sand type require high strength, more ink ejection amount is required, and the printing gray scale is high. The center portion of the sand type has lower strength requirements and higher gas permeability requirements, so less ink ejection amount is required, and the printing gray scale is lower. As the sand pattern transitions from the inner and outer contour regions to the sand center region, the strength requirement is gradually reduced, and the sand type has a certain gas permeability requirement, so that the ink ejection amount needs to be gradually reduced, and the printing gray scale is gradually lowered;

3. Premixing the sand with the curing agent, and feeding the pre-mixed molding sand into the sanding hopper;

4. Move the sanding hopper and evenly lay a layer of thick sand;

5. The mobile printing device performs different gray scale printing on each layer of the molding sand according to the contour information of the current layer section and the gray scale information;

6. Repeat steps 4-5, layering the sand and printing the layers in grayscale until the amount of sand in the sand hopper is insufficient to lay the next layer;

7. Repeat steps 3-6 until the final layer-by-layer stack solidifies into a complete sand pattern.

The above description is only the preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes can be made to the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and scope of the present invention are intended to be included within the scope of the present invention.

Claims

A sanding type adaptive gradient printing forming method, comprising the following steps:

Step 1: Convert the sand-type 3D CAD model into a file in the STL format for slice layering to obtain the contour information of each layer section;

Step 2: According to the casting process requirements including sand strength and gas permeability, determine the resin content of different parts of the sand type, and convert it into gray value to obtain the gray value information of each layer section;

Step 3: premixing the sand with the curing agent, and feeding the premixed molding sand into the sand hopper;

Step 4: Move the sanding hopper and evenly lay a layer of sand;

Step 5: moving the printing device, according to the contour information of the current layer section and the gray scale information, printing the sand of each layer on different gray scales;

Step 6: Repeat steps 4 and 5, layering the sand, and printing the layers in grayscale until the amount of sand in the sand hopper is insufficient to lay the next layer;

Step 7: Repeat steps 3 through 6 until the final layer-by-layer stack solidifies into a complete sand pattern.
A method of forming a sand type adaptive gradient printing according to claim 1, wherein said gradation level is a resin which divides a gradation according to a quantity of resin ejection, and a minimum level of gradation ejection minimum volume. The highest level of grayscale sprays the largest volume of resin.
The sand-type adaptive gradient printing forming method according to claim 1, wherein the grayscale printing refers to determining a resin content of different portions of the sand type according to a casting process requirement of a sand type strength and gas permeability, according to each The layer thickness of the layered sand, calculate the resin content required to spray different parts of each layer of sand, and convert it into the gray value information of each layer of printed pictures, thereby guiding the nozzle to spray different gray levels in different parts of each layer of sand. Grade resin.
The sand-type adaptive gradient printing forming method according to claim 1, wherein the adaptive gradient printing refers to printing of different gray scales between inner and outer contour regions of sand type and regions between different wall thicknesses. .
The method of forming a sand type adaptive gradient printing according to claim 1, wherein the adaptive gradient printing means that the transition section of each region adopts a grayscale gradient transition to perform resin printing.