The currently growing demand for metallic and polymeric products has undoubtedly changed the rules of manufacturing, enabling customers to more functionally define their products based on their needs. Nowadays, a new technique for rapid tooling, Additive Manufacturing (AM), can create customized products with more complex geometries and short life cycles (flexibility) in order to keep up with the new variables imposed by the manufacturing environment. In the last two decades, the migration from subtractive manufacturing to AM has materialized such products with reduced costs and cycle times. AM has been recently promoted to develop polymer molds for product manufacturing. This paper reviews the main findings in the literature concerning polymer molds created by AM compared to conventional (metal) molds obtained by subtractive manufacturing. Information about specific topics is scarce or nonexistent, for example, about the characterization of the most commonly injected materials and molds used in this type of technology, their mechanical properties (part and mold), designs for all types of geometries, and costs. These aspects are addressed in this literature review, highlighting the advantages of this alternative manufacturing process, which is considered a desirable technology worldwide.

Laminated piezocomposite energy harvesters (LAPEHs) are multilayer arrangements of piezoelectric and nonpiezoelectric materials. Multiple materials and physics, and dynamic analysis need to be considered in their design. Usually these devices are designed for harmonic excitation; however, they are subjected to other types of excitations. Thus, a novel topology optimization formulation is developed for designing LAPEHs that considers a combination of harmonic and transient optimization problems with the aim of designing the so-called "multi-entry" devices in which the power generated is the same for different types of excitation. LAPEHs are modeled by the finite element method, and the material model used for the piezoelectric layer is based on penalization and polarization model who controls material distribution and corresponding polarization. To optimize the RLC circuit, a novel linear interpolation model of coupled electrical impedance is also introduced to consider different magnitudes of the coupled impedance. The topology optimization problem seeks to maximize the active power generated by the LAPEH at its RLC circuit, to minimize its response time measured as the slope of the power versus time curve, and to maximize its stiffness. Numerical examples are shown to illustrate the potential of the method.

This work explores the design of piezoelectric transducers based on functional material gradation, here named functionally graded piezoelectric transducer (FGPT). Depending on the applications, FGPTs must achieve several goals, which are essentially related to the transducer resonance frequency, vibration modes, and excitation strength at specific resonance frequencies. Several approaches can be used to achieve these goals; however, this work focuses on finding the optimal material gradation of FGPTs by means of topology optimization. Three objective functions are proposed: (i) to obtain the FGPT optimal material gradation for maximizing specified resonance frequencies; (ii) to design piezoelectric resonators, thus, the optimal material gradation is found for achieving desirable eigenvalues and eigenmodes; and (iii) to find the optimal material distribution of FGPTs, which maximizes specified excitation strength. To track the desirable vibration mode, a mode-tracking method utilizing the 'modal assurance criterion' is applied. The continuous change of piezoelectric, dielectric, and elastic properties is achieved by using the graded finite element concept. The optimization algorithm is constructed based on sequential linear programming, and the concept of continuum approximation of material distribution. To illustrate the method, 2D FGPTs are designed for each objective function. In addition, the FGPT performance is compared with the non-FGPT one.

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