CN103990798B - A high temperature powder bed system for laser additive manufacturing - Google Patents

Abstract

The invention discloses a kind of high-temperature powder bed system manufactured for laser gain material, comprise the even temperature assembly of working chamber, laser instrument, workbench, Electromagnetic Heating layer, insulating assembly and laminar flow; Workbench is arranged in working chamber; Electromagnetic Heating layer is primarily of electromagnetic induction plate and coil composition; Electromagnetic Heating layer is placed on workbench lower surface and fits together with it, enables heat be directly transferred on workbench; Coolant flow channel is provided with in workbench; Insulating assembly is enclosed in Electromagnetic Heating layer bottom surface and side, to realize the heat insulation of Electromagnetic Heating layer and insulation; The even temperature arrangement of components of laminar flow is outside at working chamber, for realizing airflow circulating in working chamber, makes workbench realize uniformity of temperature profile.Work top can be heated to very high-temperature according to accessory size by the present invention, and is incubated, the refrigerating function after also hold concurrently equalizing temperature and completion of processing; The present invention can reach protection system, improve the object of capacity usage ratio and the efficiency of heating surface.

Description

A high temperature powder bed system for laser additive manufacturing

technical field

The invention belongs to the field of additive manufacturing, and in particular relates to a system for realizing conduction zone heating and heat preservation of a substrate of a high-temperature powder bed, temperature cooling, and uniform distribution of the temperature field of a circulating air flow.

Background technique

Additive Manufacturing (AM) is a widely used rapid prototyping technology. First, the computer three-dimensional solid model of the required parts is designed by CAD three-dimensional modeling software, and then decomposed into a series of two-dimensional parts according to the process requirements according to a certain thickness. Cross-section, that is to change the original three-dimensional information into two-dimensional plane information, then scan layer by layer, superimpose layer by layer, and finally form the required prototype or part.

In the process of forming metal and ceramic parts by additive manufacturing technology, due to the melting or partial melting of the powder by the heat source, a large temperature gradient is generated, and the uneven temperature distribution on the working surface will cause thermal stress inside the part, resulting in Cracks or warping deformation seriously affect the quality of parts; and for metals and ceramic materials with high melting points, the temperature of the heating system working surface is low, making it difficult or even impossible to form the material. Reducing the temperature gradient in the forming area, ensuring uniform temperature distribution on the worktable surface and increasing the heating temperature of the worktable surface are several key factors to improve the quality of parts. Check relevant information, Hunan Mina Technology Co., Ltd. invented a heating device for additive manufacturing equipment, which adopts a multi-zone heating method (public number: CN102335741A). Divide the worktable into multiple areas, and install a set of quartz heating tubes and reflectors in each area. This heating method can improve the uniformity of temperature distribution on the worktable. The heating temperature in the working area is relatively low (several hundred degrees Celsius), suitable for Non-metallic, not suitable for forming metal and ceramic materials that require high temperature. Northwestern Polytechnical University invented a laser rapid prototyping surface atmosphere heating furnace (public number CN 102322738A). The heating plate is located in the furnace body and placed between the sample backing plate and the silicon carbide rod heating element. Thermocouples are inserted into the heating plate. The furnace can reach a very high temperature (1600 degrees) to melt high melting point ceramic materials. However, the overall working space is in the furnace body, there is no cooling device after heating, and the equipment components are at high temperature, thereby reducing their service life. In the above two inventions, the powder bed preheating method in the field of additive manufacturing uses traditional resistance wire heating. The principle of resistance wire heating is to use electric current to generate heat through the resistance wire, and the heat is transferred to the area that needs to be heated in the form of heat transfer. On the object, part of the thermal energy has been lost during the heat transfer process, and another part of the thermal energy is dissipated into the air at the same time. The utilization rate of thermal energy in this way is very low. Electromagnetic heating can improve energy utilization efficiency to a certain extent. Due to the material selection and power control system of ordinary household induction cookers, the heating power of the iron core is relatively small (within 2200 watts), and the maximum heating temperature can only reach about 300 degrees. High temperature preheating requirements in material manufacturing field. How to increase the preheating temperature to reduce the temperature gradient in the forming area and improve energy utilization efficiency, as well as solve the problems of uneven distribution of preheating temperature and cooling of heating devices, are important problems faced by additive manufacturing technology for a long time.

Contents of the invention

The technical problem to be solved by the present invention is to provide a high-temperature powder bed system for laser additive manufacturing. This system can quickly and efficiently heat the worktable to high temperature and keep it warm. cooling function.

A high-temperature powder bed system for laser additive manufacturing provided by the present invention is characterized in that the system includes a working chamber, a workbench, an electromagnetic heating layer, a heat insulation component and a laminar flow uniform temperature component;

The workbench is installed in the working chamber; the electromagnetic heating layer is mainly composed of an electromagnetic induction plate and an electromagnetic coil surrounding the electromagnetic induction plate; the electromagnetic coil is connected with an electromagnetic heating power supply with temperature control function, and the electromagnetic heating power supply can change the output Voltage frequency to adjust the electromagnetic heating temperature;

The electromagnetic induction plate is placed on the lower surface of the workbench and bonded together, so that the heat can be directly transmitted to the workbench; the workbench is also equipped with a cooling channel;

The heat insulation component is surrounded by the bottom surface and the side surface of the electromagnetic heating layer, so as to realize the heat insulation and heat preservation of the electromagnetic induction plate;

The laminar flow uniform temperature component is arranged outside the working chamber, and is used to realize air circulation in the working chamber, so that the temperature distribution of the workbench is uniform.

Compared with the traditional resistance wire heating used for powder bed preheating in the field of additive manufacturing, the thermal energy utilization rate of resistance wire heating is too low, which not only wastes energy, but also reduces the output per unit time, and also has disadvantages such as easy damage or even leakage . The invention adopts electromagnetic heating, which rectifies and filters the 50HZ alternating current, and converts it into magnetic fields of different frequencies to act on the heating metal, so that eddy currents are generated on the heating metal, and the heating body itself generates heat rapidly. Because the electromagnetic coil itself does not generate heat, there is no additional loss. The magnetic field lines of the electromagnetic coil are evenly distributed on the heating metal, and the magnetic field acts on the surface of the object to be heated to generate an eddy current electric field inside, so that the object to be heated generates heat itself. In order to ensure the preservation of heat during the heating process, a heat insulation structure is used to prevent the heat from being lost too quickly. The heat insulation component can be installed with heat insulation structures on the bottom and side of the electromagnetic induction plate. The heat gathers inside the heating body, and the surface temperature of the electromagnetic coil is slightly higher than room temperature, which is safe to touch, safe and reliable. The entire heat insulation structure is simple to process, easy to install and disassemble, low in cost and clean. The heat is hardly dissipated into the air, and the energy utilization rate is very high. Under the same conditions, it saves 30-70% of electricity compared with resistance wire heating; the average preheating time is more than 60% shorter than resistance wire heating.

The system is equipped with a laminar flow and uniform temperature component, which can smoothly fill in the gas at a low speed and pump out the gas at a low speed. The whole system forms an air circulation to drive the air flow and make the temperature distribution of the work surface even. After processing, the cooling channel in the workbench can take away the heat well. The structural design of the system can effectively adjust and control the temperature of the worktable, and the forming material is heated evenly, which ensures the excellent quality of the formed parts, and can produce parts with complex shapes and structures in a short period of time.

After the electromagnetic heating layer works, the temperature inside the cavity is high, which is not conducive to manual operation to disassemble the processed parts and continue to process the next new part. At the same time, the always high temperature in the cavity is not conducive to protecting related components in the equipment, so the design The core part of the cooling channel is made of built-in cooling channels in the worktable after certain machining. Due to the above-mentioned thermal insulation structure, most of the heat from the heating plate is directly transmitted to the work surface, and since the work surface is covered with a thick powder layer after processing, it is more difficult for the heat to escape from the work surface. Countertops spread out. Therefore, if the heat of the work surface and the atmosphere above can be taken away, the cooling problem of the system will be solved. This kind of water channel is directly designed in the work table. After the processing is completed, the heat on the work table can be directly taken out from the lower part with the cooling water. The entire cooling structure can be equipped with a water flow meter to control the speed of the water flow. It can quickly reduce the temperature of the work surface.

In short, the electromagnetic heating layer is used as a heat source for preheating the substrate in the process of additive manufacturing. The heat transfer loss is small, and the maximum temperature can make the work surface reach 1800 degrees. It can be used for some metals and some ceramics that have a higher preheating temperature. .

Description of drawings

Fig. 1 is a schematic structural diagram of a specific embodiment of the system of the present invention.

Fig. 2 is a schematic structural diagram of a thermal insulation assembly provided by an example of the present invention.

Fig. 3 is a structural schematic diagram (a top view of the equipment) of the laminar flow uniform temperature assembly of the example of the present invention.

Fig. 4 is a schematic diagram of the arrangement of the cooling channels of the example of the present invention.

In the figure, 1-laser, 2-laser beam, 3-worktable, 4-support layer, 5-intermediate insulation layer, 6-heat insulation layer, 7-lower top plate, 8-ball screw, 9-electromagnetic induction board , 10-working chamber, 11-gas flowmeter, 12-inert gas source, 13-intake pipeline, 14-loop pipeline, 15-pump, 16-waterway connector, 17-inner flow channel, 18-water flowmeter , 19-water pump, 20-waterway adapter, 21-electromagnetic coil, 22-exhaust pipeline, 23-electromagnetic heating power supply.

Detailed ways

The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings. It should be noted here that the descriptions of these embodiments are used to help understand the present invention, but are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

As shown in FIG. 1 , the system of the present invention includes a working chamber 10 , a laser 1 , a workbench 3 , an electromagnetic heating layer, a thermal insulation component, a laminar flow uniform temperature component and a cooling channel.

The workbench 3 can adopt the lifting type, and is installed in the working chamber 10, specifically, it can be connected with the ball screw 8 through its lower top plate 7, so as to control the lifting of the whole workbench 3. The electromagnetic heating layer is the main heat source, and it is placed on the lower surface of the workbench 3 and tightly attached to it. The heat can be directly conducted to the workbench 3 like this.

The electromagnetic heating layer is mainly composed of an electromagnetic induction plate 9 and an electromagnetic coil 21 .

In the actual working process, the working chamber 10 needs to be heated to a very high temperature. In order to protect the additive manufacturing equipment from high temperature damage, it is necessary to perform heat insulation and heat preservation treatment in the working chamber 10, specifically by the heat insulation component. Complete, as shown in Figure 2. The heat insulation component surrounds the electromagnetic induction panel 9 from the side and the bottom surface, and the heat insulation component mainly includes three layers, which are heat insulation layer 6, middle insulation layer 5 and support layer 4 from inside to outside.

What heat insulation layer 6 material used is aluminum silicate plate. Ordinary aluminum silicate plate is made of coke gemstone as the main raw material. It has excellent thermal shock resistance and thermal stability. The material has high compressive strength and good toughness. temperature is preserved.

The middle insulation layer 5 material is glass wool, and glass wool felt is a felt-like material that is heated and solidified. Its bulk density is lighter than that of the board, has good resilience, is cheap, and is convenient for construction. Glass wool felt is a roll material made to meet the needs of large-area laying. In addition to maintaining the characteristics of heat preservation and heat insulation, it also has excellent shock absorption and sound absorption characteristics, especially for medium and low frequencies and various vibration noises. Good absorption effect is conducive to reducing noise pollution and improving the working environment. Glass wool felt with aluminum foil veneer also has strong heat radiation resistance. It is an excellent lining material for high-temperature workshops, control rooms, inner walls of machine rooms, compartments and flat roofs. Compared with asbestos, glass wool also has the advantages of being non-toxic. The function of the middle insulation layer is to keep the heating system warm. The glass wool is soft and the fibers are fine. It will not irritate the skin during construction, and can achieve the effect of processing and heat preservation very well.

The outermost layer is a supporting layer 4, and the material of this layer is preferably an aluminum plate pressing plate. Because the aluminum plate has poor electrical conductivity and magnetic permeability during electromagnetic heating, it will not generate a lot of heat under the action of an external magnetic field (although the magnetic field lines are densely covered with the electromagnetic induction plate through power control, but the external material is not easy to conduct magnetic conductivity and can play a supporting role appear more reasonable and rigorous). Because the glass wool in the middle insulation layer is a soft material, the innermost layer and the outermost layer need to be squeezed and fixed. Of course, other heat insulation materials can also be used for the three layers. During the implementation process, the three layers of boards are easy to disassemble, which can satisfy the wiring inside the electromagnetic induction board. In this way, the thermal insulation component can prevent the heat from being conducted to the side and the bottom, thereby achieving the purpose of unidirectional heat conduction. The materials mentioned above are preferred embodiments of the present invention, and are not limited to these materials.

The electromagnetic induction plate 9 and the heat insulation assembly are surrounded by an electromagnetic coil 21, and the electromagnetic coil 21 can also be directly wound on the electromagnetic induction plate 9, and then surrounded by the heat insulation assembly. The electromagnetic coil 21 is connected to the electromagnetic heating power supply 23. The power supply converts the AC voltage into a DC voltage, and then the controller inverts the DC voltage into a high-frequency AC voltage. The high-speed changing current passing through the coil 21 will generate a high-speed changing magnetic field as the magnetic field line Numerous small eddy currents will be generated when the magnetic field passes through the electromagnetic induction plate 9 . There is a temperature control module in the heating power supply 23, which can adjust the electromagnetic heating temperature by changing the output voltage frequency according to user needs. Electromagnetic induction plate 9 can be selected the vast majority of metal materials of conventional conduction and magnetism for use, and temperature can be guaranteed at about 700 degree, needs to be heated to about 1800 degree and also can adopt the better non-metallic material graphite of electric conductivity and thermal conductivity.

The laminar flow uniform temperature assembly is arranged outside the working chamber 10 to realize air circulation and make the temperature distribution of the workbench 3 uniform. In this example, the laminar flow uniform temperature assembly includes an air inlet pipeline 13 , an exhaust pipeline 22 , an inert gas source 12 and a pump 15 . As shown in Figure 3, the intake pipeline 13 and the exhaust pipeline 22 are pipelines with a "dendritic" structure, wherein the total input end of the intake pipeline 13 is connected to the inert gas source 12, and the output end of the intake pipeline 13 is set There are multiple output ports, all of which are arranged on one side of the working chamber 10, and the inert gas is evenly introduced into the upper surface of the workbench 3. The input end of the air extraction pipeline 22 is also provided with a plurality of input ports, and is arranged on the other side of the working chamber 10, and the walls on both sides of the equipment are provided with multiple input ends of the interface and the air intake pipeline and multiple outputs of the air extraction pipeline. end connected. The total output end of the pumping pipeline 22 is connected with the pump 15, and the pump 15 is connected with the inert gas source 12 through the loop pipeline 14, so as to realize a closed circuit circulation. A gas flowmeter 11 can be installed on the loop pipeline.

The inert gas at normal temperature is input into the intake pipe 13, and the gas circulates along the intake pipe 13. After traveling for a certain distance, it is evenly divided into two streams and travels in the intake pipe, and finally divided into four streams evenly and slowly introduced to the working area. The upper surface of the table 3; after that, the normal temperature gas is heated to the hot gas close to the temperature of the working chamber, therefore, when the gas is introduced into the upper surface of the work table 3, it will not cause a large temperature change. On the other side of the workbench 3, the air extraction pipelines 22 are also distributed in a "dendritic" form. The gas in the workbench 3 is divided into four airflows, which are slowly and steadily drawn into the four input ports of the suction pipeline 22. After the gas travels for a certain distance in the suction pipeline 22, the four airflows are merged into two airflows. The two airflows follow the same The direction continues to advance in the circulation pipeline, and finally gathers a stream of air to be pumped out by the pump 15. The pump 15 is connected to the total output end of the suction pipeline 22, and the extracted inert gas passes through the loop pipeline 14 and returns to the intake pipeline 13 in a closed circuit. middle.

Of course, the specific structure of the intake pipeline 13 and the exhaust pipeline 22 is not limited to the 1-2-4 branch structure in Fig. 3, 1-3-6 or other structures that can realize the uniform temperature distribution of the workbench 3 can be used .

This laminar flow uniform temperature structure can make the whole system form an air circulation, drive the gas flow on the upper surface of the workbench, make the temperature distribution of the workbench 3 uniform, and ensure the good forming quality of the processed parts; at the same time, it can also reduce the consumption of inert gas. Cost saving; avoiding the discharge of hot gas into the atmosphere, effectively reducing energy loss and improving energy utilization.

The workbench 3 is provided with a cooling flow channel, which is formed by connecting the inner flow channel 17 and the waterway connector 16. Both ends of the cooling flowway are connected with waterway adapters 20, and one of the waterway adapters 20 is used as an inlet. The water port is connected with the water flow meter 18 and the water pump 19, and another waterway adapter 20 is used as the water outlet. As shown in Figure 4, the inner runner 17 is a straight runner with several directly drilled through holes on the side of the "I" shaped workbench 3, and threaded lines are tapped at the two ends of each runner. In this way, some waterway connectors 16 can be used to connect different straight flow channels in the plate, finally forming a continuous flow channel. Then the waterway adapter 20 connects the two direct runners at the most ends, and at the same time punches holes in the bottom of the "I"-shaped workbench 3, so that it can be ensured that the waterway adapter 20 can pass through this hole and will not interfere with other places of the equipment. interference occurs. Both the waterway adapter 20 and the waterway connector 16 are sealed with corresponding sealant, which ensures the safety and stability of the system. The two waterway adapters drawn out are then connected to the water pipes at the lower part of the equipment, one is the water inlet and the other is the water outlet. Water flow meter 18 and water pump 19 are arranged on the external pipeline of water inlet, can keep low temperature water through whole pipeline system all the time.

In actual use, the laser 1 can be installed inside or outside the working chamber 10 , and the laser beam 2 works on the powder on the table 3 . After the laser additive manufacturing is completed, turn off the laser 1, turn on the switch of the water pump 19, connect the external cooling water, and start the whole cooling system. 3 The accumulated heat is taken away, and finally the water that takes away the heat flows out through the outlet and is collected.

The above description is only a preferred embodiment of the present invention, but the present invention should not be limited to the content disclosed in this embodiment and the accompanying drawings. Therefore, all equivalents or modifications that do not deviate from the spirit disclosed in the present invention fall within the protection scope of the present invention.

Claims (5)

1., for the high-temperature powder bed system that laser gain material manufactures, it is characterized in that, this system comprises working chamber (10), workbench (3), Electromagnetic Heating layer, insulating assembly and the even temperature assembly of laminar flow;

Workbench (3) is arranged in working chamber (10); Electromagnetic Heating layer is primarily of one piece of electromagnetic induction plate (9) and be centered around electromagnetic induction plate (9) solenoid composition outward; Described solenoid (21) is connected with the Electromagnetic Heating power supply (23) of band temperature controlling function, and Electromagnetic Heating power supply (23) can change output voltage frequency to regulate Electromagnetic Heating temperature;

Electromagnetic induction plate (9) is placed on workbench (3) lower surface and fits together with it, enables heat be directly transferred on workbench (3); This workbench is also provided with coolant flow channel in (3);

Described insulating assembly is enclosed in Electromagnetic Heating layer bottom surface and side, to realize the heat insulation and insulation of electromagnetic induction plate (9);

The even temperature arrangement of components of described laminar flow is outside at working chamber (10), for realizing working chamber (10) interior airflow circulating, makes workbench (3) realize uniformity of temperature profile.

2. high-temperature powder bed system according to claim 1, is characterized in that, described insulating assembly comprises three layers, is followed successively by thermal insulation layer (6), moderate soak layer (5) and supporting layer (4) from the inside to the outside.

3. high-temperature powder bed system according to claim 2, is characterized in that, described thermal insulation layer (6) is silicate aluminum board; Moderate soak layer (5) material mineral wool, supporting layer (4) is aluminium sheet.

4. according to claim 1, high-temperature powder bed system described in 2 or 3, it is characterized in that, the even temperature assembly of described laminar flow comprises air inlet pipeline (13), exhaust pipe (22), inert gas source (12) and pump (15), air inlet pipeline (13) and exhaust pipe (22) are the pipeline of " dendroid " structure, wherein, total input of air inlet pipeline (13) is connected with inert gas source (12), the output of air inlet pipeline (13) is provided with multiple delivery outlet, be arranged in the side of workbench (3), and make inert gas evenly introduce the upper surface of workbench (3), the input of exhaust pipe (22) is also provided with multiple input port, and is arranged in the opposite side of workbench (3), and the wall on equipment both sides is offered docking port and is connected with multiple outputs of exhaust pipe with multiple input of air inlet pipeline, total output of exhaust pipe (22) is connected with pump (15), and pump (15) is connected with inert gas source (12) by return (14), realizes closed cycle.

5. the high-temperature powder bed system according to claim 1,2 or 3, it is characterized in that, described coolant flow channel is formed by connecting by inner flow passage (17), water route connector (16), these coolant flow channel two ends are all connected with water route adapter (20), one of them water route adapter (20) is as water inlet, be connected with water ga(u)ge (18) and water pump (19), another water route adapter (20) is as delivery port.