CN113600753A

CN113600753A - Manufacturing method of sand casting mold

Info

Publication number: CN113600753A
Application number: CN202110926253.1A
Authority: CN
Inventors: 周飞; 张龙; 洪军; 成庆瑞; 冉松林
Original assignee: Anhui Highly Precision Casting Co Ltd
Current assignee: Anhui Highly Precision Casting Co Ltd
Priority date: 2021-08-12
Filing date: 2021-08-12
Publication date: 2021-11-05

Abstract

According to the manufacturing method of the sand casting mold, the mold is designed in a split mode according to the structure, the size and the batch characteristics of a product, and a universal mold body and a differential mold core structure are obtained. Wherein the mould body is obtained by machining a foaming foam body to obtain a foam mould, and then the foam mould is obtained by lost foam casting, heat treatment and machining; the mold core is made of H13, stainless steel or wear-resistant copper alloy materials with relatively high raw material cost through droplet jetting and 3D printing to obtain a prefabricated blank with a certain thickness following surface, and then the prefabricated blank is obtained through sintering, heat treatment and machining. And finally assembling the die body and the die core through interference fit to obtain the die. The invention effectively solves the problems of long delivery caused by the fact that the sand casting die needs to be manufactured by collecting sheets and high cost caused by manufacturing by using uniform high-cost materials, and greatly improves the manufacturing efficiency of the die on the premise of effectively controlling the cost.

Description

Manufacturing method of sand casting mold

Technical Field

The invention belongs to the technical field of casting, and particularly relates to a manufacturing method of a sand casting mold.

Background

Sand casting is a casting technique that takes compact molding sand as a mold to obtain a casting. China is a big country for casting production, and sand casting accounts for 80% -90% of casting production. The sand casting has two modes of manual molding and machine molding. The machine model has the advantages of accurate casting size, good surface quality, small machining allowance and the like, and is widely applied to small and medium castings. Machine-shaped sand molds are often made from gray iron, stainless steel, or copper alloys by machining or lost foam casting with the assistance of machining. However, the forging stock or the casting blank is directly used as a raw material for machining, so that the machining amount of the die is large, the machining time is long, the production cost is high, and high material waste is caused. The manufacturing method of adopting the lost foam casting mold to be assisted with machining reduces the machining amount to a certain extent, however, in order to reduce the cost, mold manufacturing enterprises often need to obtain enough order amount to perform lost foam casting, and the problem of long mold processing period also exists.

In recent years, 3D printing technology has been rapidly developed, and molds formed by 3D printing technology are widely used in the fields of injection molds, medical treatment, and the like. For example, chinese patent CN201710582491.9 divides the injection mold into different functional areas according to the service characteristics and forming characteristics of the mold during the injection molding process, and manufactures the injection mold with a gradient spatial structure by 3D printing. In chinese patent CN201810757238.7, in order to solve the problems of the complicated injection molding die, such as porosity, high cost for obtaining a complete martensite structure, etc., a pair of molding dies is added to the conventional injection molding die manufacturing system to axially compress the injection molding die. In order to solve the problems that austenitic heat-resistant steel obtained by laser 3D printing is difficult to process and complex parts are difficult to manufacture, Chinese patent CN201410520215.6 proposes that powder with high powder purity, fine granularity, high sphericity and good fluidity is prepared by adding C element, deoxidizing element, kang crack element and the like on the basis of the required heat-resistant die material, and expands the application of the difficult-to-process material in the fields of heat energy, power and high-end heat-resistant hydraulic dies. Chinese patent CN202110239743.4 proposes a marrow-shaped structure with bionic property, which can greatly improve the cooling efficiency and service life of the mold in the industries of injection molding, casting and stamping.

Nevertheless, the use of 3D printing technology for the manufacture of sand casting molds has been rarely reported. This may be because: on one hand, the added value of a product formed by a sand casting mold is low, and the cost of a 3D printing technology forming mold such as a selective laser sintering or selective laser melting technology is high; on the other hand, in the context of the demand for large quantities of products, the lead time of the mold has not been a critical factor that restricts the production of the products. However, with the background of increasing customization demand, product lead time has become a core competitiveness for enterprises, which requires efficient and low-cost manufacturing of sand casting molds.

Disclosure of Invention

1. Technical problem to be solved by the invention

The invention aims to solve the problems that the existing sand casting mold has long delivery period and is wasted in material in the manufacturing process by adopting the traditional forming method, the manufacturing cost is higher by adopting a 3D printing technology and the like, and provides an efficient and low-cost manufacturing method of the sand casting mold, which can meet the personalized manufacturing requirement of the sand casting mold and has lower production cost and shorter delivery period.

2. Technical scheme

The invention relates to a method for manufacturing a mold for casting a sand core, which comprises the following steps of:

step one, split type design. According to the structure, size and batch characteristics of a produced casting, a mold is designed in a split mode, a mold body structure with universality and a mold core structure with difference are designed, and particularly, the mold body and the mold structure can be connected through positioning columns;

step two, manufacturing the mold body. Processing a block-shaped foam body for the lost foam into the structural size of a die body by using ultrahigh-speed cutting processing equipment, then performing lost foam casting by using the foam body to obtain a die body primary blank, and further obtaining a die body structure with fine size by using or not using heat treatment and machining;

and step three, manufacturing a mold core. Preparing a mold core primary blank by adopting mold steel powder or copper alloy powder through 3D printing, and further obtaining a mold core structure with fine size by adopting heat treatment and machining;

and step four, assembling. And assembling the die body and the die core together to obtain the die for sand casting.

Preferably, in the split design in the step one, when the size of the casting is less than 100mm, the number of the mold cores assembled on the mold body is not more than 10; when the casting size is 100mm <200mm, the number of the mold cores assembled on the mold body is not more than 4; when the diameter of the casting piece is 200mm < the casting size is 400mm, the number of the mold cores assembled on the mold body is not more than 2; when the size of the casting is larger than 400mm, the number of the mold cores assembled on the mold body is 1.

Preferably, the mold core structure of the step one can be designed into a shape following structure according to the molding surface.

Preferably, in the die body manufacturing process in the step two, the super-high speed cutting machining speed is not lower than 3000r/s, and the feeding amount is 0.1-10 mm.

Preferably, the casting material in the second step is gray iron, 45# steel and the like.

Preferably, the die body structure in the second step has yield strength of more than 250-350 MPa, hardness of more than 50-65 HRC and roughness of 6-10 level precision.

Preferably, the 3D printing of the primary blank of the mold core in the step three is a droplet jetting bonding 3D printing process, that is, alloy powder is spread on a powder bed, a bonding agent is jetted onto the powder bed through a droplet jetting nozzle to obtain a preform of the mold core, and then the primary blank of the mold core is obtained through high-temperature sintering.

Preferably, the material of the mold core in the third step is H13, 316L, wear-resistant copper alloy and other alloy materials, and the powder granularity is 10-100 μm.

Preferably, the yield strength of the mold core structure in the third step is more than 350-450 MPa, the hardness is more than 60-65 HRC, and the roughness is 6-8-level precision.

Preferably, in the fourth step, the mold body and the mold core are assembled by interference fit.

3 advantageous effects

The technical scheme provided by the invention has the following remarkable effects:

(1) the lead time of the mold for sand casting is shortened. When the traditional 'casting mold primary blank + machining' process is adopted for manufacturing the mold, enough orders need to be gathered to start the mold processing and manufacturing, the delivery cycle of the mold is about 25-30 days, and if the debugging and the use of the mold are considered, longer time is needed. The mold body and the mold core are designed in a split mode, and the mold body is universal and can be cast in a large batch, and the delivery cycle of the mold can be shortened by about 10 days. And for the mold core, the delivery cycle is less than 10 days due to the small volume and the adoption of 3D printing technology for manufacturing.

(2) The manufacturing cost of the mould for sand casting is reduced. No matter the traditional machining or the production process of casting and machining is adopted, the die is of an integrated structure, and therefore large material waste is caused. The die body is made of ordinary materials with low cost such as gray iron or 45# steel, and the die core is made of high-added-value materials such as H13, 316L and wear-resistant copper alloy, so that the material cost is greatly reduced. And the mold core can be designed into a random structure according to the molding surface, so that the use of high value-added materials by the mold core is further reduced, and the manufacturing cost of the mold is further reduced.

(3) The number of sand casting and spare parts thereof is reduced. The used mould of present sand casting enterprise is whole mould, to the more enterprise of product specification, needs a large amount of spare parts to satisfy the production needs. Due to the adoption of the split type mold design, enterprises can design a plurality of universal mold bodies and a large number of mold cores according to the characteristics of the products, the number of the molds required to be stored in the split type mold is remarkably reduced under the same product types, and the assembly of the mold is practical, simple and flexible.

Drawings

FIG. 1 is a schematic structural view of a one-mold two-piece sand casting mold according to the present invention;

FIG. 2 is a schematic structural view of a mold core for one-mold two-piece sand casting according to the present invention;

FIG. 3 is a schematic view of a one-mold four-piece sand casting mold structure according to the present invention

The reference numerals in the schematic drawings illustrate:

1. a mold body; 2. a mold core; 3. a pouring channel; 4. positioning a rod; 5. a mold core molding surface; 6. an inner surface of the mold core; 7. locating hole

Detailed Description

Example 1

To facilitate the description of the method for manufacturing a sand casting mold according to the present invention, the present embodiment provides a sand casting mold (particularly, the method according to the present invention is not limited to this mold), which includes a mold body 1 and a core 2. Wherein, a pouring gate 3 and a positioning rod 4 are arranged on the die body 1. The mold core 2 is composed of a molding surface 5, an inner surface 6 and a positioning hole 7.

The invention relates to a molding method of a mold for sand casting, which comprises the following molding processes:

step one, split type design of the die. A die body 1 and 2 die cores shown in figure 1 are designed for a casting with the size of 200-400 mm, wherein a pouring channel 3 and two positioning rods 4 are arranged in the die body 1. Each core 2 has a forming surface 5 and an inner surface 6 and two locating holes 7.

Step two, manufacturing the mold body. Carrying out high-speed cutting processing on the foamed lost foam with the rotating speed of 3500r/s and the feeding amount of 0.1mm to obtain a foam piece, and arranging a foam casting system on the foam piece; then casting the 45# steel solution by adopting a lost foam casting method, wherein the casting temperature is 1450 +/-10 ℃, so as to obtain a steel casting; finally, the die body is subjected to heat treatment and machining, so that the yield strength of the die body reaches more than 250MPa, the hardness reaches 55 +/-2 HRC, and the roughness reaches 8-level precision.

And step three, manufacturing a mold core. Uniformly mixing H13 alloy powder with the particle size distribution of 20-80 mu m according to the particle size, paving the powder on a powder bed, spraying a binder by a microdroplet spraying 3D printer to perform the mixture, transferring the mixture to an atmosphere furnace to sinter and thermally treat the mixture after performing the mixture to ensure that the yield strength of the mixture reaches more than 350MPa and the hardness reaches 60 +/-2 HRC, and finally machining the mixture to ensure that the roughness is 8-level precision.

Example 2

step one, split type design of the die. A die body 1 and 4 die cores shown in figure 3 are designed for a casting with the size of 100-200 mm, wherein a pouring

channel

3 and 4 positioning rods 4 are arranged in the die body 1. Each core 2 has a forming surface 5 and an inner surface 6 and a locating hole 7.

Step two, manufacturing the mold body. Carrying out high-speed cutting processing on the foamed lost module-shaped foam, wherein the rotating speed is 3000r/s, the feeding amount is 0.2mm, obtaining a foam piece, and arranging a foam casting system on the foam piece; then, casting the gray iron solution in the casting mould by adopting a lost foam casting method, wherein the casting temperature is 1550 +/-10 ℃ to obtain a gray iron casting; finally, the die body is subjected to heat treatment and machining, so that the yield strength of the die body reaches more than 250MPa, the hardness reaches 55 +/-2 HRC, and the roughness reaches 8-level precision.

And step three, manufacturing a mold core. The 316L alloy powder with the particle size distribution of 20-80 mu m is uniformly mixed according to the particle size, laid on a powder bed, preformed by spraying a binder by a microdroplet spraying 3D printer, transferred to an atmosphere furnace for sintering and heat treatment after the preforming, so that the yield strength of the powder reaches more than 350MPa, the hardness of the powder reaches 60 +/-2 HRC, and finally machined, wherein the roughness of the powder is 8-level precision.

In the description herein, references to the description of "one embodiment," "an example," "a specific example" or the like are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The preferred embodiments of the invention disclosed above are intended to be illustrative only. The preferred embodiments are not exhaustive and do not limit the method of making a high strength caliper seal to the specific embodiments described. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for manufacturing a mold for sand casting is characterized by comprising the following steps:

step one, split type design. According to the structure, size and batch characteristics of a produced casting, a mold is designed in a split mode, a mold body structure with universality and a mold core structure with difference are designed, and particularly, the mold body and the mold structure can be connected through a positioning rod;

and step four, assembling. The mold body and the mold core are assembled together to obtain a mold for sand casting, preferably with an interference fit.

2. A method of making a mold for sand casting according to claim 1, wherein in step one said split design, when the casting size is <100mm, the number of cores fitted on said mold body does not exceed 10; when the casting size is 100mm <200mm, the number of the mold cores assembled on the mold body is not more than 4; when the diameter of the casting piece is 200mm < the casting size is 400mm, the number of the mold cores assembled on the mold body is not more than 2; when the size of the casting is larger than 400mm, the number of the mold cores assembled on the mold body is 1.

3. A method of manufacturing a mold for sand casting according to claim 1, wherein said core structure of step one is a conformal structure designed according to a molding surface.

4. The method for manufacturing a mold for sand casting according to claim 1, wherein in the mold body manufacturing process of the second step, the cutting speed of the foamed foam is not lower than 3000r/s, and the feeding amount is 0.1-10 mm; the casting materials are gray iron, 45# steel and other materials; preferably, the structural yield strength of the heat-treated die body is more than 250-350 MPa, and the hardness is more than 50-65 HRC; and the structural roughness of the die body obtained after machining is 6-10-level precision.

5. The method for manufacturing the mold for sand casting according to claim 1, wherein the 3D printing of the primary mold core blank in the third step is a droplet spray bonding 3D printing process, i.e. alloy powder is spread on a powder bed, a bonding agent is sprayed on the powder bed through a droplet spray nozzle to obtain a preform of the mold core, and then the primary mold core blank is obtained through high-temperature sintering; the die core material is H13, 316L, wear-resistant copper alloy and other alloy materials, and the powder granularity is 10-100 mu m; preferably, the yield strength of the manufactured mold core structure is more than 350-450 MPa, the hardness is more than 60-65 HRC, and the roughness is 6-8-level precision.