Chip formation in machining metal bonded grinding layers

Gears demand increasingly high quality regarding acoustic emissions, surface roughness and lifetime. Therefore, grinding is often the last step in the process chain of gear manufacturing. Grinding wheel grain sizes of 30 micrometers lead to high surface quality and metal bonded CBN-grains allow a high wear resistance and profile stability of the grinding tool. Consequently, an increase of the material removal rates and thus productivity is possible without increasing the thermal load on the workpiece due to the grinding wheels' high thermal conductivity. However, the time and cost intensive dressing process in combination with the high profile requirements for gear grinding prevent the wide application of metal bonded tools for this application. This challenge can be solved using a new dressing approach with geometrically defined cutting edges. Metal bonded CBN-grinding layers have a structure similar to metal-matrix-composites, which can be machined by using the turning operation. The aim of this work is to verify the machinability of metal bonded CBN-grinding layers. In the present work, the chip formation for metal bonded grinding layers is presented

Grinding and fine finishing of future automotive powertrain components

The automotive industry is undergoing a major transformation driven by regulations and a fast-paced electrification. A critical analysis of technological trends and associated requirements for major automotive powertrain components is carried out in close collaboration with industry – covering the perspectives of OEMs, suppliers, and machine builders. The main focus is to review the state of the art with regard to grinding, dressing, texturing and fine-finishing technologies. A survey of research papers and patents is accompanied by case studies that provide further insights into the production value chain. Finally, key industrial and research challenges are summarized

Influence of the process parameters on the grinding result in continuous generating grinding of cutting tools

Continuous generating grinding processes have largely replaced discontinuous profile grinding processes in gear manufacturing due to their higher productivity. On order to transfer the advantage of the productivity benefits of this process to tool grinding, the continuous generating grinding was adapted to the manufacture of cutting tools. However, this novel approach of using continuous generating grinding processes for tool grinding has not been widely investigated. Therefore, the aim of this study is to investigate the influence of cutting speed, feed and radial depth of cut on the process result and thus to generate initial knowledge for the process design. Subsequently, the influence of these parameters on the grinding worm wear as well as on the cutting edge quality and surface properties of the ground milling tools are investigated. The results show that an increase of the radial depth of cut leads to a reduction of the process time by the factor of four without significantly influencing the wear of the grinding worm tooth. Furthermore, an increase of the cutting speed only leads to an increase in the initial wear of the grinding worm after the dressing process. For this reason, the cutting speed offers the potential to further increase the productivity of the process. The microgeometry of the cutting edge of the ground milling tool is mainly affected by the feed and the macro geometry by the feed and radial depth of cut

Influence of dressing strategy on tool wear and performance behavior in grinding of forming tools with toric grinding pins

The performance of grinding tools in grinding processes and the resulting surface and subsurface properties depend on various factors. The condition of the grinding tool after dressing is one of these factors. However, the influence of the dressing process on the condition of the grinding tool depends on the selected process parameters and is difficult to predict. Therefore, this paper presents an approach to describe the influence of the dressing process on tool wear of toric grinding pins and the resulting subsurface modification. For this purpose, toric grinding pins with a vitrified bond were dressed with two different strategies and the wear and operational behavior were investigated when grinding AISI M3:2 tool steel with two different grinding strategies. In general, the investigations have shown that the dressing process influences the performance and wear behavior differently depending on the grinding strategy used. The degree of clogging is influenced by the geometric contact sizes. In the case of small engagement cross sections with simultaneously large contact lengths the thermal tool load is distributed over a small annular area of the tool and favors clogging. Crushing and additional transverse loading of the grains result in an almost clog-free tool surface. This also leads to a lower G-ratio. Crushing leads to an intensified decrease of the torus radii. The influence of the dressing strategy can also be observed in the induced residual stresses. Toric grinding pins dressed by crushing induce lower compressive residual stresses into the workpiece, which can be attributed to the self-sharpening effect. This effect reduces the mechanical and thermomechanical load of the workpiece during machining

On geometry and kinematics of abrasive processes: The theory of aggressiveness

Due to the stochastic nature of the abrasive-tool topography, abrasive processes are difficult to model and quantify. In contrast, their macro geometry and kinematics are usually well defined and straightforwardly controlled on machine tools. To reconcile this seeming contradiction, a novel unifying modelling framework is defined through the theory of aggressiveness. It encompasses the arbitrary geometry and kinematics of a workpiece moving relative to an abrasive surface. The key parameter is the point-aggressiveness, which is a dimensionless scalar quantity based on the vector field of relative velocity and the vector field of abrasive-surface normals. This fundamental process parameter relates directly to typical process outputs such as specific energy, abrasive-tool wear and surface roughness. The theory of aggressiveness is experimentally validated by its application to a diverse array of abrasive processes, including grinding, diamond truing and dressing, where the aggressiveness number is correlated with the aforementioned measured process outputs

Design and Fundamental Understanding of Minimum Quantity Lubrication (MQL) Assisted Grinding Using Advanced Nanolubricants

Abrasive grinding is widely used across manufacturing industry for finishing parts and components requiring smooth superficial textures and precise dimensional tolerances and accuracy. Unlike any other machining operations, the complex thermo-mechanical processes during grinding produce excessive friction-induced energy consumption, heat, and intense contact seizures. Lubrication and cooling from grinding fluids is crucial in minimizing the deleterious effects of friction and heat to maximize the output part quality and process efficiency. The conventional flood grinding approach of an uneconomical application of large quantities of chemically active fluids has been found ineffective to provide sufficient lubrication and produces waste streams and pollutants that are hazardous to human health and environment. Application of Minimum Quantity Lubrication (MQL) that cuts the volumetric fluid consumption by 3-4 orders of magnitude have been extensively researched in grinding as a high-productivity and environmentally-sustainable alternative to the conventional flood method. However, the lubrication performance and productivity of MQL technique with current fluids has been critically challenged by the extreme thermo-mechanical conditions of abrasive grinding. In this research, an MQL system based on advanced nanolubricants has been proposed to address the current thermo-mechanical challenges of MQL grinding and improve its productivity. The nanolubricants were composed of inorganic Molybdenum Disulphide nanoparticles (≈ 200 nm) intercalated with organic macromolecules of EP/AW property, dispersed in straight (base) oils - mineral-based paraffin and vegetable-based soybean oil. After feasibility investigations into the grindability of cast iron using MQL with nanolubricants, this research focused on the fundamental understanding of tribological behavior and lubricating mechanisms of nanolubricants as a method to improve the productivity of MQL-assisted surface grinding of ductile iron and alloy steel. An extensive investigation on MQL-assisted grinding using vitrified aluminum oxide wheel under varied infeed and lubrication condition was carried out with the scope of documenting the process efficiency and lubrication mechanisms of the nanolubricants. Experimental results showed that MQL grinding with nanolubricants minimized the non-productive outputs of the grinding process by reducing frictional losses at the abrasive grain-workpiece interfaces, energy consumption, wheel wear, grinding zone temperatures, and friction-induced heat generation. Use of nanolubricants in MQL yielded superior productivity by producing surface roughness as low as 0.35 μm and grinding efficiencies that were four times higher as compared to those obtained from flood grinding. Repeatable formation of tribochemical films of antifriction, antiwear, and extreme pressure chemical species in between the contact asperities of abrasive crystals and work material was identified with nanolubricants. The tribological behavior was characterized by this synergistic effect of the antiwear, antifriction, and load carrying chemical species that endured grain-workpiece seizures and reduced adhesion friction between the contact surfaces. Delivery of organic coated Molybdenum Disulphide nanoparticles by anchoring on the natural porosity of the abrasive wheel and eventually, sliding-induced interfacial deformation into tribolayers and alignment at the grinding zone were established as the lubrication mechanisms of the nanolubricants. These mechanisms were further validated from tribological evaluations of lubricated cubic boron nitride (cBN) superabrasives-1045 steel sliding pairs on a reciprocating tribotest rig resembling the tool-lubricant-workpiece interactions of MQL-assisted grinding

Neural network modelling of Abbott-Firestone roughness parameters in honing processes

In present study, three roughness parameters defined in the Abbott-Firestone or bearing area curve, Rk, Rpk and Rvk, were modelled for rough honing processes by means of artificial neural networks (ANN). Input variables were grain size and density of abrasive, pressure of abrasive stones on the workpiece's surface, tangential or rotation speed of the workpiece and linear speed of the honing head. Two strategies were considered, either use of one network for modelling the three parameters at the same time or use of three networks, one for each parameter. Overall best neural network consists of three networks, one for each roughness parameter, with one hidden layer having 25, nine and five neurons for Rk, Rpk and Rvk respectively. However, use of one network for the three roughness parameters would allow addressing an indirect model. In this case, best solution corresponds to two hidden layers having 26 and 11 neurons.Peer ReviewedPostprint (author's final draft

Abrasive machining with MQSL

Grinding and polishing of engineered components are critical aspects of the precision manufacturing of high performance, quality assured products. Elevated process temperatures, however, are a common and for the most part undesirable feature of the grinding process. High process temperatures increase the likelihood of microstructural change within the immediate subsurface layer and are detrimental to the strength and performance of the manufactured products. Increasing processing costs and tighter environmental legislation are encouraging industry to seek innovative fluid application techniques as significant savings in production can be achieved. In this context, and with sponsorship from three industrial partners, namely; Fives Cinetic, Fuchs Lubricants plc and Southside Thermal Sciences Ltd, and also from the Engineering and Physical Science Research Council (EPSRC), this research aimed to develop an understanding of Minimum Quantity Solid Lubrication (MQSL) as a method for abrasive machining, with particular reference to the control of surface temperatures. Improving the lubricity of Minimum Quantity Lubrication (MQL) fluids reduces the frictional source of process heat and controls the finish surface temperature. The application of effective solid lubricants is known as Minimum Quantity Solid Lubrication (MQSL). Molybdenum Disulphide (MoS2), Calcium Fluoride (CaF2), and hexagonal Boron Nitride (hBN) were compared against a semi-synthetic water soluble machining fluid (Fuchs EcoCool). A series of Taguchi factorial experimental trials assessed their performances through ANOVA (ANalysis Of VAriance) statistical method. The hBN produced the lowest grinding temperatures of the solid lubricants tested, although they still remained higher than those achieved using the EcoCool control. The reduction of the machining fluid enabled a Charged Coupled Device (CCD) sensor to be fitted into the grinding machine. The recorded movement in the emitted spectrum from the grinding chips was compared to experimental and modelled process temperatures. This showed that the wavelengths of the chip light correlated to the temperature of the finish grinding surface. This greatly contributed to determining the feasibility of constructing a non-destructive, non-invasive, thermally-adaptive control system for controlling grinding surface temperatures.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Dry grinding technology for automotive gears manufacturing: process modeling and optimization

The following thesis focused on the dry grinding process modelling and optimization for automotive gears production. A FEM model was implemented with the aim at predicting process temperatures and preventing grinding thermal defects on the material surface. In particular, the model was conceived to facilitate the choice of the grinding parameters during the design and the execution of the dry-hard finishing process developed and patented by the company Samputensili Machine Tools (EMAG Group) on automotive gears. The proposed model allows to analyse the influence of the technological parameters, comprising the grinding wheel specifications. Automotive gears finished by dry-hard finishing process are supposed to reach the same quality target of the gears finished through the conventional wet grinding process with the advantage of reducing production costs and environmental pollution. But, the grinding process allows very high values of specific pressure and heat absorbed by the material, therefore, removing the lubricant increases the risk of thermal defects occurrence. An incorrect design of the process parameters set could cause grinding burns, which affect the mechanical performance of the ground component inevitably. Therefore, a modelling phase of the process could allow to enhance the mechanical characteristics of the components and avoid waste during production. A hierarchical FEM model was implemented to predict dry grinding temperatures and was represented by the interconnection of a microscopic and a macroscopic approach. A microscopic single grain grinding model was linked to a macroscopic thermal model to predict the dry grinding process temperatures and so to forecast the thermal cycle effect caused by the process parameters and the grinding wheel specification choice. Good agreement between the model and the experiments was achieved making the dry-hard finishing an efficient and reliable technology to implement in the gears automotive industry