A Motor vehicle wheel arch has a body of thermoplastic material with an opening
and a mat closing the opening and fixed to the body by strips of thermoplastic
material. A method of making the arch includes injecting the strips onto the mat
and allowing them to solidify in contact therewith. An edge is formed on a reduced
thickness portion of the strip. In cross-section, the edge thickness relates to
the edge width l by a mathematical function f such that:
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where h is the height of the edge at its junction with the strip.