1,720,987 research outputs found
Improvement of surface flatness in high precision milling
Full text linkThe use of high precision micro components has increased in various industrial fields in recent years. Repeatable techniques are needed to face very tight tolerances and make micro fabrication processes industrially feasible against current micro machining limitation. Improving surface flatness in high precision milling is the main target of the present research. Critical issues such as machining strategy, spindle thermal transient management and tool wear compensation were considered for machining operations on a representative part
Thin wall geometrical quality improvement in micromilling
Full text linkMicromilling is one of the most versatile tooling processes being able to effectively manufacture three-dimensional complex features on moulds and dies achieving a good accuracy performance. Typical and challenging features for these microcomponents are high aspect ratio thin walls but no systematic approaches, as the one presented in this paper, exist in literature dealing with the relationship between nominal workpiece characteristics/process parameters, cutting forces, and workpiece quality. The present study focuses on 0.4 % carbon steel (C40) thin wall micromilling and evaluates two approaches for the thin wall geometrical quality improvement: a direct approach (relating process parameters, material and nominal workpiece characteristics to the workpiece quality characteristics) and a force-based approach (relating the same quantities through the cutting forces determination). The force-based approach relates the process parameters to the workpiece quality introducing physical quantities as cutting forces, which are suitable for monitoring and controlling purposes. A suitable experimental campaign has been designed in order to statistically analyze the cutting force responses, and a proper technique (ANalysis of COVAriance) has been applied to remove the tool wear effect. The relationship between cutting forces and workpiece quality has been quantitatively studied; this way, the feasibility of a general approach able to meet tolerances by controlling forces has been demonstrated
Microdrilling of ZTA and ATZ ceramic composite: Effect of cutting parameters on surface roughness
No full textCeramics are a class of materials widely used during last fifteen years for orthopaedic applications. It is
well known that they are characterized by low wear rate, and friction coefficient. However, these materials are very
difficult to machine into complex shapes because of their brittleness and high hardness. The most effective method to
increase the crack resistance is the formation of a composite structure. This class of materials, composed by two or
more different ceramics, can present higher characteristic respect to the single component, like fracture toughness and
flexural strength. This paper presents a study of the influence of cutting parameters (cutting speed, feed rate and step
number) onto the hole surface roughness and deformation due to the drill operation. The ceramic composite materials
AZT (alumina toughened zirconia) and ZTA (zirconia toughened alumina) were first characterized in terms of hardness
and roughness. After the drilling test, the holes were analyzed using scanning electron microscope (SEM) and an
advanced 3-dimensional non-contact optical profilometer
Finite element modeling of micro-orthogonal cutting process with dead metal cap
No full textDead metal cap plays an important role in the microcutting process because target material piled up on the tool–chip–
workpiece interface can alter the cutting geometry. The target of this study is to model and simulate the microorthogonal
cutting process in the presence of dead metal cap in order to investigate the effects of this phenomenon on
the micromachining process outputs (cutting force, thrust force and chip thickness) and stress distribution, equivalent
plastic strain and temperature inside the workpiece shear zones. For this purpose, the finite element method with explicit
dynamic solution and adiabatic heating effect along with arbitrary Lagrangian–Eulerian approach is used. It is shown
that the finite element models with current state-of-the-art assumptions cannot take into account the dead metal cap by
default. For this reason, dead metal cap is artificially introduced on the rounded tool edge in this study for carrying out a
proper analysis. Several simulations with different dead metal cap geometries are performed and obtained results show
that prediction of cutting force, thrust force and chip thickness are sensitive to the presence of dead metal cap and its
geometry. Micro-orthogonal cutting experiments are carried out on tubular AISI 1045 workpieces for validating and
interpreting simulated results. The error between predicted and experimental data is calculated, and it is shown that
simulation performances can be improved by considering the dead metal cap into the process model. For example, it is
possible to reduce the error to less than 5% in case of thrust force prediction. This study points out how the target
material’s Von Mises stress, equivalent plastic strain and temperature distribution are sensitive to any alteration of the
edge geometry due to the dead metal cap. The best dead metal cap configuration in terms of agreement with experiments
is also the one introducing a more homogeneous distribution of these quantities along the shear plane
Calibration and Validation of a Mechanistic Micromilling Force Prediction Model
Full text linkMechanistic force prediction models require a calibration phase to determine the cutting coefficients describing the tool–target material interaction. The model prediction performance depends on the experimental correctness and representativeness of input data, especially in micromilling, where facing process uncertainties is a big challenge. The present paper focuses on input data correctness introducing a clear and repeatable calibration experimental procedure based on accurate force data acquisitions. Input data representativeness has been directly connected to the calibration window choice, i.e., the selection of the space of process parameters combinations used to calibrate the model. Also, the model validation has to be carefully carried out to make the model significant: the present paper proposes a clear and repeatable validation procedure based on the model performance index calculation over the whole process operating window, i.e., the space of parameters where the process works correctly. An objective indication of the model suitability can be obtained by applying this procedure. Comparisons among prediction performances produced by different calibration windows are allowed. This paper demonstrates how the calibration window selection determines the model prediction performance, which seems to improve if calibration is carried out where forces assume high values. Some important considerations on the process parameters role on cutting forces and on the model capability have also been drawn from the model validation results
Performance validation of a micro quick-stop device
No full textChip removal is one of the most flexible and widely exploited processes in the microscale, but it is still not completely understood and controlled since the process cannot be effectively described simply downscaling macroscale models. The so-called quick-stop experiments are an invaluable support to study the tool-material interaction in the microscale, since they allow to freeze the chip formation in its regime condition by abruptly stop the cutting action. In this paper a new quick-stop device (QSD) is proposed by the authors to be used within the typical microscale cutting requirements; an especially developed sensor has been used to validate the device by means of suitable indexes
Microdrilling of AISI 304 Stainless Steel: process parameters range, hole quality and tool wear
No full textMicrocutting force prediction by means of a slip-line field force model
No full textMechanical micromachining is a very flexible and widely exploited process, but its knowledge should still be improved since several typical phenomena play a role on the microscale chip removal (e.g. “minimum chip thickness effect”, microstructure influence on cutting forces, stable built-up edge, etc. ). Several models have been developed to describe the machining process, but only some of them take into account a rounded-edge tool, which is a typical condition in micromachining. Among these models, the slip-line field model developed by Waldorf for the macroscale allows to separately evaluate shearing and ploughing force components in orthogonal cutting conditions, therefore it is suitable to predict the cutting forces when a large ploughing action occurs, as in micromachining. The present work aims at objectively verifying the cutting and feed force prediction performance of the Waldorf model within typical microscale cutting conditions (uncut chip thickness lower than 50 m and comparable in size to cutting edge radius) in its original version and in a modified version considering the partial effective rake angle. A suitable set-up, especially designed for microturning conditions, has been used in this research to measure forces and chip thickness. Tests have been carried out on C38500 brass (CuZn39Pb3) with different cutting speeds and different ratios between uncut chip thickness and cutting edge radius
A new micro quick-stop device for orthogonal microcutting
No full textMicro mechanical machining is applied in a wide range of industrial fields thanks to its flexibility but the tool-material interaction and the chip formation phenomena in the microscale still have not been completely investigated and understood. The so-called quick-stop experiments are an useful instrument to carry out this kind of studies since they allow to freeze the cutting action in a steady condition and to study the occurring phenomena. A new micro quick-stop device (QSD) has been deisgned to fit the typical microscale cutting requirements, to be equipped with systems and sensors suitable to validate each quick-stop experiment and, moreover, to achieve a good repeatability. Some preliminary experiments have been carried out to prove the effectiveness of the developed system
- …
