Hole Wall Surface Research Articles

Compound Finish Processes Using Grinding and Ultrasonic Electropolishing on Hole-Wall Surface

This study using ultrasonic energy transmitted into the electrolyte to assist in discharging of electrolytic product out of the machining gap in the compound finishing processes of grinding and electropolishing on hole-wall surface beyond traditional process of holes machining instead of conventional hand or machine polishing. The compound processes of grinding and ultrasonic electro polishing just require a short time to make the hole-wall surface smooth and bright in the current study. The design polishing tool includes a grinding-tool and an electrode as a hole-wall surface finish improvement that goes beyond traditional rough boring. In the experiment, the polishing tool travels across the hole-wall surface with continuous or pulsed direct current. The experimental results show that the large supply of current rating is effectively to reach the amount of the material removal and is advantageous to the finishing processes. The average effect of the ultrasonic is better than the pulsed current while the machining time needs not to be prolonged by the off-time. The finish effect is better with a high rotational speed of the polishing tool because the dregs discharge of electrochemical finishing becomes easier and is also advantageous to the finish.

Characteristics of chip formation in the micro-drilling of multi-material sheets

In order to meet the requirements of electronic product miniaturisation, the use of thinner and smaller printed circuit boards (PCBs) will be required. To achieve this, many more micro-holes must be drilled in a smaller area than before. PCBs are anisotropic multi-material sheets consisting of a dielectric layer (resin/glass fibre cloth) and a high purity metal conductor (copper foil). It is difficult to achieve high machining precision, surface quality, drilling efficiency and long drill life when drilling PCB micro-holes. In this study, micro-drills with a diameter of 0.1 mm were used to drill the PCBs at rotational speeds of up to 300 krpm. The drilling process was digitally photographed. The chip morphology and the hole wall were observed. The quality of the hole wall, such as hole wall roughness and nail head and exit burr formation were observed and measured. The influence of drilling condition on the drilling process and hole quality were studied. It was found that the morphology of the chips and the hole wall surface depended on the material properties of the printed circuit board. Chips were formed normally as conical helical chips from the aluminium entry board, conical helical chips from the copper foil and discontinuous chips from the glass fibre and softened resin. The hole wall through the copper foil seemed much smoother than that of resin/glass fibre cloth layer. However, nail heads and burrs were formed at the copper foil layers, which decreased the hole quality. Chip morphology and hole quality were affected by feed rate, spindle speed and tool wear. The basic removal mechanism of the PCB micro-holes was analysed, and this study provided a firm foundation for further work in this area.

High Air Pressure in MQL Deep Hole Drilling Workpiece Temperature

This study investigates the effect of air pressure on workpiece temperature in through tool minimum quantity lubrication (MQL) deep-hole drilling. Experiments on 200 mm deep holes drilled by a 10 mm carbide drill were conducted under regular (500 kPa) and high (1000 kPa) air pressure conditions. Torque data shows that the chip clogging problem occurring under regular air pressure can be solved by the high air pressure. An inverse heat transfer method is utilized to quantify the heat fluxes and calculate the temperature distribution during drilling based on embedded thermocouples along the depth. Results show that temperature around the hole increases rapidly when the chips start accumulating in the hole under regular air pressure and cause high heat flux on the drilled hole wall surface. The high pressure condition, prevents chip accumulation, thus reducing the total heat flux.

Grinding Finishing Merging Electropolishing on Hole-Wall Surfaces

The current study presents a method for finishing hole-wall surfaces, superior to that obtainable by traditional boring, using a simultaneous grinding and electropolishing process. A specially designed finishing tool, that includes a nonconductive grinding wheel and an electrode is employed in the process. The form of the tool and the machining process are different from those used in electrochemical grinding (ECG). A high power electrical supply is not required with this design of finishing tool because the axial feed allows for the use of a smaller interactive area between the electrode and the hole wall surface. The experimental results show that a high current flow combined with a fast axial feed rate for the tool is an important advantage to the finishing process. The finishing effect is better with high rotational tool speeds because discharge of the electropolishing dregs and grinding cuttings becomes more efficient and this is also advantageous to the grinding finishing process. Pulsed direct current can slightly improve the electrochemical finishing effect, but machining takes longer and this raises costs. A small edge radius on the electrode also provides more than sufficient discharge and gives a better finish. We intend to make a complete evaluation of the processing parameter data so that the use of this method for hole-wall surface finishing may be extended in the future. The combined application of grinding and electropolishing is crucial to this method and the specially designed tool and the new finishing process are highly efficient and inexpensive.

Synchronous finish module using completely inserted finish-tool on hole-wall surfaces

In this study, a novel completely inserted finish-tool is developed to execute the synchronous processes of electrochemical finishing and burnishing. The design finish-tool includes a burnishing-tool and an electrode for hole-wall surface finish improvement of the workpiece surface quality resulting from such a combination of synchronous finish-processes is verified with the experimental results shown here. The synchronous processes require a short time to make the hole-wall surface smooth and bright. Future experiments will result in a complete understanding of the processing parameters involved, allowing for an effective evaluation of the processing features to apply propagation to the hole-wall surface finish.

Design of a Simultaneous Module Using Burnishing and Electrofinishing on Hole-Wall Surface

This study discusses a method for increasing the efficiency and speed with which an improvement in surface roughness of a hole-wall surface can be achieved. The surface after traditional machining is discussed as well as a method for finishing the hole-wall surface using a design of finish-tool that includes a nonconductive knothole-form burnishing-tool and a ring electrode to execute simultaneous burnishing and electrofinishing (SBEF). By the dual and synchronous effect of the electrode and the burnishing-tool a superior hole-wall finish is achieved. In the experiment, the use of a small arc rounding radius and a thin finish-tool is advantageous to the finishing effect. A high rotational speed of the finish-tool produces a better finish. A high current and a faster finishing tool feed is also effective in gaining a rapid improvement of the roughness of the hole-wall surface and is recommended from the results of the current study.

Design of a Simultaneous Module Using Burnishing and Electrofinishing on Hole-Wall Surface

This study discusses a method for increasing the efficiency and speed with which an improvement in surface roughness of a hole-wall surface can be achieved. The surface after traditional machining is discussed as well as a method for finishing the hole-wall surface using a design of finish-tool that includes a nonconductive knothole-form burnishing-tool and a ring electrode to execute simultaneous burnishing and electrofinishing (SBEF). By the dual and synchronous effect of the electrode and the burnishing-tool a superior hole-wall finish is achieved. In the experiment, the use of a small arc rounding radius and a thin finish-tool is advantageous to the finishing effect. A high rotational speed of the finish-tool produces a better finish. A high current and a faster finishing tool feed is also effective in gaining a rapid improvement of the roughness of the hole-wall surface and is recommended from the results of the current study.

Jet impingement onto a tapered hole: Influence of jet velocity and hole wall velocities on heat transfer and skin friction

AbstractJet impingement onto a hole with elevated wall temperature can be associated with the high‐temperature thermal drilling, where the gas jet is used for shielding the hole wall from the high‐temperature oxidation reactions as observed in the case of laser drilling. In laser processing, the molten flow from the hole wall occurs; and in the model study, the hole wall velocity resembling the molten flow should be accounted for. In the present study, gas jet impingement onto tapered hole with elevated temperature is considered and the heat transfer rates as well as skin friction at the hole wall surface are predicted. The velocity of molten flow from the hole wall determined from the previous study is adopted in the simulations and the effect of hole wall velocity on the heat transfer rates and skin friction is also examined. It is found that the Nusselt number and skin friction at the hole wall in the regions of hole inlet and exit attain high values. The influence of hole wall velocity on the Nusselt number and skin friction is found not to be very significant. Copyright © 2008 John Wiley & Sons, Ltd.

Synchronous Finish Processes Using Grinding and Ultrasonic Electrochemical Finishing on Hole-Wall Surface

The current study using ultrasonic energy transmitted into the electrolyte to assist in discharging of electrolytic product and cuttings out of the machining gap in the synchronous finish processes of grinding and electrochemical finishing on hole-wall surface beyond traditional process of holes machining instead of conventional hand or machine polishing. The design finish-tool includes a grinding-tool and an electrode as a hole-wall surface finish improvement that goes beyond traditional rough boring. In the experiment, the finish-tool is completely inserted to the hole; the electrode is used with continuous or pulsed direct current. The electrode form and the machining process are obviously different from electrochemical grinding (ECG). The experimental results show that the large supply of current density is effectively to reach the amount of the material removal and is advantageous to the finish processes. The finish effect is better with a high rotational speed of the finish-tool because the dregs and cuttings discharge of electrochemical finishing and grinding becomes easier and is also advantageous to the finish. The average effect of the ultrasonics is more better than the pulsed current while the machining time needs not to be prolonged by the off-time. The synchronous processes of grinding and ultrasonic electrochemical finishing just require a short time to make the hole-wall surface smooth and bright.

Compound Finish Processes Using Burnishing and Ultrasonic Electrochemical Finishing on Hole-Wall Surface

This study using ultrasonic energy transmitted into the electrolyte to assist in discharging of electrolytic product out of the machining gap in the compound finishing processes of electrochemical finishing and burnishing on hole-wall surface beyond traditional process of holes machining instead of conventional hand or machine polishing. The design finish-tool includes a burnishing-tool and an electrode as a hole-wall surface finish improvement that goes beyond traditional rough boring. In the experiment, the finish-tool travels across the hole-wall surface with continuous or pulsed direct current. The experimental results show that the large supply of current rating is effectively to reach the amount of the material removal and is advantageous to the finishing processes. The average effect of the ultrasonic is more better than the pulsed current while the machining time needs not to be prolonged by the off-time. The finish effect is better with a high rotational speed of the finish-tool because the dregs discharge of electrochemical finishing becomes easier and is also advantageous to the finish. The compound processes of burnishing and ultrasonic electrochemical finishing just require a short time to make the hole-wall surface smooth and bright.

Experimental Investigation of Intermittent Rotary Ultrasonic Machining

Rotary ultrasonic machining (RUM) is considered as an effective machining method, which has been utilized to machine hard and brittle materials such as advanced ceramics. In order to improve the hole wall surface quality during RUM, it is important to wash away swarf in the gap between the tool and the workpiece as fast as possible. In this paper, a new machine process – intermittent rotary ultrasonic machining (IRUM) – is introduced for the first time. The cutting force, surface roughness and coolant flow rate in conventional rotary ultrasonic machining (CRUM) process and IRUM process are compared. It is found that compared with CRUM, the output coolant flow rate could be increased significantly by using the IRUM method. It is also found that the surface roughness of workpiece can be improved significantly in IRUM.

Using Borer-Shape Electrode in Electrochemical Smoothing of Hole

The current study discusses the improvement of surface finish of enlarge hole wall surface beyond traditional rough boring by electrochemical smoothing using different types of feeding electrodes. Higher electrical current is not required when the design electrode is used to reduce the response area for hole. In the experiment, six types of electrode are used with the application of continuous direct current and axial electrode feed. The controlled factors include the chemical composition and the concentration of the electrolyte, and the diameter of the electrode. The parameters are current rating, electrode geometry, die material, electrode rotational speed and feed rate. It was found that the electrobrightening after precise turning requires quit short working time, while the electrochemical smoothing saves the need for reaming or precise turning, thus makes the total cycle time less than electrobrightening. Smaller end radius of borer tip is associated with higher current density and provides faster feed rate and better polishing effect. A borer type electrode with small inclined angle toward to the cylinder provides more sufficient discharge space, which is advantageous for polishing. The electrode of oneside borer tip performs the best polishing effect in the current investigation.