Die Cavity Research Articles

Development of a combined bulging-piercing technique to reduce forming load for a long semihollow stepped part

This paper aims to develop a new forming technique to manufacture a long semihollow stepped part. Traditionally, hot backward extrusion is used, but this technique is not suitable because it requires a very high forming load to act on the die and punch, especially at the contact between the punch and workpiece. As a result, the service life of the punch is very low. Therefore, a new technique to overcome this problem is needed. A combined bulging–piercing technique was proposed and developed in this research. The main concept of this technique is to bulge the part by upsetting the workpiece between the punch and counterpunch to generate high frictional contact pressure, which will help to restrain the material from sliding down into the die cavity during the piercing step. In other words, this technique utilizes frictional force at the die–workpiece interface to reduce the forming load of the punch. Finite element modeling was employed to investigate and determine a suitable level of the bulging which can reduce the forming load without generating any significantly high force to the counterpunch. Only experiments with the minimum forming load were selected and implemented to validate this concept because other conditions with high load will risk damaging the punch and machine press of the product line. The results show that this technique can reduce the forming load by almost 40% and also control a good concentricity of the part and reduce the wall thickness variation.

The effect of different high pressure die casting parameters on 3D microstructure and mechanical properties of AE44 magnesium alloy

To understand the relationship between the process-microstructure-mechanical properties of the high-pressure die-casting (HPDC) AE44 magnesium alloy, 3D reconstruction and 2D characterization were carried out on the HPDC castings produced with different process parameters (low slow-shot speed, fast slow-shot speed, solidification pressure). Microstructural characterization revealed that the formation of shrinkage pores are closely related to ESCs, which were mainly controlled by the low slow-shot speed in shot sleeve (ESCs growth time) and fast slow-shot speed into the die cavity (distribution of ESCs). In addition, solidification pressure can significantly reduce the shrinkage porosity in the center by improving the feeding capacity of liquid metal. Tensile fracture revealed that the tearing ridge is mainly evolved from the slip band of ESCs. The quantity and distribution of ESCs determine the fracture mode of castings. The relationship between mechanical properties of castings and the morphology of ESCs and porosity is also statistically discussed.

Formability Assessment with Microstructural Investigations for Zirconium 702 Thin Foils: Bio-Material Applications

ABSTRACT Application of Zirconium alloys for biomedical applications have received increasing attention. Unique properties like formation of an internal bone-like apatite layer and also the interaction with magnetic resonance imaging (MRI) diagnostics with better compatibility, low magnetic susceptibility and overall excellent biocompatibility, mechanical properties and resistance to biocorrosion. Forming process is plastic deformation process wherein material undergoes permanent deformation in die cavity without fracture. Local necking, wrinkling, cracking, earing etc are few of observed errors. Due to miniaturization, manufacturing at micro level is essential. Micro forming is difficult to control as thickness of foil is below 100 microns. Hence, investigation and prediction of mechanical properties of the material at micro-level plays a very vital role. The current research focusses on the forming limit curves (FLC), which is one of the way of investigation performed to predict the formability of the material Zirconium 702 (Zr702) with the sheet thickness 100 microns. Nakajima test as per the ASTM 2218–14 standards was applied. Numerical and Experimental FLCs arrived at shows good concordance. Micro-structural study is also performed on the test specimen before and after forming to analyse the behaviour of the material.

On the In-Die Conditions and Process Parameter Settings in Indirect Squeeze Casting

The current study investigated the relationship between the process settings and in-die conditions to understand the transitions between the different filling stages and the final pressure settings in indirect squeeze casting. A pressure sensor was placed in the die cavity to indirectly measure the evolution of pressure over time and monitor the filling process to study the in-die conditions. The pressure–time profile was analysed, and the maximum pressure and acceleration of the pressure were investigated empirically. The main conclusion of this paper is that the use of increasing intensification pressures is positive for the casting soundness. However, it must be stressed that there is a strong effect from the intensification pressure on the acceleration that has a far more reaching influence than the actual speed setting. A direct practical outcome is that a high intensification pressure has a more substantial effect than the second stage fill speed. This translates directly to a possibility of reducing the second stage fill speed to stabilise the fill front. Furthermore, this also pinpoints the need for improvements in hydraulics system designs to decouple the intensification pressure from the filling piston motion control.

Al-Mn Intermetallics in High Pressure Die Cast AZ91 and Direct Chill Cast AZ80

Manganese-bearing intermetallic compounds (IMCs) are important for ensuring adequate corrosion performance of magnesium-aluminium alloys and can be deleterious to mechanical performance if they are large and/or form clusters. Here, we explore the formation of Al-Mn IMCs in Mg-9Al-0.7Zn-0.2Mn produced by two industrial casting processes, high-pressure die casting (HPDC) and direct chill (DC) casting. As Al8Mn5 starts forming above the α-Mg liquidus temperature in this alloy, we consider its formation during melt handling as well as during casting and heat treatment. In HPDC, we focus on sludge formation in the holding pot, partial solidification of IMCs in the shot chamber, and Al-Mn IMC solidification in the die cavity. In DC casting, we focus on interactions between Al-Mn IMCs and oxide films in the launder system, Al-Mn IMC solidification in the billet, and the partial transformation of Al8Mn5 into Al11Mn4 during solution heat treatment. The results show that minimising pre-solidification in the shot sleeve of HPDC and controlling pouring and filtration in DC casting are important for ensuring small Al-Mn intermetallic particles in these casting processes.

Internal flow optimization in a complex profile extrusion die using flow restrictors and flow separators

The control of flow balance at the die exit is the key for successful extrusion of polymers. The complex cross-sectional variation in real-world hollow extrusion profiles intrinsically promotes flow imbalance in the die cavity. Special considerations are required for designing extrusion dies for such profiles. The die design for a complex door frame profile was computationally optimized in this study with the aid of a commercially available software package. The velocity distribution at the die exit, post-die extrudate deformation, temperature distribution, and pressure distribution of a traditional die was investigated in detail and found to be inadequate. A modified die incorporated three distinct features, flow restrictors, flow separators, and approach angle of the torpedoes, to achieve a balanced and uniform velocity at the die exit. The flow restrictors and flow separators were added in the pre-parallel zone. Flow restrictors were added on top and bottom of the torpedoes to increase the restriction on polymer flow. A unique inclined flow restrictor was introduced to achieve uniform internal melt flow. Flow separators were added at junctions of outer wall and inner vertical walls to separate the polymer flow into different sections and minimize cross flow between these sections. The addition of these features proved to be highly effective for balancing the velocity distribution at the die exit. The combination of 3-D modeling and simulation is a cost-effective and time efficient approach for optimizing complex die designs before manufacturing.

ИССЛЕДОВАНИЕ И ВЫБОР ОПТИМАЛЬНЫХ ПАРАМЕТРОВ ПРОЦЕССА ГОРЯЧЕЙ ОБЪЕМНОЙ ШТАМПОВКИ ПОКОВКИ ТИПА "КРЕСТОВИНА" ПУТЕМ МОДЕЛИРОВАНИЯ В ПРОГРАММНОМ КОМПЛЕКСЕ QFORM

By the method of computer modeling in the QForm program, the technological process of hot die forging for a «crosspiece» type forged-piece has been developed. The influence of technological parameters on the force parameters and the filling of a die cavity was investigated. The stress-strain state and temperature fields of the forged-piece, the optimal shape and dimensions of the initial workpiece providing minimal technological efforts, forging steps, optimal conditions for filling the die cavity and conditions for cooling the forged-piece were determined. The optimal forging scheme was found.

Optimization of process parameters in rapid heat cycle molding using heater system

Plastic injection molding (PIM) is a manufacturing technology to plastic products. In PIM, weldline that affects the strength and surface quality of products, and it is then important to determine the optimal process parameters for the weldline reduction. Rapid heat cycle molding (RHCM) is an attracted PIM technology for weldline reduction that by heating up the mold temperature, the melt plastic is smoothly flowed into the die cavity and consequently the weldline is well reduced. In RHCM, since various heating systems are adopted but which have problem that long cycle time. In this paper, to quickly heat up the mold temperature, a heater system is newly introduced and the process parameters in the RHCM using heater system are optimized. A multi-objective optimization for minimizing both weldline and cycle time is considered, and the ratio of mold temperature to injection time is maximized for the weldline reduction, whereas the cycle time is minimized for high productivity. Sequential approximate optimization that the response surface is repeatedly constructed and optimized is adopted for the design optimization, and the pareto-frontier is identified. Based on the numerical result, the experiment is also conducted to examine the validity of the proposed RHCM.

Microscopic Visualization and Quantification of Molten Aluminum Alloy Flow Inside Die Cavity by Multiphase Flow Analysis

Microscopic Visualization and Quantification of Molten Aluminum Alloy Flow Inside Die Cavity by Multiphase Flow Analysis

Açılı Derin Çekme Kalıplarında Dikdörtgen Şekilli Kapların Derin Çekilebilirliğinin Araştırılması

Deep drawing is the process of obtaining three-dimensional containers of certain depths and shapes under pressing forces with the help of drawing molds of sheet materials. In this study, the numerical shaping of rectangular cups in angled deep drawing dies was investigated experimentally and by using the finite element method (FEM). For this purpose, die/blank holder surfaces have α=0°, α=3°, α=6°, α=9°, α=12° and α=15° angles in order to facilitate material flow into the die cavity. The punch and die corner radii are taken as 8 mm. St37 steel sheet with a thickness of 0,9 mm was used as the test material. The experiments were carried out by applying die/blank holder forces of 2500 N, 5000 N, 7500 N and 10000 N. The effects of angles and die/blank holder force on limit draw ratio, wall thickness and the damage of cups were investigated experimentally and numerically, and optimum punch force was determined. Obtained experimental results were compared with ANSYS results. As a result, it has been determined that the increase in die/blank holder surface angles in drawing dies with rectangular geometry with different angles provides a higher limit drawing rate than conventional dies. It has been seen that the experimental results and numerical results are approximate values.

Experimental and numerical analysis of the wear mechanism in spring coil forming die and the effects of die geometry on wear

The present work aimed at understanding the wear mechanism of spring coil forming die and the effects of die geometry on wear. The wear morphology was analyzed by scanning electron microscopy and energy dispersive spectrometer. The main wear mechanism was found to be adhesive wear, and a variant of the Archard wear model was established. The wear distribution in spring coil forming die was numerically analyzed in DEFORM software, and the effects of die geometry parameters on wear were discussed. Numerical results revealed that the wear distribution in the die was uneven and the wear mainly occurred at the sides of the die cavity. The wear depth was greatly affected by the width and angle of the die cavity, whereas the length of the die cavity had little effect. A small cavity width or angle led to severe wear, while a large cavity width reduced the forming quality of the spring coil. Moreover, a simple and effective life prediction method was proposed based on wear results. The findings of this research will be helpful for the effective design of spring coil forming die and the prediction of wear.

Assessment of the suitability of a gate design modification compared to the change in pressing velocity considering the distribution of gases in the casting volume

The qualitative properties of high pressure die castings are closely correlated with their internal structure, which is directly conditioned by the gas entrapment in the melt volume during the casting cycle. It is known that the gas entrapment in the volume of the melt and their subsequent distribution into the cast can be reduced by changing the technological parameters of the casting cycle or by the modification of the gating system design. The contribution addresses the issue of which variant of the gas content reduction is more efficient regarding the gas entrapment and the nature of the melt flow in the runners. The experiments are based on a real casting process. The established design solution of the gating system and the technological parameters setting are considered as a referential. Different gating system modifications were designed where the design modification is connected with the cross-section of a gate, in which the final acceleration of the melt flow occurs. The observed melt velocity in the gate is considered as a correlation factor, based on which the modification in the piston velocity is determined. The assessed parameter is the gas entrapment in the cast volume at the end of the filling phase. Assessment of the casting cycle and evaluation of experiments is performed using simulation program Magmasoft. Based on the performed analyses, it can be stated that the gate design modification will affect the filling regime of the die cavity by changing the melt velocity in gate, but the nature of the melt flow in runners remains unchanged. Modification of the piston velocity affects the filling regime of the die cavity, and also the nature of the melt flow as it passes through the runners, thereby promoting the gas entrapment in the melt volume. Therefore, it is necessary to pay an increased attention to the design of the gating system and only after debugging the design to proceed to the optimization of technological parameters.

A thermal-stress modelling methodology in ABAQUS for fundamentally describing the die/casting interface behaviour in a cyclic permanent die casting process

This manuscript describes a novel method for thermal-stress modelling of a cyclic, permanent die casting process in the commercial software package ABAQUS. The key element in this method is that it updates the casting's geometry according to the deformed die at elevated temperature before filling the die cavity. Using this method, the evolution of gap and/or pressure at the die/casting interface has been predicted. This in turn has allowed for a more fundamental and less empirical description of the evolution in resistance to heat transfer at the interface during a casting cycle. The new methodology has been compared to a previously published methodology, and the comparison shows a noticeable difference between the two approaches in predicting the temperature field in the die and the casting and prediction of areas prone to shrinkage-based porosity. This methodology also predicts the stress distribution in the die in the cyclic steady-state operation, which may be of value in predicting die fatigue life.

Finite element analysis of cold drawing of stainless steel bars

Drawing is a metal forming process that is carried out by pulling a work piece through a die cavity. During the process, the cross-sectional area of the work piece reduces and the shape of the product is the same as that of the die cavity. In traditional industries, the required accuracy and quality can be achieved through multiple tryouts, by which a large amount of testing samples and time are required and accordingly results in the increase in production cost and decrease in productivity. Cold drawing is an effective way to produce bars or wires with high precision in product size. However, there is still no appropriate quantitative formula to determine how the dimensions of the die and the forming parameters affect the geometric dimensions of the product. In recent years, the progress of simulation technology allows us to investigate the effects of forming parameters on finished products dimensions. However, there was no literature discussing the effects of various parameters on the precision of the product dimensions. In this paper a finite element model is established to analyze the elastoplastic deformation of the bar inside the die cavity. An empirical formula including various forming parameters is established from a series of simulation results, and the precision can reach within 0.1%.

Effect of blank holding forces and drawbead on various blank shapes for complex geometry using FE simulation

To obtain better quality parts in the stamping process, the important parameter is the flow of material into the die cavity. This flow is controlled by adapting appropriate blank holding force, initial blank shape, and geometry of drawbead. In this paper, a comparative study is carried out using blank holding force and different blank shapes such as rectangular, oblongated, and oval shapes on thinning of the formed part using hyperform as simulation software. From the simulation, it is observed that more thinning is in rectangular blank shapes as compare to oblongated and oval shapes. Formation of oblongated or oval shape blank required extra blanking die which adds more cost. Hence the use of rectangular blank is most preferable along with drawbead. Further research work is carried out to get an optimized solution on rectangular blank using circular drawbead. The result of drawbead with rectangular blank size will give a less thinning with minimum blank holding force compare to oval and oblongated blank shapes. The results obtained by finite element simulation are in good agreement with the experimental results with a permissible error of an average of 6.70%.

EFFECTS OF AIR-COOLING-HOLE GEOMETRIES ON A LOW-PRESSURE DIE-CASTING PROCESS

A significant precondition for the production of high-quality castings is keeping an optimum temperature of the respective parts of the die cavity surface. This temperature depends on the temperature of the material, the quantity of metal, the method of cooling the casting die, the thermal conductivity of the die material, and the time during which the casting remains in the die. In addition, the cooling characteristics of alloy steel dies, used in the production of aluminum-alloy wheels with the low pressure die casting (LPDC) method, have critical effects on the mechanical and metallurgical properties of the product. Ducted air coolers are widely used for the cooling of these alloy steel dies. However, the geometrical designs of the air-cooling holes are limited. In this study, we define the effects of the geometry of the cooling holes on the cooling power of the die, the efficiency of the air consumption with the Full Factorial Experimental Design method and to determine the optimum values for LPDC. Pilot production has been carried out on an industrial scale to verify the data obtained by experimental design. The experimental and real data were compared based on the values of the yield strength and the secondary dendrite arm spacing in the microstructure.

A simplified formula for determination of relative pressure in the precision forging of spur gears

In this study, the relative forging pressures of spur gears were evaluated. The precision forging of spur gears was analyzed by using the upper bound method considering corner filling and bulging effect. Numerical and experimental studies were performed to investigate the effects of various parameters, such as the number of teeth, modules, facewidth, bore diameter, and friction factor on the relative forging pressure of spur gears. The results were compared with the previous studies and a simplified formula was suggested to predict the relative pressure of precision forging of spur gears. The predicted relative forging pressures obtained by the suggested formula are shown much closer to the experimental results for the complete filling of the die cavity.

Self-bending extrusion molding of distorted channels

Using an integrated profile extrusion and bending forming process with a streamlined extrusion die, a new self-bending extrusion molding technology is proposed with an axis-distorted variable channel. By designing the streamlined extrusion die structure of the distorted central axis, the metal was made to flow non-uniformly in the die cavity, thereby directly extruding a bent profile. The central axis of the streamlined extrusion die is described by a trigonometric function and a Gaussian function. A numerical simulation was applied to analyze the metal flow pattern, equivalent strain, and strain-rate distribution during the self-bending extrusion process. The influences of the extrusion velocity and the addition of a bearing on the self-bending deformation profiles were investigated. During the extrusion process, the streamline at the center of the billet could describe the overall flow of the metal in the die cavity, and the distance between the point on the end face of the die outlet and the center of the die outlet directly determined the degree of extrusion and bending. The greater the distance was, the larger was the degree of bending. The metal strain on the convex edge of the die was greater than that on the concave edge of the die, with the extruded profile always bending toward the concave edge. The strain rate of the metal changed the fastest near the most convex point of the die. As the extrusion velocity increased or more bearings were added, the radius of curvature of the extruded profile increased nonlinearly.

Thixoforging of 332 aluminum alloy in a mechanical eccentric press

This study sought to analyze the semi-solid behavior of commercial 332 aluminum alloy during thixoforming in a mechanical eccentric press (thixoforging). The solid–liquid transition, i.e., the working temperatures corresponding to 77%, 67% and 54% fraction solid, was characterized using differential scanning calorimetry and simulation with Thermo-Calc® software. The alloy was then heated to the working temperature, held at that temperature for 0, 30, 90 and 210 s and thixoforged. The microstructure was characterized in three distinct regions of the thixoforged product: the end, the curved region and the central region. Different microstructures were observed along the product: in the central region, a completely deformed coarse dendrite microstructure was observed while in the region at the end of the product the microstructure was partially globular because the material flows into the die cavity without suffering significant deformation. The thixoforged alloy with the lowest fraction solid (52%), which was achieved at 572 ± 2 °C, had the most refined structure and smallest dendrite arm spacing (approximately 90 µm), leading to a yield strength of 151 MPa, ultimate tensile strength of 233 MPa and elongation of 0.6. These mechanical characteristics can be considered excellent as no prior preparation or modification of the raw material was carried out. The material thus has excellent potential for use in both thixoforming and rheocasting.

A novel hydrodynamic deep drawing utilizing a combined floating and static die cavity

A novel method named hydrodynamic deep drawing process utilizing a combined floating and static die cavity (HDDC) was proposed in this research, in order to depress wrinkling during hydrodynamic deep drawing process to form a conical cup with higher height. A special experimental setup of a combined die cavity, which a static chamber inlaid with an inner floating die cavity, was designed to implement the modified hydrodynamic deep drawing experiments. At first, the feasibility of the modified method was evaluated in detail by numerical analyses and experimental tests. Then, the effects of the liquid counter pressure in die cavity on the forming process were also studied. It was found that the proposed method HDDC was feasible and the suppressing wrinkling effect dramatically came into being by using a floating die cavity during the hydrodynamic deep drawing process for conical cups of higher height. The rigid contact between the crater corner of the floating cavity and the blank contributes to the suppressing wrinkle effect during the hydrodynamic deep drawing process utilizing a combined floating and static die cavity. The hydrodynamic deep drawing process of conical cups utilizing a combined die cavity becomes more robust compared with the conventional hydromechanical deep drawing process.