Ultra-precision lapping of machinable ceramic Si3N4-BN by in-process electrolytic dressing

The machinable ceramic Si₃N₄-BN is a material which is increasingly being employed for automobile bearings and machinable ceramics. This material is very hard and has high resistance against volatile temperature and wear. It's efficient quality and accurate surfaces have always been of high demand for many applications in the industrial field. Besides, this material is varied by the percentage of BN contained in it, and the characteristics of lapping also varies according to this percentage of BN. Hence, in-process electrolytic dressing for ultra-precision lapping was introduced and used to experiment with the differing BN percentages in machinable ceramic Si₃ N₄. Metal-bonded super-abrasive diamond lapping wheels have superior qualities such as high bond strength, high stability and high machinability. The major problems encountered are wheel loading and glazing, which impedes the effectiveness of the cast-iron bonded diamond lapping wheel and, therefore, dressing should be considered. In this respect, in-process electrolytic dressing (IED) is proposed as an effective method regarding continuous protruding abrasives on the surface of wheels, whereby loading and glazing phenomena can apparently disappear. In this paper, the machining characteristics of machinable ceramic Si₃N₄-BN have been studied by adapting the IED lapping process in terms of the percentage of h-BN material.     

A Study of the Mirror-Like Grinding of Sintered Carbide with Optimum In-Process Electrolytic Dressing

Sintered carbide is widely used as the material for tools and die moulds, but it is difficult to grind because of its brittleness and hardness. A superabrasive diamond wheel is required for mirror-like grinding of this material. The completion of in-process dressing of a superabrasive wheel makes possible effective precision grinding of sintered carbide. This study proposes a new in-process electrolytic dressing system for this purpose. Using optimum in-process electrolytic dressing, the surface roughness is improved and the grinding force is very low. Optimum in-process electrolytic dressing has proved to be a good method for obtaining efficiency and mirror-like grinding of sintered carbide.     

The Effect of Optimum In-Process Electrolytic Dressing in the Ultraprecision Grinding of Die Steel by a Superabrasive Wheel

In recent years, grinding techniques for precision machining of brittle materials used in dies, moulds and optical parts have been improved by using superabrasive wheels and precision grinding machines. Optimum dressing using a superabrasive wheel makes possible the effective ultraprecision grinding of die steel (STD-11). In this study, a new system and the grinding mechanism for optimum in-process electrolytic dressing are proposed. This method can carry out optimum in-process electrolytic dressing of a superabrasive wheel. Optimum in-process electrolytic dressing is a good method for obtaining efficiency and ultraprecision grinding of STD-11.     

A Study of the Development of an Ultraprecision Grinding System for Mirror-Like Grinding

In this study, a new system of optimum in-process electrolytic dressing and a microposition system are developed. This system can carry out optimum in-process dressing of superabrasive wheels, and gives effective control of the unstable dressing current and insulating layer. Therefore, ultraprecision grinding when using an optimum in-process electrolytic dressing system and microposition system is a good method for efficient mirror-like grinding of brittle materials.     

微晶玻璃超精密磨削技术研究

分析实现微晶玻璃超精密磨削的技术条件和在线电解修整超精密磨削机理,并采用铸铁基金刚石砂轮结合在线电解的磨削方法对微晶玻璃进行了精密磨削,获得Ｒａ为２．３０８ｎｍ的超光滑表面。     

钢结硬质合金的精密镜面磨削技术的研究

入引了一种在线电解修整金属基超硬磨料砂办密镜面磨削新地钢结硬质合金进行了精密面磨削,得到了粗糙度为０．００３μｍ～０．０１１μｍ的镜面,一次磨削成形。效率高,可取代目前的多级研磨工艺。     

Experimental study of wheel wear in electrolytic in-process dressing and grinding

Profile accuracy of components ground with ultra-precision machine tools is primarily dependent on wheel wear. Quantitative analysis of wheel wear is therefore an important aspect for precision grinding with electrolytic in-process dressing (ELID). In this paper, wheel wear is measured from ELID grinding experiments with different dressing and machining parameters. The grinding forces and dressing current characteristics of the experiments are also compared. Based on the results, a benchmark function is defined for wheel wear rate. A relation for identifying insufficient dressing from sufficient dressing for particular machining conditions is also identified. It is found that insufficient dressing produces pitting and/or arcing on the wheel surface, and wheel wear can be linearly correlated to ELID grinding conditions when the wheels are sufficiently dressed.     

Precision grinding of bearing steel based on active control of oxide layer state with electrolytic interval dressing

The oxide layer state directly relates to machining quality in electrolytic in-process dressing (ELID) grinding. In this paper, intermittent grinding control strategy was used to monitor and control the state of the oxide layer in interval ELID (ELID II) grinding. Some experiments were implemented based on active control of the oxide layer state. The influence of dressing current, wheel speeds, and grit size on surface roughness and waviness has been discussed in detail with ELID II grinding for bearing steel. The experimental results illustrate that the ELID II method can realize a stable grinding process based on active control of the oxide layer state. The surface roughness (Ra) and waviness (Wa) increase with increase of the dressing current. When the dressing current is constant, Ra and Wa reduce as wheel speed increases and decrease as grain size of wheel decreases. The experimental results also show that sufficient abrasive protrusion can be ensured in ELID II grinding, especially for grinding with a W2.5 super-abrasive wheel which may produce a very smooth surface quality, Ra 0.0166 μm and Wa 0.018 μm.     

Precision Grinding of Mn-Zn Ferrite with In-Process Electro-Discharge Dressing

Ferrite is widely used as a material for magnetic heads for hard disks, but it is difficult to grind because its high hardness and brittleness. Therefore, a superabrasive diamond wheel is used for precision surface grinding of this material. However, the conventional dressing method cannot be applied to a superabrasive diamond wheel. This study describes a new method for carrying out effective in-process electro-discharge dressing (IEDD) of a superabrasive diamond wheel. Using IEDD, the surface roughness of the Mn-Zn ferrite was improved, and the grinding force was reduced. IEDD is a good method for obtaining efficient surface grinding of ferrite.     

Grinding of aluminium silicon carbide metal matrix composite materials by electrolytic in-process dressing grinding

The grinding cost of metal matrix composite materials is more due to low removal rates and high rates of wear of super abrasive wheels. This electrolytic in-process dressing (ELID) technique uses a metal-bonded grinding wheel that is electrolytically dressed during the grinding process for abrasives that protrude continuously from super abrasive wheels. This research carries out ELID grinding using various current duty ratios and conventional grinding of 10% SiC_p reinforced 2,124 aluminium composite materials. Normal forces and tangential forces are monitored. Surface roughness of the ground surface, Vickers hardness numbers and metal removal rate (MRR) are measured. The results show that the cutting forces in the ELID grinding are unstable throughout the grinding process due to the breakage of an insulating layer formed on the surface of grinding wheel and are less than conventional grinding forces. A smoother surface can be obtained at high current duty ratio in ELID grinding. The micro-hardness is reduced at high current duty ratio. In ELID, the MRR increases at high current duty ratio. The results of this investigation are presented in this paper.     

Wheel variables in electrolytic grinding

This paper highlights the performance of electrolytic metal bonded aluminium oxide, silicon carbide, and diamond wheels during grinding of tungsten carbide. The metal removal rate and current density were evaluated against grinding force. The process efficiency and the Faraday efficiency were evaluated for the three types of wheels.     

Ultra-precision ductile grinding of BK7 using super abrasive diamond wheel

In this paper, a novel conditioning technique using copper bonded diamond grinding wheels of 91 μm grain size and electrolytic in-process dressing (ELID) is first developed to precisely and effectively condition a nickel-electroplated monolayer coarse-grained diamond grinding wheel of 151 μm grain size. Under optimised conditioning parameters, the super abrasive diamond wheel was well conditioned in terms of a minimized run-out error and flattened diamond grain surfaces of constant peripheral envelope. The conditioning force was monitored by a force transducer, while the modified wheel surface status was in-situ monitored by a coaxial optical distance measurement system. Finally, the grinding experiment on BK7 was conducted using the well-conditioned wheel with the corresponding surface morphology and subsurface damage measured by atomic force microscope (AFM) and scanning electric microscope (SEM), respectively. The experimental result shows that the newly developed conditioning technique is applicable and feasible to ductile grinding optical glass featuring nano scale surface roughness, indicating the potential of super abrasive diamond wheels in ductile machining brittle materials. __________ Translated from Chinese Journal of Mechanical Engineering, 2006, 42(10): 95–101 [译自: 机械工程学报]     

结合在线电解修锐高效磨削陶瓷密封件研究

本文通过设计制作金属结合剂金刚石磨具，结合电解修锐技术对Al2O3陶瓷密封进行了研磨式磨削实验在实验过程中通过检测磨具表面的磨粒出露高度及陶瓷材料的去除量，评价该磨削工艺在陶瓷材料密封件加工中的应用效果。结果表明，电解修锐可有效地修锐金属结合剂金刚石磨具，在加工过程中使磨具保持良好的切削能力，因此材料去除量较大，加大工时短，陶瓷密封件的加工成本得到控制。     

A study on wear mechanism and wear reduction strategies in grinding wheels used for ELID grinding

Metal-bonded superabrasive diamond grinding wheels have superior qualities such as high bond strength, high stability and high grindability. The major problems encountered are wheel loading and glazing, which impedes the effectiveness of the grinding wheel. Electrolytic in-process dressing (ELID) is an effective method to dress the grinding wheel during grinding. The wear mechanism of metal-bonded grinding wheels dressed using ELID is different form the conventional grinding methods because the bond strength of the wheel-working surface is reduced by electrolysis. The reduction of bond strength reduces the grit-depth-of-cut and hence the surface finish is improved. The oxide layer formed on the surface of the grinding wheel experiences macrofracture at the end of wheel life while machining hard and brittle workpieces. When the wheel wear is dominated by macrofracture, the wheel-working surface is free from loaded chips and worn diamond grits. When the oxide layer is removed from the wheel surface, the electrical conductivity of the grinding wheel increases, and that stimulates electrolytic dressing. The conditions applied to the pulse current influence the amount of layer oxidizing from the grinding wheel surface. Longer pulse ‘on’ time increases the wheel wear. Shorter pulse ‘on’ time can be selected for a courser grit size wheel since that type of wheel needs high grinding efficiency. Equal pulse ‘on’ and ‘off’ time is desired for finer grit size wheels to obtain stable and ultraprecision surface finish.     

Crack generation and the effect of in-process electro-discharge dressing in grinding single crystal MgO

Single crystal MgO is widely used in material with high temperature resistance, but is difficult to grind because of brittleness and crack generation. Therefore, a diamond wheel with superabrasive surface is required for surface grinding of this material. But the conventional dressing method cannot be applied to the diamond wheel with superabrasive. This study describes a newly proposed method for carrying out effective in-process electro-discharge dressing (IEDD) of a diamond wheel with superabrasive. Using IEDD, the surface roughness of single crystal MgO was improved, the grinding force was very low and crack generation was reduced. IEDD is a good method to obtain efficient grinding and surface grinding of single crystal MgO.     

A study of mirror-like grinding of fine ceramics with in-process electrolytic dressing

Fine ceramics have the properties of high hardness, chemical inertness, high thermal resistance and low electrical conductivity, but, because of high hardness and brittleness, they are very difficult to machine. Therefore, a superabrasive diamond wheel is used for mirror-like grinding of this material. In this study, an in-process electrolytic dressing system for carrying out mirror-like surface grinding was constructed. Using this system the grinding force for fine ceramics was reduced. This work shows that the application of electrolytic dressing is beneficial in obtaining a mirror-like surface when grinding fine ceramics.     

Magnetic field affects electrochemical grinding

This paper highlights the effect of magnetic field introduced in the electrode gap in electrolytic grinding, when a metal bonded wheel with silicon carbide abrasives was used to face grind tungsten carbide. The effect of feeding force on metal removal rate and current density is reported. Also the effect on power consumption and specific energy consumption is discussed.     

Evaluation of Y2O3 surface machinability using ultra-precision lapping process with IED

Prospects of Y₂O₃ have been more extended as a great promising and creditable material for optical, electronic and mechanical purposes. Y₂O₃ has been more observed as a fine ceramic which has great material properties: high light transparency, excellent thermal resistance and chemical inertness. But in terms of effective application of Y₂O₃, its hard and brittle nature needs to be overcome during the surface machining process. Therefore, the surface machining control of Y₂O₃ should be conducted carefully. The evaluation for stable and continuous machining should also be investigated in various industrial fields as there are only limited studies on the subject. The lapping process with in-process electrolytic dressing (IED) is widely used for surface machining of hard and brittle materials. In this study, Y₂O₃ surface machinability was evaluated by using the ultra-precision lapping process with IED method by changing three major variables: applied force, wheel speed and machining time. The most suitable value of Ra 92nm surface roughness was acquired with smooth surface quality from the following machining condition: 7kg of applied force, 60rpm of wheel speed and 30minutes of machining time. After the lapping process, the machining tendency and surface characteristics were analyzed with fracture toughness and Vickers hardness for the evaluation of Y₂O₃ surface machinability. This paper was recommended for publication in revised form by Associate Editor Dae-Eun Kim Eun-Sang Lee received B.S. and M.S. degrees in Mechanical Engineering from INHA University in 1985 and in 1987. After that time, he received a Ph.D. degree from Korea Advanced Institute of Science and Technology in 1998. Dr. Lee is currently a Professor at the School of Mechanical Engineering at INHA University in Incheon, Korea. His research fields are ultra-precision manufacturing, electro chemical micro machining and development of semiconductor wafer polishing system.     

A novel technique for dressing metal-bonded diamond grinding wheel with abrasive waterjet and touch truing

The dressing of metal-bonded diamond grinding wheels is difficult despite their availabilities on hard and brittle materials. In this paper, a novel compound technology that combines abrasive waterjet (AWJ) and touch truing is proposed for dressing metal-bonded diamond grinding wheel precisely and efficiently. The dressing experiments of a coarse-grained and a fine-grained bronze-bonded diamond grinding wheel were carried out on a surface grinder with a developed AWJ system. The feasibility of this method was verified by analyzing the wheel runout, the truing forces, and the wheel surface topography. The variations of 3D surface roughness of wheel surface topography during the compound dressing process were quantitatively analyzed. The mechanism of AWJ and touch compound dressing is also discussed. Further, a reaction-bonded silicon carbide block was ground to validate the dressing quality. The experiment results indicate that the grinding wheels that were well dressed by the proposed technique leads to a smaller grinding force and a smaller surface roughness than that of undressed wheels.     

超硬磨料砂轮的激光修锐技术研究

激光修整超硬磨料砂轮的原理,利用Ｎｄ：ＹＡＧ固体脉冲激光器进行激光修锐青铜结合剂和树脂结合剂硬磨料砂轮的试验,用扫描电镜观察了激光修锐前后砂轮表面的微观表貌,对激光作用下砂轮表面不同结合剂材料的去除机理进行了分析,通过磨削陶瓷试验,研究激光修锐的金刚石砂轮的磨削性能,并与普通砂轮磨削肖修锐的金刚石砂轮进行对比。结果表明,采用试验所确定的激光参数可选择性地去除砂轮表面的结合剂材料,而不损伤超硬磨粒,