The solution for complex welding processes:
                                 welding process control with Virtual Machine

Legal notice Virtual Machine

The process control Virtual Machine is based on in the patent DE 32 00 086 C3 (05.01.1982, Puschner P.) exposed and still valid technology for synthesizing static and dynamic behavior of electronic generators for welding applications and realizes the technical teaching described therein in a unique way.

With the advancing development of microprocessor technology, the Virtual Machine, already created in the structure in 1992 under the working title „Konzept 2000“, could be implemented for the first time in 1997 with a cycle frequency of 2 kHz - and only a few years later with 20 kHz.

The process control Virtual Machine and the process programs running in it are subject to copyright worldwide with the resulting legal protection. The only licensor is ELMA-IVG mbH in Aachen, Germany.

Currently, the Virtual Machine in its hardware, its basic program and the process programs required for the various processes, is developed and distributed worldwide exclusively by ELMA-Tech GmbH in Morsbach, Germany, and its cooperation partner Lachmann & Rink GmbH, Freudenberg, Germany.

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



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Use of the virtual machine in thermal coating

For a wide range of ambitious applications in the area of arc wire spraying and plasma coating ELMA-Tech supplies the process control Virtual Machine (VM), as well as secondary regulated high-current power sources in the power range up to 3000 A.

Objectives in these fields of application are, depending on the application, e.g. completely individualized injection processes with maximum process reliability (100%), optimized adhesive strength, finest spray textures, high layer thicknesses or also a desired higher layer porosity (the latter for example in the coating of cylinder surfaces in internal combustion engines).

General benefits of using VM process control in arc wire spraying

All optimum spray parameters for a wide variety of spray materials are already pre-set via the expert database. Spray parameter changes are possible during the injection process.

Finer spray coatings with simultaneously lower atomizing gas pressure mean a significant cost reduction. Higher adhesion values are achieved without the use of expensive spray materials.

  • Spray- / coating power sources are completely new configurable in terms of statics and dynamics with a cycle speed of 50 μS
    (Statics and dynamics in conventional power sources are in the construction and the coupling of transformer and choke and are therefore unchangeable fixed in the hardware and accordingly inflexible.)
  • Totally freely changeable current / voltage curves
  • Optional constant voltage or constant current control
  • New software-based ignition and spraying processes
  • Uniform layer application
  • Low thermal load of the substrate
  • Adaptability of the segment structure of the process
    A typical segment structure is e.g.:
    ARC START: Arc generation
    IGNITION: Arc takeover
    SPRAYING: Segment of spraying
    END OF SPRAYING: Drop separation, burn-off
  • Stable, constant arc guaranteed even at a power of only 10 amps

Arc wire spraying (AWS) with pulsed direct current (DC pulse)

Compared with other thermal spray processes, the inhomogeneity and porosity of the produced layer is usually higher when using AWS. As already mentioned, layer porosity is very desirable in some applications. A requirement to be met thereby lies in the requirement, that the pores are uniformly distributed throughout the complete cross section. Non evenly formed layers however are to be avoided!

The cause of non-uniform layer properties originates from the stochastic melting process of the wire electrodes in the arc. Due to different arc shapings at the anode and cathode, the wires are melted unbalanced. In addition, the arc length is not constant with conventional AWS power sources.

The use of AWS with DC pulse under a process control with Virtual Machine offers the following advantages:

  • Increase in the melting rate / application rate
  • Reduction of the heat load of the substrate by lowering the process temperature
  • Production of homogeneous and pore-minimized layers
  • Targeted and controlled particle separation
  • Lower process emissions

First results* of corresponding scientific accompanying research meanwhile prove the very good process results when using the DC pulse process also in the arc wire spraying:

„By varying the spray parameters in the pulsed LDS process with a prototype system and the spray gun from OSU-Hessler, a stable process characteristic and improved coating results could be demonstrated compared to conventional AWS.“

(* Abstract „Arc wire spraying with pulsed direct current“ (authors: D. Landgrebe, S. Brumm, S. Kunze, S. Weis) TU Chemnitz, Institute for Machine Tools and Production Processes; Westsächsische Hochschule Zwickau, Institute for Production Technology, Professorship for Joining and Coating Technology. 2018. (not yet published). The work carried out is currently funded by the BMWi as part of a ZIM cooperation project.)

On the control of complex, randomly influenced welding processes

Stochastic events - a requirement for the control of complex processes

All welding processes as well as processes of thermal spraying of any kind, whether hand-held or robot-controlled, must be controlled very precisely and flexibly.

Physical parameters, e.g. the material type of the materials to be welded, material thicknesses, current, voltage, wire feed, electrode forces, coating thicknesses, addiditves, process gas flow and time have to be optimally matched in different applications and also different welding technologies.

For example, in arc wire spraying the requirements vary up to an extremely individual and fine process management. At the same time, the exact reproducibility of these complex processes (process reliability) must be ensured in industrial applications.

The problem of controlling such process types

Controlling the physical quantities occurring in these processes, such as current and voltage of an electronic generator, is difficult because they are not exactly deterministic due to the complexity or degrees of freedom of the process - they are therefore stochastic (random) events in a certain context.

Process control with fixed characteristic curves only yields average values in the best case and can not react to stochastic changes in individual process phases. One could say that fixed characteristic curves do not allow „sensitive“ and customizable management of processes.

The solution: welding control with "virtual machine"

The individual process states during welding or thermal spraying are subdivided into discrete time units or segments. One basic idea is to be able to segment a process with start and end into individual areas (start, stationary area, exit), another to be able to react within a segment to process peculiarities with replacement of the generator characteristics as soon as possible.

Via the computer system of the virtual machine, those parameters which define the static and dynamic generator behavior are exchanged as often and as quickly as possible, so that a generator can be provided, which is optimally suited for each identifiable process phase.

This subdivision process into smallest time units is repeated according to the requirements of the respective welding task until the completion of the welding operation. The static and dynamic control implemented in the Virtual Machine evaluates these rapidly changing process states.

These are processes that take place in the thousandths of a second range. The Virtual Machine responds to any different condition within the range of its cycle frequency of 20 kHz, that is within 50 microseconds. The limit of the reaction time of 50μs already results from the technical possibilities to enforce modified action of the generator over connecting lines to the process. Each line between generator and sink (process) has inductive components that do not require a higher rotational speed of the slave processor, as an enforcement above 10 kHz can not succeed anyway.

Also other controls are practically replaced by the Virtual Machine: With such a structure, not only the generator character of the power source can be redefined, but also all other and peripheral controls of e.g. servo valves in welding guns or wire feeds in arc processes can be carried out.

More details

Benefits of the Virtual Machine in ELMA-Tech spot welding machines
Benefits of the Virtual Machine in ELMA-Tech arc welding machines
Benefits of the Virtual Machine in ELMA-Tech Aluminum spot welding systems

Hand and robot controlled arc welding with virtual machine

Like the spot welding machines, the ELMA-Tech arc systems also benefit from the qualities of the welding process control Virtual Machine (VM):

  • The characteristic of the current source (current or voltage source) can be freely selected depending on the process state and changed with a frequency of 20 kHz. This is made possible by an advanced design of the power source, which has no conventional resistors, but only simulates these corresponding to the shape of the current and voltage characteristics.
  • While conventional power sources usually have fixed values for their internal electrical resistances and inductances, the ELMA-Tech power source can assume any desired values. Thus, the process can be performed optimally at any time, whereas there is only one real optimal operating point with the conventional technology.
  • The VM recalculates the state of the welding process every 50 μs from the available process parameters and sets the current source characteristic to optimum parameters for this process state. The control speed is extraordinarily high at 20 kHz. Thus, even fast-running processes (Plasma, TIG, MIG-MAG, Submerged arc welding) can be controlled in a targeted manner. The individual defined process states are stored in the form of databases and the values to be set for the current source are linearly interpolated.
  • Due to the lack of internal electrical resistances the efficiency is at 95%, while conventional power sources are significantly lower. This also means a significantly lower power consumption.

Lowest heat input in aluminum arc welding

In a study of the Chemnitz University of Technology in 2015, various competitor processes were compared with ELMA-Tech AC pulsed welding. Here, the ELMA-Tech AC pulse welding proved to be the process with the lowest energy input into the lightweight materials.

ac puls EN

(The diagram shows the ELMA-Tech MIG-AC process on the far left. Abstract: Chemnitz University of Technology, Faculty of Mechanical Engineering, Institute of Machine Tools and Production Process, Chair of Forming and Joining: „Comparison of MSG standard with AC pulse welding for lightweight materials“, Author: Dipl.-Ing. Stefan Brumm, 19.06.2015.)

The scientific investigation comes to the following results:

  • "With AC-pulse welding, a stable welding process with few splatters is possible when joining aluminum."
  • "Heat input during welding with AC pulse lower than with CMT."
  • "Therefore suitable for welding thin aluminum sheets (<1 mm)"

DC pulse welding with Virtual Machine

Of course, the outstanding welding quality is also a feature of the ELMA-Tech pulse current (DC) systems, which ensure maximum gap bridging with the lowest possible energy consumption with reduced penetration depths and higher deposition rates.

For more information, visit our central website at AC pulse welding is performed, for example, by the AC welding machine MIDI MIG 300/800.


Hand and robot guided spot welding with virtual machine

The challenges in process control of resistance spot welding

The challenges of spot welding, with consistently reproducible and high-quality welding results in modern body construction as well as in the industrial production of metalworking, arise from the following factors:

  • The use of new materials (hardened, high-strength, coated, several and different thick sheets).
  • The different state of the materials on site at a time (possibly partial contacting by structural adhesive, paint residues, soiling, general oxidation, different surface properties).
  • The control of the resistance welding process requires, due to the non-constant process impedance and in part stochastic process history (see above), a perfect impedance measurement, which is, however, dealing with different problems during the running welding process. These problems can be traced back to the required voltage measurement in the immediate vicinity of the process at the location of the spot weld.
  • A process-based control of spot welding therefore requires a "virtual" measurement of the voltage to reconstruct the original waveform. For this ELMA-Tech has developed a corresponding reconstruction algorithm, which allows a technically perfect measurement of the process impedance.

In combination with the use of virtual machine and virtual measuring technology, a very fast reacting process control is made possible.


The general process model of the virtual machine for spot welding

It is possible to roughly distinguish four phases of a completely automatic spot welding, i.e. the setting of a single welding spot:

  • A targeted energy input tests the initial state of the materials to be spotted. A distinction between total insulation, partial insulation and ideal initial conditions takes place.
  • Second, a first formation of the welding nugget takes place by introducing a targeted energy input. In the most frequently encountered case of partial insulation, the introduction of a targeted amount of energy brings about an approximation of the sheets to be welded in the joining area.
  • The actual welding process is then carried out using the classic current-time program. In doing so, the amount of energy introduced is continuously added up in order to end the welding process, when a desired energy is reached.
  • Finally, there is a determination of design-related shunts or shunts resulting from the joining process itself. The energy loss of the welding nugget formation e.g. through shunts is now being added.

The Plug & Weld principle ensures that this process runs completely automatically. Incidentally, this also includes the automatic measurement of the sheet thicknesses to be welded and the recognition of the types of material of the used sheets. For these reasons, it is not necessary for the user to enter welding parameters before a welding process. The aspects just described are implemented, for example, in our mobile spot welder MIDIspot VISION.


The extended process sequence for robot-guided spot welding

In this process, the virtual machine takes over other tasks of process control, which are in other concepts usually performed by the robot controller:

  • Closing the gun arms with automatic balancing (float mode)
  • Force generation and detecting the overall sheet thickness
  • Calculation of the spot energy to be inserted
  • Start of the welding process with phase-dependent generator characteristic
  • Determining the quality of steel (normal / high-strength)
  • Terminating the process with the determined point energy
  • Qualification of the process
  • Opening of the gun (7th axis function), disabling the balance of the gun
  • Output of the FK switch contact to the roboter

A more technical description of the fully automatic spot welding system for application in automotive industry download here.


Decide on welding qualities and process properties in a whole new dimension

With the market launch of the process control ©Virtual Machine (abbreviated below also as VM) in 2008, ELMA-Tech GmbH has raised the process characteristics and welding qualities of its welding machines in resistance spot welding and arc welding to a completely new level of quality.

And in conjunction with the ELMA-Tech high-performance power sources, the ©Virtual Machine also ensures extremely fine and individually adjustable process control in the field of thermal coating (arc wire spraying and plasma spraying) with the very best coating results.

Forschung und Entwicklung 2018 web en

The Donor Association for German Science once again honors the research activities of ELMA-Tech with the seal of quality "Innovative through Research".


Areas of application of process control ©Virtual Machine:

  • Manual and automated spot welding
    Benefits, etc.: Plug & Weld without previous parameter settings.

  • Manual and automated arc welding
    Advantages and others: Outstanding process properties and welding results in DC and AC pulse welding (AC welding), keyword: Cold MIG AC process.

  • Automated thermal coating
    Benefits include: arc wire spraying with pulsed direct current for evenly distributed porosity throughout the entire layer.

You need further information or advice? Please contact our international distribution partners in your region!

For legal information about the Virtual Machine please click here ...


VM3 - benefit from the 3rd generation now: even faster, even more precise!

Only in conjunction with ELMA-Tech welding and arc wire spraying systems!

Fully automatic spot welding

Plug & Weld: Welding without any prior adjustment of welding parameters, such as material and sheet thickness.

Clear quality statement about each welding point directly at the welding gun, at the welding machine or on an external manual control!

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