View of washing machine drum wrapper joint

The goal of this case study was to improve the clinch performance in washing machine drums by the mechanical characterisation of sheet metals and FEM simulations of the clinching dies.

Advanced mechanical characterisation tests of the sheet metals were performed to examine the mechanical behaviour of the drum material. Tests included standard tensile tests, the Nakajima test and miniaturised tensile tests to extract mechanical properties such as yield stress, ultimate tensile strength, uniform elongation or total plastic elongation after failure.

Finite Element Method (FEM) simulations relating depth, pattern distances and curve form of clinching dies were carried out under the project framework to verify the current state of the process clinching and improve the mechanical strength of the clinched joint. The clinching process was optimised using different strokes and tool geometries.

Simulation of washing machine clinching tools

Results were compared with Arcelik in-house tension tests and a static explosion test (rig test) to understand the structural performance of the optimised clinched drum and compare radial force differences. These tests have permitted to demonstrate the increase of the mechanical strength of the joints of washing machine drums as a result of the clinching process optimisation using innovative characterisation methods and modelling.

This improvement in the mechanical behaviour of clinched joints is expected to improve also fatigue life of washing machine drums. In order to simulate 10-year operating life of washing machine, this fatigue life test as 2500 cycles was completed with success by optimized clinching parameters which is developed within FormPlanet project. In the next future, ARCELİK is planning to apply the clinching process optimization for the production of other models of washing machine drums.

In addition, Static Explosion Tests (Rig Test) were carried out to understand the mechanical behaviour of the clinched drum wrapper sheets. The test expands the drum wrapper sheets and measures the hydrostatic forces from the load cell, comparing it to the critical acceptance value obtained in fatigue and structural tests executed by Arçelik during the design phase.

Tests were performed with clinching tool samples with different patterns and stroke distances. Static Explosion Tests proved that with the optimisation proposed by FormPlanet partners the joining of the machine drum had increased strength.

Drum samples produced after optimisation

Micro-Tensile Tests (MTT) permit to locally assess basic tensile properties as yield stress, ultimate tensile strength, total elongation, reduction of area and uniform elongation. Furthermore, MTT can be used to study strain rate sensitivity in a wide range of temperatures.

These miniaturised testing techniques can be successfully applied when insufficient volume of material is available, for the development of new alloys, for the evaluation of the local mechanical properties of in-service components and as an input data in numerical simulation for advanced material modelling.