Effect of coating material and lubricant on forming force and surface defects in wire drawing process

A pilot wire drawing machine as well as wire end-pointing roller was developed. Using these machines, a wire drawing test for four different coating materials and two different lubricants was performed as the reduction ratio increased from 10% to 30%. Materials used for a substrate in this study are plain carbon steel (AISI1045) and ultra low carbon bainite steel. To compute the friction coefficient between the coating layer of wire and the surface of die for a specific lubricant, a series of finite element analyses were carried out. SEM observations were also conducted to investigate the surface defects of wire deformed. Results show that the behavior of drawing force varies with the lubricant-type at the initial stage of drawing. The powder-typed lubricant with a large particle causes the retardation of full lubrication on the entire contact surface and the local delamination of coating layer on the wire surface. As the flow stress of a substrate increases, the delamination becomes severe.

Design and Experiment of the High Speed Wire Drawing with Ultrasound

The previous experiments of wire drawing with ultrasonic vibration were mostly carried out on self-made machine or drawing test machine and the drawing speed didn＇t conform to practical production. In order to promote the practical application of the technology, the ultrasonic vibration system was designed and manufactured by using the classical dynamics method. The dynamic characteristic of the ultrasonic vibration system was analyzed. The performance parameters of the system were measured on the resistance analyzer. The oxygen-free brass wire drawing with ultrasonic vibration at the approximate speed of practice was carried out on the LH-200/17 drawing machine. By comparing the wire drawing through ultrasonic vibration and the conventional wire drawing, the experimental results show that the drawing process with ultrasound was steady at the high drawing speed of 1 126 mm/s, while the broken wire often occurs at the speed of 980 mm/s during the conventional wire drawing; the ultrasonic vibration reduced the drawing force by 7 %; and the ultrasound also reduced the uneven deformation of the wire and greatly improved the surface quality of the wire. The research results provide theoretical and experimental support for the practice and application of the wire drawing by ultrasonic vibration.

DRAWING OF ALUMINUM-CLAD STEEL WIRE BY FORCE-FEED LUBRICATION

The force feed lubrication method is used for drawing aluminum clad steel wire. It is studied how deformation of wire and aspect of the lubricant film are influenced by the die angle, the reduction, the drawing speed and the gap between pressure die and wire. It has been concluded that when the factors above mentioned promote to thicken lubricant film, the drawing force is reduced and this favors the homogenous deformation of aluminum coating and steel core.

A LOOP DRAWBEAD RESTRAINING FORCE MODEL IN SHEET METAL DEEP DRAWING PROCESS

In sheet metal forming, drawbeads are often used to control uneven material flow which may cause defects such as wrinkles, fracture, surface distortion and springback. Appropriate setting and adjusting the drawbead force is one of the most important pa- rameters in sheet metal forming process control. This paper derives the model of loop drawbead restraining force (DBRF) using plastic forming theory, and gives the min imum blankholding force. Experiments are carried out to verify the proposed DBRF model. The good agreement between the calculated values and experiments data justi- fies the proposed loop drawbead restraining force model.

EFFECTS OF HIGH-DENSITY CURRENT PULSES ON WORK HARDENING BEHAVIORS OF AUSTENITE STAINLESS STEEL IN WIRE-DRAWING DEFORMATION

The influence of high-density pulsing current on the work-hardening behaviour of H0Cr17Ni6Mn3 and 1Cr18Ni9 stainless steels in wire-drawing deformation processes has been studied. It was found that the drawing stress and the work-hardening rate of wires were significantly reduced by applying current pulses in drawing process. The work-hardening behavior of the multi-courses drawing deformation can be well described by Hollomon formula σ=κΕn. With the application of current pulses in drawing deformation, the work-hardening exponents of H0Cr17Ni6Mn3 steel wires and 1Cr18Ni9 stainless steel wires were reduced by 33% and 45%, respectively, and their work-hardening coefficients were reduced by 41% and 47%, respectively. It was also found that the work-hardening coefficient of wires was reduced with the increment of the frequency of current pulses, while the work-hardening exponents of both steels were insensitive to the pulsing frequency.

DETERMINATION OF BLANK HOLDER FORCE IN SHEET METAL DEEP DRAWING PROCESS

Blank holder force (BHF) is an important measure to control the sheet metal forming. BHF is identified quickly using artificial neural network (ANN) on the basis of its analytical description. And critical rupture and wrinkle BHF curves are given. A close-loop control system is established to finish the forming process.

Effect of Variable Blank Holder Force on Rectangular Box Drawing Process of Hot-galvanized Sheet Steel

At first, a series of finite element method （FEM） simulation tests were used to find the critical forming conditions of hot-galvanized sheet steel during the rectangular box drawing processing when constant blank holder forces were applied. According the test results, the reasonable alteration scope of initial variable blank holder force （VBHF） was as 1.9-2.3 T. Then, based on the test productions of blank holder force, 12 typical VBHF curves were applied to perform the simulation tests by the simulation software of DYNAFORM. The simulation test results showed that VBHF had great effects on drawing formability of hot-galvanized sheet steel during the rectangular box drawing. However, the different VBHF curves were applied to control the whole drawing and it would get great different effects. At the same tine, the VBHF had great effects on the maximum thick thinning ratio, but had little effect on the maximum thick incrassation ratio. So, reasonable application of the VBHF would greatly decrease the fractures. When the VBHF profile is taken as curve L, the best effect of drawing formability could be obtained. When curve I is used, contrary effect could be gotten. The other types of curves would cause effects between above two types of VBHF curves. Finally, the actual tests were applied to check the validity of the FEM simulation tests. The results show that the FEM simulation tests are good ways for predicting and optimizing the VBHF.

Microstructures of Ti–Ni–Fe wire after severe cold-drawing and annealing

The microstructures and mechanical properties of Ti–47 at%Ni–3 at%Fe shape memory alloy wire under the condition of severe cold-drawing at room temperature and different postdeformation annealing processes were intensively investigated using transmission electron microscope(TEM),X-ray diffraction(XRD),Vickers microhardness tester and electron tensile tester.It is indicated that the structure of the alloy evolves into a predominant amorphous structure with a trace of nanocrystalline B2 phase after the cold-drawing of 76%areal reduction.Postdeformation annealing process exerted significant influence on the microstructure and mechanical properties.Crystallization occurs when the cold-drawn wire was annealed at 300℃ for 30 min.The ultimate tensile strength and ductility as well as the superelasticity of the wire are improved significantly by cold-drawing plus postdeformation annealing.

Computer Simulation on Temperature Rise in Process of Wire Drawing

In high speed wire drawing, the temperature rise is produced by the generation heat from plastic deformation of metal material and friction between wire and tool, which greatly influences the lubrication situation and mechanical properties. During high drawing, the phenomenon that wire is embrittled and die is stuck can be formed by the notable temperature rise. In this paper, based on theory of plastic deformation work , considering friction heat generation and variable physical coefficients, the mathematical model of temperature rise of high speed drawing is established and the computer program to analogy the whole process of drawing is compiled. Also the process of wire drawing on a few of alloys are calculated theoretically. Compared the calculation value with measurement, the result shows that the theoretical value coincides with experimental data.

Rectifying control of wire diameter during dieless drawing by a deformation measuring method of interframe displacement

A deformation measurement method of interframe displacement was proposed in this paper. By online monitoring the shape di- mensions of both the deformation zone and its adjacent zone by machine vision, the initial and terminative positions of deformation were dynamically identified during dieless drawing, and the global monitoring and online closed-loop control of the deformation zone were achieved. The dieless drawing process was systematically carried out on NiTi shape memory alloy wires. It is shown that the deformation measurement method of interframe displacement can track the axial displacement of the wires, but this cannot be achieved by traditional machine vision. The initial and terminative positions of deformation can be accurately identified by this method. The proposed rectifying control technology can effectively decrease the wire diameter fluctuation during dieless drawing, that is, the standard deviation of the wire diameter fluctuation could be decreased fi＇om 0.30 to 0.08 mm after three passes of dieless drawing, indicating that the control system has a good rectifying ability.

Wear behaviors and lubrication medium of TiC/Al_2O_3 ceramic wire drawing dies

The suitable test equipment for wire-drawing was designed. Wire-drawing tests were carried on with this equipment for TiC/Al2O3 ceramic wire-drawing die. Effect of lubrication medium and drawing velocity on the drawing force was investigated. The wear mechanisms of the ceramic drawing dies were investigated. Worn bore surfaces of the ceramic drawing dies were examined by scanning electron microscopy. The results show that lubricant media have great influence on the drawing force. The drawing force is the smallest when a grease lubricant is used. But alteration of drawing velocity has scarcely any influence on the drawing force. Detailed observations and analyses of the die wear surface reveal that the most common failure of the ceramic drawing die is the wear in the invariable zone and bearing zone owing to the greater press stresses. Abrasive and adhesive wear are found to be the predominant wear mechanisms for ceramic drawing die.

Prediction and determination of both friction coefficient and forming force on sheet metal deep-drawing

On the basis of the criterion of no-wrinkle, the principle and method of prediction and determination of both friction coefficient and forming force on sheet metal deep-drawing are put forward, and proved it's expedience and practicability. They are suitable for assessment of lubricant properties. Friction coefficient and forming force are a function of material parameter, design parameter and process parameter, especially relative prevent wrinkle blank-holder force. Product of both friction coefficient and prevent wrinkle blank-holder force is only function of process parameter after determining material parameter and design parameter.

Finite element simulation on the deep drawing of titanium thin-walled surface part

The deep drawing of titanium thin-walled surface part was simulated based on a self-developed three-dimensional finite element model. After an investigation on forming rules, a virtual orthogonal experimental design was adopted to determine the significance of processing parameters, such as die radius, blank holder force, and friction coefficient, on the forming process. The distributions of thickness and equivalent plastic strain of the drawn part were evaluated. The results show that die radius has a relative major influence on the deep drawing process, followed by friction coefficient and blank holder force.

Research on Thermal Deep-drawing Technology of Magnesium Alloy (AZ31B) Sheets

Forming technology of Mg alloy (AZ31B) sheets can be investigated by thermal deep drawing experiments. In the experiments, the blank holder and die contacting with the blank were heated to the same temperature as the blank by using the heating facility. The circular blank heated in an oven is formed at a temperature range of 100~400 ℃ to obtain the optimum forming temperature range and the effects of major technical parameters on the workpiece quality. It is found that the blank is brittle at temperatures lower than 200℃. Temperatures higher than 400℃ are not suitable for forming of the sheets because of severe oxidation and wrinkling. AZ31B shows an excellent formability at temperatures from 300 to 350℃ and can be formed into a workpiece with good quality. When the blank holder force is 9 kN, extruded sheets with a thickness of 1 mm can be formed into cups without wrinkling. Workpieces show strong anisotropic deformation behavior on the flanges.

Wear Behavior of Diamond-Coated Drawing Dies

The failure behavior of diamond-coated die was investigated experimentally and analytically through finite element method (FEM) simulation in the present work. Diamond coatings were fabricated by straight hot filament chemical vapor deposition (CVD) passing through the interior hole of the drawing die using a mixture of hydrogen and acetone as source gases. The performance tests were made under real drawing condition. Scanning electron microscopy (SEM) was used for the study of coating wear after die service. The coating wear appears on two regions of the reduction zone: one is near the entrance where the contact begins, and the other is at the end of the reduction zone. FEM simulation was made for calculating the von Mises stresses distribution on the coating and substrate during the drawing process. The present work was of great practical significance for the improvement of drawing performance of diamond-coated drawing dies.

ANALYSIS OF DRAWING UNDER LUBRICATION OF NON-NEWTONIAN LUBRICATING MATERIALS

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Determination of the Friction Coefficient in the Flat Strip Drawing Test

Current work is focused on the influence of friction in deep drawing process. Friction measurements were also conducted using a modified tribotester based on strip sliding between tools. Four different tool surfaces were tested under similar contact conditions regarding contact area, normal pressure, sliding speed, lubricant and surface characteristics to calculate the friction coefficient between the tool surface and a high strength low alloy steel sheet HSLA 380. The results showed that friction coefficient varies over a wide range with different lubricating conditions and different sliding velocities. For some sliding velocities, the coefficient of friction is stable and low, while for others it is unstable and higher. Results of the experiments reveal that this novel tribotester is a very useful tool to evaluate and compare the friction between steel sheet and tool surfaces in alloyed steel for cold working applications. The outcomes have only small dispersion within the different test series, which indicates a stable process with good repeatability. The test method enables comparison of different surface finishes and treatments, lubricants and coatings in terms of friction and galling under conditions similar to those found in sheet metal forming processes. The four different types of surfaces considered for this study were grinded, polished, nitrided and quenched/tempered. The main difference among the tested tools in this work was the surface roughness, which was found to have a strong influence on friction.

Effect of wire diameter compression ratio on drawing deformation of micro copper wire

A crystal plasticity finite element model was developed for the drawing deformation of pure copper micro wire,based on rate-dependent crystal plasticity theory.The impact of wire diameter compression ratio on the micro-mechanical deformation behavior during the wire drawing process was investigated.Results indicate that the internal deformation and slip of the drawn wire are unevenly distributed,forming distinct slip and non-slip zones.Additionally,horizontal strain concentration bands develop within the drawn wire.As the wire diameter compression ratio increases,the strength of the slip systems and the extent of slip zones inside the deformation zone also increase.However,the fluctuating stress state,induced by contact pressure and frictional stress,results in a rough and uneven wire surface and diminishes the stability of the drawing process.

Modeling asymmetric fracture mechanics of Mg alloy wire in drawing process

In this study,a numerical analysis was conducted on the ductile fracture of a 2-mm diameter Mg-1Zn-0.5Mn-0.5Sr-0.1Ca alloy wire during drawing.The hexagonally close-packed crystal structure of Mg alloys causes asymmetric fracture behavior,especially in the compression region.The aim of this study is to develop a comprehensive damage model for Mg alloy wire that accurately predicts ductile fracture,with a focus on the compression region.A novel experimental method was introduced to measure the ductile fracture of Mg alloy wires under different stress states.The wire drawing process was simulated using the Generalized Incremental Stress-State dependent damage(GISSMO)Model and the Semi-Analytical Model for Polymers(SAMP)model.The damage model's prediction and the experimental results were found to be in excellent agreement,especially in determining crack initiation.Computational analysis established a safe zone diagram for die angle and reduction ratio,and experimental validation confirmed the feasibility of this approach.The proposed damage model can provide a practical and reliable analysis for optimizing the drawing process of Mg alloy wire.