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Prediction and validation of galling behavior in hot sheet metal forming processes

Kooistra, E. (2021) Prediction and validation of galling behavior in hot sheet metal forming processes.

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Abstract:Sheet metal forming is a widely used forming process. This process is applied to hot sheet material to improve product properties, like weight and strength. However, hot sheet metal forming also comes with some disadvantages in the form of wear. Due to the high temperatures during sheet deformation no lubrication can be applied, which allows for wear to occur more severely. Here, galling is the wear mechanism of interest, which is a form of adhesive wear. Material transfers from the sheet to the tool during relative contact displacement, which is called galling. This is a problem when the material build up on the tool becomes too large that it scratches the product. The tools have to be cleaned or even replaced, which is disadvantage to the flow and cost of the production. A model is implemented to predict galling behavior and critical locations on the tools. This model is an extension of the existing friction model within the TriboForm software. The galling model evaluates every contact spot between the tool and sheet (asperity) to check if it is suitable for galling. Two different galling initiation models for the asperities have been proposed, one based on the shape of an asperity (wedge formation initiation model - WFI) and one based on the strength of the asperity with respect to the sheet coating (coating fracture initiation model - CFI). If an asperity is initiated it will grow during the relative contact during sliding. The asperity growth is based on the growth model proposed by van der Linde. The initiation and growth of a single asperity is applied for multiple asperities on a surface. The multi asperity growth is approached with two different models, one based on the update of the separation height (van der Linde) and one based on the update of the tool topography. The model which updates the separation height is used in the visualization and validation. The model which updates the tool topography is used to evaluate the influence of galling on the coefficient of friction. This galling model is calibrated using experimental data from hot strip draw tests performed at Tata Steel. This data is valid for a calibration of adhered volume over temperature. Both the galling initiation models are calibrated using these experimental values. Results from the model are used to evaluate the model for CFI and WFI on a few points: 1) the amount of asperities initiated for galling 2) the relation for adhered volume over temperature, pressure and strain, 3) the interaction between asperities based on the overlap an asperity has in a multi asperity situation and 4) the coefficient of friction over sliding length. Using AutoForm and TriboForm the galling behavior on the tooling for three different part are visualized: 1) the experimental B-pillar from Tata Steel, 2) the industrial A-pillar from Volvo Cars and 3) the industrial Side Member from Volvo Cars. The predicted galling depends on the temperature, pressure and strain of the sheet during deformation and on the relative sliding distance in contact between the tool and the sheet. The experimental evaluation of the B-pillar is used to compare radii locations of the same part, where the CFI model shows the most promising results. The industrial parts from Volvo Cars are used to verify if the model can predict the galling locations observed on the tooling. The galling locations are accurately found on the industrial production parts by both models. However, the severity of a predicted galling location should be verified with further research. The CFI model is more favorable when comparing the two industrial parts.
Item Type:Essay (Master)
Clients:
TriboForm Engineering
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
Link to this item:http://purl.utwente.nl/essays/85956
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