Localized Resistive Heating Research Articles

Smart hot stamping of ultra-high strength steel parts

Smart hot stamping processes of ultra-high strength steel parts have been developed to overcome difficulties in the present hot stamping process. Using rapid resistance heating, the stamping equipment became considerably simpler than that using furnace heating. The formability was improved by high speed hot stamping using a mechanical servo press in comparison with the conventional process using a hydraulic press. Parts having a different distribution of strength were produced by tailored die quenching using local bypass resistance heating. Die-quenched steel parts and ultra-high strength steel sheets were sheared by reducing the flow stress in the shearing zone using local resistance heating. An ultra-high strength steel gear drum was produced by hot spline forming using resistance heating of side wall of a cup. V-shaped hot forming using sealed air was developed to produce ultra-high strength hollow axle beams used for suspensions of automobiles. A one shot hot stamping process consisting of resistance heating, forming, shearing and die quenching was applicable to comparatively small high strength steel parts.

Direct integration of carbon nanotubes in Si microstructures

In this paper we present a low-cost, room-temperature process for integrating carbon nanotubes on Si microsystems. The process uses localized resistive heating by controlling current through suspended microbridges, to provide local temperatures high enough for CVD growth of carbon nanotubes. Locally grown carbon nanotubes make electrical connections through guidance by electric fields, thus eventually making circuits. The process is scalable to a wafer level batch process. Furthermore, it is controlled electrically, thus enabling automated control. Direct integration of carbon nanotubes in microstructures has great promise for nano-functional devices, such as ultrasensitive chemical sensors. Initial measurements demonstrate the Si–carbon nanotube–Si circuit's potential as a NH3 sensor.

Hard-coupled model of local direct resistance heating of thin sheets

A monolithic model of local direct resistance heating of thin sheets is presented. The model respects all material nonlinearities of the system such as the temperature dependences of physical properties of individual parts of the system. Numerical computations are performed by a finite element method of higher order of accuracy and realized by our own codes Hermes2D and Agros2D. The methodology is illustrated by a typical example, whose results are discussed.

Punching of small hole of die-quenched steel sheets using local resistance heating

A punching process of a small hole in a die-quenched steel sheet having high strength using local resistance heating of a shearing zone was developed to decrease the punching load. Uniform temperature in the circular shearing zone of the hole was obtained by optimising heating conditions for a pair of rectangular electrodes. The punch load and the burnished surface area for the heating at 500°C were about 1/3 smaller and 2 times larger than those for the cold punching, respectively, and the occurrence of delayed fracture around the punched hole was prevented by the heating above 500°C.

Punching of ultra-high strength steel sheets using local resistance heating of shearing zone

A punching process using local resistance heating of a shearing zone was developed to shear ultra-high strength steel sheets. The shearing zone was heated by passing electric current between the sheet holder and the knockout in order to decrease the flow stress in the shearing, and the heating of the die and punch was prevented by no contact with the sheet during the heating. Electrode pins having an individual spring were employed to attain uniform heating of the shearing zone. The welding resistance of the heads of the electrode pins to the sheet by the heating was examined for Ag–W, Cu–W, Ag + WC and W. The Cu–W pins having the highest welding resistance were employed in a punching experiment of 980 MPa level ultra-high strength steel sheets. The punching load was considerably reduced by the heating, e.g., about 1/5 of the cold punching load at 800 °C. As the heating temperature increased, the depth of the shiny burnished surface on the sheared edge increased and that of the rough fracture surface decreased.

超高張力鋼板の局部通電加熱穴抜き加工

A punching process using local resistance heating near a circular shearing band was developed to shear ultra high strength steel sheets. The shearing band was heated by the electrification between the sheet holder and the knockout in order to decrease the flow stress in the shearing, and the heating of the die and punch was prevented by eliminating contact with the sheet during the electrification. Electrode pins having a spring were employed to attain uniform heating of the shearing band. The degree of welding of the head of a Cu-W electrode pin to the sheet by the electrification was smaller than those of Ag-W, Ag+WC and W pins, and thus the Cu-W pins were employed in a punching experiment of 980 MPa level ultra high strength steel sheets. The punching load was considerably reduced by the heating, e.g., about 1/5 of the cold load at 800 °C. As the heating temperature increased, the depth of the shiny burnished surface on the sheared edge increased and that of the rough fracture surface decreased.

Rapid thermal lysis of cells using silicon–diamond microcantilever heaters

This paper presents the design and application of microcantilever heaters for biochemical applications. Thermal lysis of biological cells was demonstrated as a specific example. The microcantilever heaters, fabricated from selectively doped single crystal silicon, provide local resistive heating with highly uniform temperature distribution across the cantilevers. Very importantly, the microcantilever heaters were coated with a layer of 100 nm thick electrically insulating ultrananocrystalline diamond (UNCD) layer used for cell immobilization on the cantilever surface. Fibroblast cells or bacterial cells were immobilized on the UNCD/cantilever surfaces and thermal lysis was demonstrated via optical fluorescence microscopy. Upon electrical heating of the cantilever structures to 93 degrees C for 30 seconds, fibroblast cell and nuclear membrane were compromised and the cells were lysed. Over 90% of viable bacteria were also lysed after 15 seconds of heating at 93 degrees C. This work demonstrates the utility of silicon-UNCD heated microcantilevers for rapid cell lysis and forms the basis for other rapid and localized temperature-regulated microbiological experiments in cantilever-based lab on chip applications.

THERMAL MODEL FOR ELECTROMAGNETIC LAUNCHERS

This paper presents a 3D model for the determination of the temperature field in an electromagnetic launcher. The large amounts of energy that are dissipated into the structure of an electromagnetic launcher during short periods of time lead to a complicated thermal management situation. Effective thermal management strategies are necessary in order to maintain temperatures under acceptable limits. This paper constitutes an attempt to determine the temperature response of the launcher. A complete three-dimensional model has been developed. It combines rigid body movement, electromagnetic effects and heat diffusion together. The launcher consists of two parallel rectangular rails and an armature moving between them. Preliminary results show the current distribution on the rail cross-section, the localized resistive heating, and the rail transient temperature response. The simulation results are compared to prior work presented for a 2D geometry by Powell and Zielinski (2008).

Local heating method for growth of aligned carbon nanotubes at low ambient temperature

We use a highly localized resistive heating technique to grow vertically aligned multiwalled nanotube films and aligned single-walled nanotubes on substrates with an average temperature of less than 100°C. The temperature at the catalyst can easily be as high as 1000°C but an extremely high temperature gradient ensures that the surrounding chip is held at much lower temperatures, even as close as 1μm away from the local heater. We demonstrate the influence of temperature on the height of multiwalled nanotube films, illustrate the feasibility of sequential growth of single-walled nanotubes by switching between local heaters and also show that nanotubes can be grown over temperature-sensitive materials such as resist polymer.

In situ Raman studies of single-walled carbon nanotubes grown by local catalyst heating

Using in situ Raman spectroscopy we investigate single wall carbon nanotube growth on Mo electrodes, using a highly localized resistive heating technique. Small diameter semiconducting single wall nanotubes grow very rapidly when the catalyst support is heated to a temperature of 800 °C. The G/D ratio shows an interesting time-dependent behaviour. It first decreases, indicating the presence of amorphous carbon and then significantly increases again after ca. 5 min growth while retaining the position and shape expected for predominantly semiconducting carbon nanotubes.

Warm and hot punching of ultra high strength steel sheet

Warm and hot punching using resistance heating was developed to improve the quality of sheared edges of an ultra high strength steel sheet. As the heating temperature increased, the depth of the shiny burnished surface on the sheared edge increased and that of the rough fracture surface decreased. The rollover depth and burr height of the sheared edge became large above 800 °C. Although the roughness of the burnished surface was almost constant, the roughness of the fracture surface increased from 650 °C. The punching load was extremely reduced by the heating, i.e. 40% of the cold punching load at 650 °C and 15% at 1070 °C. The local resistance heating of the shearing region was efficient for the warm and hot shearing. It was found that the warm and hot shearing of ultra high strength steel sheets is effective for improving the quality of the sheared edge and in reducing the shearing load.

Thermal imaging of nickel wires with a fluorescent nanoprobe

We have developed a scanning thermal microscope (SThM) that uses a fluorescent particle glued at the end of an atomic force microscope tip as a thermal sensor. When a temperature change occurs, a modification of fluorescence is detectable, enabling measurement of local temperatures and rendering of thermal images. We describe the technique and demonstrate its capability to map surface temperatures by measuring the local resistive heating in a 500nm wide nickel wire.

Survey of the in situ configuration of cold-rolled, nickel-rich NiTi sheets to create variable component functions

An outstanding feature of shape memory alloys is their potential to produce different functional effects, like thermal shape memory or superelasticity in one component. The cold-rolled NiTi sheet strips presented in this study offer various options, since they do not feature perceptible thermal shape memory or superelasticity due to a high dislocation density. Instead, to achieve a specific local function, the sheet strips are subjected to in situ heat treatment carried out by a laser or a local resistive heating element. There is a need to adjust the duration and intensity of the heat input in order to obtain different functional properties.

Structural Integrity of Flat Silicon Panels for Nanosatellites: Modeling and Testing

Microsystem interfaces to the macroscopic surroundings and within the microsystems themselves are formidable challenges that this thesis makes an effort to overcome, specifically for enabling a spacecraft based entirely on microsystems. The NanoSpace-1 nanospacecraft is a full-fledged satellite design with mass below 10 kg. The high performance with respect to mass is enabled by a massive implementation of microsystem technology – the entire spacecraft structure is built from square silicon panels that allow for efficient microsystem integration. The panels comprise bonded silicon wafers, fitted with silicone rubber gaskets into aluminium frames. Each module of the spacecraft is added in a way that strengthens and stiffens the overall spacecraft structure. The structural integrity of the silicon module as a generic building block has been successfully proven. The basic design (silicon, silicone, aluminium) survived considerable mechanical loads, where the silicon material contributed significantly to the strength of the structural element. Structural modeling of the silicon building blocks enables rapid iterative design of e.g. spacecraft structures by the use of pertinent model simplifications. Other microsystem interfaces treats fluidic, thermal, and mechanical functions. First, solder sealing of microsystem cavities was demonstrated, using screen-printed solder and localized resistive heating in the microsystem interface. Second, a dismountable fluidic microsystem connector, using a ridged silicon membrane, intended for monopropellant thruster systems, was developed. Third, a thermally regulated microvalve for minute flows, made by a silicon ridge imprint in a stainless steel nipple, was investigated. Finally, particle filters for gas interfaces to microsystems, or between parts of fluidic microsystems, were made from sets of crossed v-grooves in the interface of a bonded silicon wafer stack. Filter manufacture, mass flow and pressure drop characterization, together with numeric modeling for filter design, was performed. All in all this reduces the weight and volume when microsystems are interfaced in their applications.

Localized bonding processes for assembly and packaging of polymeric MEMS

Localized bonding schemes for the assembly and packaging of polymer-based microelectromechanical systems (MEMS) devices have been successfully demonstrated. These include three bonding systems of plastics-to-silicon, plastics-to-glass, and plastics-to-plastics combinations based on two bonding processes of localized resistive heating: 1) built-in resistive heaters and 2) reusable resistive heaters. In the prototype demonstrations, aluminum thin films are deposited and patterned as resistive heaters and plastic materials are locally melted and solidified for bonding. A typical contact pressure of 0.4 MPa is applied to assure intimate contact of the two bonding substrates and the localized bonding process is completed within less than 0.25 s of heating. It is estimated that the local temperature at the bonding interface can reach above 150/spl deg/C while the substrate temperature away from the heaters can be controlled to be under 40/spl deg/C during the bonding process. The approach of localized heating for bonding of plastic materials while maintaining low temperature globally enables direct sealing of polymer-based MEMS without dispensing additional adhesives or damaging preexisting, temperature-sensitive substances. Furthermore, water encapsulation by plastics-to-plastics bonding is successfully performed to demonstrate the capability of low temperature processing. As such, this technique can be applied broadly in plastic assembly, packaging, and liquid encapsulation for microsystems, including microfluidic devices.

Thermal and optical simulation of a photonic crystal light modulator based on the thermo-optic shift of the cut-off frequency

Ultra-compact device geometries requiring the development of new device technologies are essential for the successful implementation of active devices within photonic crystal systems. The basic operation of an ultra-compact silicon-based photonic crystal light modulator actuated by the thermo-optic modulation of the cut-off frequency about the telecommunication wavelength is discussed. A device design using highly localized high temperature resistive heating of heavily doped heating elements situated directly parallel to the photonic crystal light modulator was developed and evaluated using finite difference time domain and finite element analysis. These devices exhibited high extinction ratios and low insertion losses over a 40 nm frequency band around the telecommunication wavelength of 1550 nm with response times on the order of a few to several microseconds. The reliability implications of using these types of devices are discussed.

Thermal management and resistive rail heating of a large-scale naval electromagnetic launcher

This work presents a model that can be implemented to quickly estimate the resistive heating and the resulting transient temperature response. Quantifying the energy deposited in the rails and implementing an effective thermal management system will be key elements of an effective design for a large-scale electromagnetic launcher. The total current was divided between the inside, upper/lower, and outside surface based on the results of a current distribution calculation. The diffusion of the magnetic field into each surface was modeled in order to determine the current distribution and the resistive heating. Cooling between shots was taken into account by solving the one dimensional transient heat diffusion equation within each surface. Repeating these calculations for a number of discrete segments down the length of the rail enabled the prediction of the total resistive rail heating and the temperature profile along the length of the rail. Experimental tests were conducted that verify the presence of localized heating in the corners of a U-shaped conductor made of 7075 Aluminum. Taking into account the localized resistive heating near the surface of the conductor will become increasingly important with large-scale guns.

Manufacture of Thick Cross-Section Composites Using a Pre-Catalyzed Fabric Technique

The development of a technique is reported for the manufacture of thick unsaturated polyester matrix resin composites using pre-catalyzed glass fabric. Composites over 2 cm thick using glass fabric that was pre-catalyzed (sized) with benzoyl peroxide were compared to composites made using conventional premixed catalyst and resin compounds. The pre-catalyzed fabric is shown to result in reduced internal temperatures during curing. This allows for the construction of thick fiber reinforced composite materials that do not suffer thermal degradation during the curing process. Mechanical testing of prepared thick composites demonstrated that the pre-catalyzed glass fabric composites were significantly stronger than conventionally prepared composites. The center regions of pre-catalyzed composites were about 80% stronger under tension, 25% stronger in compression and 35% stronger under shear than those of conventionally prepared composites of the same thickness. The pre-catalyzed composites were also more uniformly consolidated. Previous work aimed at the manufacture of thick composites has utilized controlled curing by use of expert systems, local resistance heating within the composite or the addition of chemical inhibitors. A method for staged curing has also shown considerable promise. None of these methods, however, has enabled high volume production of high quality thick composites. This paper presents the results of a new method for manufacture of thick composites based on a pre-catalyzed fabric technique.

Surface hardening and deposition of coatings on metals by a mobile source of localized electrical resistive heating

A method of surface hardening, coating deposition and surface alloying based on electrical resistive heating localized at the surface of a metal substrate has been developed. Localization of resistive heating was obtained by passing electric current through the contact between a moving roller and the substrate. The small size of the contact imposed a severe constriction on the electric current causing intense resistive heating close to the contact. Simultaneous motion of the roller and substrate provided surface coverage by the heating process. Tests with steel on steel showed that this technique can generate a surface layer with a martensitic or quenched microstructure, whilst a test with zinc on copper revealed that surface alloyed layer of copper and zinc can be generated. Tests where the roller has a lower melting point than the substrate, e.g. tests with zinc on steel substrates, revealed that a strongly adhering coating can be deposited by the roller.

Hot melt ink acoustic printing

To facilitate the use of hot melt inks in acoustic ink printers of the type having a printhead including one or more acoustic droplet ejectors for supplying focused acoustic beams, such a printer comprises a carrier for transporting a generally uniformly thick film of hot melt ink across its printhead, together with a heating means for liquefying the ink as it nears the printhead. The droplet ejector or ejectors are acoustically coupled to the ink via the carrier, and their output focal plane is essentially coplanar with the free surface of the liquefied ink, thereby enabling them to eject individual droplets of ink therefrom on command. The ink, on the other hand, is moved across the printhead at a sufficiently high rate to maintain the free surface which it presents to the printhead at a substantially constant level. A variety of carriers may be employed, including thin plastic and metallic belts and webs, and the free surface of the ink may be completely exposed or it may be partially covered by a mesh or perforated layer. A separate heating element may be provided for liquefying the ink, or the lower surface of the carrier may be coated with a thin layer of electrically resistive material for liquefying the ink by localized resistive heating.