Papers by Keyword: Flatness

Abstract: Silicon Carbide (SiC) provides excellent characteristics such as superior thermal conductivity, high carrier mobility and extreme chemical stability in comparison with those of Silicon (Si). SiC is already showing significant device performance benefits in power devices, high performance communication, and LED lighting. However, SiC presents many challenges for wafer surface treatment because of its high hardness and remarkable chemical inertness. Today, mechanical polishing techniques on industrial batch CMP tools are the predominant methods for SiC wafer surface treatment, but material removal rate (MRR), surface defects and wafer flatness control are reaching fundamental limits with increasing wafer diameter. Batch processing typically results in a higher amount of surface scratches and defects, higher wafer to wafer variability, and higher wafer breakage rates. A unique single wafer chemical mechanical polishing (CMP) technique on 150mm n-doped, 4° off-axis, single crystal, 4H-SiC wafers was developed to create a virtually defect-free surface. A polishing head has been designed to manipulate polishing pressures at various zones of the wafer. This capability can modulate the removal thickness at each region on the wafer surface, resulting in a highly uniform wafer profile. Additionally, a CMP slurry has been formulated to maximize MRR from 2μm/hr to over 8.5μm/hr. Potassium permanganate has been selected as an oxidant and aluminum oxide particles as the abrasive. The oxidant concentration and abrasive content along with slurry pH level have also been optimized for ideal chemical and mechanical activity. Scratch-free wafer surfaces are observed with atomic force microscopy (AFM) and bright field (BF) and dark field (DF) inspection techniques. Roughness on the Si face is reduced to below 0.08nm. Total length of surface scratches was reduced to 10mm or less. Industrial metrics of wafer flatness, including total thickness variation (TTV) and local thickness variation (LTV) are modulated and improved. A test run completed on 25-wafers shows an overall 31% improvement of TTV post CMP process.

Abstract: To study the face milling of hardened steel, the paper considers the chemical composition of the processed material, as well as metal-cutting, measuring equipment and tools. A full factorial experiment of face milling was carried out by the method of mathematical planning and matrices of levels of variation and planning of independent variables were compiled. The flatness of the samples was measured and the causes of plastic deformation were determined. To find an adequate mathematical model of flatness, a regression analysis was performed, and the correlation analysis revealed the closeness of the relationship between the variables under one-and two-factor influence on the response function. The hypersurfaces and lines of the function levels are projected, which made it possible to determine the optimal and effective cutting conditions graphically and analytically.

Abstract: This study dealt with the rotary draw bending method most used for tube bending and investigates how applied bending such as normal bending, using mandrels or pressing with booster have an effect on machining accuracy, focusing on dimensional defects due to springback and flat deformation to the transverse plane. The study used particle swarm optimization (PSO) algorithms to investigate the optimal machining conditions for improving the accuracy of dimension and shape of a bent part. The following findings were obtained: The springback during applied machining using a mandrel, or using a mandrel and booster together, is almost the same as during normal processing; The flattening near the center of the bend in applied processing using a mandrel, or a mandrel and booster together, decreases more than with normal processing at mandrel protrusion L ≥ 4 mm, and the maximum can be suppressed to approximately 0.15%; When the sum of the springback and the flattening is taken as the objective function and the minimum value is obtained, the optimal solution is around L = 7 mm.

Abstract: Improving the production efficiency is the task with the increasing difficulty. Therefore, it is important to constantly expand the set of tools and perfect the methodology for improving the processes. Some of the losses associated with the negative technological events (breaks, drifting, etc.) are difficult to eliminate completely due to the complexity of making changes to the basic technology. But if you know in advance that the event will occur, you can significantly reduce the probability and consequences, thereby significantly improve the efficiency of the production process. Therefore, it is important to develop and introduce the applied approaches to forecasting the negative technological events in the production processes. This paper presents the method of the forecast-event statistical analysis of the cause-and-effect relationships. The technique was tested on the events of strip’s breakage during rolling at the cold rolling mill 1400 and strip’s drifting in the input storage of the continuous etching unit (CEU). Based on the presented methodology, the specialized digital service was developed and introduced in the production processes of the dynamo steels shop.

Abstract: Magnetic abrasive finishing (MAF) is a precision surface polishing method. At present, most studies on planar MAF are focused on improving the surface roughness accuracy and the uniformity of roughness. In practical applications, the initial surface of the work piece is not only a rough surface, but also a flat surface without a uniform height. While the traditional processing method improves the surface roughness accuracy, the original surface is basically unchanged. In this paper, a processing method is studied. According to the uneven distribution of magnetic brushes, the reasonable distribution of processing speed and processing time can finally achieve the purpose of improving the surface flatness. At the same time, this paper analyzes the non-uniform characteristics of the magnetic pole and the magnetic brush itself, and verifies the effectiveness of the processing method through experiments.

Abstract: High-strength steel is a type of alloy steel that provides better mechanical properties or greater resistance to corrosion than carbon steel. Strip shape is an important factor affecting the strip quality significantly for the rolled products. Because of the complex influence factors of plate shape and profile, shape detection and control technology have not been solved, especially for high strength steel rolling. In this paper, a novel three dimensional finite element simulation of the strip shape and flatness of high strength steel has been proposed. The material constitutive model has been built up based on experimental results through the Gleeble 3800 Thermal Simulator under different temperatures and stain rates. The modelling of roll elastic deformation system, roll gap profile and edge drop has been set up systematically considering the influence of the work roll transverse shifting and roll bending. Results have shown that both higher bending force and more roll shifting will significantly reduce the strip crown, and obtain improved edge drop distribution as well. The proposed numerical model has been validated through hot rolling experiments in 4-high rolling mills.

Abstract: The method of determination of the force of counter flexure of the working rolls was designed, ensuring improvement of the degree of flatness of cold rolled strips with due regard to the influence of unevenness of distribution of inter-rolls linear load. On the basis of the analysis of numerical realization of this method an essential influence of the width of the rolled strips upon the optimal value of the force of counter flexure was found out. Also, it was suggested to approximate the connection between increments of the force of counter flexure with linear equations, the application of which is promote to improvement efficiency of systems of automatic adjustment of shape and profile at rolling of sheets. For the condition of 4-stand cold rolling mill the values of transmission coefficients depending on widths of rolled strips were determined.

Abstract: A novel Micro Electro Mechanical System (MEMS) measurement device for straightness measurement with a three point method has been proposed. This device integrates three cantilever displacement sensors with a narrow pitch on a silicon chip. The authors determine appropriates shape, dimensions of the cantilever, and a fabrication process. According to simulation results, a triangular cantilever with altitude 12 mm long, base 4mm long, and 0.25 mm thickness was adopted to realize the target measuring range of 100 μm. Near the end of each cantilever, a square frustum probe 250 μm high which was fabricated by anisotropic wet etching was placed. Near the base of cantilevers, four piezo resistance gauges were formed; two are active gauges for measuring stress arise from a displacement at the probe and the others are dummy gauges for temperature compensation. Wiring and contact terminals were fabricated on the base substrate and the total size of the device is 20 mm × 32 mm. The fabrication process of this device was designed and result of a trial production was reported.

Abstract: The experimental and theoretic examination of conventional manufacturing procedures continue to be a topic of modern research. It is assisted, to a great extent, by the spread and the possibility of the application of high level software and more accurate measuring equipment. The research results obtained by the use of new equipment can open new ways for further development of conventional manufacturing procedures and their more intensive, more productive application. In this paper, an experimental method is used for examination of the surface features (e.g. flatness, 2D and 3D surface roughness parameters) of face milled aluminium parts. The aim of experiments was to determine the effect of change of the technological parameters (feed rate and cutting speed) on flatness and surface roughness features in of face milling of aluminium parts.

Abstract: In geometric and dimension tolerance investigations, especially for high precision mechanical parts, the accuracy of measurement is very important. The major equipment for the measurement is the coordinate measuring machine (CMM). However, the recommended strategies for evaluating tolerance values of geometric and dimension cannot be applied with high precision mechanical parts. Hence, in this research, the researcher introduced a new procedure that could evaluate geometric and dimension tolerance values of high precision mechanical parts accurately. This new procedure can determine the minimum sampling point for evaluating geometric and dimension tolerance values by using some performance information on the mechanical parts of the machine. This information was the waviness of the production machine’s motion. In order to evaluate the potential of new procedure, the flatness of test piece was made according to the ISO 10791-7-A160 standard as a case study. This test piece was made from the CNC milling machine (Chevalier 2040 VMC), and the waviness of the CNC milling machine’s motion was counted from the performance testing result measured by the double ball-bar model Renishaw QC10. By comparing flatness obtained by recommended and new procedures, experimental results indicated that the new procedure showed its potential in estimating the flatness.