Diamond Wire Sawing Research Articles

Nucleation location and propagation direction of radial and median cracks for brittle material in scratching

At present, diamond wire sawing technology is a mainstream method for wafering brittle materials such as silicon crystal, SiC crystal, sapphire, ceramics, optical glass and so on. Microcracks will occur on the wafers surface inevitably during sawing owing to the high brittleness and hardness of brittle material. The existence of microcracks and their size, orientation and distribution not only affect the surface quality and fracture strength of wafers, but also have an important impact on the subsequent processing effect of wafers after sawing. Therefore, the further investigation on the formation and propagation direction of microcracks is needed during diamond wire sawing. In this paper, an analytical model of the elastic stress field for brittle material is established during single abrasive scratching. The stress fields in front of and behind the indenter are analyzed respectively. Two different material removal modes, ductile removal and brittle removal, are considered. To evaluate the two different material removal modes, influence factor μ is proposed. The nucleation location and propagation direction of radial crack and median crack of several materials are predicted by analytical model. The result show that the radial crack nucleates behind the indenter. The deflection angle between propagation direction and scratching direction is about 35–60°, and its size depend on the material removal modes. The nucleation location of median crack is no longer at the bottom of the plastic zone, but will deflect toward the scratching direction during scratching. The size of deflection angle depends on the tip half angle of indenter. When the tip half angle is 55–80°, the deflection angle decreases with the increase of the indenter half angle. All predicted results are in good agreement with the experimental data of relevant scholars. At the end, the half-penny crack (radial/median crack system) presented in indentation process is extended to scratching process.

Safe technologies for cutting reinforced concrete structures by means of diamond tools

The advantages and the need to improve the safety of work when using modern diamond technologies for cutting concrete and reinforced concrete structures which are common during the dismantling and reconstruction of civil objects are shown. Improved organizational, structural and technological schemes of cutting these structures with diamond disc and wire saws with remote control are reasonably proposed. Preliminary fastening of cut elements on independent spatial scaffolding with screw jacks is a distinctive feature of the proposed schemes. In case of reconstruction by means of a device or an increase of the size of openings in load-bearing reinforced concrete and stone walls, a preliminary installation and commissioning of reinforcement steel frames provided for by the project are proposed, on them – guides of diamond disc, chain or wire saws and only then – cutting of reinforced concrete with its forced canting outside the working area for recycling.

Analysis on Vibration Characteristics of the Stringed Bead Wire of an Underwater Diamond Wire Saw

Vibration is one of the most important factors when the diamond stringed bead wire cuts pipeline, which not only affects the quality and efficiency of cutting operations but also affects the life of the stringed bead wire. The finite element model of the stringed bead wire is established by ANSYS Workbench in the paper. The all kinds of vibration of the stringed bead wire is analyzed by the dynamic simulation of diamond bead vibration, and The natural frequency and vibration amplitude of each order are obtained. The results show that the third - order model of stringed bead wire has large amplitude. The influence of the central distance of the drive wheel and the guide wheel and the diameter of the stringed bead wire on the vibration of the bead rope is studied, which obtain the third-order vibration amplitude of the stringed bead wire with the change of the two parameters and determine the best value of the amplitude of the bead rope in the saw cutting. The experimental results show that the effective cutting time of the stringed bead wire is the longer when the vibration amplitude is the optimum value,which means that service life of stringed bead wire is the longer.

Improved technology for the safe constructing of large-size openings in stone walls with diamond wire saws

Improved technology for the safe constructing of large-size openings in stone walls with diamond wire saws

Application of Diamond Wire Saw Cutting in Demolition of Large Reinforced Concrete Members

With the rapid development of construction engineering and densely populated of urban buildings, it is impossible to adopt traditional methods for demolition construction due to the constraints of the surrounding environment. This paper combines the demolition engineering practice of the foundation pit support system of Jinyuan International Plaza, expounds the superiority of the application of diamond wire saw cutting in the demolition of large reinforced concrete members, and puts forward the effective construction operation points, which can provide beneficial for similar projects reference.

An Experimental Verification on the Development of an Innovative Diamond Wire Saw Cutting Technology

An Experimental Verification on the Development of an Innovative Diamond Wire Saw Cutting Technology

The effect of cut depth and distribution for abrasives on wafer surface morphology in diamond wire sawing of PV polycrystalline silicon

Due to the existence of an acid etch resistant thin amorphous silicon layer over the smooth grooves of the diamond wire sawing polycrystalline silicon wafer surface, the anti-reflection effect is usually not ideal using the mature acidic texturization. The amorphous silicon layer will be produced on the machined surface by material ductile removal. Therefore, during the process of cutting photovoltaic polycrystalline silicon wafers, the material removed in the brittle way is expected and the surface topography of the wafers formed with the brittle fracture is better for the texture fabricating. In this paper, a mathematical model considering the influences of process parameters and wire saw parameters was developed based on indentation fracture mechanics. The variations of cutting groove profile formed by different material removal modes were also included. The effect of abrasives distributed on the wire saw on material removal and surface formation of polysilicon was analyzed. The results showed that most of abrasives removed material with ductile removal mode, however, the volume of the material removed by abrasive in ductile mode is less than 10% of the total removal volume. Brittle fracture removal mode was still the major way of material removal in diamond wire sawing. With the same ratio of the feed rate and wire speed, the faster feed rate and wire speed will not only improve the cutting efficiency, but also is easier to obtain a brittle fracture surface. There is a critical angle θc for the distribution of abrasives on the wire saw surface. Only when the position angle of the abrasive removing material in brittle mode is less than θc, the brittle fracture can be formed on the wafers surface.

Recycling and reuse of kerf-loss silicon from diamond wire sawing for photovoltaic industry

With the rapid growth of the global photovoltaic (PV) industry, the waste from PV industry cannot be ignored, especially the solid wastes from silicon kerf loss and the used quartz crucibles from silicon casting. The silicon kerf loss during wafer sawing was nearly 160,000 tonnes and the used crucible waste was nearly 70,000 tonnes in 2017. With the transition of wafering technology from the slurry-based wire to diamond wire sawing, recycling and reuse of kerf-loss silicon have become more feasible due to the lower impurity contents. In this paper, we aimed to find a simple approach to recycle the kerf loss and identify the purity for reuse. We first analyzed the contents of the as-received kerf-loss silicon from the industry. Then, suitable acids and refining procedure were proposed. The metals, especially nickel, could be easily reduced to several ppmw, boron and phosphorous to sub-ppmw, and carbon to several hundred ppmw, while oxygen was less than 5 wt%. Although the purity of the recycled silicon was not sufficient for casting feedstock, it had a comparable purity of about 5 N with the commercial silicon nitride releasing agent and crucibles used in silicon casting for solar cells. Because the nitride crucibles could be reused a few times for casting, the used crucible waste could be significantly reduced as well.

Research of the Cutting Possibility of Magnesium Alloys with Abrasive Diamond Wire Saw

Abstract Wire saw technology is a method that works great in industrial applications – it is a dominant method in the production of silicon wafers. But almost all kinds of brittle materials (ceramics, rocks, meteorite and minerals or wood) can be cut using wire saw. Question, this article will try to answer is whether this is also applicable to magnesion alloys? Article presents selected problems from an area of abrasive treatment of magnesium alloys. This includes effects of research, concerning possibilities of application of abrasive diamond wire in the process of cutting magnesium alloys AM60 and AZ91 as well as results concerning surface quality obtained after cutting with the abrasive diamond wire German Company HK Präzisionstechnik.

Thermal pretreatment of diamond wire sawn multi-crystalline silicon wafers for wet acid texturization of solar cells

Diamond wire sawn (DWS) multi-crystalline (mc) silicon wafers for solar cells are known to be difficult to texturize with the conventional wet acidic etching technology. Thermal annealing as pretreatment for wet acid texturization of the DWS mc-Si wafers has been studied. Improvement in morphology and reduction of the light reflectivity of the texture has been obtained with the pretreatment. Solar cells fabricated with the pre-treated DWS mc-Si wafers have been found to yield an ∼0.15% absolute efficiency gain in average, as compared with the solar cells fabricated in the same line with the same batch of wafers without the pretreatment. The thermal pretreatment was found to crystallize the amorphous surface layers on DWS mc-Si wafers. This is believed to be the reason for the above improvement. The present thermal pretreatment provides a promising low cost technology for texturization of DWS mc-Si wafers in photovoltaic industry.

MACE nano-texture process applicable for both single- and multi-crystalline diamond-wire sawn Si solar cells

The photovoltaic (PV) industry requires efficient cutting of large single and multi-crystalline (sc- and mc-) silicon (Si) wafers. Historically multi-wire slurry sawing (MWSS) dominated, but the higher productivity of diamond-wire-sawing (DWS) holds promise for decreasing PV costs in the future. While surface texturing of DWS wafers is more complicated than of MWSS wafers, especially in mc-Si wafers, nanotexturing has been shown to overcome this challenge. While the benefit of nanotexturing is thus clearer in mc-Si, a universal nano-texture process that also works on sc-Si would simplify and reduce the investments costs of PV production-lines. In this paper, such a nano-texture process is developed using a metal-assisted chemical etch (MACE) technique. Step-by-step characterization of surface structure and reflectance of the MACE process is used after: 1) wafering, 2) standard acidic texturing etch, 3) silver nanoparticles deposition, and 4) MACE nanotexturing for both sc and mc-Si. The results show that the same MACE process works effectively for both sc-Si and mc-Si wafers. Finally, the nano-textured wafers are processed into PV cells in an industrial process line with conversion efficiencies of 19.4% and 18.7%, for sc-Si and mc-Si solar cells, respectively.

The impact of damage etching on fracture strength of diamond wire sawn monocrystalline silicon wafers for photovoltaics use

To reduce silicon kerf loss, we have cut silicon bricks into wafers using a thin diamond wire (the diameter of core wire: 80 µm, the average size of abrasives: 10 µm). Damages caused by diamond wire sawing are responsible to have an asymmetry in fracture strength, a lower strength in parallel bending and a higher strength in perpendicular bending to the saw marks. To elucidate the asymmetry to the depth of subsurface damage, front and backside surfaces of wafers are etched in 3, 5, and 10 µm depth by 24% KOH aqueous solution. By etching 3 and 5 µm, the strength are enhanced by a factor of 1.96 and 2.9 times in parallel bending and by 1.03 and 1.31 times in perpendicular bending compared to bare wafers. Etching more than 5 µm removes the asymmetry, showing the equal strength in the bending in both directions. We cystallographically consider several fracture mechanisms of bare and etched wafers through the observation of each fracture surface.

Field stitching approach for the wave optical modeling of black silicon structures.

The interest in black silicon structures as an anti-reflective interface at the front side of silicon solar cells increased strongly with the rise of diamond wire sawing. The application of optical modeling in order to predict optimal structure parameters could be highly valuable. However, due to the random nature of the structure as well as dimensions in the range of the wavelengths of interest, optical modeling is still a challenge. Within this work, the stitching method of rigorously calculated fields is extended and applied to a black silicon structure. A Fourier transform is used to determine the angular intensity distribution in the far field. In combination with the OPTOS formalism, this allows modeling of silicon substrates with black silicon front side and shows a reasonably good agreement with optical measurement results. Implementing the investigated structure into a solar cell configuration reveals not only a low reflectance but also a very good light trapping performance close to that of a Lambertian scatterer.

Wear of diamond in scribing of multi-crystalline silicon

A practical challenge in slicing of low-cost multi-crystalline silicon (mc-Si) wafers by the fixed abrasive diamond wire sawing process is increased wire consumption due to greater wear of the diamond compared to slicing of the more expensive mono-crystalline silicon (mono-Si) wafers. In this paper, we present the results of scribing of mc-Si and mono-Si materials with two conical tip diamond indenters of the same geometry to understand the possible reasons for increased diamond wear in cutting of multi-crystalline silicon. Specifically, the scribing forces and the diamond indenter wear produced in scribing of the two silicon materials are analyzed. The results show that the forces generated in scribing of mc-Si are higher than in scribing of mono-Si. The higher forces in scribing of mc-Si are consistent with the corresponding higher tip radius of curvature (due to wear) of the diamond indenter compared to the tip radius produced in scribing of mono-Si. Scanning electron microscopy and confocal microscopy of the diamond indenters show that wear is primarily due to physical micro-fracture and blunting of the diamond. Raman spectroscopy shows evidence of stress-induced phase transformation of the diamond and the formation of compressive residual stress in the diamond. Plausible physical reasons, including the role of material inhomogeneity in mc-Si, for the wear of diamond during scribing are given.

Suppressing scratch-induced brittle fracture in silicon by geometric design modification of the abrasive grits

The overarching goal of this research was to investigate the application of spherically shaped abrasive particles in achieving ductile-mode cutting. Scratching experiments were carried out to assess the differences between arbitrarily and spherically shaped diamond and tungsten carbide (WC) grits in inducing brittle fracture or ductile plasticity in single-crystal silicon. It was observed that the arbitrarily shaped particles produce brittle fracture in contrast to the spherically shaped grits. The sharp edges and corners of grits result in high tensile stress-concentrated regions causing cracking and spalling. Contrary to this, spherically shaped WC particles induce uniform cutting pressure, which suppresses the extent of the brittle fracture and the mode of material removal was completely dominated by ductile-cutting until a threshold load for ductile-to-brittle transition (the first cracks appearance). These observations are expected to provide a suitable pathway in making the Diamond Wire Sawing machining operations more robust by providing a control on brittle damage.

The orientation and optical properties of inverted-pyramid-like structures on multi-crystalline silicon textured by Cu-assisted chemical etching

An effective low-cost texturing method based on the Cu-assisted chemical etching (CACE) technique was adopted to thoroughly texture diamond wire sawn (DWS) multi-crystalline silicon (mc-Si) wafers to form inverted-pyramid-like (IPL) structures on different grains. A mathematical model was first established to confirm the orientation of the IPL structures on grains 〈1 1 0〉, grains 〈1 1 2〉 and grains 〈1 1 3〉; this confirmation enables one to deeply understand the CACE process for mc-Si. In addition, the optical properties of IPL structures on different grains were investigated. We reveal that the IPL texture reduces the wafer reflectance to a much lower level of 22.4% and 4.4% before and after SiNx deposition, respectively. Due to the lower reflectance, the average cell efficiency for IPL textured wafers is as high as 19.03%, which is 0.52% absolute higher than that for wafers textured using HF/HNO3 mixture solutions. This CACE technique paves new insight to promote the industrial application of DWS mc-Si solar cells.

The Influence of Black Silicon Morphology Modification by Acid Etching to the Properties of Diamond Wire Sawn Multicrystalline Silicon Solar Cells

Black silicon with nanosized textures is very important to the diamond wire sawn (DWS) multicrystalline silicon (mc-Si) solar cell due to its low reflectivity. Normally the nanosized textures can be obtained by metal-assisted chemical etching (MACE) on the DWS mc-Si wafers. Here, we found that in order to improve the conversion efficiency of DWS mc-Si solar cell with nanosized textures, the textures’ morphologies must be modified by acid etching. The acid etching is the defect removal etching process. Our experimental results showed that the acid etching process influences not only the size and the reflectivity of the nanosized textures, but also the recombination velocities of the silicon wafers. A DWS mc-Si solar cell with modified nanosized textures was successfully obtained by MACE and suitable acid etching process, whose reflectivity is lower than that of a DWS mc-Si solar cell prepared by conventional acidic texturizing. The highest conversion efficiency of 19.07% was reached and a 0.6% conversion efficiency gain was obtained for a DWS mc-Si solar cell (15.6 cm × 15.6 cm), as opposed to the DWS mc-Si solar cell prepared by conventional acidic texturizing.

Improved mechanical strength and reflectance of diamond wire sawn multi-crystalline silicon wafers by inductively coupled plasma (ICP) etching

In this work the standard wet chemical and plasma texturing processes for multi wire slurry abrasive sawn multi-crystalline silicon were applied to fixed diamond wire sawn (DW) multi-crystalline silicon. The plasma etch produced an effective anti-reflective layer without any changes to the process parameters. The achieved texture features a reflectance well below 5% in the visible range. Furthermore the mechanical strength of the wafers was investigated. 4-point bending tests revealed that anisotropic strength behavior is still present for the plasma textured wafer. In addition to their excellent optical properties, the plasma textured wafers show increase of 123% in characteristic fracture stress related to the as-cut batch for the critical loading with the saw marks parallel to the rollers. This can lead to a significantly reduced breakage rates during solar cell production. It is shown, that the characteristic fracture stress of the multi-crystalline plasma textured batch is equal to the strength of mono-crystalline industrial wet etched fixed diamond wire sawn wafer.

Enhanced optoelectronic conversion in diamond-wire sawing multi-crystalline silicon solar cells through nanotexture-induced photon management

Nanotextured diamond-wire sawing (DWS) multi-crystalline silicon (mc-Si) solar cells are successfully fabricated on an industrial scale. The nanotextures are achieved through reactive ion etching (RIE). By introducing the RIE-nanotextures, the DWS mc-Si solar cells with aluminum back-surface field (Al-BSF) structure exhibit an enhanced optoelectronic conversion, and high power conversion efficiency (PCE) of up to 19.50%. This enhanced optoelectronic conversion is attributed to nanotexture-induced photon management effect, including both efficient reflection reduction and absorption enhancement, and which offset over the increased recombination of charge carriers. The DWS mc-Si solar cells are promising for industrial production due to the low raw material cost, high PCE, and manufacturing processes compatible with the existing production lines.

Novel low-cost alkaline texturing process for diamond-wire-sawn industrial monocrystalline silicon wafers

Diamond-wire-sawing (DWS) processes have been developed in recent years to overcome the problems of silicon (Si) waste and low throughput of the conventional multi-wire-slurry-sawing (MWSS) process for cutting Si ingots into wafers. However, DWS is not adopted extensively by PV industry as standard alkaline texturing is not directly applicable to these wafers to generate regular pyramidal structure. In the present work we are reporting a novel low-cost alkaline texturing process for industrial DWS monocrystalline silicon (c-Si) wafers. Our process has three novelties; firstly, it uses a low-cost saw damage removal (SDR) process with a new recipe of potassium hydroxide (KOH), sodium hypochlorite solution at 80 °C for slow Si etching. This process also successfully removes the amorphous Si layer normally present on the as-cut DWC Si wafer surface. Secondly, no initial cleaning process is required before our SDR process. Finally, a high throughput KOH/isopropyl alcohol/potassium silicate texturing process was applied successfully for pyramid formation on the DWS c-Si wafers. Small (~2–4 µm in height) and uniform pyramidal structure with reduced surface reflectance is confirmed by scanning electron microscope, Zeta 3D measurement and UV–Vis spectroscopy studies. Further, photoluminescence (PL) imaging of lifetime samples prepared with the present texturisation process, confirmed the uniformity of surface passivation, a prerequisite for solar cell fabrication. Screen-printed solar cells were fabricated in NCPRE cell fabrication laboratory. For our 6 in. pseudo-square CZ p-type c-Si wafers cell efficiencies up to 18.5% were achieved with the new texturing process. This high throughput novel texturing process thus can easily be integrated into the standard industrial process.