Welding Cell 4.0 - how to increase stability of welding quality & productivity?

Which disadvantages do traditional welding cells have?

Robotic spot welding lines for car bodies consist of individual welding cells, each of which includes a robot, welding tongs and control equipment. Traditionally used welding cells have a number of disadvantages that adversely affect the reliability of achieving welding quality and productivity. Firstly, actual welding force at electrodes differs from the set one because of the external influencing factors, such as wear of the gun or temperature change. Secondly, delivered force at each electrode might differ from each other due to variations of car body or parts position at the tooling. Productivity might be decreased because of the lower speeds limited by robot control settings. Some process functions, such as gun equalization due to gun flexion and approaching the weld spot are also not fully efficient as they are energy inefficient and require more time when performed by a robot. Finally, the processes of setting the line, retuning and maintenance procedures such as calibration are also time-consuming and require high qualification of personnel.

Variation of car body position across conveyer causes force variation at fixed electrode which results in force difference between electrodes

Gun opening/closing dynamics is limited by robot controller

To achieve a given probability of the quality in each spot, increase the overall productivity of the assembly and provide the ability for fast retuning of welding lines Diakont has developed a Welding Cell 4.0 solution

Modified cinematic scheme of a weld gun

Each electrode of a weld gun is equipped with an independent compact actuator to perform force reach and equalization without excessive robot movements. Force is managed by a new algorithm with two force feedback sensors for each actuator.

Digital twin as a core of the control unit

The controller analyzes the current welding process in real time considering all significant parameters, predicts the probability of achieving the specified welding quality based on the digital twin, and if necessary issues commands to correct the operating modes of the cell equipment.

Optimization of robot motion trajectory

Thanks to having actuators at both electrodes, robot motion trajectory is seriously optimized: it moves the gun parallel to the part from one weld spot to another, while closing / force reach / equalization is performed by actuators only. As a result, overall time for the welding program is shortened.

Welding Cell 4.0: how does it actually work?

Direct measurement of parameters affecting quality

In order to get relevant and accurate data about the welding process, a set of feedback sensors installed on the gun an other welding line equipment perform direct real-time measurement of all significant parameters (pressing force, electrodes position, welding current, temperature etc.) for the ongoing welding task.

2. Smart transmission of necessary and sufficient real-time data

For in-time reaction to the collected data from feedback sensors, fast speed of data transmission is necessary. To provide such speed and required level of data resolution, a set of digitization and prioritization devices were developed and integrated by Diakont engineers to the Welding Cell 4.0 control unit.

3. Digital Twin: prognosis and adaptive control

Welding Cell 4.0 controller analyzes the ongoing welding process by a set of significant parameters for this process, then on a base of digital twin a probability for achieving the set welding quality is being calculated. As a result, corrective commands for the welding line equipment are sent if necessary.

4. Real-time corrective commands for control units

Based on the digital twin calculation a set of commands to welding line equipment to correct the controlled parameters is sent. Thanks to specially developed algorithms and the control equipment modules overall cycle of interaction between the controller and the welding line is executed in an instant and efficient way.

What are the effects for welding lines?

Effect #1. Improving the reliability of welding quality consistency

Thanks to the improved structure and control algorithms, the welding force with Welding Cell 4.0 system is maintained more accurately during the operation of the welding line.

To assess the stability of the force, comparative tests of a traditional cell with a KUKA robot (ServoGun Basic) and a Welding cell 4.0 were carried out. As a result of the test Welding Cell 4.0 showed a better force stability. The processes occurring during the operation of the cell - heating of the equipment or electrodes tips dressing – did not cause force deviation.

Moreover, difference of force on electrodes is also substantially lower thanks to the use of a second actuator with a separate force sensor.

Better force stability and lower force difference means less defected parts, less costs for reworks & quality checks and lower unit costs as a result

Effect #2. Increasing the productivity

Tests of the Welding Cell 4.0 showed a reduction in the time for spot welding due to faster build-up and of force equalization, as well as closing and opening of the weld gun. Let’s compare a typical welding cycle performed by a conventional welding cell and Welding Cell 4.0 divided by stages of the cycle and see the results in time saving and increased productivity

Besides the advantages within the welding cycle itself, thanks to two actuators at both electrodes of the welding gun, which are used in Welding Cell 4.0 and smart control algorithms it is possible to achieve productivity advantages also when considering overall welding program. For example, thanks to the optimized gun equalization technology with two moveable electrodes, this part of the process takes less time and energy:

Additionally, it becomes possible for the robot to move the gun parallel to the surface of the welded parts and not lose time for precise and longer movements when approaching each welding spot. These smaller movements can be effectively performed by the actuators at each electrode. As a result, gun motion trajectory becomes shorter which also saves time comparing to traditional welding cells:

Shorter welding cycle = possible to make more spot welds per cell = possible to decrease number of cells required

Effect #3. Time saving with simplified tuning and less maintenance

Easier line setup and tuning

Thanks to the introduction of the digital twin, the whole welding program can be set up from the controller of Welding Cell 4.0. Adaptive functions and ability to real-time prognosis decrease the need for highly qualified welding engineers and robot specialists: the system optimizes the settings for each weld.

Less time for teaching the robot

Usually when designing a weld program operator has to carefully approach each spot manually and make sure that all the robot movements are carefully set to avoid bad welds. With Welding Cell 4.0 functionality it is possible just to move the gun to the area of the weld spot and rest of the settings for each specific weld will be automatically selected

No need for regular calibration

Less time required for tuning and calibration work – less costs involved

What are the economic benefits?

In order to evaluate the economic effect of "Welding Cell 4.0" implementation, an economical model of the robotic spot-welding line has been developed, which takes into account: