Advanced Gas Tungsten Arc Weld Surfacing Current Status and Application

Soldagem & Inspeção. 2015;20(3):300-314 http://dx.doi.org/10.1590/0104-9224/SI2003.05 Technical Papers Advanced Gas Tungsten Arc Weld Surfacing Current Status and Application Stephan Egerland1, Johannes Zimmer1, Roland Brunmaier1, Roland Nussbaumer1, Gerhard Posch1, Bernd Rutzinger1 1 Fronius International GmbH, Wels, Austria. Received: 16 July, 2015 Accepted: 05 Oct., 2015 E-mail: (SE) Abstract: Gas Shielded Tungsten Arc Welding (GTAW) – a process well-known providing highest quality weld results joined though by lower performance. Gas Metal Arc Welding (GMAW) is frequently chosen to increase productivity along with broadly accepted quality. Those industry segments, especially required to produce high quality corrosion resistant weld surfacing e.g. applying nickel base filler materials, are regularly in consistent demand to comply with “zero defect” criteria. In this conjunction weld performance limitations are overcome employing advanced ‘hot-wire’ GTAW systems. This paper, from a Welding Automation perspective, describes the technology of such devices and deals with the current status is this field-namely the application of dual-cathode hot-wire electrode GTAW cladding; considerably broadening achievable limits. Key-words: GTA weld cladding; Single-cathode GTAW; Hot-wire welding; Dual-cathode GTAW. Revestimento com GTAW Avançado: Estado da Arte e Aplicações Resumo: Gas Tungsten Arc Welding (GTAW) é um processo bem conhecido por proporcionar alta qualidade da solda mas juntas com menor desempenho. Por isto o Gas Metal Arc Welding (GMAW) é frequentemente escolhido para aumentar a produtividade, considerando que a qualidade é também amplamente aceitável. Segmentos da indústria, especialmente àqueles que requerem a produção de revestimentos resistentes à corrosão com alta qualidade, por exemplo, aplicando material de enchimento à base de níquel, estão regularmente sob consistente demanda para atender os critérios “zero defeito”. Neste contexto, limitações na soldagem podem ser superadas com o emprego de sistemas avançados GTAW ‘arame‑quente’. Este artigo, sob a perspectiva da automação da soldagem, descreve a tecnologia de tais sistemas e apresenta o estado da arte nesse campo – principalmente quanto a aplicação do revestimento por GTAW com dois cátodos e arame quente, que amplia consideravelmente os limites alcançáveis do processo. Palavras-chave: Revestimento por GTAW; GTAW cátodo único; Soldagem arame quente; GTAW cátodo duplo. 1. Introduction Arc welding, to the widest extent, is suggested utilised for fusion welding. The major remainder; i.e. weld surfacing, is supposed reasonably split into ‘hardfacing’ and ‘corrosion resistant’ weld overlay [1,2]. Economic considerations drive manufacturers to apply high performance weld surfacing processes, such as Submerged Arc Welding (SAW) or Resistance Electro Slag Welding (RESW). Although producing broadly acceptable quality, these processes are specifically limited respectively due to compulsory use of flux (limited out-of-position capabilities), high dilution, or undesirable aspect ratios. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License which permits unrestricted non-commercial use, distribution, and reproduction in any medium provided the original work is properly cited. Controlled Gas Metal Arc Welding processes (e.g. CMT), have been introduced to the industry coping with dilution related issues, e.g. corrosion [3] and thereby partially replacing SAW and RESW. Surfacing applications exist, however, defining ‘zero defect’ criteria paramount to prevent complicated rework, sustainably assure highest weld surfacing performance and maintaining long-term component durability. Though joined by limited performance in arc efficiency and weld deposition rate Gas Shielded Tungsten Arc Welding (GTAW) is frequently applied in such cases. To overcome lack of performance, systems have been developed modifying the wire feeding process hereby leading to either ‘cold-wire’ or ‘hot-wire’-GTAW. While the former was early revealing process instabilities and noticeably rather difficult deployable [4,5]; the latter appeared capable of tackling inconsistencies, mainly, by preheating the wire. Advanced Gas Tungsten Arc Weld Surfacing Current Status and Application Manz [6] early described the advantages e.g. a significant increase in weld deposition rate through beneficially using the resistive I 2 R wire heating and, compared with cold-wire GTAW, hereby achieving wire feed rates “3 to 10 times faster” into the weld pool [4]. Hot-wire GTAW systems continuously advanced, are nowadays well‑accepted because of providing user benefits [2,7,8]. Information on the operational relationship applying ‘hot-wire’ and ‘cold-wire’ GTAW is given in [6] and according to this author proper parameter set up would even allow to deposit the wire without any additional arc. This is due to electrical resistive heating of the wire of a specific composition and diameter according to Equation 1 [6]: I 2 R = I 2 L r / d 2 (π / 4 ) (1) where r is the apparent resistivity of the wire material, L is for the effective wire extension length and d is the wire diameter. The energy required for melting the wire can be expressed as Equation 2: Emelt = HF d d 2 (π / 4 ) (2) where H is the heat content of the liquid wire volume, F is the wire feed rate and d is the apparent wire density. Figure 1 adopted from [6] schematically depicts the hot-wire GTAW principle and Table 1 provides information to numbers and denotations used in Figure 1. Wire feed rate F can be computed as Equation 3: ( F = I 2 L ( ES ) / π d 2 / 4 ) 2 (3) ES is here referred to as the “extension sensitivity constant” [6] dependent only on the wire material composition. Correspondingly solving for the wire extension length, L leads to Equation 4: ( L = F πd2 / 4 ) / I ( ES ) 2 2 (4) ES can be derived from Equation 5: ES = r / H d (5) Figure 1. Schematic hot-wire GTAW system. After [6]. Table 1. Denotations and numbers in Figure 1. N Shield gas nozzle E W H M Tungsten electrode Wire reel Hot-wire power supply (CV mode) Wire feed motor Soldagem & Inspeção. 2015;20(3):300-314 R S T 10 11-14 Feed rolls GTAW power supply (CC mode) Contact tube Filler wire Welding leads 301 Egerland et al. The apparent resistivity, r, i.e. the difference between melting- and room temperature resistivity, can be approximated as Equation 6: = r r melt − r ambient / ln ( r melt / r room ) (6) while the apparent wire material density d can be obtained from Equation 7: = d d melt − d ambient / ln (d melt / d ambient ) (7) According to [6], ES is proportional to the I 2 R deposition rate value; thus, higher resistant wires comparably provide higher deposition rate vs. lower resistivity electrodes. Due to mechanised wire feeding cold-wire GTAW provides relatively high deposition rates. Frequently joined by instabilities in suppl (...truncated)