ARC / BEAM Welding

Characterization of Arc and Beam Welding

Arc and Beam Welding are thermal joining processes with an enormous range of applications

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 14610defines 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 connection 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 over 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
  • Medical engineering
    • CT and MRT devices
    • Body housing of X-ray machines
    • Implants (additive manufacturing)

Trends and Developments

Source: JUREC / pixelio.de

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 is 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.

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. They allow 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"

Challenges of Welding

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 play economically together with reduced strength of a component – the most important role for a design of a welding process.

Unexpected welding distortions are often the cause for subsequent machining and straightening steps that usually are expensive. Defective products   can generate additional costs.  When selecting materials, welding can cause degradation of desirable material properties, leading to usage of more material, higher weight, larger size, and therefore higher costs.

What are the causes of welding distortions?

Welding distortions arise:

  1. Because of a shrinkage of melted filler material
  2. Because of an upsetting of material due to heating

Plastic upsetting is a highly non-linear material behavior. Inconsistent thermal expansion of the heat affected zone leads to non-homogeneous plastic deformation through the cross section of a weld. The mechanism behind this effect is used by flame straightening. Thermal expansion and shrinkage lead to residual stresses that cause further distortions and stress redistribution through the cross section. The component takes its initial shape if no plastic deformations are present during this process. Due to changed material properties, such as yield strength, high temperatures and even small stresses lead to plastic deformations. Additional restraints by clamping or the shape of a component itself are able to increase the residual stresses.

As a result of the temperature field, there is asymmetric behavior during heating and cooling triggering the development of plastic deformations. Three main mechanisms are to be noted:

  1. Plastic deformations during heating are of a local nature. During cooling, the  surrounding material experiences effects of heating by heat conduction from the weld pool, generates pressure towards shrinking material, and permits a partial regeneration of plastic deformations
  2. The elasticity of surrounding material is reduced
  3. Plastic deformations during heating appear at positions where tensile strength is reduced and thermal expansion is increased. Compressive stresses are reduced during cooling, which leads to plastic deformation of highly shrunk material at lower temperatures and higher tensile strength. After heating and cooling, if there are plastic deformations observable, residual stresses remain in the structure. Those residual stresses lead to reduced fatigue strength.

Laser beam welding – gap formation due to welding distortions

 

Laser beam welding – distortions are prevented by tack welds

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.

Welding distortions are usually not completely avoidable. Nevertheless, they represent a problem only if product requirements are not met. The following table presents an overview of typical fields of application for Simufact.welding in order to develop an understanding of welding distortions as well as to control and minimize them.

Pain Points - welding distortions

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

Understanding of a process as well as reduction of development loops by

  • Visualization of values influencing the process, especially temperature distribution, residual stresses, and deformations
  • Virtual try-out of clamping, welding sequences, intervals, unclamping times, effects of preheating, as well as variation of materials

Welding sequences and intervals are crucial if temperatures between layers are important. For mass production, short cooling times before unclamping are desirable in order to increase the output. The influence on welding distortions is usually a matter of seconds.

A further advantage compared to experimental investigations is the possibility to study different processing setups before there has been money invested in welding equipment.

Our Welding Simulation Solution

The product line Simufact.welding

Simufact.welding offers the possibility to calculate welding stresses, distortions, and the evolution of material properties from a graphical user interface. This means:

  • You can investigate possible problems up front
    • Identification of critical distortions, i.e. with respect to assembly, bulging, imbalances, and clearances
    • You gain confidence about maintaining tolerances
  • More insight into welding processes
    • You can create a basis for  construction design and development of welding processes and manufacturing, which together lead to optimized construction
    • You have a tool which supports you during planning of welding processes
    • You are able to gather and preserve experience and results from real and virtual try-outs, as well as retain corporate knowledge
    • Make use of a powerful tool for development and training
  • Methodical optimization of processes
    • You can plan the position of welding seams as early as during the design phase, which will lead to minimization of distortions based on construction design. Thus, you can also minimize the influence of a welding operator as well as welding equipment on distortions
    • You can investigate and optimize clamping tools even before an investment in tools has been made
    • You are able to identify optimized welding directions and welding sequences
    • You can investigate the influence of unclamping on welding distortions and residual stresses
    • Use a tool which supports you during planning of welding processes
    • Use virtual try-outs which would be very expensive in reality
    • Investigate the behavior of new materials during welding
  • Verification of quality of welding seams
    • Use a tool which helps you to verify the quality of welding seams, i.e. by calculation of brittle metallurgical phases, hardness, and effects of preheating.
    • Gain knowledge about the development of the heat affected zone
    • Draw conclusions about several properties of a welding seam (i.e. residual stresses that have effect on fatigue strength and bulging), convert your results to an open format (Universal File Format), and use them for further calculations in other FE simulations
  • Investigate process chains that appear during manufacturing

 

Economic benefits of faster welding process design

  1. High efficiency of the development process due to a reduced number of expensive failed attempts
  2. Decreased expenses of manufacturing of prototypes
  3. Reduction of machining and straightening costs
  4. Reduction of development times which leads to shorter time-to-market
  5. Decrease of material and energy consumption for experimental investigations
  6. Reduction of manpower needed for experiments
  7. When bidding on a project, efficient feasibility studies lead to winning offers

Please take a look at the product description for an overview of functionalities of Simufact Welding:

Product description Simufact.welding