Circle Grid Research Articles

Experiments on mobile robot stereo vision system calibration under hardware imperfection

Calibration is essential for any robot vision system for achieving high accuracy in deriving objects metric information. One of typical requirements for a stereo vison system in order to obtain better calibration results is to guarantee that both cameras keep the same vertical level. However, cameras may be displaced due to severe conditions of a robot operating or some other circumstances. This paper presents our experimental approach to the problem of a mobile robot stereo vision system calibration under a hardware imperfection. In our experiments, we used crawler-type mobile robot «Servosila Engineer». Stereo system cameras of the robot were displaced relative to each other, causing loss of surrounding environment information. We implemented and verified checkerboard and circle grid based calibration methods. The two methods comparison demonstrated that a circle grid based calibration should be preferred over a classical checkerboard calibration approach.

Formability of aluminium sheets manufactured by solid state recycling

Conventional recycling practices for non-ferrous metallic scrap involves melting followed by purification. This practice is suitable for recycling when the large volume of scrap is available. Though such recycling reduces consumption of diminishing metallic resources, high energy requirement and material loss during melting and purification limit its applicability. In the present work, manufacturing of solid state recycled aluminium sheet by hot rolling is explored and its formability characterized. Aluminium chips were divided into smaller particles (1~2mm) by crushing. After stress relief annealing, chips were cold compacted into square slabs (75*75mm section) of different thicknesses. Another similar set of slabs was made by hot compaction. The compacted slabs were hot rolled over a number of passes at 400°C. Each slab was reduced to approximately 90% thickness to get the sheet thickness in the range of 0.6 to 1.5 mm. Microstructure revealed good interface bonding between the chip particles. Mechanical properties of the sheet from room temperature up to 200°C and at different strain rates were characterized by a number of tensile tests. Circular blanks from sheet were drawn into cylindrical cups and strain distribution was observed along different directions of rolling using circle grid analysis.

Comparison of plastic strains on AA5052 by single point incremental forming process using digital image processing

In this study, a surface based strain measurement was used to determine the formability of the sheet metal. A strain measurement may employ manual calculation of plastic strains based on the reference circle and the deformed circle. The manual calculation method has a greater margin of error in the practical applications. In this paper, an attempt has been made to compare the formability by implementing three different theoretical approaches: Namely conventional method, least square method and digital based strain measurements. As the sheet metal was formed by a single point incremental process the etched circles get deformed into elliptical shapes approximately, image acquisition has been done before and after forming. The plastic strains of the deformed circle grids are calculated based on the nondeformed reference. The coordinates of the deformed circles are measured by various image processing steps. Finally the strains obtained from the deformed circle are used to plot the forming limit diagram. To evaluate the accuracy of the system, the conventional, least square and digital based method of prediction of the forming limit diagram was compared. Conventional method and least square method have marginal error when compared with digital based processing method. Measurement of strain based on image processing agrees well and can be used to improve the accuracy and to reduce the measurement error in prediction of forming limit diagram.

On the Utilization of Circle Grid Analysis in Thin-walled Forming of Tubes: Experimental and Numerical Evaluation

Abstract This paper presents an investigation on different tube forming processes by plastic deformation, including expansion, reduction and inversion of tube ends, using circle grid analysis in order to obtain strain-loading paths in different regions of the principal strain space. The experimental work was carried out on commercial AA6063-T6 tubes and includes independent material characterization by means of tensile, stack compression and instability tests. Finite element modelling of the tube forming processes by means of an in-house computer program gives support to the presentation and allows assessing the overall accuracy, validity and reliability of using circle grid analysis to investigate formability and failure in tube forming.

Towards the characterization of fracture in thin-walled tube forming

This paper provides a simple and effective experimental procedure to determine the fracture strains and the critical values of ductile damage at the onset of failure by fracture in tube forming. The investigation is limited to crack opening in mode I (by tension) and combines experimentation in tube expansion with analytical modelling using membrane analysis, circle grid analysis and finite element modelling. The presentation is a step towards the characterization of fracture loci in tube forming and in understanding the conditions upon which necking does, or does not, precede failure by fracture in thin-walled tubes. It is showed that good engineering estimation of the fracture strains and of the critical ductile damage at the onset of fracture can be easily obtained from application of the proposed analytical model with experimental measurements of the expanded tube end radius at fracture.

Revisiting Veerman’s interpolation method

This article describes an investigation of Veerman’s interpolation method and its applicability for determining sheet metal formability. The theoretical foundation is established and its mathematical assumptions are clarified. An exact Lagrangian interpolation scheme is also established for comparison. Bulge testing and tensile testing of aluminium sheets containing electro-chemically etched circle grids are performed to experimentally determine the forming limit of the sheet material. The forming limit is determined using (a) Veerman’s interpolation method, (b) exact Lagrangian interpolation and (c) FE-simulations. A comparison of the determined forming limits yields insignificant differences in the limit strain obtained with Veerman’s method or exact Lagrangian interpolation for the two sheet metal forming processes investigated. The agreement with the FE-simulations is reasonable.

Effect of Porosity on Circle Grid Perforated Plate Performance as a Static Mixer in Laminar Flow

Mixing is one of the important processes to the many industries. Fluid mixing process typically involves three phases of fluid in the form of liquids, gases and solids. To obtain a desired type of mixing, one of the devices that can be use is a static mixer. In this study, a perforated plate static mixer with circle grid fractal design with two grades of porosity which are 50% and 75% will introduce. The purpose of implementing the two grades porosity of perforated plate in this study is to determine a performance of the two static mixers. In order to achieve the objective, the simulations of mixing fluid were carried out by using ANSYS CFX software. The simulation was carrying out primarily in cylindrical pipe with insertions of circle grid perforated plate. Three levels of laminar flow had been used which is Reynolds numbers (Re) equal to 100, 200 and 400. The performance of circle grid perforated plate static mixer will be evaluated by determining the Coefficient of Variation (COV). The simulation results also were compared in term of homogeneity level of mixing fluids to the Kenics static mixer. Based on the simulation results, the value of COV at selected plane in pipeline simulated for Kenics static mixer and the two grades porosity of perforated plate at Re = 400 are 0.000703, 0.0247and 0.00427 respectively. Since the values of COV between 0.01 and 0.05 are a reasonable target for many industry applications, the results for new approach of static mixer represent completely homogeneous mixing fluid for this application. Definitely this new approach of circle grid perforated plate with fractal design gave better results because of lower number of inserts and simple design of static mixer.

Failure in single point incremental forming

This paper revisits the formability limits of single point incremental forming (SPIF) in the light of fundamental concepts of plasticity and ductile fracture mechanics. The paper has a twofold objective of investigating the limiting strain pairs at fracture in parts showing and not showing signs of necking before cracking and of demonstrating that failure by fracture occurs by tension in crack opening mode I. The overall methodology is based on the combination of circle grid analysis, measurement of the ‘gauge length’ strains at fracture and determination of fracture toughness from experimental tests performed with truncated conical SPIF parts and double edge notched test specimens loaded in tension. The work is performed in aluminium AA1050-H111 and is a step towards comprehension of the circumstances under which failure will occur in SPIF. It is shown that fracture strain pairs of truncated conical parts, fracture forming limit lines (FFLs) determined from conventional sheet formability tests and fracture toughness in crack opening mode I can be merged to create a new understanding of plastic flow and failure by fracture above the onset of necking.

Hole-flanging of metals and polymers produced by single point incremental forming

This paper presents recent developments in hole–flanging of metal and polymers produced by single point incremental forming (SPIF) to gaining insight into the deformation mechanics of the process and providing guidelines to foster its application in rapid prototyping and small batch production of customised sheet products. Experimentation with stainless steel AISI 304L and polyethylene terephthalate (PET) that comprised mechanical characterisation and utilisation of circle grid analysis in conjunction with the formability limit diagram gives support to the presentation and allows understanding the fundamentals of plastic flow and failure in hole–flanging produced by single point incremental forming and their main differences to hole–flanging produced by conventional pressworking.

Development and applications of forming-condition-based formability diagram for split concerns in stamping

This paper introduces an advanced, forming-condition-based formability diagram for accurately assessing the formability of complex stampings. The forming-condition-based formability diagram consists of a formability index that rationally define two curves (marginal line and safe line) and two zones (marginal zone and safe zone). The formability index measures deformation severity, tracks deformation history and predicts deformation trend. The safety factor, defined as the width of the marginal zone by means of the formability index, takes into account the forming conditions including deformation zone size, forming mode, bending process model, deformation history, metal flow pattern and post-necking deformation capacity of sheet metal. It is demonstrated that, rather than the traditional formability limit diagram, this formability diagram can more accurately quantify the formability status and can be used to determine the metal flow adjustment ranges for solving split problems. Its application to an automotive body side outer panel shows that it is a robust tool for formability engineering and troubleshooting through using numerical simulations and/or circle grid analysis.

Numerical Study of Circle Fractal Grid Perforated Plate as a Turbulent Generator in Combustion Chamber

Fractal grids can be used to design turbulent flows with low power losses and high turbulence intensities for intense yet economic mixing over a region of designed length and location. The introducing circle grid perforated plate is the main aim of this present paper. In this numerical work, we want to ascertain a new approach in turbulence generators on the structure of premixes flames using perforated plate fractal-grids pattern. In this paper, we compared circle grid perforated plate by varies using its diameters, spacing and number of holes on the plate. The result showed good perceptivity of the fractal generated turbulence and the fractal flow physics. The turbulent intensity can be increased by a grid with higher blockage ratio.

Mixing Analysis of Laminar Flow in Static Mixers with Circle Grid Fractal Perforated Plate Elements

The static mixers are widely used in many industries to obtain the desired type of mixing. In the context of mixing process, two different fluids and have a different properties will mix in a single equipment to produce an another fluid with a new property. In this research, a new approach of static mixers was proposed for pipeline mixing. The flow pattern, pressure drop and mixing characteristics (coefficient of variation) were carried out by means of computer simulations. The static mixers introduced here consists of a series of perforated plate with circle grids fractal pattern elements. The simulations work were carried out by using a commercial package of Computational Fluid Dynamic (CFD), ANSYS CFX 14.0 software. Three levels of laminar flow with Reynolds numbers (Re) of 100, 200 and 400 respectively had been used to investigate the performance of the static mixers introduced here. The effectiveness of circle grid perforated plate static mixer had been evaluated by comparing the homogeneity level of mixing fluids for each flow simulated. The simulations gave a new insights in the flow pattern in circle grids fractal perforated plate elements. The pressure drop predictions compare favorably with literature data and the coefficient of variation (COV) value for circle grid perforated plate with 50% porosity at Reynolds number 100 was 0.0744 which is out of the range meanwhile at Reynolds number 200 and 400 was 0.0483 and 0.0247 respectively which are in the range of reasonable target for many applications. Mixing in the elements occurs through a combination of flow splitting and shearing at the junctions of successive elements. Besides that, simple installation and manufacturing of this type of static mixers makes the fractal perforated plate’s element an excellent static mixing device.

Critical analysis of necking and fracture limit strains and forming forces in single-point incremental forming

Single-Point Incremental Forming (SPIF) is an emerging manufacturing process especially suitable to produce small batches of metal parts. Moreover, the enhanced formability of metal sheets deformed by SPIF makes this technology useful to those industrial applications requiring high deformation levels. In this sense, the precise setting of limit strains in SPIF in relation to the conventional formability limits of the material, as well as the influence of the process parameters on these strains, are essential variables to understand how and how much can be deformed the metal sheets in real production. On the other hand, the forming force in SPIF is an essential variable, especially for the design of dedicated equipment or for the safe use of adapted machinery. This paper revisits failure in SPIF by means of an experimental analysis of the influence of process parameters, such as the tool diameter, the spindle speed and the step down, on the formability in SPIF (spifability) of AISI 304 metal sheets, studied in the light of circle grid analysis. The work also involves the independent determination of conventional formability limits by necking and fracture under laboratory conditions by using stretching tests (Nakazima tests), in conjunction with stretch-bending tests performed in order to quantify the influence of the bending induced by the tool radius. Failure strains are experimentally obtained and compared in stretch-bending and SPIF tests, being the failure mode discussed in each case. Finally, the axial forming force evolution was recorded with the aim of analyzing the range of process parameters that would guarantee the safely utilization of the non-dedicated process equipment.

Quantitative Mixing Analysis of Laminar Flow in Circle Grid Perforated Plate with 50% Porosity Static Mixer

The applications of the static mixers are widely applied in many industries to obtain the desired type of mixing. In this context, to perform the mixing process should have two different fluids that also have different properties which will combines it in a single equipment to make an another fluid. The main objective of this research study is to propose a new approach of fractal concept (circle grid perforated plate) for internal rapid mixing by determining the coefficient of variation (COV). This study was implemented by fully numerical simulations. The simulations of mixing fluid were carried out with the help of commercial computational fluid dynamic (CFD) package ANSYS CFX 14.0 software. The simulation was done primarily in cylindrical pipe with insertions of circle grid perforated plate with porosity of 50%. Three levels of laminar flow have been chosen to result in Reynolds numbers (Re) equal to 100, 200 and 400. The effectiveness of circle grid perforated plate static mixer has been evaluated by comparing the homogeneity level of mixing fluids to the Kenics static mixer that readily available in industries applications. Based on the research findings, the COV value for circle grid perforated plate with 50% porosity at Re 100 was 0.0744 which is out of the range while Reynolds number at 200 and 400 were 0.0483 and 0.0247 respectively which are in the range in term of reasonable target of mixing homogeneity. The values of COV between 0.01 and 0.05 are the reasonable target for many applications. In term of manufacturing cost and energy loss due to static mixer, definitely this new approach of 50% porosity circle grid perforated plate is better design compared to the Kenics static mixer because of lower number of inserts and simpler design of static mixer to produce.

Towards square hole-flanging produced by single point incremental forming

This paper presents the first investigation on square hole-flanging produced by single point incremental forming. The aim and objective is to provide readers with a broad understanding on the deformation mechanics of the process that will enable them to understand plastic flow resulting from the interaction between the tool and the blank, to identify the influence of the pre-cut geometry in the overall formability, and to characterize the physics of failure. The methodology comprises the mechanical characterization of the material, the use of circle grid analysis, and the fabrication of square flanges with round corners by multistage single point incremental forming using blanks with different pre-cut hole geometries. The investigation is performed in aluminium AA1050-H111 and the overall results widens and enhances current research work in hole-flanging of cylindrical parts by giving the first contribution towards the understanding of plastic flow and failure in hole-flanging of square parts produced by single point incremental forming.

Formability of AA3003 brazing sheet at elevated temperatures: limiting dome height experiments and determination of forming limit diagrams

Warm forming has some important advantages, the most significant being that forming limit strains increase at elevated temperatures. To quantify this advantage for an AA3003 brazing sheet, forming limit diagrams were determined using warm tooling developed to perform limiting dome height (LDH) experiments together with a digital image correlation (DIC) system used to perform in situ strain measurement. Forming limit curves (FLCs) were developed at several temperature levels and strain-rates. The formability experiments demonstrated that while temperature has a significant effect on formability, forming speed has a mild effect within the studied range. Elevating the temperature to 250 °C improved the formability more than 200 % compared to room temperature forming while forming at lower speeds increased the limiting strains by 10 % and 17 % at room temperature and 250 °C, respectively. A comparison between FLDs developed using DIC methods versus circle grid (CG) analysis showed good agreement between the two methods; however, the degree of scatter in the CG method increased significantly for the higher temperature tests.

CFD Analysis of Circle Grid Fractal Plate Thickness on Turbulent Swirling Flow

In this paper, steady state, incompressible, swirling turbulent flow through circle grid fractal plate has been simulated. The aim of the simulation is to investigate an effect of the circle grid fractal plate thickness in order to reduce swirling due to swirl disturbance in pipe flow. The simulation and analysis were carried out using finite volume CFD solver ANSYS CFX. Three different thickness of fractal plate were used in the simulation work with the thickness of 1 mm, 3 mm and 6 mm. The simulation results were compared with the pressure drop correlation of BS EN ISO 5167-2:2003 and turbulent model used, standard k-ε model gave the best agreement with the ISO pressure drop correlation. The effects of circle grid fractal plate thickness on the flow characteristics which are swirl angle and tangential velocity have been investigated as well.

Experimental study of circle grid fractal pattern on turbulent intensity in pipe flow

Fractal turbulence is deemed much more efficient than grid turbulence in terms of a turbulence generation. In this paper, the hotwire experimental results for the circle grids fractal pattern as a turbulent generator will be presented. The self-similar edge characteristic of the circle grid fractal pattern is thought to play a vital role in the enhancement of turbulent intensity. Three different beta ratios of perforated plates based on circle grids fractal pattern were used in the experimental work and each paired with standard circle grids with similar porosity. The objectives were to study the fractal scaling influence on the flow and also to explore the potential of the circle grids fractal pattern in enhancing the turbulent intensity. The results provided an excellent insight of the fractal generated turbulence and the fractal flow physics. Across the circle grids fractal pattern, the pressure drop was lower but the turbulent intensity was higher than those across the paired standard circle grids.

Circle grid fractal plate as a turbulent generator for premixed flame: an overview

This review paper focuses to ascertain a new approach in turbulence generation on the structure of premixed flames and external combustion using a fractal grid pattern. This review paper discusses the relationship between fractal pattern and turbulence flow. Many researchers have explored the fractal pattern as a new concept of turbulence generators, but researchers rarely study fractal turbulence generators on the structure premixed flame. The turbulent flow field characteristics have been studied tand investigated in a premixed combustion application. In terms of turbulence intensity, most researchers used fractal grid that can be tailored so that they can design the characteristic needed in premixed flame. This approach makes it extremely difficult to determine the exact turbulent burning velocity on the velocity fluctuation of the flow. The decision to carry out additional research on the effect circle grid fractal plate as a turbulent generator for premixed flame should depends on the blockage ratio and fractal pattern of the grid.

Single point incremental forming of a facial implant

The investigation draws from the fundamentals of the mechanical behaviour of titanium grade 2 to the design and fabrication of facial implants by means of single point incremental forming. To provide knowledge on the capabilities and limitations of a new manufacturing technology to fabricate low-cost, patient-specific medical implants. Rapid fabrication of a simplified model of a facial implant. Circle grid analysis and its graphical representation in the fracture forming limit diagram combined with finite element modelling are utilized to identify the failure limits and to assist the overall design of the facial implants. Fabrication of facial implants without and with failure by cracking due to excessive thinning of the sheet from where the implant is to be cut. Identification of the major operative parameters that influence fabrication of sound facial implants by means of single point incremental forming. Reduce the gap between production engineers and the medical community by presenting a state-of-the-art manufacturing technology to produce low-cost, patient-specific medical implants.