阅读说明：本技术 一种基于超高熔点合金的粉末冶金装置及冶金方法 (Powder metallurgy device and metallurgy method based on ultrahigh-melting-point alloy ) 是由 张航 孙啸宇 蔡江龙 耿佳乐 李涤尘 于 2020-12-29 设计创作，主要内容包括：本发明公开了一种基于超高熔点合金的粉末冶金装置及冶金方法,所述装置包括真空室,所述真空室包括底座和壳体,真空室中设置有隔热板,所述隔热板上设置有自内向外依次布置的模具壳、隔热层和坩埚,所述坩埚外绕设有感应线圈,感应线圈的两端伸出壳体,所述坩埚上个盖合有坩埚盖。三层设计使坩埚可以不受自身熔点的限制,而能生产高于自身熔点的金属制件。并且钨粉或碳化钛粉末层的加入,可以提高坩埚的保温性能,在加热熔化金属粉末时可以减少热量的散失,以利于炉料温度的提升,有利于炉内金属粉末的熔化,提高了效率,并且降低了能耗；还使得坩埚因为不用直接接触超高温的钨模具壳而能忍受高于自身熔点的温度。(The invention discloses a powder metallurgy device and a metallurgy method based on ultrahigh melting point alloy, wherein the device comprises a vacuum chamber, the vacuum chamber comprises a base and a shell, a heat insulation plate is arranged in the vacuum chamber, a die shell, a heat insulation layer and a crucible are sequentially arranged on the heat insulation plate from inside to outside, an induction coil is wound outside the crucible, two ends of the induction coil extend out of the shell, and a crucible cover covers the crucible. The three-layer design enables the crucible not to be limited by the self-melting point, and metal parts higher than the self-melting point can be produced. The addition of the tungsten powder or titanium carbide powder layer can improve the heat preservation performance of the crucible, reduce the heat loss when the metal powder is heated and melted, facilitate the improvement of the temperature of furnace charge, facilitate the melting of the metal powder in the furnace, improve the efficiency and reduce the energy consumption; it also allows the crucible to tolerate temperatures above its own melting point because it does not directly contact the ultra-high temperature tungsten die shell.)

1. The utility model provides a powder metallurgy device based on super high melting point alloy, its characterized in that, includes real empty room (3), real empty room (3) are provided with heat insulating board (12) including base (13) and casing (15) in real empty room (3), be provided with mould shell (7), insulating layer (8) and crucible (9) that from inside to outside arranged in proper order on heat insulating board (12), crucible (9) are outer around being equipped with induction coil (10), and casing (15) are stretched out at the both ends of induction coil (10), crucible (9) last lid has closed crucible cover (6).

2. The ultra-high melting point alloy-based powder metallurgy device according to claim 1, wherein the thermal insulation layer (8) is composed of tungsten powder or titanium carbide powder.

3. The ultra-high melting point alloy-based powder metallurgy device according to claim 1, wherein the cross-sectional shape of the induction coil (10) is square, and a hollow cooling channel is provided in the induction coil (10).

4. The ultra-high melting point alloy-based powder metallurgy device according to claim 1, wherein the heat insulating plate (12) is a zirconia fiber sheet.

5. The ultra-high melting point alloy-based powder metallurgy device according to claim 1, wherein a second seal ring (2) is embedded between the housing (15) and the base (13); and a first sealing ring (11) is arranged at the joint of the two ends of the induction coil (10) and the shell (15).

6. The ultra-high melting point alloy-based powder metallurgy device according to claim 1, wherein the crucible cover (6) comprises a first cover plate and a second cover plate which are fixedly connected, the first cover plate at the lower layer is made of tungsten, the second cover plate at the upper layer is made of graphite felt which is overlapped, and when the crucible cover (6) is covered on the crucible (9), the first cover plate covers the mold shell (7) and is not contacted with the heat insulation layer (8) and the crucible (9).

7. The ultra-high melting point alloy-based powder metallurgy device according to claim 1, wherein a galvanic thermometer (5) is installed in the vacuum chamber (3), two ends of the galvanic thermometer (5) are respectively installed on the mold shell (7) and the shell (15), a connecting wire passes through the crucible cover (6), and the temperature data of the mold shell (7) is displayed on an external display in real time.

8. The ultra-high melting point alloy-based powder metallurgy device according to claim 1, wherein the material of the induction coil (10) is red copper.

9. A powder metallurgy method based on an ultrahigh melting point alloy is characterized by comprising the following steps:

step 1, fixing a wound induction coil (10) in a vacuum chamber (3), enabling two joints of the induction coil (10) to penetrate through a shell (15), and placing a crucible (9) in the induction coil (10);

step 2, filling tungsten powder or titanium carbide powder into a crucible (9) and paving the tungsten powder or titanium carbide powder, then putting a die tungsten shell (7) into the crucible (9), and filling tungsten powder or titanium carbide powder into a gap between the crucible (9) and the die tungsten shell (7) to form a heat insulation layer (8);

step 3, pouring alloy powder into the cavity of the die shell (7);

step 4, covering a crucible cover (6);

step 5, closing the vacuum chamber (3), and vacuumizing the vacuum chamber (3) through vacuumizing equipment;

step 6, turning on the induction heating equipment to electrify the induction coil (10) and supply water;

step 7, measuring the temperature of the alloy powder in the die shell (7) by using a galvanic couple thermodetector (5) placed on the die shell (7), and adjusting the heating power of the induction heating equipment at any time;

step 8, obtaining alloy liquid after the alloy powder is completely melted, closing the induction heating equipment, and naturally cooling the alloy liquid in the die shell (7) to obtain a workpiece (14);

and 9, opening the vacuum chamber (3), taking the workpiece (14) and the mold shell (7) out together, and then taking the workpiece (14) out of the mold shell (7).

10. The ultra-high melting point alloy-based powder metallurgy method according to claim 9, wherein in the step 1, the heat-insulating plate (12) is placed on the base (13) before being placed in the crucible (9).

Technical Field

The invention belongs to the technical field of powder metallurgy, and particularly relates to a powder metallurgy device and a powder metallurgy method based on ultrahigh-melting-point alloy.

Background

With the continuous progress of high-end equipment manufacturing technology, advanced highly complex and precise thermal and power machinery puts higher requirements on the integral manufacture of high-temperature-resistant parts with complex structures. Particularly in the field of national defense and military industry, a great number of key parts need to work under extremely high temperature conditions for a long time. Under such conditions, conventional materials and manufacturing processes are not applicable, and new materials and new material processing techniques that can be used in extremely harsh environments for a long time are urgently needed.

The existing additive manufacturing methods that melt metal powder by laser have matured over time. However, laser additive manufacturing has a number of problems in practical use:

1. the laser additive manufacturing technique is to laser melt a very small powder area so that the very small portion of metal powder can be rapidly melted and solidified, and then gradually process a complete part. The efficiency of processing articles using this method is very low because it requires a point to accumulate the finished product and requires dusting each layer processed, greatly increasing the processing time. The inefficiency of this method is particularly significant when producing larger volume articles.

2. In the laser additive manufacturing technology, because laser forming has the characteristics of extremely high heating and cooling speeds, in the heating process, different parts of a workpiece have different temperatures and are not melted synchronously, and in the cooling process, solidification is not synchronous, so that great residual stress can be generated. Particularly for a large-volume part, the residual stress is accumulated continuously, the existence of the stress is likely to cause the part to have defects such as cracks, warping and the like, and particularly, when the large part is produced, the stress is accumulated continuously, so that the waste part is more likely to be generated.

3. The laser additive manufacturing technology has very high requirements on the granularity of powder and the like, and the granularity of the alloy powder is often screened for a long time after the strict screening is needed, so that the time and the cost for producing the parts are increased due to the powder screening process.

The limitations of the laser additive manufacturing technology in producing large pieces are very obvious for the three reasons.

In addition, the existing vacuum induction heating furnace is mature, and enterprises generally add raw material metal into a crucible, heat the crucible through an induction coil to melt the raw material metal, and then tilt the crucible in a vacuum chamber by operating a hydraulic system to pour a workpiece. The melting point of a crucible of a common vacuum induction heating furnace is only about 2000 ℃, so that metal with the melting point of more than 2000 ℃ cannot be smelted.

Disclosure of Invention

The invention provides a powder metallurgy device and a metallurgy method based on an ultrahigh melting point alloy, which improve the production efficiency.

In order to achieve the purpose, the powder metallurgy device based on the ultrahigh melting point alloy comprises a vacuum chamber, wherein the vacuum chamber comprises a base and a shell, a heat insulation plate is arranged in the vacuum chamber, a mold shell, a heat insulation layer and a crucible are sequentially arranged on the heat insulation plate from inside to outside, an induction coil is wound outside the crucible, two ends of the induction coil extend out of the shell, and a crucible cover covers the crucible.

Further, the heat insulation layer is composed of tungsten powder or titanium carbide powder.

Furthermore, the cross section of the induction coil is square, and a hollow cooling channel is arranged in the induction coil.

Further, the heat insulation plate is a zirconia fiber plate.

Further, a second sealing ring is embedded between the shell and the base; the joint of the two ends of the induction coil and the shell is provided with a first sealing ring.

Further, the crucible cover comprises a first cover plate and a second cover plate which are fixedly connected, the first cover plate on the lower layer is made of tungsten, the second cover plate on the upper layer is made of graphite felt in a stacked mode, and when the crucible cover covers the crucible, the first cover plate covers the mold shell and does not contact the heat insulation layer and the crucible.

Furthermore, a galvanic couple thermodetector is arranged in the vacuum chamber, two ends of the galvanic couple thermodetector are respectively arranged on the die shell and the shell, a connecting wire penetrates through the crucible cover, and temperature data of the die shell is displayed on an external display in real time.

Furthermore, the induction coil material is red copper.

A powder metallurgy method based on ultra-high melting point alloy comprises the following steps:

step 1, fixing a wound induction coil in a vacuum chamber, enabling two joints of the induction coil to penetrate out of a shell, and placing a crucible in the induction coil;

step 2, filling tungsten powder or titanium carbide powder into the crucible and paving the crucible, then putting a mold tungsten shell into the crucible, and filling tungsten powder or titanium carbide powder into a gap between the crucible and the mold tungsten shell to form a heat insulation layer;

step 3, pouring alloy powder into the cavity of the die shell;

step 4, covering a crucible cover;

step 5, closing the vacuum chamber, and vacuumizing the vacuum chamber through vacuumizing equipment;

step 6, turning on the induction heating equipment to electrify the induction coil and supply water;

step 7, measuring the temperature of the alloy powder in the die shell by using a galvanic couple thermodetector placed on the die shell, and adjusting the heating power of the induction heating equipment at any time;

step 8, obtaining alloy liquid after the alloy powder is completely melted, closing the induction heating equipment, and naturally cooling the alloy liquid in the die shell to obtain a finished piece;

and 9, opening the vacuum chamber, taking the workpiece and the mold shell out together, and then taking the workpiece out of the mold shell.

Further, in step 1, a thermal shield is placed on the base before the crucible is placed.

Compared with the prior art, the invention has at least the following beneficial technical effects:

the heated part of the invention has three layers, and the innermost layer is a tungsten mould shell processed by laser material increase manufacturing; the middle heat insulation layer is tungsten powder or titanium carbide powder with low heat conductivity coefficient and high melting point; the outermost layer is a non-conductive ceramic crucible, and the three-layer design ensures that the crucible can not be limited by the self melting point and can produce metal parts higher than the self melting point. The addition of the tungsten powder or titanium carbide powder layer can improve the heat preservation performance of the crucible, reduce the heat loss when the metal powder is heated and melted, facilitate the improvement of the temperature of furnace charge, facilitate the melting of the metal powder in the furnace, improve the efficiency and reduce the energy consumption; it also allows the crucible to tolerate temperatures above its own melting point because it does not directly contact the ultra-high temperature tungsten die shell.

Further, the heat insulation plate is a zirconium oxide fiber plate; the diameter of the fiber is the same as the inner diameter of the vacuum chamber, the fiber is contacted with the bottom surface and the side wall of the vacuum chamber and supports the whole crucible, so that the fiber is not directly contacted with the bottom and the side surface of the vacuum chamber, and the fiber can better preserve and insulate heat by utilizing the characteristics of high temperature resistance and low thermal conductivity, so that the vacuum chamber cannot be damaged due to overhigh temperature.

Further, a second sealing ring is embedded between the shell and the base; and first sealing rings are arranged at the joints of the two ends of the induction coil and the shell.

Further, crucible lid is including fixed connection's first apron and second apron, and the first apron of lower floor is made by tungsten, and the second apron material on upper strata adopts graphite felt stack to form, and when crucible lid closed on the crucible, first apron covered the mould shell and did not contact insulating layer and crucible, adopts two-layer structural design mainly because graphite felt can work at the environment more than 3000 ℃, and thermal insulation performance is good, but carbon fiber probably falls out in the use, pollutes the finished piece. Therefore, the lower layer is made of tungsten materials, so that carbon fibers can be prevented from falling into a workpiece, and humps generated by stirring during induction heating can be prevented from causing molten metal to contact graphite felt to generate impurities.

Further, a galvanic couple thermodetector is mounted on the mold shell, two ends of the galvanic couple thermodetector are respectively mounted on the mold shell and the shell, a connecting wire penetrates through the crucible cover, and temperature data of the mold shell is displayed on an external display in real time; the parameters of the induction heating equipment can be conveniently adjusted by an operator according to the temperature, so that the induction heating temperature is higher than the melting point of the workpiece and lower than the melting point of tungsten. The reason why the thermocouple of the thermocouple thermometer is fixed on the die shell and is not inserted into the molten alloy is that the tungsten has good thermal conductivity, and the temperature of the tungsten shell can well reflect the temperature of the molten alloy, so that the structure is simplified.

The method of the invention does not apply the original processing principle of laser additive manufacturing, but adopts the method of induction coil heating to directly heat the furnace charge metal powder added in the die cavity to melt and cool the furnace charge metal powder, and can greatly improve the production efficiency by controlling the parameters of the induction heating equipment, thereby greatly improving the efficiency of producing the products with larger volume. In addition, the alloy powder is directly melted by the coil heating, so that the requirement on the granularity of the alloy powder is not high, the complicated powder screening work of laser additive manufacturing is omitted, and the production efficiency is greatly improved.

The spiral induction coil is adopted to heat and melt metal, and the electric field in the induction coil is uniform, and the temperature difference is not particularly large during cooling, so that the residual stress of the part produced by adopting the method is much smaller than that of the part produced by laser additive manufacturing, and the qualification rate of the part is much higher.

The invention adopts the induction heating principle, has no requirement on the granularity of the powder, only has the requirement on the purity of the alloy, and only needs to screen out impurities in the alloy powder before production to ensure the purity, thereby greatly improving the production efficiency of the finished piece.

Drawings

FIG. 1 is a three-dimensional view of an exemplary article to be processed;

FIG. 2 is a two-dimensional view of an exemplary part to be processed;

FIG. 3 is a two-dimensional view of the overall structure of the designed induction heating apparatus;

FIG. 4 is a three-dimensional view of the overall structure of the designed induction heating apparatus;

fig. 5 is a three-dimensional sectional view showing the overall structure of the designed induction heating apparatus.

In the drawings: 1. a screw; 2. a second seal ring; 3. a vacuum chamber; 4. a vacuum equipment connection port; 5. a galvanic couple thermodetector; 6. a crucible cover; 7. a tungsten shell of the mold; 8. a thermal insulation layer; 9. a crucible; 10. an induction coil; 11. a first seal ring; 12. a heat insulation plate; 13. base, 14, finished piece, 15, casing.

Detailed Description

In order to make the objects and technical solutions of the present invention clearer and easier to understand. The present invention will be described in further detail with reference to the following drawings and examples, wherein the specific examples are provided for illustrative purposes only and are not intended to limit the present invention.

In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are used only for convenience in describing the present invention and for simplicity in description, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention. Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless otherwise specified. In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

Referring to fig. 3 to 5, the powder metallurgy device based on the ultra-high melting point alloy comprises a base 13, a heat insulation plate 12 and a shell 15, wherein the shell 15 is fixed on the base 13 through eight uniformly arranged screws 1 to form a vacuum chamber 3, a second sealing ring 2 is embedded between the shell 15 and the base 13, and the screws 1 adopt hexagon socket head cap screws M14 x 40.

The vacuum chamber 3 is internally provided with a heat insulation plate 12, a couple thermodetector 5, a crucible cover 6, a mold shell 7, a heat insulation layer 8, a crucible 9 and an induction coil 10, the heat insulation plate 12 is arranged at the bottom of the vacuum chamber 3, the crucible 9 is arranged on the heat insulation plate 12, the induction coil 10 is wound outside the crucible 9, two ends of the induction coil 10 extend out of a shell 15, and a first sealing ring 11 is arranged at the joint of two ends of the induction coil 10 and the shell 15. The crucible 9 is a ceramic crucible; the induction coil 10 is spirally wound outside the crucible 9, the coil is made of red copper, the section of the coil is in a square shape of 20mm multiplied by 20mm, and a hollow cooling water channel of 10mm multiplied by 10mm is arranged in the middle of the coil.

The thermal insulation board 12 is a plate of zirconia fiber, the diameter of which is the same as the inner diameter of the vacuum chamber 3, and the thermal insulation board contacts with the bottom surface and the side wall of the vacuum chamber 3 and supports the whole crucible 9, so that the thermal insulation board does not directly contact with the bottom and the side surface of the vacuum chamber 3.

A tungsten mold shell 7 is arranged in the crucible 9, a heat insulation layer 8 is arranged on the crucible 9 and the mold shell 7, and the heat insulation layer 8 is composed of tungsten powder or titanium carbide powder. Since tungsten is in direct contact with molten metal, the temperature is very high and cannot be in direct contact with the outer crucible, tungsten powder or titanium carbide powder with a very low thermal conductivity needs to be uniformly filled between the crucible 9 and the mold shell 7 to form the heat insulation layer 8. The tungsten powder or titanium carbide powder is used for screening out impurities in advance, so that the purity is ensured, and impurities such as gas generated at high temperature are prevented.

The crucible cover 6 is composed of a first cover plate and a second cover plate which are fixedly connected, the first cover plate on the lower layer is made of tungsten and has a size which is just right to cover the mold shell 7 and is not contacted with tungsten powder or titanium carbide powder and a ceramic shell of the crucible 9, the second cover plate on the upper layer is made of graphite felt which is overlapped, and the second cover plate on the upper layer has a size which is right to cover the whole crucible 9. The two-layer structure is designed mainly because the graphite felt can work in an environment with the temperature of more than 3000 ℃ and has good heat preservation performance, but carbon fibers can fall out in the using process to pollute a workpiece. Therefore, the lower layer is made of tungsten materials, so that carbon fibers can be prevented from falling into a workpiece, and humps generated by stirring during induction heating can be prevented from causing molten metal to contact graphite felt to generate impurities.

The top of the shell 15 is provided with a hole with a diameter of 20 as a vacuum equipment connecting port 4 for connecting external vacuum equipment. Two ends of a galvanic couple thermodetector 5 are respectively arranged on a mould shell 7 and an external shell 15, a connecting wire penetrates through a crucible cover 6 made of graphite felt, temperature data of the mould shell 7 is displayed on an external display in real time, and an operator can conveniently adjust parameters of induction heating equipment according to the temperature, so that the induction heating temperature is higher than the melting point of a workpiece and lower than the melting point of tungsten.

The thermocouple of the galvanic thermometer 5 is made of tungsten and needs to withstand extremely high temperatures because it directly contacts the mold shell 7.

The reason why the thermocouple of the thermocouple thermometer 5 is fixed to the mold case 7 without being inserted into the molten alloy is that the tungsten has good thermal conductivity, and the temperature of the tungsten case can well reflect the temperature of the molten alloy, simplifying the structure. Referring to fig. 1 and 2, a powder metallurgy method based on ultra-high melting point alloy, taking as an example the fabrication of a composite of a hemisphere with a radius of 50mm and a cylinder with a height of 150mm with the same radius of 50mm, comprises the following steps:

step 1, placing a heat insulation plate 12 at the center of a base 13, measuring whether the heat insulation plate is horizontal by using a level meter, fixedly placing two joints of an induction coil of induction heating equipment through two through holes in a vacuum chamber 3, sealing by using a first sealing ring 11, and finally placing a crucible 9 at the center of the coil on the heat insulation plate 12;

step 2, pouring tungsten powder or titanium carbide powder with a designed height into a crucible 9, paving the tungsten powder or titanium carbide powder, then placing the tungsten powder or titanium carbide powder into a die tungsten shell 7 at the center, and then filling tungsten powder or titanium carbide powder into a gap between the crucible 9 and the die tungsten shell 7;

step 3, pouring sufficient alloy powder into the cavity of the die shell 7;

step 4, covering a crucible cover 6;

step 5, closing the vacuum chamber 3, and vacuumizing the vacuum chamber 3 through an external vacuumizing device;

step 6, after the vacuum chamber 3 is vacuumized by the vacuum pump, opening the induction heating equipment to electrify the induction coil 10 and electrifying water;

and 7, measuring the temperature of the alloy by a galvanic couple thermodetector 5 arranged on the die shell 7, and adjusting the heating power of the induction heating equipment at any time.

And 8, after the temperature of the alloy powder exceeds the set melting point time, the alloy is considered to be completely melted to obtain alloy liquid, and the induction heating equipment is closed, so that the alloy liquid in the die shell 7 can be slowly cooled, and the workpiece 14 is obtained.

And 9, after the workpiece 14 is cooled, opening the vacuum chamber 3, taking out the workpiece 14 together with the mold shell 7, sticking the metal workpiece on the mold shell 7 after cooling, and cutting the workpiece by using a wire cutting device to finally obtain the workpiece. The tungsten shell 7 of the die needs to be additionally processed into a cavity by adopting a laser additive manufacturing method so as to meet the requirements of workpieces in different shapes.

The alloy powder used in the step 3 is screened in advance, so that impurities generated in the melting process are prevented, and the purity is ensured.

The alloy powder added in the step 3 is calculated to ensure sufficient quantity, which can properly exceed the required quantity, and is finally removed by wire cutting.

In step 6, an induction heating device placed outside is adopted;

in the step 8, after the induction heating equipment is closed, the workpiece is cooled slowly due to the good heat insulation effect of the structure, so that the quality of the workpiece is improved.

The structure design of the crucible and the mould with three layers is adopted: the outermost layer is a non-conductive crucible 9, the middle layer is tungsten powder or titanium carbide powder with poor heat conductivity, the innermost layer is a tungsten mold shell 7 capable of bearing ultrahigh temperature, and the innermost layer is a replaceable mold shell to meet the requirements of workpieces in different shapes. The structure can well solve the problem that the crucible cannot bear overhigh temperature, and simultaneously, the heat loss in the induction heating process can be reduced by utilizing the characteristic of poor heat conductivity of the tungsten powder or the titanium carbide powder, so that the temperature rise of furnace burden is facilitated, the cooling rate can be reduced, and the purpose of slowly cooling and improving the quality of a finished piece is achieved.

The invention adopts an induction heating method to smelt metal with the melting point higher than 2500 ℃; smelting in a vacuum environment to obtain purer metal; in order to smelt metals at extremely high temperatures and to increase efficiency; on one hand, the invention provides another ultrahigh melting point alloy forming method besides the laser additive manufacturing method, solves the problem that the speed of the additive manufacturing method is too low on the production of large workpieces, and greatly improves the production efficiency; secondly, the invention adopts a vacuum induction heating method, the heating efficiency is high, the speed is high, and the produced parts have less impurities and good quality; finally, the invention adopts a three-layer crucible and mould structure, thereby not only solving the problem that crucible materials cannot bear the limit of ultrahigh temperature, but also reducing heat loss, improving the heat preservation effect during melting and cooling, and being more beneficial to the melting of alloy and the improvement of forming quality.

The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.