Metal Clinching

The joinability of aluminium alloy sheets with reduced ductility produced by mechanical clinching is analyzed. A modified tool set geometry was developed to reduce the localization and magnitude of plastic strain. Sheets preheating was adopted to increase the material formability. Optical microscopy and scanning electron microscopy were utilized to observe possible presence of cracks in clinched connections and to perform dimensional analysis. Mechanical characterization tests comprising micro-hardness test and single lap shear tests were conducted to evaluate the influence of the processing conditions on joints strength.

The present investigation is carried out to assess the suitability of the clinching process for production of plastic-metal hybrid joints. To this end, a prototypal apparatus was developed to preheat the sheets before joining. A campaign of experimental tests was carried out on aluminium alloy AA5053 and polystyrene. Experimental tests were conducted by varying the main process parameters, i.e. pre-heating conditions (heating time and temperature of heating air) and forming pressure. The joints produced under different operating conditions were observed using optical and stereoscope microscope. In addition, the mechanical behaviours of joints were assessed by conducting single lap shear tests on single joints. Based on the achieved results, the main failure modes were identified and the effect of process parameters on mechanical behaviours of the joints were clarified.

An experimental investigation has been conducted on mechanically clinched joints, produced with fixed and extensible dies with different forming forces. Mechanical testing involving single lap shear tests, both with one and two joining points, and peeling tests were conducted under quasi-static conditions to assess the different mechanical behaviors of these joints. The effect of the processing conditions on the main mechanical response of the joints, namely the maximum strength, stiffness and absorbed energy, was investigated. The results showed that the joints produced with the extensible die exhibited a similar strength as compared to those produced with the fixed die in single lap shear tests, while they are characterized by a higher strength (up to 40%) when loaded during the peeling test because of a larger interlock. In addition, the employment of extensible dies allows a drastic reduction of the forming loads as compared to those required by adopting the fixed dies.

The choice of proper joining technology is an essential aspect of designing and manufacturing activity. New product designs enforce joining different materials in a new joining method. Clinching is a relatively new joining technology in which sheet metal parts are deformed locally without use of any additional element. Combining clinching with adhesive bonding seems to be interesting hybrid joining method with new potential applications in manufacturing industry. The paper deals with discussion of technological aspects and experimental investigations of clinched lap joints of different metal strips combined with their adhesive bonding, which can be applied for different branches of engineering. The main purpose of using different types of sheet metals was to analyze their influences on the geometry and mechanical strength of the clinched joint. The experiments with application of Digital Image Correlation (DIC) system ARAMIS allowed for exact monitoring of the deformation process of considered hybrid joint. The clinched joint test specimens were carried out with laboratory test-stand which consisted of a pair of tools (punch and die) attached to C-frame hydraulic press.

This study is based on the joint quality of zinc-coated EN 10346: 2015 DX52D + Z quality steel sheets with having different thicknesses, which are preferred in the automotive industry due to their formability. Joining problems in clinching applications with different positions and sheets of different thicknesses are discussed and experimental outcomes are discussed in terms of strength of joints. As a result of the tests carried out according to the standards, it has been found that the joining of the sheets with thickness close to each other is relatively good, as the thickness difference increases, the joint quality decreases and sometimes the joint does not form. It has been also found that if the thinner sheet is placed on the bottom die during clinching, a better joint strength is obtained. EN 10346: 2015 DX52D+Z Plakaların Form-Punta Bağlantı Performansları Anahtar kelimeler Perçinleme; Bağlantı dayanımı; Metal şekillendirme; Bağlantı kalitesi; Bağlantı testi; Birbirine kilitlenme Öz Bu çalışma, şekillendirme kabiliyeti nedeniyle daha çok otomotiv endüstrisinde tercih edilen çinko kaplanmış farklı kalınlıktaki EN 10346:2015 DX52D+Z kalite çelik levhaların clinching teknolojisi ile yapılan bağlantılarının bağlantı kalitesi üzerine yapılmıştır. Özellikle clinching uygulamalarında karşımıza çıkan farklı pozisyon ve farklı kalınlıktaki levha birleştirmelerindeki bağlantı problemleri ele alınmış ve bağlantı kalitesi için genel bir değerlendirme yapılmıştır. Standartlara uygun olarak gerçekleştirilen testler sonucunda birbirlerine yakın kalınlıktaki levhaların bağlantılarının nispeten iyi olduğu, kalınlık farkının arttığında, bağlantı kalitesinin azaldığı ve bazen bağlantıların gerçekleşmediği görülmüştür. Bağlantı sırasında daha ince olan plakanın alt matris tarafında olması, çok daha iyi bir bağlantı dayanımının sağlanabilmesinin bir gereği olduğu belirlenmiştir.

In this work, hybrid aluminum alloy/steel joints by combining clinching and bonding processes were realized. Furthermore, we investigated how the presence of an adhesive interlayer can influence the performance of hybrid joints when exposed in salt spray environment up to 15 weeks of ageing. The durability of steel/aluminum joints is a well-known problem, in particular for steel-reinforced aluminum frames, in aggressive environmental conditions. The aluminum alloy/steel joints were made by interposing an adhesive layer (modified silane (MS) polymer) and clinching before the polymerization has taken place. A proper design of experiment has been carried out, followed by the ANOVA of the results. The experimental results of long-term ageing tests (ASTM B 117) evidenced that the corrosion degradation phenomena influenced significantly the mechanical performance of the hybrid joints. By comparison with the pure mechanical clinching joints, in the same configurations studied in a previous work, the shear load trends are similar. The presence of the flexible adhesive layer gave a significant advantage on resistance to a corrosive attack but little influences the mechanical strength.

Background: The clinching is one of the most common metal joining processes in the manufacturing of metal plate based products (similar or dissimilar, pre-coated or galvanized), especially when the assembly without adding major joining elements is required. When the clinched joints work in an aggressive environment, particular attention would be placed on the electrochemical stability and corrosion resistance of the metal constituents (Mizukoshi and Okada 1997). In joining design, an appropriate material selection reduces the electrochemical potential differences and prevents significant galvanic currents (Kruger and Mandel 2011; Calabrese et al. 2014). The durability of the metal joints could be heavily influenced in a corrosive environment, whereas the less noble material will tend to increase its corrosion rate; instead the more noble one will reduce its electrochemical dissolution (He et al. 2008; Bardal 2004). Accelerated ageing tests (i.e. salt fog test) were carried out to evaluate the durability of the joints in highly aggressive environments (Calabrese et al. 2013; LeBozec et al. 2012). Although the durability for a long time of the clinched joint in a corrosion environment is a known problem, few works focus the attention on the relationship between durability of joints and electrochemical behaviour of the metal constituents. The aim of the present work is to evaluate the durability at long ageing time in salt spray test (according to ASTM B117) of carbon steel/aluminium alloy joints, obtained by clinching. Methods: The investigation has been conducted on one total thickness (2.5 mm) of unsymmetrical joints (i.e. thickness sheets of 1.5 mm and 1 mm) to inquire about the effect of corrosion on the two different unsymmetrical configurations (St1.5/Al1 and St1/Al.5). The joint resistance has been determined, by means of shear tests of single-lap joints in according to ISO/CD 12996. The samples were exposed to critical environmental conditions following the ASTM B 117 standard. To inquire the damage evolution of the samples, 0, 1, 2,3, 5, 7, 10 and 15 weeks of ageing time have been chosen. Seven samples for each combination and for each ageing time were realized. A Design of Experiment has been performed, followed by the ANOVA of the results to analyse the influence of the two factors, thickness combinations and ageing time, on the mechanical properties of the joints. Results: The two sets of joints show a different behaviour at increasing ageing time: the St1.5/Al1 batch shows a constant decay of the load values, instead the St1/Al1.5 set maintains acceptable values of resistance for several weeks of ageing, at tenth week the mechanical stability is strongly impaired. In the latter case the presence of the thin oxide layer at the overlapping interface, which behaves as an adhesive interlayer, and the larger thickness of the aluminium plate improve the resistance of the St1/Al1.5 joints. Statistical analysis confirms that the two thickness combinations and ageing time are the significant factors. At zero weeks, neglecting the effect of ageing, the maximum load values of all samples belong to the same population. This means that the resistance of the clinched joints is the same regardless the combination of thicknesses, but by considering both the ageing and thickness, the analysis of variance shows that both thickness and weeks are significant parameters distinguishing two different populations in the distribution of loads.

This study is based on the joint quality of zinc-coated EN 10346: 2015 DX52D + Z quality steel sheets with having different thicknesses, which are preferred in the automotive industry due to their formability. Joining problems in clinching applications with different positions and sheets of different thicknesses are discussed and experimental outcomes are discussed in terms of strength of joints. As a result of the tests carried out according to the standards, it has been found that the joining of the sheets with thickness close to each other is relatively good, as the thickness difference increases, the joint quality decreases and sometimes the joint does not form. It has been also found that if the thinner sheet is placed on the bottom die during clinching, a better joint strength is obtained. EN 10346: 2015 DX52D+Z Plakaların Form-Punta Bağlantı Performansları Anahtar kelimeler Perçinleme; Bağlantı dayanımı; Metal şekillendirme; Bağlantı kalitesi; Bağlantı testi; Birbirine kilitlenme Öz Bu çalışma, şekillendirme kabiliyeti nedeniyle daha çok otomotiv endüstrisinde tercih edilen çinko kaplanmış farklı kalınlıktaki EN 10346:2015 DX52D+Z kalite çelik levhaların clinching teknolojisi ile yapılan bağlantılarının bağlantı kalitesi üzerine yapılmıştır. Özellikle clinching uygulamalarında karşımıza çıkan farklı pozisyon ve farklı kalınlıktaki levha birleştirmelerindeki bağlantı problemleri ele alınmış ve bağlantı kalitesi için genel bir değerlendirme yapılmıştır. Standartlara uygun olarak gerçekleştirilen testler sonucunda birbirlerine yakın kalınlıktaki levhaların bağlantılarının nispeten iyi olduğu, kalınlık farkının arttığında, bağlantı kalitesinin azaldığı ve bazen bağlantıların gerçekleşmediği görülmüştür. Bağlantı sırasında daha ince olan plakanın alt matris tarafında olması, çok daha iyi bir bağlantı dayanımının sağlanabilmesinin bir gereği olduğu belirlenmiştir.

In this study, a thin aluminum sheet are to be joined by mechanical clinching. The diameter of the die and stroke of the punch are controlled whereas the thickness of the sheets, diameter of the punch and speed of the machine are fixed in order to obtain the best results. It was found that mechanical clinching has superior fatigue strength due to the large yield stress of the sheets and relaxation of the stress concentration. The interlocking between the sheets, the thinning of the sheet and the fracture were observed.

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The last years have seen the development of a new generation of industrial interesting mechanical joining techniques for thin sheets such as self piercing riveting, clinching, friction stir welding and laser welding. The present work concentrates on fatigue behaviour of joints obtained by clinching, a cold welding technology for thin sheets which is quickly developing in automobile, electronic and white goods industries, even if mainly in terms of static properties. The activity firstly dealt with fatigue tests and fractographic observations which evidenced different failure modes at different stress ratios. Results were then supported by FEM analyses of the clinched joints.

Economic conditions as well as comfort and safety-related requirements lead to lightweight design especially in automotive body-in-white production processes. The consequential multi-material mix limits the reliability of conventional thermal joining technologies. Innovative mechanical joining technologies need to be established. Following the lightweight-design requirements, next step for weight-reduction would be the renunciation of additional elements. Clinching technologies support this idea by creating a form- and force-fitting joint, but are limited to the formability of the joining partners. Joining by forming without additional elements even of hot formed ultra-high-strength manganese steels and ductile aluminium can be realised by shear-clinching. A precisely coordinated tool setup initialises a crack in the die-sided material with limited formability without harming the punch-sided ductile aluminium. This paper presents current and detailed investigations of the influences...

Clinching is a joining process that is becoming more and more important in industry due to the increasing use of multi-material designs. Despite the already widespread use of the process, there is still a need for research to understand the mechanisms and design of clinched joints. In contrast to the tool parameters, process and material disturbances have not yet been investigated to a relatively large extent. However, these also have a great influence on the properties and applicability of clinching. The effect of process disturbances on the clinched joint are investigated with numerical and experimental methods. The investigated process variations are the history of the sheets using the pre-hardening of the material, different sheet thicknesses, sheet arrangements and punch strokes. For the consideration of the material history, a specimen geometry for pre-stretching specimens in uniaxial tension is used, from which the pre-stretched secondary specimens are taken. A finite element...

In the course of ongoing development of mechanical joining technologies, different technologies were developed in the last years, where often the necessary die as contrary die was substituted by a flat anvil. Using the example of dieless clinching, the full potential of such process alternatives is visible. If the tools, as the punch or the blank-holder are modified and the necessary die is substituted by a flat anvil, then several advantages for the process alternative-the dieless clinching-emerges. For example, it is possible to produce a one-sided flat connection, which is not producible with any other joining technology. Additionally it is possible to enlarge the application potential of mechanical joining technologies as for example semi-finished parts made of magnesium can be partially heated and directly joined without an increase in process time or a reduction in the process stability. The tool's costs, the necessary tolerances and the tool wear are significantly reduced. The publication includes an overview over the state of the development and the application potential with practical examples of different process alternatives.

This paper proposes a new joining by forming process for connecting metal-polymer sandwich composite panels to metallic tubes. The process involves forming an annular flange with rectangular cross section by partial sheet-bulk of the tube wall thickness and performing the mechanical interlocking by upsetting the free tube end against the sandwich composite with a flaring punch. The investigation draws from the mechanical characterization of the tubular and of the individual layers of the sandwich composite materials to the fabrication of several joints with different process parameters. Experimentation is supported by numerical simulation and allows identifying the major process parameters, determining the required forming loads and discussing the feasibility of the new process to produce joints between metal-polymer sandwich composite panels and metal tubes that can be easily disassembled and recycled at the end of live. Results show that the new proposed joining by forming process...

Friction Assisted Joining process of titanium and Polyetheretherketone sheets is investigated. Laser texturing was previously performed on the titanium sheets to promote the mechanical joining between the substrates to increase the strength of the joints. Infrared thermography was conducted by means of an IR camera to measure the temperature trend and distribution during the joining process. Quasi-static single lap shear tests were performed to determine the influence of the processing conditions on the strength of the joints. Morphological analysis and fracture surface analysis were conducted to understand the influence of the energy supplied on the quality of the joints. The joints with the highest strength were achieved after the minimum heating time 7.5 s. These joints where characterized by a shear strength of 37.3 MPa corresponding to 66% of that of the PEEK material. Longer heating times resulted in severe thermal degradation (carbonization) of the polymer in the central region, which was due to the low thermal conductivity of the titanium. Nevertheless, the Ultimate Shear Force continuously increased with the heating time up to 8.85 kN (for heating time of 25 s) due to the increase in the joined area.

In the scope of reduced resource consumption and CO2 emissions, lightweight structures in multi-material-design offer a high potential for use in aviation or automotive applications. Though, to take advantage of the specific structural and functional properties of the different materials of hybrid structures, it is necessary to provide adapted manufacturing and joining technologies. This article presents the development of a new thermoclinching joining process to produce hybrid structures with continuous fiber reinforced thermoplastic composites and metallic components. Based on the principles of staking and the classical clinching process, thermoclinching technology ensures element free and form-closed joints by plastic deformation of the reinforced thermoplastic component. To approve the technological concept of the thermoclinching process, prototypic joints with both reinforced and non-reinforced thermoplastics were produced and experimentally tested, revealing up to 50% higher f...

Several studies demonstrated a close relationship between the strength of metal-polymer joints made by thermomechanical processes and the temperature reached during the process. Machine Learning techniques have been adopted to forecast the temperature trends produced during Friction Assisted Joining varying the main process parameters. This was performed in four steps. First, the design of a campaign of experimental tests and the setup of an instrumented joining machine equipped with load sensors (plunging load and torque) was implemented. The machine was also equipped with an IR camera for temperature measurements during the process. Then, the experimental data were processed and filtered to produce a robust dataset, which was subsequently used for the training, calibration, and validation of an Artificial Neural Network (ANN). The developed approach was based on a data encoding-decoding approach that initially subdivided power-temperature data for training the network. During training, the ANN had no information on the origin curve. Then, once validated, the ANN reconstructed the temperature curve sequentially starting from power curve measurements. The results indicated that starting from the absorbed (measured) power, the developed model was capable to predict the temperature evolution with great accuracy. The resulting Artificial Neural Network represents a reliable tool for process design and identification of correct process parameters e.g. Dwell time; besides, it can be used during the joining process to achieve a prescribed temperature.

Laser-Assisted Direct Joining (LADJ) has been employed for a wide variety of materials including metals, thermoplastics and reinforced thermoplastics. The feasibility of Laser-Assisted Direct Joining (LADJ) of Carbon Fibre Reinforced Polymer (CFRP) with thermosetting matrix to polycarbonate sheets is investigated in this work. The process was performed by means of a high-power diode laser with a maximum power of 200 W. Experimental tests were carried out by varying the main process conditions including the laser power and scanning speed. Morphological analysis using Optical and Scanning Electron Microscopy (SEM) as well as mechanical characterization of the welds were performed to understand the influence of the processing conditions on the weld quality, defects, and strength. Preliminary results have been encouraging: the process consists in removing the exterior epoxy layer from the CFRP and the adhesion of the carbon fibres to the PC. According to the achieved findings, the mechanical strength of the welds was highly affected by the Linear Energy Density (LE): low values of LE resulted in poor adhesion of the polycarbonate through the carbon fibres, which led to poor mechanical fastening and adhesion. On the other hand, processing conditions leading to excessive values of LE resulted in considerable damage of the composite matrix (the epoxy resin underlying the exposed carbon-fibre layer) and formation of bubbles on the PC substrate, which produced a dramatic reduction of the mechanical behaviour of the welds. The apparent shear strength, calculated as the ultimate shear force by the effective adhesion area was 8.4 MPa.

A hybrid non-linear numerical model of the thermal field produced during Friction Assisted Joining process of Metal-polymers hybrid joints is developed. The model uses experimental processing loads (plunging load and torque) measured during an experimental campaign as inputs. A hybrid approach was used to simulate the contact between the tool and the metal sheet. Indeed, the plunging load was simulated as a prescribed load acting on the punch while the friction heat owing to the interaction of the rotating tool with the metal sheet was simulated as a distributed heat flux over the tool-metal contact surface. This enabled a dramatic reduction of the complexity of the model along with a short simulation runtime. During experimental tests, an IR camera was used to measure the real temperature evolution. These data were used to calibrate and validate the FE model. The results indicated that the developed model can accurately predict the temperature field on the upper metal surface. Thus, it can be readily used to forecast the temperature evolution and distribution and the metalpolymer interface, which is the most influencing factor that determines the mechanical behavior of this type of joints.

In the recent years, high efforts have been spent concerning the development of fast mechanical joining processes. This is due to the growing employment of materials that are difficult to weld and hybrid structures involving different materials. Mechanical clinching enables to solving the major concerns in this field. However, the formability of the materials represent a limitation to the successful employment of the process. The present research illustrates a new concept of clinching, namely friction clinching that differs from the conventional process by the employment of a rotating tool, which heats up the sheet (by friction) during the process leading to an increase in the material formability. Preliminary tests were performed to verify the feasibility of the process and determine a sound processing window. The process was applied to join thin aluminium sheets and Carbon Fibre Reinforced Plastic (CFRP) laminate. Morphological analysis and mechanical characterization of the joints was performed in order to evaluate the suitability of such the rotating tool to increase the material formability and thus the aluminium sheet integrity. According to the achieved results, the employment of the rotating tool enables to avoid crack formation in the metal sheet, improves the material flow and reduces the joining forces.

The joinability of aluminium alloy sheets with reduced ductility produced by mechanical clinching is analyzed. A modified tool set geometry was developed to reduce the localization and magnitude of plastic strain. Sheets preheating was adopted to increase the material formability. Optical microscopy and scanning electron microscopy were utilized to observe possible presence of cracks in clinched connections and to perform dimensional analysis. Mechanical characterization tests comprising micro-hardness test and single lap shear tests were conducted to evaluate the influence of the processing conditions on joints strength.

The present investigation is carried out to assess the suitability of the clinching process for production of plastic-metal hybrid joints. To this end, a prototypal apparatus was developed to preheat the sheets before joining. A campaign of experimental tests was carried out on aluminium alloy AA5053 and polystyrene. Experimental tests were conducted by varying the main process parameters, i.e. pre-heating conditions (heating time and temperature of heating air) and forming pressure. The joints produced under different operating conditions were observed using optical and stereoscope microscope. In addition, the mechanical behaviours of joints were assessed by conducting single lap shear tests on single joints. Based on the achieved results, the main failure modes were identified and the effect of process parameters on mechanical behaviours of the joints were clarified.

An experimental investigation has been conducted on mechanically clinched joints, produced with fixed and extensible dies with different forming forces. Mechanical testing involving single lap shear tests, both with one and two joining points, and peeling tests were conducted under quasi-static conditions to assess the different mechanical behaviors of these joints. The effect of the processing conditions on the main mechanical response of the joints, namely the maximum strength, stiffness and absorbed energy, was investigated. The results showed that the joints produced with the extensible die exhibited a similar strength as compared to those produced with the fixed die in single lap shear tests, while they are characterized by a higher strength (up to 40%) when loaded during the peeling test because of a larger interlock. In addition, the employment of extensible dies allows a drastic reduction of the forming loads as compared to those required by adopting the fixed dies.

Clinching joints with an additional deformable rivet are modifications of the clinching joints. The clinch riveting (CR) joint is formed indirectly by a deformable rivet. The research included an analysis of CR joints’ forming process for aluminum alloy sheets made of AW 6082 in T6 state condition and AW 5754 in three different state conditions: H11, H22 and H24. As a result of forming the joint for various sheet arrangements, the highest value of blocking the upper sheet in the lower sheet (tu) was obtained for the arrangements with two 5754-H24 aluminum alloy sheets. For such a large interlock parameter tu, the greatest thinning of lower sheet (tn) was obtained, which influenced the maximum tensile shear force and the joint failure mechanism. Based on the load-displacement diagrams obtained from the static shear test of lap joints, the total energy of failure and energy to achieve the maximum load capacity were calculated. The highest energy absorption to achieve the maximum load ...

The clinching joints are more and more used when assembling sheet plate elements, especially in an automotive industry. The clinching joint is created by local stamping of joined sheets without heat effect on the material structure. This paper presents the analysis of effect of the thickness layout change and sheet type and die on the joint strength change. The shearing strength analysis of created joints has been presented. The shearing test results of the clinching joint have been compared with results achieved for spot welding joints of similar joint diameter.

W publikacji przedstawiono technologię łączenia blach za pomocą przetłaczania (ang. clinching). Clinching to proces scalania warstw materiału z udziałem odkształceń plastycznych. Przedstawiono przebieg procesu formowania złącza w klasycznej odmianie kształtowania. Scharakteryzowano fazy formowania przetłoczenia w trakcie łączenia blach. Opisano metody oceny jakości wykonania złączy, a także przykłady ich zastosowania. Obecnie istnieją różne konstrukcje używanych narzędzi, do formowania tego typu złączy. Najczęściej stosowanymi narzędziami są stempel, oraz matryca okrągła i niedzielona o zarysie osiowo-symetrycznym. Inne odmiany konstrukcji matryc pozwalają na znaczne obniżenie siły kształtowania złącza. W pracy zwrócono uwagę na rożną konstrukcję możliwych do zastosowania matryc, możliwość łączenia nie tylko materiałów metalicznych ale także kombinacji metalicznych z kompozytowymi. Opisano możliwości tworzenia złączy hybrydowych tj. klejowo-przetłaczanych. Ponadto scharakteryzowano ...

In the paper an analysis of the result obtained in numerical simulation of tools load during Al Mg 4.5Mn0.7 aluminium alloy sheets joining by SPR process. Numerical simulations of joining process were made, with use finite element method (FEM), in MSC.Marc 2010 commercial program. Experimental research of SPR joining process was made on test stand: press with electric drive and special tools. High precision of joint cross-sections from experimental and numerical research was obtained. It was observed that the surface pressure on the punch face depend on the rivet deformation and they are changing it non-linear way. The stress distribution change along line on the rivet head surface, through its center, is determined by the recess size of the tubular part of the rivet in the joined sheets. The results of numerical simulation can be used in developing process of SPR tools with shape modification.

This paper presents a research of the lap joint shear strength of S350GD+Z sheet material joined by resistance spot welding. The resistance spot welding process was done for five values of welding current. The joints strength structure analysis was done for the shearing curves. The influence of the welding current on the joints maximum strength and the shear curve of the resistance spot welded joints was presented. Welding current increase influence efficiency on the joints strength was analyzed. The analysis of the cold plastic formed joining technologies (clinching) was also presented. The clinching joints were made by using different tool types and uniform values of embossment minimum thickness. The influence of tool shape on the joint strength was described. In the case of round clinching joints the influence of forming force increase on the joints strength was studied.

This paper presents the results of experimental researches on effect of clinching joint’s load direction change on its characteristics and the maximum shearing force value. The single-folded clinching joints made of aluminum sheet AW1050A have been the subject of researches. Properly prepared specimens of rectangle clinching joints with material notch have been shear tested on the tensile testing machine UTS 100. The extreme joint destruction have been analyzed for the layout angle β = 0°, 90°. The separation mechanism has been described for all angle values β = 0o, 30o, 45o, 90o. The total separation work by joint shearing has also been mentioned.

In this work, the process of clinching was studied through practical experiments and also by computer simulation using finite element method (FEM). The influence of different joint geometries and process parameters on the strength of joints joined by clinching was studied. Subsequently, a practical study with the aim of comparing its results with FEM results was carried out. It was possible to observe that the geometry of the clinching tool and the choice of process parameters influence the interlocking strength. FEM simulations showed similar results to the practical experiments and also avoided the manufacture of different tools and the accomplishment of several experiments.

The joinability of aluminium alloy sheets with reduced ductility produced by mechanical clinching is analyzed. A modified tool set geometry was developed to reduce the localization and magnitude of plastic strain. Sheets preheating was adopted to increase the material formability. Optical microscopy and scanning electron microscopy were utilized to observe possible presence of cracks in clinched connections and to perform dimensional analysis. Mechanical characterization tests comprising micro-hardness test and single lap shear tests were conducted to evaluate the influence of the processing conditions on joints strength.

The present investigation is carried out to assess the suitability of the clinching process for production of plastic-metal hybrid joints. To this end, a prototypal apparatus was developed to preheat the sheets before joining. A campaign of experimental tests was carried out on aluminium alloy AA5053 and polystyrene. Experimental tests were conducted by varying the main process parameters, i.e. pre-heating conditions (heating time and temperature of heating air) and forming pressure. The joints produced under different operating conditions were observed using optical and stereoscope microscope. In addition, the mechanical behaviours of joints were assessed by conducting single lap shear tests on single joints. Based on the achieved results, the main failure modes were identified and the effect of process parameters on mechanical behaviours of the joints were clarified.

An experimental investigation has been conducted on mechanically clinched joints, produced with fixed and extensible dies with different forming forces. Mechanical testing involving single lap shear tests, both with one and two joining points, and peeling tests were conducted under quasi-static conditions to assess the different mechanical behaviors of these joints. The effect of the processing conditions on the main mechanical response of the joints, namely the maximum strength, stiffness and absorbed energy, was investigated. The results showed that the joints produced with the extensible die exhibited a similar strength as compared to those produced with the fixed die in single lap shear tests, while they are characterized by a higher strength (up to 40%) when loaded during the peeling test because of a larger interlock. In addition, the employment of extensible dies allows a drastic reduction of the forming loads as compared to those required by adopting the fixed dies.

Recent developments in automotive and aircraft industry towards a multi-material design pose challenges for modern joining technologies due to different mechanical properties and material compositions of various materials such as composites and metals. Therefore, mechanical joining technologies like clinching are in the focus of current research activities. For multi-material joints of metals and thermoplastic composites thermally assisted clinching processes with advanced tool concepts are well developed. The material-specific properties of fibre-reinforced thermoplastics have a significant influence on the joining process and the resulting material structure in the joining zone. For this reason, it is important to investigate these influences in detail and to understand the phenomena occurring during the joining process. Additionally, this provides the basis for a validation of a numerical simulation of such joining processes. In this paper, the material structure in a joint resul...

Clinching continuous fibre reinforced thermoplastic composites and metals is challenging due to the low ductility of the composite material. Therefore, a number of novel clinching technologies has been developed specifically for these material combinations. A systematic overview of these advanced clinching methods is given in the present paper. With a focus on process design, three selected clinching methods suitable for different joining tasks are described in detail. The clinching processes including equipment and tools, observed process phenomena and the resultant material structure are compared. Process phenomena during joining are explained in general and compared using computed tomography and micrograph images for each process. In addition the load bearing behaviour and the corresponding failure mechanisms are investigated by means of single-lap shear tests. Finally, the new joining technologies are discussed regarding application relevant criteria.

This paper presents the design of cold-formed rounded connections between a tube and a connecting block and the analysis of test results that were carried out with six fabricated samples. The joints manufactured on a specially designed prototype station were made by forming tools that were adjusted to connecting elements regarding the diameter and the shape. All of the samples prepared for this study were of the same diameters relating to the diameter of a hole in a connecting block and the outer diameter of a pipe flange. However, they were different concerning the height of the connecting block flange. The article presents features of joints that were manufactured with a designed forming tool on the prototype station. The achieved connections were examined in destructive testing (Micrography, Tensile Strength Test) and in non-destructive testing (Leakage Test). The research project aims were to state the differences in energy consumption of made connections and extend the concept ...

The production of high-strength clinched joints is the ultimate goal of the manufacturing industry. The determination of optimum tool shapes in the clinch forming process is needed to achieve the required high strength of clinched joints. The design of the tools (punch and die) is crucial since the strength of the clinched joints is closely related to the tools geometry. To increase the strength of clinched joints, an optimisation procedure using the response surface methodology, based on an adaptive moving target zone, is presented. The cost function studied here is defined in terms of the maximum value of the tensile force computed during the simulation of the sheets separation. Limitations on the geometrical parameters due to feasibility issues are also taken into account. The kriging interpolation is used to provide an approximation to the optimisation problem and to build the response surfaces.

Friction Riveting is a spot joining, which consists in rotating a cylindrical rivet and inserting it into clamped sheets. In the first friction phase, the rotational speed and the applied axial force heat the material by friction plasticizing it. After that, the spindle rotation is stopped and the axial force is increased passing to the so called forging phase. Several working parameters, such as the rotational speed, the friction and forging times, and the friction and forging pressure, have to be optimized to achieve sound connections. In the proposed work, the attention was given to the joints of sheets made of a thermoplastic material with and without short glass fiber reinforcements. Rivets were made of Titanium Grade 2. The quality of the obtained results was verified by tensile tests. Moreover, microscopic observations were performed analyzing the material deformation and integrity inside the connection volume. The influences of the monitored process parameters on the above highlighted outputs were reported providing a guideline for the process execution.

The use of new techniques and advanced materials is of major interest to automobile and aerospace manufacturing industries for reduce weight, cost and improve part performance. For this purpose, techniques for joining lightweight dissimilar materials, particularly aluminum, steel and plastics are becoming increasingly important in the manufacturing of hybrid structures and components for engineering applications. The choice of proper joining technology is an essential aspect of designing and manufacturing parts. This paper is a review the state of the art in scientific research concerning of joining techniques of dissimilar materials. The review presents the potentials of the technology and chances for further scientific investigations. KeywordsDissimilar Material Joining, Mechanical Joining, Clinching, Self-Pierce Riveting, Friction Welding, Laser Welding.

The hardening effect varies deliberately to elevate the properties of alloy specimens either in ferrous or nonferrous materials. The cup and cone fracture theory explains the effect of hardening through heat treatment of the specimen. The hardening effects are imposed on the specimen by the furnace heating and hot pressing method. The neck formation and the elongation levels are evaluated and compared for both heat-treated and non-heat-treated specimens of steel and aluminum alloys. The simulation tools are used to predict the compressive and elongation levels by obtaining the stresses and deflections at various nodal points. The suitable heat treatment was indicated by the single or twice method of heat adoption over the steel and aluminum specimens. The fracture analysis and experimental results are compared among the hardened or non-heat-treated specimens.

The aim of the paper is to review different types of modern hybrid joints applied in aerospace. We focused on three particular cases: 1) spot welding - adhesive, 2) rivet-bonded and 3) clinch-bonded joints. The numerical models presented in the paper for these joints describe their complex behaviour under mechanical loading. The numerical calculations performed using ABAQUS code were compared to experimental results obtained by application of the Digital Image Correlation system (DIC) ARAMIS. The results investigated within the paper lead to the following major conclusions: - the strengthening of joints by application of adhesive significantly improve static strength, - the final failure of the joined structural system significantly depends on the surface adhesive area, - the stiffening effects of the hybrid joint lead to higher reliability and durability of the structural joints.

One of the limitations related with joining several micro parts is the temperature generated during joining methods based on material heating. Temperature concentration could be a reason of severe difficulties with micro-manufacturing applications. It seems that modern mechanical joining technologies could significantly facilitate micro-parts fastening, since there is lack of temperature development during the process. Recently mechanical joining methods undergo considerable development and become more and more competitive in the industry. Among them, the self-piercing-SPR-technology is one of the most advanced and flexible. Initially, the automotive industry was a first application of the SPR, and then have been started to be use in other industry areas. In the paper, possibility of microrivet production by micro-forming with heat treatment elimination has been researched by means of FEM analysis. Required rivet strength is achieved by designed cold forming process and followed by effect of material hardening. Various stress distributions in the rivets are taken into account during numerical simulation to prove their influence on joining quality. Commercial FEM software MSC.Marc is used for numerical simulations.

Optionally, portions of a metal alloy substrate may be heated to temperatures between 400 °C and 800 °C when the second alloy substrate comprises coated steel. Optionally, portions of a metal alloy substrate may be heated to temperatures between 400 °C and 900 °C when the second alloy substrate comprises uncoated steel. When the substrate is or comprises a thermoplastic or a carbon-fiber-reinforced polymer, the substrate may be heated to temperatures of between 100 °C and 300 °C to modify a formability or plasticity of the substrate, for example. In embodiments, the temperature that the substrate, or a portion thereof, is heated to may be sufficient to increase formability or plasticity of the substrate, or portion thereof, at least temporarily, during the joining process. In some embodiments, heating sufficient to increase formability or plasticity of the substrate, or portion thereof, may modify a grain structure or crystal structure of the substrate, or portion thereof, such as if the temperature of the substrate, or portion thereof, exceeds a recrystallization temperature. In some embodiments, heating sufficient to increase formability or plasticity of the substrate, or portion thereof, may not modify, or may not significantly modify, a grain structure or crystal structure of the substrate, or 6 Lin et al.

The growing need of lightweight components determined a large exploitation of non metallic materials such as polymers, fibres and elastomers in the industrial production with a consequent request of specifically optimized manufacturing processes. The high optimization demands in terms of cost, weight and productivity of the modern markets determined a growing interest towards hybrid components in which two or more different materials coexist in order to achieve specifically optimized characteristics. According to these considerations the work proposed in this article is aimed at experimentally evaluate the feasibility of joining processes between metal and plastic components by means of the exploitation of a laser source. The metallic material involved in the experimental trials is AISI 304 stainless steel joined in an overlapping configuration with several different polymers: PA66, glass fibre reinforced PA66, carbon fibre reinforced PA66. The laser source involved in this activity was a 100 CW diode source equipped with a three axis cell. In order to evaluate the results of the joining process a tensile test was carried out on the obtained specimens.

Manufactur ing of comp lex tubular workpieces often requires medium-based forming processes. Because of the inaccessibility to the inside of the parts, joining of attached parts and part handling are difficult. Loss of accuracy during thermal joining is another disadvantage. A new method of spot-joining by forming is a combination of hydroform ing and clinching or hydroform ing and self-pierce riveting. In contrast to the standard method the clinch ing ar self-pierce riveting is done without die. A high pressure fluid undertakes the task of the die during joining. This die-less procedu re also extends the range of applications to areas which are not covered by standard techniques. By integrat ing joining into the hydroforming process , assembly processes can be shortened. In order to exploit velocity dependent material properties , for example increase in formability and decrease of spring back, self-pierce riveting during the hydrofarm ing process by means of impulse load has also been researched among other convent ional quasi-stat ic force transmissions. Numeric simulations were used for the theoretical description of the procedure. One goal of the simulations is the character isation of the most influential parameters on the process as a function of the material properties, tool kinematics/-geometry and of the friction conditions. The simulation results permit not only the character isation of the process, but also the theoretical predetermination of optimal joining parameters far various material and geometry combinat ions with fewer experiments.

Mechanical clinching has been widely used in the field of automotive industry in recent years. However, the clinched joint has a lower static strength than spot welding. In order to increase the static strength, a comparative investigation of two auxiliary processes for increasing the strength of clinched joints was carried out. One auxiliary process needs a rivet, while another auxiliary process needs a bumped die. Tension-shearing strength tests and cross-tensile strength tests were conducted to assess the static strengths of the joints after different auxiliary processes. Failure mode of all the joints was neck fracture in the tension-shearing strength tests and cross-tensile strength tests. Geometrical parameters of the joint profile were also investigated by comparing the two auxiliary processes. The values of energy absorption of different joints were obtained by measuring the areas between the force–displacement curve and x-coordinate. The two auxiliary processes were proved ...

The aim of the paper is to review different types of modern hybrid joints applied in aerospace. We focused on three particular cases: 1) spot welding - adhesive, 2) rivet-bonded and 3) clinch-bonded joints. The numerical models presented in the paper for these joints describe their complex behaviour under mechanical loading. The numerical calculations performed using ABAQUS code were compared to experimental results obtained by application of the Digital Image Correlation system (DIC) ARAMIS. The results investigated within the paper lead to the following major conclusions: - the strengthening of joints by application of adhesive significantly improve static strength, - the final failure of the joined structural system significantly depends on the surface adhesive area, - the stiffening effects of the hybrid joint lead to higher reliability and durability of the structural joints.