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.     

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.     

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.     

FEM-analysis of the friction process in section drawing

It is necessary to gain more detailed information about the real frictional conditions in the section drawing process to improve the drawing techniques and to expand the producible section assortment. A deformed surface grid allows to describe local displacements on the workpiece used later on as boundary conditions in an FEM-calculation. With the knowledge of local frictional coefficients an increase in friction coefficient in drawing direction with curved cross-sections can be stated. Sharply edged cross-sections show an additional increase in friction coefficient in the range of high local deformation, i.e. near the edges. This fact influences both the material flow in the forming zone and the straightness of the section. An analysis of the surface topography change by friction and deformation declares the computed distributions of the friction coefficient.     

Performance of a new piezoceramic thick film sensor for measurement and control of cutting forces during milling

Process monitoring and controlling with detailed real-time information such as the cutting force is required for improving the performance of milling processes. This paper presents a novel system for measuring the cutting force in the direct vicinity of the indexable insert. The outlined concept makes use of piezoelectric thick film sensors mounted directly below the insert. The unique design and features of the new sensor enable accurate and continuous force measurements as well as the indication of wear. The results of the experimental investigations are presented and compared to results of a conventional dynamometer.