Multi-step Drawing Research Articles

Analysis of Fiber Drawing in Wet Spinning for Surface Roughness

The drawing process behavior was investigated with focus on fiber stretching speed (spinning acceleration) to improve luster quality of fibers. Wet spinning method has a limitation of low luster at high spinning speed. It was determined that (1) luster quality could be evaluated by arithmetic average (RΔa) of fibers, which indicated the roughness, and (2) the roughness of the fiber was related to the spinning acceleration through the analysis of RΔa. Spinning acceleration was measured by chasing markers that were used to tie fibers. Regardless of the length of spinning bath, fibers were mainly stretched during the first stretching stage. Therefore, a multistep drawing method was used. In the case where the drawing ratio was 220% by one-step, RΔa was 10.1°; however by multi-step drawing (1st and 2nd drawing ratios were 148.3%), RΔa decreased to 8.3°. The multi-step drawing method enabled the reduction in fiber roughness by preventing a sudden change in fiber stress. In addition, high temperatures improved the fiber roughness. At high temperatures, roughness decreased despite the high acceleration because the fiber was easier to stretch than at low temperatures.

Fabrication and characterisation of geometry-controlled Cu microwires in porous poly(methyl methacrylate) templates using melt co-drawing and electrochemical deposition techniques

Abstract The fabrication of geometry-controlled Cu microwires (CuMWs) using melt co-drawing and electrochemical deposition techniques is reported in this study; the resulting CuMWs have good surface quality and integrity. By designing and arranging the poly(methyl methacrylate) (PMMA)/polystyrene (PS) and PMMA fibres artificially, porous PMMA templates with different coding orders (e.g. “1 × 1”, “3 × 3”, “5 × 5”, and “7 × 7”) are created after multi-step drawing followed by the dissolution of the inner PS. With these templates, coding arrays of CuMWs with diameters of 2–10 μm are fabricated. The geometries of the obtained templates and CuMWs arrays are shown to be consistent with the design values. This new approach extends the types and quality of CuMWs and makes it possible to devise extremely complex array structures with micro or even nano dimensions for diverse optical applications such as spectral sensing, laser phased arrays, and photonic crystal fibres.

Influence of reduction ratio on the microstructural evolution and subsequent mechanical properties of cold-drawn Co10Cr15Fe25Mn10Ni30V10 high entropy alloy wires

Abstract Influence of multi-pass reduction on the microstructural evolution and subsequent mechanical properties of a senary non-equiatomic Co10Cr15Fe25Mn10Ni30V10 (atomic %) high-entropy alloy was investigated. HEA rods obtained from a Y-block casting were cut, caliber rolled, annealed, and then produced into wires with of varying diameters by cold drawing at room temperature. The maximum reduction ratio of 96% was successfully used to manufacture 1-mm diameter wire. This resulted in a maximum tensile strength of 1.6 GPa without breakage during cold drawing. Both electron back-scatter diffraction (EBSD) and transmission electron microscopy (TEM) examination revealed that nano-scale ultrafine grains and deformation twins were generated by the multi-step drawing process. This phenomenon suggests that nano-twinning rather than grain refinement is dominant mechanism required for achieving high-strength in the Co10Cr15Fe25Mn10Ni30V10 senary high entropy alloy.

Hardening of A6111-T4 Aluminum Alloy at Large Strains and Its Effect on Sheet Forming Operations

In a number of sheet metal stamping and joining processes, the material undergoes large plastic deformation exceeding the range of plastic strain achievable in a standard tensile test prior to material plastic instability. In order to extend the range of effective strains, the multistep rolling process was employed which enabled prestraining of aluminum sheet above 2.0 of true strain. Tensile testing of rolled samples was used to identify the flow stress corresponding to the level of prestrain: By varying the prestrain level, several data points were obtained for the studied flow curve. The numerical simulation using Abaqus software for the cold rolling process of aluminum strips confirmed that majority of the strip is deformed in plane strain compression condition. Performed simulation of the LDH test determined that earlier fracture might occur if the curve obtained via rolling–tensile testing approach is used versus traditional power law approximation and Voce law approximation. The results of simulation for the multistep drawing of a cylindrical cup revealed possible wrinkling in the die entry area during redrawing stage of the process if the rolling–tensile testing flow curve is employed.

Elaboration of Architectured Copper Clad Aluminium Composites by a Multi-Step Drawing Process

Architectured copper clad aluminium composites processed by a restacking drawing method at room temperature are reported in this work. Wires were drawn to severe plastic strain without any intermediate annealing. Three different diameters were studied in order to examine the influence of a different plastic deformation level on the structure of the different wires. Thanks to image processing it has been shown that independently of the plastic deformation, inserted fibers remain continuous and are homogeneous in size and shape. Furthermore, XRD and TEM characterizations confirm that there is no significant intermetallic growth during the deformation. Thus, the improvement and/or degradation of the functional properties of the wires can be well controlled by performing an appropriate post-processing annealing treatment. Keywords: Cu/Al composite, architectured wire, drawing, microscopy, image processing

Design of Spinning and Subsequent Drawing Parameters to Improve the Mechanical Properties of PVA Fibers

In this study, efforts were made to enhance the mechanical properties of the poly(vinyl alcohol) (PVA) fibers of medium molecular weight(number-average degree of polymerization=1735) varying the ratio in DMSO/H2O mixed solvent and spinning/drawing conditions. The gel fibers prepared from pure DMSO were opaquely frozen in the coagulating bath of -20℃. However, transparent gel fibers were formed without freezing for the mixture to contain water less than 80wt%. As the amount of water in the mixture increased the residual solvent in the coagulated gel fibers decreased ranging from 85 to 42wt%. The complex viscosity increased with increasing PVA concentration in 80/20 DMSO/H2O exhibiting remarkable shear thinning at 18wt%. In the Cole-Cole plot, the 18wt% PVA solutions gave a deviated curve from 12 and 15wt% ones. Thus the optimum PVA concentration for the spinning processing of medium MW PVA solutions in 80/20 DMSO/H2O was determined to 18wt% with rheological concept. Low degree of drawing during hot drawing process in the dry state was available for high bath draft in the coagulation bath. The most improved mechanical properties were observed by applying the highest possible draw ratio attained by reducing bath draft over multi-step drawing process. In the given bath draft, linear relationship was observed between both tensile strength and modulus and draw ratio showing the inflection points at the draw ratio of 19.5 and 18.0 for tensile strength and modulus, respectively.

Manufacturing and mechanical evaluation of cooled cooling air (CCA) heat exchanger for aero engine

Recent studies on improving the efficiency of gas turbine engines have focused on increasing the inlet temperature of gas flowing into the turbine. For the high inlet temperature, it requires the development of a super-alloy based material that can withstand harsh operating conditions. However, it is essential to utilize alternative solutions such as turbine blade cooling technology. Unfortunately, lightweight, high performance, and high mechanical reliable heat exchangers for aircraft have not yet been examined because of the difficulties associated with design optimization and reliability verification under high temperatures and pressures. The purpose of this study is to develop a manufacturing process for a heat exchanger that can be used in aircraft gas turbine engines. The manufacturing process involved preparing fine tubes through multi-step drawing and annealing processes, and joining these to a tube sheet through brazing. In this work, we reported on the total fabrication processes and mechanical integrity tests of a cooled cooling air (CCA) heat exchanger for the aircraft turbine engine. Through the work, a prototype model of a heat exchanger based on a gas turbine assembly was then developed using each of the individual processes. An X-ray CT test and an endoscopy test were performed to inspect the heat exchanger. The results indicated good manufacturing integrity; thus, the developed heat exchanger can be used for cooling turbine blades

Numerical simulation and experimental validation of a multi-step deep drawing process

This paper presents the numerical simulation of an industrial multi-step deep drawing process. A large strain finite element formulation including a hyperelastic elastoplastic constitutive model and a contact-friction law is used to this end where the steel sheet material parameters considered in the analysis are previously derived through a characterization procedure of its mechanical response. The numerical predictions of the final shape and thickness distribution of the blank are compared and discussed with available experimental values measured at the end of three successive drawing steps. In addition, a plastic work-based damage index is used to assess failure occurrence during the process. The damage values computed at the end of the drawing process are found to be lower than that corresponding to rupture in the tensile test, considered here as the threshold of failure, confirming, as observed experimentally, that neither fracture nor necking is developed in the blank during the whole drawing process. Finally, the possibility to carry out a reduced two-step drawing process, obtained by merging the second and third steps of the three-step process, is precluded since the damage criterion predicts in this case excessively large values that indicate that failure may occur in specific zones of the sheet.

Evolution of Intercrystallite “Bridges” During Multi-Step Drawing of Gel-Spun Polyethylene Fibers

In 1978, Gibson et al. [1] observed a paradoxical x-ray scattering pattern in oriented ultra-high-molecularweight polyethylene (UHMWPE) that indicated that the crystallite thickness in the fiber exceeded significantly the long period. The researchers proposed a bridging model that assumed the presence of a large number of straightened connecting molecules (SCM) joining like bridges successive crystallites along the fiber axis in order to explain this obvious dimensional disparity. Subsequently, this model was confirmed in other x-ray investigations [2-5] and independently from results of low-frequency Raman spectroscopy [6-8]. The bridging model was used successfully to interpret several mechanical properties of highly oriented UHMWPE fibers, in particular, to explain the behavior of Young’s modulus during various sample-preparation procedures and various test conditions [9 and references therein]. The model turned out to be useful also for understanding the solid-state extrusion process [9]. Nevertheless, little reliable information about the formation of intercrystallite bridges in drawn fibers is available in terms of a general concept of the oriented state. The goal of the present work was to study the formation of SCM-bridges in gel-spun UHMWPE fibers. Hot drawing of fibers from a spinning solution is usually carried out in several stages in industry. Each stage has a different special structural organization of drawn fibers that can be characterized using instrumental methods. Herein we present results from a study of the formation of intercrystallite bridges in fibers drawn at the pilot plant (SRISF, Tver´). Fibers that were obtained at various stages of oriented drawing were studied using low-frequency Raman spectroscopy and wide-angle x-ray scattering. Samples were prepared from UHMWPE reactor powder with crystallinity degree 64% (according to differential scanning calorimetry) and molecular weight 2.7"10 6 g/mol (according to viscosity measurements). The reactor powder and drawing temperature—time regime were chosen based on previous results [10, 11]. The drawing process included the following successive stages. Reactor powder was dissolved with stirring in mineral oil at 172°C. The resulting homogeneous solution of concentration 3 mass% was forced at the same temperature by a dispensing six-channel pump through six spinnerettes with 48 openings of diameter 0.5 mm each. The ratio of capillary length to diameter was 5. The solution from the spinnerette head was fed into a cooling bath filled with mineral oil at 43.0 ± 1.5°C. The fluid lost its flowability and converted into a gel as a result of phase separation during such rapid cooling. The spun gel-threads were continuously transferred from the cooling bath to a mineral-oil bath at 70°C. Then, the threads were freely placed in a container where they were shrunk to the equilibrium state.

Effect of Blend Ratio and Draw Ratio on the Mechanical Properties of PET/PP Blended Conjugate Fibers

This study analyzes the influence of blend ratio and draw ratio on the fiber properties of blend fibers composed of poly (ethylene terephthalate), or PET, and polypropylene, or PP, (hereafter referred to as PET/PP conjugate fibers). For a comparison, PET and poly (butylene terephthalate), or PBT blends, (hereafter referred to as PET/PBT conjugate fibers) are also investigated. Various blend ratios of fibers are melt spun and drawn in a multistep drawing method. The conjugate fibers are evaluated using tenacity, Young's modulus, wide-angle X-ray diffraction, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) tests. The results show that multistep drawing using a lower first-step draw ratio provides a higher tenacity and Young's modulus. Furthermore, when the blend ratio is 75/25 in a PET/PP conjugate fiber and 50/50 in a PET/PBT conjugate fiber, the polymer components undergo a phase inversion phenomenon. A PP sub-micron (10−1 ∼ 100 micron) fiber of about 0.0001 ∼ 0.00017 tex in fineness, or about 0.4 ∼ 0.5 micron in diameter, can be obtained when PET/PP conjugate fiber is treated with a 25% NaOH aqueous solution by weight. However, A PBT sub-micron fiber cannot be achieved using a PET/PBT conjugate fiber.

Study on The Modification of Ultrahigh Molecular Weight Polyethylene Fiber with Polar Polymers

Due to the non-polar nature of ultrahigh molecular weight polyethylene (UHMWPE), surface modification was needed to improve the adhesion of UHMWPE fibers. In this paper, UHMWPE gel fibers were treated with a solution of polar polymer during the extracting process, then the modified UHMWPE fibers were made after multi-step hot drawing. The physical and chemical changes in the fiber structure were examined with scanning electron microscopy and Fourier transform infrared absorption spectroscopy. The mechanical properties and interfacial adhesion properties of modified UHMWPE fibers were investigated with tensile testing. The results showed that polar groups were introduced into the surface of UHMWPE fiber during the treatment process; this could improve the interfacial shear strength of UHMWPE fibers without damaging the excellent mechanical properties of fibers. The interfacial shear strength of UHMWPE fiber with epoxy resin increased with increasing draw ratio. It was shown that ethylene/vinyl acetate copolymer (EVA) is an effective modifier. After modification, the shear strength of the interface between the modified UHMWPE fiber and epoxy increased by 100%, and the integrated mechanical properties of the modified UHMWPE fibers were also optimum.

연속드로잉에서 아이어닝과 리드로잉의 복합공정

In deep drawing of sheet metal, there are many cases in which the uniform and thin wall thickness of the drawn products is more important than the bottom thickness. In this case, we can not easily get the deep drawn products with the uniform and precise wall thickness by only drawing process. Therefore in general the manufacturing processes which both the drawing and the ironing process are proceeded sequentially are used. But this method has the disadvantages of a cost-up, decrease of productivity and degradation of quality, because the ironing process is added after the drawing process. In this study, in order to improve those problems and to enhance the effect of deep drawing, the combined process of redrawing and ironing fur multistep drawing of cylindrical cups is used. In this experiment, we considered the characteristics of the combined process such as the relation between the drawing and ironing rates, the drawing limits and the forces needed for operations. The suggested force prediction shows that it can successfully represent experimental results.

Coating thickness variation during multistep drawing processes

Coating thickness variation during multistep drawing processes

Construction of sliding constraint surfaces and initial guess shapes for intermediate steps in multi-step finite element inverse analysis

Abstract Multi-step inverse analysis has been developed for more accurate results while one-step analysis can affirm qualitative deformation behavior. An inverse finite element approach has more capability to design the optimum blank shape from the desired final shape with small amount of computation time and effort. In forming simulation with the inverse method, multi-step inverse analysis is difficult to apply because sliding constraint surfaces and initial guesses of intermediate steps described by complex die and punch set are hard to generate with present mapping schemes. In this paper, intermediate sliding constraint surfaces for multi-step finite element inverse analysis are automatically constructed from the die–punch set at each step with the given stroke. The initial guess of intermediate steps is constructed by a direct mesh mapping scheme that is suggested to generate an initial guess on the constructed sliding constraint surface. Construction of sliding constraint surfaces and initial guesses for intermediate steps is applied to a multi-step rectangular cup drawing process and an S-rail forming process. The numerical example of the multi-step rectangular cup drawing process demonstrates that the proposed mapping scheme is applicable to construct sliding constraint surfaces and initial guesses for analysis of a multi-step drawing process with large aspect ratio. The analysis result of the S-rail forming process is compared with that of a direct finite element analysis to evaluate the effectiveness of the mapping scheme proposed.

Molar mass of poly (ethylene terephthalate) (PET) during ultimate uniaxial drawing

The changes of the average molar mass Mw, Mn, Mz, and molar mass distributions during multistep uniaxial drawing of poly(ethylene terephthalate) (PET) to achieve ultimate mechanical properties have been studied in detail by means of size exclusion chromatography (SEC) with triple detection: concentration, viscosimetry, and light scattering, using HFIP as solvent. An increase in molar mass of PET due to post-polycondensation and/or transesterification during drawing at a high temperature of 160 to 230°C was found. Moreover, drawing leads to crystallization and large orientation in the amorphous phase, which results in lower molecular mobility and prevents a further growth in chain length. Crazing under extreme drawing conditions occurs and affects a decrease in molar mass.

Manufacturing of Superconducting Silver/Ceramic Composites

Manufacturing of superconducting metal/ceramic composites is a rather new discipline within materials forming processes. High Temperature Superconductors, HTSC, are manufactured applying the Oxide-Powder-In-Tube process, OPIT. A ceramic powder containing lead, calcium, bismuth, strontium, and copper oxides is inserted into a silver tube and reduced by multi-step drawing. These single-filaments are packed in a new silver tube thus forming a multi-filament containing e.g. 37 single-filaments, which is subsequently reduced by drawing and rolling to tapes approximately 0.2 mm thick by 3 mm wide. After the mechanical deformation the tapes are heat treated at approximately 835°C whereby the powder-cores by phase diffusion and grain growth are converted into superconducting, ceramic fibres. The geometry, density and texture of the powder cores before heat treatment is essential for the quality and current leading properties of the final superconducting fibres. The present work describes studies on alternative packing geometries and process parameters in the flat rolling operations. The aim is to obtain homogenous filaments with advantageous geometry and good texture while avoiding potential defects such as cracks, shear band formation and sausaging.

Influence of process parameters in drawing of superconducting wire

Superconducting wire is often produced by the powder-in-tube method involving a number of different mechanical processes, among these is multi-step drawing operations of single filament wire. A silver tube is filled with ceramic powder (BiSrCaCuO). This composite is drawn in up to 100 steps, from an initial diameter of 20 mm to the final one of 1 mm. The present paper shows how two of the main parameters, the reduction and the semi-die angle, influences the drawing stress and the powder compaction of the single filament wire during drawing. The optimum die angle and the largest acceptable reduction per drawing step are determined. In powder compaction tests a linear relationship between microhardness and powder density is determined. This relationship is applied for determination of the density distribution in the cross section of drawn single filament wire. It is found that the drawing process causes an increase of the powder compaction near the interface between the silver and powder, whereas the density increase near the centre axis of the tube is smaller. The average density determined in this way corresponds well with the one determined by geometrical measurements.

Optimization of single and multistep wire drawing processes with respect to minimization of the forming energy

Optimization of single and multistep wire drawing processes, based on the finite element analysis and nonlinear mathematical programming techniques, is considered. Since the investigated problem involves the optimal selection of the extrusion die angles and the correspondent reduction rate sequence, it can be considered as one belonging to a class of optimum shape design problems. Characteristic to the considered problem is that the domain boundary, the shape of which is to be optimized, is subject to the shape dependent forming loads. The minimization of the objective function, which is related to the process energy consumption, is sought by taking several technological and geometrical constraints into account. The numerically evaluated examples demonstrate that by using the proposed optimization technique not only a substantial cost reduction, but also a considerable improvement in the homogeneity of plastic deformation through the cross-section of the drawn wire can be achieved.

Effect of Water on High-Strength and High-Modulus Poly(vinyl Alcohol ) Fibers from Crosslinking Wet Spinning /Multistep Drawing

The presence of water in poly (vinyl alcohol ) fibers spun from a water-soluble poly mer was investigated using differential scanning calorimetry, polarizing microscopy, scanning electron microscopy, and x-ray diffraction techniques. Poly( vinyl alcohol ) fibers were produced using the crosslinking wet spinning technique, which is an im provement on conventional noncrosslinked wet spinning. Borate ion-aided crosslinks were introduced during the coagulation process. Fibers had a higher drawability with the advanced wet-hot process and multi-step drawing. The tensile strength and modulus of drawn poly(vinyl alcohol ) fibers were 1.82 and 51.76 GPa, respectively. The presence of water in the fibers damaged their structure and drastically disturbed the orientation of their molecular chains. After tensile testing, there was a fractured circular layer in the fibers.

Preparation of high‐strength and high‐modulus poly(vinyl alcohol) fibers by crosslinking wet spinning/multistep drawing method

AbstractThis study is mainly focused on the preparation of high‐strength and high‐modulus poly(vinyl alcohol) (PVA) fibers by crosslinking wet spinning and multistep drawing. High strength as well as high modulus can be achieved by introduction of the crosslinks into the oriented chains to reduce entanglement degree and slippage between chains. The relationships between mechanical properties and fine structure of the drawn fibers were examined based on results of measurements of tensile property, thermal property, dynamic viscoelasticity, crystallinity, and orientation. The strength and Young's modulus of the drawn fibers are approximated to 1.82 and 51.76 GPa, respectively. The fiber has a sharp melting peak temperature that appeared at 236.7°C in the differential scanning calorimeter (DSC) curve. Our results indicate the multistep drawing procedure is superior to the conventional one‐step drawing procedure. These excellent mechanical properties can be directly attributed to their high orientation of the amorphous chains. © 1994 John Wiley & Sons, Inc.