Taghi Tawakoli

AN INNOVATIVE CONCEPT AND ITS EFFECTS ON WHEEL SURFACE TOPOGRAPHY IN DRY GRINDING BY RESIN AND VITRIFIED BOND CBN WHEEL

In the dry grinding process, as there is no coolant lubricant to transfer the heat from the contact zone, minimizing the grinding specific energy and grinding forces is a matter of importance. Some of the results of the systematic research works, based on a novel concept to make a step forward for pure dry grinding, are presented. The new concept is based on the fact that the optimisation of the chip formation reduces the friction and rubbing in the process. Such optimisation was achieved by a special conditioning process. The result showed a drastic reduction in grinding forces and no burning or damages on the surface of workpiece using the novel method comparing to conventional wheel with the same material removal rate. A theoretical discussion is also presented to support the experimental results.

Effects of Ultrasonic Assisted Grinding on CBN Grinding Wheels Performance

The effects of ultrasonic assisted grinding on vitrified CBN grinding wheels performance have been investigated. The ultrasonic vibration has been superimposed to the workpiece in feed and cross feed directions and the kinematics of the process in both directions have been discussed. The obtained results show that applying ultrasonic vibration to the grinding process can improve the quality of the workpiece surface, the efficiency of the process and decrease the grinding forces and specific energy considerably.Copyright

Macro-topography effects on dry grinding with CBN wheels

Grinding involves high specific energy compared to other machining processes due to the negative rake angle of grains. Almost all this energy is converted to friction, generated high heat, which can have harmful effects on workpiece surface quality specially in case of dry grinding. Based on the optimisation of chip formation process, using a new concept of special structuring by special dressing of the vitrified grinding wheels, the heat generation is reduced. The results show a significant reduction of grinding forces in the new method compared to the conventional one at the same material removal rate without burning or thermal damages on the surface of workpiece.

Study on the Effects of Abrasive and Coolant-Lubricant Types on Minimum Quantity Lubrication-MQL Grinding

In dry grinding, as there is no coolant lubricant to transfer the heat from the contact zone, generation of surface damages are not preventable. Promising alternatives to conventional flood coolant applications are also Minimum Quantity Lubricant (MQL) or Near Dry Machining (NDM) or Semi Dry Machining (SDM). This research has been conducted to study the influence of the abrasive and coolant-lubricant types on the minimum quantity lubrication (MQL) grinding performance. One type of CBN and three types of conventional wheels (corundum) were tested. The tests were carried out in presence of fluid, air jet and eleven types of coolant-lubricants, as well as in dry condition. The results indicate that the finest surface quality and the lowest grinding forces could be obtained when grinding with CBN wheels. In the case of conventional wheels, the coarser wheel induces much proper grinding results.

Dressing of CBN grinding wheels with ultrasonic assistance

Though ultrasonic assistance has been successfully used for a long time in different machining processes, the use of its positive effects in dressing of superabrasives grinding tools is rather new, which could have drawn the attention of researchers in the last decade. In ultrasonic-assisted dressing, high-frequency and low-amplitude vibrations are superimposed on the movement of dressing or grinding tool. The experimental investigation carried out at the KSF Institute showed that applying ultrasonic vibration to both a stationary diamond dressing tool and a point crushing roll reduces the grinding forces, causing a reduction of the heat generated at the grinding zone.

Experimental Investigation of Material Removal Mechanism in Grinding of Alumina by Single Grain Scratch Test

Alumina is a material that is frequently used in high performance applications. Grinding of alumina is usually associated with micro-cracks which deteriorate surface quality. In order to get a deeper knowledge of the characteristics of material removal mechanisms in alumina during grinding with and without ultrasonic vibration of the workpiece, single grit scratch tests were performed in this research. The effect of the ultrasonic vibrations and cutting speed on the material removal mechanism of alumina was investigated in the chip thickness range of 0.53 μm which is common in precision grinding operations. It was shown that the material pile-up decrease with higher cutting speed. On the other hand, the transition from ductile to brittle mode of material removal occurs earlier in higher cutting speeds. The ultrasonic vibrations showed great influence in the cutting speed 30 m/s in reducing the pile-up values.

Effects of Vibration-Assisted Grinding on Wear Behavior of Vitrified Bond Al2O3 Wheel

The total removal of grinding wheel material includes two main parts. The larger of the two is the result of dressing and truing operation and the other relatively small part is due to the wheel wear which takes place during the actual grinding process. The frequency of dressing and truing operations depends on the cutting conditions, wheel characteristic, etc. However in dry grinding as there is no cutting fluid to transfer the heat from the contact zone, the wheel wear during grinding and the frequency of dressing is much higher due to the higher grinding forces and temperatures. Vibration grinding reduces wear of the grinding wheel during the process considerably and decreases the frequency of dressing operation significantly. Hence it increases the efficiency of the process and reduces the cost. The investigation carried out in the KSF institute shows the improvement on the surface roughness, reduction of the grinding forces, thermal damage of the ground surface and radial wear of the grinding wheel in case of using vibration grinding comparing to conventional grinding. The designed and developed ultrasonically vibrated workpiece holder and the experimental investigation show a decrease of up to 80% of radial wear of the grinding wheel.

Effect of the Coolant Lubricant Type and Dress Parameters on CBN Grinding Wheels Performance

The efficiency of using of CBN grinding wheels highly depends on the dressing process as well as on the coolant lubricant used. The Institute of Grinding and Precision Technology (KSF) investigated the performance of vitrified CBN grinding wheels -being dressed using different parameters- while using two different grinding oils and two different water-miscible coolant lubricants. The obtained results show that the performance of the vitrified CBN grinding wheels regarding the quality of the workpiece surface, the grinding forces as well as the wear of the grinding wheel, highly depend on the dressing conditions and the type of the coolant lubricant used. Compared to the water-miscible coolant lubricants, the grinding oils show better results.

The Effect of Special Structured Electroplated CBN Wheel in Dry Grinding of 100Cr6

In many grinding applications, the material removal rate (MRR) is constrained by undesired thermal surface damages like burns and tensile residual stresses as well as dimensional inaccuracy. In dry grinding, due to lack of coolant, the limitation to achieve higher MRR is more critical as the major part of the heat, generated on the contact zone, is transferred to the workpiece. That is why the lower heat generation is a most important target by dry grinding. This paper presents some of the very interesting results by a comparison between a structured electroplated CBN wheel and a conventional one during surface grinding of steel. One of the grinding wheels has the normal structure and the other has special macro-structure topography developed for dry grinding. The results show a considerable reduction in grinding forces and less thermal damages using the novel electroplated CBN wheel comparing to conventional wheel.

T-Dress, A Novel Approach in Dressing and Structuring of Grinding Wheels

Since the grinding wheel topography directly influences the grinding forces and material removal mechanism, the dressing of grinding wheels has a decisive role in the desired product quality achievement. A new dressing concept is introduced in this paper in order to reach the optimum chip formation condition. The novel dresser, T-Dress, creates a new structure on the grinding wheel owing to which remarkable reduction in grinding forces occur. These lead to the lower heat generation in the wheel-workpiece contact zone and consequently lower thermal damages. The experiments prove about 40% lower grinding forces in grinding of bearing steel materials, 100Cr6, when dressing with T-Dress compared to the case of dressing with conventional profile rollers with almost no difference in the ground surface roughness values.