Investment casting process for workpiece with overlarge thickness difference of all parts

Abstract

The invention relates to the technical field of investment casting, in particular to an investment casting process for a workpiece with overlarge thickness difference at each part, which comprises the following steps of: arranging a pouring gate of a large feeding ladle and a wax mould of a riser, and pouring a sintered mould shell by adopting sand burying, so that a casting can be fully supplemented with molten metal in the solidification process, shrinkage cavity and shrinkage porosity are prevented, and the casting quality is improved. Meanwhile, quartz sand is adopted for heat preservation, the cooling speed is controlled, and the solidification temperature difference between the interior and the surface layer of the thick part is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of investment casting, in particular to an investment casting process for a workpiece with large thickness differences at various parts. Background Art

[0002] like Figure 1 In the bracket shown, the thickness of the two side plates of the U-shaped structure is greatly different from that of other parts, and defects such as shrinkage cavities, shrinkage and cracks are easily generated during the cooling of the investment casting. Summary of the invention

[0003] The purpose of the present invention is to provide an investment casting process for workpieces with large thickness differences at various parts, which adopts a large shrinkage feeding steel ladle and controls the cooling rate of the casting to prevent defects.

[0004] The technical solution adopted by the present invention to solve the technical problem is: an investment casting process for a workpiece with a large thickness difference at each part, comprising the following steps: The first step is to make a wax mold set, which includes a middle vertical runner, brackets symmetrically welded to both sides of the vertical runner, and risers respectively arranged on the outside of the two brackets, the vertical runner includes two upper and lower feeding bags and a pouring cup on the top, wherein the two feeding bags are respectively welded to the upper and lower ear groups of the bracket, the riser includes an inverted "Y"-shaped riser body and a riser cup on the top, the forked bottom ends of the riser body are respectively welded to the thickened body of the U-shaped edge of the bracket, and the upper end of the riser body is connected to the top of the U-shaped two side plates of the bracket through a T-shaped rod; The second step is to make the shell by pouring sand. Water glass + high aluminum powder (particle size <30μm) are used to make slurry. High aluminum powder of different particle sizes are sequentially coated on the surface of the wax mold. The surface sand particle size close to the surface of the wax mold is ≤50μm, then the 2-3 layers of sand particle size is ≤120μm, and the last 4-7 layers of sand particle size are 300μm, 300μm, 1mm and 2mm; after pouring sand on the surface layer, it is immersed in ammonium chloride solution for curing for 20-30 minutes, and then air-dried. After pouring sand on each of the next 2-7 layers, it is immersed in aluminum chloride solution for curing for 20-30 minutes. Similarly, each layer can be poured sand on the next layer only after air-drying, and finally the sand shell thickness is 15-20mm; The third step is to melt the wax and sinter. The wax mold is melted in a water bath and the sand shell is placed in a high-temperature furnace for sintering. The fourth step is casting. The sintered mold shell is placed in a sand box and filled with quartz sand. While the gate is leaking out, it should be filled at least 10mm above the top of the mold shell riser. While the mold shell is just out of the furnace and is in a high temperature state, 1520±10℃ molten metal is poured into the mold shell through the gate. The pouring is required to be completed within 5 seconds, and the gate is covered with asbestos for insulation. After the molten metal cools and takes shape, the casting is removed by sand casting.

[0005] Preferably, the height of the vertical runner is at least twice the height of the support, and the height of the vertical runner is greater than the riser. The higher vertical runner and riser can provide greater hydraulic pressure, so that the workpiece is fully filled.

[0006] Preferably, the cross-sectional area of ​​the pouring cup is larger than that of the feeding pack, and the volume of the feeding pack is larger than the sum of the volumes of two ears of a bracket connected to the feeding pack.

[0007] Preferably, the volume of the forked body at the bottom end of the riser body is larger than the volume of the U-shaped edge thickening body of the bracket connected thereto.

[0008] The larger volume of the feeding bag and the riser body can better keep the temperature, so that the molten metal inside solidifies later than the workpiece and is sufficient to replenish the workpiece.

[0009] The beneficial effects of the present invention are: an investment casting process for workpieces with large thickness differences in various parts, which includes a wax mold with a large shrinkage-compensating runner and a riser, and the sintered mold shell is poured with buried sand, so that the casting can have sufficient molten metal supplement during the solidification process to prevent the generation of shrinkage cavities and shrinkage. At the same time, quartz sand is used for heat preservation, the cooling rate is controlled, and the solidification temperature difference between the inside and the surface of the thicker part is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic diagram of the three-dimensional structure of the workpiece to be cast in the present invention; Figure 2 It is a schematic diagram of the three-dimensional structure of the wax model of the workpiece of the present invention.

[0011] Description of reference numerals: 1 – vertical runner, 11 – feeding bag, 12 – pouring cup, 2 – riser, 21 – riser body, 22 – riser cup, 3 – T-bar. DETAILED DESCRIPTION

[0012] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, but the implementation scope of the present invention is not limited thereto.

[0013] like Figure 2 As shown, the present embodiment is an investment casting process for a workpiece with large thickness differences in various parts, and takes the low-temperature wax casting of an automobile bracket as an example for explanation. The casting process basically includes the steps of making a wax mold, pouring sand to make a shell, melting wax sintering and casting.

[0014] Among them, in order to improve the production efficiency of casting and make the structure more balanced as a whole, this embodiment adopts one mold and two pieces for casting, that is, when making the wax mold, the wax molds of the two brackets are welded to the same pouring rod. The structure of the wax mold group after welding is as follows: the wax mold group includes a vertical runner 1 in the middle, brackets symmetrically welded to both sides of the vertical runner 1, and risers 2 respectively arranged on the outside of the two brackets, the vertical runner 1 includes two upper and lower shrinkage packs 11 and a pouring cup 12 on the top, wherein the two shrinkage packs 11 are respectively welded to the upper and lower ear groups of the bracket, the riser 2 includes an inverted "Y"-shaped riser body 21 and a riser cup 22 on the top, the forked bottom ends of the riser body 21 are respectively welded to the thickened body of the U-shaped edge of the bracket, and the upper end of the riser body 21 is connected to the top of the U-shaped two side plates of the bracket through a T-shaped rod 3.

[0015] The T-shaped rod 3 can be used to exhaust the U-shaped top of the bracket during casting, and to replenish the thin plate at the top of the U-shaped bracket during cooling, thereby preventing the formation of air holes or shrinkage holes there.

[0016] The second step is to make the shell by sprinkling sand. In this embodiment, high aluminum powder with a high melting point and a thermal conductivity lower than that of mullite powder is used to make the shell, so as to better keep the heat during pouring. The specific shell making process is as follows: water glass + high aluminum powder (particle size <30μm) is used to make a slurry, and high aluminum powders of different particle sizes are sequentially coated on the surface of the wax mold, wherein the surface sand particle size close to the surface of the wax mold is ≤50μm, and then the 2-3 layers of sand particle size is ≤120μm, and the last 4-7 layers of sand particle size are 300μm, 300μm, 1mm and 2mm; after sprinkling sand on the surface layer, it is immersed in ammonium chloride solution for curing for 20-30 minutes, and then air-dried, and after sprinkling sand on each of the next 2-7 layers, it is immersed in aluminum chloride solution for curing for 20-30 minutes, and each layer can be air-dried before sprinkling sand on the lower layer, and finally a sand shell thickness of 15-20mm is obtained.

[0017] The mold shell formed by sintering the melted wax needs to be placed in a sand box while hot and covered with sand for insulation. The specific casting process is as follows: the sintered mold shell is placed in a sand box, and the sand box is filled with quartz sand. While the gate is leaking out, it should be filled at least 10mm above the top of the mold shell riser. While the mold shell is just out of the furnace and is in a high temperature state, 1520±10℃ molten metal is poured into the mold shell through the gate. The pouring is required to be completed within 5 seconds, and the gate is covered with asbestos for insulation. After the molten metal is cooled and formed, the casting is removed by sand casting.

[0018] During casting cooling, a chiller can be placed at the bottom thickening of the U-shaped plate of the bracket and away from the riser to control the cooling of this area first. The cast casting needs to be heat treated to change the crystal state of the structure and eliminate stress at the same time.

[0019] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention, and for the convenience of describing the technical solution, the front, back, left, right, top, middle, bottom and other directions are set based on the drawings, rather than limiting the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. An investment casting process for a workpiece with large thickness differences at various parts, characterized in that: The following steps are involved: The first step is to make a wax mold set, which includes a vertical runner in the middle, brackets symmetrically welded to both sides of the vertical runner, and risers respectively arranged on the outside of the two brackets, the vertical runner includes two upper and lower feeding bags and a pouring cup on the top, wherein the two feeding bags are respectively welded to the upper and lower ear groups of the bracket, the riser includes an inverted "Y"-shaped riser body and a riser cup on the top, the bottom ends of the bifurcated riser bodies are respectively welded to the thickened bodies of the U-shaped edges of the bracket, and the upper ends of the riser bodies are connected to the top ends of the U-shaped two side plates of the bracket through T-shaped rods; The second step is to make the shell by pouring sand. Water glass + high aluminum powder (particle size <30μm) are used to make slurry. High aluminum powder of different particle sizes are sequentially coated on the surface of the wax mold. The surface sand particle size close to the surface of the wax mold is ≤50μm, then the 2-3 layers of sand particle size is ≤120μm, and the last 4-7 layers of sand particle size are 300μm, 300μm, 1mm and 2mm; after pouring sand on the surface layer, it is immersed in ammonium chloride solution for curing for 20-30 minutes, and then air-dried. After pouring sand on each of the next 2-7 layers, it is immersed in aluminum chloride solution for curing for 20-30 minutes. Similarly, each layer can be poured sand on the next layer only after air-drying, and finally the sand shell thickness is 15-20mm; The third step is to melt the wax and sinter. The wax mold is melted in a water bath and the sand shell is placed in a high-temperature furnace for sintering. The fourth step is casting. The sintered mold shell is placed in a sand box and filled with quartz sand. While the gate is leaking out, it should be filled at least 10mm above the top of the mold shell riser. While the mold shell is just out of the furnace and is in a high temperature state, 1520±10℃ molten metal is poured into the mold shell through the gate. The pouring is required to be completed within 5 seconds, and the gate is covered with asbestos for insulation. After the molten metal cools and takes shape, the casting is removed by sand casting.

2. The investment casting process for a workpiece with large thickness difference at each part according to claim 1, characterized in that: The height of the vertical runner is at least twice the height of the support, and the height of the vertical runner is greater than the riser.

3. The investment casting process for a workpiece with large thickness difference at each part according to claim 1, characterized in that: The cross-sectional area of ​​the pouring cup is larger than that of the feeding bag, and the volume of the feeding bag is larger than the sum of the volumes of two ears of the bracket connected to the feeding bag.

4. The investment casting process for a workpiece with large thickness difference at each part according to claim 1, characterized in that: The volume of the bifurcated body at the bottom end of the riser body is greater than the volume of the U-shaped edge thickening body of the bracket connected thereto.

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