阅读说明：本技术 一种近净成形空心金属结构件的方法 (Method for near-net forming of hollow metal structural part ) 是由 何新波 杨芳 张耕秋 邵艳茹 郭志猛 陈存广 张涛 于 2020-12-23 设计创作，主要内容包括：本发明提供了一种近净成形大尺寸空心金属结构件的方法,属于近净成形复杂形状材料领域,该方法包括：(1)打印中心轴；(2)打印结构件；(3)制备空心模具；(4)制备结构件模具；(5)装配模具；(6)制备浆料；(7)凝胶注模成形；(8)脱胶烧结等步骤,该方法工艺简单,可操作性强,且其制备的空心结构件的内壁光滑,质量良好。(The invention provides a method for near-net forming of a large-size hollow metal structural part, belonging to the field of near-net forming of a complex-shape material, and comprising the following steps: (1) a printing center shaft; (2) printing a structural part; (3) preparing a hollow mold; (4) preparing a structural part mould; (5) assembling a mould; (6) preparing slurry; (7) gel casting; (8) the method has the advantages of simple process, strong operability, smooth inner wall of the prepared hollow structural member and good quality.)

1. A method of near net forming a hollow metal structural member, comprising the steps of:

(1) printing a central shaft: designing and reducing the size proportion of the central shaft according to the shape and size requirements of the hollow metal structural part and the sintering shrinkage rate in the powder sintering process, and printing the corresponding central shaft by adopting a 3D printer;

(2) printing a structural part: designing and amplifying the size proportion of the structural part according to the shape and size requirements of the structural part and the sintering shrinkage rate in the powder sintering process, and printing the corresponding structural part by adopting a 3D printer;

(3) preparing a hollow mold: fixing the central shaft in the step (1), adding a curing agent accounting for 0.1-0.5 wt% of the weight of the silica gel and a thickening agent accounting for 0.5-3 wt% of the weight of the silica gel into the silica gel, uniformly stirring, pouring the silica gel along the central shaft, curing for 6-24h, and then removing the central shaft to obtain a hollow silica gel mold;

(4) preparing a structural part mould: performing reverse molding on the structural part in the step (2), adding 1-5 wt% of curing agent into silica gel, uniformly stirring, pouring into a reverse molding cavity, standing at room temperature for curing for 6-24h, and removing the mold to obtain a structural part mold;

(5) assembling a mold: filling the hollow silica gel mold in the step (3) with a granular substance, and fixing the granular substance at the corresponding position of the silica gel mold in the step (4) by using a hot melt glue gun to obtain a gel injection molding mold;

(6) preparing slurry: mixing metal powder, a gel system, oleic acid and a defoaming agent according to volume percentage, stirring uniformly, putting into a ball mill, mixing materials, wherein the ball-to-material ratio is 1:1-4:1, the ball milling speed is 100r/min-250r/min, and the ball milling time is 15-30min, so as to obtain suspension slurry;

(7) gel casting: pouring the suspension slurry obtained in the step (6) into the gel casting forming mold obtained in the step (5), curing for 0.5-3h at room temperature, then pouring out the granular substances, taking out the hollow silica gel mold, and then removing the mold to obtain a hollow metal structural part blank;

(8) degumming and sintering: and (4) carrying out corresponding degumming and sintering on the hollow metal structural member blank in the step (7), wherein the degumming temperature is 300-plus-one temperature of 600 ℃, carrying out heat preservation for 2-4h, then carrying out sintering at 800-plus-one temperature of 1350 ℃, and carrying out heat preservation for 2-5h to obtain the near-net-shape hollow metal structural member.

2. A method of near net shape forming a hollow metal structural member according to claim 1, wherein: the material of the central shaft and the structural part in the steps (1) and (2) is one or more of polylactic acid (PLA), acrylonitrile-butadiene-styrene copolymer (ABS), Polycarbonate (PC), photosensitive resin and nylon.

3. A method of near net shape forming a hollow metal structural member according to claim 1, wherein: the thickness of the hollow silica gel mold in the step (3) is 1-5 mm.

4. A method of near net shape forming a hollow metal structural member according to claim 1, wherein: the mass of the curing agent in the step (3) is 1-5% of that of the silica gel.

5. A method of near net shape forming a hollow metal structural member according to claim 1, wherein: the granular material in the step (5) comprises one or more of flour, salt and sand.

6. A method of near net shape forming a hollow metal structural member according to claim 5, wherein: the particle size of the particulate matter is 40 μm to 500 μm.

7. A method of near net shape forming a hollow metal structural member according to claim 1, wherein: the metal powder in the step (6) is one or more of stainless steel, cobalt-chromium-molybdenum alloy, copper and copper alloy or titanium and titanium alloy powder.

8. A method of near net shape forming a hollow metal structural member according to claim 7, wherein: the powder particle size of the metal powder is 5-50 μm.

9. A method of near net shape forming a hollow metal structural member according to claim 1, wherein: the gel system in the step (6) is one of a water-based or non-water-based gel system, wherein the water-based gel system is one of an acrylate system or an acrylamide system.

10. A method of near net shape forming a hollow metal structural member according to claim 1, wherein: the metal powder in the step (6) accounts for 50-65 vol% of the total volume of the metal powder, the gel system, the oleic acid and the defoaming agent, the oleic acid accounts for 0.02-0.1 vol% of the total volume of the metal powder, the gel system, the oleic acid and the defoaming agent, the defoaming agent accounts for 0.01-0.05 vol% of the total volume of the metal powder, the gel system, the oleic acid and the defoaming agent, and the balance is the gel system.

Technical Field

The invention belongs to the technical field of material forming, and particularly relates to a method for forming a hollow metal structural part near net shape, and further relates to the metal structural part obtained by the method.

Background

The gel casting technology skillfully combines the traditional wet colloidal forming process and high polymer chemistry, and introduces a method for polymerizing high polymer monomers into the powder forming technology. The suspension with low viscosity and high solid phase volume fraction is prepared to realize a uniform blank with high strength and high density, and the blank after demoulding is subjected to degumming and sintering to remove the high molecular adhesive, so that the required ceramic or metal part is finally obtained.

Generally, parts with complex shapes and large sizes can be prepared by utilizing a gel injection molding technology, but for preparing hollow metal structural parts, the problems of single shape, poor demolding, easy generation of cracks and the like are often existed. At present, only hollow metal structural parts with simple shapes can be prepared, generally, in the gel casting forming process, a solid rod is fixed at the center of a mould, then suspension slurry is poured for forming, and after the slurry is solidified, the middle solid rod is separated to obtain the hollow structural part. However, the demoulding process is not good, and the surface quality of the inner wall is not high and scratches are more due to the fact that the surface friction force between the rod and the blank is larger because the strength of the blank is not high in the rod demoulding process; meanwhile, cracks are easily generated on the inner wall of the blank, and the quality of the structural part is poor. In addition, the internal structure of the hollow metal structural member is simple, so that a complex hollow structure cannot be formed, and the application of the gel-casting titanium alloy is limited.

CN101722306A discloses a near-net forming method of porous metal parts, comprising the steps of: firstly, designing a three-dimensional CAD model of a part, storing the three-dimensional CAD model as an STL file, and conveying the STL file to SLM rapid forming equipment; secondly, vacuumizing the equipment and introducing protective gas; thirdly, the powder feeding mechanism spreads a layer of metal powder with the thickness of 0.05-0.15 mm and the particle size of 10-100 mu m on the metal substrate; fourthly, scanning the outer contour of the slice boundary by adopting a laser beam with the laser power of more than or equal to 100W to melt the outer contour; fifthly, repeating the steps from the third step to the fourth step to finish the straight forming; sixthly, putting the shell of the formed part and the powder loaded in the shell into a high-temperature sintering furnace to be sintered and formed. Although this patent application achieves near net shape forming of complex structural metal structures, the process is cumbersome, requires expensive equipment, and is a complex process.

Therefore, it is necessary to provide a method for preparing a hollow metal structural member with smooth inner wall, good quality and complex structure.

Disclosure of Invention

The invention aims to provide a method for forming a hollow metal structural part by near net shape, which combines a 3D printing technology with a gel casting forming technology, prints a central shaft with a complex structure by the 3D printing technology, obtains a central shaft thin die by reverse die, and adds granular substances into the thin die, so that the thin die can play a role of fixing and supporting in the gel casting forming process, the granular substances are easy to pour out after slurry is solidified and formed, the demoulding is convenient, the problems of cracks, defects and the like caused by demoulding are avoided, and the hollow metal structural part with a complex internal structure can be obtained. The hollow metal structural member prepared by the method has smooth inner wall, good quality, flexible shape design, simple process and strong operability.

The technical scheme of the invention is as follows.

A method for near-net forming a hollow metal structural member is prepared by the following steps:

(1) printing a central shaft: designing and reducing the size proportion of the central shaft according to the shape and size requirements of the hollow metal structural part and the sintering shrinkage rate in the powder sintering process, and printing the corresponding central shaft by adopting a 3D printer;

(2) printing a structural part: designing and amplifying the size proportion of the structural part according to the shape and size requirements of the structural part and the sintering shrinkage rate in the powder sintering process, and printing the corresponding structural part by adopting a 3D printer;

(3) preparing a hollow mold: fixing the central shaft in the step (1), adding a curing agent accounting for 0.1-0.5 wt% of the weight of the silica gel and a thickening agent accounting for 0.5-3 wt% of the weight of the silica gel into the silica gel, uniformly stirring, pouring the silica gel along the central shaft, curing for 6-24h, and then removing the central shaft to obtain a hollow silica gel mold;

(4) preparing a structural part mould: performing reverse molding on the structural part in the step (2), adding 1-5 wt% of curing agent into silica gel, uniformly stirring, pouring into a reverse molding cavity, standing at room temperature for curing for 6-24h, and removing the mold to obtain a structural part mold;

(5) assembling a mold: filling the hollow silica gel mold in the step (3) with a granular substance, and fixing the granular substance at the corresponding position of the silica gel mold in the step (4) by using a hot melt glue gun to obtain a gel injection molding mold;

(6) preparing slurry: mixing metal powder, a gel system, oleic acid and a defoaming agent according to volume percentage, stirring uniformly, putting into a ball mill, mixing materials, wherein the ball-to-material ratio is 1:1-4:1, the ball milling speed is 100r/min-250r/min, and the ball milling time is 15-30min, so as to obtain suspension slurry;

(7) gel casting: pouring the suspension slurry obtained in the step (6) into the gel casting forming mold obtained in the step (5), curing for 0.5-3h at room temperature, then pouring out the granular substances, taking out the hollow silica gel mold, and then removing the mold to obtain a hollow metal structural part blank;

(8) degumming and sintering: and (4) carrying out corresponding degumming and sintering on the hollow metal structural member blank in the step (7), wherein the degumming temperature is 300-plus-one temperature of 600 ℃, carrying out heat preservation for 2-4h, then carrying out sintering at 800-plus-one temperature of 1350 ℃, and carrying out heat preservation for 2-5h to obtain the near-net-shape hollow metal structural member.

The method for preparing the large-size hollow metal structural part combines the 3D printing technology and the gel casting forming technology, and prepares the large-size hollow metal structural part with a complex structure. The matched central shaft is printed out by adopting a 3D printing technology according to the shape requirement of the hollow structural part, the matched thin sheath is prepared, and the granular substances which are easy to pour out are filled in the thin sheath, so that the thin sheath can play a role of fixed support in the gel injection molding process, the granular substances are easy to pour out after the slurry is solidified and formed, the demolding is convenient, and the problems of cracks and the like caused by the demolding are avoided. The hollow structural member prepared by the method has smooth inner wall, good quality, simple process and strong operability, and in addition, the method can lead designers to flexibly design hollow structural members with various complex shapes, thereby widening the application range of the method.

Further, the material of the central shaft and the structural member in the step (1) and the step (2) is one or more of polylactic acid (PLA), acrylonitrile-butadiene-styrene copolymer (ABS), Polycarbonate (PC), photosensitive resin and nylon.

Further, the thickness of the hollow silica gel mold in the step (3) is 1-5 mm.

Further, the mass of the curing agent in the step (3) is 1-5% of the mass of the silica gel.

Further, the particulate matter in step (5) comprises one or more of flour, salt and sand.

Further, the particle size of the particulate matter is 40 μm to 500 μm.

Further, the metal powder in the step (6) is one or more of stainless steel, cobalt-chromium-molybdenum alloy, copper and copper alloy or titanium and titanium alloy powder.

Further, the powder particle size of the metal powder is 5 to 50 μm.

Further, the gel system in step (6) is one of a water-based or non-water-based gel system, wherein the water-based gel system is one of an acrylate system or an acrylamide system.

Further, the metal powder in the step (6) accounts for 50-65 vol% of the total volume of the metal powder, the gel system, the oleic acid and the defoaming agent, the oleic acid accounts for 0.02-0.1 vol% of the total volume of the metal powder, the gel system, the oleic acid and the defoaming agent, the defoaming agent accounts for 0.01-0.05 vol% of the total volume of the metal powder, the gel system, the oleic acid and the defoaming agent, and the balance is the gel system.

In addition, the invention also provides a large-size hollow metal structural part prepared by the method.

Compared with the prior art, the invention has the beneficial effects that:

1. the method combines the 3D printing technology and the gel casting forming technology, has simple process and strong operability, and can prepare structural parts with complicated shapes, sizes and internal structures.

2. According to the invention, the central shaft thin die with a complex shape structure can be obtained by performing reverse die on the central shaft for 3D printing, and then the granular substance is added, so that the central shaft thin die can play a role of fixing and supporting in the gel injection molding process, and the granular substance is easy to pour out after the slurry is cured and formed, thereby being convenient for demolding, not damaging the inner wall structure and the like.

3. The method avoids the problems of inner wall cracks, scratches and the like generated in the demoulding process of the hollow metal structural part in the traditional process, and is beneficial to obtaining the hollow metal structural part with excellent internal surface quality.

4. The hollow metal structural part obtained by the method has smooth inner wall and good quality, and the shape of the hollow metal structural part can be complicated and changeable.

Detailed Description

The following further illustrates embodiments of the invention:

preparation examples

Example 1:

a method for near-net forming of a hollow metal structural member comprises the following specific steps:

step (1): printing a polylactic acid (PLA) central shaft and a structural member prototype with complex shapes by using a 3D printer;

step (2): adding 0.2g of curing agent (hydroxyethyl methacrylate and N-dimethylaniline system) and 0.5g of thickening agent (hydroxymethyl cellulose) into 100g of silica gel, uniformly stirring, pouring the silica gel along the central shaft of printed polylactic acid (PLA), curing for 6 hours, and removing the central shaft to obtain a hollow silica gel mold with the thickness of 2 mm;

and (3): the method comprises the following steps of (1) carrying out reverse molding on a polylactic acid (PLA) structural part prototype, adding 3g of curing agent (hydroxyethyl methacrylate and N-dimethylaniline system) into 100g of silica gel, uniformly stirring, pouring into a reverse molding cavity, standing at room temperature for curing for 14h, and then removing the mold to obtain a silica gel mold of the structural part;

and (4): filling salt with the particle size of 250 mu m into a hollow mold, and fixing the hollow mold at a corresponding position by a hot melt adhesive gun to obtain a gel injection molding mold;

and (5): mixing 65ml of titanium alloy powder with the particle size of 25 mu m, 0.1ml of oleic acid, 0.02ml of defoaming agent (isooctanol) and 34.88ml of tolyl gel system, uniformly stirring, putting into a planetary ball mill, mixing, wherein the ball-to-material ratio is 1:1, the ball-milling speed is 100r/min, and the ball-milling time is 15min to obtain suspension slurry;

and (6): pouring the suspension slurry into a gel injection molding forming die, curing for 0.5h at room temperature, then pouring out salt particles, taking out the hollow silica gel die, and removing the die to obtain a hollow metal structural part blank;

and (7): and (3) insulating the hollow metal structural member blank at 300 ℃ for 4h, and then insulating at 1350 ℃ for 2h to obtain the near-net-shape hollow titanium alloy structural member P1.

Example 2:

preparation process of embodiment of the invention embodiment 1 is the same, and the difference is that the stainless steel powder in the step (5) is changed into cobalt-chromium-molybdenum alloy powder to obtain a near-net-shape hollow cobalt-chromium-molybdenum alloy structural member P2.

Example 3:

inventive example preparation process inventive example 1 was the same except that the stainless steel powder in step (5) was changed to copper powder to obtain a near net shape hollow copper structural member P3.

Example 4:

preparation process of embodiment of the invention the preparation process of embodiment 1 is the same, except that the curing time in step (2) is changed to 15h, and a near-net-shape hollow stainless steel structural member P4 is obtained.

Example 5

Preparation process of embodiment of the invention the preparation process of embodiment 1 is the same, and the difference is that the ball-to-material ratio in step (4) is changed to 2:1, the ball milling speed is changed to 175r/min, and the ball milling time is changed to 22.5min, so that the near-net-shape hollow stainless steel structural member P5 is obtained.

Examples of Performance

The hollow structural members P1-P5 prepared in inventive examples 1-5 and a similar hollow structural member P6 commercially available were subjected to performance tests in accordance with the following methods, and specific results are shown in Table 1 below.

Inner surface roughness: testing according to the testing method specified in GB/T13288;

tensile strength and yield strength: the test was carried out according to the test method specified in ASTM E381-2001.

Table 1 results of performance testing

	Inner surface roughness (mum)	Yield strength (MPa)	Tensile strength (MPa)
				P1	2.4	932	1056
P2	2.1	935	1078
				P3	2.7	915	1025
P4	2.5	943	1136
				P5	2.8	946	1034
P6	6.5	823	875

The above table shows that the matched central shaft is printed out according to the shape requirement of the hollow structural member by adopting a 3D printing technology, then the matched mold is prepared, the granular substance which is easy to pour out is filled in the mold, then the slurry is prepared for gel injection molding, finally the granular substance is poured out, the mold is taken out and degummed and sintered, the mold can play a role of fixing and supporting in the gel injection molding process, the granular substance is easy to pour out after the slurry is solidified and molded, the demolding is convenient, the problems of cracks, defects and the like caused by demolding are avoided, and meanwhile, the hollow structural member prepared by the method also has better mechanical property.

Variations and modifications to the above-described embodiments may occur to those skilled in the art, which fall within the scope and spirit of the above description. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and variations of the present invention should fall within the scope of the claims of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.