Polishing Path Research Articles

Development of a Polishing Jig for Machining Centres

A polishing jig was designed and manufactured to enable polishing of metal surfaces on CNC machining centres, on which these surfaces are normally finish-machined first. The jig accommodates ring-type tools rotated by a high speed spindle, rendering the machining centre’s own spindle redundant. Passive control of the polishing force is materialized through the machining centre’s Z axis displacement acting on the jig’s springs. Jig design is explained laying special emphasis on calculations pertaining to the springs employed. Functionality of the jig was tested with trochoidal polishing paths and typical results are presented in terms of peak-to-valley surface roughness attained, verifying that a uniform ‘mirror range’ finish is achievable.

A practical approach for automated polishing system of free-form surface path generation based on industrial arm robot

In manufacturing environment where a robot arm is programmed to follow a specified path such as in polishing, the geometric coordinate transformation of an automated polishing system frames is needed for polishing workpiece surface. As the presence of kinematic singularities can extremely affect the robot’s performance, singularity regions in the task space for robot are clearly identified using determinant of the robot’s Jacobian matrix. Based on the free-form surface polishing requirements, programing an industrial robot with Teach Pendant manually is skill dependent and time consuming. Therefore, a scheme of an automatic polishing system is proposed, which includes a 6DOF arm robot. An automatic planning and programming system based on data from a CAD system is described to create robot paths. The robot program which contains the polishing path is generated in certain order using RoboGuide software in virtual environment. A Human Machine Interface has been used to control the entire polishing system online. Finally, the generated path is successfully applied in robotic polishing system. The experimental results prove that the proposed method is effective and feasible. The outcomes of this work contribute to enhancing the use of arm robot for polish free-form workpiece surfaces.

Five-axis abrasive belt flap wheel polishing method for leading and trailing edges of aero-engine blade

Surface quality and profile accuracy of the leading and trailing edges (LTE) have a direct influence on the performance and lifetime of an aero-engine. The artificial buffing polishing for LTE has the drawbacks of heavy workload, poor consistency, experience-dependence, and so on. To solve these problems, the five-axis abrasive belt flap wheel (ABFW) polishing method for LTE of an aero-engine blade is proposed in this manuscript. Firstly, the flexible deformation law of ABFW is studied based on the Hertz elastic contact theory. Then, the control system of the contact force is established to keep the stability of the material removal rate in ABFW polishing. Furthermore, the key technologies of LTE polishing path planning with ABFW such as path direction determining, row space determining, and tool posture calculating are studied. After that, the polishing path of LTE with ABFW is generated. Finally, the verification experiments are carried out. The results suggest that the ABFW flexible deformation law is reliable, and the proposed polishing method for LTE is feasible and effective.

Study on the inner surface finishing of irregular spatial elbow pipe by the centerline reconstruction

Due to the compact space structure of aerospace engine, the structure of the inner spatial elbow pipe of the engine exhibits irregular geometric characteristics, which makes the inner surface of the curved pipe difficult to polish, especially the bending place’s surface quality cannot be ensured. It is centerline reconstruction that can be a good solution to this problem, which measures the outer surface contour line and generates the spatial point cloud of the elbow pipe and thus, the irregular geometric centerline of the spatial elbow pipe is rebuilt. Furthermore, the polishing path of the spatial elbow pipe is calculated and optimized. At the same time, using of magnetic abrasive finishing (MAF) has well in flexible machining characteristics, the outer space of the elbow pipe is loaded with rotating magnetic field, so as to get form a “magnetic abrasive brush” inside the tube, achieve the purpose of bending the inner surface finishing. Under the same processing time, compared with the pure manual measuring magnetic grain processing, the reconstruction of the center line of the magnetic processing can make the space bend surface roughness lowered to 0.11 μm, which improves the processing quality of the tube surface and the processing efficiency.

Polishing path planning for physically uniform overlap of polishing ribbons on freeform surface

This paper presents a new polishing path planning method for physically uniform overlap of polishing ribbons instead of traditional geometrically uniform coverage of polishing path on freeform surfaces, which attempts to achieve the even material removal on the polished surface in consideration of contact mechanics in polishing process. The polishing ribbon is defined as the ribbon with varying width generated by continuous contact areas along the polishing path. The boundary extraction algorithm (BEA) is proposed to determine the specific polishing ribbon boundary which is next to the to-be-planned path. The path extraction algorithm (PEA) is given to predict the location of the adjacent polishing path. Those BEA and PEA make the overlap of polishing ribbons along two adjacent polishing paths physically uniform. Proposed polishing path planning is implemented for a typical freeform surface and the polishing paths with physically uniform overlap of polishing ribbons between two adjacent paths are obtained, while the under-polishing and over-polishing phenomena occur when the traditional scanning path is applied. In addition, the comparative experiments and analysis are also conducted and the experimental results further verify the feasibility of the proposed polishing path to promote even material removal.

Magnetic field-assisted finishing of a mold insert with curved microstructures for injection molding of microfluidic chips

Microfluidics has a wide application ranging from ink-jet printing to lab-on-chip in biomedical research and diagnostics chemical processing. For many disposable applications, injection molding process is usually adopted for mass production of microfluidic chips. Therefore, fabricating high quality mold inserts with precise geometry and smooth surface becomes a challenge. Recently, precision machining technologies such as cutting and milling have been increasingly employed for fabricating microstructures in the size of tens to hundreds of micrometers considering the advantages in design flexibility, productivity and economical cost. However, due to the limitation of the achievable surface quality attributed to defects such as burrs and tool marks, a post-polishing process which can maintain the shape of micro features while improve surface finish becomes an indispensable step. In this paper, magnetic field-assisted finishing (MFAF) method was firstly adopted to finish a mold insert which has curved microstructures on the surface for injection molding of microfluidic chips. The working principle of the configuration was illustrated, and the experimental setup and conditions were detailed. Abrasive flow simulation was conducted to analyze material removal around microstructures and the results were verified by experiments. When the abrasive flow direction was perpendicular to the side of microstructures, abrasives became easy to access to the corners of the microstructures and less material was removed. According to the results of material removal analysis, the polishing path was planned by dividing the mold insert surface into 5 zones to ensure abrasive flow direction perpendicular to the side of microstructures. The results show that the heights of the microstructures were maintained although the edges were rounded after polishing while the surface roughness was reduced to approximately 0.11µm Ra, achieving a mirror finish. The surface quality before and after polishing regarding microhardness, residual stress, friction and wear characteristics were compared.

Paths of Improving the Technological Process of Manufacture of GTE Turbine Blades

The article provides an analysis of the problems at manufacture of blades of the turbine of gas-turbine engines and power stations is provided in article, and also paths of perfecting of technological process of manufacture of blades are offered. The analysis of the main systems of basing of blades in the course of machining and the control methods of the processed blades existing at the enterprises with the indication of merits and demerits is carried out. In work criteria in the form of the mathematical models of a spatial distribution of an allowance considering the uniform distribution of an allowance on a feather profile are developed. The considered methods allow to reduce percent of release of marriage and to reduce labor input when polishing path part of a feather of blades of the turbine.

Modeling and control of robotic automatic polishing for curved surfaces

This paper presents the solutions adopted for a robotic automatic polishing platform for finishing machining on curved surfaces to reduce cost and improve quality on such manual finishing operations. The polishing platform was built and the polishing process was studied. In order to accomplish the control of polishing force, the relationship among the robot, sensor, polishing tool (cutter) and the force impacted on the polished parts is established. On this basis, the model of removal distribution is built for each polishing path, a suitable path spacing algorithm further obtained by the same scallop height, and an effective planning algorithm of tool location is proposed. An active and passive compliance control polishing model is set up by explicit force control based on position and the methods of tilting polishing tool with elastic sponge disk. Finally, validation experiments are performed on mold parts of NAK80 steel. The experiments display that the robot achieves a relatively constant force control effect by the active and passive compliance force control. The results show that the proposed automatic polishing platform has the good ability of effectiveness and feasibility for polishing on curved surfaces, and is able of achieving a mirror effect surface and keep a good global uniformity.

Corrective polishing of freeform optical surfaces in an off-axis three-mirror imaging system

The application of freeform surface in the off-axis three-mirror imaging system can greatly improve its optical performance. However, it is difficult for fabrication of freeform optical surface to high precision by traditional machining technology. This paper focuses on the corrective polishing of the primary mirror and tertiary mirror, which are fabricated on one monolithic substrate and described by NURBS-based freeform surfaces, in an off-axis three-mirror imaging system. The integrated polishing process system is proposed for polishing the two mirrors on the 4-axis CNC polishing machine by use of spherical polishing tool. The tool influence function (TIF) module, polishing path generation and dwell time calculation module included in the integrated polishing process system are described respectively. The material removal on the measurement line of part surface is predicted to validate the dwell time calculation algorithm. The polishing experiments of the primary mirror and tertiary mirror are performed to verify the proposed integrated polishing process system.

Research on unbounded abrasive polishing process with assisted ultrasonic vibration of workpiece

Ultrasonic-assisted machining was an effective method to improve the material removal quality especially to difficult-to-cut metal materials. The ultrasonic vibration was usually superimposed on the machining tool but seldom on the workpiece, although the ultrasonic vibration of workpiece could improve the processability of material more effectively. In this paper, a rectangle hexahedron ultrasonic sonotrode with optimized slots was developed as a platform to realize the assisted ultrasonic vibration of workpiece and the ultrasonic-assisted polishing process of austenitic stainless steel was also studied. The unbounded abrasive was selected as polishing medium, and the path compensation strategy of soft polishing tool was carried out for getting uniform polishing force. The orthogonal experiments were designed to study the optimization of ultrasonic polishing parameters and the relation between different types of ultrasonic polishing path and polishing quality. The results appear that the horizontal ultrasonic vibration of workpiece can reduce polishing force and improve polished surface roughness, which can also reinforce the proportion of plastic shear effect in the material removal process. The ultrasonic polishing path keeping consistent with workpiece vibration direction can get more uniform polishing force and better surface roughness. And the 45° oblique crossing ultrasonic path can get the maximum average polishing force reduction by 75.2 %.

A micro-model of the material removal depth for the polishing process

In this paper, a prediction model of the material removal depth for the polishing process is developed from the microscopic point of view. Based on the statistics analysis, and by the use of the elastic contact theory and the plastic contact theory, the relationship between the pressure and the depth of indentation is obtained. Moreover, the calculation equation for the linear removal intensity, which is the material removal depth per unit contact length along the polishing path, is presented. Finally, by integrating the linear removal intensity, the micro-model of the material removal depth for the polishing process is developed. Analyzed from the perspective of the abrasive grains, the model takes the grit designation and the structural number as the two basic variables for abrasive grains characteristics, and it is assumed that the shape of an abrasive grain is conic with spherical tip and the distribution of its protrusion heights is taken to be Gaussian distribution, which fully takes into account the impact of the abrasive grains characteristics on the depth of removal. In the model, different stages of the polishing process are decomposed in detail, and the reality that the plastic deformation is accompanied by the presence of elastic deformation is taken into consideration, which makes the model more realistic. Experimental results are compared with the prediction results to verify the theoretical model. The model can be used as the theoretical foundation for the selection of abrasive grains and the process parameters.

Modelling of the Polished Profile in Computer-Controlled Polishing by a Sub-Aperture Pad

High-quality part surfaces with high surface finish and form accuracy are increasingly in demand in the mold/die and optics industries. The computer-controlled polishing (CCP) is commonly used as the final procedure to improve the surface quality. This paper presents a theoretical and experimental study on the polished profile of CCP with sub-aperture pad. A material removal model is proposed based on the evaluation of the amount of material removed from the surface along a direction orthogonal to the tool path. The model assumes that the material removal rate follows the Peterson equation. The distribution of the sliding velocity at the contact region is presented. On the basis above, the approaches to calculate the polished profiles are developed for the sub-aperture pad polishing along a straight path and a curved path. The model is validated by a series of designed polishing experiments, which reveals that polishing normal force, angular spindle velocity, feed rate and polishing path all have effects on the polished profile. The result of experiments demonstrates the capability of the model-based simulation in predicting the polished profile.

Investigation into material removal influenced by edge effect in polishing

Edge effect is unavoidable in polishing process when the polishing pad passes by the workpiece edge, which influences the entire form accuracy of free-form surfaces of optical components in computer-controlled polishing, or even reduces their effective aperture. This article focuses on a theoretical and experimental investigation into the material removal influenced by edge effect for polishing along a certain path. The contact pressure distribution models for polishing the workpiece edge are summarized and modified into four representative models: linear model, skin model, linear skin model and divided skin model, which are adopted to calculate the theoretical material removal profiles orthogonal to the straight or curved polishing path, in this article. So, the material removal models are built in the process of polishing along tool path instead of polishing on a single point. And experiments are carried out to choose the most suitable contact pressure distribution model according to the comparison of experimental profiles and the different theoretical profiles. Experimental results reveal the influences of edge effect on material removal and a modified parameter is introduced into the theoretical material removal profile for the curved path to coincide with the experimental profile better. In addition, some qualitative analyses about how to reduce the edge effect are also given in this article.

An adaptive uniform toolpath generation method for the automatic polishing of complex surfaces with adjustable density

During automatic polishing process, path trajectory is an important factor affecting the quality of machining. In this paper, a path generation algorithm based on adaptive Hilbert curves which can cover the curved surface evenly is proposed. The generated path not only makes the coverage density adjustable but also is able to pass through the points on the curved surface in more directions which is helpful to get a finished part without stripes. Using the proposed algorithm, the uniform distributed grid points are obtained in the parameter domain and then these node points with adjustable density can be calculated accordingly. Thus, according to the construction rule of adaptive Hilbert curve, the objective toolpaths are subsequently obtained. After that, by means of a mapping strategy, the path trajectory can be obtained on the physical space. To verify the proposed algorithm, uniform polishing paths with variable density are planned on two typical curved surfaces. The result of the machining experiment shows that the curved mirror-like surface can be achieved, and it also indicates the applicability of the proposed method.

Material removal profile for large mould polishing with coated abrasives

This paper analytically develops a type of model for predicting material removal depth in large mould polishing with coated abrasives. This model based on the statistical theory, and the abrasive material surface contact mechanics is established. The material removal depth is calculated by integrating the linear removal intensity or the removal depth per unit time along the polishing path. The material removal depth profiles of the circular abrasive tool and the annular abrasive tool are presented when polishing paths are a straight line and a curve, respectively. The effects of process parameters on the material removal depth are simulated and analyzed, such as polishing pressure, feed rate, tool speed, and internal radius, when the polishing path is a straight line. The workpiece surfaces after milling were polished by using annular abrasive tool moving along a straight line in the experiment. This model is evaluated by comparing the theoretical material removal depth with those experimental results available. It is concluded that the experiment results are approximately consistent with the model predictions.

Path planning of mechanical polishing process for freeform surface with a small polishing tool

Products with freeform surface are widely applied in industries, and the surface quality plays an important role in order to fulfill the targeted functions. As polishing path of small polishing tool affects the polishing removal function considerably, it is highly necessary to study the polishing path of freeform surface for obtaining good polishing efficiency and well-proportioned surface quality. By combining the Preston polishing removal function, the material removal model of small polishing tool under the control of constant polishing force and pressure is established. Based on this model, the material removal functions of scan line, Archimedean spiral, and Hilbert fractal polishing path are derived. The simulation results show that the Hilbert fractal polishing path has the best comprehensive performance. By using the projection relation of differential geometry, the optimal path generation algorithm of the Bezier surface based on Hilbert fractal polishing path is established. The polishing experiments are conducted on a self-developed polishing machine which is based on a parallel manipulator. The experimental results demonstrate that the surface roughness is improved from level 9 to level 11.

Development and Polishing Process of a Mobile Robot Finishing Large Mold Surface

□ A novel self-determination polishing robot finishing large mold free-form surface is developed, and the finishing process method is researched. Contrary to traditional approaches, our premise is that a large mold surface can be polished by using a small robot. This robot system is mainly composed of a polishing robot part, a computer system and a visual positioning system. A type of robot with four uniform distribution wheels was designed, which has two driving wheels and two driven wheels. Active compliant control of the polishing tool was provided by a pneumatic servo system, and a new special compliant abrasive tool was proposed on the basis of robot characteristics. The process planning steps consisted of subdividing the free-form surface, choosing an abrasive tool, planning the polishing path and optimizing machining parameters. Based on the orthogonal experiment and the grey relational analysis method, the optimal parameter combination was obtained for polishing force, tool speed and feed rate. Aiming to polishing times, the surface roughness method and polishing efficiency method were studied in detail. The polishing experiments were carried out in the robot using process parameters obtained by the efficiency method. These research results provided significant theory foundation and experimental data for a mobile robot planning polishing to realize intelligible process parameter selection.

Planetary motion combined with two-dimensional vibration-assisted magnetic abrasive finishing

This study develops a new surface polishing approach by combining planetary motion (PM) with two-dimensional vibration-assisted magnetic abrasive finishing (PM-2DVAMAF). Planetary motion involves both rotation and revolution, thus generating radial acceleration, which strengthens the normal force exerted on the workpiece surface, and in turn enhances the cutting power of the abrasives and their polishing performance. Assisted by two-dimensional vibration, PM results in uniform, intersecting, and closely packed polishing paths, which contribute to better surface quality within a shorter processing time. This study also uses the Taguchi experimental design method to obtain the optimal combination of PM-2DVAMAF parameters for surface roughness improvement. The optimal combination obtained includes working gap, 1 mm; amplitude of vibration, 0.1 mm; particle size of steel grit, 0.125 mm; weight of SiC, 3 g; weight of steel particles, 0.5 g; weight of machining fluid, 5 g; frequency of vibration along the X- and Y-directions, 16.67 Hz; and rotational speed of magnet, 500 rpm. Experimental results reveal that 12.5-min PM-2DVAMAF under optimal combination of parameters can reduce surface roughness of a stainless steel SUS304 workpiece from 0.14 to 0.032 μm, an improvement rate of 77.1 %. PM-2DVAMAF can indeed improve surface quality with a short machining time and less abrasives required, both of which contribute to cost reduction and more environmentally friendly machining method in industry.

Evaluation of Metallic Mold Surfaces Polished by an Industrial Robot with Stick Whetstones

Our ultimate goal is to develop an automatic polishing system that uses an industrial robot equipped with whetstones. The robot mimics the movements skilled workers make as they polish surfaces manually. This paper, the first step in the development of our system, presents experimental results to prove that our system completely removes the marks, which is the most time-consuming and crucial process for human workers, from the flat surfaces of metallic molds produced through the Electrical Discharge Machining (EDM) process. We build a polishing system that consists of a small 6-DOF industrial robot for material handling. Attached to its wrist is a six-axis force-torque sensor and it employs a whetstone holding mechanism. Before the robot system begins its polishing work, the normal force to be applied to the flat surface can be adjusted to a target value by altering the height of the hand. We adopt two polishing paths for the whetstone, reciprocating and zigzag. We then conduct experiments using the two paths, visually inspect the surface, and measure the surface roughness and shape. Based on the experimental results, we confirm that the system has completely removed the EDM mark layer. Although we find that the zigzag path leaves striped patterns on the polished surface, we are not able to determine their cause. Finally, we test three combinations of the two paths under different conditions to find the most suitable combination.

Edge effect of optical surfacing process with different data extension algorithms

This study presents a strategy which integrates extra polishing path (EPP) and error map extension to weaken the edge effect in the ultraprecise optical surfacing process. Different data extension algorithms were presented and analyzed. The neighbor-hood average can be selected as the frequently-used method, as it has not bad precision and time-saving performance for most surface forms through the simulation results and practical experiment. The final error map was obtained, its peak-to-valley (PV) was 0.273λ and root mean square (RMS) was 0.028λ (λ = 632.8 nm). The edge effect was weakened and suppressed well through the experiment.