Open architecture provides a sustainable product framework for mass personalised production. Applying personalised modules and common interfaces, an open-architecture product can satisfy changes in the user requirements of an application. Planning product modules for the open-architecture product structure using the existing method is challenging. The quality function deployment is extended in this study to decide the open-architecture product module types. The customer requirements are divided into two parts: basic function needs and changes of the individual customer needs. Based on the axiomatic design, the functional requirements are mapped into design parameters to establish the design matrix. A degree of variety is proposed as a quantitative measure for the component variability of product modules. According to the relationship of components and degree of variety, the product components are clustered into openarchitecture product modules. The proposed method is used to design a paper-bag-folding machine to satisfy requirement changes during the machine application.