Alternative methods for heat stress relief

Ferruform AB in Luleå is a manufacturer of chassi components for Scania’s truck production. At the department for Axle production sheet metal is processed to produce rear axle housings. The main processes include shearing, forming, welding and machining. High amount of residual stresses are built up in the material because of the extensive weld operations. Residual stresses are reduced with a very time and energy consuming heat treatment method called heat stress relief.

The purpose with this thesis was to investigate alternative methods for heat stress relief and then suggest the best solution for Ferruform.

Our main tasks in this thesis has been literature studies, investigation of prior work, market analysis, contact and visits from suppliers, production tests and weekly meetings with our supervisor. Finally we have presented the thesis verbally at the company and at Luleå University of Technology. A written report has also been made.

Two alternative methods for heat stress relief has been found and further investigated. Tests have been made regarding these two methods for stress relief. One test with a method called vibratory stress relief and one test with a simulated bend-straightening operation.

Layouts have been created to easier visualize the space required for the different methods. Seen from the layouts is that both methods requires less space than the heat stress relief oven. Single piece flow is achieved with bend-straightening and batched flow is achieved with vibratory stress relief.

Bend-straightening provides single batch flow, low cycle times and is utilized by a competitor, therefore it is recommended as a primary option to heat stress relief at Ferruform.

However, verification tests have to be made in order to evaluate the effects of the two different alternative methods. We have suggested that a fatigue test with spectrum loads should be carried out in order to get a reliable result.

Also a third method is taken into account in this thesis, hot formed banjo halves. This is not an option for Ferruform but may be an alternative to Scania Sao Paolo in Brazil.

Author: Holmgren, Jonas; Lindqvist, Stefan

Source: Lulea University of Technology

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