Edge Chipping Research Articles

Performance of water-based TiO2 nanofluid during the minimum quantity lubrication machining of aluminium alloy, AA6061-T6

The effects of cutting parameters on the wear mechanisms in the end milling of aluminium alloy AA6061 with minimum quantity lubrication (MQL) conditions using water-based TiO2 nanofluid were investigated. Three different cutting speeds of 5200, 5400 and 5600 rpm were used. The MQL flow rates used were 0.65 ml/min and 1.0 ml/min, while the TiO2 nanoparticles used were of different volume fractions in the aqueous solutions of 0.5, 2.5 and 4.5%. The results showed that the adhesion of the work material is the major tool damage phenomenon. In addition, abrasion was observed. The major benefit from the water-based nanofluid MQL was shown in the edge integrity i.e., edge chipping and edge fracture were seen in very few cases especially with a higher depth of cut higher. This is attributed to the cooling effect produced by the latent heat of vaporization of the water resulting in the lowering of temperature in the cutting zone. The volume fraction of 2.5% TiO2 nanoparticles appeared more feasible in terms of tool damage. The effectiveness of the non-conventional nanofluid MQL was also discussed. A non-deterministic component of the sustainability index, for the milling process with the MQL, was calculated using fuzzy logic. The basic objective is to quantify the non-deterministic component of the sustainability index by using the fuzzy rule-based model for the performance analysis of machining with MQL. The results show the prospective utilization of water-based TiO2 nanofluid as the MQL medium. Thus, it is beneficial for the higher cooling rates of water integrated with the lubrication characteristics of nanoparticles.

On the mechanism of edge chipping reduction in rotary ultrasonic drilling: A novel experimental method

Edge chipping induced by the mechanical machining of holes in brittle materials restricts the applications of the brittle materials. Rotary ultrasonic drilling is a suitable approach for the machining of holes in brittle materials with a smaller size of edge chipping. A good understanding of the mechanism of edge chipping reduction when employing rotary ultrasonic drilling is helpful to the application and optimization of the drilling technique. In this study, a novel edge chipping mechanism for the machining of holes considering machining-induced cracks was proposed and verified by experiments on quartz glass. The size of the machining-induced crack was evaluated experimentally. Experimental results indicate that the initiation of edge chipping is determined by both the magnitude of the driving force and the size of the machining-induced crack. However, the size of edge chipping strongly depends on the undrilled thickness following a directly proportional relation. Moreover, the geometric similarity of edge chipping is evidence for the consistency of the crack propagation direction when edge chipping begins. Finally, experiments conducted under various machining conditions demonstrate that the reduction of the size of machining-induced cracks in rotary ultrasonic drilling is another important factor contributing to the reduction of the size of edge chipping in rotary ultrasonic drilling, comparing with conventional diamond drilling.

Experimental investigation of the tool wear in micro-milling of stainless steel 316

The objective of this paper is to experimentally investigate the micro-machinability of stainless steel 316 under both dry and minimum quantity lubrication conditions. The machinability was assessed in terms of tool wear, tool life, cutting forces and surface finish. The tool life was characterised as the amount of material removed, instead of the conventional cutting times. The machining performance under MQL is superior to the dry machining for both process conditions in terms of the tool life. The magnitude of the machining forces showed cyclic pattern for both MQL and dry machining. The SEM images and the cutting force signals suggested that the dominant mode of the tool wear in micro-milling is edge chipping and abrasive wear at the tool tip. The surface roughness at the bottom of the slots improved significantly with the application of MQL for all levels of the tool wear.

Experimental Studies on the Cutting Characteristics of Hybrid CFRP/Ti Stacks

Owing to their enhanced mechanical properties and improved structural functions, the use of hybrid CFRP/Ti stacks (a sandwich of one CFRP laminate and one Ti alloy) has experienced an increasing trend in modern aerospace industry. The emergence of such composite-to-metal alliances, however, poses a series of new challenges to the manufacturing sectors for high-quality finishing of the material-made components. The key machining problems usually arise from the disparate natures of the stacked constituents (CFRP laminate and Ti alloy) and their respective poor machinability. To study the fundamental cutting characteristics of the bi-material assembly, this paper presents an experimental study concerning the machinability evaluation of the hybrid CFRP/Ti stacks. An orthogonal cutting configuration (OCC) derived from the real manufacturing operation was adopted to finalize the CFRP/Ti cutting comprehension by using the polycrystalline diamond (PCD) tipped tools. The cutting trials were performed under the reasonable cutting sequence strategy of CFRP → Ti as pointed out by most experimental studies. The key cutting responses including cutting forces, machined surface quality and tool wear mechanisms were precisely addressed versus the utilized cutting conditions. The experimental results highlight that a parametric combination of high cutting speeds and low feed rates often facilitates the reduction of cutting forces and induced damage extents. The basic damage modes promoted on the machined CFRP/Ti surfaces are observed to be fiber pullout, resin loss, surface cavity, deformation of feed marks and re-deposited materials. Moreover, the key wear mechanisms governing the PCD tool cutting are confirmed to be crater wear and flank wear, while the tool failure mode is edge chipping. To ensure the excellent machined surface quality, a stringent control of tool wear should be implemented when cutting hybrid CFRP/Ti stacks.

Obstruction-type Chip Breakers for Controllable Chips and Improved Cooling/Lubrication During Drilling – A Feasibility Study

During drilling, long stringy chips resulting from ductile plastic deformation of engineering materials cause severe chip clogging within the narrow helical flutes and edge chipping, leading to premature tool wear and breakage, poor tool life, poor hole quality and the productivity. Cutting fluid cannot efficiently access to the cutting edge that plays a vital role for improving machining performance. To address the localized heat and chip control issues during drilling, research was previously performed using conventional flood cooling, modified tool geometry, tool coating materials, and internal coolant via through hole(s). This works focuses on design and insertion of some obstruction-type chip breakers such as ribs and pins on the drill flutes and their influence on chip formation behavior. For feasibility experiments, small round pins made of stainless steel at a diameter of about 0.8-0.85mm diameter are prepared and attached on the electro-discharge machined (EDM) blind holes on twisted drill flutes. By varying spindle speed and feed rate, drilling experiments are performed on two engineering materials including Al6061 and Inconel 625 superalloys at four cutting conditions. Most chips are found to be broken and some split into two fractions due to the pins. Force and power values with pin-inserted drill bits were found to be reduced from 5-9%. This finding indicates that there is a good potential to implement such obstruction-type chip-breakers on the drill flutes for obtaining controllable chip while also improving coolant flow at the cutting edge through the tiny tool-chip interface.

微細表面テクスチャを有するCBN工具によるInconel 718の高速切削加工

Nickel-based superalloys such as Inconel 718, which are widely used especially in the aircraft industry, are known to be among the most difficult-to-cut materials because of their mechanical and chemical properties, and tools used for this purpose have extremely short lifetimes. Recently, cubic boron nitride (CBN), which is the second hardest of all known materials, has received significant attention as a material for cutting tools and has already established itself in many fields of application. However, the performance of CBN tools is still insufficient for practical use, especially in the high-speed machining of Inconel 718. To overcome this problem, we first conducted orthogonal cutting experiments on Inconel 718 and performed cross-sectional observations of the CBN cutting tool in order to identify its wear mechanisms in continuous cutting operations under high-speed machining conditions (300 m/min). Based on the results, a CBN cutting tool with a textured flank face was newly developed to improve the cutting tool life. Experimental results showed that micro grooves generated on the flank face significantly suppressed the cutting edge chipping and remarkably extended the CBN tool life during high-speed machining of Inconel 718.

Electrical Discharge Conditioning for Indexable Insert Grinding

Metal bonded diamond grinding wheels have a great potential for grinding hard materials. However, the toughness of the metal bond in combination with fine grit sized and highly concentrated diamonds makes these wheels very hard to condition conventionally. This paper presents a novel approach for conditioning metal bonded grinding wheels using Electrical Discharge Conditioning (EDC). Here, a rotating electrode is continually sharpening, cleaning and shaping the optimized grinding wheel with bronze alloy bond. Experimental results regularly show a doubling of the material removal rate and simultaneously reduced edge chipping and finer surface finish. The process is fast, stable and leads to excellent product quality in terms of dimensional accuracy, surface- and edge-integrity. Over all, the presented industrial-strength Electrical Discharge Conditioning technology boosts productivity and quality.

Modified maximum tangential stress criterion for fracture behavior of zirconia/veneer interfaces

The veneering porcelain sintered on zirconia is widely used in dental prostheses, but repeated mechanical loadings may cause a fracture such as edge chipping or delamination. In order to predict the crack initiation angle and fracture toughness of zirconia/veneer bi-layered components subjected to mixed mode loadings, the accuracy of a new and traditional fracture criteria are investigated. A modified maximum tangential stress criterion considering the effect of T-stress and critical distance theory is introduced, and compared to three traditional fracture criteria. Comparisons to the recently published fracture test data show that the traditional fracture criteria are not able to properly predict the fracture initiation conditions in zirconia/veneer bi-material joints. The modified maximum tangential stress criterion provides more accurate predictions of the experimental results than the traditional fracture criteria.

High-speed and crack-free direct-writing of microchannels on glass by an IR femtosecond laser

Fabrication of high-resolution 3D structures with laser radiation on the surface of brittle materials has always been a challenging task. Even with femtosecond laser machining, micro-cracks and edge chipping occur. In order to evaluate processing modes optimal both in quality and productivity, we investigated high-speed (50kHz) femtosecond laser processing of BK7 glass with the use of design of experiments and regression analysis. An automated inspection technique was developed to extract quality characteristics of test-objects. A regression model was obtained appropriate to fabricate microchannels with a predefined depth in the range of 1–30µm with average accuracy of 5%. It was found that high quality machining modes are in the range of 0.91–2.27µJ energy pulses, overlap of 53–62%, three and more number of passes. A material removal rate higher than 0.3mm3/min was reached and microfluidic structures were formed based on data obtained.

Experimental Investigation and Optimization of Cutting Force and Tool Wear in Milling Al7075 and Open-Cell SiC Foam Composite

In the present study, aluminium alloy-based metal matrix composites were fabricated by infiltrating Al7075 into a three-dimensional open-cell silicon carbide (SiC) foam using the liquid metallurgy method. The effects of machining variables on the milling force and tool wear during milling of both Al7075 and the open-cell SiC foam metal matrix composite (MMC) using an uncoated carbide cutting tool were studied. The milling experiments were performed based on the Taguchi $${{\rm L}_{27}}$$ full-factorial orthogonal array, and the milling variables were optimized for cutting force and tool wear. The test results showed that the cutting depth was the most significant cutting parameter affecting milling force in the milling of both workpiece materials. Cutting tool wear was directly affected by the cutting depth in the milling of MMC, and the feed rate was the most influential factor on the tool wear in the milling of Al7075. Uncoated carbide tool showed an excellent machining performance below a machining speed of 220 m/min in finish milling Al7075 workpiece material, but excessive edge chipping was observed on the cutting tool surface in the milling of MMCs. Second-order mathematical models with respect to milling parameters were created for prediction of cutting force and tool wear.

Modeling the dependency of edge chipping size on the material properties and cutting force for rotary ultrasonic drilling of brittle materials

Edge chipping induced by rotary ultrasonic drilling (RUD) restricts the applications of brittle materials. It should be possible to reduce or eliminate edge chipping by optimizing the process parameters based on efficient theoretical modeling of the size of the edge chip. However, to date, no publications are available on the predictive modeling of edge chipping during RUD of brittle materials. This paper presents an analytical model for predicting the edge chipping size during RUD of brittle materials by considering both effects of cutting force and subsurface cracks induced by machining on the occurrence of edge chipping. The relationships between the edge chipping size, processing variables (material properties and ultrasonic amplitude), and the cutting force were established theoretically. The coefficients in the model were obtained by conducting RUD tests on K9 optical glass specimens. Subsequently, the model was validated by conducting RUD tests on sapphire specimens. Using this model, the edge chipping size can be predicted during RUD of brittle materials. The experimental and predicted results were in good agreement.

On-machine measurement of microtool wear and cutting edge chipping by using a diamond edge artifact

This paper presents precision on-machine measurement of microwear and microcutting edge chipping of the diamond tool used in a force sensor integrated fast tool servo (FS-FTS) mounted on a three-axis diamond turning machine. A diamond edge artifact with a nanometric sharpness is mounted on the machine spindle with its axis of rotation along the Z-axis to serve as a reference edge artifact. The diamond tool is placed in the tool holder of the FS-FTS to generate cutting motion along the Z-axis. By moving the X-slide on which the FS-FTS is mounted, the reference edge can be scanned by the diamond tool. During the scanning, the Z-directional position of the tool is closed-loop controlled by the FS-FTS in such a way that the contact force between the tool tip and the reference edge is kept constant based on the force sensor output of the FS-FTS. The tool edge contour can be obtained from the scan trace of the tool tip, whose X- and Z-directional coordinates are provided by the output of the linear encoder of the X-slide and that of the displacement sensor in the FS-FTS, respectively. Since the reference edge artifact has a good hardness and a nanometric sharpness to ensure the lateral resolution of measurement, a microwear on the cutting edge of the diamond tool can be indentified from the measured tool edge contour. Experiments of on-machine measurement of tool edge contour and microtool wear are carried out to demonstrate the feasibility of the proposed system.

Flank Wear Characterization in Aluminum Alloy (6061 T6) With Nanofluid Minimum Quantity Lubrication Environment Using an Uncoated Carbide Tool

This study is focused on the categorical analysis of flank wear mechanisms in end milling of aluminum alloy AA6061 with minimum quantity lubrication (MQL) conditions using nanofluid. Wear mechanisms for the water-based TiO2 nanofluid with a nanoparticle volume fraction of 1.5% are compared with conventional oil-based MQL (0.48 ml/min and 0.83 ml/min) using an uncoated cemented carbide insert. Micro-abrasion, micro-attrition, and adhesion wear leading to edge chipping are identified as the main wear mechanisms. Aluminum deposits on the tool flank surface are observed. Results show that the water-based nanofluid shows potential as a capable MQL cutting media, in terms of tool wear, replacing the conventional oil-based MQL.

Fabrication of micro-flow channels on graphite composite bipolar plates using microplaning

A new method of manufacturing micro-flow channels on graphite composite bipolar plate (GCBPP) microplaning using specially designed multi-tooth tool is proposed. In this method, several or even dozens of parallel micro-flow channels ranging from 100 µm to 500 µm in width can be produced simultaneously. But, edge chippings easily occur on the rib surface of GCBPP during microplaning due to brittleness of graphite composites. Experimental results show that edge chippings result in the increase of contact resistance between bipolar plate and carbon paper at low compaction force. While the edge chippings scarcely exert influence on the contact resistance at high compaction force. Contrary to conventional view, the edge chippings can significantly improve performance of microfuel cell and big edge chippings outperform small edge chippings. In addition, the influence of technical parameters on edge chippings was investigated in order to obtain big, but not oversized edge chippings.

Multi-Strata Stealth Dicing Before Grinding for Singulation-Defects Elimination and Die Strength Enhancement: Experiment and Simulation

We report on defects characterization and reduction as well as die strength enhancement using stealth dicing (SD) on high-backside reflectance (82%) 2-D NAND memory wafers. This is performed using three-strata subsurface infrared (1.342 μm) nanosecond pulsed laser die singulation with a partial-SD before grinding integration approach. In this paper, a combination of simulation, characterization, and optimization of the multi-strata SD process has led to the elimination of mechanical and absorptive laser singulation related defects such as frontside and backside surface ablation, and topside, backside, and edge chipping. At the same time, the kerf width and kerf straightness are robust against the effects of test element structures located along the dicing streets. There is a consistent coverage of high-quality SD kerf production with near-zero kerf loss across the 300 mm wafer. Multi-strata SD-unique defects such as interference effects and inter-strata cleavage plane {111} damage have been addressed. SD-related integrated defects including Si dust residue post-backgrinding and die attach film-related defects post-die separation have also been resolved. We illustrate the performance of this approach by demonstrating defect-free eight die stacks of 25 μm thick memory dies.

The Effect of Mechanical Stress on Electromigration Behavior

AbstractThree-dimensional integrated circuit packages with through-silicon vias (TSVs) provide a good solution to the integration of different chips and help achieve high performance. The signals are transmitted to different layers directly through the vias, thereby enabling the high performance of the chips. Plasma-enhanced chemical vapor-deposited SiO2, polyimide, and benzo-cyclo-butene are commonly used as the passivation layer for three-dimensional packages. In the 3D stacked chips, mismatch of the coefficient of thermal expansion between the passivation material and silicon will generate thermal/mechanical stress in the metal trace and the stress affects the behavior of electromigration. However, few studies have examined the relationship among the external mechanical stress and critical product of electromigration. In the present study, external stress is applied to the aluminum thin film by a four-point bending equipment. In order to apply higher external stress in the aluminum thin film, the fracture strength of the silicon substrate should be improved. Reduces the edge chipping of the test sample is a key factor for improving the fracture strength of the silicon substrate and a special cutting approach is employed to obtain higher silicon strength. A two-step cutting method is applied to reduce front side chipping and also a dicing before grinding approachis adopted to reduce backside chipping, the above-mentioned technology can enable more than 275MPa of external stress on the aluminum thin film and can make the critical length effect more visible. The residual stress of the aluminum thin film is at stress-free state after annealing at 300°C for 10h. The critical product is found to be reduced from 1,294A/cm to 1,281A/cm when 120MPa of mechanical tensile stress is applied. It increased to 1,315A/cm under 120MPa of mechanical compressive stress. Clearly, electromigration behavior is enhanced by tensile stress and decreased by compressive stress. In the current research, a modified equation for Blech condition is proposed with a stress-dependent effective charge number, the effective charge number increased when tensile stress was applied and decreased when compressive stress was applied.

Fracture resistance of lithium disilicate restorations after endodontic access preparation: An in vitro study

Statement of problemEndodontic access preparation through a lithium disilicate restoration is a frequently encountered clinical situation. The common practice of repairing the accessed crown with composite resin may result in a weakened restoration. PurposeThe purpose of this in vitro study was to determine the effect of endodontic access preparation on the fracture resistance and microstructural integrity of monolithic pressed and monolithic milled lithium disilicate complete coverage restorations. Material and methodsTwenty monolithic pressed (IPS e.max Press) and 20 monolithic milled (IPS e.max CAD) lithium disilicate restorations were fabricated. Ten of the pressed and 10 of the milled crowns were accessed for a simulated endodontic treatment and subsequently repaired by using a porcelain repair system and composite resin. All specimens were submitted to cyclic loading and then loaded to failure. Force data were recorded and analyzed with 2-way ANOVA followed by a post hoc test (Sidak correction) to indicate significant differences among the groups (α=.05). A Weibull analysis was also performed for each group. Eight (4 pressed and 4 milled) additional restorations were fabricated to complete a scanning electron microscope (SEM) analysis and evaluate the surface damage created by the endodontic access preparation. ResultsA statistically significant difference (P=.019) was found between the pressed intact and pressed repaired restorations and between the pressed intact and milled repaired restorations (P=.002). Specimens that were examined with an SEM showed edge chipping involving primarily the glaze layer around the access openings. ConclusionsEndodontic access preparation of lithium disilicate restorations resulted in a significantly reduced load to failure in the pressed specimens, but not in the milled specimens.

The effects of pilot hole geometry on tool-work engagement efficacy in deep hole drilling

Deep hole drilling using single-lip drill (SLD) without a starting bush induces a severe cutting edge chipping if the pilot hole profile is not selected properly. In this paper, a new parameter ‘Engagement Ratio’ (ER) is introduced to determine appropriate pilot hole profile. ER depends on pilot hole and tool geometry combination. Application of ER is illustrated with geometrical model for four different engagement conditions. The range of values of ER for Inconel 718 was defined based on experimental results to ensure smooth engagement. Moreover, this approach can be extended to select the pilot hole geometry for other materials.

Surface and subsurface characterisation in micro-milling of monocrystalline silicon

Abstract This paper presents an experimental investigation on surface and subsurface characterisation of micro-machined single-crystal silicon with (100) orientation. Full immersion slot milling was conducted using solid cubic boron nitride (CBN) and diamond-coated fine grain tungsten carbide micro-end mills with a uniform tool diameter of 0.5 mm. The micro-machining experiments were carried out on an ultra-precision micro-machining centre. Formal design of experiments (DoE) techniques were applied to design and analysis of the machining process. Surface roughness, edge chipping formation and subsurface residual stress under varying machining conditions were characterised using white light interferometry, SEM and Raman microspectroscopy. Tens of nanometre-level surface roughness can be achieved under the certain machining conditions, and influences of variation of cutting parameters including cutting speeds, feedrate and axial depth of cut on surface roughness were analysed using analysis of variance (ANOVA) method. Raman microspectroscopy studies show that compressive subsurface residual stress and amorphous phase transformation were observed on most of the micro-machined subsurface, which provides evidence of ductile mode cutting. Surface and subsurface characterisation studies show that the primary material removal mode is ductile or partial ductile using lower feedrate for both tools, and diamond-coated tools can produce better surface quality. Silicon brain implants were fabricated with good dimensional accuracy and edge quality using the optimised machining conditions, which demonstrated that micro-milling is an effective process for fabrication of silicon components at a few tens to a few hundreds of micron scale.

Determination of Initial Crack Strength of Silicon Die Using Acoustic Emission Technique

The current market demand for high-efficiency, high-performance, small-sized electronic products has focused attention on the use of three-dimensional (3D) integrated circuits (IC) in the design of electronic packaging. Silicon wafers can be ground and polished to reduce their thickness and increase the chip stacking density. However, microcracks can result from the thinning and stacking process or during use of an electronic device over time; therefore, estimation of the cracking strength is an important issue in 3D IC packaging. This research combined the ball breaker test (BBT) with an acoustic emission (AE) system to measure the allowable force on a silicon die. To estimate the initial crack strength of a silicon die, the BBT was combined with finite-element (FE) analysis. The AE system can detect the initial crack and the subsequent bulk failure of the silicon die individually, thus avoiding overestimation of the die strength. In addition, the results of the modified ball breaker test showed that edge chipping did not affect the silicon die strength. However, the failure force and silicon die strength were reduced as the surface roughness of the test specimen increased. Thus, surface roughness must be controlled in the BBT to prevent underestimation of the silicon die strength.