Thermal Joining Processes

Characterization of thermal joining processes

Thermal joining processes: A broad range of applications

Body in white (Source: fotolia)
Body in white (Source: fotolia)

Commercial application of welding processes in industrial production requires a high degree of planning reliability. The proper development of a welding schedule, which is necessary for the definition of welding sequences, intervals, and programming of welding robots, is important for the quality of a welding process. Additionally, one should be able to choose the right material, the applied welding process, as well as the correct application of clamping tools.

EN 14610 defines welding as a “permanent connection of components through application of heat and/or pressure”. The components are connected either by melting or by heating, and by applying additional forces (pressure). There is no other joining process which allows such resilient and dense connections with minimal space requirements. Furthermore, welding is the method of choice when it comes to the joining of assemblies with high levels of complexity. There are more than 100 different welding processes depending on the specifics of heat input and pressure application. Besides the usual application of welding as a joining method for metals, the importance of the welding process for joining of plastics and glasses is increasing.

Although joining is the main application field of welding processes, it is also used in deposition processes in order to create durable and hard surfaces by means of cladding.

Typical Industries and Fields of Application

Welding technology is used in following industries:

  • Transportation
    • Automotive industry (car body and frame, exhaust systems, mounted parts, i.e. doors and hatches)
    • Special purpose vehicles (agricultural machinery, crane construction)
    • Railway vehicle manufacturing (exterior body shells, pivot mountings)
    • Aerospace industry (exterior body shells, engines, tanks)
    • Shipbuilding (hulls, propulsion)
  • Energy sector
    • Offshore (windmill towers, foundation structures)
    • Turbines
    • Pipeline construction
  • Structural steelwork and plant engineering
    • Bridges
    • Towers
    • Pressure vessels
  • Medical engineering
    • CT and MRT devices
    • Body housing of X-ray machines
    • Implants (additive manufacturing)

Trends and Developments

Assembly line with robots (source: KUKA GmbH)
Assembly line with robots (source: KUKA GmbH)

There have been two main demands from industry to researchers during the past few years. First, in order to move further towards energy efficiency in the automotive industry, the importance of lightweight construction is increasing. The development of new high-strength materials, as well as welding of dissimilar alloys, like steels, titanium and aluminum alloys, are representing a serious challenge for joining technology. Second, decreasing energy consumption during the production itself is desirable. The amount of filler material is reduced and lap joints are replaced with butt joints in order to reduce the overall weight of the product. Welding processes with low energy input, numerical welding simulation, and application of virtual welding trainers contribute to the overall goal to make joining technology more energy- and material-efficient.

A lot of progress has been made concerning the combination of different welding processes (hybrid welding). The combination of metal arc welding with laser beam welding in particular has been successfully adapted for industrial production through utilization of the advantages of both processes. These advantages include high energy density, penetration depth, and the feed rate of a laser beam welding process as well as high gap bridging ability and the minimal welding defects of an arc welding process. Both processes combined allow single pass welding of components with thick walls, which would be not possible for each process applied by itself. Furthermore, if it comes to joining of aluminum components, such hybrid approach helps to reduce the usage of fluxing agents, simplifying the process chain and reducing the number of needed production steps.

Hybrid processes such as these have a high economical potential. On the other hand, industry tends to reduce investments in welding technology wherever possible instead of making investments in new technologies. Expensive staff training is often reduced by subcontraction, which also reduces required manpower. Thus, at the moment it seems that recently developed welding processes will not succeed on the market. Only welding equipment for established processes seems to be worth the investment. In this case, there is a higher probability for investment in new welding equipment when it comes to replacement of older equipment. Due to a lack of experienced welding specialists, available professionals are forced to complete more demanding work in less time. Simultaneously, “easy” tasks are given to less experienced workers. This situation leads to an increased amount of mistakes due to insufficient abilities of staff members and overloading of experienced specialists. Labor costs, as well as overall costs for development and trial tests, are expected to increase.

Welding simulation software offers the possibility to capture the institutional knowledge of welding processes, allowing virtual try-outs that help to investigate process parameters and their influence on the results of an applied welding process, as well as support in finding and documenting convenient process parameters.

Based on T.A. Cook study: „Schweißtechnik in der Prozessindustrie: Der unerkannte Kostentreiber /Welding technology in the production industry – the unknown cost driver"

 

Thermal Joining challenges

General weldability

In order to prove the general weldability of a structure, one has to consider and plan the weld reliability (design), weldability (choice of material), and welding feasibility (manufacturing). These domains interact with each other – particularly with regard to welding distortions.

 

Welding distortions and other physical effects

Distortions simulated with Simufact Welding
Distortions simulated with Simufact Welding

Welding distortions play economically together with reduced strength of a component - the most important role for a welding process design or of a welding assembly design. Unexpected welding distortions often cause expensive subsequent machining and straightening steps.

Additionally, further effects might influence the quality of the final product. Depending on the choice of material, welding sequence and welding process, residual stresses can significantly reduce the strength of single joints or of the whole assembly. Furthermore, the material properties can change due to heating and cooling, also leading to undesirable effects (i.e. notching effects and stress concentration due to phase transformations). Compensation of such effects usually leads to more and thicker materials, making the assembly heavier and bigger and therefore more expensive, also influencing the joining process itself, i.e. leading to multilayer welding.

Read more about the causes of welding distortions.

Typical Applications for Welding Simulation

The main goal of calculations made by Simufact Welding is a prediction of welding distortions. Due to the implementation of material models, we are also able to calculate phase proportions, material conditions, and resulting local material properties, as well as further effects like transformation induced plasticity and transformation strains.

How can Simufact welding provide support during the design of a welding process or of a welding assembly?

Depending on the expected result quality and the desired calculation time, Simufact Welding can be used during

Both applications can significantly reduce the experimental efforts allowing studies of different assemblies, clamping tools and fixtures as well as welding sequences before there has been time and money invested in prototypes, components and welding equipment. The above mentioned advantages of Simufact Welding also reduce the time-to-market of the final product largely reducing development time and costs.

Economical benefits of faster welding process design

App. Economical benefits
(Source: Fotolia - Africa Studio)
  • High efficiency of the development process due to a reduced number of expensive failed attempts
  • Decreased expenses of manufacturing of prototypes
  • Reduction of machining and straightening costs
  • Reduction of development times which leads to shorter time-to-market
  • Decrease of material and energy consumption for experimental investigations
  • Reduction of manpower needed for experiments
  • When bidding on a project, efficient feasibility studies lead to winning offers

 

Please read the product description for an overview of Simufact Welding functionality:

Product description Simufact Welding