Grinding Chip Thickness Research Articles

Modeling of grinding chip thickness distribution based on material removel mode in grinding of SiC ceramics

Modeling of grinding chip thickness distribution based on material removel mode in grinding of SiC ceramics

Heat flux distribution and temperature prediction model for dry and wet cylindrical plunge grinding

The grinding heat is generally partitioned into the workpiece, wheel, chips and fluid in grinding process. The total amount of heat flux entering into the workpiece greatly affects the final workpiece surface temperature, which may cause undesirable workpiece burn. Moreover, the variable grinding chip thickness and fluid injection speed along the grinding contact zone could substantially change the specific energy and the shape of the heat source correspondingly. In this article, a Weibull heat flux distribution model for both dry and wet grinding temperature prediction was proposed by analyzing two key parameters: energy partition Rw and shape parameter k. The value of Rw was obtained by considering the real contact length, the active grits number and the average grit radius r0 on the basis of traditional formulas. The relationship between shape parameters k and useful flow was established by a FLUENT simulation of the convective grinding fluid applied in grinding contact zone with wheel-workpiece minimum clearance. The grinding temperature and grinding force experiments were conducted on a grinding machine MGKS1332/H to validate the proposed heat flux model. The calculated workpiece surface temperature distribution was obtained by using the experimental heat flux obtained by the reverse algorithm, and the error between calculated temperature and experimental temperature was analyzed. With the monitored force signals and the proposed temperature prediction model, the grinding temperature for both dry and wet grinding can be predicted, which will be helpful to the optimization and control of temperature in grinding process.

Material removal mechanism of PTMCs in high-speed grinding when considering consecutive action of two abrasive grains

An effective finite element (FE) simulation model characterizing the material removal behavior of TiCp/Ti-6Al-4V titanium matrix composites in high-speed grinding process was developed when considering consecutive action of two abrasive grains. The resultant stress and grinding force have been analyzed to study the crack propagation behavior. The effect of the undeformed chip thickness on the ground surface defects was discussed. It was found that in the material removal process of PTMCs, the brittle removal of TiCp and the plastic removal of Ti-6Al-4V matrix would happen simultaneously until the reinforcing particle completely failed in the grinding process. The maximum Mises stress and single-grain grinding forces fluctuate weakly and smoothly once the crack is produced in the reinforcing TiCp. As for the reinforcing TiCp without crack inside, the crushing depth increases with the increase of the undeformed chip thickness in grinding. However, as for the TiCp with residual crack inside, due to the stress concentration in the tip of the crack, the TiCp is always cracked in chunks when the undeformed chip thickness changes from 0.3 to 0.9 μm in grinding. Finally, the FE simulation results are validated true through the high-speed grinding experiment of PTMCs.

Theoretical study on brittle–ductile transition behavior in elliptical ultrasonic assisted grinding of hard brittle materials

The elliptical ultrasonic assisted vibration can lead to a higher comprehensive performance with better machined quality and lower grinding force during brittle materials machining. The undeformed chip thickness in grinding can be defined as the distance between two consecutive grinding surfaces formed by the adjacent abrasive grain trajectories. The ductile–brittle transition point of chip formation in brittle materials machining is believed to be represented by the threshold value of undeformed chip thickness (critical undeformed chip thickness). In this paper, an energy based method is proposed to predict the critical undeformed chip thickness in elliptical ultrasonic assisted grinding (EUAG). The effects of vibration parameters on grinding force and specific grinding energy are analyzed in detail. Results show that the axial vibration amplitude leads to a slight reduction in grinding force, whereas the vertical vibration amplitude results in a significant reduction of grinding force. The increase of wheel speed and ultrasonic vibration frequency can reduce the grinding force as well. Nevertheless, the grinding force ratio remains relatively steady fluctuating from 1.37 to 1.56. Additionally, the critical undeformed chip thickness increases with the increasing grinding speed, axial vibration amplitude and ultrasonic vibration frequency, while firstly increases and then decreases with the increasing vertical vibration amplitude. Especially, a ductile-mode grinding in micron-level can be achieved when the axial vibration amplitude is above 3μm and a totally brittle fracture occurs when the axial vibration does not exist. Thus, a reasonable selection of vibration parameters in EUAG process is required. The above theoretical evaluations coincide well with the variable experimental results.

Development and Research on the Dynamics Simulation System for Surface Grinding Process with Diamond Wheel

Vibration during high-speed surface grinding process is one of important factors to influence surface precision of machined workpieces and lead to low efficiency of grinding machine. Process parameters are usually obtained from empirical data or reference manuals for the avoidance of serious vibration even chatter and its effect. As a result, it generally leads to low rated power of machine tool and long processing cycle. To solve the problem, designing and development on a dynamics simulation system for surface grinding with high accuracy ,which will be capable to predict a series of dynamic characteristics in time and frequency domains, such as grinding force-vibration, as well as phase/frequency characteristics, relative power spectral analysis etc is necessary and shows good application prospect. Meanwhile, the system will be used to indicate the process parameters optimization and investigate distribution characteristics of grain chip thickness and surface topography precision. In the paper, surface grinding process with diamond wheel is chosen as the study object and its dynamic characteristics are investigated. Based on studies on the comprehensive influence mechanism of regenerative chatter theory and wheel run-out rotational model on instantaneous grinding chip thickness of grain unit, analytical models of grinding force are improved. Differential equations of damper grinding vibration system with two-degree-of-freedom and a close-loop control system model with regenerative chatter feedback circle on the basis of interaction behaviors of force and vibration are built. Several relevant numerical methods are introduced to develop the simulation system of grinding dynamics. By comparative analysis on solution accuracy, steadiness and convergence of the correlative algorithms, explicit Runge-Kutta formula is identified as the best solution to simulation system modeling. On the basis of the above work, main subsystems and functional modules in the system are presented. The whole designs of framework and prototype systems are finished.

Improving surface integrity and economics of grinding by optimum coolant application, with consideration of abrasive tool and process regime

As compared to machining, the chip thickness in grinding is small and the specific grinding energy is generally much higher than the specific cutting energy in machining. With such small chip thickness values, a lot of heat is created by non-chip removal interactions, such as ploughing and rubbing. These interactions occur between the chip and grain, chip and bond, and the chip and the work. Identification and manipulation of these interactions can allow the engineer to minimize the thermal limitation, improve surface finish, increase wheel life, etc. This paper discusses the thermal energy partitioning that occurs with different modes of grinding, and guides the reader towards processes with a lower specific energy and more desirable energy partitioning with respect to the energy that enters the final workpiece surface. The high efficiency deep grinding regime, is compared to creep-feed and shallow-cut grinding. The paper also looks at the cooling effect of grinding fluids and how they can be applied more effectively to cool and lubricate the workpiece surface. Best practices will be presented, based on analytical models and field experience. Flowrate and pressure models are used to optimize the main fluid jet that is applied to the grinding process. The heat transfer characteristics of superabrasive wheels, as compared to conventional abrasives, will also be presented and discussed. Finally, a case study is presented, that clearly shows the economic and technological advantages of coherent-jet nozzles over a more conventional approach.

Heat flux distributions and convective heat transfer in deep grinding

By using experimental data including the monitored temperature and power signals, combined with detailed theoretical analysis, the relationship between the undeformed grinding chip thickness and specific grinding energy has been studied and used to derive the heat flux distribution along the wheel-work contact zone. The relationship between the grinding chip thickness and specific grinding energy (SGE) has been shown to follow an exponential trend over a wide range of material removal rates. The distribution of the total grinding heat flux, q t, along the grinding zone does not follow a simple linear form. It increases at the trailing edge with sharp gradients and then varies nearly linearly for the remainder of the contact length. The heat flux entering into the workpiece, q w, is estimated by matching the measured and theoretical grinding temperatures, and it has been found that the square law heat flux distribution seems to give the best match, although the triangular heat flux is good enough for most cases to generate accurate temperature predictions. With the known heat flux distributions of q t and q w, the heat flux to the grinding fluid can then be estimated once the heat partitioning to the grinding wheel is determined by the Hahn model for a grain sliding on a workpiece. The convective heat transfer coefficient of the grinding fluid has been shown to vary along the grinding zone. An understanding of this variation is important in order to optimise the grinding fluid supply strategy, especially under deep grinding conditions when contact lengths are large. It has been demonstrated that the down grinding mode can provide a beneficial fluid supply condition, in which the fluid enters the grinding zone at the position of highest material removal where a high convective cooling function is needed.

The Role of Chip Thickness in Grinding

Abstract Grinding chips are classified into five types depending upon their relative thickness-to-length ratio and equations are derived for computing the length or thickness of chips of all types for external, surface, internal, and plunge-grinding operations. Representative experimental grinding data are presented and discussed to illustrate the use of the equations and to emphasize the importance of chip thickness as a grinding parameter. The force on a single grain is derived and the result applied to explain relative wheel hardness.