Rigid Die Research Articles

The effect of unloading and ejection conditions on the properties of pharmaceutical tablets

This study investigates decompression and ejection conditions on tablet characteristics by comparing compact densities and tensile strengths made using regular rigid dies and custom-built die systems that enable triaxial decompression. Die-wall pressure evolution during decompression and ejection stresses did not meaningfully impact the density and tensile strength of the materials tested: microcrystalline cellulose, crystalline lactose monohydrate, and mannitol. Furthermore, the apparent differences in tensile strength between rectangular cuboids and cylindrical compacts are unrelated to decompression and ejection conditions, but rather a consequence of their shapes and of the test configurations. This suggests that elastic and plastic deformations that may occur during decompression and ejection are not significantly influenced by die-wall pressure evolution. We thus conclude that while triaxial decompression and constraint-free ejection may allow the production of defect-free compacts for materials that otherwise are defect prone using a rigid die, they seem to pose no benefits when the materials already produce defect-free compacts using a rigid die.

Automatic trajectory adaptation for the control of quality characteristics in a powder compaction process

The manufacturing process of sintered components requires the compaction of powder in a rigid die and the sintering of the resulting green parts. To produce green parts of the same constant quality over a long period of time, regular quality checks and trajectory adjustments are needed to account for changing operating conditions due to e.g. varying temperature, humidity, stroke rate, or powder quality. Also the first setup of the machine requires manual measurements and iterative adjustments of trajectory key points. To overcome these labour-intensive, manual measurements and adjustments, we propose an algorithm for the automatic adaptation of trajectory key-points that for the first time allows bringing and keeping more than one quality characteristic (mass and dimensions) fully automatically within predefined intervals. To safe costs, we further present two real-time capable, model-based solutions by employing grey-box and black-box models for the online estimation of the workpiece mass and height instead of their direct measurement. The grey-box model combines a filling and analytical compaction model and allows estimating mass and height rather than density as typically investigated in literature. The black-box model based on neural networks represents a complete novelty in the field as no similar data-driven approach could be found that aims at estimating mass and dimensions of green compacts. We finally compare the performance of these models to the baseline of sensor measurements as well as study their effect on the overall control performance. Results indicate that for both sensor-based and model-based solutions it is possible to reach and keep aforementioned quality characteristics within desired intervals. While overall the sensor-based approach performed best, also for the model-based approaches a good estimation performance is observed with the black-box model based on neural networks outperforming the grey-box model. While the black-box approach is fully data-driven and thus allows to widely avoid manual modelling activities, it still requires the presence of expensive sensors for capturing training data. The proposed grey-box approach, on the other hand, requires some manual modelling and model calibration activities, but provides a cost-effective solution to the problem and represents an alternative to more expensive, sensor-based implementations.

Clinching of inductively heated aluminum die casting

The aim of the investigations described in this article is to improve the clinching of aluminum die casting. The focus is on clinching an aluminum die casting alloy by local heat treatment and hence to join them in a process-safe manner. For this purpose, a heating strategy is used to warm up the die casting alloys to reduce temporarily and reversibly the elongation and the yield strength in the material. In preliminary investigations, three different heating strategies (heating plate, resistance heating and inductive heating) have been investigated. Induction heating has been selected as the most suitable method due to the short heating time and the production of crack-free clinch points. In this paper, two clinching tool systems (one with a flexible die, one with a rigid die) were used. For these tools, two inductors with different diameter were manufactured. The effects of each inductor and clinching tool on an aluminum die casting alloy, such as heating time and crack behavior, were investigated. Surface images of the clinch points in regard to the heat treatment temperature were analyzed. Furthermore, the characteristic parameters of the joints such as interlock, bottom thickness and neck thickness were examined. In addition, the strength of the joined parts was investigated by head tension tests. The results of the developed method showed that it is possible to produce crack-free clinching joints below 6 s. Furthermore, the local heating led to an increasing interlock resulting in a 26% increase of the head tensile strength.

Hybrid Forming - A Novel Manufacturing Technique for Metal-LFT Structural Parts

<div class="section abstract"><div class="htmlview paragraph">Hybrid structural parts combining aluminum or steel sheets with long glass fiber reinforced thermoplastics (LFT) offer a great opportunity to reduce component weight for automotive applications. But due to high manufacturing cost, metal-LFT hybrid components are still scarcely used in automotive large-scale production. Thus in this work a novel cost- and time efficient manufacturing process for simultaneous metal sheet forming and compression molding of long fiber reinforced thermoplastics to manufacture automotive lightweight components is presented. In this manufacturing process, which is referred to as “Hybrid forming”, a fiber reinforced thermoplastic melt is used as a forming medium in the manner of well-known hydroforming processes. After forming the metal sheet by polymer melt in combination with the rigid die, the melt solidifies and forms a local reinforcement structure in the hybrid component. Since the metal sheet is pre-coated with a bonding agent prior to the forming process, a firmly bonded connection between metal and LFT can be achieved.</div><div class="htmlview paragraph">For proof of concept a longitudinal control arm in a multi-link rear axle is chosen. By utilizing Hybrid forming a hybrid steel-LFT control arm is manufactured with weight savings of 20 % with regard to the metal reference component. Weight savings are derived by reducing the metal thickness and compensate stiffness and strength with local load-conforming LFT ribs. The metal part of the hybrid control arm guaranties the same positive fail-safe behavior of a metal component in contrast to the brittle failure mechanics of pure CFRP/GFRP components.</div><div class="htmlview paragraph">To verify the resilience of the hybrid component and especially the bonding surface between steel and LFT quasi-static tests and fatigue tests were conducted. The results are compared with the FE-simulations to validate the simulation technique, which can be used to design metal-LFT structural parts manufactured by hybrid forming for future applications.</div></div>

Гидроупругая реакция трехслойной пластины со сжимаемым заполнителем, взаимодействующей со штампом через слой вязкой жидкости

Гидроупругая реакция трехслойной пластины со сжимаемым заполнителем, взаимодействующей со штампом через слой вязкой жидкости

Шлифование и полирование рабочих поверхностей коленчатых валов и кулачков распределительных валов бесконечными алмазными лентами

A technology and a tool for processing work surfaces in crankshafts and cams of camshafts by endless diamond belts are considered. The characteristics of endless diamond belts and their potentialities in assurance of roughness and efficiency at work surface grinding and polishing are shown. The purposefulness in assurance of an optimum curvilinear transverse section of cams in camshafts by grinding with endless belts is defined. It is shown, that it is possible to control a curvilinear profile of cams in camshafts at the expense of a belt width and a belt tension. It is based on a theoretical basis of the interaction of a rigid die (cam) with the elastic half-space (belt). 
 An optimum curvilinearity of the transverse section of a cam ensures the increase of its life.

Numerical simulation of electrohydraulic processes

Using the finite element software complex LS-DYNA 971, the technique of simulating processes of Electro-Hydraulic forming is developed. The law of energy deposition is obtained from semi-analytical calculation. A simulation of complex EHF process, which includes discharge chamber with electrodes, plasma channel, water, deformable blank that is formed into a rigid die, is performed using the developed technique. The simulation is validated by experimental results. The developed technique significantly extends practical usage of numerical simulation of electrohydraulic forming and other electrohydraulic-based technologies.

Drawability and size effects for micro-arrayed deep drawing of Ni-Co/GO nanocomposite foils

For the first time, three different male dies (a rigid male die, an aluminum male die, and a nanoceramic powder male die) are used for a micro-arrayed deep drawing process using graphene oxide (GO) reinforced Ni-Co nanocomposite. Micro-parts with different shapes can be formed using the different male dies, and models to predict crack positions are established. The nanocomposite size effect leads to an increased depth-diameter ratio for decreasing female die diameters, and the conservation of volume leads to higher depth-diameter ratios and thinning rates. The reinforcing GO phase not only is able to improve the micro formability of the composite, but also inhibits grain growth at high temperature.

Study on the deformation theory of a parabolic part based on solid granules medium forming

Solid granules medium forming (SGMF), a new flexible die forming technology, uses solid granules instead of a rigid male or female die (or elastomer, liquid) for sheet metal drawing. The good fluidity and compressive capacity of a solid granules medium can improve the forming limit of complex shell parts. The sheet metal drawing process of SGMF is a compound process of drawing and bulging, which is very different from the conventional drawing process. A parabolic part is used as the research object for a study of the forming process. Two concepts, drawing weight and bulging weight, are originally proposed in the sheet metal drawing of SGMF (replacing the rigid male die), and the corresponding expressions are obtained. The computational formulas of geometrical conditions and strain in the sheet metal drawing of SGMF are established, and the radius of the strain dividing circle is obtained by calculation. The established theoretical model is applied to the research object, an aircraft part, to analyze the forming process. The results show that the proposed theory can be applied to analyze the strain in different deformation regions of SGMF. This original theory provides a new theoretical analysis for studying the sheet metal drawing of SGMF.

Wear of PVD coated tools for joining by clinching method

Abstract Clinching is a joining method in which sheet metal parts are deformed locally by creating a mechanical interlock without the use of any additional elements such as screws or rivets. Steel sheets are plastically deformed and the shape of the tools remains theoretically unchanged during the clinching process. The clinching tool with a rigid die of ø5 mm with a specially formed gap and a punch of ø3.6 mm were used for mechanical joining of hot-dip galvanized dual-phase steel sheets HCT600X of 0.8 mm thickness. The punch and die were deposited by PVD coating of CrN and TiCN type with LARC technology. The state of the coating was evaluated and documented by scanning electron microscopy – SEM. The wear of the coating was evaluated after each 50 manufactured joints starting with the initial state of tool.

Application of a piston equation to describe die compaction of powders

Compaction of metal powders in a rigid die is an important step in the fabrication of parts by the conventional powder metallurgy (P/M) route. It is thus important to find out the relationship between the applied pressure exerted by the pressing tool and the densification of the compacted part (green compact). In this work, an expression based on the piston-equation approach is presented. The expression describes the relation between the applied pressure and the average relative density of the compact with considering two simultaneous mechanisms for powder compaction. These mechanisms are particle rearrangement and particle deformation. It is also possible to obtain the contribution of each mechanism in the material densification from the equation. Since porous materials contain only isolated closed pores at relative densities greater than about 0.95, it would be hard to have densification due to the rearrangement mechanism after achieving this value of relative density. This analysis is applied and verified for the die compaction of Fe, Cu and Ni powders.

THE SHEAR STRENGTH OF THE ROUND CLINCHING JOINTS FORMED BY USING EXTENSIBLE DIES

The clinching joining technology is one of the most popular joining technologies by redrawing sheet material. The joining process parameters, the sheet material and its arrangements influences joints’ strength. Cylindrical axial-symmetrical joints formed by using rigid die and punch are still developed. The change of the rigid die on the die with movable segments affect the forming process and joint strength parameters. So there is a need to do experimental researches of the possibilities of joint formation by unchanged punch geometry and different die shape. In this article the forming process parameters (forming force, process energy consumption and its standard deviations) and joints strength parameters (maximum shearing force, total dissipated energy and dissipated energy up to 0.3 maximum force), according to the ISO 12996 standard, for the joints formed with using die with 2, 3 and 4 movable segments were presented. The punch geometry was unchanged and the minimum thickness of the embossment was also unchanged. For the die with 2 and 4 segments the load force direction influ ence on the joints strength was also presented.

Research on the Micro Sheet Stamping Process Using Plasticine as Soft Punch.

Plasticine is widely used in the analysis of metal forming processes, due to its excellent material flow ability. In this study, plasticine is used as the soft punch to fabricate array micro-channels on metal sheet in the micro sheet stamping process. This is because plasticine can produce a large material flow after being subjected to force and through the material flow, the plasticine can cause the sheet to fill into the micro-channels of the rigid die, leading to the generation of micro-channels in the sheet. The distribution of array micro-channels was investigated as well as the influence of load forces on the sheet deformations. It was found that the depth of micro-channels increases as the load force increases. When the load force reaches a certain level, a crack can be observed. The micro sheet stamping process was also investigated by the method of numerical simulation. The obtained experimental and numerical results for the stamping process showed that they were in good agreement. Additionally, from the simulation results, it can be seen that the corner region of the micro-channel-shape work piece has a risk to crack due to the existence of maximum von Mises stress and significant thinning.

The Rigid Die on a Half-Space with Thermal Relaxation and Convection: Influence of Sliding Speed, Die Temperature, and Geometry

A rigid die slides without friction on the surface of a coupled thermoelastic half-space at a constant sub-critical speed. A 3D dynamic steady state is treated, i.e., contact zone and its traction are invariant in the frame of the die. The die is maintained at a temperature that differs from the uniform ambient temperature prior to sliding, and die/half-space thermal convection occurs. The half-space exhibits thermal relaxation governed by the Lord–Shulman model. Three cases are treated: The die is a sphere in Case I and a cone in Case II. Case III involves a wedgelike die, formed by joining the bases of two cones. Asymptotic expressions in analytic form are derived for contact zone traction. Expressions and calculations for contact zone geometry are also given. These show that unstable behavior occurs when die ambient temperature exceeds that of the half-space by a critical value that itself may depend on die shape and speed.

Numerical simulation as a tool for optimizing tool geometry for rubber pad forming process

To produce a new component there are a trial and error stage to obtain a part without defects, which strongly depends on operator's experience. At this stage, the experience of designer and manufacturers should give an important aid to reduce trials to realize the minimization of response time and cost with maximization of the product equality. Rubber pad forming highly improves the formability of the blank because the contact surfaces between the rigid die and the rubber pad is flexible. This method enables to produce sheet metal components with complex contour by relatively low cost because only one rigid die is required. However, in aerospace field, parts are produced in small sheet metal bending and small number of components. It means that it is not worthy for large investments in tools and process design. For these reasons, it is necessary to use FE simulation of manufacturing process during the conceptual design.

Study on the Forming of Box-shaped Parts Based on Solid Granule Medium Forming

Solid granule medium forming(SGMF) is used for sheet metal deep drawing,where solid granule microsphere replaces the rigid punch or female die(or elastomer,liquid).Certain non-metallic granules(NMG) are selected as the research subjects.On the basis of the volume compression experiments and the ones of friction strength test,with both at a high stress level working on the solid particles medium,The finite element model of solid particles medium materials is constructed by the extended Drucker-Prager linear model in powder mechanics.The square box-shaped parts of non-axial symmetry is taken as an example,numerical analysis in respect of forming process of SGM is conducted;the flow characteristics of sheet and the wall thickness distribution law in the forming process are studied.Typical square box-shaped parts are successfully trial-produced.Loading curves,deformation characteristics in forming process and wall thickness distribution curves are proved in basic agreement with the result of finite element simulation.Studies show that the deformation characteristics and the force parameters,which is closed to the experiments can be generated from the numerical analysis on the SGM material model based on powder mechanic.At the same time,it can be the basis of the process plan which will in turn,play an important role in guiding the further application of the technique in sheet metal forming.

Investigation of Forging Process Parameters Effects on Die Fatigue Life Using Numerical Methods

In this study, the hot forging process of spline hub was simulated using the finite volume method. The proposed simulation model was compared with experimental samples and approved. Then, stress analysis of the rigid die was undertaken using the finite element method. On the basis of proposed model, the full factorial design of experiments was performed for investigating the influence of forging temperature and flash thickness on the die fatigue life. Results show that the increase in forging temperature and flash thickness, both cause the increase in the fatigue life. It is also shown that the effect of forging temperature on the fatigue life is greater than that of flash thickness. In drop-hammer forging, when number of blows decreases, the die fatigue life increases considerably.

Computer Aided Modelling of Rubber Pad Forming Process

Rubber pad forming (RPF) is a novel method for sheet metal forming that has been increasingly used for: automotive, energy, electronic and aeronautic applications [1]. Compared with the conventional forming processes, this method only requires one rigid die, according to the shape of the part, and the other tool is replaced by a rubber pad [1]. This method can greatly improve the formability of the blank because the contact surface between the rigid die and the rubber pad is flexible. By this way the rubber pad forming enables the production of sheet metal parts with complex contours and bends. Furthermore, the rubber pad forming process is characterized by a low cost of the die because only one rigid die is required [2]. The conventional way to develop rubber pad forming processes of metallic components requires a burdensome trial-and-error process for setting-up the technology, whose success chiefly depends on operator’s skill and experience [4][5]. In the aeronautical field, where the parts are produced in small series, a too lengthy and costly development phase cannot be accepted. Moreover, the small number of components does not justify large investments in tooling. For these reasons, it is necessary that, during the conceptual design, possible technological troubles are preliminarily faced by means of numerical simulation [4],[6]. In this study, the rubber forming process of an aluminum alloy aeronautic component has been explored with numerical simulations and the significant parameters associated with this process have been investigated. Several effects, depending on: stamping strategy, component geometry and rubber pad characterization have been taken into account. The process analysis has been carried out thanks to an extensive use of a commercially finite element (FE) package useful for an appropriate set-up of the process model [7],[8]. These investigations have shown the effectiveness of simulations in process design and highlighted the critical parameters which require necessary adjustments before physical tests.

PM Titanium – Based Composites with Improved Biocompatibility

Although titanium is considered to be the most successful metal for uncemented endosseous implants, its biocompatibility may be unsatisfactory in certain clinical cases. As an early osseointegration is essential in order to reduce the implant failure risk, the bioactive fixation becomes the appropriate solution for bone applications. The method requires bioactive materials such as hydroxyapatite (HA) to facilitate the chemical bonding to tissue. The present work refers to Ti-HA composites designed for endosseous implants and obtained through the classic PM route. Grade 1 c.p. Ti powder obtained through the hydriding – milling – dehydriding process, 63 - 100 μm grain size, was used. Sol-gel HA powder, grain size of less than 100 μm, was obtained through the sol-gel method. Blends of Ti and 5 to 50% HA were compacted in a rigid die (0.5 cm2), without the use of any lubricant, with 400, 500 and 600 MPa, then vacuum sintered (10-6 torr) at 1160°C for 60 minutes. Samples are well sintered with a compactness that increases with the applied compaction pressure. A transition layer can be seen in the EDX at the interface between the Ti matrix and the HA particles and is expected to increase the overall mechanical stability of compacts. The pores, essential for osseointegration, are interconnected, with irregular shapes and sizes that reach 100 μm, the critical size needed for the formation of a vital new bone. The HA content has to be limited to 30%, not to lead to an excessive brittleness. The biologic viability of compacts was assessed by immersion for 7 days into a simulated body fluid (SBF). The subsequent XRD analyses have proven that a new HA layer is formed on the surface of samples. This layer is essential for accelerating the cellular response of osteoblasts in the body.

Quasistatic periodic contact problem for a viscoelastic layer, a cylinder, and a space with a cylindrical cavity

This paper considers the contact problem of interaction of a rigid die, a rigid band, and a rigid insert with a viscoelastic layer, a viscoelastic cylinder, and viscoelastic space with a cylindrical cavity, respectively. It is assumed that the die, band, and insert move at a constant velocity along the boundaries of the viscoelastic bodies. In the first stage, the displacement of the boundaries of the above-mentioned bodies is determined as a function of the applied normal loads ignoring friction in the contact area. In the second stage, integral equations are derived to determine contact pressure in the contact problems. In the third stage, approximate solutions of the integral equations are constructed using a modified Multhopp-Kalandia method.