Micromachining of Metals, Alloys and Ceramics by Picosecond Laser Ablation

Microhole drilling and microstructure machining with a picosecond (ps) Nd:YVO4 laser (pulse duration of 10 ps) in metals, alloys and ceramics are reported. Blind and through microholes were drilled by percussion drilling as well as trepanning drilling. The diameters of the holes were in the range from 20 μm to 1000 μm. Microfeatures were machined and the flexibility of ps laser machining was demonstrated. The quality of drilled holes, e.g., recast layer, microcrack and conicity, and that of the microstructures, were investigated by optical microscope, surface profilometer, or scanning electron microscope (SEM). Ps laser ablation rate was investigated by experiments as well as a simplified laser ablation model.

Fatigue Crack Growth Behavior of High Carbon Steel (SM53C) by Using Induction Hardening

Recently, with the high performance and efficiency of machine, there have been required the multi-functions in various machine parts, such as the heat resistance, the abrasion resistance and the stress resistance as well as the strength. Fatigue crack growth tests were carried out to investigate the fatigue characteristics of high carbon steel (SM53C) experienced by high-frequency induction treatment. The influence of high-frequency induction treatment on fatigue limit was experimentally examined with the special focus on the variation of surface microstructure and the fatigue crack initiation and propagation through fractography. Also, the shape of hardening depth, hardened structure, hardness, and fatigue-fracture characteristics of SM53C composed by carbon steel are also investigated.

Force/Velocity Control of a Pneumatic Gantry Robot for Contour Tracking With Neural Network Compensation

In this paper, the application of a pneumatic gantry robot to contour tracking is examined. A hybrid controller is structured to control the contact force and the tangential velocity, simultaneously. A previous study provided controller tuning and model validation results for a fixed gain PI-based force/velocity controller. Performance was limited by system lag and Coulomb friction. New results demonstrate that even with perfect friction compensation, the limiting factor is the system lag. A neural network (NN) compensator was subsequently developed to counter both effects. Results for straight and curved edged workpieces are presented to demonstrate the effectiveness of the NN compensator and the capabilities of a pneumatic gantry robot.

Embedding of Micro Thin Film Sensors Into Polycrystaline Cubic Boron Nitride (PCBN) for Potential Tooling Applications Via Diffusion Bonding

Polycrystalline cubic boron nitride (PCBN) is increasingly being used in manufacturing processes to increase tool life and processing speed. Existing sensors in PCBN tools are unable to provide accurate time- and space-resolved measurements of the thermo-mechanical phenomena at and near the tool-work interface. Using microfabrication techniques along with diffusion bonding, thin film palladium-13wt% chromium (PdCr) alloy micro strain gage sensors were successfully embedded into PCBN structures for potential tooling applications. This article reports on the design, fabrication and characterization of a sensor consisting of three PdCr sensing elements embedded into a PCBN sample. The embedded sensors show good linearity and sensitivity.

Characterization of a Nano-Composite Sensor in Multiple Environmental Domains

A sensor composed of a composite material formed of a polymer and nano-carbon conductive filler is characterized for measurement of pressure through the relationship to contact resistance. The sensor has the physical attributes of polymer, but is electrically conductive and can therefore be used on a conductive substrate to gauge pressure and subsequently load. Benefits over traditional force sensing include reduced cost, full control of geometry, reduced form factor, resistance to impact and to corrosion. A test circuit was developed to study the behavior of the sensor at different loads and surface conditions, and behavior over time. Prospective applications on manufacturing and automotive fields are proposed.

A Comparative Study on the Effect of Surface Topography by Hard Turning vs. Grinding on Frictional Performance at Dry and Lubricated Sliding Contact

Machining-induced surface topography has a significant effect on tribological performance of machined components in sliding contact. However, the effect of different surface topography by turning versus grinding on tribological performance has received very little attention. In this study four types of surface topography by turning and grinding AISI 52100 bearing steel (62 HRc) were prepared and characterized to study its effect on friction and wear in sliding contact. Dry and lubricated reciprocating sliding wear tests with an on-line acoustic emission (AE) sensor were carried out using a ball-on-disk tribometer. The experimental results have shown that: (i) the turned surfaces, regardless of the presence of a white layer, yield smaller friction of coefficients in sliding along feed marks than across sliding at both dry and lubricated conditions. However, the opposite hold true for the ground surfaces; (ii) friction of coefficients (0.6∼0.8) at dry conditions is higher for both turned and ground fresh surfaces than their white layer counterparts regardless of sliding direction. At lubricated conditions, Friction of coefficients (0.1∼0.12) are smaller for the both turned and ground fresh surfaces than the white layer surfaces in along sliding, while it is equivalent in across sliding; (iii) the trends of acoustic amplitude amplitude are consistent with those of frictional coefficients for the turned or ground surfaces at dry conditions. Similar trends are also true for the turned surfaces at lubricated conditions, but not for the ground surfaces; and (iv) the wear debris on the track may act as solid lubricants to reduce the sliding frictional coefficient. Machining induced white layers leads to a better wear resistance than the fresh surfaces in either along or across sliding.

Viscoelasticity Effects of Polymeric Material in Micro Injection Molding

An experimental study has been carried out to determine the effect of viscoelasticity in comparison to viscosity on micro-injection molded parts. In this study, two different polymeric materials — Polystyrene (PS) as a viscous material and High Density Poly-Ethylene (HDPE) as a viscoelastic material — have been selected to observe the effect of melt elasticity on the filling phase of micro molding based on cavity pressure of molded part. All process parameters except temperature are the same for both polymers. Process temperatures have been selected in order to match the viscosity for both polymers used. Polymer viscosity was characterized at different shear rate and temperature. Viscoelasticity of both polymers were investigated using rotational rheometry in the oscillation mode. The mold geometry with high aspect ratio has been used and the effect of viscoelasticity on cavity pressure has been discussed. It was observed that there is retardation on the response of pressure because of elastic response of material during filling. Despite the differences in slope, peak value, area, and cycle time between two curves, they share similar trends. The only difference is their response during solidifying because of material property.

Design of a Stamping Test for Investigating Surface Distortion in Sheet Metal Parts

Surface distortions/deflections are frequently introduced into the Class “A” surfaces during sheet metal stamping processes. However, the origins of the draw die related surface distortion/deflection have not been well understood. This paper presents our design of a stamping test for the investigation of the distortion phenomenon. Five geometric parameters are first identified to represent basic geometry of typical automobile outer panel depression features around the surface distortions. Experimental stamping dies are then designed to reflect various combinations of these five geometric parameters with the assistance of numerical simulations to ensure that the designed dies are able to replicate the surface distortion phenomenon. Also, real-time dynamic measurement techniques are designed to collect historical data of strains and deflection on the stamping panels. Our preliminary tryouts show that the designed stamping test successfully replicates the distortion phenomenon observed in production stamping processes. It provides a platform for the investigation of the root-cause of the draw die related surface distortions.

Damped Vibration Response at Different Speeds of Wire in Slurry Wiresaw Manufacturing Operations

Wiresaw has become a standard slicing tool especially for large ingots in the wafer preparation industry since late 1990s. To meet the requirements of the surface finish and topology, it is critical to control the process parameters to render good surface finish and to minimize kerf loss. The vibration of moving wire in the wiresaw manufacturing operation affects the wafer surface finish and kerf loss; therefore, the study and analysis of vibration of moving wire become very important and relevant to this manufacturing process. Built on the previous research, the free vibration response of axially moving wire with damping is a combination of infinite sets of response solutions, with trigonometric functions due to end constraints. The apparent damping due to the increase of speed on the first several components of responses will be presented and discussed in this paper. The results also show that the increase in speed will excite components of response except the dominating one. Since the free vibration response is a combination of infinite sets of solutions, it is not possible for the system to be completely critically-damped or over-damped because of the existence of under-damped modes at higher order. Therefore, a damped index is introduced to help in understanding the behavior of such system. When the physical damping is increased (for example, by using a more viscous carrier fluid in slurry), all components are more damped accordingly. However, in addition to the physical damping, the apparent damping caused by the increase of wire speed will also damp out the response. These two parameters, physical damping and apparent damping, control the behavior of an axially moving wire. This is a new finding in vibration analysis of moving wire that, to our best knowledge, has not been reported in the previous literature.

Enhancing Safety in Manufacturing Systems by Integrating Diagnostic Information

Integrating traditionally separate industrial control systems can derive factory-wide benefits by leveraging more information about the ongoing process. This paper shows that connecting a networked safety system and a process control system leads to an extension of the individual benefits provided by each system. A safety system gains the ability to protect not only the machines and workers but also the product that is being built. A diagnostic system can also raise safety alarms when a process variable is outside the expected range of safe operation. This connection is explored to determine the practical impact of different methods of integration on machining and system processes. Three integration methods are possible depending on which portions of the system can be classified as “safe”. A case study integrating a diagnostics system as a non-safe sensor proves that this connection, when it is implemented on an industrial testbed, provides all of the benefits described and does not require significant changes to control software.