Single-sided Lapping Research Articles

Study on the wear characteristics of a 3D printed tool in flat lapping of Al2O3 ceramic materials

Widespread and popular use of ceramic products in various industry sectors necessitates the search for methods of their efficient processing. Lapping technology, which enables obtaining high dimensional and shape accuracy and high surface flatness, is one of the basic methods of finishing hard and brittle technical ceramics with a porous structure. This study analyzed the characteristics and wear value of an SLS-printed abrasive tool intended for single-sided lapping of Al2O3 technical ceramics. As earlier research demonstrated, introduction of a 3D printed lapping plate by selective laser sintering (SLS), leads to a significant development in the field of precision machining technology. This method showed not only efficient machining performance on oxide technical materials, but was also characterized by relatively low abrasive wear. Straightness errors were evaluated with the use of a least-squares method (LSQ) and minimum zone method based on control line rotation scheme (CLRS). The proposed model proved the experimental results by identifying a similar location of a higher contact density on the lapping tool, where this location is expected to be the one for bigger wear. Surface topography of the lapping tool depends on the tool wear intensity and as a consequence on its shape error. An SLS-printed lapping plate, by obtaining good technological effects, revealed its potential ability in machining hard and brittle technical ceramics.

Optimizing the flatness of 4H-silicon carbide wafers by tuning the sequence of lapping

In this letter, we optimize the flatness of 4H silicon carbide (4H-SiC) wafers by tuning the sequence of single-sided lapping, enlightened by the different mechanical properties of the Si face and C face of 4H-SiC. After wire sawing, the coarse lapping and fine lapping are carried out to rapidly remove the surface damage and optimize the flatness of 4H-SiC wafers. From the point of view of controlling the values of the bow and warp of 4H-SiC wafers, the coarse-lapping sequence of the C-face lapping followed by Si-face lapping is beneficial, while the preferred fine-lapping sequence is Si-face lapping followed by C-face lapping. Nanoindentation tests indicate that the C face has higher hardness and lower fracture toughness than the Si face. This gives rise to thicker surface damage at the C face after the wire sawing. After removing the same amount of wire-sawing induced surface damage, the thickness of residual surface damage of the C face is higher than that of the Si face after the coarse lapping. The fine lapping basically removes all the surface damage and creates the near-perfect C face and Si face. The higher amount of surface damage of the C face after the coarse lapping and the higher fracture toughness of the near-perfect Si face after the fine lapping can tolerate more plastic deformations, which gives rise to the superior flatness of the C-face-followed-by-Si-face coarse lapped and the Si-face-followed-by-C-face fine lapped 4H-SiC wafers, respectively.

Dynamics and control of vibratory finishing machine with translational motion of lapping-polishing plates

The lapping and polishing operations are of the most important ones considering the finishing treatment of machine parts. These operations can be performed by numerous methods, among which the vibration-driven ones are of the most widespread. The present paper is focused on studying the dynamic behavior of the vibratory finishing machine providing the single-sided lapping and polishing of flat surfaces of cylindrical and prismatic parts. The major scientific novelty of this research consists in an improved control technique of generating the translational oscillations of the lapping (polishing) plates by means of implementing the double-magnet excitation system. In order to investigate the machine’s double-mass vibratory system dynamics, the corresponding mathematical model is developed using the Lagrange-d’Alembert principle. The numerical modeling is carried out with the help of the Mathematica software and presents the time dependencies of the lapping (polishing) plates kinematic parameters. The simplified experimental prototype of the vibratory lapping machine is developed and tested under different operational conditions. The proposed design ideas and obtained theoretical and experimental results can be effectively used by the designers of lapping and polishing equipment, as well as by the technologists implementing new techniques of finishing treatment.

A novel measurement method for the torque acting on the upper platen in a three-way double-sided lapping/polishing machine

In double-sided lapping and polishing processes, the friction coefficients between the workpiece and platens or pads are important parameters for understanding or improving the lapping and polishing processes. However, the friction coefficients have not been investigated in detail owing to insufficient measurement methods for the torques acting on the upper and lower platens, which are necessary to evaluate the friction coefficients. Thus, a novel measurement method for the torque acting on the upper platen in a three-way double-sided machine was proposed in this study. In the method, the torque is measured based on the forces acting on the holders supporting the upper platen rotation. The torques were measured with the method in double-sided lapping experiments, and they were confirmed to agree with the theoretical torque variation. Furthermore, the friction coefficient between the workpiece and upper pad identified with the proposed method was also verified by comparing with the friction coefficient measured in the single-sided lapping experiment. In addition, the estimation method of the lower platen torque based on the motor torque was investigated by utilizing the proposed method, and we found the lower platen torque was estimated accurately by taking a sufficient warm-up time or by modeling the torque loss in transmission path. Therefore, accurate measurement of the torques acting on the upper and lower platens, which is an effective tool for understanding or improving the process, was realized.

Modelling the operation of vibratory machine for single-sided lapping of flat surfaces

Lapping is one of the finishing technological operations. It can be performed using various manual and automated techniques. One of the most efficient lapping techniques is carried out with the help of vibratory equipment. Among a great variety of vibratory lapping, polishing and grinding machines, the ones of the overhead (suspended) type with double-mass oscillatory systems are not thoroughly investigated. Therefore, the novelty of the present study consists in development and investigation of the double-mass vibratory machine for single-sided lapping of flat surfaces. It consists of the upper lap and the lower carrier connected to one another by six springs radially directed and uniformly distributed along the circle of the lap. The parts, whose upper end faces are to be treated, are fixed in the lower carrier. The lapping process is performed due to the oscillatory motion of the lap relative to the carrier. The differential equations describing the motion of the machine’s oscillatory system are derived. The analytical dependencies for calculating the stiffness coefficients of the springs ensuring the energy-efficient resonance operation mode are deduced. Based on the results of experimental studies of friction forces exerted by each moving surface on the other one during the lapping process, the numerical modelling and computer simulation of the lapping machine operation are carried out. The obtained results can be used while investigating the technological parameters (surface roughness, flatness, accuracy etc.) of the lapping process carried out with the help of vibratory equipment.

Tool Wear Prediction in Single-Sided Lapping Process

Single-sided lapping is one of the most effective planarization technologies. The process has relatively complex kinematics and it is determined by a number of inputs parameters. It has been noted that prediction of the tool wear during the process is critical for product quality control. To determine the profile wear of the lapping plate, a computer model which simulates abrasive grains trajectories was developed in MATLAB. Moreover, a data-driven technique was investigated to indicate the relationship between the tool wear uniformity and lapping parameters such as the position of conditioning rings and rotational speed of the lapping plate and conditioning rings.

Influence of pellet shape and size on the pattern performance of textured fixed-abrasive pads in single-sided lapping

ABSTRACTLapping with fixed-abrasive pads is regarded as a potentially efficient machining technology due to the precise controllability of abrasive trajectory. For trajectories can be changed by pellet patterns of textured fixed-abrasive pads (T-FAPs), it is essential to studythe influence of pellet shape and size on the pattern performance of T-FAPs. In this paper, different pellet shapes and sizes were studied based on a T-FAP design algorithm in a single-sided lapping, and the pattern performance of T-FAPs was evaluated by the non-uniformity of trajectory (NUT). Based on the results, it is found that pellet shapes and sizes have an obvious influence on the performance of T-FAPs. When circular pellet shape with its size of 4, 8, or 14 mm, NUT value can be lower than 0.08. Therefore, much lower NUT values can be obtained when matching selection of pellet shape and size in pad pattern design.

Experimental investigation on the ultrasonically assisted single-sided lapping of monocrystalline SiC substrate

This paper studied the effect and optimization of ultrasonically assisted single-sided lapping for monocrystalline SiC wafer using grey relational analysis method. 27 experiments based on the Taguchi method of orthogonal arrays were performed to determine the best factor level condition. Besides, the comparative experiments using three lapping plates (cast iron, copper, and aluminum) were also performed under ultrasonic lapping and non-ultrasonic lapping, respectively. Material removal rate (MRR) and surface roughness (Ra, Rmax) were selected as the output indexes. The degree of influence that the controllable process factors exert on the indexes was studied by investigating the correlation between them. By analyzing the signal-to-noise ratio and grey relational grade, the most influential process factor is the interaction item of normal pressure and rotating speed. Ultrasonically assisted vibration has a positive correlation with the MRR, while simultaneously increases the surface roughness, but the higher ultrasonic power is beneficial to inhibit the increase of surface roughness. The lower hardness of lapping plate can obtain the better surface at the cost of decreasing MRR, but much too low hardness may destroy the machined surface.

Development an identification method of friction coefficient between wafer and carrier in double-sided lapping

Behavior of a wafer is one of the most significant concerns in double-sided lapping since it depends on the distribution of material removal rate. Though the wafer behavior is affected by the friction coefficient between the wafer and a carrier, the coefficient has hardly been discussed. In this study, an identification method of the friction coefficient based on variation of wafer rotational speed with wafer position in the carrier during single-sided lapping operation on double-sided lapping machine is developed for accurate estimation of the wafer behavior. The friction coefficient is identified by comparing experimental and theoretical variation of the rotational speed of the wafer. The experiment is carried out under the condition where lubrication condition between the wafer and the carrier is similar to that in double-sided lapping, and the variation is measured by image processing of the wafer behavior. The theoretical variation is calculated based on the equilibrium of force and moment applied to the wafer. It is confirmed that the theoretical rotational speed of the wafer under a friction coefficient condition agrees well with the measured one in terms of not only the highest and the lowest speed but also the variation with the wafer position in the carrier. Thus, it is assumed that the practical coefficient is identified by utilizing this method. In addition, the behavior of the wafer in double-sided lapping is calculated using the identified friction coefficient, and it is suggested that precise consideration of the contact status between the wafer and the carrier, i.e., non-slip, slip, and non-contact is essential for practical estimation.

Non-conventional approach in single-sided lapping process: kinematic analysis and parameters optimization

The lapping process is strongly affected by a number of input parameters. One of the fundamental mechanical processes in lapping is the abrasive effect of particles. In order to examine the influence of the kinematic parameters on the lapping uniformity of unconventional single-sided machine, numerical simulations of particles sliding trajectories are performed. Changing the kinematic parameters, e.g., rotational velocities or position of the conditioning rings together with the workpieces can be used for correcting the profile of an active surface of the lap. This paper provides a basic guide to the kinematic parameter settings of single-sided lapping process. Furthermore, an unconventional single-sided lapping system, where a conditioning ring performs additional motion during the machining, is described. Simulation results show that the rotational speed ratio of the conditioning ring to the lapping plate k1 and the period ratio of the reciprocating motion to the lapping plate rotary motion k2 represent the relationships among the three basic motions of unconventional lapping systems and are major factors affecting trajectory distribution. Material removal rate and trajectory density parameter are proposed to optimize the kinematic parameters for better uniformity of lapping plate wear. The preferred kinematic parameter values for single-sided lapping system with reciprocating motions and the assumed size of the machine are k1 = 0, 78 and k2 = 2. The general results were validated on a specially designed test stand.

Self-dressing effect using a fixed abrasive platen for single-sided lapping of sapphire substrate

Single-sided lapping is crucial in sapphire wafering processes for improving flatness and achieving the target wafer thickness using loose abrasives. In single-sided lapping process, the Material removal rate (MRR) is a key factor for reducing process time and cost. However, the MRR is limited when using loose abrasives because abrasives mostly act by rolling and sliding. Many researchers have studied fixed abrasives to increase the MRR, but the MRR decreases with time. To solve this problem, the self-dressing effect was studied with various pressures, velocities, cutting fluids and wafers. The MRR decreased due to the wear of abrasives, and the pressure and velocity have little effect on the self-dressing. Lapping experiments were done using cutting fluid with a lapped wafer and sawed wafer. The MRR, plate roughness and thickness were measured to study the wear of the abrasive and the self-dressing effect. The cutting fluid delayed the wear of the abrasives and thus improved the decrease in MRR, but it had little effect on the self-dressing effect, like in the case when water was used. When using cutting fluid and a sawed wafer, the MRR was high and did not decrease. A concentrated load on the plate caused by shape error and saw marks on the sawed wafer could produce the self-dressing effect. We verified that a sawed wafer could produce the self-dressing effect on even a worn plate.

Optymalizacja parametrów kinematycznych w docieraniu powierzchni płaskich

In this paper the influence of selected kinematic parameters on the geometrical results of the single-sided lapping process was presented. The purpose of parameters optimization is to improve the flatness and quality of the machined surfaces. The basic optimization criterion is the uniformity of tool wear. The simulation and experimental results were presented and compared.

Badania i analiza dokładności powierzchni docieraka docierarki jednotarczowej z ruchem posuwowym pierścienia prowadzącego

Badania i analiza dokładności powierzchni docieraka docierarki jednotarczowej z ruchem posuwowym pierścienia prowadzącego

Effect of platen shape on evolution of total thickness variation in single-sided lapping of sapphire wafer

Total thickness variation (TTV) of sapphire wafer is one of the most important geometrical parameters as it is related with the quality of LED. In the wafer manufacturing, single-sided lapping is the final process to correct wafer TTV, but there are few understanding about the mechanism of TTV generation. The authors focused on the effect of platen shape on TTV generation. Because changes of platen shape make changes of pressure distribution on wafer witch is resulted in different material removal rate. For analyzing wafer TTV evolution by platen shape, wafer was projected onto the platen. And then, the distance between platen surface and wafer which related with material removal rate was analyzed. From the analysis on the platen shape, TTV could be calculated. Experiments were conducted with different platen shapes to verify theoretically predicted TTV. Experimental conditions were chosen to exclude effects of the sliding distance on TTV as setting the rotational speed of wafer and platen under the same. Experimental results showed that TTV of lapped wafers were well matched with analyzed TTV considering thermal deformation of platen during lapping process. This novel platen shape model can be helpful to understand mechanisms of TTV generation and to improve TTV.

Analysis of Abrasive Particle Trajectories during Single-Sided Lapping Process with Driven Conditioning Ring

In this paper new kinematics systems were studied for a single lapping process. In order to ensure the constant profile wear of the tool a standard kinematic system can be changed. Lapping is carried out by applying loose abrasive grains between two surfaces and causes a relative motion between them. The result is a finish of multi-directional lay. During process, the mechanism of surface formation are decisively affected by a pressure force, a process time and a motion type of grains. It has been proven, that providing the additional movements of the conditioning ring affects the profile wear of the lapping plate. First of all, the kinematics equations of the lapping process have been developed and the process has been simulated. A type of the abrasive particle trajectories in standard single-disk lapping depends on rotational speed ratio of a tool and a conditioning ring. In addition, two new kinematic systems were presented: with radial and secant movement of the conditioning ring. Finally, comparison and analysis of abrasive trajectories were carried out.

New Kinematic Systems in Single-Sided Lapping and their Influence on Lap Wear

Previous studies on one-sided lapping allow to state that not only parameters of lapping elements (i.e. properties of workpiece, abrasive grains and lapping plate) impact on a lapping efficiency. Influential are also kinematics and dynamics of the process. It is crucial to control an average velocity of lapping (v), a distribution of tangential acceleration (at), a nominal pressure (p), a lapping time (t) and disposal of workpiece in separator.Based on kinematics equations and the tribological models, the dimensionless distribution of the material removal volume and the trajectories of abrasive grains cutting on the lap were numerically simulated. Obtained information about excessive wear on lapping plate was the starting point to work out non-standard, single-plate lapping systems.In this paper ideas of unconventional lapping systems were presented. After numerous simulations and careful analysis it was observed, that the most desirable system is radial lapping system. It was point out that other systems are not very different from the standard kinematic system. Generated trajectories of an abrasive grain were almost identical. What is more, effects of kinematical parameters on the trajectories, velocities and accelerations observed in radial lapping system are shown.

Effects of mixed abrasive grits in slurries on free abrasive machining (FAM) processes

Effects of mixed abrasive grits in slurries on free abrasive machining (FAM) processes are studied using a single-sided lapping machine. Impacts of mixing abrasives on various parameters such as amount of material removed, material removal rate, surface roughness, particle size distribution and relative angular velocity are studied. The material removed is monitored as a function of time. The experimental results suggest that (i) mixing abrasive grits can increase the amount of material removed, (ii) smaller abrasives can directly or indirectly affect the material removal process, (iii) slurries undergo severe grain size transition during lapping, and (iv) the surface roughness did not change significantly under different loading. The results of this study may have profound implication on the FAM processes that practitioners use today because the mixed abrasive grits increase material removal rate and reduce the grain size transition, while rendering similar surface roughness.

Model for Simulation and Optimization of Liquid Crystal Displays Cell Thinning Process

An abrasive single-sided lapping approach is applied to the thinning of assembled cells of liquid crystal displays (LCDs). The approach reduces the thickness and weight of the panels, thereby enhancing the aesthetics and ease of use of portable display devices. In this study, a new mathematical model has been developed to describe the mechanism applied to this advanced technology and verified by experiments. The model can help find the optimum parameters for the thinning process and the suitable dimensions of a single-sided lapping machine for the LCD cell thinning process.

Environmental Cell Thinning of Advanced Liquid Crystal Displays

A structured abrasive is applied to a thinly assembled liquid crystal display (LCD) cell in single-sided lapping. This effectively reduces the overall thickness and weight of the panels, thereby enhancing the aesthetics and ease of use of portable display devices. The technology enables an environmentally friendly means of mechanical thinning. Moreover, compared with conventional slurry lapping, it achieves a better surface roughness (0.24 µm), a higher cut rate (11.6–13.4 µm/min) and a lower operating pressure (45 g/cm2) for different specimens. Furthermore, it can be used to process 3.5G (610×720 mm2) glass substrates on a 1200-mm-diameter tool.

砥粒加工による超薄型水晶の加工技術

This paper presents an investigation into processing technology of ultra-thin quartz with abrasives. Quartz plate is processed industrially with double-sided lapping equipment. The thinner thickness of quartz, the larger obtained frequency. However, it is impossible to make quartz plate with a thickness of less than 30μm due to the distinct limit in the thickness of the carrier. In this experiment, single-sided lapping equipment was used for lapping and polishing to create ultra-thin quartz. It was noted that protection of the quartz edge and the flatness of the lapping plate and polishing pad are important. Therefore, an iron washer was used to protect the quartz edge and the lapping plate and polishing pad were made flat by facing. During the experiment, this flatness was maintained by placing a conditioning ring with a weight of 3kgf on the lapping plate. By maintaining the flatness of the lapping plate, a high reproduction was achieved. During polishing, the rotating speed was varied and a nonwoven fabric was used with a slurry containing Si02 with 0.5μm in diameter and CeO2 with 0.7μm in diameter. As a result, a quartz sample with a thickness of around 10μm was produced.