Workpiece Topography Research Articles

Investigation on the generation of the waviness errors along feed-direction on flycutting surfaces

Ultra-precision single-point diamond flycutting (SPDF) is an irreplaceable technology for cutting KH2PO4 (KDP) crystals with large size. However, some undesirable waviness errors along feed-direction exist on the machined surface, which could greatly deteriorate the optical performance of KDP crystals. The spindle dynamic characteristic of SPDF plays an important role in the formation of such waviness errors. This paper presents an on-line measurement method with five-capacitance displacement sensors in nanometer range for monitoring the motion errors of the aerostatic spindle. An error transform theory which is based on kinematic error propagation was introduced to obtain the three-dimensional trajectory of the cutting tool. Then, the spindle motion errors and the cutting tool trajectory were analyzed in frequency domain to investigate the main source of the waviness errors. Simultaneously, the three-dimensional topography of work-piece was simulated by combining the motion trajectory and the geometrical morphology of the cutting tool. The results showed that the waviness errors along feed-direction were caused by the spindle rotation fluctuation with a frequency about 10.8 Hz, and the topography simulations showed good agreement with the machining results. Besides, the experimental results indicated that the error can be diminished by changing the spindle control system to the digital control method. This study established the contact between the measured spindle motion errors and the machined surfaces, which contributes to deeper understanding of the dynamic characteristics of the spindle in SPDF.

Research on machining topography of point grinding based on correlation function method

Point grinding uses the point contact to shape surface topography of workpiece which has high machining precision. Its surface topography has a close relation with its service performance. In order to study the topography of point grinding, these authors carried out the experiment and established a new assessing model based on the correlation function method. The inner characteristics of topography are revealed by self-correlation and mutual correlation function method and its mechanism is analyzed. The study shows that the topography of point grinding has obvious periodical portions, which means it is consistent and uniform. The mutual correlations of every direction show the surface topography of point grinding is isotropic. Point grinding surface has better consistency under larger included angle and smaller grinding depth. And it has better isotropy under larger included angle. Surface roughness has the opposite rule from the consistency and isotropy. The influence of point grinding angle on surface topology is much larger than grinding depth.

Grinding performance of textured monolayer CBN wheels: Undeformed chip thickness nonuniformity modeling and ground surface topography prediction

Abstract The ground surface roughness and topography are commonly used to characterize the surface finishing. In the application of textured monolayer CBN wheels, the nonuniformity of wheel topology will render a nonuniform undeformed chip thickness which greatly affects the ground surface. In order to predict the ground surface topography more accurately and efficiently, grinding experiment has been conducted in the current study, with measured grinding wheel topology. The measured surface topology of textured monolayer CBN wheels has been reconstructed by using the Johnson transformation and its inverse transformation. The influence of wheel topology evolution on the undeformed chip thickness nonuniformity has been determined with an improved model. It has been found the ground surface roughness is improved with a continuous reducing undeformed chip thickness nonuniformity. The percentage of active grains, the mean value and standard deviation of undeformed chip thickness have been found the main factors in determining the surface roughness. The reconstructed wheel surface topology has been used to predict the workpiece topography in different stages of the grinding process.

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.

An analytical force and surface roughness model for cylindrical grinding of brittle materials

In this paper, an analytical approach is proposed for the modelling of ground surface and grinding forces in cylindrical grinding of ceramic materials. The model incorporates the near-actual distribution of cutting grains over the grinding wheel surface and a kinematic approach for the engagement of the grains with the workpiece surface per grinding parameters and conditions. To interpret the stochastic engagement of arbitrary grains with the workpiece, and to distinguish the dominant material removal mechanism, fracture mechanics of single-grain indentation is applied. The approach based on the fracture mechanics accounts for grain size and geometry and material properties. The results of a previously performed research on single-grain scratch tests are taken for interpreting force and workpiece surface characteristics. Without losing generality, the model was applied to a cylindrical plunge grinding of an alumina ceramic. The experiments show qualitative agreement of model predictions with the experimental force and ground workpiece topography.

The application of computational fluid dynamics to vibratory finishing processes

Vibratory finishing processes are finding increased application in the finishing of high value metallic components. Despite the growth of these processes, few models exist to predict workpiece material removal variations and surface finish uniformity. This paper explores the potential of modelling the media as a continuum and utilizing commercial computational fluid dynamic (CFD) packages to predict local velocity and pressure fields around stationary workpieces. Predicted 2D velocity fields are compared to those measured via Particle Image Velocimetry. Initial insights are provided on how local media fields and the system’s driving frequency combine to affect the resulting workpiece topography.

An analytical force and surface roughness model for cylindrical grinding of brittle materials

In this paper, an analytical approach is proposed for the modelling of ground surface and grinding forces in cylindrical grinding of ceramic materials. The model incorporates the near-actual distribution of cutting grains over the grinding wheel surface and a kinematic approach for the engagement of the grains with the workpiece surface per grinding parameters and conditions. To interpret the stochastic engagement of arbitrary grains with the workpiece, and to distinguish the dominant material removal mechanism, fracture mechanics of single-grain indentation is applied. The approach based on the fracture mechanics accounts for grain size and geometry and material properties. The results of a previously performed research on single-grain scratch tests are taken for interpreting force and workpiece surface characteristics. Without losing generality, the model was applied to a cylindrical plunge grinding of an alumina ceramic. The experiments show qualitative agreement of model predictions with the experimental force and ground workpiece topography.

OCT for Efficient High Quality Laser Welding

AbstractHigh requirements for duration and quality of laser welding are the main topics in the line production nowadays, especially in the automotive industry. With acquisition rates up to 100 kHz and microseconds duration capture times, optical coherence tomography (OCT) is a powerful adaptive tool, with a few microns resolution, for real‐time direct non‐contact investigation of material processing. The measurement system used to acquire the workpiece topography enables high accuracy automatic seam tracking, process monitoring and quality assurance (QA), and these functions are executed simultaneously.

Evolution of topography and material removal during nanoscale grinding

In this work we perform molecular dynamics simulations to quantify and parametrize the evolution of a bcc Fe work piece topography during nanometric grinding with multiple hard abrasive particles. The final surface quality depends on both the normal pressure and the abrasive geometry. We fit the time development of the substrate’s root mean squared roughness to an exponential function, allowing the definition of a run-in regime, during which the surface ‘forgets’ about its initial state, and a steady-state regime where the roughness no longer changes. The time constants associated with smoothing and material removal are almost inversely proportional to each other, highlighting the distinctiveness of these two simultaneously occurring processes. We also describe an attempt to reduce the time required to achieve the smoothest possible surface finish by periodically re-adjusting the normal pressure during the grinding process.

Research on simulation and experiment for surface topography machined by a novel point grinding wheel

Grains motion path will be changed in the point grinding process due to the existence of variable angle α. To verify the difference between point grinding and traditional grinding, the moving relationship and coordinate transformation between grinding wheel and workpiece are used to put the grain movement function equivalent to parabola, then point grinding cutting path is concluded. Based on grains distribution on the grinding wheel surface, the 3D geometry simulation topography of workpiece is obtained by extending the effective interference trails along the axial direction. Furthermore, a vitrified bond CBN wheel with a coarse grinding area angle θ is proposed and the principle of design and preparation of these novel grinding wheels are studied. The typical processing parameters are chosen to grind QT700 ladder shaft; the simulation results are verified by using the VHX-1000E microscope and the non-contact 3D surface profilometer to observe the workpiece surface topography and measure the surface roughness. The results indicated that the simulation microstructures coincide well with the experimental measurements and the values of simulation roughness are 0.5 times of experiments. So, the geometric simulation model provided an auxiliary and prediction method for the actual processing topography analysis. In addition, grinding wheels with different θ are used to grind ladder shafts with a series of grinding parameters. The influence trend of inclining angle α, cutting depth ap, axial feeding speed vf and grinding wheel speed vs on surface roughness is obtained. It is concluded that the values of workpiece surface roughness using novel grinding wheel are less than using the traditional grinding wheel under the condition of the same processing parameters.

A time based method for predicting the workpiece surface micro-topography under pulsed laser ablation

The generation of micro-features in a predictable and repeatable manner by use of pulsed laser ablation requires an understanding of the temporal and energetic distributions of the laser beam upon the workpiece surface. Modelling the response of the material to known energetic and kinematic parameters of the pulsed laser ablation process can be carried out in a discretised time-based approach, allowing the workpiece topography to be simulated mathematically to reflect a real-life process. Considerations of the antecedent workpiece surface texture such as increases in irradiated area due to the surface gradient, and increases in laser spot size due to beam divergence throughout the elevation of the workpiece are used to predict energy densities and hence the resultant ablated depth and texture of the targeted surfaces. A fully calibrated Yb:YAG pulsed fibre laser (SPI G3.0 RM) was used to validate the model on three materials, highlighting the models strengths for different material types. It was found that Ni based workpieces presented redeposition phenomena under these laser ablation conditions. To analyse the model without redeposition, validations trials on materials that do not present such side effects, e.g. diamond, were carried out and differences were found to be up to 9.39%.

Development of mirror like surface characteristics using nano powder mixed electric discharge machining (NPMEDM)

This paper reports the results of an experimental study to develop mirror-like surface finish on the surface of AISI-D2 die steel by electric discharge machining (EDM) using carbon nanotubes (CNTs). The CNTs will be mixed into the dielectric fluid of EDM in defined proportion to develop and analyze the surface characteristics of AISI-D2 die steel. The newly developed proposed technology is called nano powder mixed electric discharge machining (NPMEDM). This research presents the influence of various processing parameters namely concentration of CNTs, peak current, and pulse duration on surface topography of workpiece machined by NPMEDM. The obtained experimental results indicate significantly improved performance of NPMEDM over EDM. The appropriate addition of CNTs into dielectric fluid of EDM increases the machining rate and decreases the surface roughness. At 3A peak current, 0.2 mm3/min MRR has been obtained by EDM which has been increased to 1 mm3/min after addition of CNTs into dielectric fluid of EDM. Similarly, the surface roughness has been reduced to 0.4 from 1.2 μm after mixing the CNTs into dielectric fluid of EDM. The improvement in SR and MRR is obtained at the CNT concentration of 4 g/l mixed into the dielectric fluid. The experimental results further indicate that the CNTs concentration and peak current are the most influential variables.

A High Resolution Surface Model for the Simulation of Honing Processes

The demand for highly resistant surfaces is driven by the requirement for resource efficiency and rising environmental concerns. Finishing processes like long-stroke honing for the machining of boreholes of chuck components make it possible to create surfaces with favourable tribological properties. Since variations of process parameter values have complex effects on the resulting workpiece topography and its characteristic values, many experiments might be necessary to achieve certain properties. To avoid this, a simulation-based approach has been developed that relies on a high resolution model of the tool and the workpiece. For its calibration and validation, systematic investigations of a honing process and the machining parameter values have been conducted, and the measured surfaces are compared to the computed workpiece topographies.

Study on Surface Topography and Texture of Workpiece Machined by Tangential Turn-Milling

By measure and calculate related parameters of Tangential Turn-milling machined surface profile, the fractal dimension of the surface was got when machined in different feeding and rotating speed . Results show that the fractal trait can express the information of workpiece profile surface texture ; With the increase of feeding, workpiece surface fractal dimension was reduced and the structure of surface texture was become thin; along the increase of ratio of revolution, workpiece surface fractal dimension was increased, the structure of surface texture was become compactness and have the lower surface texture height.

Material Flow in Sheet-Bulk Metal Forming

Innovative trends like increasing component functionality, the demand for automotive lightweight constructions and the economic issue to optimize existing process chains, require new ways in manufacturing. Today, the traditional sheet metal and bulk metal forming processes are often reaching their limits if closely-tolerated complex functional components with variants have to be produced. A promising approach is the direct forming of high-precision shapes starting from blanks. Thus, classic sheet metal forming operations, such as deep drawing, are combined with bulk metal forming operations like extrusion of complex variants as for example teeth. This combination of sheet and bulk metal forming operations leads to a side by side situation of different tribological conditions according to the locally varying load situations within the same forming process. This new class of forming processes is defined as sheet-bulk metal forming (SBMF). The tribological conditions in sheet-bulk metal forming processes are of major importance for the process realization, its stability and for the quality of the produced part. The objective of this paper is the investigation of material flow in SBMF in general and the attempt to improve the material flow by local adapted tribological conditions. First the material flow was analyzed by FE-simulation of a model geometry that is typical for SBMF. The investigations with FE-simulation have shown, locally adapted tribological conditions are leading to an improvement in material flow and thus to an increased mould filling. As frictional conditions are directly connected to the topography of workpiece and tool, the modification of the workpiece topography is leading to an alteration in friction values. For the modification of workpiece topography grit blasting was used. The increase in friction of grit blasted surface towards untreated surface was investigates by using the laboratory friction tests. To manufacture specimens with locally adapted topographies for forming tests a masking technique has been developed. The masks are designed after the preliminary findings determined by FE-simulation.

Effect of Machining Parameters on Surface Roughness During Wet and DryWire-EDM of Stainless Steel

Surface integrity of Machined parts is one of the major machining characteristics that play an important role in determining the quality of engineering components. It is well-known fact that good quality surfaces improve the fatigue strength, corrosion and wear resistance of workpiece. The purpose of this study was to investigate the effects of Wire-Electrical Discharge Machining (WEDM) variables on surface topography of stainless steel. In the present work, the effects of pulse current and gap voltage on surface topography during wet and dry WEDM of stainless steel were investigated. It was evident that as the two process parameters increase the surface topography of workpiece becomes worse. The effect of both dry and wet machining conditions on surface topography is also reported in this paper.

New Process Simulation Procedure for High-Rate Plasma Jet Machining

Surface figuring using chemically reactive plasma jet machining (PJM) is a promising non-conventional technology for deterministic ultra-precision machining of optical components. Based on chemical reactions between plasma generated radicals and the surface atoms this technology is capable to fabricate complex shaped free form surfaces. Since the material removal rate during PJM depends strongly on the surface temperature which itself is influenced by the jet heat flux to the surface, the arising nonlinear effects on the etch result have to be regarded. Conventionally applied dwell time calculation algorithms do not consider those effects leading to significant machining errors in some cases. In order to improve the machining procedure with respect to deterministic material removal yielding predictable results a process simulation model has been developed. This model considers spatio-temporal variations of surface temperature and temperature dependent material removal and is able to predict the final workpiece topography after machining.

Basic investigations on boundary lubrication in metal forming processes by in situ observation of the real contact area

In metal forming processes tribology plays a significant role for process feasibility and tool lifetime. Boundary and mixed lubrication conditions are predominant in metal forming processes. Hence the appearing real contact area which is mainly influenced by the topography of tool and workpiece has a major impact on friction conditions. For an improved understanding of friction at the interface between tool and workpiece, the flattening behavior of idealized asperities under boundary lubrication conditions is investigated by applying a translucent tool. Various liquid lubricants have been used. It has been revealed that the usage of certain lubricants leads to higher resistance of the asperity against flattening which would be in favor of reduced friction. Topography analysis and finite element simulations have been performed in order to get more insight into the mechanisms leading to this effect. The findings have been transferred to real topographies by micro upsetting tests with ground surfaces.

Modeling of Virtual Grinding Wheel and its Grinding Simulation

Based on virtual reality technology, a friendly human-computer interaction interface and virtual machining environment were developed by Visual C++ and OpenGL. Considering the inhomogeneity of grain size and randomicity of grain distribution, virtual grinding wheel was modeled by taking ortho-hexahedron as basic shape of abrasive grains and randomly distributes them on the wheel base. Mathematic model of interference between abrasive grain and workpiece was established. By using the virtual grinding wheel modeled, surface grinding processes with different machining parameters were simulated. The simulation results show that the system could make operators have a further understanding to chip formation, and the machining results could reflect realistic surface topography of workpiece. Complex grinding process can be realistically simulated. It provides visualization models for the research of grinding mechanism and production forecast.

Surface characterisation in forming processes by functional 3D parameters

Tribology in metal forming plays a significant role for process feasibility and process quality. Especially in micro forming the influence of the tribological condition is very essential due to an extensive increase in friction which is observed while scaling processes from macro to micro. As friction depends considerably on the surface topography of tool and workpiece, functional surface characterisation concerning the tribological properties becomes even more relevant. Standardised 2D roughness-measurements and -parameters are notable to fulfil this task satisfactorily. Hence the surface has to be measured three dimensionally. An appropriate method is given by confocal white light microscopy. New 3D parameters are defined with respect to the functional behaviour of the surface. These parameters are derived from a mechanical-rheological model which describes the transmission of the forming load from the tool to the workpiece. In order to calculate these parameters, the software WinSAM has been developed. Especially the maximum closed void area ratio and the volume of closed lubricant pockets have already proven their capability of characterising the tribological behaviour of the surfaces in the macro world. It is expected that these parameters are a basis for a functional characterisation of the topography in micro-forming applications as well.