Cup Extrusion Research Articles

Study on Backward Extrusion of Large-Sized and Hollow Cup Using High-Strength Al-Zn-Mg-Cu Alloy

Study on Backward Extrusion of Large-Sized and Hollow Cup Using High-Strength Al-Zn-Mg-Cu Alloy

Investigation on friction characteristics of micro double cup extrusion assisted by different ultrasonic vibration modes

Ultrasonic-assisted plastic micro-forming is a research hotspot in metal-forming process. The friction characteristic is a key factor affecting the micro-forming properties of metal in ultrasonic-assisted micro-forming process. However, the existed researches were mostly focused on the friction characteristics of free surfaces, while few were studied on the friction characteristics between sample and mold cavity. In this paper, the micro double cup extrusion experiments of copper T2 were conducted to investigate the friction characteristics between sample and mold cavity with multiple ultrasonic vibration modes. Furthermore, the numerical model was developed to quantify the friction stress reduction caused by multiple ultrasonic vibration modes and estimate its contribution to decreasing the forming stress, which was usually considered mainly affected by acoustic softening, stress superposition, and friction reduction. The results show that the forming stress and the surface roughness of extruded samples are decreased sequentially with the multiple ultrasonic vibration modes of tool vibration (TV), workpiece vibration (WV), and compound vibration (CV). The cup height ratios of double cup extrusion are also increased sequentially with the ultrasonic vibration modes. But the increase of cup height ratio does not indicate the increase of friction coefficient. The friction stress reduction between sample and mold cavity is increased sequentially with TV, CV, and WV modes, and its contribution to decreasing the forming stress is 48%, 15%, and 49%, respectively.

Punch Motion Curve in the Extrusion–Drawing Process to Obtain Circular Cups

Servo press technology is gaining attention because its punch motion curve offers greater formability than that of a conventional stamping press. This study investigated the effect of punch motion curves on the circular cup extrusion–drawing process. Various punch motion curves were analyzed, and the optimal curve for application was determined. Both the extrusion–drawing process and spring back of U-shaped sheet metal were investigated. In the circular cup extrusion–drawing process, the punch motion curve of a conventional stamping press (Case A) and three punch motion curves of a servo press (Cases B–D, the strokes of which differed from that of Case A by 0.5, 1.5, and 2.5 mm, respectively) were compared, particularly regarding the effect of the coefficient of friction on the circular cup extrusion–drawing process. The simulation analysis was performed using the software program DEFORM. A set of simulated parameters were compared with experimental results. The formability, cup shape, cup height, cup thickness, extrusion force–displacement curve, stress distribution, and strain distribution were analyzed for the design of the die required. Additionally, experimental and simulation results were compared to determine the reliability and precision of the DEFORM simulations. The results indicated that the conventional punch motion curve resulted in a shorter cup, greater stress, greater strain, and the need for a greater extrusion force. By contrast, the servo punch motion curves resulted in taller cups, less stress, and less strain. The findings can serve as a reference for the development of servo presses.

The surface effect of ultrasonic vibration in double cup extrusion test

Ultrasonic vibration has been widely studied because of its excellent utility and performance in the plastic forming of metals. The mechanism and effects of ultrasonic vibration on material flow and deformation have therefore become a focus for current research. The mechanisms of ultrasonic vibration as it acts on materials include the volume effect and the surface effect. Double Cup Extrusion (DCE) testing is an ideal method for studying the surface effect but there have been few studies and some conclusions from those studies have been contradictory. For the present study, a new ultrasonic vibration-assisted DCE device was specifically designed and used for the experiment. In the tests, friction factors were calibrated and analyzed using the finite element method (FEM). The results show that ultrasonic vibration can effectively improve interface friction conditions in DCE. By changing ultrasonic loadings, an explanation was found for the ‘illusion’ that ultrasonic vibration increased interface friction, as had previously been reported. It was also shown that ultrasonic vibration exhibits a significant size effect, which can efficiently offset the negative size effect of friction in the micro-forming process. Further, it was found that the ultrasonic effect is influenced by the wall thickness of the formed part—the smaller the wall thickness, the more significant the effect of ultrasonic vibration.

Component residual stress control in forward rod extrusion by material flow and tribology\u2014experiments and modeling

The forward rod extrusion of ferritic stainless steel X6Cr17 (DIN 1.4016) is here investigated with the objectives to experimentally identify and numerically verify the effect of the lubrication system and die opening angle on residual stresses. Three lubricants – MoS2, soap and polymer – are considered whose tribological properties are characterized via double cup extrusion tests. The effect of material flow is also studied by forming in conical dies featuring three different opening angles. The extrusion experiments revealed a decrease in the near-surface tensile stresses with decreasing friction for all the considered opening angles. An opening angle of 2α = 90° led to the highest tensile residual stresses. Both an increase to 2α = 120° and a decrease to 60° resulted in reduced tensile stresses and even a shift to compressive stresses.Furthermore, a previously developed numerical model of forward rod extrusion is optimized and validated against the experimentally measured residual stresses. The effect of the spatial and temporal discretizations of the model on the predicted residual stresses is investigated. Based on the experimental and numerically verified results, the recommendation to reduce friction in forward rod extrusion is derived as a means to obtain a less detrimental to the lifecycle of extruded parts residual stress state.

Evaluation of anti-galling ability of zinc phosphate coating by backward extrusion of cylindrical cup

Abstract A method using backward extrusion of a cylindrical cup to evaluate the anti-galling ability of a zinc phosphate coating is proposed. In this method, galling generation on the inner surface of the cup is judged by the rapid increase in the extrusion load in the extrusion load-stroke diagram. By using a divided punch, the tip of the punch is left at the extrusion end when the main body of the punch is returned after extrusion, thus the galling situation on the inner surface of the cup is perfectly maintained. It is confirmed that the rapid increase in the extrusion load is caused by the generation of galling, and the residual coating thickness measured by FE-AES at the galling generation position is smaller than the reduced peak height Rpk of the punch tip.

Automatic re-lubrication by pulsating motion with punch having dimple bottom in backward extrusion of cylindrical cup

To utilise liquid lubricants for cold forging and extrusion operations causing severe deformation without phosphate-conversion coatings, automatic re-lubricating using pulsating motion of a servo press was enhanced. Although in spline forming, there is a gap between the punch and the billet, in the extrusion of a cylindrical cup, there is almost no-gap and it is difficult to feed the lubricant. To apply the automatic re-lubrication by pulsating motion in the extrusion of cylindrical cup, a punch having dimple bottom was utilised. The lubricant is trapped in the dimples at the punch bottom. While the punch is downstrokes, the lubricant remains in the dimple, while the punch is upstrokes slightly, the lubricant in the dimple is feed to the bottom of the billet. The effects of the dimple punch were compared with the result of the flat punch. The behaviour of the re-lubrication during forging was also investigated.

Experimental and numerical prediction of extrusion load at different lubricating conditions of aluminium 6063 alloy in backward cup extrusion

Experimental and numerical prediction of extrusion load at different lubricating conditions of aluminium 6063 alloy in backward cup extrusion

Evaluation of Anti-galling Ability of Zinc Phosphate Coating by Backward Extrusion of Cylindrical Cup

Abstract A method using backward extrusion of a cylindrical cup to evaluate the anti-galling ability of a zinc phosphate coating is proposed. In this method, galling generation on the inner surface of the cup is judged by the rapid increase in the extrusion load in the extrusion load-stroke diagram. By using a divided punch, the tip of the punch is left at the extrusion end when the main body of the punch is returned after extrusion, thus the galling situation on the inner surface of the cup is perfectly maintained. It is confirmed that the rapid increase in the extrusion load is caused by the generation of galling, and the residual coating thickness measured by FE-AES at the galling generation position is smaller than the reduced peak height Rpk of the punch tip.

Changes in Surface Quality and Shape of Extruded Part by Torsional Oscillation in Cold Backward Cup Extrusion

Changes in Surface Quality and Shape of Extruded Part by Torsional Oscillation in Cold Backward Cup Extrusion

Reduction in Axial Extrusion Load by Torsional Oscillation in Cold Backward Cup Extrusion

To reduce axial load in cold backward extrusion, torsional oscillation with a maximum frequency of 1.5 Hz around the extrusion axis was superposed with axial deformation. A cylindrical aluminum workpiece was simultaneously extruded in the axial direction and twisted in the circumferential direction between extrusion and knockout punches with a maximum axial speed of 0.1 mm/s, an alternating amplitude of 5°, and a maximum angular speed of 5 rpm at room temperature. The relationship between the torsional oscillation conditions and the axial load was investigated in backward extrusion with reductions in cross-sectional area of 0.17-0.69. The maximum reduction in axial load was obtained with approximately 20% in backward extrusion with a reduction in cross-sectional area of 0.51 under rotation/extrusion speeds higher than 60°/mm. The influence of the friction condition, the work-hardening characteristic of the workpiece, and the reduction in cross-sectional area on the reduction in axial load was discussed using the results of finite element simulation.

The effects of lubricants on temperature distribution of 6063 aluminium alloy during backward cup extrusion process

Backward extrusion has received several applications in the production and manufacturing sectors, most importantly in the bulk forming processes and various researchers have carried out several studies about backward extrusion processes in the time past varying from experimental, theoretical, empirical, analytical to numerical methods in order to analyze and optimize it. In this present investigation, backward cup extrusion of AA6063 was successfully carried out experimentally and theoretically using tropical coconut oil and castor oil as lubricants. The experiment was also carried out without lubrication. With the different lubricating conditions, the strain rate was varied at 1.5×10−3s−1, 2.0×10−3s−1, 2.5×10−3s−1 and 3.0×10−3s−1 respectively. A numerical analysis using DEFORM 3D software for backward cup extrusion at strain rates of 2.0×10−3s−1 and 2.5×10−3s−1 were then performed to determine optimum lubricated condition and temperature distribution during the deformation. It was found that the temperature increased with increasing strain rates. At a higher strain rate, the temperature of both punch and lower die also increased. The highest temperature was observed when lubricated with tropical coconut oil at a strain rate of 3.0×10−3s−1 which was observed to be above 33°C when compared to other lubricants. The punch temperature showed a higher temperature compared to the lower die temperature in all cases. The extrusion load–stroke curve of the simulation result was consistent with the experimental results.

Influence of tribological conditions on cold forging of gears

Gears are integral and vital machine elements in the field of drive and transmission technology. With regard to economic and ecological aspects, cold forging represents a promising approach compared to conventional cutting processes for producing highly-loadable gears. A possible extrusion process for manufacturing helical gears is the so-called “Samanta”-process. In comparison to conventional extrusion processes, an additional ejector system is avoidable. Thus, in particular for helical gears, a negative impact on the gear quality by the ejector operation is prevented. Furthermore, the process chain during the component production cycle is shortened which leads to a more efficient production. The achievable gear accuracy as well as insufficient tool life are major challenges while establishing the “Samanta”-process in industry. To enable an industrial application, basic process understanding as well as knowledge about the influences on the process results is required. For influencing component and process properties within cold forging, approaches from the tribological system can be generally used. The aim of this study is to analyze the influence of the friction conditions on selected component and process properties within cold forging of gears by the “Samanta”-process. For adjusting the occurring friction, various lubrication systems were applied, which have been qualified using a double cup extrusion test (DCE-test). The results reveal that the lubrication system determines the friction conditions during forming. Within cold forging of helical gears by the “Samanta”-process, the friction influences the resulting strain hardening of the components and the required maximum forming force as well as the energy amount.

Work efficiency in a double cup extrusion process

A double cup extrusion process (DCEP) has been analyzed numerically to investigate the characteristics of energy consumptions for a selected model material, AA 2024 aluminum alloy. The forming energy in a double cup extrusion process was analyzed in terms of ideal, redundant and frictional energy or work, which constitute of a total forming energy in metal forming process. Ideal and theoretical forming or deformation efficiencies were also examined for various process parameters chosen for analysis. The objective of this study is to investigate the influence of geometrical process parameters in DCEP on the characteristics of energy consumption or dissipation. It was revealed from this study that frictional energy was expected to be more dissipated for high reductions and low thickness ratios. It was also found that the theoretical work efficiency would decrease as the thickness ratio increases and the reduction decreases.

Use of liquid lubricant for backward extrusion of cup with internal splines using pulsating motion

To use liquid lubricants for cold forging and extrusion operations causing severe deformation without phosphate-conversion coatings, automatic re-lubricating using pulsating motion of a servo press was enhanced. In backward extrusion of a cup with internal splines, negative pressure for supplying the lubricant to the inner surface of the cup was generated under the punch bottom by the pulsating motion. Since the punch grooves are not fully filled with metal during extrusion, the gaps are formed in the grooves, and thus the liquid lubricant is supplied through these gaps up to the punch bottom without completely taking the punch from the cup. The effects of the holding time after each punch upstroke, the viscosity of the lubricant and the number of cycles on the seizure prevention and the surface quality of the formed cup were examined from experiments of extrusion with pulsating motion. To shorten the forming time, lubricant pockets on a punch bottom and billet top and increase in punch upstroke were employed.

カップの後方押出し成形における3次元局所分岐後の劈開不安定による破断限界予測

We investigated a method of determining the geometry of the die and punch, which are not allowed to fracture in the forming process of backward extrusion of cup. On the basis of the localized bifurcation theory, it is suggested that final fracture, which is recognized as the separation of a continuum material, may occur in the shear band zone with cleavage. A newly proposed instability condition to the cleaving action in the shear band zone is applied to predict the fracture limit on the forming process. Finite element analysis of the forming process is performed to know the stress state, which is required in the theory. The experimental observation using an optical microscope is also conducted to recognize fracture occurrence during the forming process. Results show that the combination of the punch shoulder radius and the die shoulder radius ensures forming without fracture.

A novel backward extrusion process through rotating die and open punch

Abstract In this study, a new method of backward extrusion through rotating die and open punch, named rotating backward extrusion (RBE), is proposed. In this new process, a torque is imposed on the die that drives billet rotating. The rotating billet was backward extruded with the use of the punch with end face groove. To investigate the capability of this process, the experiment and finite element (FE) analysis were carried out for AZ80 magnesium alloy used as experimental material. The effects of rotating speed on the effective strain and process load were analyzed. The effective strain of the final part and process load were compared for cup extrusion by both the conventional and the new process respectively. The results showed that the average effective strain through the processed sample was approximately higher in 3 times the value of the sample processed via the conventional backward extrusion. The reduction of process load is about 20% in maximum in comparison with the conventional backward extrusion process. This new process has proven to be promising for the hollow parts production because of lower process force and imposing higher effective strain. The potential for grain refinement and mechanical properties improvement are required to fully evaluate for the new process.

Influence of the Preforming Material State in Common Tribological Tests

Different tests to determine friction factors for cold forging processes are given in the literature. The double cup extrusion test, the ring compression test and the T-shape compression test are three of the common tests, which are compared in this investigation. From former investigations it is known that there is an influence of the work-hardening of the test sample on the friction factor, which is determined by the test. At this study, the influence of the work-hardening of the material on the three named tests is investigated by using a wire drawing process. In addition, the drawn wire from the originally thermo mechanical rolled wire is also annealed to have a second material state without any work-hardening. The used material and its numerical modelling as well as the analyzed tribological conditions of the real specimens are described. Afterwards the three test setups are explained for the numerical as well as for the real experiments. In the end, the influence of the drawing respectively the work-hardening for the three tests is presented and discussed.

New punch design for the elimination of punch ejection load through manipulation of the elastic strain field in the punch nose

The extreme tribological conditions present during both the forward stroke and the punch ejection stroke of a backward cup extrusion process can adversely affect the quality of the extruded part and diminish the life of the punches. A novel punch design based on the segmentation of the extrusion punch into a main body and a nose cone insert is proposed to reduce or eliminate the pressure between the punch and work piece during the punch removal stroke. This is facilitated by manipulating the elastic strain field at the punch nose. With the aid of the finite element analysis, a parametric study on the segmented elastic punch assembly was carried out to establish optimal conditions and punch design guidelines. Experiments were carried out to determine the effectiveness of the segmented elastic punch. A significant reduction in the punch ejection load was observed along with a reduction in material pickup on the punch and galling on the surface of the part. The elastic deflection of the punch also allowed the researchers to discover that a significant amount of damage could occur during the punch ejection stroke.

Numerical investigation of manufacturing hollow preforms by combining the processes backward cup extrusion and piercing

Hollow or tubular preforms are used to meet lightweight requirements and reduce production costs of cold formed components. In order to increase efficiency of manufacturing, a combined forming process was developed, which will be presented in this paper: manufacturing of hollow preforms by combining processes backward cup extrusion and piercing. With regard to combined forming processes in the field of cold forging, disclosed work consists of numerical identification of significant process input variables, process outcomes, and the process limits.