Modular product design-sharing components across multiple 
products;is viewed as a convenient way to offer high product 
variety with low production cost. This study presents a novel 
method for the early identification of shareable components 
within a family of structures. Component sharing is first 
enforced as a constraint, and then posed as the outcome of the 
minimization of production costs considering the economies of 
scale. Based on the decomposition-based assembly synthesis 
method, the modular structural component design problem is posed 
as the optimal selection of joint locations and joint types within 
two structures, evaluating the geometric similarity of the 
resulting components as potential modules during the optimization 
process. For the given variant structures the designer defines the 
possible locations where a joint can be placed, and for each 
possible joint location also provides feasible types of joints, 
including a type for "no joint", among which the optimal selection 
can be made. The problem is solved to (1) minimize the reduction 
of structural strength due to the introduction of welds in each 
structure, (2) maximize the manufacturability/assemblability or 
equivalently minimize the manufacturing costs of two structures, 
considering the opportunities of cost reduction via component 
sharing under given production volumes. A multi-objective genetic 
algorithm is utilized for effective evaluation of trade-offs between 
different criteria. Real life case studies including automotive 
body-in-white models are presented to demonstrate the capabilities 
of the method.