Grinding Of Workpieces Research Articles

Detection of thermo-mechanical damages by in-process Barkhausen Noise Analysis combined with Grinding Power Evaluation

Grinding of workpieces from hardened steel, especially in case of safety relevant components, usually requires a reliable method for the detection of thermo-mechanical surface damages. Compared to the common post-process methods, in-process detection promises saving of detection time and, particularly, a fast reaction to negative influences on the surface integrity. The present work shows the suitability of magnetic Barkhausen noise (BN) for the in-process detection of thermo-mechanically influenced regions during an outer diameter cylindrical grinding process. Different from other non-destructive inspection methods, BN allows the detection of changes of the residual stress state even before the occurrence of visible tempering zones. However, in case of pronounced tempering or rehardening zones, a single BN value does not enable an unambiguous statement about the surface state. Therefore, additionally the specific grinding power Pc” in dependence of the contact time Δt is considered, which allows to exclude grinding burn starting from light tempering zones. A particular focus of this study is the BN analysis during grinding with different types of grinding wheels.

Key technologies for laser-assisted precision grinding of 3D C/C-SiC composites

Due to their exceptional and distinctive qualities, 3D C/C-SiC composites are widely utilized in producing high-end equipment and the aerospace national defense industries. However, the hard and pseudo plastic nature of the material and its anisotropies make it challenging to process. To improve the processing quality of 3D C/C-SiC composites, laser-assisted precision grinding technology is introduced in this paper, which innovatively controls the depth of the thermally induced damage layer by adjusting the laser process parameters to reduce the hard brittleness of the material, and then the surface is created by precision grinding with a grinding wheel on this basis. Experiments on laser-induced damage, laser-assisted grinding, and diamond scratching were carried out to investigate the effect of laser parameters on material damage and the effect of laser-assisted grinding processes, with an emphasis on revealing the mechanism of material removal. The results show that laser irradiation causes complex reactions such as sublimation, decomposition, and oxidation of 3D C/C-SiC composites, resulting in SiO2 and Si and recondensed SiC, causing surface/subsurface damage. A maximum reduction in normal grinding force, tangential grinding force, specific grinding energy, and surface roughness of 35.6%, 43.6%, 43.58%, and 24.22%, respectively, compared to conventional grinding processes with laser-assisted grinding. After laser irradiation, the degree of brittle fracture in the precision grinding of workpieces is significantly reduced due to the degradation of matrix and fiber damage caused by laser irradiation, which reduces the hard and pseudo plastic properties of the material. The removal mechanism shows a trend of ductile domain removal in the grinding of thermally damaged layers, which reduces the grinding force and improves the surface quality.

The Study of the Flat Grinding Process of Workpieces of Composite Materials

The paper shows the results of the carried out examination of the grit of the processed surface and the intensiveness of the flat grinding of workpieces of composite materials. The processing has been carried out using of a special grinding tool with anti-frictional fillers produced in accordance with the microwave technology. The grit and components of grinding forces of workpieces of aluminomatrix composite materials with various carbon contents have been determined.

Coordinate stitching measurement of highly steep freeform surfaces

A coordinate measuring machine (CMM) is widely used for surface measurement during milling and grinding of workpieces. However, the measurement uncertainty increases with the surface slope for highly steep freeform surfaces. In addition, local features sometimes exist on the surface out of the accessible space of the CMM. This study presents a coordinate measurement method based on stitching multiple subpatches. The complex freeform surface of a large slope is first divided into subpatches which are individually tilted and measured with smaller uncertainty due to reduced slopes. A global stitching algorithm is then proposed to compensate the motion error and stitch all the subpatches together simultaneously, based on configuration optimization to minimize the overlap inconsistency. The coordinate stitching measurement method is first validated through simulation, which shows that the motion error of the order of 0.05°/0.5 mm is tolerable for a highly steep surface. It is then experimentally verified using the stitching measurement of an optical spherical surface and a steep freeform surface. An ordinary multi-axis adjustment stage is suitable for subpatch repositioning because the stitching algorithm compensates the motion error to a level lower than the CMM uncertainty.

Comparative analysis between resinoid and vitrified bond grinding wheel under interrupted cutting

The final quality of mechanical components is directly linked to the efficiency of the machining processes to which it is subjected. In this sense, grinding can provide high standards of surface and geometric quality for mechanical components, since these characteristics are increasingly necessary for the automotive and aerospace sectors. However, the complexity of the mechanical components creates increasing difficulties for grinding. Workpieces with geometric interruptions, as in the case of gears, splined shafts, pistons, and crankshafts generate mechanical impacts and aggravate the thermal gradients during grinding, causing errors of shape, drop in surface quality and reduction in the life of the cutting tool. However, few studies on better conditions for interrupted cut grinding are seen, thus making it difficult to determine ideal grinding conditions. Thus, the present experimental investigation aims to make a comparison between cylindrical grinding of workpieces of hardened AISI 4340 steel with two, six, and twelve geometric interruptions, comparing them with the grinding workpieces without interruptions, applying white aluminum oxide wheels with vitrified and resinoid bonds. Results in terms of surface roughness, roundness deviation, acoustic emission, grinding power, diametrical wheel wear, and micrography are pointed out, indicating that the greater rigidity of the vitrified bond can be harmful during the grinding of workpieces with interrupted geometry.

Simulation of thermal strength of the process of flat grinding of workpieces in intermittent circles

The present article is concerned with numerical schemes of the radial Py and the tangential Pz components of the grinding pressure and with the average contact temperature T, °С. These characteristics give an opportunity to assess the level of the thermal power strain at every path of the operational cycle of the flat pendulum grinding using a standard grinding wheel (SW), an intermittent grinding wheel (IGW) and a composite grinding wheel (CGW). Value forecasting of forces Py,pz and the temperature T will make it possible to manage the grinding process and will give the opportunity to avoid the defects precipitation at the grinding finish of the workpiece.

Rapid Modelling and Grinding of Workpieces’ Inner-surface by Robot with Impedance Model Based Fuzzy Force Control Algorithm

To achieve rapid automatic grinding of workpieces’ inner-surface by industrial robot, a rapid translational detection strategy of workpieces’ inner-surface and fuzzy force control algorithm of grinding are proposed in this paper. The rapid translational detection strategy introduces a way to establish an inner-surface’s model quickly by recording key points of the axial section contour which reflects big curvature changes of the contour. The established model is feasible but imprecision. The force control algorithm is based on impedance model. To promote adaptability to the imprecision of the established inner-surface’s model, a fuzzy adjusting strategy is introduced in the force control algorithm. By adopting an adjusting factor, which determined by force response and a fuzzy logic, the strategy can adjust the reference trajectory of impedance model in time. Taking advantage of proposed detection and force control method, grinding experiments shows that the contact normal force maintains approximately constant, the relative mean error is within 6.5%, and the material removal thickness of the inner-surface is approximately consistent. The proposed strategy’s feasibility is verified.

The effect upon grinding fluid demand and workpiece quality when an innovative zonal centrifugal provision method is implemented in the surface grinding of steel CrV12

The article presents an innovative system of zonal centrifugal grinding fluid provision into the grinding zone. This system enables a major reduction in grinding fluid flow rate by precisely supplying the fluid directly into grinding wheel's and machined material's contact area. This work describes results of experimental tests aimed at determining the most advantageous conditions of operation for this innovative system when applied in the process of surface grinding of workpieces made of steel CrV12. This paper also presents results of analyses of residual stress profiles of the workpiece's surface layer, as well as workpiece's surface roughness after using the described grinding method. The herein presented research results were compared with results of tests conducted using centrifugal cooling without zonal limitation, as well as the flood cooling method. The developed method caused a 10-times reduction in grinding fluid consumption, when compared with the less efficient flood method. As a result, the grinding fluid expenses, usage and disposal can be greatly reduced and the environmental impact can be considerably diminished. It has been proven that application of the zonal centrifugal cooling method, combined with lubrication of the grinding zone, positively impacts on residual stresses in the workpiece's surface layer, despite the grinding fluid flow rate having been limited by 90%. The obtained values of the machined surface's roughness values indicated that this parameter could be significantly influenced by means of precise delivery of controlled amounts of grinding fluid directly into the grinding zone. A 10-times reduction of the grinding fluid flow rate may lead to an approximately 35% increase of the ground surface roughness. However, optimum conditions resulted in values which were even lower than those of the surfaces shaped using the flood method.

Influence of Solid Contaminants in Metal Working Fluids on the Grinding Process

Metal working fluids (MWF) are widely used in grinding processes to lubricate and to remove the heat and chips from the contact zone. Apart from the chips, abrasive particles from the worn grinding wheel contaminate the metalworking fluid. The solid contaminants, in particular the abrasive particles crumbled from the grinding wheel, are believed to cause several negative effects like for example damaging the guideways of the machine tool. Furthermore, it is assumed that a pronounced interaction of the solid particles and the machined surface will decrease the achievable surface quality of the ground surfaces. Cleaning units are employed within the fluid circuit to prevent failure of the machine tool and to ensure the desired surface quality. The economic efficiency of such cleaning plants cleaning plants depends strongly on the choice of the grade of filtration (the particle size which has to be retained). A grade of filtration which exceeds the actual needs of the machining process adds unnecessary costs for operating the cleaning unit. To enable cost efficient design of filtration units the interaction between solid contaminants and the machining process has to be understood. The results of grinding experiments (face grinding of workpieces made of AISI 52100) confirm a significant increase of the surface waviness when corundum particles are added to the MWF. The underlying effect is an extraordinary tool wear combined with a locally varying effective depth of cut. The excess particles block the pores of the grinding wheel and are transported into the grinding gap. An increasing ratio of the size of solid contaminants and the size of the bonded grains on the wheel accelerates the wear of the tool.

Accurate robotic belt grinding of workpieces with complex geometries using relative calibration techniques

Robotic belt grinding operations are performed by mounting a workpiece to the end effector and commanding it to move along a trajectory while maintaining contact with the belt grinding wheel. A constant contact force throughout the grinding process is necessary to provide a smooth finish on the workpiece, but it is difficult to maintain this force due to a multitude of installation, manipulation, and calibration errors. The following describes a novel methodology for robotic belt grinding, which primarily focuses on system calibration and force control to improve grinding performance. The overall theory is described and experimental results of turbine blade grinding for each step of the methodology are shown.

5-Axis Control Machining and Grinding Based on Solid Model

The study deals with 5-axis control machining and grinding of workpieces with sculptured surface like impellers. The 5-axis control machining and grinding allows complex workpieces to be produced efficiently and accurately. Then, it is of importance to avoid the collision between tool and workpiece due to the arbitrariness of tool attitude. The system developed in the study generates the collision-free tool path for machining and grinding workpieces with sculptured surface, based on the CAD/CAM system employing the solid modeling technique. As a result, the validity of the system is experimentally confirmed.

５軸制御マシニングセンタによる切削・研削加工 凸型自由曲面について

This study deals with 5-axis control machining and grinding of workpieces with sculptured surface. The 5-axis control machining and grinding allows sculptured surface to be produced efficiently and accurately. The system developed in the study generates the collision-free tool path for machining and grinding workpieces with sculptured surface, based on the CAD/CAM system P-CAPS employing the solid modeling technique. For grinding, the high speed spindle attachment is used to increase the rotational speed of grinding tool, which consists of rubber pad and diamond abrasive cloth. The system realizes the surface roughness of 0.23 μm for the workpiece with sculptured surface. As a result, the system has potential of producing workpieces with high accuracy and efficiency.

The Grinding of Workpieces Exhibiting High Adhesion. Part 1: Mechanisms

Three distinct grinding mechanisms have been found to occur when 304 L stainless steel is ground by alumina wheels. The first results in the grits becoming worn by attritious wear and occurs when temperatures in the grinding zone are relatively high, the second occurs at lower grinding temperatures and results in isolated, tiny areas of workpiece material adhering to grits while the third becomes manifest at relatively low grinding temperatures and results in areas of the wheel, large in comparison to the size of a grit, being covered by adherent workpiece material. Previous proposals advanced to explain metal build-up on the grinding wheel are shown to be inadequate and the phenomenon of large-scale metal transfer to the grinding wheel is shown to be related to the ductility of the workpiece along with the degree of protection conferred by the oxide of the workpiece material. This explanation is confirmed by grinding experiments performed on a series of oxide-resistant workpieces ground in air and, in particular, by the grinding of mild steel in an argon atmosphere under which conditions large-scale transfer of workpiece material to the wheel occurred.

被削材との関連よりみた砥粒の破壊特性

As a part of research for the adaptability of abrasive grains to various workpieces, this paper presents the results of the theoretical and experimental analysis of fracture characteristics of the cutting edge of abrasive grains when applied to grinding of workpieces with various hardness.On the assumption that the brittle fracture takes place at a certain stress in the grain, the expressions that show the condition of fracture are derived for the cutting edges with the assumed geometry of wedge shape, by analysing the slip line field that is produced in it by cutting force. Considering the average cutting edge geometry, practical parameters which characterize fracture are proposed as follows : B2=HV/5.9k and B3=HV/14k for the wedge shaped edge with and without flank face respectively, where Hv is the micro-Vickers hardness of workpieces and k the shear strength of the grain. The fracture takes place when B>1 and not when B<1. The critical hardness of workpieces predicted by the parameters is about 1000kg/mm2 for diamond, 100kg/mm2 for aluminum oxide and 120kg/mm2 for silicon carbide.The theory well explains the results of observation of fracture and wear on the cutting edge of various abrasive grains.