Resistance Welding Control

Resistance Welding Controller 

Manual

I   Introduction

1. Basics of the Variable Frequency Controller

The Variable Frequency Controller takes three-phase AC 50/60Hz power input. This is rectified and smoothed into direct current. The IGBT inverter stage then switches this DC voltage across the primary side of the welding transformer. IGBT K1 provides the variable AC frequency and IGBT K2 switches the voltage at the high frequency carrier frequency of 5kHz. This provides a combination of adjustable AC frequency and precise control of the welding current.

2. Variable Frequency vs. AC Welding Controller Comparison

Compared to AC welding controllers, Variable Frequency Controllers have higher heating efficiency and lower peak currents for the same welding performance.

The figure on the left below shows a AC welding waveform at 50Hz input power frequency and a 10kA secondary current with an 80:1 turns ratio on the transformer. On the right is a Variable Frequency Controller producing the same output current.

  Compared to AC welding controllers, the Variable Frequency Controller has the following advantages:

1. The three-phase AC mains input exhibits more balanced power usage and a higher power factor

2. For the same weld, the weld time is shorter, saving electricity

3. The welding stability region enlarges, providing better process control

4. The electrode life is longer

5. A wider range of materials can be welded with good results, including aluminum, galvanized sheet, high-tensile steel, stainless steel, magnesium alloy, carbon steel, titanium, etc.

6. Also produces good results when welding three-layer materials and thin materials

7. Fewer expulsion events are generated, resulting in higher weld strength and better cosmetic results

8. Higher weld spot quality due to faster electric current control response due to the high-frequency switch driver

II   Components of the Control System

The entire control system consists of the welding controller, the welding transformer, and the welding gun. The welding controller consists of the power supply, the rectifier, the capacitor, IGBT, and the CPU.

 1. Main features:

1. Welding frequency: programmable between 15.0Hz and 400.0Hz. 

2. Can program up to 15/31 welding schedules.

3. Three section of thermal processes: Preheating, welding, tempering. Each process has its own current stepper.

4. Programmable output: 3-stage outputs can interface with PLCs, robots, etc.

5. Spot weld count monitoring function.

 2. Technical parameters:

1. Input voltage: 3-phase 380V/400V/480V, 50Hz/60Hz, power variation +10%, - 20%.

2. Output voltage: PWM 500V/550V/600V.

3. Output current: When the duty cycle is no more than 10%, depending on the control model, the maximum electric current output is 200A,400A, 800A, 1000A,1200A,1600A, 2400A. Model D ending controller, When the duty cycle is no more than 5%, depending on the control model, the maximum electric current output is 800A,1000A, 1600A.

4. Cooling water: : Flow rate base in nameplate ，PH=6-8,0.2MPa≤hydraulic≤0.4MPa,differential pressure≧0.15MPa,can not moisture condensation. Ambient temperature: 0-50℃.

5. Air valve voltage: DC 24V.

III   Weld Control Functions

The weld control system has two modes: spot welding and seam welding.

Spot Welding

There are two spot welding modes: single spot welding & repeated spot welding

1. Single Spot Welding: When the start signal is asserted, the welding process begins immediately. When the welding process is complete it will generate a signal to indicate completion. In all our control systems there is a standard parameter that can be set to “prohibit initiation”. This permits or prohibits the initiation of the welding process. When this parameter is ON it will not allow the use of the welding operation; when this parameter is OFF the user is able to use the welding control system. The figure below shows the time sequence for the single spot welding process:

2. Repeated Spot Welding: during the process of repeated spot welding, the welding proceeds according to programmed parameters as long as the Start signal is asserted. In each weld cycle, the solenoid actuates, the weld is performed and the solenoid valve is released. At this time a delay equal to the OFF time begins. After the OFF time has elapsed, the solenoid valve will close, and resume the next welding process. The following figure shows the process for Repeated Spot Welding:

Seam  Welding

There are two seam welding modes: Normal Start Seam & Pulse Start Seam

1. Normal Start Seam (Pulse Start OFF): In this mode, the second pulse output circulates to form the seam weld process, based on the seam welding wheel, the electric current outputs continuously until the start signal is disabled, at which time the welding process ends. The following picture shows the process for Normal Start Seam welding.

2. Pulse Start Seam (Pulse Start ON): According to this mode, after Start signal is asserted once, the electric current outputs continuously until the start signal is asserted for a second time, at which point the welding process ends

When the welding controller is in seam welding mode, the welding current switches between up to 4 “segments”, which represent 4 different currents and timing pairs. When the “SEAM TIMING” parameter is ON, the Cycle Current switch is valid, and is used to cycle between the segments in the order SEAM 1, 2, 3, 4.

Not all segments have both a time and current setting, and some of the segments can be disabled by setting the values to 0.

· SEAM 1 TIME (1-9999ms) and 2. HEAT give the current and and time for the first segment. Neither parameters can be set to 0 – this segment is always enabled.

· SEAM 2 TIME (0-9999ms) and SEAM 2 HEAT give the time and current for the second segment, if used (set to 0 otherwise).

· SEAM 3 TIME (0-9999ms) and SEAM 3 HEAT give the time and current for the third segment, if used (set to 0 otherwise).

· SEAM 4 HEAT gives the current in the final weld segment. Time in this segment is controlled by the start switch. After completion of this segment, welding ends. When the weld time is complete, but the start switch remains ON, the welding current will be as set by SEAM 4 HEAT until the Start switch turns off, whereupon welding is over. When weld time is complete and the start switch is already off, welding is immediately complete.

3. Cool ratio (0-99.99%): (half cycle-welding time)/half cycle *100.0%

This is the ratio of weld current active time to current off time. The figures below show cool ratios of 0% and 20%:

4. DC/AC

Set by parameter “DC/AC”: 0/DC, 1/AC. It is AC by default.

The AC welding controller every cycle time is set by parameter “INVERTER/SCHEDULE” frequency, when the  “INVERTER/SCHEDULE” is 0, it is determined by “INVERTER Frequency”; when the SCHEDULE Frequency<15 and isn’t equal to 0, the controller will alarm “ILLEGAL DATA!” while the start switch is on.

When the controller works in DC mode, seam welding is not possible.

DC mode

Note: in this mode, 1.WELD CYCLE (i.e. pre-heat) must be greater than 2ms. If it is less than 2ms, the controller will emit an “ILLEGAL DATA!” alarm when the start switch is triggered, and welding will not proceed.

a. 2.WELD CYCLE is equal to 0 – there is only one weld phase:

b. 2.WELD CYCLE isn’t equal to 0: the pre-heat phase is followed by one or more phase cycles:

AC mode

Note: in this mode, 2.WELD TIME can’t equal to 0, or else, the controller will emit an “ILLEGAL DATA!” alarm when the start switch is triggered.

IV   Programming Console

Welding Modes

The welding controller can operate in several modes, which can be selected by the “Mode” button on the user interface. The modes are as follows:

1. Welding mode (WELD): In this mode the welding control operates normally, and performs actual welds.

2. Test mode (TEST): In this mode, the welding control only allows outward movement and there is no actual welding current output.

3. Programming mode (PROG): In this mode, the parameters of the welding controller can be programmed.

4. Monitor mode (MONI): Under this mode, the user can manually advance each step in order to check for accuracy and investigate possible problems in the welds.

5. Press mode (PRES): the start switch controls the value output.

HMI:

Basic interface introduction：

   Password setting page: password input and modification：

Welding sequence page: basic welding parameter Settings

 Welding Settings page: basic welding parameters Settings

       System parameters page: set system parameters

               System Settings page: system Settings related parameters

                Current monitoring page: welding current monitoring related parameter Settings

 Step increase control page: step increase related parameter Settings

Monitor page: monitor welding results

 Free Programe output: free programe output parameter Settings

Seam weld: seam weld parameter Settings