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 open-architecture product modules. The proposed method is used to design a paper-bag-folding machine to satisfy requirement changes during the machine application.