WO2021058837A1

WO2021058837A1 - Intelligent local protection system with temperature control for wire and arc additive manufacturing processes

Info

Publication number: WO2021058837A1
Application number: PCT/ES2019/070634
Authority: WO
Inventors: Pedro ÁLVAREZ MORO; Lexuri VAZQUEZ MARTÍNEZ; Iker RODRIGUEZ RUBIO
Original assignee: Lortek S. Coop.
Priority date: 2019-09-24
Filing date: 2019-09-24
Publication date: 2021-04-01
Also published as: ES2907813R1; ES2907813A2; ES2907813B2

Abstract

The present invention relates to an intelligent gas protection system for wire and arc additive manufacturing, comprising: a welding wire (5); a welding torch (3); a local protection hood (1) surrounding the space containing the part to be manufactured; a protective gas feed system (10); a solenoid valve (9) for controlling the protective gas feed system; a robotic arm, to which the welding torch (3) and the local protection hood (1) are coupled; and a temperature sensor (2). A robotic arm controller (8), connected to the solenoid valve (9) and the temperature sensor (2), sends a signal to the solenoid valve to stop the gas flow when the temperature is below a predetermined value and to move the torch and the hood in order to continue with the manufacturing. Thus, the time for which the gas must protect the manufactured part in order to prevent the oxidation thereof is regulated automatically, optimising the manufacturing time and reducing the consumption of protective gas.

Description

INTELLIGENT LOCAL PROTECTION SYSTEM WITH TEMPERATURE CONTROL FOR ADDITIVE MANUFACTURING PROCESSES THROUGH

BOW AND THREAD

OBJECT OF THE INVENTION

The present invention falls within the technical field of additive manufacturing using electric arc and wire; which is technically called WAAM (Wire and Are Additive Manufacturing for its acronym in English). More particularly, the invention resides in an intelligent local protection system against the oxidation of reactive materials that integrates a temperature control and automatic regulation of the passage of the protection gas. The local protection system can be integrated into both robotic welding installations and Cartesian kinematics machines, with path control for welding operations and additive manufacturing using electric arc and wire.

BACKGROUND OF THE INVENTION

Additive manufacturing by electric arc and wire, also known as WAAM is an additive manufacturing technology where a large amount of material provided is deposited in the form of wire that is melted by an electric arc. This process achieves high deposition rates, reducing the amount of starting material and the need for machining compared to exclusively subtractive manufacturing processes, which represents significant savings, especially in materials with high added value and difficult to machine, as is the case. of the TÍ-6AI-4V alloy.

This alloy is widely used in the aerospace sector mainly due to its high mechanical strength and excellent corrosion resistance. In contrast, it is common that, during additive manufacturing with the TÍ-6AI-4V alloy, the surface of the deposited material oxidizes, affecting its mechanical properties, thereby reducing the quality of the material it will form. part of the final piece. According to the regulations of the aeronautical sector, the amount of oxygen in the final piece must not exceed 2000 ppm in any case.

Currently, to prevent the oxidation of this material during the WAAM process, closed chambers or systems filled with a protective gas, for example argon, are used. Many of these systems require a constant flow of that gas. Their main disadvantage is that they restrict the space or volume of the part to be manufactured. In other cases, local protection systems are used that provide a constant flow of gas, which implies considerable consumption, low efficiency and limitations to achieve homogeneous protection in the part.

The use of gas during a constant time interval after the deposition of material (what is known in the art as post-gas time) generates an unnecessary gas expenditure in some points and on the contrary a protection deficit in others, Obtaining pieces with gradients in the oxygen content and therefore with heterogeneous mechanical properties. Likewise, if the post-gassing time is excessively short, oxidation of the material can occur, particularly when a high number of layers have been deposited and the part is hotter.

We must also consider the large dimensions of the target parts of this technology, which usually range between 0.25 and several meters. During the manufacture of these, the temperature of the piece or specific parts increases considerably, which also increases the risk of oxidation.

Different systems are known in the current state of the art for protecting reactive materials against oxidation during welding processes, such as closed chambers (rigid or flexible) or trailing protection systems. For example, the publication “Development of a laminar flow local shielding device for wire + are additive manufacture” (J. Ding et al., Cranfield University, 2015) describes a local protection device for reactive materials during the WAAM process. Other works by the same authors claim to apply a fixed time each time they finish the deposition of material (“Residual stress and texture control in TÍ-6AI-4V wire + are additive manufactured intersections by stress relief and rolling ”, JR Hónnige et al., Cranfield University, 2018). Patent EP3184226 uses a closed chamber that allows maximum part dimensions of 900 x 600 x 300 mm and where it works in an atmosphere of inert gas to avoid oxidation of the Ti-6AI-4V alloy.

However, there is a need for devices that allow optimizing the local protection of the reactive materials deposited by means of additive manufacturing by arc and wire in a precise and efficient way in the use of shielding gas, to achieve a part with a minimum percentage of oxygen. (<0.2% by weight for grade 5) and avoiding heterogeneities.

DESCRIPTION OF THE INVENTION

The object of the invention is to provide an intelligent local protection system against oxidation for the manufacture by means of WAAM of components of large dimensions of reactive materials. The system has a temperature control and automatic regulation of the gas flow that allows optimizing the time and the volume of shielding gas in such a way as to avoid oxygen gradients and therefore heterogeneities in the mechanical properties of the final part.

The intelligent system for local protection against the oxidation of reactive materials during additive manufacturing by electric arc and wire, comprises:

- a welding torch;

- a welding wire provided in the form of a coil that exits through the welding torch and melts by means of the electric arc forming weld seams. These are what will form the piece by deposition of one on another.

- a local protection hood to cover the welding torch and the piece that is being formed by WAAM;

- a protective gas circuit to transport the gas from a supply system to the protective hood;

- an electronic valve for the control of the shielding gas flow;

- a mechanism for fastening the hood to the welding torch, - a robotic arm to jointly move the hood with the welding torch and manufacture the part using WAAM;

- a non-contact temperature sensor for temperature measurement at the welding point located just below the torch, in the area closest to the part;

- a controller of the robotic arm to receive the data of the temperature measurements and give the order to close the solenoid valve and move the robotic arm to continue with the manufacturing.

Preferably, the protection hood is provided with a lamella structure inside for generating a laminar gas flow.

Prior to the start of the weld deposition of each weld bead, a flow of gas must be applied for a time called the pre-gas time. The gas flow continues during welding and once the deposition of the material in each section is completed, the protection must continue for a time called post-gas. This time depends on the rate of cooling of the material to a temperature low enough to ensure slow oxidation kinetics. In the case of the TÍ-6AI-4V alloy, this temperature must be less than 300 - 400 ° C (D. Poquillon et al., Oxidation and Oxygen Diffusion in Ti - 6al - 4V Alloy: Improving Measurements During Sims Analysis by Rotating the Sample. Oxid. Met, 2013).

The method and system for measuring and controlling the temperature of the material deposited according to the invention is based on the measurement of the temperature of the material deposited in the hottest zone, that is, at the end of the weld bead deposited last, in the part closest to the piece. The system has an electronic and non-contact high temperature sensor (micropyrometer or other type of pyrometer), integrated in the local protection hood. The sensor measures the temperature and passes it to the controller of a robotic arm which decides when it can move to the next layer or bead after the required post gas time has been completed. Likewise, the robotic arm controller regulates the operation of the electronic valve that activates and deactivates the passage of shielding gas to the protective hood. In this way, the time that the gas must affect to avoid its oxidation is automatically regulated, optimizing the manufacturing time and reducing the consumption of shielding gas. The temperature sensor is coupled to the external part of the local protection hood ensuring precisely the measurement just below the welding torch, that is, at the hottest point of each weld bead. Optionally, the space from the temperature sensor located on the outside of the hood, to the part just below the welding torch, can be isolated by a cylindrical tube to avoid interaction with shielding gas or with the fumes from welding.

The steps to work with the intelligent local protection system described include:

- Placement of the local protection hood on the welding torch;

- connection of the shielding gas supply system through the solenoid valve;

- regulation of the focus position of the temperature sensor to ensure its alignment with the required measurement point;

- Component ignition: robotic arm, welding equipment, sensor, solenoid valve;

- programming of trajectories of the robotic arm and sequence of operations for the manufacture of the part by deposition of weld seams, either manually or with CAM tools, a constant pre-gas time is used, while the post time -gas after each welding is regulated through the controller of the robotic arm. The robot arm controller constantly receives the temperature value measured by the sensor and once this value falls below the imposed limit, the robot arm controller gives the command to close the gas valve and immediately afterwards the command to move the robot arm. ;

- start of manufacturing by WAAM.

The system works autonomously during the manufacturing process and at the end of the process the components are disconnected.

The temperature recording during the process not only serves to avoid the oxidation of the deposited material, but it is also useful to design manufacturing strategies that involve less heat accumulation, in order to optimize manufacturing times by reducing waiting times. or cooling and thus guaranteeing its mechanical quality. Likewise, the temperature control allows to avoid collapses, excessive grain growth and with elongated grain shapes due to the high temperature, as well as the appearance of martensite due to high temperature gradients. In this way it is possible to achieve better and homogeneous mechanical properties in the pieces.

The proposed intelligent local protection system for WAAM is a robust, economical and reliable solution to optimize waiting times, automatically adapting to the geometry of each part to be manufactured and avoiding trial and error operations.

The final oxygen content in TÍ-6AI-4V parts manufactured by this process is less than 2000 ppm (in compliance with ASTM E1409 and AMS 2249 standards).

DESCRIPTION OF THE FIGURES

To complement the description of the intelligent protection system for WAAM and in order to help a better understanding of the characteristics of the invention, according to a preferred example of practical implementation of the same, it is attached as an integral part of said description, some Figures where, with an illustrative and non-limiting nature, the following has been represented:

Figures 1a and 1b.- They show a schematic view of the intelligent local protection system, in which its main components can be seen: temperature sensor (2), protective hood (1), welding torch (3), clamping mechanism ( 4), welding wire (5).

Figure 2.- Shows a schematic view of the connections for the operation of the intelligent local protection system, in which its main components can be seen: manufactured part (6), protective hood (1), welding torch (3), mechanism of clamp (4), welding wire (5), arm (7), temperature sensor (2), robotic arm controller (8), solenoid valve (9), gas bottle (10). Figure 3.- Schematic of the robotic arm controller that regulates the operation of the solenoid valve and the passage of shielding gas and post-gas times.

PREFERRED EMBODIMENT OF THE INVENTION

A detailed explanation of a preferred embodiment of the object of the present invention is provided below, with the aid of the aforementioned figures.

The intelligent local protection system for WAAM with temperature control described is intended to optimize the post-gas times necessary to ensure correct protection of the material deposited in any specific part geometry. In this way, it is possible to avoid the oxidation of highly reactive alloys (for example, titanium or aluminum alloys), optimizing gas consumption and reducing manufacturing times.

The WAAM equipment allows to deposit weld seams layer by layer, generating a part with a geometry very close to the final one. For this, robots or CNC equipment equipped with arc welding sources (MIG-MAG, TIG or plasma) are used.

The protection device, shown schematically in figure 1, comprises a temperature sensor (2), coupled to the local protection hood (1) through which the protection gas will flow, which is joined in a solid way to the torch welding (3) by means of a clamping mechanism (4) surrounding it. The welding wire (5) comes out through the torch and melts forming weld seams that become part of the piece. In the preferred embodiment described here and as shown in figure 2, the device additionally comprises a solenoid valve that regulates the passage of gas (9) through the circuit and is connected to the gas supply system (10), to the hood ( 1), and to the robotic arm controller (8) that will send the order to the robotic arm to move the torch along with the bell and continue manufacturing. The hood has a lamellar structure inside to generate a laminar gas flow. As summarized in figure 3, the non-contact sensor for high temperature (2) is coupled to the local protection hood (1) installed in the WAAM equipment and measures the temperature of the material deposited at the end of each weld bead until the recorded temperature drops to a previously set temperature that prevents oxidation of the material. Once this condition is met, the robotic arm controller gives the order to close the gas and then to move the arm (7) or CNC axis system to continue with the deposition of layers.

The small size of the temperature measurement device allows a compact design of coupling to the protection device, without a significant increase in weight and integrable in conventional welding robots and WAAMs.

The procedure for optimizing local protection during additive manufacturing using WAAM, associated with the device described above, comprises the following stages:

- Placement of the local protection hood (1) on the welding torch (3);

- regulation of the focus position of the temperature sensor (2) to ensure its alignment with the required measurement point (6)

- connection of the shielding gas supply system (10) through the solenoid valve (9);

- connection of the solenoid valve (9) and temperature sensor (2) to the robotic arm controller (8);

- programming of trajectories and sequence of operations, either manually or with CAM tools, a constant pre-gas time is used, while the post-gas time after each weld is regulated through the robotic arm controller;

- start of welding and manufacturing operations through WAAM.

Claims

1. Intelligent local gas protection system for additive manufacturing processes using arc and wire, comprising the following elements: a welding wire (5) provided in the form of a coil that melts by means of the electric arc forming weld seams; a welding torch (3); a local protection hood (1) surrounding the space where the part to be manufactured is located; a shielding gas feed system (10); a solenoid valve (9) to control the shielding gas supply system; a robotic arm to which the welding torch (3) and the local protection hood (1) are attached; characterized in that the system also includes: a temperature sensor (2), coupled to the local protection hood (1); a robotic arm controller (8) connected to the solenoid valve (9) and the temperature sensor (2) so that the robot arm controller is programmed to send a signal to the solenoid valve to stop gas flow when the temperature is below a predetermined value and move the torch and hood to continue manufacturing.

2. Intelligent local protection system according to claim 1, characterized in that the local protection hood (1) is provided inside with lamellas to produce a laminar gas flow.

3. Intelligent local protection system according to any of the preceding claims, characterized in that the hood is integrally attached to the welding torch (3) by means of a clamping mechanism (4).

4. Additive manufacturing method using bow and wire with a system according to any of the preceding claims, characterized in that it comprises the following steps:

- Placement of the local protection hood on the welding torch; -connection of the shielding gas supply system controlled through the solenoid valve;

-placing the temperature sensor in the hood and checking the location of the measurement point-turning on the robotic arm, robotic arm controller, temperature sensor and solenoid valve;

-programming of trajectories of the robotic arm and sequence of operations for the manufacture of the piece by means of the deposition of weld beads;

- opening the solenoid valve for gas application; - deposition of the weld bead according to the programmed manufacturing sequence;

- where the robot arm and solenoid valve receive a signal from the robot arm controller to stop the gas flow when the temperature is below a predetermined value detected by the temperature sensor and move the torch and hood to continue manufacturing .