CN118650266A - A friction stir welding stirring head downward pressure control system and method - Google Patents

Abstract

A friction stir welding stirring head pressing amount control system and method aim to achieve improvement of stability of a welding process and quality of a welding joint under the condition that the welding process is not directly measured through a distance sensor. The device comprises a spindle motor 04, a current and voltage sensor 10, a data signal acquisition board 11, a control computer 12, a Z-axis motor driver 13, a Z-axis motor 01 and a mechanical transmission device 02, wherein the spindle motor 04 provides the spindle rotation speed required during welding, and the spindle rotation is realized by inputting current and voltage; the spindle motor 04 is connected with the spindle clamp 03 through a mechanical connection and with the stirring head clamp 05 through a mechanical connection; the current and voltage sensor 10 converts the current and voltage electric signals input into the spindle motor 04 and the mechanical transmission device 02 in real time and transmits the converted electric signals to the data signal acquisition board 11; the control method can be used for realizing the improvement of the stability of the welding process and the quality of the weld joint by collecting the current and the voltage of the spindle motor, calculating the friction power and the instant torque in the friction stir welding process and performing real-time adjustment on the pressing quantity of the stirring head after comparing the friction power and the instant torque with the set torque value.

Description

A friction stir welding stirring head downward pressure control system and method

Technical Field

The invention belongs to the technical field of welding process parameter regulation and control, and in particular relates to a control system and method for the downward pressure amount of a stirring head in a friction stirring process.

Background Art

Friction stir welding is a solid-state connection technology for plate connection. During the welding process, friction heat causes the temperature of the welded part of the material to rise to a plastic state. The main process parameters such as the amount of pressure on the stirring head and the speed of the stirring head directly affect the temperature field in the welding area and the change in the thickness of the plastic layer. The change in the elastic-plasticity of the material also affects the torque and power of friction. The published invention patents (publication numbers CN 104625393 B and CN 205437482 U) use a distance sensor to detect the distance between the stirring head and the Z axis, which can regulate the amount of pressure on the stirring head during the friction stir welding process. However, these devices are often easily restricted by space in actual production applications, and the installation and maintenance steps are relatively complicated. In fact, by synchronously monitoring the current, voltage and speed of the spindle motor, calculating the spindle input power and analyzing the power loss during the welding process, the heating power acting on the friction and the dynamic torque of the welding process can also be obtained. From the welding heat input, it can be known that the stirring head rotation speed is a constant value. If the welding speed is too low, a wider thermomechanical affected zone will be generated, which will reduce the joint strength; if the welding speed is too high, the material will not soften enough and loose void defects will be easily generated. Therefore, the stirring head pressure amount needs to be accurately adjusted as the main parameter. For the circular closed Z axis where the stirring friction welding heating temperature field overlaps, the degree of softening of the plastic layer in the welding area is inconsistent, and the stirring head pressure amount needs to be dynamically adjusted. The present invention does not require a distance sensor, but directly collects the spindle motor current and voltage to calculate the real-time torque and feedback, and makes real-time adjustments to the stirring head pressure amount, which can improve the stability of the welding process and the quality of the joint welding.

Summary of the invention

The purpose of the present invention is to achieve the improvement of welding process stability and weld joint quality without direct measurement by a distance sensor.

The present invention is a control system and method for the downward pressure of a stirring head of a friction stir welding. The control system for the downward pressure of a stirring head of a friction stir welding comprises a spindle motor 04, a current and voltage sensor 10, a data signal acquisition board 11, a control computer 12, a Z-axis motor driver 13, a Z-axis motor 01, and a mechanical transmission device 02. The spindle motor 04 provides the spindle speed required for welding, and the motor inputs current and voltage to realize the constant speed rotation of the spindle; the spindle motor 04 is connected to the spindle fixture 03 through a mechanical connection, and is connected to the stirring head fixture 05 through a mechanical connection; the current and voltage sensor 10 performs real-time level conversion on the current and voltage electrical signals input to the spindle motor 04 and the mechanical transmission device 02, and transmits the current and voltage electrical signals ... to the data signal acquisition board 11; the current and voltage sensors 10 are connected to the data signal acquisition board 11 and the spindle motor 04 respectively through data signal lines; the data signal acquisition board 11 can perform digital discrete processing on continuous voltage and current level signals and transmit them to the control computer 12; the data signal acquisition board 11 is connected to the control computer 12 and the current and voltage sensors 10 respectively through data signal lines; the control computer 12 can analyze and process the data input by the data signal acquisition board, and after comparing with the set value, adjust the pulse frequency and output it to the motor driver; the control computer 12 is connected to the Z-axis motor driver 13 and the data signal acquisition board 11 respectively through data signal lines.

The control method of the friction stir welding stirring head downward pressure control system described above specifically includes the following steps:

Step 1: Initialize the control computer 12 and the data signal acquisition board 11;

Step 2: Collect the idling current and voltage of the spindle motor 04 when no welding is performed, and calculate the idling power of the spindle motor 04;

Step 3: Collect the idling current and voltage of the spindle motor 04 during welding and calculate its power, subtract the idling power of the spindle motor 04 to obtain the real-time welding friction power; in addition, establish a linear relationship model between the stir friction welding power and the downward pressure of the stirring head;

Step 4: When the welding friction power value is equal to the power value corresponding to the preset optimized stirring head pressure, maintain the current stirring friction welding stirring head pressure parameter unchanged; when the stirring friction power value exceeds this threshold, according to the preset process specifications, reduce the pulse frequency and reduce the speed of the Z-axis motor 01 in the welding direction; when the stirring friction power is lower than this threshold, increase the pulse frequency and increase the speed of the Z-axis motor 01 in the welding direction; the welding stirring friction power value is continuously fed back to the control computer 12, thereby dynamically adjusting the stirring head 06 pressure, forming a closed-loop control to achieve continuous and stable welding.

The beneficial effects of the present invention are as follows: 1. The Z-axis motor is a device for controlling the downward pressure of the stirring friction. It can directly monitor the real-time torque of the stirring head during the welding process without an external distance sensor, and dynamically reflects the degree of softening of the plastic layer of the welded metal during the welding process. 2. The real-time torque is obtained and fed back through the current and voltage of the spindle motor to adjust the downward pressure of the stirring head, thereby improving the stability of the welding process and the welding quality of the joint.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic diagram of the control system of the present invention, and the figure numbers and corresponding names are: 01-Z-axis motor, 02-mechanical transmission device, 03-spindle clamp, 04-spindle motor, 05-stirring head clamping device, 06-stirring head, 07-welding Z-axis, 08-workbench, 10-current and voltage sensor, 11-data signal acquisition board, 12-control computer, 13-Z-axis motor driver.

DETAILED DESCRIPTION

As shown in FIG1 , the present invention is a control system and method for the downward pressure of a stirring head of a friction stir welding. The control system for the downward pressure of a stirring head of a friction stir welding comprises a spindle motor 04, a current and voltage sensor 10, a data signal acquisition board 11, a control computer 12, a Z-axis motor driver 13, a Z-axis motor 01, and a mechanical transmission device 02. The spindle motor 04 provides the spindle speed required for welding, and the motor inputs current and voltage to realize the constant speed rotation of the spindle; the spindle motor 04 is connected to the spindle fixture 03 through a mechanical connection, and is connected to the stirring head fixture 05 through a mechanical connection; the current and voltage sensor 10 performs real-time level conversion on the current and voltage electrical signals input to the spindle motor 04 and the mechanical transmission device 02. And transmit it to the data signal acquisition board 11; the current and voltage sensor 10 is connected to the data signal acquisition board 11 and the spindle motor 04 respectively through the data signal line; the data signal acquisition board 11 can perform digital discrete processing on the continuous voltage and current level signals, and transmit them to the control computer 12; the data signal acquisition board 11 is connected to the control computer 12 and the current and voltage sensor 10 respectively through the data signal line; the control computer 12 can analyze and process the data input by the data signal acquisition board, and after comparing it with the set value, adjust the pulse frequency and output it to the motor driver; the control computer 12 is connected to the Z-axis motor driver 13 and the data signal acquisition board 11 respectively through the data signal line.

In the above-mentioned friction stir welding stirring head downward pressure control system, the Z-axis motor driver 13 can simultaneously output the electric energy required to control the rotation of the Z-axis motor 01 by controlling the pulse frequency; the Z-axis motor driver 13 is connected to the control computer 12 and the Z-axis motor 01 respectively through data signal lines.

In the above-mentioned friction stir welding stirring head downward pressure control system, the Z-axis motor 01 drives the motor to rotate with the electric energy output by the motor driver to achieve direction and speed control; the Z-axis motor 01 is connected to the Z-axis motor driver 13 through a data signal line, and is connected to the mechanical transmission device 02 through a mechanical connection.

The above-mentioned friction stir welding stirring head downward pressure control system, the mechanical transmission device 02 can convert the rotational motion of the Z-axis motor 01 realized by the mechanical transmission device 02 into the vertical linear motion of the spindle clamp 03; the mechanical transmission device 02 is connected to the Z-axis motor 01 and the spindle clamp 03 respectively through mechanical connection.

The control method of the friction stir welding stirring head downward pressure control system described above specifically includes the following steps:

Step 1: Initialize the control computer 12 and the data signal acquisition board 11;

Step 2: Collect the idling current and voltage of the spindle motor 04 when no welding is performed, and calculate the idling power of the spindle motor 04;

Step 3: Collect the idling current and voltage of the spindle motor 04 during welding and calculate its power, subtract the idling power of the spindle motor 04 to obtain the real-time welding friction power; in addition, establish a linear relationship model between the stir friction welding power and the downward pressure of the stirring head;

Step 4: When the welding friction power value is equal to the power value corresponding to the preset optimized stirring head pressure, maintain the current stirring friction welding stirring head pressure parameter unchanged; when the stirring friction power value exceeds this threshold, according to the preset process specifications, reduce the pulse frequency and reduce the speed of the Z-axis motor 01 in the welding direction; when the stirring friction power is lower than this threshold, increase the pulse frequency and increase the speed of the Z-axis motor 01 in the welding direction; the welding stirring friction power value is continuously fed back to the control computer 12, thereby dynamically adjusting the stirring head 06 pressure, forming a closed-loop control to achieve continuous and stable welding.

In the control method of the friction stir welding stirring head downward pressure control system described above, the data signal acquisition board 11 can simultaneously acquire current and voltage and feed them back to the control computer 12 for processing.

The control method of the friction stir welding stirring head downward pressure control system described above, the stirring head downward pressure adjustment method in step 2 is as follows:

The motor friction torque M(t) and friction heating power P are:

(1)

(2)

in, is the friction coefficient; p(r,t) is the friction pressure; R is the radius of the Z axis; r is the distance from a point on the Z axis friction surface to the center of the Z axis; n(t) is the friction speed;

Since n(t) is independent of r, then:

(3)

A computer can be used to realize real-time synchronous detection of the stator voltage and current of the spindle motor 04 and the friction speed. First, the input power of the spindle motor 04 is calculated, and then the heating power acting on the friction welding joint is calculated by analyzing and calculating various power losses in the friction welding process. The dynamic torque of the friction welding process is calculated according to formula (3).

The control method of the friction stir welding stirring head downward pressure control system described above calculates the relationship between the torque and the stirring head downward pressure: when the stirring head 06 rotates the welding material 07 at high speed, the current and voltage signals of the spindle motor 04 are collected and fed back to the data signal acquisition board 11 through the current and voltage sensor 10, and the data signal acquisition board 11 summarizes and generates a data curve to the control computer 12. The control computer 12 can calculate the real-time torque of the motor: when the stirring head torque exceeds a certain threshold, the stirring head 06 downward pressure is reduced; when the stirring head torque is less than a preset threshold, the stirring head 06 downward pressure is increased.

In order to better explain the present invention and facilitate understanding, the technical solutions and effects of the present invention are described in detail below through specific implementation modes in conjunction with the accompanying drawings.

As shown in FIG1 , the friction stir welding stirring head downward pressure control system of the present invention includes 01-Z-axis motor, 02-mechanical transmission device, 03-spindle fixture, 04-spindle motor, 05-stirring head clamping device, 06-stirring head, and 13-Z-axis motor driver, 10-current and voltage sensor, 11-data signal acquisition board, and 12-control computer. The workbench 08 is used to support and clamp the welding workpiece 07. The spindle motor 04 is connected to the current and voltage sensor 10, and the current and voltage sensor 10 is connected to the data signal acquisition board through a signal line. The data signal acquisition board is connected to the control computer 12 through a signal line, and the control computer 12 is connected to the Z-axis motor 01 driver 13.

The method for controlling the downward pressure of a friction stir welding stirring head of the present invention specifically comprises the following steps:

Step 1: Initialize the data signal acquisition board 11 and the serial port, timer and register inside the control computer 12.

Step 2: Adjust the data signal acquisition board and the control calculation program, record the current and voltage values collected when the spindle is idling without welding, and calculate the corresponding output torque value;

Step 3: Measure multiple groups of stirring head pressure data through preliminary tests, obtain the spindle motor torque value corresponding to the stirring head pressure when the welding area is in the most ideal state, input it into the control computer 12, and determine the stirring head 06 torque by measuring the difference between the spindle torque and the torque when the spindle is idling, use the control computer 12 to set the initial stirring head pressure, and establish a linear relationship model between the spindle motor 0404 torque and the stirring head pressure of the stirring head 04 according to the relationship between the stirring head pressure and the spindle motor 04 torque. At the same time, according to the preset ideal stirring head pressure value, calculate the stirring head pressure correction parameter of the stirring head 04, so as to realize the real-time adjustment of the stirring head pressure during the stir friction welding process; the method for correcting the stirring head pressure is as follows:

When the stirring head 04 rotates at high speed to weld the Z axis 07, the current and voltage sensor 10 collects the real-time current and voltage of the spindle motor at a fixed frequency and feeds it back to the data signal acquisition board 11. The data signal acquisition board 11 can feed back the real-time current and voltage signals to the control computer 12 in the form of signals that can be recognized by computer software. The control computer 12 calculates the real-time torque of the spindle motor 04 using the collected current and voltage data and obtains the real-time torque of the stirring head 03 by subtracting it from the torque when the spindle motor 04 is idling.

Step 4: When the spindle motor 04 torque is equal to the motor torque corresponding to the preset ideal stirring head pressure amount, maintain the current spindle rotation speed parameters unchanged; when the motor torque exceeds this threshold, reduce the stirring head 04 stirring head pressure amount according to the preset process specifications; when the motor torque is lower than the threshold, increase the stirring head 04 stirring head pressure amount; the control computer 12 feeds back the adjustment of the stirring head pressure amount to the numerical control system of the welding equipment, forming a loop control to achieve continuous steady-state welding.

Claims (8)

1. A friction stir welding stirring head downward pressure control system, comprising a spindle motor (04), a current and voltage sensor (10), a data signal acquisition board (11), a control computer (12), a Z-axis motor driver (13), a Z-axis motor (01), and a mechanical transmission device (02), characterized in that: the spindle motor (04) provides the spindle speed required during welding, and the motor inputs current and voltage to realize the spindle constant speed rotation; the spindle motor (04) is connected to the spindle fixture (03) through a mechanical connection, and is also connected to the stirring head fixture (05) through a mechanical connection; the current and voltage sensor (10) performs real-time level conversion on the current and voltage electrical signals input to the spindle motor (04) and the mechanical transmission device (02), and transmits them to the data signal acquisition board (11). The board (11) comprises a current and voltage sensor (10) connected to the data signal acquisition board (11) and the spindle motor (04) through data signal lines; the data signal acquisition board (11) can perform digital discrete processing on continuous voltage and current level signals and transmit the signals to a control computer (12); the data signal acquisition board (11) is connected to the control computer (12) and the current and voltage sensor (10) through data signal lines; the control computer (12) can analyze and process the data input by the data signal acquisition board, and after comparing the data with the set value, adjust the pulse frequency and output the data to the motor driver; the control computer (12) is connected to the Z-axis motor driver (13) and the data signal acquisition board (11) through data signal lines. 2. The friction stir welding stirring head downward pressure control system according to claim 1 is characterized in that the Z-axis motor driver (13) can simultaneously output the electric energy required to control the rotation of the Z-axis motor (01) by controlling the pulse frequency; the Z-axis motor driver (13) is connected to the control computer (12) and the Z-axis motor (01) respectively through data signal lines. 3. The friction stir welding stirring head downward pressure control system according to claim 1 is characterized in that the Z-axis motor (01) drives the motor to rotate to achieve direction and speed control when the electric energy output by the motor driver is used; the Z-axis motor (01) is connected to the Z-axis motor driver (13) through a data signal line, and is connected to the mechanical transmission device (02) through a mechanical connection. 4. The friction stir welding stirring head downward pressure control system according to claim 1 is characterized in that the mechanical transmission device (02) can convert the rotational motion of the Z-axis motor (01) realized by the mechanical transmission device (02) into the vertical linear motion of the spindle clamp (03); the mechanical transmission device (02) is connected to the Z-axis motor (01) and the spindle clamp (03) respectively through mechanical connection. 5. The control method of the friction stir welding stirring head downward pressure control system according to claim 1 is characterized in that it specifically comprises the following steps: Step 1: Initializing the control computer (12) and the data signal acquisition board (11); Step 2: collecting the idling current and voltage of the spindle motor (04) when no welding is performed, and calculating the idling power of the spindle motor (04); Step 3: The idling current and voltage of the spindle motor (04) during welding are collected and its power is calculated, and the idling power of the spindle motor (04) is subtracted to obtain the real-time welding friction power; in addition, a linear relationship model between the stir friction welding power and the downward pressure of the stir head is established; Step 4: When the welding friction power value is equal to the power value corresponding to the preset optimized stirring head pressure, the current stirring friction welding stirring head pressure parameter is maintained unchanged; when the stirring friction power value exceeds this threshold, according to the preset process specifications, the pulse frequency is reduced and the speed of the Z-axis motor (01) in the welding direction is reduced; when the stirring friction power is lower than this threshold, the pulse frequency is increased and the speed of the Z-axis motor (01) in the welding direction is increased; the welding stirring friction power value is continuously fed back to the control computer (12), thereby dynamically adjusting the stirring head (06) pressure, forming a closed-loop control to achieve continuous and stable welding. 6. The control method of the friction stir welding stirring head downward pressure control system according to claim 5 is characterized in that: the data signal acquisition board (11) can simultaneously collect current and voltage and feed them back to the control computer (12) for processing. 7. The control method of the friction stir welding stirring head downward pressure control system according to claim 5, characterized in that: the stirring head downward pressure adjustment method in step 2 is as follows: The motor friction torque M(t) and friction heating power P are: (1) (2) in, is the friction coefficient; p(r,t) is the friction pressure; R is the radius of the Z axis; r is the distance from a point on the Z axis friction surface to the center of the Z axis; n(t) is the friction speed; (3) A computer can be used to realize real-time synchronous detection of the stator voltage and current of the spindle motor (04) and the friction speed. First, the input power of the spindle motor (04) is calculated, and then the heating power acting on the friction welding joint is calculated by analyzing and calculating various power losses in the friction welding process. The dynamic torque of the friction welding process is calculated according to formula (3). 8. The control method of the friction stir welding stirring head downward pressure control system according to claim 5 is characterized in that the relationship between the calculated torque and the stirring head downward pressure is: when the stirring head (06) rotates the welding material (07) at a high speed, the current and voltage signals of the spindle motor (04) are collected and fed back to the data signal acquisition board (11) through the current and voltage sensor (10), and the data signal acquisition board (11) summarizes and generates a data curve to the control computer (12), and the control computer (12) can calculate the real-time torque of the motor: when the stirring head torque exceeds a certain threshold, the stirring head (06) downward pressure is reduced; when the stirring head torque is less than a preset threshold, the stirring head (06) downward pressure is increased.