CN107716855B

CN107716855B - Forming method for sand mold self-adaptive gradient printing

Info

Publication number: CN107716855B
Application number: CN201710803799.1A
Authority: CN
Inventors: 刘丰; 单忠德; 赵蒙蒙
Original assignee: Advanced Manufacturing Technology Research Center Of General Research Institute Of Mechanical Science
Current assignee: Advanced Manufacturing Technology Research Center Of General Research Institute Of Mechanical Science
Priority date: 2017-09-08
Filing date: 2017-09-08
Publication date: 2020-08-11
Anticipated expiration: 2037-09-08
Also published as: CN107716855A; WO2019047926A1

Abstract

The invention belongs to the field of rapid forming and discloses a forming method for sand mold self-adaptive gradient printing. The method comprises the steps of firstly, slicing and layering a sand mould three-dimensional CAD model to obtain outline information of each layer of section, and determining resin contents of different parts of a sand mould according to casting process requirements such as strength and air permeability of the sand mould to obtain gray value information of each layer of section; pre-mixing sand and a curing agent, then sending the sand and the curing agent into a sand paving hopper, moving the sand paving hopper, and uniformly paving the molding sand with one layer thickness; and moving the printing device, and printing the molding sand paved on each layer at different gray levels according to the profile information and the gray information of the section of the current layer, paving the sand layer by layer, and printing the gray level layer by layer until finally stacking and solidifying the sand layer by layer to form the complete sand mold. The method has higher printing precision, and the printed sand mold can meet the requirements of overall strength and local strength and has good gas forming amount and air permeability as a whole.

Description

Forming method for sand mold self-adaptive gradient printing

Technical Field

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

Background

The 3D printing technology is also called three-dimensional printing technology, which is a technology for manufacturing an object by depositing materials using a print head, a nozzle or other printing technologies, belongs to an additive manufacturing technology, and is an important direction of current research in the field of rapid prototyping. It refers to the combination of converting a complex three-dimensional model of a workpiece to be formed into a simple two-dimensional cross section by slicing. The material powder is used for printing layer by layer and stacking layer by layer to form a three-dimensional model with any complex structure from bottom to top.

Sand inkjet printing is a rapid prototyping technology based primarily on droplet ejection prototyping. The sand mold printing technology based on the droplet jetting principle mainly refers to an advanced forming technology for rapidly manufacturing casting sand molds by jetting 'ink' and bonding gravel by using a printing head. The working principle is that three-dimensional model data is converted into a two-dimensional section through slicing in a model processing stage, then an injection printing head is utilized to inject adhesive on sand grains, the sand grains are adhered together, and then the required sand mould/core is directly produced through layer-by-layer superposition. The technology adopts the micro-droplet array printing head, has low cost, can manufacture large-volume sand moulds, and has high manufacturing speed, high precision and good application prospect.

However, the strength of sand molds for sand mold ink jet printing is often lower than the strength of hand molding, and in order to meet the strength requirement of sand molds, the ejection amount of resin binder is generally large, and sand molds produced therefrom have disadvantages such as increased gas evolution, decreased air permeability, and poor collapsibility. The large gas evolution can cause the casting to generate gas hole defects, even the pouring can not be finished. If the collapsibility of the core is poor, the shrinkage of the casting is hindered in the cooling process of the casting, so that internal stress remains in the casting, and even cracking occurs.

Disclosure of Invention

The invention provides a forming method for sand mold self-adaptive gradient printing, aiming at the comprehensive requirements of the sand mold of the current sand mold ink-jet printing on the performances of strength, gas forming amount, air permeability and the like.

In order to achieve the purpose, the invention adopts the following technical scheme:

a forming method for sand mold adaptive gradient printing comprises the following steps:

step 1: converting the sand mold three-dimensional CAD model into a file in an STL format for slicing and layering to obtain the profile information of each layer of section;

step 2: determining the resin content of different parts of the sand mold according to casting process requirements such as strength and air permeability of the sand mold, and converting the resin content into a gray value to obtain gray value information of each layer of section;

and step 3: pre-mixing sand and a curing agent, and feeding the pre-mixed molding sand into a sand paving hopper;

and 4, step 4: moving a sand spreading hopper, and uniformly spreading the molding sand with one layer thickness;

and 5: the mobile printing device is used for printing the molding sand paved on each layer with different gray levels according to the profile information and the gray level information of the section of the current layer;

step 6: repeating the step 4 to the step 5, paving sand layer by layer, and printing gray level layer by layer until the amount of the molding sand in the sand paving hopper is not enough to lay the next layer;

and 7: and (6) repeating the steps 3-6 until finally stacking and solidifying layer by layer to form the complete sand mold.

By adopting the technical scheme, the method has the following advantages:

1. in the ink-jet printing process, the ink-jet amount is controllable, and meanwhile, the printing precision of the sand mold can be ensured to be unchanged;

2. the self-adaptive gradient printing can be carried out according to different requirements of actual casting structures, casting precision and performance, different printing gray levels are selected for different parts of the sand mold, the printed sand mold can meet the strength requirement, and meanwhile, the whole sand mold has good gas forming amount and air permeability.

Drawings

FIG. 1 shows a three-dimensional model of a sand mold;

FIG. 2 is a flow chart of a molding method of sand mold adaptive gradient printing;

FIG. 3 is a schematic gray scale printing diagram of a portion of a sand mold with a smaller wall thickness;

fig. 4 is a schematic view of a gradient transition print of a larger portion of the sand mold wall thickness.

Detailed Description

As shown in fig. 1, a three-dimensional model of a sand mold is shown, and the specific operation steps are as follows:

1. converting the sand mold three-dimensional CAD model into a file in an STL format for slicing and layering to obtain the profile information of each layer of section;

2. and determining the resin amount of different parts of the sand mold according to the requirements of casting processes such as strength, air permeability and the like of the different parts of the sand mold, converting the resin amount into a gray value, and obtaining gray value information of the section of each layer. As shown in fig. 2 and fig. 3, which are schematic diagrams of gradient printing of upper and lower portions with different wall thicknesses of a sand mold, respectively, since the contour portion of the inner and outer surfaces of the sand mold needs higher strength, a larger amount of ink is needed, and the printing gray level is higher. The central part of the sand mold has lower requirement on strength and higher requirement on air permeability, so that less ink jet amount is required and the printing gray level is lower. The strength requirement of the sand mold is gradually reduced along with the transition of the inner and outer contour areas of the sand mold to the center area of the sand mold respectively, and the whole sand mold has a certain air permeability requirement, so that the ink jet amount is required to be gradually reduced, and the printing gray level is gradually reduced;

3. pre-mixing sand and a curing agent, and feeding the pre-mixed molding sand into a sand paving hopper;

4. moving a sand spreading hopper, and uniformly spreading the molding sand with one layer thickness;

5. the mobile printing device is used for printing the molding sand paved on each layer with different gray levels according to the profile information and the gray level information of the section of the current layer;

6. repeating the steps 4-5, paving sand layer by layer, and printing gray level layer by layer until the amount of the molding sand in the sand paving hopper is not enough to lay the next layer;

7. and repeating the steps 3-6 until finally stacking and solidifying layer by layer to form the complete sand mold.

Claims

1. A forming method for sand mold adaptive gradient printing comprises the following steps:

step 2: determining the resin content of different parts of the sand mold according to the requirements of the strength and air permeability casting process of the sand mold, and converting the resin content into a gray value to obtain gray value information of each layer of section;

and 7: repeating the steps 3-6 until finally stacking and solidifying layer by layer to form a complete sand mold;

the gray scale is divided according to the injection amount of the resin, the lowest gray scale injects the resin with the minimum volume, and the highest gray scale injects the resin with the maximum volume;

the gray printing is to determine the resin content of different parts of the sand mold according to the strength and air permeability casting process requirements of the sand mold, calculate the resin content required to be sprayed at different parts of each layer of molding sand according to the layer thickness of each layer of molding sand, and convert the resin content into gray value information of each layer of printed picture, thereby guiding the spray head to spray resin with different gray levels at different parts of each layer of molding sand.

2. A method of forming an adaptive gradient print for a sand mold according to claim 1, wherein the adaptive gradient print is a print with different gray levels between an inner and outer contour region and a region between different wall thicknesses of the sand mold.

3. A method for forming an adaptive gradient printing sand mold according to claim 1, wherein the adaptive gradient printing is performed by performing a resin printing by using a gray gradient transition in each region transition section.