One of the main undesired phenomena that affects the dimensional accuracy and shape of the cold formed parts made from metallic sheets is the springback. An important cause that determines and ...influences the intensity of this phenomenon is the distribution of stresses generated by the cold forming process in the deformed material. The determination of a relationship between springback and generated stresses distribution needs the knowledge of the law of stresses and springback parameters variation and of their causes and factors of influence. A model for prediction of springback parameters in the case of U stretch–bending process as a function of stresses distribution in the sheet thickness was established and analyzed in the paper. The results obtained from the performed analysis show that the normal anisotropy influences the level of stresses on the inner and outer faces and finally the springback intensity. The blankholder force and friction coefficient have not a major influence on the stresses level but the increase of their values determines the increase of the distance between the neutral and middle axes of sheet and hence the decreases of springback intensity. Based on the established model the prediction of springback was done in the phase of tools design and hence the drawn part accuracy was increased.
► The model for prediction of springback parameters was constructed using the Hill’48 yield criterion. ► The springback was predicted as a function of stresses distribution in sheet thickness. ► The stress in sheet thickness was determined based on strains due to bending and tensile loadings. ► The neutral axis position was determined based on strains due to bending and tensile loadings. ► The unloading moment was expressed using the equality: strain energy=external loadings energy.
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► Multiple headspace extraction measurements to study the release of aroma compounds from solid support. ► The release rate of Mentha Piperita essential oil components from inclusion complex was ...controlled. ► Determination of formation constant between aroma and cyclodextrins by static headspace gas chromatography.
In this paper, the controlled release of aroma compounds from cyclodextrins (CDs) and CD polymers was studied by multiple headspace extraction (MHE) experiments. Mentha piperita essential oil was obtained by Soxhlet extraction and identification of the major compounds was performed by GC–MS analysis. Menthol, menthone, pulegone and eucalyptol were identified as the major components. Retention of standard compounds in the presence of different CDs and CD polymers has been realised by static headspace gas chromatography (SH-GC) at 25°C in the aqueous or gaseous phase. Stability constants for standard compounds and for compounds in essential oil have been also determined with monomeric CD derivatives. The obtained results indicated the formation of a 1:1 inclusion complex for all the studied compounds. Molecular modelling was used to investigate the complementarities between host and guest. This study showed that β-CDs were the most versatile CDs and that β-CD polymers could perform the controlled release of aroma compounds.
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► Cyclodextrin polymers for the controlled release of fragrance compounds. ► Multiple headspace extraction measurements to study the release of fragrance from solid support. ► Determination of ...formation constant between aroma and cyclodextrins by static headspace gas chromatography.
In the present study, we investigated the feasibility of preparation of novel controlled release systems for the delivery of essential oil used as ambient odors. The inclusion interactions of cyclodextrins (CDs) and β-cyclodextrin polymers with linalool and camphor in Lavandula angustifolia essential oil were investigated by static headspace gas chromatography (SH-GC). The stability constants with monomeric CD derivatives were determined for standard compounds and for the compounds in essential oil. All studied CDs and CD polymers reduce the volatility of the aroma compounds and stable 1:1 inclusion complexes are formed. The retention capacity of the CD derivatives was measured in static experiments. The feasibility of preparation of novel controlled release systems for the delivery of fragrances was investigated by multiple headspace extraction (MHE) experiments.
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Stretch forming is a metal forming process that implies bending and stretching a sheet of metal over a die, with the sheet being plastically deformed into the desired shape. The purpose is to obtain ...large parts. One of the main aspects is that the metal sheet is locked into position by gripping jaws. A hydraulic ram is raised into the metal sheet, therefore increasing the tensile forces. This process is used to draw intro shape materials like aluminium, magnesium, titanium alloys, stainless steel, Inconel. These materials have in common the fact that they have poor formability or the elastic spring-back has unacceptable values. Taking this into consideration, the nature of the materials along with the fact that the metal sheet can crack, due to excessive strain, we propose a self-adaptive stretch forming process. Underlining this process is the stress-strain curve, that has three inputs: force, sample section area and strain. For each of these factors, our method uses a particular approach, as in a Python-based software and Android-based IoT solution, that uses stress and strain data. Furthermore, it controls, in real-time the hydraulic press to the point at which the material is stretch close to its ultimate yield strength.
The formability of magnesium alloy sheets at room temperature presents anisotropy in mechanical properties and difficulties in terms of occuring cracks easily, especially in regions with bend radius. ...In addition, the elastic spring-back is significant, leading to massive deviations from the desired shape. Recent studies conducted in this field lead to stretch forming magnesium alloys sheets using thermo-mechanical treatments at temperatures up to 400°C. The present study was conducted on 1 mm thick magnesium alloy AZ31B sheet to investigate its formability when stretching at room temperature by several dies with different radius. The stretching process was conducted on a hydraulic press, using 3D printed PLA dies with the following values: R180, R320, R540, R720, R900 and R1080. The samples were stretched until fracture to highlight the fracture force, distance to fracture, deviation from the die radius and bend angle.
•The sheet thickness variation in the case of mini drawn parts was analyzed.•New tools were made to minimize the sheet thickness variation and its effects.•The blankholder plate was made from two ...concentric rings with different widths.•The rings were made from different materials and were pressed with different forces.•The new tool geometries were verified/validated by simulation and experiment.
Thickness variation is a major defect of the drawn parts made from sheet metals, which influences the intensity of part defects and may cause part failure. In the case of mini deep drawing, sheet thickness variation along part's profile has the following effects on the drawn part geometry: increased non-uniformity of diameter variation, variation of springback parameters (part edge radius deviations and angle of wall inclination), different wrinkling intensities, and part cracking and fracture. The present paper analyses the experimental results of the investigations concerning the sheet thickness variation in the case of mini cylindrical drawn parts made from a copper alloy. Some constructive solutions of tool components that allow the control and minimization of sheet thickness variation by controlling the blank holder force, contact and friction forces (especially in the part flange zone) are also proposed and tested by simulation and experiment. The constructive solutions of the new tools were obtained by constructing the blank holder plate from two concentric rings made from different materials with equal or unequal widths.
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3D printing is a maturing technology, that can be used from fast prototyping to industrial scale. A key aspect of 3D printing is the ability to control the material density, thus it's hardness. This ...factor assures that 3D printing is not only economical competitive, but it also provides parts with improved mechanical properties. Furthermore, it is a good alternative for manufacturing stretch-forming dies. Implementing 3D printed dies offers an economical advantage, as cost for producing are a fraction of the cost of standard metal die, and the technology behind the process is simpler. Therefore, in this paper we have chosen to study stretch forming on a die that has components 3D printed from polylactic acid (PLA). The length and width of the punch is maintained constant while the radius varied from R180 ÷ R1080 mm, with an increment of 180 mm. A total number of 6 punches were used in these experiments to stretch sheet metal stripes made of aluminium 2024-T0, a material specific for aircraft skin. In addition to the shape of the resulted part, in the present study other process parameters have been investigated (punch force, part radius and deviation from circularity).
The surface response method is widely used in many sectors of the industry, this method is a set of statistical and mathematical techniques used to minimize or maximize the factors of production by ...optimizing inputs factors. The use of this method helps to improve the quality of the products and processes while reducing the time and cost of producing the products. Our goal is to use this method to reduce the number of experiments and analyse the interaction between the cutting parameters (cutting speed, feed rate and depth of cut) and to predict the response (cutting temperature) during the machinability of the AISI 1060 steel, by turning. The results found the predicted values obtained by the mathematical model show good agreement with the experimental results, the error percentage of the numerical models and the accuracy were 5.15% and 94.85% respectively.
The main context in which abrasive water cutting is used is the reduction of thermal deformation induced by thermal (plasma arc PAC, oxyfuel OFC, laser) of electrothermal (electroerosion EDM) cutting ...methods. Although it is not the cheapest or time-efficient technique it can be used on a wide variety of metallic and non-metallic materials. Among other benefits are the lack of burrs, high precision and improved surface finish, low setup time and stress-free cutting. This leads to no secondary processing required in many other applications. Depending on the material hardness the cutting thickness can reach up to 300 mm. The present study proposes an analysis of high-pressure abrasive water jet cutting of a 19 mm thick plate. The aluminium alloy used in this study was Al-6061-T651. This alloy is being used especially in the aeronautics industry due to is excellent welding properties. The experiments were conducted using multiple input and output factors. The design of experiments (DOE) takes into account input factors and offers models for responses. The study was organised according to response surface methodology, with an I-optimal design type and a quadratic design model. The input factors were: cutting pressure, standoff distance, programmed quality of the cut. The responses analysed were: entrance (Iw) and exit (Ow) width of cut, and taper angle (α). An ANOVA analysis was performed for each response. This interpretation implies the significance (p-value) that the input factors have on the variation of the responses. For Iw and Ow a reduced 2FI model was proposed, while for θ a linear model was suggested. The p-value obtained for each response is smaller than 0.0001, which classifies the models as significant. The ANOVA fit statistics determine the R-squared error between 0.964 and 0.995, meaning that the responses are well defined by the input value variations. This high confidence in the results leads to accurate mathematical models.
An important problem encountered in the deep drawing processes of sheet metals is represented by the sheet thickness variation that can influence and affect the quality of drawn parts, may cause ...stress concentration in different zones of drawn parts or may conduct part fracture. The variation of sheet thickness during cold formation can have a greater importance when the drawn parts are made with small dimensions from metal sheets having small thickness. The present paper analyses experimental and numerical simulation results concerning the thickness variation in the case of micro/milli-cylindrical drawn cups made from sheets, called foils, having thicknesses from 0.05 to 0.20mm. A mathematical model for predicting the thickness variation is also developed, based on the variation of the unit radial forces developed in foil thickness, as a function of part geometry and material yielding trajectory. On this basis it is possible to control and minimise the thickness variation in the following part zones where such phenomena can generate negative effects: part wall where the variations of part diameter, wall inclination and wall curvature are the negative effects caused or influenced by the foil thickness variation and wall–bottom connexion zone where a negative effect can occur if the foil thickness variation results in the loss of material integrity.
► The analysis was performed based on experimental and simulation results using the DynaForm software. ► The factors that influence sheet thickness variation for micro/mili drawn parts were analysed. ► A model for the thickness variation prediction was developed based on the radial forces variation. ► The developed model was used to optimise process parameters and tools geometry.
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