Analysis of the mechanical expansion process of thin-walled tubes for air heat-exchanger production

Abstract

Finned tube air heat-exchangers are built by joining the tubes to the fins by various techniques. A technique mostly used for large heat-exchangers consists of fitting the tubes into the holes of the fins by expanding the tubes using a mechanical process. The expansion is achieved by inserting an ogive of a larger diameter into the tube. The intimate contact of tubes and fins due to the press fitting ensures the proper thermal connection. This work tries to describe an experimental-numerical procedure useful to study and predict the mechanical process and the process parameters. The procedure, based on material properties obtained from tensile tests and the use of the inverse method to identify the material parameters, is based on bi-dimensional finite element (FE) models used to simulate the expansion process. The FE model is then used for process optimisation regarding such parameters as the ogive shape and ogive sizes, friction coefficient and speed of insertion of the ogive into the tube. Indeed, size and shape uncertainties strongly influence the process parameters and the process quality, as well as the heat-exchanger efficiency. The use of numerical models was proven highly effective in predicting and optimising the process by quickly analysing the influencing factors and optimising the production.

Improvement of material flow in tube hydroforming by advanced sealing methods

“…Tube hydroforming is a near-net shape manufacturing process with continuously growing application in the automotive industry for the production of complex hollow components. [1][2][3] In this process, the workpiece which is in the form of a tube is first sealed from its ends by two punches (see Figure 1). Then, the oil is injected inside the tube and its inner surface is pressurized.…”

Formability limits by local buckling in thin-walled tubes

“…In fact, the selection of materials for tube forming, contrary to that of sheet forming is fundamentally based on design charts and procedures that only account for the relationships between the different process parameters. 14,15 Under these circumstances, the aim and objectives of this paper is to present a methodology to determine the formability limits by local buckling in thin-walled metal tubes. The proposed approach is an extension to tube forming of a method that was earlier developed and validated by the authors to characterize the formability limits by wrinkling in thin metal sheets.…”

“…In fact, the selection of materials for tube forming, contrary to that of sheet forming is fundamentally based on design charts and procedures that only account for the relationships between the different process parameters. 14,15…”