Grit Shape Research Articles

A new analytical model of ploughing friction for arbitrary grit shape on any unflat surface

To gain better knowledge of the grinding process especially the grinding force and efficiency, the friction characteristics between workpiece and abrasive grains has been investigated extensively. However, the calculation of coefficient of friction (COF) in previous studies is limited to indenters with optimized shapes, e.g. pyramidal shape from Berkovich and Vickers indenter or conical shape from conical indenter. In the kinematic simulation of grinding, the applicability of previous models in estimating the contact area and COF is limited due to the very irregular grit shapes of the grinding product. In this study, a new model for calculating the COF for scratches by arbitrary grit shape on any unflat surface is proposed, which only involves the elastic recovery ratio, the pile-up ratio, the grit profile and the workpiece surface profile prior to scratch. To verify the model, single scratch tests under two different shape indenter were conducted on a Nanoindenter. The model is then used to analyze the influence of indenter tip shape on the COF by applying it to a few typical shapes of grinding grits. Finally, good agreement was found on the variation trend of the COF in double scratch tests under different separation distances.

A new model of grit cutting depth in wafer rotational grinding considering the effect of the grinding wheel, workpiece characteristics, and grinding parameters

Wafer rotational grinding is widely employed for back-thinning and flattening of semiconducting wafers during the manufacturing process of integrated circuits. Grit cutting depth is a comprehensive indicator that characterizes overall grinding conditions, such as the wheel structure, geometry, abrasive grit size, and grinding parameters. Furthermore, grit cutting depth directly affects wafer surface/subsurface quality, grinding force, and wheel performance. The existing grit cutting depth models for wafer rotational grinding cannot provide reasonable results due to the complex grinding process under extremely small grit cutting depth. In this paper, a new grit cutting depth model for wafer rotational grinding is proposed which considers machining parameters, wheel grit shape, wheel surface topography, effective grit number, and elastic deformation of the wheel grit and the workpiece during the grinding process. In addition, based on grit cutting depth and ground surface roughness relationship, a series of grinding experiments under various grit cutting depths are conducted to produce silicon wafers with various surface roughness values and compare the predictive accuracy of the proposed model and the existing models. The results indicate that predictions obtained by the proposed model are in better agreement with the experimental results, while accuracy is improved by 40%–60% compared to the previous models.

Effect of the grit shape on the performance of vitrified-bonded CBN grinding wheel

Abstract This paper deals with the effect of the CBN grit shape on the grindability of a low alloy chrome steel, 100Cr6. Firstly, a simple wheel-workpiece interaction model is introduced to investigate the grinding response. The formulation considers the global grinding forces, which embodies all the properties of the wheel acting at the interface. The use of this approach eliminates the need to consider the interaction of each individual grit with the workpiece during the grinding process. Next, a series of tailored grinding tests conducted with a creep-feed grinding machine are used to evaluate the grinding performance and the wheel wear. The results have shown that the specific grinding energy ( u e ) is affected by the CBN grit shape, and the wheel wear is proportional to the ratio of the CBN shape factor (Aspect Ratio) and the overall bearing surface of the wheel-workpiece contact area ( a f ).

Effect of abrasive grit shape on polishing of β-Ga2O3(100) substrate

β-Ga2O3 can be cleaved easily, where the (100) surface is the main cleavage surface. This surface encounters local stress concentration during ultra-precision machining and is prone to local fragmentation, resulting in formation of micro-cleavage pits. The effects of different abrasive grit shapes on polishing are studied in order to ensure smooth processing of β-Ga2O3(100). First, a contact mechanics model for different shapes of abrasive grits and crystal surfaces is established in accordance with the theory of elasticity. Then, the contact mechanism between the abrasive grits and the crystal surfaces is analyzed using a theoretical model. Finally, the feasibility of the theoretical model is verified in experiments. The results show that blunt spherical abrasive grits are more suitable for polishing of β-Ga2O3(100) than sharp diamond-shaped abrasive grits. Compared to sharp abrasive grits, the crystal surfaces processed using blunt abrasive grits are smoother, with surface roughness (Ra) of approximately 14 nm. During polishing, the sharp and blunt abrasive grits remove brittle and plastic material, respectively. Therefore, blunt abrasive grits are more suitable for the polishing of β-Ga2O3 than sharp abrasive grits.

Diamond Wire Sawing of Solar Silicon Wafers: A Sustainable Manufacturing Alternative to Loose Abrasive Slurry Sawing

Slicing silicon wafers for solar cells and micro-electronic applications by diamond wire sawing has emerged as a sustainable manufacturing process with higher productivity, reduced kerf-loss, thinner substrates that save material, and reduced environmental impact through the use of water-based cutting fluids, compared to the conventional loose abrasive slurry sawing process. This paper reviews recent research on diamond wire sawing of photovoltaic silicon wafers and compares it with the loose abrasive wire sawing process from a standpoint of sustainable manufacturing. Various aspects of the diamond wire sawing process including surface morphology, total thickness variation (TTV), surface and subsurface damage, fracture strength, residual stress, stress induced phase transformation, effect of microstructure and abrasive grit shape are critically reviewed and areas of future need are identified.

Analysis of Grinding Surface Creation by Single-Grit Approach

This paper presents some new research findings in the investigation of single-grit grinding in terms of surface creation. The investigation demonstrated that rubbing–plowing–cutting hypothesis of grinding material removal mechanism is valid in both experiments and simulations. A finite element model (FEM) was developed to simulate the material deformation during the grit interacts with the workpiece. It was found that the cutting mechanism is the more effective in the first half of the scratch where the grit penetrates the workpiece. The plowing is a prominent mechanism in the second half of the scratch where the grit is climbing up along the scratch path and uplifting the material at the front and the sides of it. This observation is very important to provide a greater insight into the difference between up-cut and down-cut grinding material removal mechanisms. Multipasses scratch simulations were performed to demonstrate the influence of plowing on the ground surface formation. Moreover, by analyzing the effects of grinding conditions, the shape of cutting edges, and friction in grinding zone on the grinding surface formation, some useful relations between grinding performance and controllable parameters have been identified. It has demonstrated that plowing has significant influences on ground surface formation and concluded that the influence of grit shape, friction, and grinding kinetic condition should be considered together for the plowing behavior control, which could provide a good guidance for the improvement of grinding efficiency.

Effect of grit shape and crystal structure on damage in diamond wire scribing of silicon

AbstractFundamental understanding of the fixed abrasive slicing of photovoltaic silicon wafers is crucial for producing low‐cost wafers with superior surface quality and mechanical strength. With the goal of understanding the diamond wire sawing process, this paper investigates the scribing of mono‐ and multi‐crystalline silicon by the abrasive grits on an actual diamond wire. Specifically, the effects of grit shape and silicon crystal structure on the resulting surface morphology, subsurface damage, and the critical depth of cut at which ductile‐to‐brittle transition occurs are investigated. Results show that surface cracking depends on the grit shape. Scribing across the grain and twin boundaries in multi‐crystalline silicon impacts the resulting surface morphology, with grit shape producing a greater effect than crystallographic orientation in the grain interior relative to the grain boundary. Subsurface damage depends on the grit shape and crystal structure. Differences in the critical depth of cut for ductile‐to‐brittle transition in scribing of mono‐crystalline silicon are explained via analysis of the stress state produced by idealized grit shapes.

Modeling and analysis of the grit level interaction in diamond wire sawing of silicon

This paper analyzes the interaction between diamond grits and crystalline silicon (c-Si) in the ductile regime of diamond wire sawing through theoretical calculations and finite element modeling (FEM). Cutting depth per grit is calculated based on the sawing parameters and is found to be in the range of 41 to 143 nm for a typical diamond wire sawing operation. These depths are smaller than the critical depth of cut for brittle-to-ductile cutting mode transition in single point diamond turning/scribing of c-Si as well as the value derived from indentation fracture mechanics. The shape of the cutting grit plays an important role in determining the normal force and the critical depth of cut. The cutting force calculated by the FEM is approximately 12 mN for a spherical grit/indenter shape and 30 mN for a faceted pyramidal (Vickers) indenter at a 70-nm scribing depth. It is shown ductile mode cutting performance is sensitive to grit shape, and grits with sharp edges can easily lead to brittle fracture. The theoretical cutting depth per grit indicates the likely dominance of ductile mode cutting in diamond wire sawing, albeit, in reality, it is usually a mixture of ductile and brittle cutting. This discrepancy is more likely related to the grit size and shape variation in an actual diamond wire as well as to the dynamics of the operation.

Research on Processing Mechanism of Multi-Cell-Disc

this paper relates to the following studies: The model of cutting depth distribution of grains of Multi-cell-disc was analyzed and established. The shape of the abrasive grit has been discussed and the abrasive grit shape model of unit-bold was simplified. The superficial characters of elastic elements were tested by Nano-indentation tests and the loading-displacement character of superficial abrasive particles during loading was gotten. By using probability and statistics, the model of cutting depth distribution of grains was obtained.

Analysis of Grit Cut Depth in Fixed-Abrasive Diamond Wire Saw Slicing Single Crystal Silicon

A mathematical model to calculate the grit average cut depth in wire sawing single crystal silicon was founded. So the grit average cut depths were calculated theoretically by choosing different process parameters, and influences of process parameters on grit cut depths of slicing silicon crystal were analyzed. Analysis results indicate that the grit average cut depth relates to the silicon mechanical properties, grit shape and size, wire speed and ingot feed speed, etc. And there is a monotone increasing non-linear correlation between grit average cut depth and the ratio i value of ingot feed speed and wire speed, when the i value is lower, the average grit cut depth is lower.

To characterise diamond mill wear

This work shows two alternative methods to characterise diamond tool wear. The macro-geometric method involves readily measurable variables and, therefore, it requires little time. However, it allows only a partial understanding of the phenomena involved in tool wear. The micro-geometric method implies a deeper understanding of mechanical and tribological mechanisms involved in tool wear and, therefore, it requires a longer time. An optical microscope, a SEM and an electronic balance allowed the observation of the mill and diamond grit shape, and the measurement of the relevant variables. Test protocols are used to implement both the methods. The results show that two sets of quantitative variables may be used to predict the tool wear in a synergic way and, therefore, improve the tool use.