Balance spring stud for a timepiece

A method for attaching a balance spring to a balance spring stud comprising:

• producing said balance spring stud for receiving a balance spring of reference thickness, said stud including, around a housing provided for receiving said balance spring, at least one one-piece component made of a shape memory alloy and including at least two lugs, defining together an air-gap wherein, in the free state of said stud, the minimum width of said air-gap is greater than the maximum value of said reference thickness when said component is in an open position in a martensitic structure, and wherein the maximum width of said air-gap is less than the minimum value of said reference thickness when said component is in a closed position in an austenitic structure;
• producing said balance spring, locally including at least one area of lesser thickness whose minimum thickness is said reference thickness, for which said stud is devised, and which is surrounded by areas of large thickness whose minimum thickness is greater than said reference thickness;
• effecting a first phase of deformation to open said component in a martensitic state and at a lower temperature than a first transformation start temperature, characteristic of the start of transformation of the martensitic structure into an austenitic structure on heating;
• inserting a balance spring into said housing in a determined position or until a stop position is reached;
• and
• effecting a second phase of deformation to close said component, in which said lugs are clamped onto said balance spring by heating said component to a higher temperature than a second temperature at which the transformation from the martensitic structure to the austenitic structure ends.

A method for attaching a balance spring to a balance spring stud wherein the method includes the following steps:

• producing said balance spring stud for receiving a balance spring of reference thickness, said stud including, around a housing provided for receiving said balance spring, at least one one-piece component made of a shape memory alloy and including at least two lugs, defining together an air-gap wherein, in the free state of said stud, the minimum width of said air-gap is greater than the maximum value of said reference thickness when said component is in an open position in a martensitic structure, and wherein the maximum width of said air-gap is less than the minimum value of said reference thickness when said component is in a closed position in an austenitic structure at an operating temperature;
• producing said balance spring is produced, locally including at least one area of lesser thickness whose minimum thickness is said reference thickness, for which said stud is devised, and which is surrounded by areas of large thickness whose minimum thickness is greater than said reference thickness;
• effecting a first phase of deformation to open said component in a martensitic structure;
• inserting said balance spring in said housing, and the spring and housing are properly positioned with respect to each other;
• and
• maintaining the spring and the housing in position until the ambient temperature is reached again.