In Memoriam

J. Manuf. Sci. Eng. 2017;139(12):120101-120101-1. doi:10.1115/1.4038213.
Commentary by Dr. Valentin Fuster

Guest Editorial

J. Manuf. Sci. Eng. 2017;139(12):120301-120301-1. doi:10.1115/1.4038169.

This special issue of the ASME Journal of Manufacturing Science and Engineering commemorates the scientific contributions by the late Professor Stephen Malkin, and his legacy that spans the whole spectrum of grinding science and technology. Professor Malkin's contributions and reminiscences from his many friends were dedicated by Professor Yoram Koren and colleagues at the ASME International Manufacturing Science and Engineering Conference held in 2014, less than a year after Professor Malkin's untimely death. Professor Koren has kindly edited and updated the memoriam dedicated to Professor Malkin, and it is included in this special issue alongside the many research papers submitted by so many of his colleagues.

Commentary by Dr. Valentin Fuster

Research Papers

J. Manuf. Sci. Eng. 2017;139(12):121001-121001-6. doi:10.1115/1.4036638.

Many scientists contributed to the analysis of temperatures in grinding leading up to present-day understanding. This paper draws together important developments from various papers and aims to identify an improved general approach to thermal analysis with wide applicability including for conventional fine grinding, creep feed grinding, and high efficiency deep grinding. Complexity of the basic derivation is avoided since the resulting temperature model is based purely on heat balance. Challenges for future thermal analysis are indicated. Emphasis is placed on fundamental principles for improved accuracy and for convenience of application in process control.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(12):121002-121002-6. doi:10.1115/1.4036995.

In the literature, cemented carbides are described as hard and brittle materials. The material removal mechanisms in grinding of brittle materials, such as cemented carbides, significantly differ from the material removal mechanisms of ductile materials [13]. The material removal mechanisms in grinding of ductile materials are comparatively well investigated in comparison to the material removal mechanisms in grinding of brittle materials. In the existing literature, it has been shown that the material removal mechanisms in grinding of cemented carbides can be ductile or brittle. The present material removal mechanisms are dependent on the thermomechanical stress collective, which acts on the surface zone of the cemented carbides. In this paper, the material removal mechanisms in grinding of cemented carbides are discussed fundamentally. In order to analyze the occurring material removal mechanisms in grinding of cemented carbides, single grain cutting tests were carried out. Subsequent to the tests, the surface zone of the cemented carbide has been analyzed in detail. Therefore, scanning electron micrographs have been made to analyze the workpiece surface to identify the transition from predominantly ductile to predominantly brittle material behavior. Furthermore, focused ion beam (FIB) preparation, which has minimum invasive influence on the subsurface, was applied in order to get an insight into the surface zone. The FIB lamellae have been analyzed with transmission electron microscopy (TEM) to get a better understanding of the impact of material removal mechanisms on the surface zone. The drawn conclusions contribute to an improved process understanding in grinding of cemented carbides.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(12):121003-121003-7. doi:10.1115/1.4038149.

The application of cutting fluid in grinding operations is crucial to control temperature levels and prevent thermal damage to the workpiece. Water-based (emulsions and solutions) coolants are used in grinding operations owing to their excellent cooling capability and relatively lower cost compared to neat oils. However, the cutting fluid efficiency is not only dependent on its type, but also on other parameters including its concentration and flow rate. In this context, this work aims to analyze the influence of the coolant concentration and flow rate on the grinding process. Two different workpiece materials for the production of plastic injection moulds were machined: VP80 and VPATLAS steel grades. Six grinding conditions (combinations of depth of cut values of 5, 15, and 25 μm with coolant concentration of 3% and 8%, respectively) were employed in the former, while two grinding conditions were used for the latter. The output parameter used to assess the influence of coolant concentration and flow rate on the grinding operation focused on the integrity of the workpiece materials (surface roughness and microhardness below the ground surface). The results showed that the surface integrity of VP80 after grinding was more sensitive to depth of cut than to cutting fluid concentration. Furthermore, the highest coolant concentration outperformed the lowest one when grinding under more severe conditions. With regard VPATLAS steel, no influence of the coolant flow rate on surface roughness was observed.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(12):121004-121004-5. doi:10.1115/1.4038055.

The article presents the results of calculating the blunting area of abrasive grains of grinding wheels, determined in accordance with the previously developed model. The mathematic model of the size of the blunting area of an abrasive grain considers the main mechanisms of its wear—mechanical and physicochemical. These mechanisms are taken into account in the model. For the first time, the kinetic theory of strength was used for determining the mechanical wear of abrasive grain. The mass transfer theory was used to study the physicochemical wear: coefficients of chemical affinity with the abrasive material are experimentally defined for the assortment of workpiece materials. The developed mathematic model is a multiple-factor one and this will allow to predict the size of wear of the abrasive wheel for different technological conditions. Also, the article presents the experimental method for determining the blunting area of abrasive grains of grinding wheels, which allows making a direct measurement of wear parameters of grinding wheels. The main parameter of grinding wheel wear is the length of the blunting area of the grain, which was measured out in the direction of the cutting speed vector. The grinding wheels of different graininess were studied—F60 and F46. The grinding wheel working surface was studied by numerical photos and microscope. The results of these experiments have confirmed the adequacy of the design model.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(12):121005-121005-7. doi:10.1115/1.4037939.

The paper offers a simulation model of the grinding force with account for the current condition of the grinding wheel's working surface—the value of the abrasive grain blunting area. The model of blunting area takes into account various wear mechanisms for abrasive grains: the mechanical wear is realized on the provisions of the kinetic theory of the strength of a solid subjected to cyclic loads, and the physicochemical wear is based on the intensity of interaction between the abrasive and the treated material at grinding temperatures. The offered model of the grinding force takes into account the unsteady stochastic nature of the interaction between abrasive grains of the grinding wheel and the working surface and the intensity of workpiece material deformation resistance. The model is multifactorial and complex and can be realized by supercomputer modeling. The numerical implementation of the model was performed with application of supercomputer devices engaging parallel calculations. The performed experiments on measurement of the grinding force during circular grinding have shown a 10% convergence with the calculated values. The developed grinding force model can be used as a forecast model to determine the operational functionality of grinding wheel when used in varying technological conditions.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(12):121006-121006-25. doi:10.1115/1.4037991.

This paper provides a comprehensive review on the dressing techniques of diamond grinding wheels. The common techniques with different tools were discussed in detail, which included the bonded SiC and diamond abrasive tools, loose abrasives, soft-elastic abrasive belts, and profiled diamond wheels. Meanwhile, laser dressing, electrical discharge dressing (EDD), and electrolytic in-process dressing (ELID) were also addressed. Some critical problems in the above dressing techniques were then analyzed and summarized for further investigation.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(12):121007-121007-10. doi:10.1115/1.4037992.

This paper presents some new research findings in the investigation of single-grit grinding in terms of surface creation. The investigation demonstrated that rubbing–plowing–cutting hypothesis of grinding material removal mechanism is valid in both experiments and simulations. A finite element model (FEM) was developed to simulate the material deformation during the grit interacts with the workpiece. It was found that the cutting mechanism is the more effective in the first half of the scratch where the grit penetrates the workpiece. The plowing is a prominent mechanism in the second half of the scratch where the grit is climbing up along the scratch path and uplifting the material at the front and the sides of it. This observation is very important to provide a greater insight into the difference between up-cut and down-cut grinding material removal mechanisms. Multipasses scratch simulations were performed to demonstrate the influence of plowing on the ground surface formation. Moreover, by analyzing the effects of grinding conditions, the shape of cutting edges, and friction in grinding zone on the grinding surface formation, some useful relations between grinding performance and controllable parameters have been identified. It has demonstrated that plowing has significant influences on ground surface formation and concluded that the influence of grit shape, friction, and grinding kinetic condition should be considered together for the plowing behavior control, which could provide a good guidance for the improvement of grinding efficiency.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(12):121008-121008-7. doi:10.1115/1.4038123.

The production process grinding deals with finishing of hardened workpieces and is one of the last stages of the value-added production chain. Up to this process step, considerable costs and energy have been spent on the workpieces. In order to avoid production rejects, significant safety reserves are calculated according to the present state of the art. The authors introduce two approaches to minimize the safety margin, thus optimizing the process’ economic efficiency. Both control concepts use the feed rate override of the machining operation as regulating variable to eliminate thermal damage of the edge zone. The first control concept is developed to avoid thermal damage in cylindrical plunge grinding by controlling the cutting forces. Therefore, the industrial standard Open Platform Communications Unified Architecture (OPC-UA) is used for the communication between a proportional–integral–derivative (PID) controller and the SINUMERIK grinding machine tool control system. For noncircular workpieces, grinding conditions change over the circumference. Therefore, thermal damage cannot be ruled out at any time during the grinding process. The authors introduce a second novel control approach, which uses a micromagnetic measure that correlates with thermal damage as the main control variable. Hence, the cutting ability of the grinding wheel and thermal damage to the workpiece edge zone is quantified in the process. The result is a control concept for grinding of noncircular workpieces, which opens up fields for major efficiency enhancement. With these two approaches, grinding processes are raised on higher economic level, independently of circular and noncircular workpiece geometries.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(12):121009-121009-11. doi:10.1115/1.4037239.

Grinding is an important abrasive machining process at the end of many process chains. Understanding energy transformation in grinding is not only important to improve energy efficiency but also crucial for understanding the chip formation process itself. Grinding energy can be studied at the macroscopic or microscopic levels, wherein the entire grinding tool is considered or the phenomena at the single cutting edges are studied. This paper explores existing energy modeling approaches in grinding with particular emphasis on physical models. Models on energy transformation during the ductile grit–workpiece engagement for three regimes —being friction, plowing, and shearing —are explained. In addition to the critical depth of cut (DOC) when chip formation starts, a critical depth when plowing begins is introduced to divide between the different regimes. Selected models for each regime are combined to an integrated grinding energy model that allows researchers to investigate forces and energy during grit engagement.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(12):121010-121010-6. doi:10.1115/1.4037969.

Specific material removal rate (MRR) q was calculated for five-axis grinding in a virtual machining simulation environment (VMSE). The axis-symmetric tool rotational profile was arc-length parameterized. The twisted grazing curve due to the concurrent translation and rotation in every move was modeled through an exact velocity field and areal MRR density q, positive in the front of the grazing curve on the tool surface. Variation of q and equivalent chip thickness h within the instantaneous engagement contour were deduced from q. Illustrative results with a five-axis impeller blade finishing simulation are shown. The results were benchmarked against an average q calculated from the instantaneous MRR from the VMSE. As a function of time, maximum chip thickness hmax within the extents of contact along the tool profile in every move showed more isolated peaks than corresponding qmax. Maximum cumulative material removed per unit length Qmax along the tool profile from all the moves was calculated to predict axial location of maximum risk of cutter degradation.  Qmax and hmax are useful metrics for tool path diagnosis and tool wear analysis.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(12):121011-121011-5. doi:10.1115/1.4038109.

This study investigated the sawing of A-plane and C-plane sapphires using the reciprocating diamond wire saw. The influences of process parameters and sapphire crystal structure on sawing force were experimentally researched. The experimental results indicated that, in sapphire sawing process, the sapphire crystal structure, the wire speed, and the feed rate had effects on the tangential sawing forces, and the tangential forces had good linear relationships with the material removal rates (MRRs). The specific sawing energies in the stable stage were clearly smaller than in the unstable stage.

Topics: Wire , Sawing , Diamonds , Sapphire
Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(12):121012-121012-10. doi:10.1115/1.4037889.

This work considered the finishing precision grinding process at a small ferrous metal roll manufacturer. A design of experiments (DOE) methodology was used to evaluate the process and ascertain whether the degree of confidence gained from the process offers an acceptable level of risk in the conformance of end products to customer requirements. A thorough identification of the process variables and measurement considerations relevant to the process was carried out, before assessing and categorizing these variables using the grinding cycle as a “black box” system. Coolant temperature, environment temperature, work speed, and traverse speed were all considered against measured size change, surface finish, and circular run-out in a full factorial experimental design. The experiments were carried out on a manual cylindrical grinding machine retrofitted with digital encoders on the driven axes, with a chrome-plated roll 300 mm in diameter as the workpiece. Experiments were conducted over a period of 11 months during which the machine used was part of ongoing production environment. The results show that control of temperature, both of the coolant and of the environment in which the machine was operated, was the most important of the variables studied, but the skill of the machine operator remains dominant in the process overall.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(12):121013-121013-14. doi:10.1115/1.4038056.

With the rising trend of miniaturization in modern industries, micro manufacturing processes have made a significant position in the manufacturing domain. Demands of high precision along with super finish of the final machined product have started rising. Grinding, being largely considered as a finishing operation, has large potential to cater to such requirements of micro manufacturing. However, stochastic nature of the grinding wheel topography results in a high degree of variation in the output responses especially in the case of microgrinding. With an aim to obtain a good and predictable surface finish in brittle materials, the current study aims at developing a surface generation model for wall grinding of hard and brittle materials using a microgrinding tool. Tool topographical features such as grit protrusion height, intergrit spacing, and grit distribution on the tool tip of a microgrinding pin have been calculated from the known mesh size of the grits used during tool manufacturing. Kinematic analysis of surface grinding has been extended to the case of wall grinding and each grit trajectory has been predicted. The kinematic analysis has been done by taking into consideration the effect of tool topographical features and the process parameters on the ground surface topography. Detailed analysis of the interaction of the grit trajectories is done to predict the final surface profile. The predicted surface roughness has been validated with the experimental results to provide an insight to the surface quality that can be produced for a given tool topography.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(12):121014-121014-6. doi:10.1115/1.4037183.

This paper reports an experimental study on grinding of chromium carbide coatings using electroplated diamond wheels. The work was motivated by machining carbide coatings in gas turbine engine applications. The objective is to explore the process conditions and parameters satisfying the ground surface quality requirements. Surface grinding experiments were conducted with water-based grinding fluid on chromium carbide coated on flat surfaces of aluminum blocks for rough grinding at a fixed wheel speed vs = 30 m/s, and finish grinding at vs = 30, 60 m/s. The effects of depth of cut and workspeed on grinding power, forces, and surface roughness were investigated for each of the wheel speeds. Material removal rate Q = 20 mm3/s for rough grinding at a grinding width b = 101.6 mm was achieved. It was found that the maximum material removal rate achievable in rough grinding was restricted by chatters, which was mainly due to the large grinding width. The specific energy ranged from 27 to 59 J/mm3 under the tested conditions. Surface roughness Ra = 3.5–3.8 μm were obtained for rough grinding, while Ra = 0.6–1.5 μm were achieved for finish grinding. Surface roughness was not sensitive to grinding parameters under the tested conditions, but was strongly dependent on the diamond grain sizes. Imposing axial wheel oscillations to the grinding motions reduced surface roughness by about 60% under the tested condition. It was proved that it is feasible to grind the chromium carbide coating with electroplated diamond wheels.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(12):121015-121015-11. doi:10.1115/1.4037241.

In the grinding process, high temperature in grinding area is generated by the frictional resistance between workpiece and abrasive grains on the grinding wheel cylindrical surface. Grinding fluid application is an optimal option to reduce the thermal effect and crack on the workpiece ground surface. In this paper, a grinding process heat transfer model with various grinding fluid application is introduced based on computational fluid dynamics (CFD) methodology. The effect of specific heat, viscosity, and surface tension of grinding fluid are taken into account. In the model, the grinding contact area is considered as a heating resource. Most of the heat energy is conducted into the workpiece. The rest of the energy is taken away by the grinding wheel, grinding fluid, and chips. How many percentage of the generated heat is conducted into the workpiece is a key issue, namely, the energy partition ratio ε. An energy partition equation is introduced in this paper with the cooling effect of different grinding fluid. Generated heat energy based on the calculation from energy partition equation is applied on the grinding contact area in the heat transfer model.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(12):121016-121016-17. doi:10.1115/1.4038138.

Abrasive finishing is one among several surface generation processes, of which grinding process is a subset. In a typical grinding process, six different interactions can be identified at the grinding zone, resulting in surface generation. Among these six interactions, one is governed by the principles of machining, while the others are governed by the principles of tribology. A systematic analysis of these interactions helps to understand the role of both tribological mechanisms and machining interactions in a typical grinding process. Analysis and study of such microscopic interactions and their time-dependent variations also provide an ability to develop a common scientific framework that can be applied for a wide variety of grinding processes and applications. Such framework and associated system thinking enables engineers to be capable of addressing the needs to support a wide variety of industries and end user needs at a time of hyper specialization and narrow boundaries that constrain the professionals.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(12):121017-121017-8. doi:10.1115/1.4037890.

This paper presents a semi-automated grinding system for the postprocessing of metalcastings. Grinding is an important procedure in the “cleaning room” of a foundry, where the removal of gate contacts, parting line flash, surface defects, and weld-repaired areas is performed, and almost always manually. While the grinding of repetitive locations on medium to high production castings can be automated using robotics or otherwise, it is not as practical for larger castings (e.g., > 200 kg) that are typically produced in smaller production volumes. Furthermore, automation is even more challenging in that the locations of the required grinding are not a constant depending on the unique conditions and anomalies of each pouring of a component. The proposed approach is intended for a simple x−y−z positioner (gantry) device with a feedback controlled grinding head that enables automated path planning. The process begins with touch probing of the surfaces that contain the anomaly requiring grinding, and then the system automatically handles the path planning and force control to remove the anomaly. A layer-based algorithm for path planning employs a search-and-destroy technique where the surrounding geometry is interpolated across the grind-requiring surface patch. In this manner, each unique condition of the casting surface after initial torch or saw cutting can be handled cost effectively without the need for human shaping and the egregious ergonomic problems associated. Implementation of the proposed grinding control is prototyped at a lab scale to demonstrate the feasibility and versatility of this strategy. The average error for the prototype was on the order of 0.007 in (0.2 mm) with a flatness of the ground surface within 0.035 in (0.9 mm), which is within the cleaning room grinding requirements, as per ISO and ASTM dimensional and surface tolerance requirements. A significant contribution of the work is the layer-based algorithm that allows an effective automation of the process planning for grinding, avoiding robot programming or numerical control code generation altogether. This is a key to addressing the largely unknown and unpredictable conditions of, for example, the riser contact surface removal area on a metalcasting.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(12):121018-121018-8. doi:10.1115/1.4037041.

Grinding is an abrasive process mostly used in finishing operations to provide low roughness and narrow limits of form and dimensioning to the workpiece. Due to the large amount of heat generated by friction between the abrasive and the workpiece in this process, the use of large volumes of coolant is encouraged to avoid thermal damage, such as burning and hardness variation caused by subsurface damage. On the other hand, environmental impacts and human health problems caused by coolants have been a key issue toward sustainable manufacturing, mainly because of the chemistry behind them. Thus, is important to seek for strategies to reduce the volume of fluids and their risks as well as guarantee grinding efficiency. One machining strategy is the minimum quantity of lubricant (MQL) technique, which is well consolidated over the past 25 years and one that uses low volumes of fluid mixed with compressed air flow, as well as provides less waste. However, it has generally been reported that sludge formed during grinding is forced into the wheel pores, consequently clogging its pores, thereby reducing the wheel cutting potential and its performance. A possible solution for this problem is to use an auxiliary compressed air system to clean the grinding wheel surface during machining, since the MQL conventional system is not able to clean it. In this context, this work evaluated the performance of the MQL technique with an auxiliary cleaning of the grinding wheel cutting surface in relation to the conventional cooling techniques (flood cooling) during a cylindrical plunge grinding of N2711 steel. N2711 steel is widely employed in manufacturing of molds for plastic injection processes and is one of steels more susceptible to grinding burn. The following output parameters were used to assess the performance: surface roughness, roundness, microhardness, grinding power, and grinding wheel wear. The results showed that the MQL technique, in addition to the environmental and economic advantages achieved, provided superior workpiece quality, and lower power consumed compared to the flood technique. The MQL technique proved to be an alternative method compared to the conventional technique under the conditions investigated. Also, the Malkin’s model was used to predict the grinding ratio (G-ratio) based on the experimental data obtained in this work. After regression analysis, the model predicted the G-ratio from the specific material removal rate and the cutting speed with a satisfactory accuracy of approximately 92%.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(12):121019-121019-10. doi:10.1115/1.4037940.

Advanced ceramic materials like sintered and presintered zirconia are frequently used in biomedical applications, where minimum quantity lubrication (MQL) assisted grinding is required to achieve a good surface finish instead of conventional flood coolant. However, insufficient cooling and wheel clogging are the major problems that exist in the MQL grinding process, which depends upon the type of work piece material and the grinding wheel being used. The present study is to determine the performance of the grinding wheels on presintered zirconia under MQL conditions in terms of grinding forces, specific energy, surface integrity, and wheel wear. Experiments are conducted with two different types of grinding wheels as silicon carbide (SiC) and diamond grinding wheels under the same condition. The results indicated that the diamond wheel provided a better surface finish and reduced tangential force under MQL condition, compared to the conventional SIC wheel. This was due to the reduction of wheel loading in the diamond grinding wheel. The specific energy of diamond grinding wheel was reduced with higher material removal rate compared to the conventional SiC wheel. The ground surfaces generated by the diamond grinding wheel showed fine grinding marks with better surface finish. The percentage of G-ratio calculated for the diamond wheel was higher than the SiC wheel by 77%. This was due to the sliding of the grains and less wheel loading in the diamond wheel. The cost difference between the corresponding wheels was discussed to improve the productivity of the grinding process.

Commentary by Dr. Valentin Fuster
J. Manuf. Sci. Eng. 2017;139(12):121020-121020-8. doi:10.1115/1.4038027.

Abrasive flow machining (AFM) technology is getting more and more interest by the industry and research community particularly in the context of increasing demands for postprocessing of the additively manufactured and complex components. It is essentially important to develop an industrial feasible approach to controlling and improving the profile accuracy (form and dimensional) of components as well as their surface roughness. In this paper, a multiscale multiphysics simulation-based approach is presented to model and simulate the AFM process against the component form and dimensional accuracy control in particular. The simulation is developed in comsol which is a multiphysics computational environment. Well-designed AFM experiment trials are carried out on a purposely configured blade “coupon” to further evaluate and validate the simulations. The AFM machine and specific machining media for the experiments are provided by the industrial collaboration company, with their further industrial inputs. Both the simulation and experimental trial results illustrate that the approach is applicable to the blade profile prediction and accuracy control, which is used as a foundation for developing the simulation-based AFM virtual machining system.

Commentary by Dr. Valentin Fuster

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