How does the Virtual Machine works?

Note: the following section provides a very rough and fuzzy explanation of the Virtual Machine (VM). The explanation of the structural sequences in the computer system of the VM itself has been omitted.

The basic idea behind the concept of the VM as welding process control for electronic generators is highly simplified as follows: do not attempt to control the physical variables occurring in the welding process such as current and voltage of an electronic generator, since these are not exactly deterministic predeterminable due to the complexity or freedom degrees of the process.

Instead: break down the individual process conditions during welding in very small time units or segments. Provide for your real welding machine for each of this time units a "complete machine" or an optimized generator, which are optimized exactly for this unit. Repeat this dismantling process according to the requirements of the respective welding task up to the end of the welding process.

The static and dynamic control implemented in the VM evaluates these rapidly changing process conditions. These are sequences which are happening in the thousandth of a second. The VM responds to each different state in the range of its cycle frequency of 20 kHz, thus within 50 microseconds.

In other words: depending on the process state, the VM provides within one second up to 20,000 different generators with optimum characteristics for a high-quality and optimal welding result. For this purpose, it uses a database, which is designed as an expert system with all necessary physical parameters, which optimally describe such generators in terms of their dynamic and static operating behavior.

Therefore the control concept of the VM makes it possible to configure the electronic generator of the welding machine with a cycle time of 50 microseconds completely new in terms of statics and dynamics. The parameters for statics and dynamics can be selected in physical quantities as “real text”, so that a 100% reproducibility of the process control is given.

This makes it possible to adjust the current source characteristics optimally for different process requirements in the simplest phase-dependent manner and, for example, to meet the requirements of the arc or its plasma..

Why are we talking about a ‘Virtual’ Machine?

Since each of these generators, looked at from the outside, represents classical elements of electrical engineering in their effect, for example, internal resistors or chokes, which actually act in conjunction with the process, but which are not present in reality and therefore do not generate losses, the use of the term "virtual" machine will be clarified - namely, as an option for a variety of possible generator states to be realized.

On the other hand, the computer system of the virtual machine has characteristics of a virtual system from the point of view of information theory.

Thirdly, the measuring technology of the ELMA-Tech spot welding machines have a virtual character, because it "acts" as if it would measure certain electrical quantities directly on the surfaces of the electrode caps of a spot welding gun, even though no measuring leads are placed there..

Advantages of the Virtual Machine

The immense advantages of using the ELMA-Tech process control vary depending on the application. However, there are some basic advantages common to all applications.

• High process reliability means reproducibility
  The splitting of a welding process or even of a thermal injection process into a multitude of individual processes, each of which is maximally optimized by a practice-oriented, evidence-based parameter database, ensures maximum reproducibility in accordance with carefully prepared welding programs. This is especially true for very complex processes.
  
  
• Best welding quality
  The exact process control of the ELMA-Tech welding machines by the welding process control Virtual Machine guarantees a very high quality of the welding results and the results of thermal spraying. In arc welding, for example, the "very cold" MIG AC process produces superior, warp-free seam qualities with absolutely spatter-free droplet transfer for thinnest aluminum plates and stainless steels.
  
  
• Maximum flexibility and fast adaptability
  Complexe process types can be decomposed into different, arbitrary optimizable phases or segments, as required for example in MIG-MAG welding or in further arc welding processes. Thus, the current energetic guidance can be adapted precisely to process requirements.
  
  
• High energy efficiency
  A generator controlled by the virtual machine always works with the efficiency of the power section (90 - 95%) irrespective of the current process state and thus is significantly superior to conventional generators in the energy yield.
  
  Generators powered by a virtual machine do not offer fixed parameters to a stochastically running process, but a workspace in which the source and the process can agree on current optimal working points. This provides excellent process stability.
  
  Especially in resistance spot welding this principle, combined with a virtual measurement of voltage and current at the electrode cap surfaces of the spot welding guns, ensures an optimum energy input, which can dispense with high contact pressure of the electrode arms and massive current application.
  
  

Plug & Weld spot welding by fully automatic

A particular advantage is the use of the virtual machine in resistance spot welding. The fully automatic point welding process is a clear and unique feature of the ELMA-Tech resistance technology and has introduced the Plug & Weld principle since 2003:

Start the machine - select automatic mode - weld!
Sheet thicknesses and material types are automatically detected by the welding control.

• No welding sample preparation required in advance
• No further parameterization necessary
• Recognize and weld high-strength steels
• Mix different materials without parameter setting in one welding process
• Weld easily up to 10 mm total sheet thickness
• Aluminum welding of thin plates up to 3 mm (car body repair)
• No need to teach staff anymore
• Effective energy input (as much energy as necessary for an optimal result
• Welding parameter assurance and quality assurance during spot welding
• The SpotQS Viewer software is used to record and evaluate welding parameters for vehicle-specific spot welds. The parameters as well as the welding result can be written to the USB flash drive after finishing a welding job. The recording of the welding result corresponds to the image of the QS traffic light in the operating front of a spot welding machine.

 

The process sequence in resistance spot welding

The process model of the Virtual machine has 4 distinguishable tasks to carry out to ensure a high-quality weld:

• Test of initial state through targeted energy input. Distinction between total-, partial isolation and ideal initial conditions. Detection of total thickness and steel type.
• Induce an initial “first-spot” by introducing a specific energy input. E.g. in case of a partial isolation, which is one of most common cases, the introduction of a specific energy input will cause the workpieces to join more easily.
• Carrying out the actual welding process (current-time program). Here the applied energy amount is continuously added up so that the welding process will end when the machine reaches the desired value.
• Determination of shunts etc. and compensation of possibly lost energy in the welding spot.
  
  

The Virtual Machine thus recognizes the condition of the parts to be welded, in particular whether there are shunts through structural adhesives, paint residues or other contaminants and adjusts the program accordingly to ensure a reproducible high quality spot weld.

Process control of the robot gun

Unique automatic system, in which the robot positions the welding gun in place of the point to be welded and then gives the full responsibility to the gun and the welding control (Virtual Machine). The control performs the following steps:

• Closing the gun’s arms with automatic balancing (float operation)
• Force build-up and detection of the overall sheet thickness
• Calculation of the point energy to be applied
• Starting the welding process with a phase-dependent generator characteristic
• Energy-guided welding process and terminating the process with the calculated spot energy
• Determination of steel quality (normal / high strength)
• Reheating according to the determined steel quality
• Qualification of the course of the process
• Opening of the clamp (7th axis function)
• Disable the gun’s balance
• Output of the accelerating contact FK to the robot

 

Applications

ELMA-Tech GmbH is the only manufacturer in the field of welding and coating technology with such a wide product spectrum. All systems are based on fast-clocked power parts with very low transformer weights in the range of resistance and arc.

• Resistance technology
  Mobile and stationary spot welding machines
  Manual- and robot-guided spot welding guns
  
  
• Arc technology
  Mobile arc welding machines
  High-power current sources for stationary heavy-duty applications
  
  
• Surface coating
  Mobile power sources for thermal spraying
  High-performance current sources for thermal spraying (arc welding)

VM3 - the third generation

On the one hand, the constant optimization of the VM technology consists of the up to date improvement and adaptation of the hardware and operating software of the control module.

On the other hand, a substantial consolidation and expansion of welding programs as well of the physical process parameters take place. These parameters have either been gained in the course of customer projects or have been developed in the in-house application engineering during test welds and are now running evaluated into the VM database. In this sense the "knowledge" of the VM is constantly growing. Thus the VM3 is "wiser" than the VM2.

Compared with the predecessor generation, the third generation of the VM comes with faster processors and a more up-to-date operating system for the communication exchange with the actual process control, which responds even much faster to adjustments of operator or robotic intervention.

The front panel of the VM3 (see picture) has been redesigned and consists of a 7 "TFT color display (16: 9) with an 800 x 480 px resolution as well as LED backlight. The user interface of the VM3 is now completely multilingual. For example, the interface can be offered to Chinese-speaking users in Chinese language. Furthermore, the VM3 is prepared for networking in applications with the organizational design concept Industry 4.0.

For the use of ELMA-Tech welding technologies, these innovations on the operator's side guarantee noticeable improvements in the user-friendliness. With regard to the industrial process quality, the quality of the welding results or the results in the thermal spraying as a whole, the VM3 raises the bar once more upwards.

Front panel of VM3

Legal Notice

VM structure and programs, all rights reserved, licensed by ELMA-IVG mbH, Aachen © Prof. Dr.-Ing. Peter Puschner, 1997.