Weld defects

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Weld seam defects in a welded connection are an expression of a reduced production quality. No statements can be made about the usability of the manufactured product when it is determined. Geometric irregularities in metallic welded joints are described in DIN EN ISO 6520 parts 1 and 2. Part 1 deals with fusion welds and part 2 deals with pressure welds. The standard means by the term irregularity (engl .: imperfections ) a "defect in the weld or a deviation from the intended geometry" and an error an "undue irregularity" . That is, there are permissible and impermissible irregularities.

Limit values ​​for the evaluation of the irregularities are the various evaluation standards z. B. ISO 5817, ISO 10042, ISO 13919-1 / -2. The DVS leaflet 0703 is to be seen in addition to ISO 5817. It describes the causes of the occurrence of the irregularities and also provides information on remedial measures.

Fusion welding

The DIN EN ISO 6520-1 identifies six main groups of geometric irregularities:

  1. Cracks
  2. Cavities
  3. Solid inclusions
  4. Defective bonding and insufficient penetration
  5. Form and size deviations
  6. Other irregularities.

Cracks are local separations in the solid state of the material and arise during cooling or later as a result of stresses in the weld seam or in the heat-affected zone. Different types of cracks are distinguished depending on the direction of the crack course and the location of the crack occurrence.

Cavities can arise from gas inclusions. Spherical cavities are called pores, which can be evenly distributed in the solidified weld metal or can appear as pore cells or pore nests. Cavities also appear as a gas channel parallel to the weld seam axis. If the cavity reaches the seam surface at the moment of solidification, i.e. if it is open to the surface, we speak of surface pores. A cavity that is created by material shrinkage when the weld metal solidifies is called a blowhole .

Solid inclusions are deposits of foreign matter in the weld metal. It can be slag, remnants of flux or oxides in different arrangements. Inclusions of foreign metal (e.g. tungsten in the electrode in TIG welding) are also among these irregularities. Unwanted oxide film deposits due to insufficient protection against ingress of air are also irregularities that fall into this main group.

Of bonding errors is when there is no firm connection between the weld metal and base material or multi-layer weld between the individual layers. If the actual penetration is less than intended, this is referred to as insufficient penetration.

The form and dimensional deviations include poor weld seam geometries and all forms of undercuts. In addition, one also counts on large elevations of the seam and seam root, too abrupt seam transition, the weld metal overflow on the surface or seam root and the burning through of the weld seam, so that a continuous hole is created. Every type of seam misalignment falls into this main group, as does the underwhelming of parts of the weld seam. Dimensions deviating from the prescribed weld seam dimensions are irregularities in this main group.

Irregularities that cannot be classified in the first five main groups are referred to as other irregularities . These can be ignition points or spatter that occurs during welding and adheres to the welded workpiece. Notches that can occur during post-processing, such as grinding or chisel notches, are such irregularities. Discolouration caused by tarnishing is also often undesirable, as are residues of flux, slag and scale.

The currently valid ISO 6520-1 was published in 2007.

Pressure welding

For pressure welded connections, the DIN EN ISO 6520-2: 2013-12 standard defines irregularities in pressure welded connections. Six main groups similar to fusion welding are also defined, with the letter P denoting pressure welding.

  1. P1 - cracks
  2. P2 - cavities
  3. P3 - solid inclusions
  4. P4 - missing link
  5. P5 - shape and dimensional deviations
  6. P6 - Other irregularities.

The cracks that occur during spot welding can be shaped in many ways and run in different directions. Special features are cracks in the upsetting bulge during butt welding, which are often associated with inclusions. Cavities also occur in pressure welding as gas inclusions and pores. Solid inclusions are mostly deposits of foreign matter in the form of oxides. In the case of butt-welded joints, impurities can also be contained in residual melt that has not been compressed. Defects in fusion can be found in butt welding, as well as in foil roll seam welding . Deviations in shape and dimensions arise in butt welding due to an oversized upset bulge or misalignment of the welding edges, in resistance spot welding due to deviations from the prescribed lens geometry or the permitted indentation depth , and when butt welding pipes, expanded pipe diameters in the welding area.

The DIN EN ISO 6520-2: 2013-12 standard contains a table with a summary of which irregularities can occur in which pressure welding processes.

The VW group standard PV6702 summarizes the description of the irregularities and their permissible orders of magnitude depending on the desired quality level for spot welded joints .

Individual evidence

  1. ↑ DVS : Limits for irregularities in fusion welds according to DIN EN ISO 5817 DVS data sheet 0703: 2008-07: 2008
  2. ↑ DIN EN ISO 6520-1: 2007-11 Welding and related processes - Classification of geometric irregularities in metallic materials - Part 1: Fusion welding , 2007
  3. ↑ DIN EN ISO 6520-2: 2013-12 Welding and related processes - Classification of geometric irregularities in metallic materials - Part 2: Pressure welds , 2007
  4. ↑ Volkswagen AG : "Spot Welding Joints on Steel Materials - Testing of Body Assemblies" , PV 6702 (2010)