High Efficiency Deep Grinding Research Articles

High-performance grinding of ceramic matrix composites

Ceramic matrix composites (CMCs) are highly promising materials for the next generation of aero-engines. However, machining of CMCs suffers from low efficiency and poor surface finish, which presents an obstacle to their wider application. To overcome these problems, this study investigates high-efficiency deep grinding of CMCs, focusing on the effects of grinding depth. The results show that both the surface roughness and the depth of subsurface damage (SSD) are insensitive to grinding depth. The material removal rate can be increased sixfold by increasing the grinding depth, while the surface roughness and SSD depth increase by only about 10%. Moreover, it is found that the behavior of material removal is strongly dependent on grinding depth. As the grinding depth is increased, fibers are removed in smaller sizes, with the fiber length in chips being reduced by about 34%. However, too large a grinding depth will result in blockage by chip powder, which leads to a dramatic increase in the ratio of tangential to normal grinding forces. This study demonstrates that increasing the depth of cut is an effective approach to improve the machining efficiency of CMCs, while maintaining a good surface finish. It provides the basis for the further development of high-performance grinding methods for CMCs, which should facilitate their wider application.

Grindability of γ-TiAl intermetallic compounds during ultrasonic vibration-assisted high efficiency deep grinding process

Grindability of γ-TiAl intermetallic compounds during ultrasonic vibration-assisted high efficiency deep grinding process

Coolant condition and spindle power in high-efficiency-deep-grinding of nickel-based superalloy profile part

ABSTRACT Coolants play an important role in controlling thermal damage in high-efficiency deep grinding (HEDG). The cooling condition in the grinding contact zone (GCZ) determines the cooling effect during the grinding process. Furthermore, when profile grinding is performed, owing to the complexity of the shape, the cooling effect varies at different positions. Therefore, in this study, a device that includes a pressure sensor and semi-natural thermocouples was introduced to evaluate the cooling conditions in the GCZ during HEDG. Thereafter, the influences of the grinding parameters and outlet velocity of the coolant on the pressure distribution were investigated. The grinding speed and outlet velocity of the coolant have significant impacts on the cooling condition, whereas the influences of the infeed speed and depth of cut are limited. The coolant pressure distributions during the profile grinding were measured, analyzed, and optimized. The needle-shaped nozzle, which adapts to the profile, has a better cooling effect than the shoe-shaped nozzle. Moreover, the influence of the coolant delivery on the spindle power was discussed. The outlet velocity of the coolant jet and grinding speed have significant effects on the idle and grinding powers. Therefore, it is recommended to consider the influence of grinding speed during HEDG.

Creep-Feed Grinding Wheel Development for Safely Grinding Aerospace Alloys

Creep-feed grinding wheels have been associated with advances in processing difficult-to-cut materials used in the aerospace industry for many years. Since the late 1960s, the development of grinding wheels used for creep-feed grinding (CFG) operations and high-efficiency deep grinding (HEDG) operations has placed great responsibility on grinding wheel manufacturers to produce bonding systems of high strength and bonding bridges with smaller cross-sectional area. The safety of grinding wheels has become very important in recent years due to the increases in porosity (~ 50% vol.) and reductions in bond content (~ 5% vol.). This has necessitated the development of very strong bonding systems that can withstand high rotational, thermal, clamping and contact stresses. The paper not only provides a review of work performed on conventional grinding wheels, but also explains how the use of computational modeling techniques are used to simulate the stresses experienced by superabrasive wheels that are used at high-speeds in creep-feed grinding (CFG), high-efficiency deep grinding (HEDG) and peel grinding (PG) processes. Superabrasive materials of choice for use on difficult-to-machine alloys are typically cubic boron nitride (cBN) and diamond bonded with a vitrified glass-ceramic bonding system. The current work also explains how Weibull statistics are used to characterize the strength of the abrasive-porosity-bond composite structure and how the computational and Weibull statistical analyses are unified through the use of a simple measure of operational integrity known as the safety factor. The paper concludes by showing the reader how computational techniques can be used to design CFG wheels by optimizing abrasive segments bonded to a reinforcing material of high strength operating at a specific peripheral speed. It should be noted that this study is applicable to multi-layered CFG wheels and not to single-layer electroplated grinding wheels that are also used in CFG operations.

On the tribology and grinding performance of graphene-modified porous composite-bonded CBN wheel

In order to provide the effective reinforcement and lubrication for reducing the friction on the interface of the grinding wheel and workpiece during the high-efficiency deep grinding of difficult-to-machine materials, an in-house developed porous composite-bonded (Cubic Boron Nitride) CBN wheel with graphene nanoplatelets was explored to meet the increasing demand for industrial purpose. It can be found from experimental study that by adding the appropriate concentration of graphene, 0.01 wt%, both of the flexural strength and tribology performance have been enhanced in the graphene-modified porous composite-bonded CBN wheel, and then the related grinding wheel was fabricated to perform the grinding experiments on the Ti–6Al–4V titanium alloy (TC4). It has been found that by adding the graphene the sharpness of the abrasives on the surface of the grinding wheel always keeps at a certain range and the grinding wheel may have self-sharpening ability which can guarantee the stability during the high-efficiency deep grinding process. Finally, by considering process parameters in this study the graphene-modified porous composite-bonded CBN grinding wheel could be used to achieve the high-efficiency deep grinding of TC4 as well as guarantee its surface quality under the grinding wheel speed of 80 m/s, grinding depth of 0.1 mm and workpiece feed speed of 0.6 m/min.

Profile grinding of DZ125 nickel-based superalloy: Grinding heat, temperature field, and surface quality

• Increase of grinding speed and undeformed chip thickness decreases grinding heat. • Temperature field is characterized by experiments and simulation. • DZ125 is well ground by HEDG with good quality and residual compressive stress. • DZ125 blade root is ground with material removal rate over 50 mm 3 /(mm·s). During the high-efficiency deep grinding of a turbine blade root, localized thermal damage of the profile surface could easily occur owing to the complexity of the grinding dynamics and cooling conditions in the grinding zone. Therefore, it is worthwhile to investigate the generation of the grinding heat, the grinding temperature and its distribution, and the grinding surface quality, particularly for superalloys used to produce aero-turbine blades. In this study, the specific grinding energy and grinding heat flux during the profile grinding of a fir tree-shaped root of a DZ125 superalloy turbine blade were investigated. The grinding temperature at four points on the profile were measured and the results were used to conduct a three-dimensional simulation to analyze the temperature distribution on the machined surface and in the direction of the cutting depth. The effects of the heat source shape and contact length on the temperature distribution were also examined. A moderately high material removal rate was found to be beneficial to the surface quality, with a maximum material removal rate of 50.6 mm 3 /mm·s producing a surface roughness of Ra 0.6 μm without saturation or microstructural changes. Residual compressive stress was also achieved on the ground surface.

Study on material removal mechanism of electrochemical deep grinding

Deep grinding, such as creep-feed grinding and high efficiency deep grinding, offers the possibility of high process efficiency. However, deep grinding is also suffering from grinding heat and grinding wheel wear, resulting in serious surface damage and precision error. Hybrid machining process is generally regarded as effective way to improve the machining performances. Electrochemical machining (ECM) is an anodic electrochemical dissolution process that can effectively remove materials without limitations in terms of the mechanical properties of the alloys. Therefore, this paper attempts to combine deep grinding with ECM process, which can be named electrochemical deep grinding (ECDG). During ECDG process, mechanical grinding and ECM process are simultaneously applied on the anode workpiece. With the aid of high-speed ECM process, the cut-depth is greatly increased without damaging the workpiece. The feed rate and machining stability are also further improved by scraping the electrolyte product and insoluble components. The removal mechanism of anode material during ECDG process was studied through experiments in detail. Based the detailed analysis of material removal phenomenon, a qualitative model of material removal mechanism of ECDG was established. This research provides valuable insights into the material removal mechanism and the dependence of MRR and surface quality on machining conditions in the hybrid process of ECM and deep grinding.

Surface hardness improvement in high efficiency deep grinding process by optimization of operating parameters

The grinding is one of the most important methods that directly affects tolerances in dimensions, quality and finished surface of products. One of the major problems in the material removal processes specially grinding is the heat generation during the process and the residual tensile stress in the surfaces of product. Therefore, optimization of High Efficiency Deep Grinding (HEDG) process is the main goal of this study to reduce the generated heat and residual tensile stress and increase strength and surface hardness of AISI1045 annealed steel. To this end, the effects of main parameters e.g. depth of cut, wheel speed, workpiece speed and cross feed on surface hardness has been investigated. The experimental results demonstrated the reduction in surface temperature and increase in hardness as optimum conditions are applied to the grinding process. Moreover, the experimental results were validated by comparing with other experimental results and analyzing of surface microhardness, surface temperature and normal and tangential forces.

Experimental investigation of cooling characteristics in wet grinding using heat pipe grinding wheel

High grinding temperature restricts the machining efficiency and precision of some aeronautical difficult-to-machine materials. Aiming to enhance heat exchange with the grinding zone and reduce grinding temperature, heat pipe grinding wheel (HPGW) provides a novel method through improving the thermal conductivity of grinding wheel assisted by heat pipe. In this paper, the structure of HPGW is introduced and the workpiece temperature and energy partition in wet grinding using HPGW based on a wheel-fluid composite surface model is analyzed. Wet grinding experiments including creep feed grinding, high-speed shallow grinding and high-efficiency deep grinding (HEDG) are carried to investigate the cooling characteristics of HPGW according to the workpieces of titanium alloy Ti-6A1-6 V and Inconel 718. Compared with using the traditional grinding wheel, the results show that using HPGW in creep feed grinding and HEDG can maintain a lower grinding temperature and avoid the burnout under a relatively high removal rate, but cooling effect of HPGW is not obviously different from the traditional grinding wheel in high-speed shallow grinding due to a small heat input at the evaporator of HPGW.

Temperatures in Grinding—A Review

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.

A review of the design of grinding wheels operating at excessive speeds

The design of grinding wheels operating at excessive peripheral speeds has improved significantly since the 1970s, which was largely prompted by the development of the creep-feed grinding process (CFG) and its derivatives including high efficiency deep grinding (HEDG), peel grinding (PG), and the high-speed stroke grinding process (HSSG). The current work reviews the design of grinding wheels that operate within the specified safety factors that are applied by the industry through the application of various codes and industry standards developed since the introduction of high-speed grinding processes. The paper focuses on the design of plain and clamped homogeneous structure grinding wheels, reinforced and recessed grinding wheels, superabrasive segmented grinding wheels, and high-speed slotted grinding wheels that use both conventional bonded abrasive structures and vitrified and electroplated superabrasive materials such as cubic boron nitride (cBN) and diamond. The implications of grinding wheel safety are stressed, and recommendations are provided to ensure that grinding wheels continue to be operated safely at excessive peripheral speeds.

Experimental and modeling characterization of wear and life expectancy of electroplated CBN grinding wheels

Abstract Wear and life expectancy of a nickel-electroplated monolayer of cubic boron nitride grinding wheels are characterized based on the wheel surface topological evolution, observed after grinding Inconel 718 super-alloys. The wheel is for surface or cylindrical grinding, and having 250 mm diameter, 10 mm thickness and B40/50 coarse grit size. A unique grit-workpiece interaction process, leading to a non-uniform spatial distribution of the grit wear has been identified. Largest grits have been observed to pullout rapidly, resulting in load redistribution to their surroundings, and leading to the attritious and fracture wear phase. The detailed analysis showed that the stresses on the cutting grits arising from the thermal shock are 3–5 folds those arising from mechanical cutting forces, and reach an order of magnitude differences for the high efficiency deep grinding (HEDG) process. It is also found that the grit wear rate is primarily dependent on the workpiece feed rate rather than the grinding wheel speed. The total wheel life is then constructed as the sum of pullout life (Phase-I) and attritious and fracture wear life (Phase-II). Model predictions for the total wheel life compare well to the experimental observations. This facilitates comparisons of different types of grinding configurations and design space exploration. As an example, the HEDG process is compared to a regular high speed grinding, and it is observed that HEDG configuration can deliver much higher material removal for the same amount of wheel wear.

Investigation on the heat source profile on the finished surface in grinding based on the inverse heat transfer analysis

Grinding temperature field analysis is very significant to achieve controlled stress grinding and controlled grinding of affected layer depth. Heat source profile is an important basis for the grinding temperature field analysis. The heat source on the finished surface is more convenient than the heat source on the contact surface to perform grinding temperature field analysis both analytically and numerically. At present, the heat source profile on the finished surface was modeled to be rectangular, right triangular, triangular, or other shapes. However, all the modeled heat source profiles are not universally applicable under different grinding conditions. Therefore, the heat source profile on the finished surface under different grinding conditions needs to be further investigated. In this research, the inverse heat transfer analysis was performed to investigate the heat source profile on the finished surface under different grinding conditions. The investigation showed that the heat source profile on the finished surface is nearly right triangular in conventional shallow grinding, is triangular in creep feed grinding, and is close to be parabolic in HEDG (high efficiency deep grinding). Based on the investigation, the heat source profile on the finished surface was modeled as simple shapes to accommodate different grinding conditions. It was modeled to be right triangular in conventional shallow grinding and in creep feed grinding, and was modeled to be parabolic in HEDG. Error analyses of the predicted grinding temperatures obtained from the modeled heat source profiles were performed. The results showed that the modeled right triangular heat source profile is applicable in conventional shallow grinding and in creep feed grinding. The modeled parabolic heat source profile is applicable to most of the grinding parameters employed in HEDG. The modeled heat source profiles can conveniently serve as useful tools for grinding temperature field analysis in engineering.

Effects of undeformed chip thickness on grinding temperature and burn-out in high-efficiency deep grinding of Inconel718 superalloys

High-efficiency deep grinding experiments of nickel-based superalloy Inconel718 were conducted with a vitrified cubic boron nitride wheel. An investigation was made to detect the relationship between the undeformed chip thickness and grinding temperature and burn-out behavior of the workpiece material. The results display that the grinding forces and grinding power increase with the increase of the undeformed chip thickness. When the coolant is in the nucleate boiling state, the grinding temperature keeps stably at below 140 °C; however, the grinding temperature increases rapidly to the materials burn-out point once the coolant enters the film boiling state. The critical range, 0.65 ∼ 0.75 μm, is determined for the undeformed chip thickness under the defined experimental condition, which could take a great effect on controlling the grinding burn-out and increasing the grinding efficiency.

High Efficiency, High Speed Grinding of a Composite Material Consisting of Polymer Concrete and Steel Structures

Polymer concrete (PC) displays superb vibration dampening qualities and is dimensionally and thermally stable, dense, rigid, resistant to water and chemicals and will not twist or bend in reaction to stress. Therefore PC has become the preferred base to ensure rigidity in a machine tool. Hybrid polymer concrete beds composed of steel structures and polymer concrete are challenging for the grinding process, due to the completely different material properties of steel and PC. Which complicates the selection of suitable grinding tool and limits the achievable material removal rates. A promising technique to overcome these technological constraints is the use of High Efficiency Deep Grinding (HEDG), where high cutting speeds and material removal rates are utilized. This paper presents the experimental investigation of HEDG of a hybrid material consisting of polymer concrete and integrated steel inserts. A vitrified bond CBN-grinding wheel was utilized and the grinding parameters are optimized in this study. The obtained results show that the application of HEDG can increase the material removal rates considerably. There was no evidence of thermal damages on the surface and subsurface of ground workpieces. The microscopic studies of the induced chips by the HEDG process showed, that both brittle and ductile grinding modes occur during the applied HEDG process.

Effect of process parameters on convective heat transfer coefficient of fluid and heat partitioning in high efficiency deep grinding with water-based coolant

A statistical analysis was undertaken to study the role of process parameters on the convective heat transfer coefficient of fluid (hf) and heat partitioning ratios in HEDG. Heat partitioning ratios have been calculated by using experimental data and models developed by previous researchers. Regression models between grinding process parameters and partitioning ratios has been developed using DoE technique and RSM. Heat partitioning ratio to chip increases with MRR and takes around 20% of grinding heat. Very less amount of heat is carried away by workpiece and cubic boron nitride grinding wheel. The hf increases with wheel speed and reduction in contact length. This enables the grinding fluid to take most of heat and limits the rise in temperature up to 140°C despite of high MRR. Previous researchers considered constant value of hf, but in present study variation in hf with process parameters has been considered to calculate the heat portioning ratios.

Grinding temperature and wheel wear of porous metal-bonded cubic boron nitride superabrasive wheels in high-efficiency deep grinding

High-efficiency deep grinding experiments of Inconel 718 nickel-based superalloy was carried out with the porous metal-bonded cubic boron nitride superabrasive wheel, in which the uniform and large pores were formed by the broken alumina bubble particles in the working layer after wheel dressing. Grinding temperature, energy partitioning into workpiece, and wheel wear were investigated. Results obtained show that long maintenance of low grinding temperature, that is, 50 °C–170 °C, is obtained in high-efficiency deep grinding with the porous metal-bonded cubic boron nitride wheel. The energy partitioning into the ground workpiece is ranged from 2% to 6%, which is smaller than that with the conventional vitrified cubic boron nitride wheels and alumina abrasive wheels. Sufficient storage space for chips and coolants contributes to the excellent performance of the porous metal-bonded cubic boron nitride wheel in high-efficiency deep grinding. Abrasion wear and grain fracture are the dominant wear patterns of the porous cubic boron nitride wheel in the steady wear stage, while chips loading and grain pullout play a critical role in the final dramatic wear behavior of the porous wheel.

Grinding temperature during high-efficiency grinding Inconel 718 using porous CBN wheel with multilayer defined grain distribution

Porous cubic boron nitride (CBN) wheel with multilayer defined grain distribution was developed based on pore-forming effect of alumina bubbles and sintering technology. High-efficiency grinding experiments were carried out on a typical nickel-based superalloy Inconel 718, and grinding temperatures within the contact arc were measured. A strategy to control the grinding burn by clapping flake graphite around the workpiece was proposed, which was verified could improve the cooling effect in contact zone and increase the specific material removal at least three times higher in deep grinding. Being an attribute to the faster heat moving speed and good thermal conductivity of metal bond and CBN grains, grinding temperature reached 790 °C in the contact arc but nonvisible burnout marks were found on ground surface at Q′w = 25 mm3/(mm·s). At a wheel speed of 80 m/s, force ratio remains around 6 and specific grinding energy decreased from 187 to 67 J/mm3 at elevated specific material removal from 3 to 25 mm3/(mm·s). Results show that the developed porous CBN wheels have a promising application in high-efficiency deep grinding nickel-based alloy.

An experimental investigation into resonance dry grinding of hardened steel and nickel alloys with element of MQL

Current policies on environmental issues put extra pressures on manufacturing processes to be resource efficient and eco-friendly. However, in grinding processes, large amounts of cutting fluids are used. These fluids are not environmental friendly thus require proper management before disposal with associated cost. Hence, this work sets to explore low-frequency vibration in grinding in order to improve coolant application in conventional grinding at the first stage with the aim to introduce this into high efficiency deep grinding (HEDG) at latter stage. An attempt is made to grind nickel alloys with minimum quantity lubricant (MQL) as oppose to flood cooling. To achieve this with minimum alterations to the machine tool, a piezo-driven workpiece holder was developed for surface grinding. This simple innovative workpiece holder allowed oscillating during actual grinding process. However, this paper presents the results of low-frequency oscillatory grinding in dry and near-dry conditions. The response of the machine tool spindle unit is presented alongside with the workpiece holder response. In this investigation, hardened steels and nickel alloys were ground with vibration assistance. The grinding forces are illustrated together with the surface finish. The wheel performance is given in terms of grinding ratio.

Rail grinding for the 21st century – taking a lead from the aerospace industry

Rail grinding is a key maintenance activity for Network Rail. It is performed at night through possession of the track, so process speed is critical. Increasing the metal removal rate (MRR) of the rail grinding operations would be a way to improve the time taken for this operation. The aerospace industry has recently seen advances in grinding technologies that have increased MRR. This work was aimed at assessing their best practice and its application to rail grinding operations. Current Network Rail grinding operations include preventative and corrective re-profiling of the rail head. The majority of work performed in the UK is preventative re-profiling with current train speeds ranging from 1 to 10 mile/h. Opportunities exist to increase train speed and improve the productivity of this operation through the use of more advanced grinding technologies. The most relevant aerospace technology is high efficiency deep grinding (HEDG). This approach uses: a high surface speed of the grinding wheel, superabrasive tooling, and high workpiece feed rates to remove material quickly from the cut-zone. Productivity improvements were identified by applying theory on power requirements (by assessing the specific grinding energy) and chip thickness of the grinding process. Computer CAD/CAM modelling was also performed to assess the effect of changing grinding techniques on potential gouging of the track infrastructure and/or interference with example trackside obstructions. The work concluded that opportunities do exist to improve the current productivity of grinding operations. Utilizing HEDG technology theoretically provides a 100% train speed increase (utilizing the same power available with the current setup) for preventative re-profiling. This requires the application of high surface speeds of the grinding wheel and superabrasive technology. Further increases in train speed require increased spindle power. The chip thickness experienced by grinding grains is reduced for a peripheral grinding setup and high wheel surface speeds that is beneficial for wheel wear. The application of HEDG technology cutting on the periphery of the wheel provided optimum conditions during CAD/CAM simulation to avoid rail gouging, and any potential collision of the grinding stone with modelled trackside obstructions.