WO2022250633A1

WO2022250633A1 - Protective shield providing temperature control in wire arc additive manufacturing method

Info

Publication number: WO2022250633A1
Application number: PCT/TR2022/050446
Authority: WO
Inventors: Oguzhan YILMAZ; Ebubekir Dogan
Original assignee: Gazi Universitesi
Priority date: 2021-05-26
Filing date: 2022-05-18
Publication date: 2022-12-01

Abstract

The present invention relates to a system that provides the control of rapid and uncontrolled heat transfers that will occur in the production area in wire arc additive manufacturing, and the resulting residual stress and distortions that will occur in the produced part by forming a controlled temperature shield (zone).

Description

PROTECTIVE SHIELD PROVIDING TEMPERATURE CONTROL IN WIRE ARC ADDITIVE MANUFACTURING METHOD

Technical Field of the Invention

State of the Art

Wire arc additive manufacturing method is one of the production methods studied to be used in the production of large-sized structural parts. In this field, although there are very few commercial machine and system developments, it has not become widespread in the world yet. The most important reason thereof is that the technology is not mature enough, the investment costs are expensive, and the production systematics do not provide convenience for the end user yet.

In the researches, it is seen that the cooling properties of the structures used as a secondary heat source are generally prominent. Leonardo et al. (da Silva, Souza et al. 2000) studied the concept of an active cooling technique to reduce heat accumulation in wire arc additive manufacturing. Fang et al. (Li, Chen et al. 2018) studied thermoelectric cooling assisted fabrication for weld geometry control in wire arc additive manufacturing. Interlayer cold work-based approaches are generally used for residual stress and distortion control. Paul et al. (Colegrove, Coules et al. 2013) performed interlayer high pressure rolling for residual stress and distortion control. Reza et al. (Tangestani, Farrahi et al. 2020) studied vertical and compression rolling for residual stress control. l In the state of the art, another study using a second heat source belongs to Xingwang Bai et al. (Bai, Zhang et al. 2015). They used mobile induction heating as a secondary heat source and made a model study on this method.

The document numbered "W0 2020261233 A1", which is in the state of the art, provides solutions for reducing residual stresses, increasing ductility, eliminating post heating treatment operations and homogenizing the grain structure. For related problems, the invention uses hot forging to improve the grain structure of the metal heated and melted by arc energy during the WAAM process. It solves the problem with a vibrating actuator configured to hot forge the workpiece to plastically deform the workpiece layer. In said system, it only controls the area where the torch heats and melts, it is not aimed to control the entire workpiece.

The document numbered "CN 109746444 B", which is in the state of the art, relates to a system that is expected to reduce residual stress and optimize the unsteady state of manufacturing in additive manufacturing by optimizing the substrate in the field of additive manufacturing. The invention optimizes the shape of the substrate for related problems. This optimization is made by taking the shape of the part to be produced as a reference. Thus, distortion of the substrate during production is prevented. It is claimed that with the optimization, the temperature gradient in the substrate will be controlled and the problems will be controlled. In said system, control is provided only in certain layers, not in the entire workpiece. There is a new optimization need for every workpiece.

The system mentioned in the document numbered "CN 108637504 A", which is in the state of the art, aims to improve the mechanical properties of the workpiece comprehensively. It aims to provide solutions to problems such as improvement in surface roughness, wear resistance and corrosion resistance by rolling, which creates a compressive tension layer that provides grain thinning of the workpiece after stacking in additive manufacturing. The invention provides hydraulic rolling, which is actuated by the temperature sensor in order to realize related improvements. In said system, the rolling process requires new equipment and applies this rolling process on the hot workpiece. As a result of this rolling process, there may be undesired changes in the geometry of the part. The study called "Thermoelectric Cooling-Aided Bead Geometry Regulation in Wire and Arc-Based Additive Manufacturing of Thin-Walled Structures" in the state of the art, provides a solution to eliminate the difference in heat distribution between the upper and lower layers. With this solution, it claims to reduce bead width error, reduce production time, and refine the average grain structure. The study adds active cooling based on thermoelectric cooling technology to the WAAM process in order to eliminate heat distribution between the upper and lower layers. Said system works on bead geometry, processing time and grain structure.

Considering the state of the art, as the size of the piece increases in welding methods, the heat on the piece increases. In an uncontrolled cooling condition, the parts cool down rapidly and the parts heat up again with the continued welding process. In productions where heating and cooling are irregular (uncontrolled), excessive residual stress occurs on the part. Again, in cases of irregular heat, the parts are distorted.

The solutions used in the state of the art affect only the last layer that is stacked during the production process. Residual stress and distortion production continues in other untreated layers since the thermal instability of the environment and the material continues due to the physical and chemical events occurring in the micro and macro dimensions in the produced material.

In the current system, excessive heat inputs during production, the difficulty of controlling the heat, the need for additional processing (heat treatment, machining, cutting, etc.) of the produced parts and the difficulties in obtaining the desired mechanical properties can be stated as the disadvantages of the related technology.

In the state of the art, there are already various methods in the technology for residual stress and distortion control. The solutions offered by the existing approaches in solving the problem make the process more complex and increase the investment costs.

Consequently, the disadvantages disclosed above and the inadequacy of available solutions in this regard necessitated making an improvement in the relevant technical field. Brief Description and Objects of the Invention

The most important object of the present invention is to reduce or eliminate the distortion and residual stress that may occur in the parts due to the heating and cooling instability of the production area in wire-fed arc-melting additive manufacturing. Another object of the present invention is to reduce the need for heat treatments or to minimize cost and time losses by preventing them.

Yet another object of the present invention is to use the protective and balancing effect of heat in order to prevent sudden heating and cooling, which is the biggest cause of residual stress and distortion. Thus, the thermal balance of the environment is achieved and thermal controls are achieved in every layer of production.

Description of the Figures

FIGURE-1 is the drawing that illustrates the view of the protective shield of the present invention. FIGURE-2 is the drawing that illustrates the view of the welding torch, base, and workpiece in the system of the present invention.

FIGURE-3 is the drawing that illustrates the view of heating resistance, heating wire, and protective shield in the system of the present invention.

FIGURE-4 is the drawing that illustrates the view of the ceramic plate and protective shield in the system of the present invention.

Description of Elements/Parts of the Invention

Parts shown in the figures are enumerated and numbers corresponding the respective parts are provided below in order to provide a better understanding for the system of the protective shield providing heat control in the wire arc additive manufacturing method developed with the present invention. 1. Industrial welding robot arm

2. Welding Machine

3. Welding wire feeding unit

4. Shielding gas feeding unit

5. Welding torch

6. Production table

7. Base

8. Workpiece

9. Ceramic plate

10. Heater resistance

11. Heater wire

12. Protective shield

Detailed Description of the Invention The present invention relates to a system that provides the control of rapid heat losses/heat transfers and the resulting residual stress and distortions in the production area wire arc additive manufacturing by using the protective effect of temperature.

In the wire arc manufacturing method, which is a metal melting manufacturing method, as a result of excessive heat input and uncontrolled heat movement in the production area, residual stresses and distortions that occur in the produced parts and negatively affect the working life of the parts are prevented. In addition, microstructural isotropic structure is provided. It is that it shows the same material properties (mechanical, thermal, electrical, etc.) in all directions microstructurally independent of the direction. Showing the same properties independent of the direction causes the reliability of the manufactured part to be high and the usability of the production method to increase. By means of the protective shield (12) to be formed in the production area, uncontrolled heating and cooling are prevented, and defects are prevented by providing control over the internal structure.

In the system developed with the present invention, it is primarily aimed to use the protective and balancing effect of heat in order to prevent sudden heating and cooling (thermal fluctuation), which is the biggest cause of residual stress and distortion.

Said protective shield (12) structuring comprises; industrial welding robot arm (1) that moves and directs the welding torch (5) (shielding gas and welding wire) in accordance with the geometry of the part to be produced, welding machine (2), welding wire feeding unit (3), shielding gas feeding unit (4), welding torch (5), production table (6), base (7), workpiece produced by wire-fed arc-melting manufacturing method (8), ceramic plate (9), heater resistance (10), and heater wire (11).

The size of the workpiece (8) used in said system has certain limits when considering the state of the art. In terms of material, gas metal arc welding is limited by technology. It is limited to the technology of all commercial alloys that are produced and can be produced by gas metal arc welding technology methods. Metals in engineering materials are within the limits of technology.

The welding machine (2) has gas metal arc welding technology in the system developed with the present invention. Welding machine (2) is shown in Figure-1. It is also known in the art as CMT (cold metal transfer) welding. It also has the ability to perform MIG/MAG welding, that is, gas metal arc welding. It comprises a welding machine (2) with a welding wire supply unit (3) and a power unit combined or separate, with a current protection circuit against overloading, that has shielding gas unit and welding voltage adjustment, and that provides control of the wire feeding speed. Here, in case the welding wire feeding unit (3) and the power unit are combined or separate, there are two types of gas metal arc welding machines according to the position of the wire feeding unit. In combined (compact) type welding machines, the wire feeding unit is with the machine in vertical or horizontal position. In separable type welding machines, the wire feeding unit can be separated from the machine. The welding machine (2) creates the arc for MIG and MAG welding and provides melting of the welding wire. In said system, there is a welding wire feeding unit (3) that provides the feeding of the melted wire in the manufacturing area in accordance with the information it receives from the welding machine (2) and the part to be manufactured (as a composition). The welding wire supplied to the system from the welding wire feeding unit (3) has the same chemical composition according to the workpiece to be produced. Gas metal arc welding technology was used.

Shielding gas feeding unit (4), which provides the protection of the heat-affected area in the production area, which has not yet solidified and is open to external factors, provides the shielding gas consisting of a mixture of gases and/or gases such as CO2 (Carbon Dioxide), Ar (argon), He (helium). As mentioned above, inert and active gases such as carbon dioxide, argon, and helium are used in gas arc welding methods. Relevant gases or mixtures are used according to the welding method and material. In addition to the specified gases, nitrogen and oxygen can also be used.

The welding torch (5) provides the shielding gas and the welding wire required for manufacturing to be transmitted to the manufacturing area.

The production table (6) works synchronously with the industrial welding robot arm (1 ) throughout the production in the wire arc additive manufacturing system and ensures the positioning of the production area. The base (7), on the other hand, is placed on the production table (6) and provides the basis for the part to be produced.

In order to ensure the heat and temperature balance in the production area, a protective shield (12) consisting of fragmented and mountable ceramic plates (9) is used to ensure that the ambient temperature of the production area, that is, the production area, is brought to a certain level. The specified ambient temperature is also higher than the room temperature.

In the wire arc additive manufacturing method, ceramic plates (9), which are placed on the production table (6) and cover 360 degrees around the workpiece to be produced, are in a structure that can take the form of a flexible wall. Ceramic plates (9) place the workpiece (8) to be produced on the production table according to its geometry, that is, its shape, and it is ensured that it is a closed environment. The term flexible here refers to a rectangular shaped workpiece (8) that will be formed as a rectangle for geometry, and a wall to be formed as a square for a square. Ceramic plates (9) consist of segmented and mountable parts to ensure that the ambient temperature of the production environment is brought between 150°C and 400°C, and provide a closed environment.

There are heater wires (11) on the ceramic plates (9). The heater resistance (10), on the other hand, converts the electrical energy passing over it into heat energy and provides heat control.

Heater wires (11 ), which are capable of converting electrical energy into heat energy, are passed through the ceramic plates (9) in order to generate heat and to control the heat generated. The heater wires (11) are also a subsystem of the heater resistance (10) system. By means of heater wires (11 ) to be placed inside the ceramic plates (9), the heat control is provided according to the material to be made during the production, the shape of the part and the process parameters. Thus, the least distortion, residual stress caused by thermal expansion and contraction, and the best mechanical properties are achieved.

Part geometry (shape) is an important parameter for the heat that will be generated in the production area during the manufacturing process. For example, heat gradient increases rapidly for small sized parts, while heat accumulation is slightly slower for large sized parts. Therefore, the heat provided by the protective shield (12) is dependent on the part size. Welding method varies according to variables such as shielding gas type and amount, welding wire, geometry, and process parameters such as changing layer thickness, feed rate, and stacking path.

The heat environment formed with this system is kept within a certain temperature range. Thus, it prevents sudden heating and cooling in the production area, as well as air currents due to environmental conditions.

By means of the present invention, residual stress and distortion control will be provided, so there is freedom in design and the ability to manufacture large-sized structural parts. Energy efficiency is also ensured with the control to be provided. The control made to ensure energy efficiency is the control of the heat that will occur in the production area. In said system, as the part size increases, the amount of residual stress and distortion in the produced parts also increases. With the developed method, it is possible to manufacture large-sized parts by means of the residual stresses and distortions that will be controlled. Controlling residual stresses and impacts is the main reason for residual stress generation mechanisms such as heat that will occur during production in the production area, thermal changes due to thermal fluctuations and phase transformations. Residual stress and distortion will be prevented by preventing thermal fluctuation with the protective heat shield. In addition, by controlling the irregular thermal fluctuations, residual stress and distortion in the parts are also reduced.

The use of the WAAM method in the industry, which allows for producing especially large-sized structural parts and offers advantages in terms of time while providing this opportunity, is becoming more widespread in the industry. Residual stress and distortion control, which is a major problem for the end user, is controlled by the system developed with the present invention.

The system can be applied in aerospace, defense, automotive, machine manufacturing, metalworking, medical, molding and other metal industries in which the wire arc additive manufacturing industry is used. In addition to being included in the existing wire-fed arc-melting production processes in the relevant fields, it can also be installed in systems to be manufactured by system manufacturers.

Claims

1. A system that can be used in the wire-fed arc-melting additive manufacturing, aerospace, defense, automotive, machine building, metalworking, medical and molding industries, and is developed to prevent residual stress and distortion resulting from thermal fluctuations in the production area, which is the cause of sudden heating and cooling, characterized in that, it comprises;

• Industrial welding robot arm (1 ) that moves and directs the welding torch (5) in accordance with the geometry of the part to be produced,

• Shielding gas feeding unit (4), which provides the protection of the heat-affected area, which has not yet solidified in the production area and is open to external factors,

• Welding torch (5), which ensures that the shielding gas released from the shielding gas feeding unit (4) and the welding wire required for production are transmitted to the manufacturing area,

• Production table (6), which works synchronized with the industrial welding robot arm (1) throughout the production and ensures the positioning of the production area,

• Welding wire feeding unit (3), which supplies the wire to be melted in the manufacturing area with the information it receives in the welding machine (2) and the wire in a composition suitable for the part to be manufactured,

• Welding machine (2), which creates the arc for gas metal arc welding, melts the welding wire and controls the wire feeding speed,

• Protective shield (12) to ensure that the ambient temperature of the production environment is brought to a certain level in order to maintain the heat and temperature balance in the production area, Ceramic plate (9) that covers 360 degrees around the workpiece (8) by being placed on the production table (6) in order to maintain the heat and temperature balance in the production area, that consists of fragmented and mountable parts and provides creating a closed environment to ensure that the ambient temperature of the production environment is brought between 150°C and 400°C, that generates heat energy with a heater resistance (10) that converts electrical energy into heat energy placed therein, that provides the formation of a protective shield (12) comprising a heating wire (11 ) capable of converting electrical energy into heat energy in order to control the heat generated,

Heater wire (11 ), which is the subsystem of the heating resistance (10) system and placed in ceramic plates (9), that provides heat transfer to the production area and heat control to the material to be made during production, that can convert electrical energy into heat energy to generate heat and control the heat generated.

2. A system developed to prevent thermal fluctuations in the production area according to Claim 1 , characterized in that, it comprises a welding machine (2) with an overload current protection circuit.

3. A system developed to prevent thermal fluctuations in the production area according to Claim 1 , characterized in that, it comprises a shielding gas feeding unit (4) where the shielding gas consisting of carbon dioxide and argon and helium gases or nitrogen and oxygen or a mixture of these gases is positioned.

4. A system developed to prevent thermal fluctuations in the production area according to Claim 1 , characterized in that, it comprises a heater wire that is placed in ceramic plates (9), that provides temperature control according to the material to be produced and the shape of the part in order to provide minimum residual stress formation due to distortion, thermal expansion and contraction.

5. A system developed to prevent thermal fluctuations in the production area according to Claim 1, characterized in that, it comprises a protective shield (12) aiming to provide energy efficiency by controlling the heat that will occur in the production area.

6. A system developed to prevent thermal fluctuations in the production area according to Claim 1, characterized in that, it comprises a protective shield (12) that reduces residual stress and distortion in parts by controlling irregular thermal fluctuations.