Thickness Reduction Ratio Research Articles

Effect of flow forming on mechanical properties of high density polyethylene pipes

Flow forming is a single rotary-contact-point cold-forming process, in which the thickness of a tubular pre-form is reduced while its length increases without any change in internal diameter. Although metal flow forming has been studied by many researchers and industries, there does not appear to be any published study on the flow forming of polyethylene pipes. The main purpose of this study was to find out the applicability of flow forming on polyethylene pipes and the effects of process parameters on mechanical properties of polyethylene flow formed parts. The experiments were carried out using HDPE80 tubular pre-forms. Thickness reduction ratio, feed rate and rotation speed of mandrel were considered as variables. An L9 orthogonal array of Taguchi method was applied to carry out the experiments. Tensile and impact tests were performed to examine the failure behavior of specimens. Scanning electron microscopy (SEM) was implemented to find out the relation between mechanical properties and microstructure of the material. Stress at break, yield Stress, percentage of elongation at break and impact endurance were measured as indicators of mechanical properties. It was found that mechanical properties of HDPE increase significantly during flow forming. The solid state deformation makes material more oriented and anisotropic that leads to an enhancement in mechanical properties of HDPE. Through SEM it was found that the material experiences a transformation from an isotropic spherulite structure into an anisotropic lamellar-fibrous structure at large deformation.

Damage evaluation in tube spinnability test with ductile fracture criteria

Spinnability, the maximum thickness reduction ratio a material can undergo without fracture, has important effects on product quality and production efficiency in tube spinning. However, predicting the rupture limit and spinnability poses challenges due to the complexity of tube spinning process. This study aims to select appropriate ductile fracture criteria (DFCs) in terms of the damage limits, which were obtained by mechanical tests, to accurately predict the forming limit and damage evolution in the tube spinnability test. The periodic stress triaxiality and periodic Lode parameter were firstly introduced by considering the periodical changes of the stress and strain components in the spinning process. Based on the evolution of the two parameters, the out layer of TA2 titanium tube exhibited a higher damage potential, which was consistent with the experiment results. Nine ductile fracture criteria were incorporated into the finite element software (ABAQUS) to simulate the damage evolution in tube spinnability tests. The results show that, except for the Freudenthal, R–T and Ayada models, all of the other ductile fracture criteria are suitable for predicting the damage distribution on TA2 titanium tubes in spinnability tests. The variation of stress triaxiality under different cut-off values in tensile test were much closer to that in spinnability test relative to upsetting test throughout the entire forming process, which led to higher prediction accuracy of the spinnability by the tensile test. For all of the DFCs considered, the C–L criterion provides the most accurate predictions on the spinnability of TA2 titanium tubes.

A Novel Ironing Process with Extra High Thickness Reduction: Constrained Ironing

A new ironing method entitled constrained ironing is proposed for producing thin-walled cans and components with uniform thickness. This method based on compressive stresses could reach a higher ironing limit ratio or thickness reduction ratio (TRR) without interruption for additional processing such as multi-stage ironing and annealing between different stages. When the constrained ironing starts, the punch pushes the constrained material to reduce the thickness from the outer surface of the cup. The state of the stresses is fully compressive in this new process while it is tensile in the conventional ironing method. The results showed that after constrained ironing process, the tensile strength and hardness increased to 204 MPa and 85 HV, respectively, from the initial values of 71 MPa and 25 HV. Thus, very high TRR is achievable in the constrained ironing process. Obtaining a higher TRR about 80% after only single stage ironing, removing the annealing stages, and obtaining higher strength and hardness of the ironed cup are several advantages of the proposed method. This novel and simple process could be very promising for the industrial applications to replace the conventional process and to reduce the final product cost.

Wear debris generation during cold rolling of stainless steels

The production of pollution can be a significant industrial problem during cold rolling. Pollution is often attributed to the formation of wear debris during rolling, which mixes with the lubricant oil used to cover the rolled sheet. The cleanliness of the rolled sheet, its consequent aesthetics, and the downstream performance of the process are affected by the production of pollution. In the first stage of this study, the pollution formed during industrial cold rolling was collected and found to be composed of a mixture of small stainless steel debris and lubricant. Second, the study investigated the effect of rolling conditions on the generation of wear debris. Tests were carried out using laboratory cold rolling mills. The effects of the type of stainless steel (ferritic or austenitic), of the surface finish of the sheets before rolling, of the thickness reduction ratio, of previous annealing of the sheet, and of lubricant temperature on the wear of sheets due to rolling were investigated. Cold rolling resulted in weight reduction of the sheets due to the formation of wear debris. Weight loss for sheets finished by conventional acid pickling was greater than for sheets finished using shot blasting. A further reduction in the wear of the sheets due to rolling was observed when their surface roughness was decreased by polishing. An increase in the thickness reduction ratio lowered the elongation to fracture of the rolled sheets and increased their wear. Previous annealing of the sheets was then used to successfully reduce wear of the rolled sheets. An increase in the temperature of the oil used during rolling increased wear of the sheets due to rolling. Finally, industrial trials were carried out applying the rolling conditions that had resulted in lower weight loss for the sheets during the laboratory-scale tests. This significantly reduced the amount of pollution produced during industrial cold rolling of stainless steel, improving the final quality of the product.

The FEM Analysis for Feed Rate of Plate Multi-Point Composite Incremental Forming

Combined with the advantages of multi-point composite incremental forming(MPCIF) of uniform deformation, high formability and efficiency, and can efficient restrain plate’s instability, basing on 3D finite element analysis model of MPCIF, different feed rates were used to form the typical truncated pyramid-shaped work-pieces, the process of MPCIF was simulated and analyzed, and the equivalent plastic strain, forming precision and thickness reduction ratio of deformed parts were studied. The simulation results show that the maximum thickness reduction occur at the diagonal of the parts; plate’s thickness thinning can be more serious with the feed rate is bigger, and plate becomes more easy to crack; more uniform wall thickness and better shape accuracy can be obtain with the feed rate is smaller, but the forming efficiency is lower due to longer forming time.

Semi-solid Powder Rolling of AA7050 Alloy Strips: Densification and Deformation Behaviors

Semi-solid powder rolling (SSPR) is a novel strip manufacturing process which combines the features of semi-solid rolling and powder rolling. SSPR involves rolling procedure of metallic alloy powders when both liquid and solid phases coexist. In this study, densification process and deformation mechanisms of AA7050 powder in the presence of liquid phase were investigated. The relationships between the apparent plastic Poisson’s ratio and the relative density as well as the thickness reduction ratio and relative density were calculated. The relationship between deformation strain and relative density was calculated as well. The experimental data of relationship between rolling forces and relative density were achieved. The results show that the densification process of SSPR also can be divided into three stages and liquid phase mainly affects stage I. In stage I, semi-solid particles’ rearrangement and restacking are the main densification mechanisms when the initial liquid fraction is lower than 20 pct. When the initial liquid fraction is higher than 20 pct, flowing and filling of liquid, semi-solid particles rearrangement and restacking are the densification mechanisms. In stage II, severe deformation of particles associated with a rapid increase in the apparent plastic Poisson’s ratio and interparticle contact area contributes to the densification process. In stage III, the densification mechanisms are the deformation and collapse of isolated pores. The calculated deformation strain increases gradually with the same slopes as the relative density increases in stages II and III no matter how much the liquid fraction is. Higher liquid needs less deformation degree that contributes to the densification.

A study of manufacturing tubes with nano/ultrafine grain structure by stagger spinning

A new method of manufacturing tubes with nano/ultrafine grain structure by stagger spinning and recrystallization annealing is proposed in this study. Two methods of the stagger spinning process are developed, the corresponding macroforming quality, microstructural evolution and mechanical properties of the spun tubes made of ASTM 1020 steel are analysed. The results reveal that a good surface smoothness and an improved spin-formability of spun parts can be obtained by the process combining of 3-pass spinning followed by a 580°C×0.5h static recrystallization and 2-pass spinning with a 580°C×1h static recrystallization annealing under the severe thinning ratio of wall thickness reduction. The ferritic grains with an average initial size of 50μm are refined to 500nm after stagger spinning under the 87% thinning ratio of wall thickness reduction. The equiaxial ferritic grains with an average size of 600nm are generated through re-nucleation and grain growth by subsequent recrystallization annealing at 580°C for 1h heat preservation. The tensile strength of spun tubes has been founded to be proportional to the reciprocal of layer spacing of pearlite (LSP), and the elongation is inversely proportional to the reciprocal of LSP. This study shows that the developed method of stagger power spinning has the potential to be used to manufacture bulk metal components with nano/ultrafine grain structure.

Roughness optimization of flow-formed tubes using the Taguchi method

The present study reports the effect of various flow-forming process parameters and roller geometry on the roughness of flow-formed tubes of commercial pure copper UNS C11000. Thickness reduction ratio, feed rate, angular speed of mandrel, attack angle of roller, roller tip radius, and smooth angle of roller were considered as variable parameters. The effects of these input parameters on the roughness have been critically analyzed using the Taguchi method. Through ANOVA analysis, it has been found that the roller tip radius is the most important parameter affecting roughness followed by thickness reduction ratio. Selection of an optimum combination of variable parameters was performed based on “average of results.” The minimum roughness of 1.37 μm was achieved when the process parameters were set at their optimum values.

두께감육 평가를 위한 비접촉식 초음파 센서 네트워크를 이용한 토모그래프 기술 개발

This paper describes a tomographic imaging technique for evaluating the thickness reduction of a plate-like structure using a noncontact sensor network based on an electromagnetic acoustic transducer that generates shear horizontal plate waves. Because this technique is based on the effect of mode cutoff and time of flight of guided waves caused by a change in thickness, the tomographic image provides information on the presence of defects in the structure. To verify the performance of the method, artificial defects with various thickness reduction ratios were machined in an aluminum plate, and the tomographic imaging results are reported. The results show that the generated tomographic image displays the thickness reductions and can identify their locations. Therefore, the proposed technique has good potential as a tool for health monitoring of the integrity of plate-like structures.

Internal structural evolution and enhanced tensile plasticity of Ti-based bulk metallic glass and composite via cold rolling

The influence of cold rolling on the tensile mechanical properties and deformation behavior of Ti-based bulk metallic glass (BMG: Ti40Zr25Ni8Cu9Be18) and β-Ti dendrite reinforced bulk metallic glass matrix composite (BMGMC: Ti40.2Zr18Ni2.85Cu7.65Be12.3Nb19) has been investigated. The cold-rolled BMG and BMGMC samples with 20% thickness reduction ratio exhibit a pronounced tensile plasticity of 0.8% and 4%, respectively. The malleable behavior of the cold-rolled samples originates from the internal structural evolution and modulation of elastic properties.

Multi-objective Optimization of Medium Frequency Induction Heating Process for Large Diameter Pipe Bending

Medium frequency induction heating for large diameter pipe bending is an advanced technique that has been widely used. However, the thickness control of outer wall and inner wall of pipe is still difficult in the actual production: outer wall tends to be thinner and inner wall tends to be thicker. Therefore, it is necessary to optimize the process parameters of bending. Combined central composite experimental design and a proper selection of design parameters sample, an accurate response surface model was built in order to decrease ovality, thickness reduction ratio and forming load. The response value of objective function was analyzed; and important influence factors for system stability were found, i.e heating temperature, heating width and advance speed. The results indicate that the optimal value range were heating temperature of outer wall t=1030∼1070°C, while advance speed v=0.3∼0.4mm/sec. Practical results from multi-objective optimization could achieve qualified products.

Theoretical Analysis of Effects of Wall Suction on Entropy Generation Rate in Laminar Condensate Layer on Horizontal Tube

The effects of wall suction on the entropy generation rate in a two-dimensional steady film condensation flow on a horizontal tube are investigated theoretically. In analyzing the liquid flow, the effects of both the gravitational force and the viscous force are taken into account. In addition, a film thickness reduction ratio,Sf, is introduced to evaluate the effect of wall suction on the thickness of the condensate layer. The analytical results show that, the entropy generation rate depends on the Jakob number Ja, the Rayleigh number Ra, the Brinkman number Br, the dimensionless temperature differenceψ, and the wall suction parameterSw. In addition, it is shown that in the absence of wall suction, a closed-form correlation for the Nusselt number can be derived. Finally, it is shown that the dimensionless entropy generation due to heat transfer,NT, increases with an increasing suction parameterSw, whereas the dimensionless entropy generation due to liquid film flow friction,NF, decreases.

An Approximate Approach to Predict the Degree of Starvation in Ball–Disk Machine Based on the Relative Friction

This article focuses on analyzing the correlation between the degree of starvation and friction under the sliding motion in a ball–disk machine. The objective of this study was to define approximately the degree of starvation in the contact based on measuring one parameter (the relative coefficient of friction). Such an approximate approach could be useful in cases of opaque contacts where the optical interferometry technique cannot be used; for example, a steel ball on a metal disk. Experimental measurements were conducted under different degrees of starvation using a tribometer equipped with a torque sensor and a high-speed digital camera. The results showed agreement between the theoretical equations and the experimental measurements. Thus, it can be stated that the approximate ratio of the film thickness reduction can be predicted based on accurate measurements of friction.

Submicrocristalline Structure and Dynamic Recovery of Cold Flowformed ELI Grade Ti-6Al-4V

Flowforming is a means to produce seamless tubes by plastic deformation at room temperature. It consists in reducing the thickness of a tubular part mounted on a mandrel by deforming it using several rollers translating along the tube axis, while the tube is rotating along its axis. Thanks to the high compressive stresses, and to the incremental nature of the deformation process, flowforming can lead to a high thickness reduction and thus to high elongation of the deformed tubes. Ti-6Al-4V (Extra Low Interstitial grade) tubes have been deformed by cold flowforming, with a thickness reduction ratio higher than 60%, and their microstructures have been investigated using light optical microscopy (LOM), scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). Based on EBSD data, a post-processing analysis has been performed in order to study the texture of the flowformed parts. Optical Microscopy showed that the material could be deformed without displaying flow instability such as adiabatic shear banding, despite the fact that it has been processes out of the stable processing maps (high strain rate and low temperature). It also evidenced a major deformation along the tube axis accompanied with a slight twist due to torsion stress. EBSD analysis indicated the occurrence of continuous dynamic recrystallization, which is rarely reported in the α-β domain of such alloys. The recovery/ recrystallization effects resulted in a submicrocrystalline equiaxed structure, which is consistent with that previously reported for Ti-6Al-4V subjected to severe plastic deformation (SPD). The texture of the hexagonal α-phase appeared to be similar to that obtained on extruded Ti-6Al-4V, with a basal component perpendicular to the tube axis.

Effect of processing parameters on the relative density of spray rolling 7050 aluminum alloy strip

Spray rolling is a novel metallic semisolid near-net-shape forming technology. The problem of controlling the density of spray rolling aluminum strips is taken into two considerations: eliminating porosity before rolling and providing enough thickness reduction ratios during rolling. This simulation study reveals the relationship among the processing parameters of spray rolling, average solid fraction, and the relative density of a strip. The calculated values agree well with the experimental data. The densification mechanism during spray rolling process corresponds to the removal of porosity dominant regime. The relative density of spray rolling aluminum alloy strip depends heavily on both the solid fraction and thickness reduction ratios. The solid fraction in the range of 65–70 % corresponds with a good spray deposition condition and a high density level of strips. The present theoretical and experimental analyses suggest that spray rolling can be optimized to manufacture directly strips with a high density and excellent mechanical properties from liquid metal within one step.

Optimum design of pipe bending based on high-frequency induction heating using dynamic reverse moment

Pipe bending by high-frequency local induction heating is an advanced technique used to bend pipes having a small bending radius and a large diameter. Although pipe bending is a widely used engineering process, the optimum process parameters are decided on the basis of a trial and error method by highly experienced field engineers. Hence, it is necessary to develop an integrated methodology for the optimum design of the pipe bending process. During hot-pipe bending using induction heating, the thickness of the outer wall of the pipe decreases because of tensile stress, but the thickness is not allowed to decrease by more than 12.5%. The use of the DOE method and a dynamic reverse moment is proposed for maintaining the thickness reduction ratio to within 12.5%, when D/t is high. The results of the proposed approach are found to be in good agreement with those of FEA.

Sheet Metal Forming Limit Prediction with Maximum Thickness Reduction Ratio

Maximum thickness reduction ratio is used to predict sheet metal forming limit in the numerical simulation of forming process. The maximum thickness reduction ratio under different stain path is not a constant for the same material. The effect of strain path and strain hardening exponent on forming limit is considered. The relationship between the maximum thickness reduction ratio that the material can obtained and the strain path between tensile to equi-biaxial is established. The parameter in the criterion can be determined by tensile experiment combined with numerical simulation of the same forming process. Then the limit strains under other linear strain paths between tensile to equi-biaxial can be determined by the criterion combined with numerical simulation of corresponding forming process. Forming limits of three kinds of sheet metals are predicted with the modified maximum thickness reduction ratio criterion. Good agreement is achieved between the predicted data and the experimental data.

Optimization of Process Parameters of Tube Hydroforming Based on Orthogonal Experiment

Numerical simulation was made on parameters like internal pressure and axial force as well as friction coefficient of tube that affect the formation of variable cross-section tube. Through numerical simulation and orthogonal optimization, the most thickness reduction ratio and thickness uniformity on different conditions were contrasted and analyzed. An optimum scheme was obtained and it could improve the formability of variable cross-section tube. The result indicates that the axial force plays the most important role on thickness reduction ratio. The result provides technical support for the variable cross-section tube hydroforming research.

Instabilities and multiplicities in non-isothermal blown film extrusion including the effects of crystallization

Stable operating regions for blown film extrusion are mapped using a dynamic model that includes the effect of crystallization on the rheological properties of the polymer. In the computations, the bubble air mass and take-up ratio were held constant, and the machine tension and bubble inflation pressure were treated as dependent variables. For a given bubble air mass, the take-up ratio was used as the continuation parameter for mapping steady-state solutions. The take-up ratio varies smoothly, but not necessarily monotonically, with the machine tension. Curves of either blow-up ratio or thickness reduction versus take-up ratio reveal that there are take-up ratios where no, one, or multiple solutions exist. The heat transfer coefficient from the polymer film to the external air and surroundings has a marked influence on the qualitative and quantitative features of the blow-up ratio versus thickness reduction curves. Generalized eigenvalue analysis of the linearized blown film equations indicates that increasing the heat transfer rate increases the stability of operations. A corresponding decline occurs, however, in the thickness reduction of the blown film for a given blow-up ratio.

고주파 유도가열 및 동적 반력 모멘트를 이용한 파이프 벤딩 공정의 최적설계

Abstract The Pipe bending process using high frequency local induction heating is an advanced technique to bend pipes with a small bending radius and a large diameter. Even though the pipe bending process is a quite widespread engineering practice, it depends heavily upon trial and error method by field engineers with several years of experience. So it is necessary to develop an integrated methodology for optimum design of the pipe bending process. During hot pipe bending using induction heating, outward wall thickness of a pipe is thinned due to tensile stress and the reduction of wall thickness is not allowed to exceed 12.5%. Taguchi method and dynamic reverse moment is proposed to maintain a reduction ratio of thickness within 12.5%, when D/t ratio is high. An application of the proposed approach was compared with those of the finite element analysis and has good in agreements Key Words : Pipe Bending, High Frequency Induction Heating, Dynamic Reverse Moment, Reduction of Wall Thickness, FEA, Design of Experiment Method, Taguchi Method