Continuous finishing processes using a combination of burnishing and electrochemical finishing on bore surfaces

A novel finishing tool was developed by using the two finishing processes of burnishing and electrochemical finishing. The finishing tool design included a burnishing tool and an electrode as a bore surface finish improvement, which goes beyond traditional boring by utilizing the continuous processes of burnishing and electrochemical finishing. Only a short time is required to make the bore surface smooth and bright with the use of these continuous finishing processes. The experimental results show that the large current rating is closely concerned with the fast feed rate of the finishing tool and is advantageous to the finishing processes. A small end radius or a small thickness of the electrode provides a more sufficient discharge, which is advantageous for the finish. The finishing effect is better with a high rotational speed of the finishing tool, since the dregs discharge the electrochemical machining, and burnishing becomes easier, which is also advantageous to the finishing processes. The finishing time using continuous current was not as prolonged as with the pulsed current.     

Synchronous finishing processes using a combination of grinding and electrochemical smoothing on end-turning surfaces

A new finishing mode has been utilized as an effective finishing tool design with an electrode and a nonconductive grindstone to execute grinding and electrochemical smoothing synchronously. This mode can be used for various end-turning operations. Through simple equipment attachment, grinding and electrochemical smoothing can follow the cutting process on the same machine. Among the factors affecting electrochemical smoothing, grinding performance combined with electrochemical smoothing, is primarily discussed. In the experiment, different types of electrodes are used with continuous and pulsed direct current. The control factors include die material, chemical composition, and concentration of the electrolyte. The experimental parameters are finish tool and workpiece rotational speed, flow rate of electrolytes, gap width between electrode and workpiece, electrical current density and pulsed period, and finishing tool geometry. High workpiece and electrode rotational speed produces a better finish. A thin electrode is associated with higher current density and provides larger discharge space for a better finish. Pulsed direct current can promote the effect of electrochemical finishing. Decreasing the height of the finish tool to a partial-form tool is associated with less restricted electrolyte flow and more discharge space, which creates better finishes than the full-form tools. The grindstone, with an adequately convex shape, also appeared to have an adequate initial gap width between the electrode and workpiece, which matches enough current density and obtains a better finish. The most effective geometric design for the finishing tool and the advantage of the low-cost equipment in electrochemical smoothing, following end-turning, is investigated in this study.     

Design of continuity processes of electrochemical finishing and grinding following turning

A newly designed finishing process utilizing an effective electrode and a grinding tool to execute the continuous electrochemical finishing and grinding processes following turning is described in this paper. The proposed process can be used for a variety of turning operations. Electrochemical finishing and grinding can be performed following the finishing process on the same machine by using a simple attachment. The factors affecting electrochemical finishing, grinding performance, and electrochemical finishing are discussed. The electrode was tested with both continuous and pulsed direct current. A higher work piece rotational speed produced a better finish. Changing the electrode design from a semicircle to a wedge form with a small end radius caused the electrolytic products and heat to dissipate more rapidly and provided the best finishing. Pulsed direct current finishing was slightly better than using continuous direct current finishing. However, the use of pulsed current would increase machining time and cost. This paper was recommended for publication in revised form by Associate Editor Dae-Eun Kim Dr. P.S. Pa obtained his doctorate at National Tsing Hua University, Taiwan. Presently he is an Associate Professor at Graduate School of Toy and Game Design of National Taipei University of Education. His fields of interest are innovative design and manufacturing processes. His current research includes ECM process for mould and die materials, precision finishing, toy design, and electro-optical engineering.     

Ball burnishing of tool steel

In place of the traditional methods of finishing a surface, the ball-burnishing process was investigated. Experimental work was conducted on a vertical machining center to establish the effects of various burnishing parameters on the surface finish of ASSAB XW-5 steel (high-carbon, high-chrome steel), including burnishing speed, ball material, lubricant, burnishing forces (depth of penetration), and feed. Within the parameter space explored, it was found that the burnishing speed affects the surface finish, with a burnishing speed of 1,200 mm/min giving the worst surface finish. WC (Tungsten carbide) ball gave the best and most consistent surface finish. Grease was a better lubricant than cutting oil. By varying the burnishing speed, the burnishing forces varied also, and these forces showed no obvious relationship to the surface finish of the burnished workpiece.     

Design of effective plate-shape electrode in ultrasonic electrochemical finishing

This research provides a process of ultrasonic aided electrochemical finishing using a low-cost electrode with high efficiency. It requires no expensive special-purpose equipment or high material removal as the conventional ECM does. It offers fast improvement of the surface roughness of the workpiece and is a new area in ECM. In the current study, the electrochemical finishing is classified into electrochemical smoothing and electrobrightening, higher electrical current is not required when an effective plate-shape electrode is used to reduce the response area. This process can be used for various turning operations including profiling, form turning, and flute and thread cutting. Through simple equipment attachment, electrochemical smoothing and electrobrightening can follow the cutting on the same machine and chuck. The controlled factors include the chemical composition and concentration of the electrolyte, the initial gap width, and the flow rate of electrolyte. The experimental parameters are the current density, rotational speed of the workpiece, on/off period of pulsed current, frequency and power level of ultrasonics, and the electrode geometry. Smaller end radius and smaller angle of declination are associated with higher current density and provides larger discharge space and better polishing effect. The electrode of inclined plane with slant discharge flute performs the best. The average effect of the ultrasonics is better than the pulsed current while the machining time needs not to be prolonged by the off-time. It was also found that electrobrightening after precise turning needs quite a short time to make the workpiece smoothing and bright, and the electrochemical smoothing saves the need for precise turning, making the total process time less than the electrobrightening.     

Effects of ball burnishing parameters on surface finish—A literature survey and discussion

Ball burnishing, a plastic deformation process, is becoming more popular as a finishing operation. A literature survey and discussion on the effects of the various types of burnishing (normal, vibratory and ultrasonic) and related parameters—force, speed, feed-rate, lubrication, ball material and diameter, workpiece material, pre-machined roughness and frequency of oscillation—on the final surface roughness are presented. The effect is an interaction between the process parameters with burnishing force and feed-rate as the two most significant factors. A particular surface finish can be obtained by appropriate selection of the parameters     

Prediction of surface characteristics obtained by burnishing

To reduce the irregularities of machined surface, burnishing is used as a finishing process by plastic deformation. This process does not only improve surface finish but also generates compressive residual stresses throughout the surface. In this work, an analytical study and a finite element modelling were performed to provide a fundamental understanding of the burnishing on an AISI 1042 workpiece. The analytical results were concentrated on the surface roughness and on some burnishing parameter effects. The simulations were devoted to the study of the surface profile, the residual stresses and the influence of burnishing parameters (penetration depth, feed rates, diameter of the ball of burnishing tool and initial surface quality) on surface roughness and the residual stress distribution. It has been noted that burnishing improves surface quality and introduces compressive residual stresses. These results were successfully compared to experimental data obtained in previous works.     

Design and fabrication of a novel polishing tool for finishing freeform surfaces in magnetic field assisted finishing (MFAF) process

Surface finish is a critical requirement for different applications in industries and research areas. Freeform surfaces are widely used in medical, aerospace, and automobile sectors. Magnetic field assisted finishing process can be used very efficiently to finish freeform surfaces. In this process, magnetorheological fluid is used as the polishing medium and permanent magnet is used to control its rheological properties to generate finishing force during polishing. To avail sufficient magnetic field in the finishing zone, it is necessary to design an optimum polishing tool. In the present study, a specially designed polishing tool is designed using a finite element based software package (Ansys Maxwell^®) based on Maxwell equations. At first, dimension of the permanent magnet is determined for designing optimum tool geometry. After that, dimension and configuration of the magnet fixture are optimized. A special type of metal named mu-metal which is a nickel-iron based alloy is selected for magnet fixture due to its magnetic-field shielding property. Mu-metal directs the magnetic flux lines in such a way that in the finishing zone the magnetic flux can be concentrated on the workpiece surface required for finishing. Also, the Mu-metal magnet fixture shields the magnetic field from outside environment so that MR fluid as well as any surrounding magnetic materials do not stick to the polishing tool. Experiments are carried out to validate the Maxwell simulation results to compare the magnetic flux distribution on the workpiece surface which shows good agreement between them. Also, finishing of flat titanium workpieces are carried out and it is found that the novel polishing tool has the capability to finish the workpieces in the nanometer range.     

Nanofinishing of freeform surfaces (knee joint implant) by rotational-magnetorheological abrasive flow finishing (R-MRAFF) process

Freeform complex surfaces have become an inevitable part of many devices to perform specific functions. Some of these components require nanolevel surface roughness value to meet the desired requirements in their applications. Finishing of freeform surfaces to nanometer surface roughness value is always difficult for any process. Rotational-magnetorheological abrasive flow finishing (R-MRAFF) process has been applied so far for finishing internal surfaces of relatively simple geometry. In this work, an attempt has been made to improve external topography of freeform surfaces using this process. Large hydrodynamic pressure coupled with magnetic fluid is the principal idea behind these experiments. A smooth mirror like finished surface is achieved with improved finishing rate (nanometer/min) by controlling two motions (axial and rotational) simultaneously on stainless steel workpiece similar to knee joint implant. Magnetorheological polishing fluid with different mesh sizes of abrasive particles and at different extrusion pressures is used to reduce final surface roughness value, to increase uniformity of surface finish on the freeform surface and to enhance finishing rate. Surface roughness ranging from 35 to 78 nm is achieved at various locations as compared to larger variation in Ra value obtained in the earlier research work.     

Design of rib plate of electrode in electrochemical smoothing and electrobrightening of large hole

This study discusses the improvement of surface finish of medium or large holes beyond traditional drilling, boring, rough turning, or extruding by electrochemical smoothing using inserted rib-plate electrodes. High electrical current is not required when the rib plate is used to reduce the engaged area for large hole. Traditionally, the hole polishing requires a sequence of complicated premachining or scarce manual skill. In the current experiment, six types of electrode are completely inserted and connected to both continuous and pulsed direct currents. The controlled factors include the chemical composition and the concentration of the electrolyte, and the diameter of the electrode. The experimental parameters are the current density, on/off period of pulsed current, rotational speed of electrode, and the electrode geometry. For the inserted electrodes, a thin rib plate with small wedge angle towards the root of the plate provides more sufficient discharge space, which is advantageous for polishing. The electrode of single plate performs better than the double-plate electrode. The electrode of a single plate with slant discharge flute performs the best polishing effect. Pulsed direct current can slightly improve the polishing effect at the expense of increased machining time and cost. It was also found that electrobrightening after reaming or precise turning uses quite a short time to make the hole bright, and the electrochemical smoothing saves the need for reaming or precise turning, making the total process time less than the electrobrightening.     

Automated surface finishing of plastic injection mold steel with spherical grinding and ball burnishing processes

This study investigates the possibilities of automated spherical grinding and ball burnishing surface finishing processes in a freeform surface plastic injection mold steel PDS5 on a CNC machining center. The design and manufacture of a grinding tool holder has been accomplished in this study. The optimal surface grinding parameters were determined using Taguchi’s orthogonal array method for plastic injection molding steel PDS5 on a machining center. The optimal surface grinding parameters for the plastic injection mold steel PDS5 were the combination of an abrasive material of PA Al₂O₃, a grinding speed of 18000 rpm, a grinding depth of 20 μm, and a feed of 50 mm/min. The surface roughness R_a of the specimen can be improved from about 1.60 μm to 0.35 μm by using the optimal parameters for surface grinding. Surface roughness R_a can be further improved from about 0.343 μm to 0.06 μm by using the ball burnishing process with the optimal burnishing parameters. Applying the optimal surface grinding and burnishing parameters sequentially to a fine-milled freeform surface mold insert, the surface roughness R_a of freeform surface region on the tested part can be improved from about 2.15 μm to 0.07 μm.     

Differential finishing of freeform surfaces (knee joint) using R-MRAFF process and negative replica of workpiece as a fixture

It is difficult and challenging to achieve uniform nanoscale surface finish in the contact zone, particularly on freeform (or sculptured) surfaces having different curvatures at different locations. Femoral (or, Knee joint component) is one of such biomedical freeform component which has complex profile along its curvature. Surface conditions of a femoral decide the life of the implant and they play a crucial role in its functionality. The variation in surface roughness of the femoral should be minimum in the contact zone. For this purpose, a special tooling is being proposed for rotational magnetorheological abrasive flow finishing (R-MRAFF) process. A negative replica of the workpiece (knee joint) as a tool (or a fixture) is used so that the medium flow velocity in the fluid flow channel is almost constant (or minimum possible variations) along the medium flow direction. It is able to do differential finishing also along the curvature. In addition, pulsating magnetic field has been used to generate vibrations in the medium in the finishing zone so that the possibility of fresh abrasive particles interacting with the surface of femoral is high. The surface finish has been achieved ranging from 26 nm to 62 nm using the proposed finishing technique and negative replica of the workpiece (femoral) as a fixture.     

IMPROVEMENTS IN THE SURFACE CHARACTERISTICS OF STAINLESS STEEL WORKPIECES BY BURNISHING WITH AN AMORPHOUS DIAMOND-COATED TIP

Burnishing is a cold working process that can be used to improve surface finish and surface hardness of workpieces. Conventionally, diamond or hard metal burnishing tools are used. In the present work, a novel burnishing tool was created by depositing amorphous diamond coating (AD) on a stainless steel tip. This tool was used to improve the surface finish and surface hardness of Nitronic-50 HS stainless steel workpieces. Nitronic-50 HS is used in a wide range of applications in industry. The burnishing process was carried out at different burnishing parameters (force, revolution speed, feed and number of tool passes). Burnishing parameters had a significant effect on the finishing process and they had to be optimized to achieve the best results. Remarkable improvements in surface finish (70% decrease in roughness) and hardness (25% increase) could be achieved with this tool and process in the surface finishing of Nitronic-50 stainless steel workpieces. From the tribological point of view, the AD-coated tip performed slightly better than a corresponding tip modified from a commercial polycrystalline diamond tip. AD coating seems to be very suitable for use in mechanical surface finishing tools such as a burnishing tip.     

<Emphasis Type="Bold">Effective Form Design of Electrode in Electrochemical Smoothing of Holes</Emphasis>

This study discusses electropolishing of holes using feeding electrodes as well as inserted electrodes for several common die materials. Traditionally, the hole polishing of a die requires a sequence of complicated premachining operations or scarce manual skill. In the current experiment, eight types of electrode are used and supplied with both continuous and pulsed direct current and another eight types of electrode are fed into holes using continuous direct current. The design features of the electrodes are of major interest for the effective electrochemical of holes. The controlled factors include the diameter of the electrode as well as the chemical composition and the concentration of the electrolyte. The experimental parameters are current density, current rating, electrode design, die material, rotational speed and feedrate of the electrode. For inserted electrodes, an electrode with a helical discharge flute performs better than one without a flute or with a straight flute. Pulsed direct current can improve the polishing effect at the expense of increased machining time and cost. For feeding electrodes, an electrode of a borer type performs better than one with a cycle lap on the leading edge. It was also found that electrobrightening after reaming needs only a short time to make the hole bright, and electropolishing saves the need for reaming, making the total process shorter than for electrob-rightening.     

Effect of hybrid electrochemical smoothing–roller burnishing process parameters on roundness error and micro-hardness

In this paper, a novel finishing process, which integrates the merits of electrochemical smoothing (ECS) and roller burnishing (RB) for minimizing the roundness error and increasing surface micro-hardness of cylindrical parts, is proposed. Through simple equipment attachments, electrochemical smoothing–roller burnishing (ECS–RB) can follow the turning process on the same machine. To explore the optimum combinations of the ECS–RB process parameters in an efficient and quantitative manner, the experiments were designed on the basis of the response surface methodology technique. The effect of ECS–RB parameters, namely, burnishing force, applied voltage, inter-electrode gap, and workpiece rotational speed on the roundness error and surface micro-hardness was studied. From the multi-objective optimization, the optimal combination of parameter settings are burnishing force of 350 N, applied voltage of 8.2 V, inter-electrode gap of 2.75 mm, and rotational speed of 970 rpm for achieving the required lower roundness error and higher surface micro-hardness. Surface micro-hardness considerably increases about 31.5% compared to the initial surface micro-hardness, and about 2.32 μm roundness error can be achieved using the optimum combination of process parameters. Therefore, the combination of ECS and RB is a feasible process by which it potentially reduces roundness error and surface micro-hardness of axis-symmetric parts improving their reliability and wear resistance.     

Investigating the Tribological Characteristics of Burnished Polyoxymethylene—ANFIS and FE Modeling

ABSTRACT

Polymers are utilized in numerous tribological applications because of their excellent characteristics; for example, accommodating shock loading and shaft misalignment. A high surface finish is required to ensure consistently good performance and extended service life of manufactured polymeric components. Burnishing is the best choice as a finishing process for this study due to its ability to increase hardness, fatigue strength, and wear resistance and also introduce compressive residual stress on the burnished workpiece. Due to the complexity and uncertainty of the machining processes, soft computing techniques are preferred for anticipating the performance of the machining processes. In this study, ANFIS as an adaptive neuro-fuzzy inference system was applied to anticipate the workpiece hardness and surface roughness after the roller burnishing process. Five burnishing variables, including burnishing depth, feed rate, speed, roller width, and lubrication mode, were analyzed. A Gauss membership function was used for the training process in this study. The predicted surface roughness and hardness data were compared with experimental results and indicated that the Gauss membership function in ANFIS has satisfying accuracy as high as 97% for surface roughness and 96% for hardness. Furthermore, the generated compressive residual stress on the burnished surface was studied by a 2D finite element model (FEM). The simulated results of residual stress were validated with the experimental results obtained from X-ray diffraction (XRD) tests.     

EQUIVALENT NORMAL CURVATURE APPROACH MILLING MODEL OF MACHINING FREEFORM SURFACES

A new milling methodology with the equivalent normal curvature milling model machining freeform surfaces is proposed based on the normal curvature theorems on differential geometry. Moreover, a specialized whirlwind milling tool and a 5-axis CNC horizontal milling machine are introduced. This new milling model can efficiently enlarge the material removal volume at the tip of the whirlwind milling tool and improve the producing capacity. The machining strategy of this model is to regulate the orientation of the whirlwind milling tool relatively to the principal directions of the workpiece surface at the point of contact, so as to create a full match with collision avoidance between the workpiece surface and the symmetric rotational surface of the milling tool. The practical results show that this new milling model is an effective method in machining complex three- dimensional surfaces. This model has a good improvement on finishing machining time and scallop height in machining the freeform surfaces over other milling processes. Some actual examples for manufacturing the freeform surfaces with this new model are given.     

Effects of working parameters on surface finish in ball-burnishing of hardened steels

Burnishing is a chipless finishing method, which employs a rolling tool, pressed against the workpiece, in order to achieve plastic deformation of the surface layer. Recent developments made possible burnishing of heat-treated steel components up to 65 HRC. Features of burnishing include a good roughness (comparable to grinding), as well as improvement of mechanical characteristics of the surface (fatigue strength, corrosion resistance, and bearing ratio), due to implementation of compressive stresses into the surface layer. This paper will present influences of certain burnishing parameters upon roughness, for a hardened steel component (64 HRC).     

Development of a new magnetic abrasive finishing process with renewable abrasive particles using the circulatory system

In order to improve the finishing efficiency of the Magnetic Abrasive Finishing process, we proposed a new MAF process with renewable abrasive particles using compound magnetic finishing fluid circulatory system in this paper. This new finishing process has a circulating system that uses a conveyor belt to renew the mixed abrasive particles. This not only maintains the stability of the finishing but also ensures that the processing does not need to be interrupted. In this study, we investigated the magnetic field distribution, finishing force, and finishing behavior of the processing area. Furthermore, we designed experimental device to finish the sus304 stainless steel plate, to verify the feasibility of this process and understand its characteristics through processing experiments. Moreover, the influence of important process parameters, including magnetic particles, abrasive particles, conveyor belt line speed and working gap, on the surface quality of the workpiece is studied through the experiment. The experimental results indicate that the present process can achieve stable processing of the material surface without interruption, and the surface roughness of the sus304 stainless steel plate has been improved from 273 nm to 23 nm through this process.     

Ultra-precision grinding of hard steels

Hardened bearing steel, M50, has been ultra-precision ground to produce an optical quality surface (<10 nm R_a) using a novel ultra-stiff machine tool, Tetraform ‘C’. It has been shown that a repeatable surface finish of <10 nm R_a can be produced using a 76 μm CBN grit and 500 μm wheel depth of cut. This represents a significant improvement over previous published work using conventional precision machine tools where nanometre surface finish can only be obtained at the expense of process efficiency.

The development of optical quality surfaces is considered in terms of the processes occurring in the primary and secondary finishing zones of the cup-wheel, with the final surface finish enhanced by the burnishing action of worn CBN grits. It is shown that surface finish is limited by the pull-out of carbides in the secondary finishing zone. However, this can be overcome by using electrolytic in-process dressing (ELID), which maintains CBN grit protrusion and sharpness. This promotes cutting of the carbides at the ground surface and ensures a high level of surface integrity although the burnishing action of grits is reduced resulting in a slightly higher roughness for the steel matrix.