Conventional Grinding Process Research Articles

Characterization of material removal in ultrasonically assisted grinding of SiCp/Al with high volume fraction

Due to the significant difference between the reinforcement grains and matrix phase, the machining of SiC particle-reinforced aluminum composites (SiCp/Al) is difficult and costly, especially for SiCp/Al with volume fraction higher than 50%. Ultrasonically assisted grinding (UAG), which has unique advantages in the machining of both ductile and brittle materials, is a promising solution of the machining of SiCp/Al. This study conducts both UAG and conventional grinding (CG) process on SiCp/Al with an electroplated diamond wheel. The study explores material removal mechanisms involved in UAG in comparison to that in the CG. It also investigates grinding forces, surface integrity, subsurface damage, and wheel wear. The study finds that material removal in grinding of SiCp/Al is dominated by SiC particle fracture that is induced in the grinding process. The ground workpiece is smeared with an aluminum layer, making it difficult to evaluate surface integrity. Compared with CG, UAG of SiCp/Al results in similar surface integrity in terms of surface roughness and subsurface damage, but a much lower grinding force (35–50% lower).

Effects of dressed wheel topography on patterned surface textures and grinding force

This paper presents a series of analytical and experimental investigations into the patterning effect of a grinding wheel-dressed surface on workpiece surface texture and grinding forces. An analytical model is built for the profile of the dressing tip and utilized to describe the kinematics of the dressing process on the grinding wheel surface. The model also reflects the ground workpiece surface texture. The model describes patterned surface textures according to ridge width, ridge length, texture angle, and ridge function parameters. Comparison against modeled and measured values strongly suggests that conventional dressing and grinding processes can be pre-determined via the proposed model to generate a patterned workpiece surface. The measured grinding forces are investigated as they relate to tangential and normal components at a series of dressing and grinding parameters; these two components increase dramatically as dressing overlap ratio increases, nearly regardless of dressing depth. Under a given workpiece velocity, the measured forces are much greater at overlap ratio of 6 than at ratios of 1 or 3. There is an average difference of only 5.8% for all grinding forces. Conversely, the measured tangential and normal grinding forces increase markedly as workpiece velocity increases at a specific dressing overlap ratio. Dressing overlap ratio of 1~3 is recommended for generating patterned texture surfaces in a conventional grinding process. Grinding force ratio can serve to monitor the patterned grinding process (error within 12.9%) under the conditions discussed here.

Surface and subsurface damage in Zerodur® glass ceramic during ultrasonic assisted grinding

The material removal process in grinding and lapping of brittle materials leads to different kinds of defects such as microcracks, fractures, scratches, and deformed areas which can exist under the finished surface in the layer called subsurface damage (SSD). In this work, experiments were carried out to study the impact of the ultrasonic assistance during grinding machining of the Zerodur® glass ceramic. The effect of the process parameters on the surface formation and the subsurface damage was investigated. The SSD depth was measured using the dimple method in combination with the use of the optical microscopy for the morphological study of the SSD, while the surface roughness was measured using the mechanical profilometer. The experimental results showed that the SSD depth generated within the ultrasonic assisted grinding is about 35 % less than that of the conventional grinding process. On the other hand, the surface quality obtained by the conventional grinding was superior to that of ultrasonic assisted grinding. To validate the experimental results, the SSD values measured by the dimple method are compared with the values obtained in both the experiments and other theoretical previous studies. It was concluded that machining of the Zerodur® glass ceramic with ultrasonic assistance is more suitable than that with the conventional grinding. This study provides valuable insights into the material removal mechanism and the dependence of surface and subsurface integrities on grinding mode with/without ultrasonic assistance.

Study on strengthened layer of workpiece in prestress dry grinding

The prestress dry grinding which combines with prestress grinding and surface strengthening is an innovative approach to substitute conventional grinding process. The residual stress and the thickness of strengthened layer have an important effect on surface performance of workpiece. In order to analyze the effect mechanisms of prestress on residual stress and thickness of strengthened layer, experiment and simulation are carried on for 45 steel. The result of prestress dry grinding experiment shows that the grains in the strengthened layer are refined with increase of prestress. The thickness of strengthened layer tends to decrease first and then increase with increase of prestress. The simulation model of temperature field is created. The effect of temperature field on the thickness of strengthened layer and different grinding parameters especially the prestress on temperature field are analyzed. Then, the relationship between prestress and residual stress on different directions are analyzed. The variation curve of residual stress shows that tensile residual stress can transform to compressive residual stress on the surface of workpiece by controlling the prestress. Besides, compressive residual stress increase first and then decrease with the increase of depth.

Subsurface damage depth and distribution in rotary ultrasonic machining and conventional grinding of glass BK7

The morphology, depth, and distribution of subsurface damage (SSD) on glass BK7 specimens produced in rotary ultrasonic machining (RUM) and conventional grinding (CG) processes with three diamond tools were investigated. The ultrasonic effects on the SSD characteristics were also explored with respect to the material removal mechanisms and the specific kinematics principles of the abrasives. The experimental results demonstrated that the increased cutting velocity would improve the subsurface qualities, while the increased feed speed and cutting depth would deteriorate SSD depth of the RUM/CG specimens. Superimposition with the ultrasonic vibration increased the maximum cutting depth of each abrasive by an amplitude and also resulted in the cyclical variation in abrasive trajectories, hereby worsening the SSD depth of the final RUM surfaces. A large amount of incipient cracks which pulverized the material were just concentrated on the top RUM surface, thus increasing the subsurface crack distributions. With the abrasive moving ahead, these incipient cracks would propagate forward, hereby hindering the nucleation of the fresh cracks, and decreasing the subsurface crack obscurations of the RUM surface at a local level. Some rogue cracks were occasionally found to be located in deeper subsurface of the RUM/CG specimens, and the mutual interactions between the adjacent abrasive indentations would promote the propagations of the subsurface cracks, which gave rise to the nucleation of these rogue cracks.

High Performance Grinding

The efficient processing of innovative materials, the further development of grinding tools and machine concepts as well as an increasing economic and environmental pressure are current challenges in grinding technology. High Performance Grinding processes offer a huge potential to overcome these challenges and increase productivity. They are characterized by a significant increase in material removal rate and component quality plus a reduced need of resources. In this paper, possibilities are presented and discussed for extending the process boundaries of conventional grinding processes in order to create High Performance Grinding processes. Based on current research, potentials to increase productivity of conventional grinding processes are described. In addition to process-specific optimization of the machine and the grinding tools, opportunities are pointed out for the numerical prediction of the process boundaries as well as methods for mathematical interpretation and analysis of grinding wheel structures and topographies. Moreover, opportunities are presented for future increases in productivity by combining High Performance Grinding processes with other manufacturing technologies.

다물체 동역학 해석을 이용한 커버글라스 Edge 연마용 Abrasive Film Polishing 시스템 개발

In recently, the demand of cover-glass is increased because smart phone, tablet pc, and electrical device has become widely used. The display of mobile device is enlarged, so it is necessary to have a high strength against the external force such as contact or falling. In fabrication process of cover-glass, a grinding process is very important process to obtain high strength of glass. Conventional grinding process using a grinding wheel is caused such as a scratch, chipping, notch, and micro-crack on a surface. In this paper, polishing system using a abrasive film was developed for a grinding of mobile cover-glass. To evaluate structural stability of the designed system, finite element model of the polishing system is generated, and multi-body dynamic analysis of abrasive film polishing machine is proposed. As a result of the analysis, stress and displacement analysis of abrasive film polishing system are performed, and using laser displacement sensor, structural stability of abrasive film polishing system is confirmed by measuring displacement.

Force Controlled Grinding of Ceramic Materials

Brittle materials like ceramics or glass can be machined by cutting with negative rake angles and by abrasive machining processes. Especially grinding allows for low surface roughness and high shape accuracy. Conventional path-controlled grinding processes may damage functional surfaces if brittle fracture occurs and may thus lead to lateral, radial and axial cracks. High grinding forces can be a reason for brittle fracture when grinding ceramic materials. A solution for this effect may be the application of force controlled grinding processes. In this paper adapted control algorithms were implemented for force controlled grinding and verified in grinding experiments. As an example, cylindrical grooves were ground with an injection moulded spherical grinding tool in alumina and zirconia ceramics. After grinding surface roughness, shape accuracy and process forces are analysed and discussed.

A model for prediction of subsurface damage in rotary ultrasonic face milling of optical K9 glass

Subsurface damage (SSD) induced by the rotary ultrasonic face machining (RUFM) considerably influences the technological application of the optical components. However, currently, there is no method to detect the depth of SSD in real time. For the purpose of precise and nondestructive evaluation of the SSD depth generated in RUFM processes, a predictive model was developed by applying the indentation fracture mechanics of brittle material. This was the first time that the correlation between the measured cutting force and SSD depth had been established. It was found that the SSD depth was directly proportional to the exponent of the measured cutting force (namely d SSD = γF c χ ). Using this model, the depth of SSD could be predicted rapidly and precisely in the RUFM of optical glass even in real time using the measuring cutting force. Subsequently, this method was verified by conducting RUFM tests on K9 glass specimens with Sauer Ultrasonic 50. Meanwhile, the cutting force and SSD depth were compared experimentally between RUFM and conventional grinding (CG) process, indicating that RUFM is a beneficial manufacturing method for optical glass with reduced cutting force and SSD depth.

Wear Behavior of Grain Cutting Edge in Ultrasonic Assisted Grinding Using Mini-Size Wheel

This paper deals with the wear behavior of the mini-size diamond wheel used in Ultrasonic Assisted Grinding (UAG). The aim is to understand the wheel wear behavior. Sequential changes of the surface topography of the mini-size wheel, such as the number and shape of grains of the cutting edge, during the on-surface UAG process were observed and evaluated quantitatively using a Scanning Electron Microscope with four electron probes (3D-SEM). The obtained results show that a good wheel surface is maintained during the UAG process compared with the Conventional Grinding (CG) process. In particular, a number of sharp grain cutting edges are larger in the UAG process than those of the CG process. Additionally, these results are closely related to the stability of grinding forces and the reduction of the finished workpiece surface.

MLCC 적층용 진공척의 자기연마와 ELID연삭을 이용한 미세버 제거 기술

This study has focused on the deburring technology of a vacuum plate for MLCC lamination using electrolytic in-process dressing (ELID) grinding, and the magnetic-assisted polishing (MAP) process. The surface of the vacuum plate has many micro-holes for vacuum suction. They are easily blocked by the burrs created in the surface-flattening process, such as the conventional grinding process. In this study, the MAP process, the ELID grinding process, and an ultrasonic vibration table are examined to remove the micro-burrs that lead to the blockage of the holes. In the results of the experiments, the MAP process and ELID grinding technology showed significant improvements of surface roughness and deburring performance.

Hard Turning of AISI D2 Steel by Polycrystalline Cubic Boron Nitride (PCBN)

The machining of hard turning is performed on hardened steel in the range of 45 to 68 Rockwell hardness using a variety of tool materials such as Polycrystalline cubic boron nitride (PCBN) , Polycrystalline diamond (PCD) and Cubic boron nitride (CBN). It is an alternative to conventional grinding process is a flexible and effective machining process for hardened metals and hence broadly used in various applications such as dies, moulds, tools, gears, cams, shafts, axles, bearings and forgings. Although the process is performed within small depth of cut and feed rates, estimates to reduce machining time as high as 60 % in hard turning. This paper discusses the importance of hard turning of AISI D2 steel. In this study, Experimental investigations are carried out on conventional lathe using prefixed the cutting conditions. The responses studied in the investigation are cutting forces (Fa, Ft and Fz). The cutting parameters considered for the investigation are cutting speed, feed and depth of cut. The influence of machining parameters on response is studied and presented in detail.

Influence of the cutting edge radius on surface integrity in hard turning of roller bearing inner rings

Hard turning is used as a finishing process to machine hardened parts with very high accuracies. During the last decades it asserted as an alternative to conventional grinding processes due to higher flexibility and productivity. Furthermore, hard turning also increases positive effects on the surface integrity compared to grinding processes. Process parameters such as cutting speed, feed and cutting edge geometry influence the effect on subsurface area as well as the surface roughness. Many researchers have been analyzing these effects during the last years. However, they all cover one or two aspects of the surface integrity. Due to the fact that all researchers applied different experimental conditions it is almost impossible to compare the effects of hard turning on the surface integrity. The presented paper covers the effects of cutting speed, feed and cutting edge radius on the main factors of surface integrity residual stress, roughness, microstructure and hardness of roller bearings in a summarizing overview to identify the optimal parameter values for machining roller bearings with an increased endurance. Hard turning tests are conducted and the effects on residual stresses, surface roughness, hardness and white layers are analyzed. This overall view on surface integrity of roller bearings is necessary to improve the endurance of bearings due to a specific surface integrity design. The interactions between the surface integrity and the expected resulting endurance are discussed at the end of this article.

Experimental Investigation of Electro-Discharge Face Grinding of Metal Matrix Composite (Al/SiC)

Surface quality and process productivity are the challenging performance measures in grinding of difficult-tomachine materials these are measured in terms of Surface Roughness (Ra) and Material Removal Rate (MRR). Metal Matrix composites are the materials having aggregate properties of constituents like higher strength to weight ratio, toughness, stiffness and hardness. Because of having these superior properties MMCs are highly desirable in applications ranging from commercial aircraft to sports equipment but still facing challenges in machining of MMCs. Machining of MMCs by conventional machining process results poor surface finishand frequent tool failure due to presence of ceramic particles. Grinding of MMCs by conventional grinding process produces poor surface finish and low material removal rate due to frequent wheel loading. Electro-Discharge Face Grinding (EDFG) process is used on work specimen of the material Al/SiC MMC to investigate the effects of Wheel speed, Gap current, Pulse on-time and Pulse off-time on Surface Roughness (Ra) and Material Removal Rate (MRR). Surface Roughness (Ra) increases with increase in Wheel RPM, Gap current and Pulse on-time. MRR also increases with increase in Gap current and Pulse on-time while it is almost constant on increasing Wheel RPM. SEM micrograph of machined surface is taken for analysis of surface texture.

Energy aspects and workpiece surface characteristics in ultrasonic-assisted cylindrical grinding of alumina–zirconia ceramics

Ultrasonic assisted grinding is a novel method for improving the grinding process of difficult-to-cut materials. In the present research a novel setup has been designed and manufactured for utilizing ultrasonic vibrations in external cylindrical grinding. The designed ultrasonic head vibrates a rotating workpiece in axial direction. An alumina–zirconia ceramic (AZ90) has been selected as the workpiece material. Energy aspects and workpiece surface characteristics of ultrasonic assisted cylindrical grinding (UACG) and conventional cylindrical grinding (CG) processes have been analytically modeled and corresponding grinding experiments have been performed. The combined kinematics of the cylindrical plunge grinding process and axial ultrasonic vibrations provide a unique surface treatment conditions, which leads to reduced peak heights and increased valley depths of the surface topography. The main axial vibration mode provides the overlap of the adjacent cutting traces and consequently smoothens the surface topography in cylindrical plunge grinding. It has been analytically and experimentally shown that, applying ultrasonic vibrations, grinding energy can be reduced up to more than 35% depending on the process parameters. The surface characteristics of the ground workpieces have been investigated in terms of four surface roughness parameters and the roundness error.

Optimizing the Dry Grinding Process on the Basis of Bond Materials

In order to decrease the negative environmental impacts of the cutting fluids (for example, disposal of grinding sludge) and also to reduce the manufacturing costs and the required space for the machines the dry grinding can be a conceivable alternative for the conventional grinding processes. Nevertheless, dry grinding has not been widely introduced into industry because of the high temperature generated in the grinding zone and difficulties of heat transfer without coolants. Selection of the proper grinding wheel bonds, grit sizes and concentration has significant effect on the grinding performance and the generated heat in the contact zone. This paper addresses the effects of the grinding wheel bond and the concentration on the dry grinding process efficiency through comparing the results of the carried out experiments with three resin bonded cBN-cup-wheels, each consisting different bond components. For this purpose, surface roughness and thermal damages during dry and wet grinding (utilizing grinding oil) by three different resin bonds were measured. The results show almost identical surface roughness values for dry and wet grinding. Furthermore, using the resin-kryolith-graphite bonded wheel leads to a reduction in thermal damages on the workpiece. Through different experiments, it was shown that the different bonds, used in this study, have significant influence on the chip loading of the grinding wheels. This is contributed to the different chip formation mechanisms and induced grinding temperatures when grinding by the different wheel bonds.

Magnetorheological finishing: a perfect solution to nanofinishing requirements

Finishing of optics for different applications is the most important as well as difficult step to meet the specification of optics. Conventional grinding or other polishing processes are not able to reduce surface roughness beyond a certain limit due to high forces acting on the workpiece, embedded abrasive particles, limited control over process, etc. Magnetorheological finishing (MRF) process provides a new, efficient, and innovative way to finish optical materials as well many metals to their desired level of accuracy. This paper provides an overview of MRF process for different applications, important process parameters, requirement of magnetorheological fluid with respect to workpiece material, and some areas that need to be explored for extending the application of MRF process.

Compression molding of glass freeform optics using diamond machined silicon mold

Abstract In precision glass molding of freeform optics, mold material selection and mold fabrication are two major challenges. In this letter, we propose a method to fabricate silicon molds for micro freeform optics using ultraprecision diamond machining. Specifically, two microlens arrays and a kinoform lens molds were created on a 5.0 mm thick silicon wafer using ultraprecision diamond machining. The fabricated silicon molds were coated with a graphene-like carbon coating using chemical vapor deposition to prevent glass to silicon adhesion. To demonstrate the functionality of the single point diamond machined silicon molds, glass micro components were fabricated using precision compression molding. Compared with conventional grinding process required for tungsten carbide, the method investigated in this research provides a more flexible, faster and affordable alternative to fabricate molds for complex precision glass freeform optics.

C13 サファイアウエハのスパイラル超音波援用研削における砥石摩耗特性 : ビトリファイドダイヤモンド砥石の作用面トポグラフィー(OS7 研削・砥粒加工(1))

This paper deals with the wear characteristics of grinding wheel on spiral ultrasonic assisted grinding of sapphire wafer. The spiral ultrasonic assisted grinding (SUAG) using vitrified diamond grinding wheel have been carried out and sequential changes of the wheel working surface topography have been observed during grinding process using a scanning electron microscope with four electron probes (3D-SEM). The obtain results show that the wheel wear in SUAG process is reduced compared with conventional grinding (CG) process. Especially, these results are closely related that a maintaining of good wheel surface in SUAG is demonstrated based on quantitative evaluation using number of grain cutting edges.

Elimination of surface spiral pattern on brake discs

Nowadays, brake disc manufacturers are seeking new finishing techniques to offer economical solutions to their customers and so become more competitive. The elimination of the surface spiral pattern after turning operation is a challenge to avoid braking problems at the early life of the component. This paper presents a practical low-cost solution to finishing this kind of component. Concretely, a detailed study of the brushing process as an alternative solution to the conventional grinding process is performed. The limited literature regarding this topic implies the necessity of a full study of the process prior to any industrial application. The influence of process variables on the final surface was analyzed in this work. In addition, the tool wear and tool life behavior, the influence of the abrasive type used and the originating forces during the process were taking into account. Once the process was established, various prototypes were finished in order to check the feasibility of the process and to pass the required quality control. Results show that brushing is a feasible and economical alternative for brake disc finishing. The surface quality obtained was shown to be equal or better than grinding, with reduced costs and manufacturing time.