The mechanism governing cutting of hard materials with hybrid Laser/Waterjet system through controlled fracture

Ceramics are generally difficult to machine due to their inherent natures of high hardness and low toughness. The present dissertation investigated the mechanism governing cutting of hard ceramic materials with a novel hybrid CO2-Laser/Waterjet (LWJ) system through controlled fracture propagation. It has been proved that the hybrid machining method is more efficient and is capable of providing high quality cutting that overcomes the major drawbacks with current machining techniques including EDM and Nd:YAG laser. The LWJ method implements a high power laser heating followed by low pressure waterjet quenching which subsequently dictates fracture initiation and propagation along the cutting path. The driving force of fracture can be categorized into two groups based on the specific material’s thermal properties and phase transformation capabilities. For materials with low thermal conductivity such as Alumina and Zirconia, laser heating and waterjet quenching cooperatively induce large thermal stresses, which drive the crack and hence achieves material separation. For materials with high thermal conductivity such as Aluminum Nitride, Polycrystalline Cubic Boron Nitride and Polycrystalline Diamond, the stresses that drive the crack propagation result from phase transformation induced volume expansion, rather than thermal stresses. Based on the two mechanisms, the material merit indices governing thermal shock induced fracture and transformation induced fracture can be derived respectively for material selection. The cutting mechanism of high-conductivity materials including PCBN and PCD was studied through combined experimental and numerical methods. Surface deformation, morphology, and phase compositions were characterized on the cut sample using profilometry, scanning electron microscopy, and Raman spectroscopy in order to identify the mechanistic origin underlying the material separation. A finite element model was developed to predict the surface deformation, which was compared with surface profiling measurements by optical profilometry in order to estimate the expansion strain and dimensions of the phase transformed region. Fracture mechanics analysis based on the obtained expansion strain and transformed zone was performed to predict crack configurations and to validate experimental cutting results. Based on comparison between experimental observations and numerical predictions, a “score and snap” mechanism is identified: (1) The laser beam results in scoring the sample through localized laser heating and subsequent waterjet quenching transform PCBN near the top surface from sp3-bonded phases into sp2-bonded phases (cBN transforms to hBN, diamond transforms to graphite); (2) The phase transition leads to volumetric expansion that induces tensile stresses in the surrounding material and drives the crack through the specimen leading to material separation. Cutting results indicate that as line energy of the laser was increased the sample response transitioned from scribing to through cutting. Good agreement between simulation and experimental observation was achieved. The results show that transformation induced crack propagation is the feasible mechanism for cutting during CO2-LWJ machining

The mechanism governing cutting of Polycrystalline Cubic Boron Nitride (PCBN) tool blanks with phase transformation induced fracture

The thesis presents a combined experimental and computational investigation of a novel thermochemical material removal mechanism for cutting of polycrystalline cubic boron nitride (PCBN) substrates through controlled crack propagation. The CO2-Laser/Waterjet machining system developed by the Iowa State University\u27s Laboratory for Lasers, MEMS, and Nanotechnology was utilized to achieve specimen cutting. It has been proved that the hybrid machining method is more efficiency and able to provide high quality cutting that overcomes the major drawbacks with current EDM and Nd:YAG laser machining techniques. The LWJ method implemented a high power laser heating followed by low pressure waterjet quenching that achieved fracture initiation and propagation along the cutting path. The purposes of water in LWJ machining are: (1) help the phase transformation as to induce larger tensile stresses for crack propagation and (2) provide thermal shock that reduce the fracture toughness of material in specimen. Two forms of PCBN specimens: the solid compact and the composite with tungsten carbide substrate were studied in this thesis. The mechanism governing the fracture behavior was studied through Raman spectroscopy, Scanning Electron Microscopy (SEM), and surface profile measurement with profilometer. FEA model associated with machining parameters was developed to validate the machining mechanism and provide prediction of fracture behavior. Good agreement between simulation prediction and experimental observation was achieved

Ultrahard materials through surface heat treatment

Ultrahard materials that are chemically inert and thermally stable at high temperatures are desirable for enhancing machining and wear performance in demanding chemical and thermal environments. Single and polycrystalline diamonds are the hardest materials (75–100 GPa); however, at high temperatures, diamond loses its chemical inertness and thermal stability. In contrast, cubic boron nitride (cBN) has exceptional chemical and thermal stability but has much lower hardness (35–45 GPa). Increasing the hardness of BN to the level of diamond is expected to result in chemically and thermally inert ultrahard material that is suitable for range of demanding wear and machining applications. An innovative laser/waterjet heat treatment (LWH) technique was designed and applied to polycrystalline 50% cBN/50% wBN tool inserts to reach the hardness level of polycrystalline diamond. The LWH processing consisted of surface heating samples using a continuous wave CO2 laser beam followed by tandem waterjet quenching of the laser beam path to cause stress-induced microstructural changes. Dispersive Raman spectroscopy, high-resolution scanning electron microscope and surface grazing XRD were used to identify the BN phase signatures, grain size changes, and phase transitions. The laser-waterjet heat treatment increased the hardness of binderless cBN sample by 20% (nominal 60 GPa) while it increased the hardness of binderless cBN/wBN sample by 100% (nominal 75 GPa) reaching the hardness of polycrystalline diamond (65–80 GPa). Microstructural analysis of the samples revealed three major features due to heat treatment. First is the formation of amorphous phase as noted by presence of the interfacial layer at grain boundaries. Such phase is expected to introduce the grain-boundary strengthening mechanism via inhibiting ease of dislocation movement across the boundary. Second is the formation of zones with nanosized grains that are expected to increase the energy needed to introduce plastic deformation. Third is the extensive fragmentation and cracking of the lamellas that also reduced the effective grain size and may contribute to the strengthening. A combination of amorphous phase formation at the grain boundaries and nanosized grain formation are suggested as the mechanisms responsible for the increased hardness

Electrode Cap with Electrical Insulator and Related Methods

A resistance spot welding system includes an electrode with a cap that includes a tip having an outer surface that defines a pocket, and an electrical insulator positioned within the pocket. A method of manufacturing the electrode includes forming a pocket in the outer surface of the tip of the electrode cap, and positioning the electrical insulator within the pocket. A method of resistance spot welding includes positioning a first metal sheet and a second metal sheet between two electrodes where at least one of the two electrodes includes the cap with the electrical insulator. A weld nugget joining a first metal sheet with a second metal sheet includes a center region surrounded by an outer region, and a thickness of the center region is less than a thickness of the outer region

Electrode with Tip Life Improvement and Related Methods

A resistance spot welding system includes an electrode with a cap that includes a cap body having a tip, a body cavity defined within the cap body, and a tip cavity defined within the cap body that extends from the body cavity towards the tip. A method of manufacturing the electrode includes forming a body cavity within a cap body of the electrode, and forming a tip cavity within the cap body of the electrode such that the tip cavity extends from the body cavity towards a tip of the cap body. In other aspects, a resistance spot welding system includes a first electrode, a second electrode, and an external cooling unit that is configured to inject a coolant adjacent to at least one of the first electrode and the second electrode during welding

Apigenin C-glycosides of Microcos paniculata protects lipopolysaccharide induced apoptosis and inflammation in acute lung injury through TLR4 signaling pathway

Acute lung injury (ALI) and its more severe form acute respiratory distress syndrome (ARDS) are life-threatening conditions with high morbility and mortality, underscoring the urgent need for novel treatments. Leaves of the medicinal herb Microcos paniculata have been traditionally used for treating upper airway infections, by virtue of its content of flavonoids such as apigenin C-glycosides (ACGs). C-glycosides have been shown to exert strong anti-inflammatory properties, although their mechanism of action remains unknown. Herein, hypothesizing that ACGs from M. paniculata inhibit progression of ALI, we used the experimental model of lipopolysaccharide (LPS)-induced ALI in BALB/c mice to evaluate the therapeutic potential of purified ACGs. Our results showed that M. paniculata ACGs inhibited lung inflammation in animals undergoing ALI. The protective effects of ACGs were assessed by determination of cytokine levels and in situ analysis of lung inflammation. ACGs reduced the pulmonary edema and microvascular permeability, demonstrating a dose-dependent down-regulation of LPS-induced TNF-α, IL-6 and IL-1β expression in lung tissue and bronchoalveolar lavage fluid, along with reduced apoptosis. Moreover, metabolic profiling of mice serum and subsequent Ingenuity Pathway Analysis suggested that ACGs activated protective protein networks and pathways involving inflammatory regulators and apoptosis-related factors, such as JNK, ERK1/2 and caspase-3/7, suggesting that ACGs-dependent effects were related to MAPKs and mitochondrial apoptosis pathways. These results were further supported by evaluation of protein expression, showing that ACGs blocked LPS-activated phosphorylation of p38, ERK1/2 and JNK on the MAPKs signaling, and significantly upregulated the expression of Bcl-2 whilst down-regulated Bax and cleaved caspase-3. Remarkably, ACGs inhibited the LPS-dependent TLR4 and TRPC6 upregulation observed during ALI. Our study shows for the first time that ACGs inhibit acute inflammation and apoptosis by suppressing activation of TLR4/TRPC6 signaling pathway in a murine model of ALI. Our findings provide new evidence for better understanding the anti-inflammatory effects of ACGs. In this regard, ACGs could be exploited in the development of novel therapeutics for ALI and ARDS

Condensation of 2-((Alkylthio)(aryl)methylene)malononitrile with 1,2-Aminothiol as a novel bioorthogonal reaction for site-specific protein modification and peptide cyclization

Site-specific modification of peptides and proteins has wide applications in probing and perturbing biological systems. Herein we report that 1,2-aminothiol can react rapidly, specifically and efficiently with 2-((alkylthio)(aryl)methylene)malononitrile (TAMM) under biocompatible conditions. This reaction undergoes a unique mechanism involving thiol-vinyl sulfide exchange, cyclization, and elimination of dicyanomethanide to form 2-aryl-4,5-dihydrothiazole (ADT) as a stable product. An 1,2-aminothiol functionality can be introduced into a peptide or a protein as an N-terminal cysteine or an unnatural amino acid. The bioorthogonality of this reaction was demonstrated by site-specific labeling of not only synthetic peptides and a purified recombinant protein but also proteins on mammalian cells and phages. Unlike other reagents in bioorthogonal reactions, the chemical and physical properties of TAMM can be easily tuned. TAMM can also be applied to generate phage-based ADT-cyclic peptide libraries without reducing phage infectivity. Using this approach, we identified ADT-cyclic peptides with high affinity to different protein targets, providing valuable tools for biological studies and potential therapeutics. Furthermore, the mild reaction conditions of TAMM condensation warrant its use with other bioorthogonal reactions to simultaneously achieve multiple site-specific modifications

The mechanism governing cutting of Polycrystalline Cubic Boron Nitride (PCBN) tool blanks with phase transformation induced fracture

The thesis presents a combined experimental and computational investigation of a novel thermochemical material removal mechanism for cutting of polycrystalline cubic boron nitride (PCBN) substrates through controlled crack propagation. The CO2-Laser/Waterjet machining system developed by the Iowa State University's Laboratory for Lasers, MEMS, and Nanotechnology was utilized to achieve specimen cutting. It has been proved that the hybrid machining method is more efficiency and able to provide high quality cutting that overcomes the major drawbacks with current EDM and Nd:YAG laser machining techniques. The LWJ method implemented a high power laser heating followed by low pressure waterjet quenching that achieved fracture initiation and propagation along the cutting path. The purposes of water in LWJ machining are: (1) help the phase transformation as to induce larger tensile stresses for crack propagation and (2) provide thermal shock that reduce the fracture toughness of material in specimen. Two forms of PCBN specimens: the solid compact and the composite with tungsten carbide substrate were studied in this thesis. The mechanism governing the fracture behavior was studied through Raman spectroscopy, Scanning Electron Microscopy (SEM), and surface profile measurement with profilometer. FEA model associated with machining parameters was developed to validate the machining mechanism and provide prediction of fracture behavior. Good agreement between simulation prediction and experimental observation was achieved.</p

The mechanism governing cutting of hard materials with hybrid Laser/Waterjet system through controlled fracture

Ceramics are generally difficult to machine due to their inherent natures of high hardness and low toughness. The present dissertation investigated the mechanism governing cutting of hard ceramic materials with a novel hybrid CO2-Laser/Waterjet (LWJ) system through controlled fracture propagation. It has been proved that the hybrid machining method is more efficient and is capable of providing high quality cutting that overcomes the major drawbacks with current machining techniques including EDM and Nd:YAG laser. The LWJ method implements a high power laser heating followed by low pressure waterjet quenching which subsequently dictates fracture initiation and propagation along the cutting path. The driving force of fracture can be categorized into two groups based on the specific material’s thermal properties and phase transformation capabilities. For materials with low thermal conductivity such as Alumina and Zirconia, laser heating and waterjet quenching cooperatively induce large thermal stresses, which drive the crack and hence achieves material separation. For materials with high thermal conductivity such as Aluminum Nitride, Polycrystalline Cubic Boron Nitride and Polycrystalline Diamond, the stresses that drive the crack propagation result from phase transformation induced volume expansion, rather than thermal stresses. Based on the two mechanisms, the material merit indices governing thermal shock induced fracture and transformation induced fracture can be derived respectively for material selection. The cutting mechanism of high-conductivity materials including PCBN and PCD was studied through combined experimental and numerical methods. Surface deformation, morphology, and phase compositions were characterized on the cut sample using profilometry, scanning electron microscopy, and Raman spectroscopy in order to identify the mechanistic origin underlying the material separation. A finite element model was developed to predict the surface deformation, which was compared with surface profiling measurements by optical profilometry in order to estimate the expansion strain and dimensions of the phase transformed region. Fracture mechanics analysis based on the obtained expansion strain and transformed zone was performed to predict crack configurations and to validate experimental cutting results. Based on comparison between experimental observations and numerical predictions, a “score and snap” mechanism is identified: (1) The laser beam results in scoring the sample through localized laser heating and subsequent waterjet quenching transform PCBN near the top surface from sp3-bonded phases into sp2-bonded phases (cBN transforms to hBN, diamond transforms to graphite); (2) The phase transition leads to volumetric expansion that induces tensile stresses in the surrounding material and drives the crack through the specimen leading to material separation. Cutting results indicate that as line energy of the laser was increased the sample response transitioned from scribing to through cutting. Good agreement between simulation and experimental observation was achieved. The results show that transformation induced crack propagation is the feasible mechanism for cutting during CO2-LWJ machining.</p

Extreme Hardness Achievements in Binderless Cubic Boron Nitride Tools

Binderless cubic boron nitride tools are available in two forms: single phase cBN and dual phase wBN/cBN (w is wurtzite phase). In this work, a novel heat treatment process involving surface heating using a continuous wave CO2 laser followed by tandem waterjet quenching of the laser beam path was applied to increase the hardness of both forms of boron nitride. Stress-induced phase transitions and nanometric grain sizes accompanying the rapid quench heat treatment enabled a hardness increase of 20% in single phase cBN (nominal 60 GPa) and 100% in dual phase wBN/cBN (nominal 75 GPa) that attest the ability of cBN to reach the hardness of polycrystalline diamond (65-80 GPa). The effects of laser heat treatment are identified by an examination of the changes in phase and microstructure by Raman spectroscopy, high resolution scanning electron microscopy and X-ray diffraction