Cold Extrusion Research Articles

Fabrication and Mechanical Characterization of Cold Extruded Aluminum Bronze Planar Microsprings

A microspring is an important actuating component used widely in micro-electromechanical systems. It is important to develop microforming techniques for high-fatigue life microsprings manufactured. In this work, a micro-extrusion die was designed and manufactured for a plane microspring, and a CuAl7 copper alloy plane microspring was fabricated by cold extrusion. Effects of pre-annealing treatment, extrusion velocity, and lubrication conditions on the extrusion loading, surface crack and fatigue life of the spring were studied. The spring microstructure was characterized by equiaxed grains on the spring ends, and elongated grains exhibited the spring interior. Both internal and surface cracks were present in the springs. A good lubrication condition, an appropriate pre-annealing treatment, and a suitable extrusion velocity would reduce surface cracks. The fatigue life of the spring extruded at higher velocity was larger than that extruded at lower velocity under the same surface crack density. The fatigue life decreased with increasing annealing treatment temperature and holding time. A good lubrication condition during the extrusion process would improve the fatigue life of the spring. The maximum fatigue life of these extruded microsprings was 19,260 cycles when the cycle force was 10 N.

Present Situation of the Anti-Fatigue Processing of High-Strength Steel Internal Thread Based on Cold Extrusion Technology: A Review

The adoption of cold-extrusion forming for internal thread net forming becomes an important component of anti-fatigue processing with the development of internal thread processing towards high performance, low cost and low energy consumption. It has vast application foreground in the field of aviation, spaceflight, high speed train and etc. The internal thread processing and anti-fatigue manufacture technology are summarized. In terms of the perspective of processing quality and fatigue serving life, the advantages and disadvantages of the processing methods from are compared. The internal thread cold-extrusion processing technology is investigated for the purpose of improving the anti-fatigue serving life of internal thread. The superiorities of the plastic deformation law and surface integrity of the metal layer in the course of cold extrusion for improving its stability and economy are summed up. The proposed research forecasts the development tendency of the internal thread anti-fatigue manufacturing technology.

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.

Characteristics of metal flow in cold extrusion under electric-hydraulic chattering

An experimental setup for cold extrusion process with electric-hydraulic chattering was developed and its working principle was introduced. The finite element (FE) model for a kind of cup part (material: 20Cr) was built by using the software Deform-3D. FE simulation experiments with and without electric-hydraulic chattering were carried out to analyze the velocity fields and the metal grid flow lines. The extrusion experiments of the cup part were also performed under different conditions. The difference of metal flow lines with and without electric-hydraulic chattering was discussed via a scanning electron microscope (SEM) and the Keyence super-depth three-dimensional microscopic system. The results showed that with the electric-hydraulic chattering, the velocity of material flow increases, whereas deformation resistance decreases. Electric-hydraulic chattering results in easy metal flow, small bending degree of metal flow lines, slender and dense metal grains, and thereby an improved quality of the deformed parts.

Effect of graphite content on the tribological behavior of Al/2SiC/Gr hybrid nano-composites processed via mechanical milling

AbstractThe influence of 0 – 7 vol.% graphite addition on the dry sliding wear characteristics of Al/2SiC/Gr hybrid nanocomposites was examined. The composites were synthesized via ball milling of Al6061, nano-sized SiC and micron-sized graphite particles followed by cold pressing and hot extrusion. While the hardness of composites decreased almost linearly with their graphite content, the samples containing 2 % and 5 % of graphite exhibited minimum values of wear rate and friction coefficient, respectively. Addition of only 2 vol.% of graphite to the Al/2SiC nanocomposite resulted in changing the wear mechanism from a combination of adhesive and abrasive micro-cutting to abrasive and delamination wear. The superior tribological properties of the hybrid nanocomposites investigated in the present study as compared to those of Al/30SiC/Gr hybrid composites containing micron-sized SiC particles are discussed.

The analysis of distributions of effective strain and flow stress in longitudinal sections of cold backward extruded copper cans for different punch-face shapes

The paper presents computer modelling results of researches on cold backward extrusion of copper cans. The calculations were carried out using the commercial code QFORM-2D, based on the Finite Element Method (FEM). The simulation of cold backward extrusion process was performed for different punch-face shapes (flat; flat and conical with conical angle 900 and 1500; as well as concave). On the basis of obtained results, the analysis of distributions of effective strain and flow stress in longitudinal sections of cold backward extruded copper cans was conducted.

Improvement of surface quality of aluminum product in cold extrusion by using reuse tool with groove array formed on tool surface

Abstract Surface smoothness of aluminum product was investigated with regard to viscosity range of naphthenic mineral oil N1 (VG10), N2 (VG22) and N3 (VG460) by carrying out cold extrusion tests using the plane strain extrusion apparatus constructed with the taper die, plane plate tool and container. The plane plate tools without or with the fine groove arrays scraped on the tool surface were prepared for the present investigation. Fine smooth surface of the products could not be obtained in case of N1 and N3 in extrusion tests. While, surface roughness of the product was fine in 0.04μmRa in case of N2 and tool surface roughness 0.05μmRa. Cross sectional profile of the groove of groove array was self-reformed at the first time extrusion process using different lubricants. Then, extrusion tests for achieving smoother surface of the product were carried out by using reuse tool with the selected groove array and lubricants, N1 and N3. Surface smoothness of the product could be improved by using the reuse tool with the self-reformed groove array having selected cross sectional groove profile and at lubrication condition using N1 or N3. It was found that combination of the cross sectional profile of the groove of groove array and viscosity of lubricant could control the thickness of oil film and contribute to achieve smoother surface of the extruded products.

Application of semi-physical modeling of interface surface roughness in design of pre-stressed microforming dies

Permissible internal pressure in dies for cold extrusion may be increased by the use of one or two shrink rings. The design essentially boils down to defining the diametrical interference fit of the die/ring assembly. There are two methods of design: analytical one based on Lame’s solution and numerical one based on finite element modelling (FEM). None of these methods includes roughness of the interface surfaces of the die insert and the shrink ring. However, when designing the pre-stressed micro-dies, the interface roughness cannot be disregarded and the classical design of the diameter interference must be corrected. In this paper, a semi-physical modelling of interface roughness (SPMIR) is used as novel method which determines the interference correction value. A set of FEM models created on the base of Abbot-Firestone curves, determined from the roughness profile, enables determination of a contact surface stiffness curve and further the interference correction. Relative correction of the die diameter interference increases with the diameter decrease, which might be recognized as a pre-stressed micro-die assembling scale effect. In the experimental part, three miniature dies, with interface diameter 2.8 mm and different levels of interface surface roughness, Ra=0.16, Ra=0.43, Ra=0.60, have been manufactured by WEDM. Relative interference corrections calculated by the SPMIR method reached respectively 17.6, 27.9 and 43.3 %. A practical design advice has been formulated as follows: interference correction based on the interface surface topology is recommended for micro-dies with the interface diameter less than 10, 15 and 25 mm, for the three levels of the surface roughness investigated.

Stress and Strain Analysis and Microstructure of Al/Cu Clad Composite Fabricated by Cold Extrusion

Abstract A five-zone describing model for extrusion of aluminum/copper clad composite was established. Stress and strain were also analyzed by finite element method. The distribution rules of grain size were researched by critical shear strain theory, and zoning phenomenon of grain size was discovered. The grain size of deformed aluminum material becomes gradually finer from center to the interface. The grain size is much fine and the critical shear strain reaches the maximum value in the interface. The grain size of copper material reduces gradually from center to both the interface and exterior surface, which is caused by the higher value of critical shear strain in the interface and exterior surface. The analysis results were verified by microstructure observation and mechanical properties test, indicating that the distribution of grain size for cold extrusion forming can be interpreted by critical shear strain theory.

Microstructure evolution and thixoforming behavior of 7075 aluminum alloy in the semi-solid state prepared by RAP method

The effects of isothermal treatments on the microstructural evolution and coarsening rate of semi-solid 7075 aluminum alloy produced via the recrystallization and partial remelting (RAP) process were investigated. Samples of 7075 aluminum alloy were subjected to cold extrusion, and semi-solid treatment was carried out for 5–30 min at temperatures ranging from 580 to 605°C. A backward-extrusion experiment was conducted to investigate liquid segregation during the thixoforming process. The results revealed that obvious grain coarsening and spheroidization occurred during prolonged isothermal treatments. In addition, higher soaking temperatures promoted the spheroidization and coarsening process because of the increased liquid fraction and the melting of second phases. Segregation of the liquid phase caused by the difference in fluidity between the liquid and the solid phases was observed in different regions of the thixoformed specimens.

Effects of sintering parameters on the microstructure and mechanical properties of carbon nanotubes reinforced aluminum matrix composites

Abstract

Modeling and optimization of cold extrusion process by using response surface methodology and metaheuristic approaches

Obtaining the optimal extrusion process parameters by integration of optimization techniques was crucial and continuous engineering task in which it attempted to minimize the tool load. The tool load should be minimized as higher extrusion forces required greater capacity and energy. It may lead to increase the chance of part defects, die wear and die breakage. Besides, optimization may help to save the time and cost of producing the final product, in addition to produce better formability of work material and better quality of the finishing product. In this regard, this study aimed to determine the optimal extrusion process parameters. The minimization of punch load was the main concern, in such a way that the structurally sound product at minimum load can be achieved. Minimization of punch load during the extrusion process was first formulated as a nonlinear programming model using response surface methodology in this study. The established extrusion force model was then taken as the fitness function. Subsequently, the analytical approach and metaheuristic algorithms, specifically the particle swarm optimization, cuckoo search algorithm (CSA) and flower pollination algorithm, were applied to optimize the extrusion process parameters. Performance assessment demonstrated the promising results of all presented techniques in minimizing the tool loading. The CSA, however, gave more persistent optimization results, which was validated through statistical analysis.

Compressive and tensile deformation behaviour of TRIP steel-matrix composite materials with reinforcing additions of zirconia and/or aluminium titanate

The mechanical properties and the related microstructure of metal-matrix composites (MMC) based on a high-alloyed CrMnNi steel with varying particle reinforcements (5% or 10 vol%) of magnesia partially stabilized zirconia and/or aluminium titanate were investigated. The powder metallurgical processing comprised the cold extrusion and conventional solid-state sintering at 1350 °C. The mechanical properties were examined by quasi-static compressive and tensile loading tests at ambient temperature. The microstructure characteristics contributing to significant changes in strength and ductility and affecting the failure mechanisms during deformation were characterised by scanning electron microscopy including energy-dispersive X-ray spectroscopy and electron backscatter diffraction, and by X-ray diffraction. For all compositions the stress-strain and the deformation behaviour were mainly controlled by dislocation hardening and α’-martensite formation in the steel matrix, but it was further improved by the particle strengthening of the ceramic reinforcement. Thus, the composite materials showed higher strength and work hardening than unreinforced steel specimens over a wide strain range. The pressureless sintering triggers several reactions at the metal/ceramic interface, which leads to pronounced destabilisation of the initial metastable zirconia particles with a lack of transformation toughening capability, and the formation of invalid olivine. These MMC suffer from early particle/matrix displacement and particle fracture under loading. A more positive effect of interfacial reactions was observed in the composites with addition of aluminium titanate. Here, the formation of a dense spinel structure and the reliable matrix/particle interface bonding during firing provides a significant particle strengthening effect. The combination of zirconia and aluminium titanate provides mechanical and microstructural benefits as well. Thus, aluminium titanate facilitates the consolidation of powder metallurgical processed steel-matrix MMCs via the conventional sintering for advanced load applications. The results of the study help to understand essential hardening mechanisms in composite materials and provide potential for future cellular MMC structures.

The Effect of Equivalent Strain on Punch Load for Cold Backward Extrusion of Copper Cans

The paper presents experimental and computer modelling (FEM) results of investigations into cold backward extrusion of copper cans. The simulations were performed using QFORM software based the finite element method (FEM). The samples used in investigations were pieces of copper rods having the diameter d0 = 24,5 mm and height h0 = 16 mm (h0/d0=0,65). The billets were heat treated (annealed). Heat treatment is used to increase the plasticity of the material before cold backward extrusion. The material was annealed at 550°C for a period of 1 h, and then subjected to solution treatment in water. The flat and conical punch-face shapes with different diameter of punch used for cold extrusion (ds=15mm; 16mm; 17mm; 19mm and 20mm, respectively). The deformation ratios of material in paper was defined as relative: strain of can bottom thickness εh =Δh/h0 (where Δh – the punch displacement, h0 – billet height), reduction in area εA= (A0-A1)/A0 and equivalent strain ε= ln (A0/A1) (where A0 – cross sectional area of the billet, A1 - cross sectional area of the die stamping). In investigations, computer calculated and experimental force waveforms as the function of displacement and εh were obtained. Comparing changes in forces in cold backward extrusion for different diameter of punch, it is stated that the load Pw increases with an increase in εh. The effect of equivalent strain ε on punch load Pw for cold backward extrusion of copper cans is presented. Both in experimental and modeling investigations, the axial force increased together with an increase in the equivalent strain.

Surface Texturing and Alternative Lubricant: Tribological Study of Tapered Die Sliding Contact Surface in Cold Extrusion Process

ABSTRACTRecently, there is greater concern for industries to maintain lubricant flow along the extrusion process, which is important to obtain the best quality of the final products. One of the most cost-effective methods is surface texturing. In this research, surface texturing was embedded on a tapered die sliding contact surface to explore its effectiveness on a finished product from a cold extrusion process. Palm oil–based lubricant was tested for cold extrusion processes and mineral oil was used for comparison purposes. It was found that a textured tapered die (TA) performed a diminished extrusion load compared to an untextured tapered die (NA) and improved the performance of other test parameters. As an alternative lubricant, refined, bleached, and deodorized (RBD) palm kernel oil presents results similar to those of commercial extrusion oil in terms of extrusion load and product quality. Based on the results, it is proven that surface texturing and palm oil–based lubricant can be considered as an alternative approach for implementation in industry.

Coupled process simulation of cold extrusion and heat treatment distortion of steel shafts

A simulation study will be presented regarding effects of cold extrusion – a forming process – on heat treatment distortion of a 20MnCr5 (SAE 5120) steel. Therefore, both cold extrusion and heat treatment simulations with transferring the geometry and the stresses from the cold extrusion to the heat treatment were done. The influence of two degrees of deformation, two friction coefficients, and two heat transfer coefficients between workpiece and tool on the heat treatment distortion was studied. Additionally, heat treatment simulations were done regarding only the geometry without transferring the stress (as machined state). Stress relief annealing and case hardening were applied as heat treatment. Finally, the simulated length changes of the shafts were compared with experimentally determined length changes using different lubricants, degrees of deformation, and heat treatments.

Beneficial effect of prestrain due to cold extrusion on the multiaxial fatigue strength of a 27MnCr5 steel

Cold extrusion is a process commonly used to manufacture drive train components in the automotive industry. Large plastic strains can be applied during this operation (up to 1.5) and greatly changes the mechanical properties of the resulting material. This study focuses on the impact of cold extrusion process parameters on the multiaxial fatigue behaviour of steel components. A specific set of forward rod extrusion tools was developed to get original fatigue specimen able to characterise the effect of the manufacturing process on the fatigue behaviour. The specimens were extruded from two different initial diameters, giving two different reductions in cross-section of 18% and 75% respectively.To understand the influence of cold extrusion, the following analyses have been undertaken for each condition and on the initial material: monotonic tensile properties, microstructure, EBSD, residual stresses and hardness. Simulation of the forming process and microstructural observations show that the plastic strain is homogeneous in the specimen section. For both reduction factors, the forming process has a positive effect on the components properties: induced residual stresses in compression and improved hardness and roughness (Ra decreasing). Tension, plane bending and torsion fatigue tests show that the fatigue strength is about 30% higher for the batch with 75% reduced cross-section. All investigations show that strain hardening is the principal material parameter responsible for the increase in fatigue strength. A multiaxial fatigue criterion taking into account the effects of the forward rod extrusion process was also developed.

Physicochemical and Functional Properties of Extruded Sorghum‐Based Bean Analog

AbstractThe objective of this study was to develop and evaluate the physicochemical and functional properties of a bean like product made from cold extrusion of sorghum, soy and wheat flours. Formulated samples comprised of sorghum (25–70%), wheat (0–35%) and soy (30–50%) flours. The degree of gelatinization ranged from 54.1 to 93.6%. Pasting curves showed minimal starch damage with peak and final viscosities in the range of 456.0–1138.5 and 297–584 cP, respectively. Textural properties of the extrudates were significantly impacted by starch content and cooking time. There was significant cooking loss due to poor binding properties of the extrudates. Cooking the product for 30 min after 2 h soaking gave comparable hardness to cooked navy bean. Texture profile analysis showed that mostly starch‐based ingredients contributed to hardness and cohesiveness, while formulations high in protein showed increased adhesiveness and gumminess.Practical ApplicationsThis study addressed a major gap in access to sufficient nutrient in navy beans, a common staple, the processability subject, and offers a novel approach to addressing them. Beans are common staple in many regions where malnutrition is prevalent, and some types of beans take long to cook to a texture acceptable due to changes during storage. Reforming beans using extrusion allows manipulation of ingredients that can help to address deficiencies in nutrient, flatulence and the “hard to cook” characteristics seen in some beans. Bean analog, as we refer to extruded bean in this study, is a major mechanism for nutrient delivery which has the potential to help address macronutrient and micronutrient deficiencies in diets of people where beans is a staple.

Influence of micro-pits indentation and palm based-oil on taper die sliding contact surface in cold extrusion process

Surface texturing is among the cheapest solutions for die modification if compared to tool change and hot works. In extrusion die design, the addition of micro-pits has increasingly been used to balance the metal flow. Such balance is particularly important for multiple cavity dies or sections with varying thicknesses in order to maintain a uniform velocity profile across the face of the die. In this research, surface texturing (called as micro-pits) was embedded on taper die sliding contact surface to explore its effectiveness on finish product of cold extrusion process. Palm oil based lubricants were tested for cold extrusion processes and mineral oils were used for comparison purpose. It was found that taper die with micro-pits (PA) performed a lessened extrusion load than taper die without micro-pits (NA), so as enhanced the performance of other tests parameter. In addition, viscosity of lubricant seems to be very important in ensuring that no material and tribological failures occur during the metal forming process.

Regression Analysis of Gluten-Free Pasta from Brown Rice for Characterization andIn vitroDigestibility

The paper explores the possibility of utilizing brown rice for preparation of gluten-free pasta using twin screw extruder. Response surface methodology was used to analyse the effect of feed moisture (28–34%), barrel temperature (70–110C) and screw speed(120–220 rpm) on quality responses (degree of gelatinization, minimum cooking time, water absorption, volume expansion, and gruel solid loss) and regression analysis was carried out to fit mathematical models to the experimental data. The selected pasta samples were examined further for pasting properties, color, texture, in vitro starch, and protein digestibility. Higher feed moisture exhibited dominant effect on cooking quality of pasta. The degree of gelatinization showed a positive correlation with feed moisture and barrel temperature. Luminosity enhanced with increasing screw speed and feed moisture. Firmness of cooked pasta elevated with an increase in the barrel temperature. Extrusion cooking significantly increased in vitro protein and starch digestibility, however, higher feed moisture favored protein and starch digestibility. Practical Applications Pasta products are normally produced using cold extrusion process 40–50C temperature. Generally single screw extruder is used for pasta manufacture. In the present scenario of convenience and newer products, we explored the possibility of using brown rice along with twin screw extruder for preparation of gluten-free pasta. Effect of feed moisture, barrel temperature, and screw speed on the quality parameters of pasta were studied. Pasta produced at higher feed moisture and screw speed showed higher in vitro starch and protein digestibility.