Conventional Grinding Machine Research Articles

Investigation of cycle time behavior in the robotic grinding process

The production of power transmission components such as gears and bearing rings involves precision finishing of highly specialized and dedicated precision grinding machine tools. Six degree-of-freedom (6-dof) articulated arm industrial robots are less expensive and more versatile than precision grinding machines because they can be readily reconfigured for a variety of production tasks including precision grinding of free-form surfaces. However, the high compliance of such robots poses a challenge in high-precision operations, particularly as it relates to the overall cycle time of the process. The paper presents an analysis of the effects of robot compliance and grinding parameters on the cycle time of a precision grinding process. Specifically, a process model for robot-workpiece interaction and grinding process cycle time is developed. This model is used to analyze the behavior of a face grinding process cycle. The results show that for a given robot stiffness, minimizing the face grinding cycle time requires the process to be operated at the highest achievable wheel speed and infeed rate with a wheel of higher hardness. The paper also shows that a 6-dof robot offers the flexibility of modifying the Cartesian stiffness at the end effector by varying the robot pose, which is difficult to achieve in conventional grinding machines. This capability, along with the process cycle time model, permits optimization of process cycle times for precision grinding of surfaces, including free-form surfaces, using 6-dof robots.

Research into processes of production of hydrides of materials containing rare-earth metals and their corrosion

Production of permanent magnets on basis of rare earth elements (REE) is implemented by means of powder metallurgy, therefore a technologically important operation is the multistage mechanical crushing of materials to the extent of domains. The promising technique of crushing of magnetic materials is their consistent hydrogenation-dehydrogenation that allows obtaining nano-dispersed powders which are stable enough in air. Hydrogenation apparatuses, as opposed to conventional grinding machines, do not comprise motion works and their producing capacity is much higher. Hydrogenation process does not require any additional preparation of materials and it excludes undermilling and overmilling as well as material oxidation. The paper presents the results of investigation on the temperature effect on the hydrogenation process of Nd-Fe alloys. The study results on the corrosion stability of ligature hydrides under various conditions are also given. Kinetic parameters of the hydrogenation process of ligatures are determined. The phase composition of corrosion products is detected. Guidelines on hydride powder storage are given.

A novel method for grooving and re-grooving aluminum oxide grinding wheels

In this paper, a new grinding wheel grooving system is proposed that is able to both groove as well as re-groove a grinding wheel using a single-point diamond dressing tool. The re-grooving capability of the new system is achieved by synchronizing the grinding wheel angular position with the dressing tool translational position. This position synchronization enables the diamond dressing tip to repeatedly engage the grinding wheel at the same angular position around the wheel and then proceed to trace the existing groove pattern along the wheel surface to, for example, refresh a worn groove geometry. Furthermore, the proposed system can be mounted on either a non-CNC or a CNC conventional grinding machine and can groove and re-groove the grinding wheel without the need to remove it from the grinding wheel spindle. The novel wheel grooving system was experimentally validated by creating helically shaped circumferential grooves on the grinding wheel surface. The resulting maximum differences in groove width and depth were found to be 0.015 and 0.013 mm, respectively, for ten consecutively cut grooves. These small discrepancies are believed to be primarily due to the brittle fracture mechanism of the abrasive grits. Furthermore, the new wheel grooving system was shown to be able to create a wide range of different groove patterns on the wheel surface. A wear study was then carried out to compare the performance of both grooved and non-grooved grinding wheels. For the conditions used in this research, the results of this wear study showed that a grooved wheel not only exhibits less wear than a non-grooved wheel but also can remove approximately twice as much workpiece material before failure occurs.

Application of Response Surface Methodology and Enhanced Non- dominated Sorting Genetic Algorithm for Optimisation of Grinding Process

Optimisation of grinding process during grinding of Al6061-SiC composites is investigated in this study. Stir cast Al6061-SiC composites with varying volume percentage of SiC reinforcement were ground on a conventional grinding machine with diamond grit grinding wheel. Three grinding variables were studied for simultaneous optimization of material removal rate and surface roughness. Initially, the response surface models for grinding process parameters were developed using response surface methodology. Further, the developed models were optimized using enhanced elitist non-dominated sorting genetic algorithm (enhanced NSGA-II), a time saving algorithm in comparison to conventional NSGA-II. The suitable grinding conditions for multi-objective optimization of the grinding process were obtained from enhanced NSGA-II. Finally the confirmation tests were performed to validate the results obtained from response surface methodology and enhanced NSGA-II. It is observed that, experimental results and the results obtained from enhanced NSGA-II are in close conformance. Hence it is concluded that the developed algorithm can effectively be used for optimization of grinding process.

Loose abrasive edge wear effects and final surface topography in conventional grinding machines

Applying Cordero-Davila's edge ring pressure increase to upper disk kinematics equations has led to excellent agreement between theoretical loose abrasive wear computer simulations and their experimental counterparts. Experiments to verify Cordero's ring equations over long grinding periods, up to 40 min, and their computer simulations are presented in detail. These experiments led to a new improved version of Kumanin's loose abrasive wear equation. Maximum wear rate and final topography errors, between theory and experiment, were slightly larger than instrumental uncertainty. Now it became possible to compute exact pressure, relative speed and wear, at any contacting point pair and over the entire upper free disk surface.

Relative velocity and loose abrasive wear in conventional grinding machines

A model to compute relative velocity for arbitrary tool-work point pairs in conventional grinding machines is presented. This model is based on experimental data collected by means of an electronic system to measure kinematics variables in real time. Exact machine kinematics equations and an approximate equation representing upper disk rotational speed as a function of machine operation regime are introduced. With these equations, it became possible to calculate relative velocity among arbitrary tool-work point pairs. As a consequence, the amount of wear produced on optical elements, applying Preston's or Kumanin's abrasive wear equations, can be calculated.

GRINDING OF NICKEL-BASED SUPER-ALLOYS AND ADVANCED CERAMICS

This paper studies grinding of Inconel 718, Hastelloy, and some advanced ceramics. A newly developed ultra-high-speed grinding machine and a conventional grinding machine were used for the experiments. The ultra-high-speed grinding machine is equipped with a specially designed and built spindle unit that can run up to 200 m sec−1 and deliver a maximum output of 12 kW. The surface roughness and residual stress values of the ground super-alloys and advanced ceramics were measured using a profilometer and a residual stress analyzer, respectively. The ground surfaces were also assessed using a scanning electron microscope. The effect of h m (undeformed chip thickness) on surface topography of the difficult-to-machine materials was also investigated. A higher grinding wheel speed produces a smaller cutting depth and undeformed chip thickness, and thus smaller grinding force, decreased residual surface stress, and better surface finish. High productivity and good surfaces with ductile streaks could be obtained by employing ultra-high-speed grinding, even at very large wheel depths of cut such as 400 μm, without cross feed.

Analysis of the Grinding Process of Shaving Cutters with Offset Pitch Block. 2nd Report. Determination of Grinding Conditions by Optimization Method.

A method is proposed for achieving a topological tooth profile using a conventional grinding machine which cannot feed a shaving cutter toward the face width direction and generates an involute form by pitch band and pitch block with offset from the center of rotation. The first report showed an analysis method for generating shaving cutter profile by a conventional grinding machine based on a conjugate principle between grinding wheel and cutter. This report introduces a method of optimization in order to determine grinding machine setting conditions and cone grinding wheel profile which can generate a shaving cutter with the desired tooth profile. RMS value of the profile difference between ground cutter and defined cutter is adopted as the objective function for optimization. By analyzing a helical gear with bias modification, it is proven that the developed method can determine machine setting conditions and grinding wheel profile.

Analysis of the Grinding Process of Shaving Cutters with Offset Pitch Block. 1st Report. A Model of the Grinding Process and Analysis Method.

We propose a method for achieving a topological tooth profile using a conventional grinding machine. The first step defines the coordinate systems for the grinding wheel and shaving cutter and specifies their coordinated interactive relationship. The shaving cutter coordinate system includes a pitch block with offset and the pitch band. The second step specifies the grinding wheel profile in a generic way using an nth-order polynomial such that it can be used in any grinding analysis. The third step analyzes the interaction between the grinding wheel and shaving cutter based on the conjugate principle and characteristies related to the symmetry of the grinding wheel profile. The last step determines the combined motions of the grinding wheel and shaving cutter and the equations for the ground profile are formulated. Using these steps, the finished shaving cutter profile can be calculated by defining the grinding wheel profile and machine setting conditions.

A piezoelectric-drive table and its application to micro-grinding of ceramic materials

A micro-positioning table with a 0.005 μm resolution has been developed to enhance the performance of a conventional grinding machine in the fine grinding of ceramics. A piezoelectric actuator with high stiffness and resolution has been applied to drive the table and to provide small depths of cut for the workpiece. The performance of the table is investigated with both open and closed-loop operation to drive the actuator. The accuracy and stiffness of the positioning are improved by means of the closed-loop control. Grinding experiments with ceramics, such as partially stabilized zirconia (PSZ) and hot-pressed silicon nitride (Si 3N 4), were carried out to demonstrate the performance of the table. The actual resolution of depth-of-cut control was determined by measuring ground groove depths on the ceramic surface. A mirror-like surface on the ceramic was easily obtained by grinding at the small depth of cut of 0.1 μm with the aid of the table.

A rig to investigate both cylindrical and external grinding under steady and vibrational conditions and some preliminary results appertaining to vibrational grinding as a production technique

The vibration associated with the grinding process may be divided into two categories, namely, self-excited and forced. To understand the characteristics of grinding vibration, it is necessary to separate and independently study the influence of many of the variables present in the grinding process. It is not possible to separate sufficient influential variables by using commercially available grinding machines. Hence, a special grinding test rig, which contains many novel features, was designed for this purpose. The rig design is very versatile and allows both steady and vibratory grinding upon cylindrical and centreless grinding to be investigated thorougly. Whilst the test rig was being manufactured and assembled, preliminary vibratory grinding tests were carried out upon a conventional grinding machine, the vibrations being introduced into the grinding process by slots cut around the circumference of the grinding wheel. High strength, heat resistant alloys were ground and it was found that vibratory grinding results in lower grinding temperatures when compared with the corresponding, non-vibratory grinding thereby giving large improvements in grinding performance and production rate. The tests indicated that the vibratory grinding technique is advantageous but that optimization tests are necessary. It is proposed that these optimization tests be carried out upon the grinding test rig when available.