Cold Forming Research Articles

In-situ computed tomography and transient dynamic analysis – failure analysis of a single-lap tensile-shear test with clinch points

Clinching is a mechanical joining technology, in which a mainly form-fit joint is created by means of local cold forming. To characterize the load-bearing behavior of such joints, they are typically analyzed destructively, for example by tensile-shear tests in combination with metallographic sections. However, both the initiation and progress of failure can only be described to a limited extent by this method. Furthermore, these tests allow only limited conclusions about clinch points under in-service loading. More purposefully, clinch points can be analyzed nondestructively by combining in-situ computed tomography (CT) and transient dynamic analysis (TDA). The TDA continuously measures the dynamic behavior of the specimen and indicates failure events like crack initiation, which then can be evaluated thoroughly by stopping the test and performing a CT scan. To qualify the TDA for this task, it is necessary to link the observed damage behavior with specific dynamic characteristics. In this work, the complementation of in-situ CT and TDA is investigated by testing a clinched single-lap tensile-shear specimen made of aluminum. The testing procedure is stepwise: at certain displacement levels, the specimen is investigated by in-situ CT and TDA. While the in-situ CT provides the location, extent, and development of the failure phenomena, the TDA uses this information to evaluate the dynamic signal and detect relevant frequency ranges, which indicate damage events. The results demonstrate, that failure initiation and progression can be analyzed efficiently by combining both measuring systems. The TDA reliably detects relevant signal changes in the monitored frequency band. By means of in-situ computed tomography, the corresponding failure phenomena can be described in detail, enhancing the understanding of the load-bearing and deformation behavior of clinch points. The concatenation of characteristic signal changes and observed failure phenomena can henceforth be transferred to analyze complex structures during operation nondestructively by TDA.

Formation of non-evaporitic gypsum in gas hydrate-bearing sediments at Håkon Mosby mud volcano, SW Barents sea

Authigenic minerals such as carbonate and iron sulfide are known features at cold seeps worldwide and form as a result of the anaerobic oxidation of methane in the sulfate-methane transition zone (SMTZ). Recent findings of seep-related non-evaporitic gypsum raise questions regarding its distribution, formation mechanisms, and relationships with the other proxies for confident paleo-seep reconstructions. Here, we report new findings of gypsum in the seep-impacted sediments of the hydrate-bearing Håkon Mosby mud volcano, SW Barents Sea. We combined sediment core logging (XRF, X-Ray) with optical microscopy and scanning electron microscopy - electron dispersive energy to characterize the authigenic mineral fraction of the sediment. Three paleo-SMTZs marked by the co-occurrence of pyrite and gypsum accumulations were found at 7–10 cm, 13–18 cm and 19–21 cm, above the modern one (at ∼50 cm) and match with carbonate-poor and foraminifera-free sediment intervals. Our results indicate that gypsum formation required a descending SMTZ (decreasing methane flux), triggering the oxidation of previously-formed pyrite which supplied extra SO42− to the pore water. Acidic conditions caused by pyrite oxidation would have promoted the dissolution of carbonate particles, thus releasing Ca2+ that is available for gypsum formation. As seen in other studies, the presence of shallow gas hydrates seems to play an important role as a calcium source for gypsum precipitation, via ion exclusion during hydrate formation. HMMV represents an optimal natural laboratory to investigate the interplay between different processes in gypsum biogeochemistry and its potential use as a proxy for methane seeps in modern and ancient settings.

The Influence of Cold Forming and Heat Treatment Processes on the Mechanical and Fracture Properties of AA6016 Aluminum Sheets.

In order to ascertain the mechanical properties and fracture performance of AA6016 aluminum sheets after cold forming and heat treatment processes, uniaxial tensile tests and fracture tests were conducted under various pre-strain conditions and heat treatment parameters. The experimental outcomes demonstrated that pre-strain and heat treatment had significant impacts on both stress-strain curves and fracture properties. Pre-strain plays a predominant role in influencing the mechanical and fracture properties. The behavior of precipitation hardening under different pre-strains was investigated using Differential Scanning Calorimetry (DSC). The results indicated that pre-strain accelerates the precipitation of the β″ strengthening phase, but excessive pre-strain can inhibit the heat treatment strengthening effect. To consider the influences of pre-strain and heat treatment, a constitutive model, as well as a predictive model for load-displacement curves, was established using a backpropagation (BP) neural network. An analysis of the number of hidden layers and neuron nodes in the network revealed that the accuracy of the model does not necessarily improve with an increase in the number of hidden layers and neuron nodes, and an excessive number might actually decrease the efficiency of the machine learning process.

Nondestructive material characterization and component identification in sheet metal processing with electromagnetic methods

Electromagnetic methods for non-destructive evaluation (NDE) are presented, with which sheet metal components can be identified and their material properties can be characterized. The latter is possible with 3MA, the Micromagnetic Multiparametric Microstructure and stress Analyser. This is a combination of several micromagnetic NDE methods that make it possible to analyse the microstructure in a ferromagnetic material and to determine quantitative values of the mechanical material properties or the stress state. In the case of cold forming, the 3MA application for pre-process testing of sheet metal is discussed. Based on the 3MA information, the formability of the sheets can be predicted. To apply 3MA in-line, the influence of the relative speed and the relative distance between the 3MA probe head and the sheet was investigated. In a second study, a spatially resolved eddy current (EC) method was used to create an image of the intrinsic material microstructure of a component for its identification and traceability. It turned out, that these intrinsic fingerprint images can still be recognized even after subsequent plastic deformation or coating of the surface. This enabled the development of a marker-free traceability method for sheet metal processing. It is based on a low-cost array sensor and a specimen identification using robust and partly redundant features of the fingerprint images processed by machine learning (ML).

SAE 1015, CEN C15, ISO C15

Abstract 1015, C15E, and C15R are wrought low-carbon (carbon equals 0.12 to 0.18 percent) non-alloy steels that are used in the as rolled, annealed, normalized, or cold worked condition. They are widely used for lightly and moderately stressed parts that require higher strength levels than can be achieved by the lower carbon grades, and also for applications where a combination of low-to-medium strength, excellent cold formability, and excellent weldability are required. These steels may also be used in the case hardened, nitrided, or nitrocarburized condition. This datasheet provides information on composition, physical properties, microstructure, hardness, and tensile properties. It also includes information on forming and heat treating. Filing Code: CS-266. Producer or source: Heat Treater’s Guide.

Cold formability of friction stir processed 5754-H111 and 6082-T6 aluminum alloys: an experimental and numerical study

Aluminum has become increasingly important in the automotive sector due to its ability to reduce vehicle weight without compromising structural performance. However, joining different types of aluminum alloys can be challenging due to their different thermal and mechanical characteristics. Concurrently, friction stir processing (FSP) is a material processing technique that has garnered considerable attention for its versatility and industrial applicability, and it may represent a preliminary phase to correctly perform friction stir welding, which is a welding technology used to join different types of aluminum alloys. In this context, this study presents an extensive experimental campaign of FSP performed on 5754-H111 and 6082-T6 alloys, varying two rolling directions and four welding speeds. The processed materials were characterized, including cupping and tensile tests, microstructure analysis, and a correlation between welding parameters, microstructure, and mechanical resistance. In addition, a numerical method was proposed to simulate the Erichsen tests and predict the formability of the materials, before and after the FSP processes. The results showed that both alloys exhibited good formability after the FSP process, but with different behavior. AA6082 underwent internal decohesion and dynamic recrystallization, resulting in the absence of defects and an increase in ductility and cold formability. AA5754 experiences more difficulty with material flow during FSP and showed the presence of tunnel defects in all analyzed process conditions. However, the alloy 5754 did not undergo softening and had comparable mechanical behavior and cold formability to the base material. These results were validated by the numerical method proposed.

Cold Formability of Twin-Roll Cast, Rolled and Annealed Mg Strips

This study investigates the cold formability of twin-roll cast and rolled magnesium strips, specifically focusing on AZ31 and ZAX210 alloys. The aim is to assess the suitability of these alloys for various forming processes. The mechanical properties and formability characteristics of the strips were thoroughly examined to provide insights into their potential applications in transportation industries such as automotive and aerospace. The AZ31 and ZAX210 alloys were subjected to twin-roll casting and rolling processes to produce thin strips. The resulting strips were then evaluated for their cold formability. The results indicate that both alloys exhibit favourable cold formability. The ZAX210 alloy, in particular, demonstrates medium strengths with an average tensile strength of approximately 240 MPa at room temperature. The 0.2% proof stress values range between 136 MPa and 159 MPa, depending on the sampling direction. The total elongation values vary from 28% in the transverse direction to 32% at a 45° angle, indicating excellent ductility. Comparing the two alloys, the AZ31 alloy shows higher strengths due to its higher aluminium content. However, it also exhibits a more pronounced directional dependence of mechanical properties due to the formation of a strong basal texture during hot rolling. The transverse direction experiences reduced total elongation compared to the rolling direction, achieving only about 50% of the total elongation. The average Erichsen Index recorded for AZ31 and ZAX210 strips were 4.9 mm and 7.1 mm, respectively. The ZAX210 strip displays superior formability, which can be attributed to the fine-grained microstructure and the texture softening resulting from the weakening of the basal texture intensity and the splitting of the basal pole towards the rolling direction. In conclusion, the investigated twin-roll cast, rolled and annealed AZ31 and ZAX210 magnesium strips exhibit promising cold formability characteristics. The findings of this study contribute to the understanding of their mechanical behaviour and can guide the selection and optimisation of these alloys for various forming applications.

Effects of Mean Normal Stress on Strain-Hardening, Strain-Induced Martensite Transformation, and Void-Formation Behaviors in High-Strength TRIP-Aided Steels

To analyze various types of cold formability in TRIP-aided polygonal ferrite (TPF), annealed martensite (TAM), and bainitic ferrite (TBF) steels, the effects of the mean normal stress on the strain-hardening, strain-induced martensite transformation, and void-formation behaviors were investigated. The strain-hardening behavior was influenced by positive mean normal stress and was hardly influenced by zero and negative mean normal stresses in all steels. Positive mean normal stress promoted the strain-induced martensitic transformation behavior, especially in TBF steel due to the high mechanical stability of the retained austenite. The void-formation behavior was also promoted by positive mean normal stress, especially in TPF steel. These behaviors were also related to the microstructural properties, such as the matrix structure, retained austenite characteristics, and second phase.

Research on effective communication forms and characteristics of public service advertisements for nurturing parenting skills in China

This study is part of a larger research aimed at enhancing effective communication of parenting skills knowledge to Chinese parents. The purpose is to explore how to transform public service advertisements into effective training methods for Chinese parents by studying the media form, content expression, symbolic elements and other aspects of public service advertisements in China. This study documents the identification of effective communication characteristics of PSAs, in which advertisements in the form of cold and hot media have different sensory experience characteristics, their expressions of the central processing path, and the expression of the peripheral processing path of advertisements, which could be transformed to improve information transmission and are attractive to observers. The results found different characteristics in terms of language and nonverbal advertising content, which could create different effects on observers. This article mainly studies the different roles of different media forms, content expression, and symbolic elements in public service advertisements, as well as the communication effects of different forms of public service advertisements under different themes. The results have significant implications for developing a theoretical framework for the efficient dissemination of public service commercials and, consequently, for promoting happier families for developing children by improving parents' parenting knowledge.

Application of the process of joining sheet by mechanical cold forming (clinching) using dissimilar materials

In the metalworking industry in general, the need to join components made of sheet metal is very common. The automotive sector, for example, needs to join components made of sheet metal to assemble vehicle bodies. The aeronautical sector needs to join sheets, mainly aluminum, when assembling aircraft. In white goods, there is a need to join low-carbon steel sheets that make up a wide range of household appliances, as well as other sectors such as metal structures, packaging and others. The joining of sheet metal components can be done through some permanent joining process, such as welding and riveting; or by some type of detachable connection, made by screw, nut, stud, pin, among others. A joining technique that has been gaining ground in the industry is plastic deformation joining. Groche et al. (2014) reviewed this technique and present the various existing variations. The most common is known as clinching union. According to Varis (2006), it emerged in the 1980s in an automotive industry in the assembly of chassis. The technique consists of cold joining sheets through the action of a punch that plastically deforms the sheets against a die. The deformation produces an interlook region that joins the sheets, giving the appearance of a spot weld. Sarmento and Pereira (2012) cite the main advantages of this technique: (I) it allows joining a vast amount of materials including metals with non-metals; (II) lower distortions, embrittlement and residual stress; (III) high process repeatability and simple quality control, and (IV) safe working environment.

Web crippling behaviour of sigma sections under end two flange loading – Numerical investigation

Cold-Formed (CF) sections have emerged in the construction industry due to their merits, including ease of fabrication for different section profiles, sustainability, and cost-effectiveness. As a result, various innovative section profiles have been introduced to the CF industry. Sigma sections are one such innovative profile that has been introduced in the CF industry. The inclusion of longitudinal stiffeners in Sigma sections improves their bending capacity. Additionally, Sigma sections offer high stiffness, increased torsional rigidity, and superior load-carrying capacity. However, the inclusion of web longitudinal stiffeners might induce localised failures under concentrated loads, known as web crippling failures. Therefore, it is necessary to explore the web crippling behaviour of Sigma sections to effectively employ them in the industry. However, limited research has been conducted on Sigma sections in terms of web crippling. Thus, this research intends to investigate the web crippling behaviour of Sigma sections under the ETF load case. A comprehensive numerical study consisting of 1512 numerical models was conducted on Sigma sections made of aluminium (432 numerical models), carbon steel (648 numerical models), and stainless steel (432 numerical models) after successfully validating the numerical approach. The results obtained from the numerical study were compared using parameters such as section depth, thickness, yield strength, bearing length, and radii. The numerical results were also compared with existing design equations and considering their inaccuracy in predicting the web crippling capacity of Sigma sections made of CF carbon steel, stainless steel, and aluminium under the ETF load case, modified design provisions were proposed. In addition, a numerical investigation was conducted to analyse the web crippling performance of Sigma section with conventional sections, and it was concluded that similar web crippling performance was observed for Sigma sections. Hence, the Sigma sections were highly recommended for extensive applications in the industry.

Testing and design of cold-formed high strength steel square hollow section columns

An experimental and numerical investigation into the flexural buckling behaviour of cold-formed (CF) high-strength steel (HSS) square hollow section (SHS) members is reported in this paper. A series of 12 flexural buckling tests were conducted on S700 and S900 CF SHS columns. Finite element (FE) models were developed to simulate the experimental observations, which were utilized in a parametric study encompassing a broader range of steel grades and specimen geometries. Subsequently, the current buckling curves in European, North American, and Australian codes was evaluated through reliability analyses. Meanwhile, the effective width method (EWM) and the modified generalized slenderness-based resistance method (GRSM) were compared for slender cross-sections. According to the results of reliability analyses, the modified buckling curves were proposed for CF HSS SHS columns.

Research on Cold Roll Forming Process of Strips for Truss Rods for Space Construction.

In this paper, a new technology for on-orbit cold forming of space truss rods is proposed. For the cold roll forming process of asymmetric cross sections of thin strips, the effects of roll gap and roll spacing on the forming of asymmetric cross sections of strips were investigated using ABAQUS simulation + experiments. The study shows the following. When forming a strip with a specific asymmetric cross section, the stresses are mainly concentrated in corners 2/4/6, with the largest strain value in corner 2. With increasing forming passes, when the roll gap is 0.3 mm, the maximum equivalent strain values are 0.09, 0.24, 0.64 sequentially. Roll gaps of 0.4 mm and 0.5 mm equivalent strain change amplitude are relatively similar, and their maximum equivalent strain values are approximately 0.07,0.15, 0.44. From the analysis of the stress-strain history of the characteristic nodes in corners 2/4/6, it can be seen that the stress and strain changes in the deformation process mainly occur at the moment of interaction between the upper and lower rollers, where the stress type of node 55786 shows two tensile types and one compressive type, the stress type of nodes 48594 and 15928 shows two compressive and one tensile type, and the strain of the three nodes is in accordance with the characteristics of plane strain. When the roll gap is about 0.4 mm, the forming of the strip is relatively good. With increased roll spacing, the strip in the longitudinal stress peak through the rollers shows a small incremental trend, but the peak stresses are 380 Mpa or so. When the roll spacing is 120 mm, the longitudinal strain fluctuation of the strip is the most serious, followed by the roll spacing at 100 mm, and the minimum at 140 mm. Combined with the fluctuation in strip edges under different roll spacings, manufacturing cost and volume and other factors, a roll spacing of 100 mm is more reasonable. It is experimentally verified that when the roll gap is 0.4 mm and the roll spacing is 100 mm, the strip is successfully prepared in accordance with the cross-section requirements. When the rolling gap is 0.3 mm, due to stress-strain concentration, the strip is prone to edge waves in forming. The top of corner 2 of the flange triangular region is susceptible to intermittent tear defects, and the crack extension mechanism is mainly based on the cleavage fracture + ductile fracture.

SAE 1010, CEN C10, ISO C10

Abstract 1010, C10E, and C10R are wrought low-carbon (carbon = 0.07–0.13%) non-alloy steels that are used in the as rolled, annealed, normalized, or cold worked condition. These steels are characterized by low strength, high ductility, excellent cold formability, and excellent weldability. Within the carbon range of these steel grades, strength and hardness will increase with increase in carbon content and with cold work. Such increases in strength are at the sacrifice of ductility or the ability to withstand cold deformation. 1010, C10E, and C10R are widely used for lightly stressed parts where cold formability is the primary requisite. They are less expensive than 1008 and can be used when the requirements for cold forming are less exacting. 1010, C10E, and C10R may also be used in the case hardened, nitrided, or nitrocarburized condition. This datasheet provides information on composition, physical properties, microstructure, hardness, and tensile properties. It also includes information on forming and heat treating. Filing Code: CS-265. Producer or source: Heat Treater's Guide.

Effect of roughness, contact pressure and lubrication on the onset of galling of the 6082 aluminium alloy in cold forming, a numerical approach

The effect of surface roughness, contact pressure and lubrication on the onset of galling of aluminum 6082-T6 is studied with a pin-on-plate tribometer. The design of experiments involves pins with mean arithmetic roughness Ra equaled to 0.2, 0.35 and 0.6 μm, normal loads ranging from 5 to 600 N, and 4 different lubrications: without lubricant, with MoS2 dry lubricant, with pure mineral oil and with a highly chlorinated paraffin oil. Tests are performed at room temperature and are repeated three times. Experimental results show the great sensitivity of the onset of galling to the roughness and the beneficial effect of dry and liquid lubricants. The occurrence of galling is study by optical micrographs, by the analyses of the coefficient of friction, and by the use of finite element simulations. It comes that the variation of the coefficient of friction is not self-sufficient to detect the onset of galling. The finite element computations involves Wilson’s lubrication model and Xue’s damage model. Galling is assumed when finite elements near the contact area reach the critical damage Dc. This numerical approach leads to a good prediction of the onset of galling for the tests performed under constant normal load. For tests performed with increasing normal loads and various lubricants, the numerical prediction overestimate the sliding length before galling occurs.

Mechanisms controlling friction and material transfer in sliding contacts between cemented carbide and aluminum during metal forming

Cold forming of aluminum alloys is frequently associated with problems related to severe adhesion and material transfer onto the forming tools which results in high friction forces and negatively affects the surface quality of the formed parts, a phenomenon frequently named galling. In the present study, well controlled laboratory tests using a scratch testing equipment have been performed to evaluate the friction characteristics and investigate the mechanisms controlling the initial transfer of aluminum in dry sliding contact with five different cemented carbide grades. In the tests, an aluminum pin (representing the work material) with a conical tip slides against a flat, fine-polished, cemented carbide surface (representing the tool). During sliding, the mechanical contact results in plastic deformation and flattening of the work material against the tool surface, thus simulating a metal forming contact. The small scale and well-defined tribo contact in combination with post-test surface characterization using optical surface profilometry, high resolution SEM and EDS makes it possible to evaluate the influence of material transfer on the friction characteristics.The results show that sub-μm surface irregularities in the cemented carbide surface trigger mechanical interaction with the softer aluminum surface which promotes aluminum transfer to the cemented carbide surface resulting in high friction. Common surface irregularities, promoting aluminum transfer, are sharp edges of slightly protruding carbide grains, surface steps in connection to binder phase pockets, surface steps in connection to surface pores, etc. It should be noted that even very small surface steps, < 20 nm in height, constitute efficient cutting edges able to effectively cut off the passing aluminum material and thus have a very strong impact on material transfer. In contrast, the effect of carbide composition, e.g. the presence of cubic carbides of different composition, seems to be of minor importance to reduce the adhesion and the tendency to material transfer.

SAE 1008, CEN C8, ISO C8

Abstract 1008 and C8C are wrought low-carbon (carbon ≤ 0.10%) non-alloy steels that are used in the as-rolled, annealed, normalized, or cold worked condition. These steels are characterized by low strength, high ductility, excellent cold formability, and excellent weldability. Within the carbon range of these steel grades, strength and hardness will increase with increase in carbon content and with cold work. Such increases in strength are at the sacrifice of ductility or the ability to withstand cold deformation. 1008 and C8C are widely used for lightly stressed parts where cold formability or drawability is the primary requirement. In general, they are not intended for heat treatment after cold working.1008 may, however, be used in the case hardened, nitrided, or nitrocarburized condition. This datasheet provides information on composition, physical properties, microstructure, hardness, and tensile properties. It also includes information on forming and heat treating. Filing Code: CS-264. Producer or source: Heat Treater's Guide.

Effects of Material Properties on the Teeth Accuracy of Spline Shafts in Cold Form Rolling

Effects of Material Properties on the Teeth Accuracy of Spline Shafts in Cold Form Rolling

Numerical Simulation and Experimental Study of Cold and Hot Composite Forming of Sharp-Edged High-Strength Steel Sections.

This paper describes the use of cold and hot composite forming technology to produce pointed curtain wall profiles. An electromagnetic-temperature coupling model was constructed using ANSYS to study the temperature and electromagnetic field distribution during the forming process. Numerical simulation was used to optimize the process parameters to obtain the optimum heating parameters with a current of 4000 A, a frequency of 35 kHz, and a duration of 2 s. The accuracy of the model was also verified through experiments. The simulation results show that the use of a conductive magnet can improve the induction heating efficiency, increasing the heating frequency and the temperature peak; however, it also increases the temperature difference. Sharp-corner curtain wall profiles were successfully produced using the optimized process parameters. The temperature of the heating zone was measured using an infrared thermal imager, and the relative errors between the maximum heating temperature obtained from the simulation and the actual measured values were 5.37% and 5.02%, respectively, indicating that the finite element model performs well in terms of prediction.

Recent Research Advances in High-Performance Steel Tubular Members: Material Properties, Stub Columns, and Beams

This paper presents recent advances in research on high-performance steel tubular members, including beams and columns. The term high-performance steel has been used for steels that have unparalleled characteristics such as high strength, cold formability, corrosion resistance, and ductility. Stainless steel (SS) and high-strength steel (HSS) are classified as high-performance steel. In the context of this paper, high-performance steel refers to SS and HSS, where HSS is with a nominal yield strength equal to or higher than 690 MPa. This paper initially illustrates the applications of high-performance steel as a construction material for buildings and infrastructures. Subsequently, the material properties of high-performance steel with constitutive models in response to the stress–strain curves are summarized. Furthermore, this paper reviews research on the structural performance of high-performance steel stub columns and beams and presents the associated design equations. Finally, insights into future work on the structural behavior of high-performance steel to promote its widespread use for building and infrastructure construction are provided.