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.)