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Purpose -The purpose of this paper is to present a methodology that integrates design and assembly planning in an augmented reality (AR) environment. Intuitive bare-hand interactions (BHIs) and a combination of virtual and real objects are used to perform design and assembly tasks. Ergonomics and other assembly factors are analysed during assembly evaluation. Design/methodology/approach -An AR design and assembly (ARDnA) system has been developed to implement the proposed methodology. For design generation, 3D models are created and combined together like building blocks, taking into account the product assembly in the early design stage. Detailed design can be performed on the components and manual assembly process is simulated to evaluate the assembly design. Findings -A case study of the design and assembly of a toy car is conducted to demonstrate the application of the methodology and system.Research limitations/implications -The system allows the users to consider the assembly of a product when generating the design of the components. BHI allows the users to create and interact with the virtual modes with their hands. Assembly evaluation is more realistic and takes into consideration the ergonomics issues during assembly. Originality/value -The system synthesizes AR, BHI and a CAD software to provide an integrated approach for design and assembly planning, intuitive and realistic interaction with virtual models and holistic assembly evaluation.

Assembly planning is very critical in the product design process. Previously, computer-assisted assembly planning is mostly conducted in either an automated or interactive manner. Automated approaches can only be applied to products with simple component configurations, whereas extensive user input in the tedious form of answering questions is required for interactive approaches. Both kinds of approaches do not address issues related to human factors and ergonomics, which cannot be ignored in assembly planning especially in manual assembly. Using augmented reality technologies, an intuitive and efficient approach is proposed for manual assembly planning and evaluation by combining the potential strengths of the two kinds of approach. An AR-assisted assembly planning and evaluation system has been developed to implement the proposed methodology with the use of a 3D bare-hand interaction (3DBHI) tool. After loading all the parts of an assembly into the proposed system, assembly modelling is first completed through assembly geometrical constraint recognition and assembly location refinement with the use of the proposed 3DBHI tool. By analysing the disassembly process, precedence constraints are captured and used to search for feasible assembly sequences from all possible sequences, which are generated using an existing method. Finally, practical or good sequences are selected from the feasible sequences by exploiting an assembly index based on objective evaluation. A case study is conducted to demonstrate the application of the methodology and system. IntroductionAs the competition of the manufacturing industry is increasing throughout the world, many companies tend to improve product quality, reduce product development cost and shorten time of design-to-assembly for new products. Assembly processes constitute a majority of the cost of a product (Boothroyd and Dewhurst 1989). In the assembly planning process, assembly sequences which are the backbone of assembly plans are generated and assembly operations which describe how different parts will be assembled together are formalised. Production efficiency will be improved and a large amount of cost will be reduced if a product is assembled according to a well-planned assembly sequence.Traditionally, assembly sequence planning has been conducted by either product designers or production engineers manually using either 2D drawings or physical prototypes of the product based on their intuition and experience. Nowadays, since products have become increasingly complex and the number of components has increased exponentially, manual assembly sequence planning has become impractical. In addition, physical prototyping is time-consuming and expensive for users to verify the ease of assembly. Moreover, additional cost will be incurred if there is any design change of certain components of the product. The rapid development of computer science and technology provides an alternative to solve this issue. In order to ease assembly sequence planning, research efforts have been made ...