Thermal deformations of cutting tools: measurement and numerical simulation

Challenges for machining include greater and greater material removal rates coupled with an increase in the use of difficult to machine materials, as well as environmental-friendly dry or minimum quantity lubrication machining, small manufacturing batches and frequently changed manufacturing orders. These trends are accompanied by high temperatures in the machining process and large, variable heat flows causing thermo-elastic displacements of the tool, the workpiece and the clamping devices. Although the displacements are small, in the range of a few micrometers, they have assumed more and more importance because of growing requirements for manufacturing accuracy. Thermo-elastic displacements of the tool due to heat flow during machining are investigated and analysed in this paper. Temperatures and displacements are measured on a test bed equipped with measuring instruments. The identification of the thermal boundary and contact conditions is supported by finite element models. Knowledge of the heat flows resulting from the machining process is a prerequisite for control of and compensation for displacements. Since these heat flows either cannot be measured or can only be measured with enormous effort, heat flows are determined by means of numerical simulation of the machining process itself. This strategy has been previously used as a systematic approach for turning in orthogonal cutting conditions. However, further investigations are needed for oblique turning conditions, milling and drilling operations.     

Sheet metal forming of piezoceramic-metal-laminar structures—Simulation and experimental analysis

Adaptive systems with piezoelectric components offer significant opportunities for the active control of dynamic behaviour. Vibration and acoustics control as well as structural health monitoring are also possible. However ineffective production technologies prevent industrial applications. The authors are therefore proposing the integration of piezo-modules inside a double-layer sheet. The use of semi-cured adhesive avoids shear-forces being transferred to the piezo-modules during forming. After forming the adhesive will cure and the transfer of piezoelectric strain to the sheet is made possible. A detailed finite-element-model incorporating the electro-mechanical characteristics of the piezo-modules has been developed. The simulation results were validated experimentally.     

A process and load adjusted coating system for metallic inserts in hybrid composites

According to the concept of an intrinsic hybrid composite, adhesive bonding is designed for generating the connection between the applied fiber reinforced polymer and a metallic insert. To induce adhesive bonding, a metallic insert, made of aluminum, is coated. This contribution focusses on the development of a suitable coating system. To this end, the coating system must meet certain requirements. On one hand, demands on the coating like ductility can be deduced from analyzing the manufacturing process. On the other hand, requirements like corrosion protection as well as high static and dynamic strength arise from specific applications under considerations. The utilized coating system is based on organically modified silicate layers (Ormosil) applied using a sol–gel process. To prove that this coating system fulfils the requirements, the corrosion protection is analysed by impedance spectroscopy. Furthermore, different mechanical experimental investigations are performed to verify the ductility of the coating as well as the strength of the resulting interface. Hence, it is shown that the considered coating system can be applied for the analysed intrinsic hybrid composite manufactured in series.     

Multi-layer compounds with integrated actor-sensor-functionality

A method is presented to integrate the cost and time consuming afterwards-joining technologies of piezo actors and sensors direct in the forming processes for metal blank structures. Possible applications for such parts are vibration/ noise damping, deformable shape control, energy harvesting or several sensor tasks. Different forming processes are experimentally investigated and the limits according to deformation of the brittle piezo components discussed. In the numerical research the piezomodule components (piezo fibre, electrodes and plastics embeddings) are homogenized to create a computation-time reducing simplified material model. In a back-transfer of global loads in the forming simulation a representative volume element (RVE) with cyclic boundary conditions is used to evaluate the loading of the piezoceramic material to describe the function degradation due to forming operation. The comparison of numerically and experimentally determined results in a linear manner lead to the necessarity of further numerical research. The location of maximum piezo-patch loading corresponds well with the numerical investigation. The numerical integral model for function degradation shows a large difference in comparison to the integral experimentally determined values. Therefore extensive experimental research direct on the piezomodule outside the forming compound is planned to fit the degradation model in a nonlinear manner.     

Investigation of a force-locked connection of micro piezo elements with aluminium carrier material

Within the Transregional Collaborative Research Centre PT-PIESA “High-Volume Production-Compatible Production Technologies for Lightmetal and Fiber Composite-Based Components with Integrated Piezo Sensors and Actuators” effective technologies for the production of active components are investigated. One concept is the direct integration of piezo material as fibers or rods in sheet metal like for instance aluminum sheets. This paper deals with the production step of the joining process. Based on a finite element simulation different dimensional layouts are experimentally investigated. The results show, that with an appropriate fill ratio a force-locked connection between piezo material and carrier material can be achieved.     

Monitoring concept for structural integration of PZT-fiber arrays in metal sheets: a numerical and experimental study

ABSTRACT

The technique joining by forming allows the structural integration of piezoceramic fibers into locally microstructured metal sheets without any elastic interlayers. A high-volume production of the joining partners causes in statistical deviations from the nominal dimensions. A numerical simulation on geometric process sensitivity shows that the deviations have a high significant influence on the resulting fiber stresses after the joining by forming operation and demonstrate the necessity of a monitoring concept. On this basis, the electromechanical behavior of piezoceramic array transducers is investigated experimentally before, during and after the joining process. The piezoceramic array transducer consists of an arrangement of five electrical interconnected piezoceramic fibers. The findings show that the impedance spectrum depends on the fiber stresses and can be used for in-process monitoring during the joining process. Based on the impedance values the preload state of the interconnected piezoceramic fibers can be specifically controlled and a fiber overload.     

Numerical and experimental characterizations of longitudinally polarized piezoelectric d 15 shear macro-fiber composites

This contribution presents original numerical and experimental characterizations for prototyped longitudinally polarized piezoelectric d ₁₅ shear macro-fiber composites (MFC). The numerical characterization consists of a finite element (FE) simulation based on a representative volume element. It implements an enthalpy-based homogenization method (EBHM), recently proposed by the authors, as an extension of the so-called strain energy method to orthotropic piezoelectric fiber-reinforced composites. The numerical validation is carried out on a previously assumed layout of shear MFC. Later on, the EBHM is used to get the effective electromechanical material parameters of the shear MFC actual layout. These parameters are further validated experimentally through their use in the FE simulation of an original actuation benchmark that is proposed for the manufactured shear MFC experimental characterization. The latter is based on low-frequency (quasi-static) displacement measurements where the shear MFC serves as a voltage-driven actuator. Due to the small overall dislocation, a laser vibrometer is used for the measurements. The comparison of experimental and numerical results shows a reasonably good agreement and a nonlinear actuation response is observed. This work’s major outcomes are the experimental validation of the EBHM and the actuation functional operability of the manufactured longitudinally polarized piezoelectric d ₁₅ shear MFC. This opens the possibility for their application as actuator and sensor of shear-induced bending and torsion for vibration, shape and health control, or as a transducer for energy harvesting.