In the development of luxury watches, the watchmaker's trade has to keep aesthetic design aspects in mind in addition to functional characteristics. In collaboration with Chopard, CADFEM has brought the world of engineers and designers into harmony. In addition to the physical requirements, the high aesthetic criteria are now also met.
From a mechanical point of view, coil springs have the task of providing specific load torques at corresponding torsion angles. For the ideal geometry of luxury watches, aesthetic aspects must also be taken into account. In order to achieve a concentric spiral shape, a parametric simulation to determine the stiffness behaviour should be carried out.
The analysis was set up as a parametric setup in the ANSYS Workbench simulation environment. With variations of typical geometric dimensions, different torque curves for the operating process could be efficiently investigated. In addition to the purely technical parameters, aesthetic boundary conditions ensured compliance with the design guidelines.
With the analysis carried out, all previously defined goals could be achieved:
- Design of an optimal design taking into account technical and aesthetic parameters
- Reduction of practical tests to a single remaining prototype
- Significantly shortened development time at considerably reduced costs
The intersection between art and engineering makes it very special to develop luxury watches. Each step of the development of a new component is conducted under the careful supervision of mechanical engineers and designers working hand in hand. It is a real challenge to fulfill the technical requirements in an excellent way on the one hand but also to meet the high aesthetic criteria on the other.
From a mechanical point of view, a spiral spring has to meet precise specifications pertaining to its torque at specific loading angles and over many cycles as well as geometric requirements for its manufacturing. From a visual perspective it is important that the windings of the spiral stay concentric at all times (Fig. 1). The challenge is to find a geometry meeting all the requirements by only changing geometric parameters such as the number of windings, the dimensions and the shape of the spiral.
A parametric structural simulation model was created in Ansys Workbench to vary the size of the pocket containing the spring and the characteristic dimensions of the spiral spring. In addition different anchoring options for the end of the spring have been assessed. The simulation setup considered a full loading and unloading cycle in order to analyze time history of the torque developed by the spring.
The ease with which geometrical parameters can be changed allowed new designs to be tested rapidly. The following technical requirements were considered in addition to the aesthetic criteria; pre-load, maximum torque, allowable stresses and strain relaxation due to creep.
In very little time the development team could achieve a working design meeting both technical and aesthetic criteria.
With this new parametric simulation approach the number of prototypes was reduced from several units in former developments to just one. This has significantly reduced development time while reducing costs for prototypes, test equipment and of course also human resources.