Reduction Of Waviness Research Articles

Fibre waviness reduction in thermoplastic pultrusion by using DREF yarns

Non-reactive thermoplastic pultrusion impregnation issues are mitigated by using hybrid input materials. Co-wound (CW) and commingled yarns are an assembly of continuous polymer and reinforcement fibres. Continuous thermoplastic fibres have shown to induce waviness in the reinforcement fibres during pultrusion due to their shrinkage at high temperature. DREF yarns are composed of a core of continuous reinforcement fibres onto which discontinuous polymer fibres are applied using the friction spinning process. This study, based on the application of 3N and 0N tension on CW and DREF yarns, aimed to highlight the contribution of discontinuous polymer fibres on reducing reinforcement waviness in pultruded rods. CW yarns’ reaction to heating showed continuous polyethylene terephthalate (PET) fibres shrinkage resulting in wavy glass fibres (GF). Conversely, the GF in DREF yarns remained straight. Pultrusion experiments with yarn tension of 3N were done to alleviate the GF waviness. However, the porosity was rather high at 4.2% for CW rods and 2.3% for DREF rods. Pultrusion experiments without tension showed lower porosity of level of 2.9% for CW yarns and as low as 1.1% for DREF yarns. However, CT-scan image indicated GF waviness in CW rods. GF in DREF rods remained straight. The in-plane shear strength reached 119 MPa. Thermoplastic pultrusion using DREF yarns resulted in composites without reinforcement fibre waviness, lower porosity level and superior shear strength.

Surface Treatment of Additively Manufactured Polyetheretherketone (PEEK) by Centrifugal Disc Finishing Process: Identification of the Key Parameters.

Polyetheretherketone is a promising material for implants due to its good mechanical properties and excellent biocompatibility. Its accessibility to a wide range of applications is facilitated by the ability to process it with an easy-to-use manufacturing process such as fused filament fabrication. The elimination of disadvantages associated with the manufacturing process, such as a poor surface quality, is a main challenge to deal with. As part of the mass finishing process, centrifugal disc finishing has demonstrated good results in surface optimization, making it a promising candidate for the post-processing of additively manufactured parts. The objective of this study is to identify the key parameters of the centrifugal disc finishing process on the waviness of additively manufactured PEEK specimens, which has not been investigated previously. The waviness of the specimen was investigated by means of confocal laser scanning microscopy (CLSM), while weight loss was additionally tracked. Six parameters were investigated: type, amount and speed of media, use of compound, amount of water and time. Type of media, time and speed were found to significantly influence waviness reduction and weight loss. Surface electron microscopy images demonstrated the additional effects of deburring and corner rounding. Results on previous studies with specimens made of metal showed similar results. Further investigation is required to optimize waviness reduction and polish parts in a second post-processing step.

The Selection of Leveler Parameters Using FEM Simulation.

The aim of this research was to select parameters for the roll pre-leveler to provide sheet metal waviness reduction after unwinding from the coil. Straightening parameters were selected based on the results of numerical simulations with the use of an FEM-based computer program. The material used for research was a hot-rolled sheet metal of grade S235JR + AR with a thickness of 3 mm and width of 1500 mm after unwinding from the coil. A mathematical model was developed to determine straightening roll arrangements in the pre-leveler. It enabled roll arrangement selection and a straightening scheme to be elaborated. The model's innovative feature was conducting straightening numerical simulations for the real sheet metal geometric models obtained as a result of 3D laser scanning, which increased the accuracy of the numerical calculations.

Application of the ABA cladding technique to a wire based laser cladding process

In this study, the application of the ABA cladding strategy in coaxial wire-based cladding processes is investigated. Individual weld seams (A) are first welded on the substrate and additional weld seams (B) are deposited into the intermediate spaces in the second step. Thereby, two different seam geometries are present in the cladding. Unidirectional AAA and ABA claddings are generated using laser hot-wire cladding and analyzed with respect to the quality criteria height, waviness, degree of dilution, and defects. Three different welding parameter sets are used to consider the effect of the contact angle on the applicability of the ABA cladding strategy. When the same process parameters and seam-to-seam offsets are used for the ABA cladding, as for the AAA cladding, the B weld seams are higher than the A weld seams and an uneven ridged cladding surface is present. Two approaches to solving this problem are considered. The cross-sectional area of the B weld seams is reduced by adjusting the welding speeds or an increase in the seam-to-seam offset. Both measures result in a significant reduction in waviness of 30%–58% compared to the AAA cladding. However, lack of fusion defects occurs more frequently at the deposition regime of the B weld seams. It was, therefore, necessary to adjust the process parameters for weld seam B.

Design of parallel multiple tuned mass dampers for the vibration suppression of a parallel machining robot

Parallel machining robots have the potentials of high precision and high flexibility. However, their pose-dependent vibration characteristics may cause accuracy problems during machining, which poses a great challenge to the vibration suppression. Multiple tuned mass dampers (MTMDs) are widely used to suppress the vibration, owing to their significant vibration suppressing effect, great robustness, and compact structure. In this paper, a parallel MTMD system is designed to mitigate the forced vibration of a parallel machining robot. The elasto-dynamic model of the parallel robot is established to identify the modes and natural frequencies of the robot, and the results show that the frequency of the resonant mode varies from 91.0 Hz to 128.1 Hz. Based on the structure and natural frequency scope of the robot, the MTMD system is designed to be a parallel configuration in two directions and the impedance model of the MTMD system is built. Considering the pose-dependent dynamics and compact inner space of parallel robots, a multi-objective optimization method for varied vibration characteristics is proposed based on the impedance model. In this method, the suppression amplitude, robustness, and compactness are the main concerns. In the structural design, small-sized polymer material springs and viscous fluid damping inside the mass blocks are used to compose the MTMD system. Therefore, wide-band vibration suppression is realized in narrow spaces. Finally, verification experiments are performed. Modal tests show that the amplitudes of the resonant modes are decreased by 38.8% along the X axis and 40.7% along the Y axis. Machining tests show that a 20%-30% reduction of the vibration in the feed direction, a 40%-50% reduction in the radial direction, a 48%-55% harmonics reduction at the natural frequency are achieved. Precise surface measurements show a 32% reduction in waviness and a 17% reduction in roughness. This study provides a new structural design and optimization method of MTMDs adapted to vibration suppression for parallel machining robots.

A Review of Self-Sensing in Carbon Fiber Structural Composite Materials

Sensing is a basic ability of smart structures. Self-sensing involves the structural material sensing itself. No device incorporation is needed, thus resulting in cost reduction, durability enhancement, sensing volume increase and absence of mechanical property diminution. Carbon fiber renders electrical conductivity to a composite material. The effect of strain/damage on the electrical conductivity enables self-sensing. This review addresses self-sensing in structural composite materials that contain carbon fiber reinforcement. The composites include polymer-matrix composites with continuous carbon fiber reinforcement (relevant to aircraft and other lightweight structures) and cement–matrix composites with short carbon fiber reinforcement (relevant to the civil infrastructure). The sensing mechanisms differ for these two types of composite materials, due to the difference in structures, which affects the electrical and electromechanical behaviors. For the polymer–matrix composites with continuous carbon fiber reinforcement, the longitudinal resistivity in the fiber direction decreases upon uniaxial tension, due to the fiber residual compressive stress reduction, while the through-thickness resistivity increases, due to the fiber waviness reduction; upon flexure, the tension surface resistance increases, because of the reduction in the current penetration from the surface, while the compression surface resistance decreases. These strain effects are reversible. The through-thickness resistance, oblique resistance and interlaminar interfacial resistivity increase irreversibly upon fiber fracture, delamination or subtle irreversible change in the microstructure. For the cement–matrix composites with short carbon fiber reinforcement, the resistivity increases upon tension, due to the fiber–matrix interface weakening, and decreases upon compression; upon flexure, the tension surface resistance increases, while the compression surface resistance decreases. Strain and damage cause reversible and irreversible resistance changes, respectively. The incorporation of carbon nanofiber or nanotube to these composites adds to the costs, while the sensing performance is improved marginally, if any. The self-sensing involves resistance or capacitance measurement. Strain and damage cause reversible and irreversible capacitance changes, respectively. The fringing electric field that bows out of the coplanar electrodes serves as a probe, with the capacitance decreased when the fringing field encounters an imperfection. For the cement-based materials, a conductive admixture is not required for capacitance-based self-sensing.

Light-curing process for clear aligners’ attachment reproduction: comparison between two nanocomposites cured by the auxiliary of a new tool

BackgroundAttachments’ configuration play an important role during Clear Aligner Treatment (CAT) for aligner retention and control of movements planned. The aims were to compare the macroscopic morphology of attachments reproduced with flowable (FNC) and conventional (CNC) composites and the effects on them of two light-guide tips with different dimensions.Methods4 resin casts derived from the initial scan of the same patient were obtained. 10 vestibular attachments were replaced on both upper and lower arches of each model with CNC (Models A, B) and FNC (Models C, D). Each composite was cured by means of the same LED lamp with both regular light-guide (Models A, B) and push and light tool® (Models C, D). The 80 attachments were qualitative analyzed by means of a digital stereo microscope. Surface roughness and waviness measurements were assessed by contact probe surface profiler (TalySurf CLI 2000; Taylor Hobson, Leicester, United Kingdom). Statistical analysis was performed with independent samples t-tests. Significance was established at the P < 0.05 level.ResultsModel A showed lower values of surface roughness (Ra − 1.41 µm, Rt − 3.46 µm) and waviness (Wa − 2.36 µm, Wt − 10.95 µm) when compared with Model C. Significant reduction of waviness (Wa − 3.85 µm, Wt − 4.90 µm) was observed on Model B when compared with Model D. Significant increase of roughness and waviness parameters (Ra 3.88 µm, Rt 21.07, Wa 2.89 µm, Wt 14.74 µm) was found when CNC sample (Model A) was cured with regular light-guide tip. Higher values (Ra 2.33 µm, Rt 24.07 µm, Wa 1.67 µm, Wt 20.79 µm) were observed after regular light-guide tips curing on FNC sample (Model C).ConclusionsCNC resins determine more regular surfaces of attachments profiles. The additional use of a smaller light- guide of the LED push and light tool® allows to improve the macroscopic morphology of the attachments and to maximize light irradiance delivering by enhancing the polymerization process and the integrity of the features during the treatment.

Structuring by laser remelting as a method for waviness reduction on additive manufactured parts

The surface roughness of parts manufactured by laser powder bed fusion (LPBF) is often not sufficient for the intended application. Therefore, surface finishing is necessary. Conventional finishing techniques have many disadvantages like accessibility of complex geometries, high time and cost consumption and a negative environmental impact due to the use of abrasives. As a solution laser polishing is investigated. In this study it was found that surface roughness of LPBF parts up to a spatial wavelength of 0.5 mm can be reduced by ∼96% with laser polishing, while waviness can only be reduced by ∼55%. To further reduce waviness, structuring by laser remelting (WaveShape) is investigated. The basic idea is to structure the inverse of the initial structure and thus to “de-structure” the waviness. A structured profile of a laser polished LPBF surface is “de-structured” with a variation of process parameters. The results show the potential of a waviness reduction of 85%.

Experimental investigation of electrodeposited Ni-Al2O3/ZrO2 nano composite on HSLA ASTM A860 alloy

Nano composite coatings on HSLA ASTM A860 alloy, adds to the barrier efficacy by increase in the microhardness, wear and corrosion resistance of the substrate material. Additionally, reduction of delamination of the nano composite coating sample is ascertained. Ball milling is availed to curtail the coating samples (Al2O3/ZrO2) to nano size, for forming a electrodeposited product on the substrate layer. The curtailment in grain size was ascertained to be 17.62% in Ni-Al2O3/ZrO2 nano composite coating. During the deposition process, due to the presence of Al2O3/ZrO2 nano particles an increase in cathode efficiency is ascertained. An XRD analysis of the nano composite coating indicates a curtailment in grain size along with increase in the nucleation sites causing a surge in the growth of nano coating layer. In correlation to uncoated HSLA ASTM A36 alloy sample, a surge in compressive residual stress by 47.14%, reduction of waviness by 32.14% (AFM analysis), upsurge in microhardness by 67.77% is ascertained in Ni-Al2O3/ZrO2 nano composite coating. Furthermore, in nano coated Ni-Al2O3/ZrO2 composite a reduction is observed pertaining to weight loss and friction coefficients by 27.44% and 13% in correlation to plain uncoated alloy respectively. A morphology analysis after nano coating indicates, Ni-Al2O3/ZrO2 particles occupy the areas of micro holes, reducing the wide gaps and crevice points inside the matrix of the substrate, enacting as a physical barrier to upsurge the corrosion resistance by 67.72% in correlation to HSLA ASTM A860 base alloy.

Conditions for Obtaining High-Modulus Polymer/Carbon Nanotube Nanocomposites

We consider physical foundations for the realization of high-modulus and high-strength polymer/carbon nanotube nanocomposites with mechanical characteristics comparable with those for steel. We have determined two main factors that make it possible to obtain such nanocomposites, i.e., the structure of the nanofiller in the polymer matrix and a quite high concentration of the nanofiller. The fractal dimension of such a structure must be close to that of the surrounding Euclidian space (i.e., 3). It is shown that additional stretching of the nanocomposite gives two positive effects: the reduction of waviness of carbon nanotubes and the increase of the elastic modulus of the polymer matrix due to alignment of its macromolecules.

Условия получения высокомодульных нанокомпозитов полимер/углеродные нанотрубки

The physical basis of realization of high-modulus and high-strength nanocomposites polymer/carbon nanotube, having mechanical characteristics comparable with the same ones for steel, were considered. Two main factors, allowing to create such nanocomposites, were defined – the structure of nanofiller in polymer matrix and large enough content of nanofiller. The indicated structure fractal dimension should be close to dimension of surrounding Euclidean space, i.e. three one. Besides, elastic modulus of nanofiller depends on stiffness of polymer matrix. Therefore additional drawing of nanocomposite gives two positive effects: reduction of waviness of carbon nanotubes and enhancement of elastic modulus of polymer matrix owing to orientation of its macromolecules.

An investigation of the surface waviness features of ground surface in parallel grinding process

The high precision tungsten carbide (WC) and silicon carbide (SiC) optical mold inserts used in glass molding are usually machined by ultra-precision grinding, but the residual surface waviness error is difficult to be eliminated. This paper mainly focused on the surface waviness features related to the grinding wheel run-out error and the non-integer rotation-speed-ratio (RSR) in parallel grinding process. After the integrate consideration of grinding kinematics and microscopic material removal, the generation mechanism and distribution trend of surface waviness features were revealed. In order to simulate the surface waviness topography of parallel ground components, a mathematical model was developed and experimentally proved, which was appropriate for both integer and non-integer RSR. Besides, the mechanism of surface waviness reduction was explained when RSR was non-integer, which was due to the material removal again by the secondary grinding zone of grinding wheels. Then prediction models for the surface-waviness-period-feature (SWPF) and surface-waviness-amplitude-feature (SWAF) was built and experimentally verified, which was based on the waviness profiles overlapping effect. It found that the wave-shift resulted from the non-integer RSR had significant influence upon the surface waviness features. In the end, a convenient method was proposed to reduce the surface waviness error of parallel ground components through proper adjustment of grinding wheel rotation speed to achieve proper non-integer RSR and wave-shift, which was proved practically feasible and effective for both plane components and Fresnel components.

Machining of Smooth Optical Surfaces by Ultraprecision Milling with Compensated Feeding Mechanisms

Waviness tends to be generated on cut surfaces even when an ultraprecision milling machine with a single-crystal diamond tool is used. The present study deals with the reduction of waviness by controlling the feeding mechanisms of the milling machine. A machining experiment on a spherical surface of a mirror element in a mirror array showed that the machined surface exhibited periodic waviness with a height of 30 nm and a wavelength of 300 μm. To investigate the reason for such waviness, a slope was machined under simultaneous multiaxis motion control of the feeding mechanisms of the milling machine. This proved that the interpolation errors of the encoders used in the milling machine produce the waviness on the machined surface when machining is carried out under simultaneous multiaxis motion control. To reduce such interpolation errors, the positioning accuracy of the machine stages was measured using a laser interferometer. On the basis of the measured results, the feeding mechanisms were compensated such that the positioning errors including the interpolation errors were corrected. Using the machine with the compensated feeding system, a mirror element was shaped. Consequently, waviness was reduced and the surface smoothness was less than 10 nm, demonstrating that such compensation can produce superior optical surfaces.

Study on surface topography of workpiece in prestress dry grinding

Workpiece surface topography has a significant influence on workpiece performance, especially on the roughness which has been a topic of extensive research. The workpiece surface topography can be considered as the result of individual grain action. This interaction is very complex depending on various factors involving the wheel topography, the grinding parameters, and the grinding temperature. The wheel surface is frequently non-Gaussian. In order to better research workpiece surface topography, a numerical procedure for generating the grinding wheel topography has been proposed, and the simulation of the grinding process is described in detail. The simulation considered the effect of temperature field on surface profile and the kinematic relationship between the grains and grinding wheel. The experiment of the grinding process is carried on 45 steel. The SEM micrograph shows that the roughness and waviness reduction with increase of prestress is consistent with the simulation results. The effect of prestress on phase transformation is analyzed; the metallographical micrographs show appropriate prestress can increase the thickness of the strengthened layer and refine grains. Therefore, prestress dry grinding is an effective method to improve workpiece surface properties.

Active reduction of waviness through processing with modulated laser power

A new approach to the reduction of the waviness of metal surfaces is based on laser remelting with modulated laser power. Waviness reduction is reached due to the modification of direction of solidification of a molten pool. The changes of the molten pool are induced by laser radiation in which amplitude is modulated in accordance with initial topography of surface. The laser process with modulated laser power allows decreasing the waviness up to 80%–95% depending of the wavelength of the initial structure. Results are given for milled steel 1.2343. This new approach shows better results in comparison with laser polishing with nonmodulated laser power.

Investigations of silicon wafer grinding using finite element analysis

Silicon wafers are used as substrates to build more than 90% of integrated circuits. One of the manufacturing processes for silicon wafers is grinding. This paper reports the investigations of silicon wafer grinding using Finite Element Analysis (FEA). FEA models are first used to study the effects of process parameters on waviness reduction in the grinding of wire-sawn wafers on a rigid chuck. Then, soft-pad grinding of wire-sawn wafers is modelled using FEA to study the effects of pad properties on waviness reduction. Finally, FEA is used to study the elastic deformation of the grinding wheel, providing an explanation for the central dimples on ground wafers.

Modelling and analysis of waviness reduction in soft-pad grinding of wire-sawn silicon wafers by support vector regression

The manufacturing of silicon wafers forms the most important step in the construction of integrated circuit (IC) chips. One of the difficulties in this manufacture process is the removal of the waviness from the resulting wafers. In this paper, mathematical modelling and analysis of this removal process is carried out by the use of the support vector regression (SVR) algorithm. The results show that SVR is ideally suited for the modelling of this complicated process. Furthermore, by the use of the learning ability of SVR, the model can be continuously improved as more data become available. Based on the resulting model, the influences of the various factors on the rate of removal and the ease of control of the removal process are also discussed.

A Fuzzy Adaptive Network Model for Waviness Removal in Grinding of Wire-Sawn Silicon Wafers

Silicon is the primary semiconductor material used to fabricate microchips, and the quality of microchips depends directly upon the quality of the starting silicon wafers. One of the manufacturing problems in silicon wafer manufacturing is the presence of waviness on the surface as a result of wire-saw slicing. Various factors influence the waviness reduction capacity during soft-pad grinding; the grinding process is very complicated and difficult to define. In this research, fuzzy adaptive network, which is ideally suited to the modeling of vague phenomena, is used to model the waviness problem. Fuzzy adaptive network has the learning ability of a neural network and the linguistic representation of a complex, not well understood phenomenon. Simulation data are used to illustrate the applicability of fuzzy adaptive network. The results, even though based on some very limited data, indicate the influences of the independent parameters clearly.

Finite Element Analysis on Soft-Pad Grinding of Wire-Sawn Silicon Wafers

Silicon is the primary semiconductor material used to fabricate microchips. The quality of microchips depends directly on the quality of starting silicon wafers. A series of processes are required to manufacture high quality silicon wafers. Surface grinding is one of the processes used to flatten the wire-sawn wafers. A major issue in grinding of wire-sawn wafers is the reduction and elimination of wire-sawing induced waviness. Several approaches (namely, combination of grinding and lapping, reduced chuck vacuum, soft-pad, and wax mounting) have been proposed to address this issue. Finite element analysis modeling of these approaches was conducted and the results were published earlier. It was shown that soft-pad grinding was a very promising approach since it was very effective in reducing the waviness and very easily adopted to conventional grinding environment. This paper presents a study of finite element analysis on soft-pad grinding of wire-sawn silicon wafers, covering the mechanisms of waviness reduction and the effects of pad material properties.

Effect of nanorope waviness on the effective moduli of nanotube sheets

Using a micromechanics approach, we recently investigated the theoretical limits on achievable moduli in nanotube mats by stiffening of bonds. However, the waviness intrinsic to many manufacturing processes also clearly plays an important role in stiffness of these materials. To study the effect of waviness on mechanical properties, we modeled fiber segments as sinusoids, generated networks comprised of these fibers, and performed simulations of deformations of the networks. In contradiction of classical work by Kallmes and Corte [Tappi J. 43, 737 (1960)], we found the number of fiber crossings in these networks to be independent of fiber waviness, leading to identification of the number of fiber crossings as a necessary and sufficient parameter to specify network geometry, for either wavy or straight fibers. Our mechanical modeling results suggest that reducing the waviness of nanotube ropes would significantly improve Young’s moduli in these materials. However, reduction of waviness would not produce the improvements achievable with higher bond density; for random sheets, assuring connections among all intersecting ropes appears to be the most direct route toward improving the overall sheet properties. There remains a persistent discrepancy between statistically predicted bond densities and physical bond densities, based on moduli of these materials.