Microstructure refinement by a novel friction-based processing on Mg-Zn-Ca alloy. - In: Material forming, ESAFORM 2024, (2024), S. 2031-2040
Insufficient mechanical properties and uncontrollable degradation rates limit the wide application of Mg alloys in bioimplant materials. Microstructure refinement is a common method to improve both the mechanical properties and the corrosion resistance of Mg alloys. In order to efficiently obtain Mg alloys with fine microstructures for potential applications in bioimplant materials, a novel constrained friction processing (CFP) was proposed. In this work, the resulting compression properties of ZX10 alloy obtained by CFP with optimized processing parameter are reported. Additionally, the microstructure evolution during CFP was studied. The results show that during CFP, materials are subjected to high shear strain at the transition zone between the stir zone and thermo-mechanical affected zone, leading to recrystallization with strong local basal fiber shear texture. As the shoulder plunges down, the fraction of recrystallized grain and grain size increase. ZX10 alloy obtained by CFP exhibited higher compressive yield strength by more than 300% and ultimate compressive strength improves by 60%, which indicates the bright prospect of CFP for Mg processing.
https://doi.org/10.21741/9781644903131-224
Updates on the new Kibble balance at NIST. - In: ASPE Annual Meeting 2023, (2024), S. 194-195
Calibration of positioning microsystems with subatomic accuracy. - In: Engineering for a changing world, (2023), 1.4.117, S. 1-6
Multidimensional positioning, measuring and manipulation with a spatial resolution in the subatomic range are an upcoming demand in the area of nanotechnology. Nanopositioning and measuring machines (NMM) enable to measure and manipulate objects within a large addressable 3D-range of up to a few hundred millimetre in each dimension with a specified spatial resolution of down to 0.1 nm [1]. New approaches are needed to extend the potential of NMM technology to even smaller scales. In previous work [2] a proof-of-concept positioning system has been designed to achieve reproducibility and resolution for precise motion on subatomic scale. In a first approach, a scanning probe microscope will be used to measure a nanosized periodic lattice that serves as a scale for the position according to [3]. Here, we present a microsystem design with an addressable positioning range of ±100 μm that will carry the lattice structure. In order to precisely control the motion, the electrostatic drive and position sensor characteristics of the demonstrator must be calibrated thoroughly by means of an optical measuring system. A focused, range-resolved fibre-optic laser interferometer is comprised as the calibration standard. An uncertainty estimation for the measurement setup is carried out. It is shown that the desired positioning accuracy for the first tip- and grating-based setup can be achieved with the presented microsystems.
https://doi.org/10.22032/dbt.58741
Monolithic compliant mechanism for an EMFC mass comparator weighing cell. - In: Engineering for a changing world, (2023), 1.4.112, S. 1-14
Mass comparator weighing cells based on electromagnetic force compensation (EMFC) find application in the most demanding force and mass measurement applications. The centerpiece of these devices is a highly sensitive compliant mechanism with thin flexure hinges. The compliant mechanism forms the mechanical part of the mechatronic overall system. A novel mechanism based on an advanced adjustment concept has been developed, manufactured, and experimentally investigated. The adjustment is designed to further reduce the measurement uncertainty for mass comparisons by canceling out first-order error components. The focus is on the mechanical properties: stiffness, tilt sensitivity, and off-center load sensitivity. The elastic stiffness of the compliant mechanism is compensated by introducing a negative gravitational stiffness to enable the compensation of manufacturing deviations and to increase mass resolution.
https://doi.org/10.22032/dbt.58738
Preliminary characterization of anelastic effects in the flexure mechanism for a new Kibble balance at NIST. - In: Engineering for a changing world, (2023), 1.4.101, S. 1-13
A new Kibble balance is being built at the National Institute of Standards and Technology (NIST). For the first time in one of the highly accurate versions of this type of balance, a single flexure mechanism is used for both modes of operation: the weighing mode and the velocity mode. The mechanism is at the core of the new balance design as it represents a paradigm shift for NIST away from using knife edge-based balance mechanisms, which exhibit hysteresis in the measurement procedure of the weighing mode. Mechanical hysteresis may be a limiting factor in the performance of highly accurate Kibble balances approaching single digit nanonewton repeatability on a nominal 100 g mass, as targeted in this work. Flexure-based mechanisms are known to have very good static hysteresis when used as a null detector. However, for larger and especially longer lasting deformations, flexures are known to exhibit anelastic drift. We seek to characterize, and ideally compensate for, this anelastic behavior after deflections during the velocity mode to enable a 10 accurate Kibble balancemeasurement on a nominal 100 g mass artifact with a single flexure-based balance mechanism.
https://doi.org/10.22032/dbt.58743
A laser beam deflection system for heat treatments in large scale additive manufacturing. - In: Engineering for a changing world, (2023), 1.4.082, S. 1-15
Large Scale Additive Manufacturing (LSAM) based on plastic raw material is known for high material output and thus, increased productivity. For an improvement of part properties LSAM is combined with a laser process. Depending on the deposition direction, the laser beam needs to be repositioned to reach the space between two adjacent and consecutively printed strands. Therefore, an optomechanical design is required that allows variable orientation of the laser beam. It consists of a combination of an elliptical, tube-like mirror with an additional, rotatable flat mirror in one of its focal axes. The deflected laser beam hits the second focal axis where the extruder nozzle is located. Thus, > 75% of the nozzle circumference is covered during a laser beam treatment. Both mirrors are individually designed custom-made parts. Its functional verification lays the foundation for an improved additive manufacturing process, which aims to homogenize the component structures to improve the mechanical properties of 3D-printed components.
https://doi.org/10.22032/dbt.58739
Validation of experimental setup for aerostatic bearing simulation. - In: Engineering for a changing world, (2023), 1.4.079, S. 1-10
Aerostatic bearings are extensively used in precision engineering applications that require high positional accuracy and low friction motion. In these bearings, externally pressurized gas is fed through a restrictor into the bearing gap. The viscous shear in the gap restricts the flow, thus forming a pressurized film between the bearing and the guide surface. In the development of models and in investigations of, for example, effects of manufacturing errors and porous material permeability properties, characterization of bearing performance is required. The performance is commonly characterized with a measurement setup, either under static or dynamic conditions. In the present study, an experimental setup for the measurement performance of aerostatic bearings is presented. The investigated measurement setup is validated with a comparison to a literature model. The results of the present study include the load capacity, stiffness, air consumption, and pressure distribution of a commercially available axisymmetric graphite thrust bearing. The results show good agreement between the measurements and the model. Thus, the results show corroborative evidence on the usability of the measurement setup in future aerostatic bearing research.
https://doi.org/10.22032/dbt.58841
Cement-bound mineral casted parts in precision engineering. - In: Engineering for a changing world, (2023), 1.4.077, S. 1-14
The design of a machine frame, supporting a plurality of components/modules, is a major challenge during the development of precision systems. The geometric stability of the supporting parts under thermal and mechanical loads has a decisive influence on the achievable accuracy. Common materials like cast iron or natural stone have preferable properties but often come with high costs and long lead times due to sourcing or manufacturing process and required geometric precision. Concrete is an interesting alternative. Polymer concrete and cement-based concrete such as self-compacting concrete have been considered as cost-effective alternatives for quite a while now. This paper summarizes recent research and findings on these alternative materials and reviews their applicability in machine frame design. Aspects of the cold primary shaping process will be covered with an emphasis on ready-to-use features with geometric tolerances in the order of magnitude of micrometers. The potential for integrating functional elements is discussed. The advantages of concrete as an alternative material are summarized with regard to the application of the design principle "functional material at the location where functionality is required".
https://doi.org/10.22032/dbt.58740
Synthesis of optimized compliant mechanisms for ultra-precision applications. - In: Engineering for a changing world, (2023), 1.4.071, S. 1-9
Compliant mechanisms for ultra-precision applications are often required to achieve highest accuracy over largest possible ranges of motion along multiple axes. The typical synthesis approach for such high demands is based on the substitution of the revolute joints of a suitable rigid-body model with optimized flexure hinges. However, during the transition from rigid-body model to compliant mechanism, the effects of multiple input parameters are still widely unknown. Among them are the degrees of freedom of the rigid-body model, the integration of the drive elements, as well as the coupling of mechanisms to achieve multiple motion axes. The following contribution expands the fundamentals of the synthesis of compliant mechanisms based on rigid-body models for their application in ultra-precision technologies. Based on the investigation of the aforementioned parameters as well as the knowledge gained from previous research work, a novel synthesis method has been developed.
https://doi.org/10.22032/dbt.58844
Development of a tool-changing system for nanofabrication machines. - In: Engineering for a changing world, (2023), 1.4.025, S. 1-6
The frequent use of a growing diversity of tools in nanofabrication machines raises the need for a highly reproducible tool-changing system that is capable of working with tools of different weights and moments of inertia. Since the tool-changing system is designed beneficially based on an open, force-paired kinematic coupling, means to apply a holding force are required. The holding force needed is about 40 N in total and has to be applied without heat dissipation or other disturbances. Since variations in the elastic deformation at the contact points of the coupling directly influence the reproducibility of the tool position, the force application needs to be highly reproducible. An analytical model is developed to determine the force application requirements, taking into consideration elastic deformation and friction. Based on this model, the allowable variation of the holding force in amount and direction, as well as the allowable deviation of the force application point, are determined. Thereby, the resulting influence of the force application on the reproducibility of the position of the tool-center point is intended to be 5 nm or less. Eleven solution principles for force application are developed based on the physical effects of magnetic force, spring force, and weight force. Based on a systematic evaluation, an arrangement of three permanent magnets with flux guide pieces at an angle of 120˚ to each other has been chosen at the fixed side. On the tool side, ferromagnetic plates are used to close the magnetic circuit. Thereby, the air gap and, thus, the holding force can be adjusted individually for each tool. During the tool change, the magnetic force is switched off by short-circuiting the magnetic flux with an additional rotatory-mounted flux piece, which is driven by a gear motor. The designed prototype will be tested and further optimized within a nanofabrication machine.
https://doi.org/10.22032/dbt.58846