Focus Variation Technique Research Articles

Digitization Methods of Grinding Pins for Technological Process Planning

The paper presents different techniques for digitizing grinding pins and discusses the use of digitalized pins and the results of measurements in technological process planning (TPP), focusing on the challenges of the digital era. It describes the potential of different measuring devices, taking into account the digitization of a real tool shape into virtual 2D and 3D models. The following methods for measuring grinding pins are presented in the study: contact and non-contact coordinate measurements – performed on coordinate measuring machines (CMM); optical measurements on microscopes (i.e. focus-variation technique); optical measurements using tool presetters; optical measurements with measuring arm; laser micrometer measurements; and laser triangulation sensor measurements. Moreover, the use of testers which are applied in contour measurements is analyzed. On the basis of the presented methods, taking into account their possibilities and limitations, we discuss how the obtained digital data can be used in the planning of technological processes.

Application of Focus-Variation Technique in the Analysis of Ceramic Chips

The paper presents the method of a microscopic study of ceramic chips which can be useful in the analysis of physical phenomena regarding machining of ceramic materials. The analyzed chips were obtained on the milling machine tool from the Al2O3 based ceramic material. The measurements were performed using focus-variation technique (FVT). The InfiniteFocus Real3D microscope from Alicona Imaging company was applied. The paper mainly focuses on the methodology of measurements and the application of microscope’s software tools which can be used in the analysis of chips' 3D scans. The conditions of measurement process are discussed on the basis of the results of exemplary measurements of ceramic chips.

Topography of as built surfaces generated in metal additive manufacturing: A multi scale analysis from form to roughness

Topographies are one of the challenges for the development of the metal additive manufacturing promising technique. The article investigates multi scale topographies (from form to roughness) of as built surfaces generated by selective laser melting (SLM). Different building inclinations of samples were observed both for upskin and downskin surfaces with a wide range of measuring techniques. The two main aims are: (i) to make a critical review of measuring techniques at different scales, (ii) to enlighten the different surface generation phenomena (and the corresponding scale) occurring during additive manufacturing. The effect of heat treatment on each scale of the topography is also discussed. It is found that the focus variation technique is well suited for AM surfaces. Concerning the observation of the inclined surfaces, some parameters are emphasized as good indicators of typical signatures of AM surfaces: isotropy for the weld track component, the skewness and Rsm for the staircase effect, fractal dimension for the presence of partly melted particles. The different parameters studied helps to model and understand the different surface generation phenomena aforementioned.

Delamination assessment of punched holes on laminated composite panels based on the profile measurement technique

Assembly for a structural material such as a composite panel cannot be avoided. Typically, composite panels are assembled using a fastener through a drilled hole. The main problem of drilling is delamination, which affects the strength of the assembly. In addition, the cost of drilling is high because of repeated regrinding of the drill bit. The main goal of this research is to develop a new method as an alternative to drilling hole preparation. In this study, a new simpler method to determine delamination is based on the profile measurement technique. The 2D profile of the punched hole obtained through the focus variation technique is utilized to determine the delamination. A comparison to the developed measurement method shows a good agreement.

Measurements of Surface Texture Parameters After Ultrasonic Assisted and Conventional Grinding of ZrO2 Based Ceramic Material Characterized by Different States of Sintering

The article presents the results of measurements of surface texture parameters after ultrasonic assisted grinding (UAG) and conventional grinding (CG) of ZrO2 based ceramic material. The machined samples are characterized by different states of sintering. Ultrasonic 20 linear machine tool and two different diamond grinding pins were applied to machine ceramic samples. Surface roughness measurements were performed and the values of parameters were computed using Infinite Focus Real 3D microscope (optical focus-variation technique) and 3D scanner Talyscan (contact measurement). The results of measurements were analyzed in order to state the influence of machining conditions on surface texture parameters.

Nucleation and early crack path in fretting fatigue

The initial crack path is analysed in a series of fretting fatigue tests with cylindrical contact. In such tests, both specimens and pads are made of Al7075-T651 alloy and a non-proportional multiaxial stress state with a significant stress gradient is present. The crack initiation path along the fracture surface is optically measured using a focus variation technique. The contact stress/strain fields analytically obtained, in conjunction with either the Fatemi-Socie (FS) or Smith-Watson-Topper (SWT) multiaxial fatigue parameters, allow us to determine the controlling parameters of the crack initiation process observed in the tests, and to estimate the crack path during the early stage of the crack growth. These estimations are compared with the experimental results. Finally, a fracture mechanics approach is also employed where the crack paths measured are compared with the stress intensity factor (SIF) of cracks with different lengths and orientations showing also good results.

Analysis of fretting fatigue initial crack path in Al7075-T651 using cylindrical contact

This paper analyses the initial crack path in a fretting fatigue test of Al7075-T651 alloy with a cylindrical contact and compares the capability of some multiaxial fatigue criteria to predict the crack initiation path. The experimental crack initiation paths obtained in the tests are optically measured along the fracture surface using a focus variation technique. The Fatemi-Socie (FS) and Smith-Watson-Topper (SWT) multiaxial fatigue parameters obtained from an analytical model, allow us to determine the controlling parameters of the crack initiation process observed in the tests and to estimate the crack path during the early stage of the crack growth.

Analysis of initial crack path in fretting fatigue

The initial crack path is analysed in a fretting fatigue test with cylindrical contact, where there is a stress gradient and a multiaxial and non-proportional stress state. For this, a cylindrical pad is pressed, with a constant normal load, N, against a dog-bone type fatigue test specimen. Then, the test specimen is subjected to a cyclic axial stress, ?. Due to the cyclical axial stress, the assembly used and the friction between the contact pair, a tangential cyclic load Q is generated. In these tests, both components are made of Al7075-T651 alloy. The crack initiation path along the fracture surface is optically measured using a focus variation technique. The contact stress/strain fields obtained analytically, in junction with the Fatemi-Socie (FS) and Smith-Watson- Topper (SWT) multiaxial fatigue parameters, allow us to determine the controlling parameters of the crack initiation process observed in the tests and to estimate the crack path during the early stage of the crack growth.

Precision hole making on laminate composite: a tool wear analysis and comparison between drilling and punching

Hole precision is highly critical for accurate and strong fastener assembly. This factor is considerably important for structural materials, such as composite materials. Drilling is the most commonly used process for producing holes on composites. However, drilling causes excessive tool wear, which may affect the quality of holes and result in damage, such as delamination. The main objective of this study is to compare the drilling and punching processes in terms of tool wear by using the focus variation technique. The scanned images of both the puncher and drill bits are obtained by using a 3D optical surface measurement device called Alicona IFM. Tool wear patterns from both drilling and punching are analysed and compared, and the effects of the processes on the quality of the produced holes are observed.

Verification of an optical micro-CMM using the focus variation technique: Aspects of probing errors

Optical systems based on the focus variation technique are able to collect surface topography measurements from machined parts at high speed and a considerably lower cost than a contacting coordinate measuring machine (CMM). This paper presents a preliminary study of probing characteristics of a focus variation instrument within a single field of view, following the guidance of the international standard ISO 10360-8 (a recently published standard for acceptance and reverification testing of CMMs which use optical distance sensors). The selection of test samples and test strategies is also discussed, with specific emphasis on the adaptations made to the ISO 10360-8 guidance to realise accurate measurements.

Application of focus-variation Technique in Measurements of Ultrasonic Vibrations of Grinding pins

The paper presents the application of focus-variation technique in measurements of ultrasonic vibrations of grinding pins. Ultrasonic vibrations of tools are applied in ultrasonic assisted grinding. Their measurements are significant for development of this hybrid machining process. Alumina and zirconia ceramic materials in the final fired state were machined in experiments which are known as scratch tests. Diamond grinding pin was used as a tool to machine scratches. Marks of diamond grains, left on the surface of workpieces after machining process, were investigated using The Infinite Focus Real 3D optical microscope. Focus-variation is the principle of operation of this microscope. Investigations concerned possibilities of measurements of an amplitude of axial and radial vibrations in the case of two ceramic materials. Results of performed measurements are presented and discussed for selected machining parameters.

Measurement of Polycrystalline Diamond Craters in Electrical Discharge Machining

The electrical discharge grinding method is widely used to machine polycrystalline diamond tools because diamond is the hardest material and the traditional abrasive grinding method leads to high tool wear rate. The aim of this study was to find a method to precisely measure the individual diamond crate morphology during the electrical discharge process. A 3D microscopy with the focus-variation technique was chosen to obtain the stereolithography file of the polycrystalline diamond craters. The measurements were shown that the polycrystalline diamond crater morphology is more complex than that of normal tungsten carbide material. This finding can help build more accurate model of polycrystalline crater formation during electrical discharge process.

Fracture toughness modification by using a fibre laser surface treatment of a silicon nitride engineering ceramic

Surface treatment of a silicon nitride (Si3N4) engineering ceramic with fibre laser radiation was conducted to identify changes in the fracture toughness as measured by K1c. A Vickers macro-hardness indentation method was adopted to determine the K1c of the Si3N4 before and after fibre laser surface treatment. Optical and a scanning electron microscopy (SEM), a co-ordinate measuring machine and a focus variation technique were used to observe and measure the dimensions of the Vickers indentation, the resulting crack lengths, as well as the crack geometry within the as-received and fibre laser-treated Si3N4. Thereafter, computational and analytical methods were employed to determine the K1c using various empirical equations. The equation K1c = 0.016 (E/Hv)1/2 (P/c3/2) produced most accurate results in generating K1c values within the range from 4 to 6 MPa m1/2. From this it was found that the indentation load, hardness, along with the resulting crack lengths in particular, were the most influential parameters within the K1c equation used. An increase in the near surface hardness of 4% was found with the Si3N4 in comparison with the as-received surface, which meant that the fibre laser-treated surface of the Si3N4 became harder and more brittle, indicating that the surface was more prone to cracking after the fibre laser treatment. Yet, the resulting crack lengths from the Vickers indentation tests were reduced by 37% for the Si3N4 which in turn led to increase in the K1c by 47% in comparison with the as-received surface. It is postulated that the fibre laser treatment induced a compressive stress layer by gaining an increase in the dislocation movement during elevated temperatures from the fibre laser surface processing. This inherently increased the compressive stress within the Si3N4 and minimized the crack propagation during the Vickers indentation test, which led to the fibre laser-radiated surface of the Si3N4 engineering ceramic to have more resistance to crack propagation.