Die Cavity Research Articles

노비드스탬핑 공법을 이용한 공정최적화에 관한 연구

As the shape of stamped part is complicated and as the trend toward light weight continues, the higher level of difficulty is required in making stamping die because of inevitably poor formability. The poor formability can be improved if the material flow during the stamping is carefully controlled. Application of drawbead became commonsense used to retard metal flow of blank into the die cavity at the region where wrinkle is expected. In the study, the concept of beadless stamping process is proposed and the method how to realize the beadless stamping process is presented. The validity of the proposed method is confirmed by the application of the real auto part.

Influence of the fabrication process on the functionality of piezoceramic patch transducers embedded in aluminum die castings

Piezoceramic patch transducers are integrated into aluminum components using high-pressure die casting. Expanded metal has proven suitable as a supporting structure for placing the patch transducers inside the die cavity and for stabilization during the injection of molten metal. However, difficulties arise when the transducers are positioned off the neutral axis within the wall of the casting. Numerical simulations of the die filling are performed to analyse the evolution of the integration process. The asymmetric infiltration of the supporting structure is identified as the major factor contributing to the formation of cracks and perforations inside the piezoceramic transducer. By means of measurements and numerical calculations of the electrical impedance of the transducer, a close relation is established between mechanical damage patterns observed in radiographs of the patch transducers and loss of performance.

Optimization‐driven design of dies for profile extrusion: Parameterization, strategy, and performance

AbstractA computational design optimization environment is developed, handling, for the first time, streamline dies used for profiles in unplasticized polyvinyl chloride (uPVC) having multiple complex features, as well as simpler designs. Die cavity cross sections are described by planar contours, such as the cutting paths for wire electrical discharge machining of the plates from which streamline profile dies are constructed. Contours are parameterized using key points, and by joining the contours with ruled surfaces, the three‐dimensional geometry can be reconstructed. For the optimization a developed flow analysis on each die cross section is used with the avoid‐cross‐flow strategy. Cross sections are partitioned and the die is balanced to obtain the required flow rate through each. A robust and efficient parallel decoupled optimization strategy is developed. In application to a uPVC window profile, five cross sections were optimized. The number of design variables on each ranged from 2 to 46, and the cross section optimizations converged within one to seven cycles. Compared with the work of an experienced designer making manual changes to the computer‐aided design model, guided by computational fluid dynamics analyses, the design quality was comparable or better and computational demands similar; however, the time required from the designer was reduced seven times. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Evaluation of Compaction Behaviour of Spray-Dried Alumina by Hg Porosimetry and SEM

The powder compaction process is the most widely used forming technique for shaping ceramic products, since traditional ceramic as floors until advanced ceramics for technical applications. This process is characterized by high productivity but it has a serious problem, namely the density gradient originated during the die cavity filling and the subsequent compaction operation[. Therefore, the process requires a high control of all parameters involved in order to guarantee to obtain samples with high homogeneity of the green density, which ensures a sintered body of high quality and low population of microstructural defects. Thus, it is extremely important to understand the variable that controls the compaction mechanisms and interfere in the homogeneity of the green density along the compacted body.

Development of a super ductile diecast Al–Mg–Si alloy

The super ductile diecast aluminium alloys have been developed particularly for application in automotive body structure. On the basis of the reviewing aluminium alloys currently available, the requirement of diecast aluminium alloys is summarized and the Al-Mg-Si system is focused in the development. The effect of various alloying elements on the microstructure and the mechanical properties, such as yield strength, ultimate tensile strength and elongation is assessed. The optimized composition of the super ductile Al–Mg–Si alloy has been found to be at 5.0–5.5wt% Mg, 1.5–2.0wt% Si, 0.5–0.7wt% Mn, 0.15–0.2wt% Ti with Fe <0.25wt% for the best combination of strength and ductility, which shows 150MPa of yield strength, 300MPa of ultimate tensile strength, and 15% of elongation under as-cast condition. The paint baking hardenability of the optimized alloy is found to be insignificant. Less than a 10% increase in the yield strength was achieved, with a slight decrease in the elongation after aging at 180°C for 30min, which is a simulated process of paint baking. Cu is found to slightly increase the yield strength under the as-cast condition and after the heat treatment, but with a significant reduction in the ductility. Therefore, Cu should be limited in the super ductile aluminium alloy. The microstructure of diecast aluminium alloys at the optimized composition consists of the primary α-Al phase, the α-AlFeMnSi intermetallics and the Al–Mg2Si eutectics. There are two types of primary α-Al phase: dendritic or fragmented dendritic α-Al phase solidified in the shot sleeve and globular α-Al particles solidified in the die cavity. The α-AlFeMnSi intermetallics is in the form of compact morphology and with a size of less than 3μm. The eutectic cells are at size of 10μm with a typical lamellar morphology of α-Al phase and Mg2Si phase.

Modeling of microstructure evolution of magnesium alloy during the high pressure die casting process

Two important microstructure characteristics of high pressure die cast magnesium alloy are the externally solidified crystals (ESCs) and the fully divorced eutectic which form at the filling stage of the shot sleeve and at the last stage of solidification in the die cavity, respectively. Both of them have a significant influence on the mechanical properties and performance of magnesium alloy die castings. In the present paper, a numerical model based on the cellular automaton (CA) method was developed to simulate the microstructure evolution of magnesium alloy during cold-chamber high pressure die casting (HPDC) process. Modeling of dendritic growth of magnesium alloy with six-fold symmetry was achieved by defining a special neighbourhood configuration and calculating of the growth kinetics from complete solution of the transport equations. Special attention was paid to establish a nucleation model considering both of the nucleation of externally solidified crystals in the shot sleeve and the massive nucleation in the die cavity. Meanwhile, simulation of the formation of fully divorced eutectic was also taken into account in the present CA model. Validation was performed and the capability of the present model was addressed by comparing the simulated results with those obtained by experiments.

상용 열유동 해석 소프트웨어를 이용한 다이캐스팅 칠벤트의 성능평가

Chill vent has a zigzag venting path which allows residual air or gases to exhaust out very quickly from the die cavity. However molten metal sometimes comes out through the gas venting surfaces causing flash. Effect of designing factors of chill vent and processing variables in high pressure die casting on the performance of chill vent was investigated through a series of calculations by using a commercial code. The most influential factor was the thickness of chill vent, followed by inlet velocity, vent width and die temperature.

Experimental Investigations on Electromagnetically Assisted Corner-Fill Performance of AA5052 Sheets

To establish the efficacy of electromagnetically assisted sheet metal stamping (EMAS), the corner-fill ability of AA5052 sheets specified in conventional deep drawing was experimentally demonstrated and evaluated within a two-step EMAS process. First, conventional axisymmetric deep drawing was conducted to make a cylindrical cup with a rough-shaped bottom corner. The second step utilized a shaped coil to force the pre-formed cup into the die cavity, and the related electromagnetically assisted corner-fill performance was investigated. Experimental results show that the ideal of hybrid stamping-EMF sequence can successfully solve the formability problem involved in conventional stamping. During electromagnetically assisted corner-fill process, the deformation dispersion effect of dynamic phenomenon works remarkably on the fully deformed sheets, which will inhibit local instability of deformation and thus enhance materials formability.

The Optimization of the Technological Parameters of Precision Die Forging of a Spur Gear Using a Computer Simulation

This paper deals with the optimization of the technological parameters of precision die forging in closed die in order to achieve a proper material flow in the die cavity for spur gears with a hub. This paper also studies the material flow in die cavity, effective plastic stress and strain, and temperature of drop forging using simulation software called SimufactForming. Forging cost is also compared between the closed and open die forging.

Numerical simulation of sheet hydroforming taking into account analytical pressure and fluid flow

The paper treats the modeling and simulation of sheet metal hydroforming taking into account fluid pressure and fluid velocity effects. A hydro-mechanical model is proposed to determine the fluid flow and the pressure variation in the die cavity in case of sheet hydroforming. The hydrodynamical model for the fluid flow between the sheet and the blank holder is based on Reynold's equation. A numerical and experimental hydromechanical deep drawing of a cylindrical cup validates the predictions of the proposed approach.

Theoretical and Experimental Analyses for the Forward Extrusion of Nonsymmetric Sections

A new generalized formulation for the analyses of the forward extrusion of nonsymmetric sections is presented in this article. In the formulation presented by the authors it is assumed that all points on the cross-section of the initial billet map to similar points on the final section of the extruded profile. The division of deforming region into subsections is done in such a way so that the theoretical concept for the material flow follows the real situation more closely than was done in previous works. This procedure provides a simpler and better way to tackle the extrusion of nonsymmetric shapes and could be used for shapes that could not been analyzed before. Based on the new formulation upper bound solutions were obtained. Using the present analysis the positioning of the die cavity was also optimized. Dies were designed and manufactured for the nonsymmetric C section profile, and experiments were carried out. Theoretical results were obtained for the extrusion pressure, force, optimum die length, and the influence of friction and reduction of area were investigated. Theoretical and experimental data were compared, and close agreement was observed. Also comparing the previous works with the present method, improvements on upper bound values were observed.

Slope plate 공법을 이용한 반응고 박판 및 제조 장치 개발

In this study, semi-solid thin plate of A 356 aluminum alloy was fabricated by using slope plate apparatus and vacuum pressurization. Slope plate was used to produce semi-solid material with spheroidal microstructures. After molten metal was poured into the slope plate connected to the pouring hole of die, semi-solid material flowed into the die cavity by vacuum degree. The primary crystals of the cast metal became spheroidal. In order to increase the working pressure, gas pressurization of U shape was designed for fabrication of thin plate. For 3 bar of gas pressure and 60 mmHg of vacuum degree, thin plate was fabricated without defects on surface.

In-situ X-ray microtomography study of the movement of a granular material within a die

AbstractOptimising the manufacture of powder-processed components requires an understanding of the 3-D movement and behaviour of granular materials during processing. X-ray microtomography has been employed to study the 3-D flow behaviour of a metallic powder in-situ within a die as a function of the displacement of a punch into the die. In particular, the powder transfer behaviour for various open and closed die/punch geometries has been compared, including situations where features exist within the die and on the punch, cases where the die is both open and closed at the top, and finally where the punch itself contains a groove in the centre providing a gap into which powder can flow. Digital image correlation (DIC) has enabled the determination of local vector displacements of powder around the features within the die cavity as a function of punch movement and powder constraint to reveal bulk granular movement and densification. Zones of relatively stagnant flow are observed above a fixed insert within the die cavity, at the opening of a gap within a punch, and as a result of a closed die configuration, the latter showing transitions between the stagnant zones and much more mobile regions and the resulting powder compaction/dilation. As well as providing a means of developing practical die fill and compaction strategies that homogenise densification and thus improve product quality, the technique can also provide unique 3-D flow trajectories for model development.

A universal formulation for the extrusion of sections with no axis of symmetry

The subject of theoretical analysis for the extrusion of profiled sections has been heavily worked on by many researchers. However most of these have concentrated on the extrusion of sections with some axes of symmetry. This paper aims to provide a new formulation for the analysis of the extrusion process for non symmetric profiled sections with no axis of symmetry. The upper bound theorem has been used to obtain an approximate solution. Both flat faced dies and bilinear dies were used in the present work. In fact this formulation could be applied to the extrusion process of hollow sections as well as solid parts. The advantage of the proposed method is the new way of discretizing the deforming region in the extrusion of shaped sections based on which a generalized kinematically admissible velocity field was formulated. For a given extruded profiled section this method employs fewer number of sub-divisions than before, giving a lower upper bound value for the extrusion power. The generality, easy application to different sections, short computing time and fairly realistic outcomes of the analysis could be regarded as other strengths of the present method. The lack of incorporation of temperature effects for hot extrusion processes could be mentioned as one of the disadvantages of the present method. The position of the die cavity was also optimized using the new method. A design map for the extrusion die geometry was also given as a graph of extrusion pressure versus the optimum die length for the bilinear dies with different frictional conditions and reductions of area. The extrusion of L-shape profiled section was chosen as a sample since it had no axis of symmetry. Extrusion dies were also manufactured and experiments carried out to verify the theoretical results. Finite element simulation for the extrusion of U, T and I-shape profiled sections was also carried out using ABAQUS\\CAE\\Explicit commercial software.

Study on Binder System for Micro Powder Injection Molding of ZrO&lt;sub&gt;2&lt;/sub&gt; Ceramic

Micro powder injection molding has been accepted as a potential forming technology for large-scale production of miniature components in industries. However, mold filling capability is often poor due to the blind hole structure of the die cavity, which restricts the widespread application of this technique. In this paper, ZrO2 micro gears with addendum circle ranging from 900μm to 200μm were studied. Instead of using traditional PW-HDPE-SA binder as in powder injection molding, thermoplastic binder system is optimized here for better replication of micro gear. It is found that the dimensional accuracy and demold after injection molding can be improved by utilizing proper binder system. ZrO2 feedstock with a powder loading of 46vol.% and the binder system consisting of BW, HDPE and SA was successfully injection molded and demolded, which indicates good mold filling capability and sufficient demolding strength. The binder system was successfully removed by debinding process in two steps, solvent debinding followed by thermal debinding. Debound components free of defects were obtained. Keywords: Micro powder injection molding, ZrO2 feedstock, Binder system, Molding filling capability, Demolding strength

Optimal load path input in tube hydroforming machines

Tube hydroforming (THF) is a metal-forming process in which a tube is plastically deformed to conform to the die cavity by injecting a pressurized fluid inside the tube. To ensure that enough material is supplied to the die cavity, the tube ends are usually pushed towards the die cavity to feed the material. To successfully hydroform a part, good coordination between fluid pressure and material feed is necessary. This pressure–material displacement relationship is known as a load path. The load path is specific to a part, and it is entered in a THF machine as pressure versus time and displacement versus time input variables. A methodology of decomposing the pressure–displacement loading path as a time variable to obtain pressure–time and displacement–time variants that are optimal for the THF machine system is presented. The THF experiments for double T-shaped parts are carried out to demonstrate that using different pressure–time and displacement–time variants can result in a significant increase in the maximum power required by the THF machine actuators.

Prediction of Wrinkling and Determination of Minimum Blankholding Pressure in Multistage Deep Drawing

Wrinkling in the flange region has been observed during redrawing operation by a few researchers. In the present work an analysis methodology, based on a combination of upper bound and energy approaches, is proposed for the prediction of number of wrinkles and minimum blankholding pressure necessary to avoid wrinkling in redrawing operation. Thickness variation predicted by the upper bound formulation is used as input for the wrinkling analysis by assuming a suitable waveform based on geometrical and process conditions. The flange is constrained at both ends, i.e., by the blank holder profile radius and at the die entry point (where the sheet enters into the die cavity). The waveform for present analysis is assumed such that it has zero displacement at both ends (since it is constrained) and the maximum amplitude of the wave at some point in between those ends. The wrinkling predicted by the present methodology seems to be reasonably accurate considering the geometrical and process constraints of the redraw.

Real-Time Friction Error Compensation in Tube Hydroforming Process Control

Tube hydroforming (THF) is a metal-forming process that uses a pressurized fluid in place of a hard tool to plastically deform a given tube into a desired shape. In addition to the internal pressure, the tube material is fed axially toward the die cavity. One of the challenges in THF is the nonlinear and varying friction conditions at the tube-tool interface, which make it difficult to establish accurate loading paths (pressure versus feed) for THF. A THF process control model that can compensate for the loading path deviation due to frictional errors in tube hydroforming is proposed. In the proposed model, an algorithm and a software platform have been developed such that the sensed forming load from a THF machine is mapped to a database containing a set of loading paths that correspond to different friction conditions for a specific part. A real-time friction error compensation is then carried out by readjusting the loading path as the THF process progresses. This scheme reduces part failures that would normally occur due to variability in friction conditions. The implementation and experimental verification of the proposed model is discussed.

Geometric parameter-based optimization of the die profile for the investment casting of aerofoil-shaped turbine blades

Dimensional accuracy is one of the most important criteria in the investment casting of turbine blades for aero engine applications. Although investment casting is an ideal route for producing net-shaped components, it necessitates accurate determination of the casting die profile. To avoid extensive modifications on the die cavity shape, this study proposes a simple but efficient inverse design method that adjusts certain geometric parameters to establish the die profile. Parameterized modeling is achieved by identifying the geometric parameters that describe the mean camber line of the blade profile. Meanwhile, blade shrinkages at different positions are effectively remedied through the adjustment of the parameters using the inverse iteration algorithm proposed in this paper. The relative positions among the cross-sections can also be varied to rectify the twist deformation of the blade, thereby guaranteeing the dimensional accuracy of the turbine blades. The applicability of this method is validated using numerical simulation data and experimental results.

Numerical simulation and metal flow analysis of hot extrusion process for a complex hollow aluminum profile

The most important way to improve the quality of aluminum profiles is to assure the material flow through die land exit with the same velocity. In this paper, a numerical model was developed to investigate metal flow behavior during aluminum profile extrusion. Firstly, the numerical model for a complex hollow aluminum profile was built based on the arbitrary Lagrangian–Eulerian program HyperXtrude. Then, with the numerical model, metal flow behavior at each stage during the whole extrusion process was analyzed and dead zones in the die cavity were also investigated by means of the particle tracking method. Finally, the numerical results were validated by comparing with the nose ends of two extrudates in practice, and the comparison showed that the numerical model developed in this work could provide the effective guidance for practical production.