Specific Grinding Energy Research Articles

Using the size effect of specific energy in grinding for work hardening

The present research was undertaken to analyse the size effect of specific energy in grinding. The possibility of using the size effect in grinding for a controlled surface layer work hardening of metal parts is shown. To study these phenomena, an advanced grinding process of abrasive material removal in combination with plastic deformation has been designed and used for the investigations. To achieve high specific energy values and to minimise thermal effects counteracting the work hardening, the approach used requires the application of low depths of cut in combination with low cutting speeds. Experimental results show a good correlation between the specific grinding energy, that is, the size effect on the one hand and compressive residual stresses and their penetration depth characterising the work hardening on the other hand.

Experimental investigations of advanced ceramics in high efficiency deep grinding

In order to improve machining efficiency and grinding surface integrality of advanced ceramics, the effect of different grinding conditions (different wheel speed, different depth of cut or different feed rate) on surface characteristics, grinding force, specific grinding energy and material remove modes of advanced ceramics, including alumina, nitride silicon and yttria partially stabilized zirconia, are studied under high efficiency deep grinding condition. Special grinding efficiency and depth of cut arrive at 120 mm/(mm·s) and 6 mm respectively. Experiments indicate that the increase in wheel speed and decrease in depth of cut, i.e., decrease in maximum undeformed chip thickness, result in decrease in specific grinding force, increase in specific grinding energy and plough striations. It is shown that the grinding efficiency increases and the surface integrality does not become worse under grinding condition of great depth of cut.

Study on the Material Removal Mechanism of Precision Surface Grinding of Nanostructured WC/12Co Coating

Nanostructured ceramic coatings has excellent properties, their industrial application depends not only on their fabrication but also on their precision grinding technology, so it is necessary to study the material removal mechanism in grinding of nanostructured ceramic coatings. This paper presents experimental results on how the grinding processes parameters affect the grinding force ratio and specific grinding energy as well as surface roughness in precision surface grinding of nanostructured WC/12Co (n-WC/12Co) coating and also presents SEM observations of surface and subsurface of n-WC/12Co coating ground under different grinding conditions. Furthermore this paper discusses the material removal mechanism in grinding of n-WC/12Co coatings and gives priority to inelastic deformation instead of brittle fracture, which provides theoretical basis for the precision grinding of nanostructured ceramic coating.

The Use of the Size Effect in Grinding for Work-hardening

This paper shows the possibility of using the size effect of the specific grinding energy for a targeted surface layer work-hardening of metal parts. The research includes the combination of abrasive material removal and plastic deformation in a single grinding step. Therefore high specific energy values are needed and thermal effects counteracting the work-hardening have to be minimised. This can be achieved by low cutting speeds in combination with low depths of cut. The new approach results in an in-process work-hardening of the surface layer, which was found to lead to higher hardness, a compressive residual stress state, and higher wear resistance.

EFFECTS OF THE MAXIMUM UNDEFORMED CHIP THICKNESS ON ROUGHNESS AND SPECIFIC ENERGY IN SURFACE GRINDING

In this study, effects of the maximum undeformed chip thickness on roughness of ground surface and specific grinding energy were investigated. The acoustic emission (AE) signals generated during grinding processes have been analyzed to find out the appropriate AE parameters for assessing the processes. SM45C steels were ground under conditions yielding volumetric removal rate per unit width of 100, 200, 300 and 400 mm3/min. From the experimental results, it is found that surface roughness ( Ra ) increases but grinding power (P), energy rate of AE signal (AErms2) and specific grinding energy(e) consumed decrease as the maximum undeformed chip thickness(g) increases.

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.

Fabrication of Highly Efficient Dicing Blade for Cutting Al2O3-TiC Composite

Highly efficient dicing blades with 28 vol% porosity were fabricated by using a doctor blade casting method and pulsed electric current sintering (PECS). WC and W2C were formed between diamond grains and tungsten matrix materials during a sintering and enhanced the bonding strength between diamond grains and the matrix materials. Fabricated dicing blades and commercial dicing blades which were 0.09 mm in thickness, were evaluated by a constant feeding force dicing machine under 3.0 N constant feeding force. Al2O3-TiC composites which had 1.2 mm in thickness were used as a cutting sample. Speeds of fabricated dicing blade and commercial dicing blade were 6.2 mm/s and 2.9 mm/s at 750 mm of cutting length, respectively. Number of diamonds on surfaces of the fabricated dicing blades was kept constant before and after dicing tests, however, that on the commercial dicing blades decreased to half. Specific grinding energy for the fabricated dicing blades and the commercial ones were 133 GJ/m3 and 213 GJ/m3, respectively. Therefore, efficient dicing blade was produced by introducing pores and increasing bonding strength between diamond grains and matrix.

Vitreous bond silicon carbide wheel for grinding of silicon nitride

This study investigates the grinding of sintered silicon nitride using a SiC wheel with a fine abrasive grit size and dense vitreous bond. The difference of hardness between the green SiC abrasive and sintered Si 3N 4 workpiece (25.5 vs. 13.7 GPa) is small. Large grinding forces, particularly the specific tangential grinding forces, are observed in SiC grinding of Si 3N 4. The measured specific grinding energy is high, 400–6000 J/mm 3, and follows an inverse relationship relative to the maximum uncut chip thickness as observed in other grinding studies. The SiC wheel wears fast in grinding Si 3N 4. The G-ratio varies from 2 to 12. Two unique features in SiC grinding of Si 3N 4 are the trend of increasing G-ratio at higher material removal rate and the excellent surface integrity, with 0.04–0.1 μm R a and no visible surface damage. For a specific material removal rate, surface cracks along the grinding direction are generated on the ground surface. The problem of chatter vibration was identified at high material removal rates. Periodic and uneven wheel loading marks and clusters of workpiece surface cracks across the grinding direction could be observed at high material removal rates. This study demonstrates that the SiC grinding wheel can be utilized for precision form grinding of Si 3N 4 to achieve good surface integrity under a limited material removal rate.

Analysis of Grinding Temperature Considering Surface Generation Mechanism

Grinding temperature was analyzed considering heat generation by cutting with each abrasive on the wheel working periphery. A geometrical analysis of interference between the abrasives and workpiece gave the instantaneous cutting cross section, and visualized the surface topography generated by the time. Using the specific grinding energy and the instantaneous cutting cross sections, the instantaneous distribution of heat generation on the wheel-workpiece contact area was obtained. Then grinding temperature was calculated for a given heat partition into the workpiece. Since a cutting with an abrasive generated an impulse of heat flux, temperature distribution calculated for grinding carbon tool steel varied drastically, and very high local temperature or temperature spikes appeared.

Analysis of the different forms of application and types of cutting fluid used in plunge cylindrical grinding using conventional and superabrasive CBN grinding wheels

The work reported here involved an investigation into the grinding process, one of the last finishing processes carried out on a production line. Although several input parameters are involved in this process, attention today focuses strongly on the form and amount of cutting fluid employed, since these substances may be seriously pernicious to human health and to the environment, and involve high purchasing and maintenance costs when utilized and stored incorrectly. The type and amount of cutting fluid used directly affect some of the main output variables of the grinding process which are analyzed here, such as tangential cutting force, specific grinding energy, acoustic emission, diametrical wear, roughness, residual stress and scanning electron microscopy. To analyze the influence of these variables, an optimised fluid application methodology was developed (involving rounded 5, 4 and 3 mm diameter nozzles and high fluid application pressures) to reduce the amount of fluid used in the grinding process and improve its performance in comparison with the conventional fluid application method (of diffuser nozzles and lower fluid application pressure). To this end, two types of cutting fluid (a 5% synthetic emulsion and neat oil) and two abrasive tools (an aluminium oxide and a superabrasive CBN grinding wheel) were used. The results revealed that, in every situation, the optimised application of cutting fluid significantly improved the efficiency of the process, particularly the combined use of neat oil and CBN grinding wheel.

Surface Waviness Controlled Grinding of Thin Mold Inserts Using Chilled Air as Coolant

The ongoing trend of miniaturization in electronic related parts, which is an average of two times every 5 to 7 years, introduces machining challenges. Surface grinding of thin miniature parts is an ardent task due to its warpage, induced by high specific grinding energy (10–100 J/mm3). Therefore, coolant is used to avoid thermal damage, improve surface integrity, and prolong wheel life. However, coolant, the incompressibility media, introduces high forces at the grinding zone, that create dimensional and shape instability. This article presents the results of a new grinding method when using chilled air as coolant media for thin mold insert, two-stage vapor compression refrigeration cycle was adopted for production of chilled air of temperature, −35°C; pressure, 0.2–0.3 MPa; and flow rate, 0.4 m3/min. Along with chilled air, traces of vegetable oil mist was also impinged to the grinding zone. Both chilled air and vegetable oil mist were applied through two independent paths of a specially designed twin compartment nozzle for maximizing the penetration.

An Experimental Study of Specific Energy in Grinding Granite

An investigation is reported of the characteristics of specific energy in grinding of granite using diamond abrasives. The effects of many parameters, such as the types of diamond tools, the types of abrasives, the properties of granite, the conditions of lubrication, and the working conditions of diamond tools, were studied. The power consumed in grinding was measured in order to obtain the specific energy, which is defined as the energy expended per unit volume of material removal. It is found that the specific energy for grinding of granite was closely related to the removal mechanisms of granite, the failure modes of diamonds and the interactions of the swarf with the applied fluid and bond matrix.

Studies on Exploiting Further the Potential of High Efficiency Grinding

Aiming at the existent problems in the application of high efficiency grinding, some countermeasures are put forward to further exploit its potential, including the topography optimization design for high efficiency grinding wheel and cooling enhancement technology with jet impingement in grinding zone. The optimization model advanced here can be used to optimize the grinding wheel topography for different grinding processes with the minimum specific grinding energy. The cooling enhancement technology employed in creep feed deep grinding experiment of titanium alloy shows remarkable cooling capability. It is able to steadily control the temperature on workpiece surface at an extremely low lever under 100°C,when the workpiece is seriously burn with the conventional coolant supply. Further studies on the combination of these two countermeasures will not only enable us to increase the available material removal rate to a new lever but also solve the workpiece burn problem for those difficult-to-machining materials in high efficiency grinding.

Modelling the Specific Grinding Energy and Ball-Mill Scaleup

We propose a new model for the prediction of the specific grinding energy, which proved to approach very well the values calculated with the help of the Denver slide rule. The proposed model, combined with a model giving the ball-mill power draw, is used for the ball-mill scale up. Comparisons with the Bond procedure showed a good agreement for the prediction of the ball-mill dimensions, due to the fact that the proposed model is not sensitive to the various corrections associated with the Bond methodology.

Energy and temperature analysis in grinding

Energy consumption and dissipation are discussed, leading into a thermal model for grinding. The analysis developed over many years applies to shallow-cut conventional grinding processes and also to deep grinding processes. Energy analysis provides insights into the grinding process and suggests avenues for process improvements. The thermal model provides a good estimation of contact temperatures as well as temperatures on the finish surface. Case studies are presented to demonstrate how operational efficiency, component quality and removal rates are affected by process conditions. Examples are included for High Efficiency Deep Grinding (HEDG). HEDG is defined as deep grinding at high workspeeds and very high removal rates. Tawakoli [20], Klocke [21]. The contact between the workpiece and wheel is represented as a circular arc. Experiments show that high removal rates and absence of thermal damage can be achieved. HEDG can achieve low specific grinding energy compared with shallow grinding and creep grinding. The chips take away most of the heat generated in the grinding process. As in creep grinding, bum-out of the coolant causes a steep rise in contact temperature of the workpiece.

Ultra-fine grinding mechanism of inorganic powders in a stirred ball mill

An experimental investigation on grinding mechanism for calcite used in a stirred ball mill was carried out. The slurry concentration and the amount of grinding aids were chosen as main experimental factors of the grinding process. The effect of grinding aids on particle size distribution and grinding efficiency, defined as the increases of specific surface area per the specific grinding energy, was investigated. It was demonstrated that the grinding rate for calcite could be improved by addition of grinding aids. The grinding energy efficiency by adding a specific grinding aids was improved approximately 45.2% in comparison with and without grinding aids (n=700rpm, J=0.7, dB= 1.0 mm, Cs=60wt%).

Experimental Studies on the Grind-Hardening Effect in Cylindrical Grinding

In recent years high-strength and high-temperature alloys are used for structural and other applications. These newer high-performance materials are inherently “more difficult to machine” and also necessitate the need for higher dimensional and geometrical accuracy. Grinding is one of the most familiar and common abrasive machining processes used for the finishing operation. Compared to other machining processes such as turning, milling, etc., the specific energy developed during grinding is very high. At a critical level of specific grinding energy, the temperature rise[1]experienced by the workpiece may be such that thermal damage is induced. Heat damage induced by the grinding process is well documented and may be categorized by temper colors that are at least unsightly and probably indicative of more serious damage, including thermal cracks, tempered zone, etc.,[2]which can lead to catastrophic failure of critical machine parts that shortens the life of products subject to cyclic loading. In this work, a new heat treatment process called “grind hardening” and a mathematical model are introduced, and this work deals with how the in-process energy in grinding can be effectively utilized to improve the surface hardness and surface texture, and also to prevent damages. An experimental study has also been carried out in grinding AISI 6150 and AISI 52100 steels with an alumina wheel, and the results are discussed.

Specific Grinding Energy Causing Thermal Damage in Helicopter Gear Steel

Thermal damage (burn) in carburized and hardened helicopter gear steel caused by grinding was investigated. Excessive grinding temperatures cause grinding burn and result in excessive scrap or reduced fatigue life. Vasco X2M gear steel, used in helicopters, was prepared and heat-treated by a research partner, U.S Army. Grinding tests were conducted on this steel. Nital etching was used to detect grinding burn. Model was established to predict onset of thermal damage for Vasco X2M steel based on specific grinding energy determined from grinding force measurements. The model was compared to results published for other steels. A control strategy is suggested based on the model to avoid grinding burn.

High Efficiency Deep Grinding of a Low Alloy Steel with Plated CBN Wheels

High efficiency deep grinding (HEDG) of a low alloy steel (51CrV4) has been carried out on an Edgetek 5-axis CNC grinding machine, using electroplated CBN wheels. The initial tests were conducted in a surface grinding mode over a wide range of grinding conditions, to evaluate the levels of specific grinding energy, workpiece surface integrity and wheel wear. The burn threshold conditions for the ground workpiece surface have been proposed in terms of a critical heat flux which is shown to vary with material removal rate. Cylindrical grinding in HEDG mode has also been carried out based on the knowledge obtained from the surface grinding. It has shown that the HEDG technology can be transferred successfully to the field of cylindrical grinding to achieve very high specific material removal rates in excess of 400mm 3/mm.s. The successful application of HEDG to cylindrical components depends on the appropriate selection of grinding parameters and also the grinding fluid supply strategy. Thermal modelling of the HEDG process combined with surface integrity studies, has shown that under cylindrical grinding conditions a significant reduction in grinding fluid supply is possible even when operating within the HEDG regime.

Temperatures in High Efficiency Deep Grinding (HEDG)

A thermal model is presented for deep grinding with particular relevance to the HEDG process. HEDG is defined as deep grinding at high workspeeds and very high removal rates. The contact between the workpiece and wheel is represented as a circular surface. It is found that the contact angle and also the Peclet number (widely used in heat transfer and defined below) have strong effects on the grinding zone temperatures. Experiments were carried out to demonstrate the high removal rates achievable and to measure the resulting contact temperature. It was found that high removal rates and absence of thermal damage could be achieved as predicted. The new model is shown to provide a good estimation of contact temperatures. It is also confirmed that HEDG can achieve low specific grinding energy compared with shallow grinding and creep grinding. The chips take away a substantial proportion of the heat generated in the grinding process. As in creep grinding, burn-out of the coolant causes a steep rise in contact temperature of the workpiece.