Multi-materials of metal-polymer and metal-composite hybrid structures (MMHSs) are highly demanded in several fields including land, air and sea transportation, infrastructure construction, and healthcare. The adoption of MMHSs in transportation industries represents a pivotal opportunity to reduce the product’s weight without compromising structural performance. This enables a dramatic reduction in fuel consumption for vehicles driven by internal combustion engines as well as an increase in fuel efficiency for electric vehicles. The main challenge for manufacturing MMHSs lies in the lack of robust joining solutions. Conventional joining processes, e.g., mechanical fastening and adhesive bonding involve several issues. Several emerging technologies have been developed for MMHSs’ manufacturing. Different from recently published review articles where the focus is only on specific categories of joining processes, this review is aimed at providing a broader and systematic view of the emerging opportunities for hybrid thin-walled structure manufacturing. The present review paper discusses the main limitations of conventional joining processes and describes the joining mechanisms, the main differences, advantages, and limitations of new joining processes. Three reference clusters were identified: fast mechanical joining processes, thermomechanical interlocking processes, and thermomechanical joining processes. This new classification is aimed at providing a compass to better orient within the broad horizon of new joining processes for MMHSs with an outlook for future trends.

A State-of-the-Art Review on Advanced Joining Processes for Metal-Composite and Metal-Polymer Hybrid Structures.

One thin 5000 series aluminium alloy sheet and two thin 980 MPa grade cold rolled ultra-high strength steel sheets were joined by self-pierce riveting and mechanical clinching processes. The joinabilities for a combination of the aluminium and steel sheets in both processes were investigated for different die shapes in the experiment and finite element simulation. In self-pierce riveting, the three sheets were successfully joined for both combinations of the upper and lower aluminium alloy sheets by optimizing the shapes of a die and rivet. In mechanical clinching, the three sheets were successfully joined by an optimum die for the configuration of the upper aluminium alloy sheet. On the other hand, the three sheets for the configuration of the lower aluminium alloy sheet were not joined even by optimizing the die shape in the both finite element simulation and experiment, because the material flow of the steel sheets was insufficient to form the two interlocks. The tension-shear loads for the clinched and riveted sheets with the adhesive were almost the same, because the load for the adhesive was the highest. In the cross-tension test, however, the load by the adhesive was comparatively small.

Mechanical Clinching and Self-Pierce Riveting of Thin Three Sheets of 5000 Series Aluminium Alloy and 980 MPa Grade Cold Rolled Ultra-High Strength Steel.

Research advances in residual thermal stress of ceramic/metal brazes

Clinching technology is widely used in the connection of lightweight materials. However, the conventional clinching with a round punch performs poorly in connecting thick sheets and hard sheets. In the present study, the clinching process with rectangle punch is investigated by the experimental method. The clinching process with rectangle punch can join the sheets by cutting sheets and generating an interlock. Al5052 sheets were joined using the rectangle punch with different forming forces. The forming process, shear strength, tensile strength, and failure mode were analyzed. The result shows that the shear strength is higher than the tensile strength of the joint generated with the same forming force. The forming force of 25 kN is proved to be the best forming force to join the Al5052 sheet with a thickness of 1.8 mm. The average tensile strength and shear strength of the joint are 1052 N and 1585 N respectively.

Investigation of the clinching process with rectangle punch

Recently, lightweight materials have been increasingly used to build engineering structures, especially automotive structures. Mechanical clinching, an advanced joining technology, is widely used to join lightweight materials on the structures. The clinched joint may be deformed or damaged when it bears higher shearing forces. Till now, there is no effective repairing technology to repair deformed/damaged clinching joints. A novel repairing process is thus proposed and studied in this paper. A custom-built rivet and two flat dies were used as main repairing tools. Different damaging forces were applied on clinched joints to produce different damaged joints. The damaging force, cross-sectional profile, neck thickness, and shearing force of the repaired joints were investigated. The novel process is suitable to repair deformed/damaged clinching joints. As for the deformed joint, the deformed neck can be reshaped to restore to its original shape in the repairing process. As for the damaged joint, the separated sheets are hooked by a new interlock generated by the custom-built rivet. Compared with clinched joint, the repaired joint can get higher shear strength, which is significant for the safety of engineering structures.

Research on the mechanical properties of repaired clinched joints with different forces

Clinching technology has been widely applied in automobile assembly industries to join sheet materials of different thicknesses and properties. It does not require any auxiliary parts and only depends on the plastic deformation of materials themselves to form a joint. Furthermore, clinching tools that include the punch and the die are simpler than other thermal joining methods. However, the usability of the clinched joint is restricted by a low joining strength. In order to expand the application range of clinching technologies, researchers have conducted extensive researches on how to improve clinching technologies. In this article, the latest advances of clinching technologies are reviewed on the development of clinching tools and processes. The improved clinching processes including flat clinching, hole clinching, reshaping the clinched joint without a rivet, reshaped joint with a rivet, rivet clinching, rectangular clinching, dieless clinching, roller clinching, laser shock clinching, hydro-clinching, injection clinching, adhesive clinching, resistance spot clinching, friction-assisted clinching, and laser-assisted clinching are introduced. The advantages and disadvantages of different clinching technologies are proposed. In addition, some suggestions for the future development of clinching technology are given in this paper. The clinching technology is developing towards a hybrid joining technology with high strength, high stability, and high efficiency.

Recent development of improved clinching process

Forming mechanism of the repairing process on clinched joint

Clinching technology is widely used on thin-walled structures, but the joining of some special functional surfaces that require high strength is ignored by researchers. In the present work, a new joining technology suitable for functional surfaces, especially flat surfaces, called two-strokes flattening clinching (TFC), was introduced, which performs high-strength connections with a flat sheet surface. AA5052 sheets with thickness of 2.0 mm were adopted for experimental study of TFC process. The bottom dies are composed of the bottom ring, flap gaskets and anvil. AA5052 sheets are extruded by the punch into the bottom dies to form the initial clinched joint in the first stroke. The initial clinched joint is reverse stamped by different forces to form the TFC joint in the second stroke. The tension-shearing and cross-tension experiments were conducted to evaluate the mechanical performance of TFC joints. The material flow, static strength and energy absorption were investigated in this work. Furthermore, the relationship between neck thickness and interlock of the TFC joints under different flattening forces was studied. The result showed that the TFC joints have good mechanical performance. The tension-shearing and cross-tension strength reached 2951 N and 1646 N, respectively. The protrusion of joint disappears completely at a force of 35 kN, which means that the TFC process is able to join some functional surfaces and ensure good mechanical performance.

Research on the material flow and joining performance of two-strokes flattening clinched joint

Glass and metal have wide applications in various industries due to their excellent properties. To make the most use of their properties and enlarge their applications, it is important to bond the glass and metal. Many bonding methods of glass and metal in recent years are reviewed in this article. The advantages and deficiencies of different bonding methods are discussed. The main problems between glass and metal in bonding process are proposed, and some suggestions to solve these problems are introduced. Finally, the development direction of bonding methods for glass and metal in the future is discussed.

The bonding between glass and metal

Clinching technology can join thin sheets of various materials, including aluminum alloy, magnesium alloy, steel, titanium alloy, and polymers. Nowadays, with the popularization of the lightweight concept and the application of various sheet materials in manufacturing, clinching technology has highlighted the advantages of being able to adapt to the joining of different sheet materials. With its unique advantages, clinching technology gains wide development space in the field of metal sheet connection. The application of clinching technology in various sheet materials is summarized and analyzed. The clinching process of special materials is also discussed. In addition, some unaddressed issues in the clinching process of special materials are identified in this paper.

Hao Peng

Papers

Recent development of improved clinching process

Forming mechanism of the repairing process on clinched joint

Research on the material flow and joining performance of two-strokes flattening clinched joint

The bonding between glass and metal

Development of clinching process for various materials