Delay (mechanics)

In general, the term warpage is understood to mean the change in the dimensions and shape of a workpiece, for example through targeted or application-related, unavoidable heat treatment such as. B. in casting and welding . The dimensional change refers to the purely linear change in size without changing the geometric shape; Changes in size and shape can occur individually, but are usually superimposed.

During production , distortions are introduced into a component by various mechanisms, which may lead to the component not reaching the desired quality class. The application of the distortion engineering method is suitable for examining a manufacturing process for the causes of resulting distortions and for compensating them. This means that the distortion on the finished component can be minimized.

A typical example of undesired distortion is the impact or imbalance on a brake disc , which occurs during operation due to incorrect manufacture or overheating and which has a lasting effect on the braking effect.

Furthermore, an electrical assembly may warp during soldering . This occurs when an assembly is only heated at individual points, a component is soldered in this area while it is warm and then cools down again. If the component does not have the same coefficient of change in length and did not have the same temperature during soldering, there are tensions in the assembly which, depending on the characteristics, can lead to the assembly being warped.

Warpage at the joints of a crawler panel on a boat

Another typical and common occurrence is the delay in articles made from wood or other natural materials manufactured are, in particular furniture , boats or floor coverings . Here the delay is already proverbially known with "wood works". The distortion of the geometric shape of wooden parts is based on processes either swelling or shrinking due to moisture and temperature .

The distortion of components during welding depends , among other things, on the specific thermal conductivity of the components to be welded. Austenitic steel has a lower specific thermal conductivity than unalloyed steel . This means that the heat is more poorly dissipated, which leads to an inhomogeneous heat distribution. In the inhomogeneous heat zone, the material wants to expand more, but the colder surrounding material inhibits expansion , resulting in internal compressive stresses . The stresses in the component become so great that the material flows. After the temperature equalization, the material bends where the material that flowed away was before.

Thinner components have a higher distortion when welding than thick-walled components. This results from the lower rigidity in the joint in the thin components.

Warpage measurement on a stainless steel sample (1.4301)

Web links

• Alois Payer: Wood for the tropics / material science, therein "4.1. Swelling, shrinking, throwing, tearing"
• Vocational school, section "Shrinkage and swelling of wood"
• Timber construction - quality class 1
• Bauversuche.de - Wood, sources and shrinkage

Individual evidence

1. ^ Mirko Langhorst: Mastery of welding distortion and residual welding stresses. Dissertation, Chapter 3 Welding distortion and residual welding stresses. Retrieved July 23, 2017 . 
2. ↑ Mirko Langhorst: Mastery of welding distortion and welding residual stresses - dissertation