ADVANCED MATERIALS & PROCESSES | OCTOBER 2023 37 A NEED FOR NEW STANDARDS: COMMUNICATING SHAPE TRANSFORMATIONS IN THE TECHNICAL DOCUMENTATION OF PRODUCTS The use case of a generic mini-gripper sheds light on the benefits that a new standard could bring to the engineering and design of shape memory materials. Eujin Pei, Brunel University London Christopher Leung, University College London Shape memory materials have been used in a growing number of commercial applications, including stents, heart valves, and guidewires in medical applications; anchors, sleeves, and screw devices in mechanical applications; vortex generators, torque tubes, and flaps in aerospace applications; industrial bearings, gears, and ventilators in automotive applications; as well as blinds and shades in architectural applications. Taking a step further, research over the past decade has shown that shape memory materials can be effectively utilized with additive manufacturing processes to produce high-value products. 4D PRINTING Advances in additive manufacturing have enabled functional grading and multi-material deposition to produce what are termed “4D printed” parts that are net or near net shape; creating highly complex features that are difficult to produce with conventional manufacturing processes. In this context, 4D printing affords the design engineer with the possibility to program shape transformations that are required to meet different functions by selectively distributing the stimuli-responsive properties of shape memory materials into a part’s geometry. An operational implication of 4D printing is a shape transformation or variable properties in response to the passive exposure to an environmental stimulus by the free exchange of energy or matter. With greater awareness of the environmental impact of industrial activity and emphasis on low-impact sustainable development, circular economy, and net zero targets, 4D printed parts have the potential to foster the creation and development of specialized high-value products. Examples may include parts that operate passively without the need for an external power source or with fewer electro- mechanical components through part consolidation, greater material efficiency, and the potential for material recoverability at end-of-service. A fundamental challenge exists: How to ensure that the design, manufacturing, and functional intent for 4D printed parts can be accurately and unambiguously communicated between stakeholders across the design, manufacturing, inspection, and supply value chain? One argument states this requirement is not exclusive to shape memory materials used with additive manufacturing processes, but can also be applied to shape memory material properties used in conventional manufacturing processes. Until now, the main emphasis has been on the need to develop standards that can be used by engineering and design teams to accurately represent the shape transformation of non-rigid bodies so that shape memory products can be more widely adopted, more comprehensively tested, and reach a high level of industrial maturity and acceptance. With such a standard being made available at the engineering and design stage, it is expected that the end product would be able to con- form to stringent industrial testing, metrology, and quality control requirements. BRITISH STANDARDS In the context of national standards for technical product realization (TPR), the British Standards Institution committee TPR/1 is responsible for the U.K.’s input to the international ISO/TC 10 Technical Product Documentation and ISO/TC 213 Dimensional and Geometrical FEATURE Fig. 1 — Use-case generic mini-gripper. 5
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