Friction Stir Forming Research Articles

Visualization of Contact-Pressure Distribution between Material and Backing Plate in Friction Stir Processing

In this study, the authors evaluated pressure distribution on a backing plate in friction-stir processing (FSP) utilizing an embedded pressure pin connected to a load sensor. They conducted FSP on aluminum alloy plates repeatedly offsetting the path-lines from the center of the pin and recorded change of forming pressure with tool position, which was compiled from the bearing load of the pin. The authors mapped the results to visualize the two-dimensional contact pressure distribution on a backing plate during FSP. They then compared the height distribution of the wall fabricated by friction-stir forming (FSF) utilizing a die having a groove with the observed distribution of pressure. Consequently, maximum pressure was observed beneath the rim of the tool probe at the retreating side (RS), and the highest points of the wall were observed at the RS.

Evaluation of Material Deformability and Pressure Distribution on a Die Surface under a Tool in Spot FSF

Friction-stir forming (FSF) is a friction-stir process invented by Nishihara in 2002. In FSF, a material is put on a die, and friction stirring is then conducted on its back surface. The material deforms and precisely fills the cavity of the die due to high pressure and heat caused by friction stirring. Materials in the process often display outstanding deformability and moldability. However, behavior of the material during the friction-stir process has not been sufficiently clarified as a metal forming process. In this paper, material deformability under a tool in spot FSF, i.e. FSF without tool travel, was investigated employing a die having holes. The authors conducted spot FSF on 3mm-thick A5083P-O aluminum plates at offsetting points from the center of a hole and evaluated the height and volume of cylindrical extrusions to evaluate the deformability distribution under a tool. In addition, forming pressure distribution on the die surface was evaluated by an embedded pressure pin connected with a load sensor. The authors conducted spot FSF on 3mm-thick A5083P-O aluminum plates at offsetting points from the center of a pin as well as deformability tests and evaluated forming pressure compiled from the bearing load of the pin. In the deformability test, the extrusions without offsetting were shorter than the ones with 2mm offset. However, the forming pressure without offsetting was higher than the pressure with 2mm offset. Surface sink of the product without offsetting was observed below the tool probe. This implies that the probe restricts supplement of material volume to the die cavity directly below it, though it effectively extends the deformable material volume.

Friction Stir Forming for Mechanical Interlocking of Ultra-Thin Stainless Steel Strands and Aluminum Alloys

In this study, a novel method of mechanical interlocking of super-thin stainless steel strands with different aluminum alloys was conducted by using friction stir forming (FSF). The potential for the development of a multi-functional composite material was studied experimentally. It was concluded that FSF can successfully interlock stainless steel strands and different Al alloys and presents the possibility of improving the mechanical properties of the alloy. Trials of FSF were carried out on a modified vertical milling machine. The results are discussed in terms of microstructure observations, hardness distributions and tensile tests.

Evaluation of material deformability and pressure distribution on die surface around centerline of tool travel in friction-stir forming

Friction-stir forming (FSF) is a friction-stir process developed for fabricating product shapes. In FSF, friction stirring is conducted on the back surface of a material plate that is put on the die. The material deforms and fills the cavity of the die due to high pressure and heat caused by friction stirring, and it often has outstanding deformability and moldability. Conventional studies on friction-stir welding have not sufficiently clarified it as a metal-forming process. In this paper, material deformability along the tool travel path of friction-stir forming was investigated using a die having hole-cavities with various diameters on a straight line. The authors conducted FSF on 3 mm-thick A5083P-O aluminum plates on parallel-offsetting paths from the centerline of holes and evaluated the height of cylindrical extrusions to determine the deformability distribution of the material around the centerline of the tool movement path. In addition, forming pressure distribution on the die surface was evaluated using an embedded pressure pin connected with a load sensor. The authors conducted FSF on offsetting path lines from the center of the pin repeatedly as well as deformability tests and recorded the change of forming pressure with tool position, which was compiled from the bearing load of the pin, and mapped it two-dimensionally.

Trials of Mechanically Interlocking Zn-22Al Superplastic alloy with Optical Fiber by Using Friction Stir Forming

Trials of Mechanically Interlocking Zn-22Al Superplastic alloy with Optical Fiber by Using Friction Stir Forming

Effect of hole diameter on joint strength and joint formation in Dieless friction stir form joints between dissimilar aluminum alloy sheets

This paper presents preliminary analysis of a new friction based solid-state joining technology named Dieless Friction Stir Forming (Indian patent application No: 201741040528) for lap joining of dissimilar grade aluminum alloy sheets. The influence of pre-drilled hole size on the fracture load of the joint is evaluated through lap shear test. Macrostructure analysis, microstructure analysis, and failure mode examination are also performed. An average lap shear fracture load of 7 kN is obtained throughout the hole diameter range. The fracture load of the joint is better than that of other commercially used spot joining technology like friction stir spot welding. The macrostructure analysis revealed the existence of various zones within the joint and the change in hole diameter has influenced the form of mechanical interlocking. Microstructure analysis revealed that various zones of the joint are subjected to recrystallization under frictional heat flux and plastic deformation. Two critical zones are identified, which are responsible for various modes of failure of the joints.

Friction stir forming of dissimilar grade aluminum alloys: Influence of tool rotational speed on the joint evolution, mechanical performance, and failure modes

Friction stir forming (FSF) is a solid-state, eco-friendly spot welding technique primarily applied for lap joining dissimilar sheet metals. The details related to the process are scarce in literature. The present work explores the potential of the FSF process for joining dissimilar grade alloys of same metal, namely aluminum. The effect of tool rotational speed on the joint formation and mechanical performance of FSF joints between AA5052-H32 and AA 6061-T6 sheets is studied through systematic experimentation and macrostructure analysis. Hardness distribution across the joint, joint morphology, and failure modes at varying rotational speeds are also presented. The tool rotational speed shows significant effect on the mechanical performance results, zones formed within the joint, and hardness distribution across the joint. Maximum lap shear strength, about 6 kN, obtained in the present work is superior than that of joints fabricated on same material combination with other friction-based joining technologies. The lower and medium tool rotational speeds, between 500 and 1500 rpm, are the best choices for fabricating FSF joints for the materials used. Macrostructure analysis revealed that at lower tool rotational speed ( 1500 rpm), localized stir zones are distributed over the cross-section. Friction stir form samples showed an inverted “W”-shaped hardness profile over the cross-section, and the joint morphological features are independent of the tool rotational speed. Failure modes such as partial bond delamination, tear-off, and pull-out occur randomly and have no systematic correlation with the tool rotational speed.

Fastenerless-Riveting Utilizing Friction Stir Forming for Dissimilar Materials Joining

This paper proposes a new joining approach for dissimilar materials, called ‘the fastenerless-riveting,’ employing the friction stir forming (FSF). The FSF is a friction stir process invented by Nishihara in 2002. In FSF, a substrate material was put on a die firstly. Next, friction stirring was conducted on the back surface of the material. The material then deformed and precisely filled the cavity of the die due to high pressure and heat caused by the friction stirring. The authors utilized the FSF approach to generate rivet like joints as followings. First, a substrate which is capable for friction stirring, i.e. an aluminum alloy plate, was put on a dissimilar material plate having holes, i.e. a steel plate. The authors call the former ‘the host member,’ the latter ‘a joined member.’ These members were put on a die having the cavity to fabricate the head of the rivet-like structure. Then FSF was conducted to form the stems and heads of the structure. Joint members are able to be stacked within the forming limit. In the study, the authors firstly conducted the proof of the concept (PoC) tests to generate rivet-like structure between steel and aluminum alloy plate and between CFRP and aluminum alloy plate, then investigated the forming conditions, i.e. tool feed rate, tool pass and the corresponding results, including the volume of the generated stem and head of the individual rivet-like structure. 3mm-thick A5083P-O aluminum alloy plates was utilized as the host member, and a 0.7mm-thick SPCE steel plate and a 0.8mm-thick CFRP plate as the joined members.

Vertical Wall on an Aluminum Alloy Plate Fabricated by Friction Stir Forming

This paper describes utilization of friction-stir forming (FSF) to generate a single wall on an aluminum alloy plate. The proposed process is as follows. The authors placed a material plate on a die having a variable-width groove and conducted friction stirring on its back surface. The material filled the cavity due to high pressure and heat caused by friction stirring. This process can be applied to generate thermal plate-fins and rib structures. The present study investigates the forming conditions and the corresponding results including the height limit of walls to obtain reference data for applications. In the experiment, a 3mm-thick JIS A5083P-O aluminum plate was utilized as the substrate. With a grove of less than 0.2mm-width, the wall was difficult to generate. The maxim height of the 0.2mm-thick wall formed by FSF was 2.8mm, and its aspect ratio was 14, which was difficult to form using conventional forging. Overall, the relationship between groove width of the die cavity and aspect ratio of maximum wall height to wall thickness followed the fractional curvature. This results implies that the deformable material volume generated by friction stirring is a key factor for wall height.

Observation of Material Flow in Friction Stir Forming for A5083 Aluminum Alloy Gear-Rack

This paper reports observation of material flow in friction-stir forming of aluminum alloy gear racks. Friction-stir forming was newly developed by Nishihara and is dedicated for material forming. In the process, a material plate is placed on the die and friction stirring is conducted on its back surface. The material deforms due to high pressure and heat caused by the friction-stir process and deforms precisely to the shape of the die. The process has mainly been studied for microforming and mechanical jointing; however it was successfully utilized for net-shape forming of A5083 aluminum alloy gear racks. The authors observed the appearance of products, change of mark-off lines on its surface, and deformation of its longitudinal cross section by photo-processing. In addition, we evaluated the distribution of hardness in transverse cross sections of a product tooth. As a result, it was observed that the material did not flow in the transverse direction of the cavity of the gear-rack die, though more material filled at the retreating side than at the advancing side. The material filled the tooth-cavity mostly before passage of the tool probe over the tooth.

Cylindrical Pin Embossment on A5083 Aluminum Alloy Substrate Fabricated by Friction Stir Forming

This paper reports friction-stir forming (FSF) of cylindrical pin embossments on JIS A5083 aluminum alloy medium gauge plate. A substrate material was put on an emboss die and conducted friction stirring on its back surface. The die has 1mm diameter and 0.5mm deep fine holes at 1.5mm pitch on its top, and the material successfully filled them due to high pressure and heat caused by friction stirring. Three tools having different shoulder diameter were utilized to investigate the deformable area with a single pass. As a consequence, faster spindle speed, slower tool feed rate, and larger tool shoulder contribute to a wider range of completely formed pins. Extrusion of the material to the die cavity seemed to be mostly limited under the area of the shoulder. The ratios of the band width of the complete pins to the shoulder diameter were increased with the larger diameter of the shoulder of the FSF tool. Therefore, a larger shoulder was more effective for wide-range embossing with a single pass. In addition, we evaluated the shape of formed pins with a non-contact 3D measurement system. Accuracy of the height of the completely formed pins was within ±0.013mm, which was comparable with machining.

Rib-Structures on A5083 Aluminum Alloy Sheet Generated by Friction Stir Forming

Abstract Reinforcing a plate with a rib structure to increase the moment of inertia of its cross-sectional area is a common technique for the design of lightweight parts. However, this technique is not as popular for sheet-metal forming as for die-casting and injection molding because there is no effective industrial way to generate ribs for sheet-metal forming. This paper describes a new forming technology, friction-stir forming (FSF), to generate a rib structure on an aluminum alloy plate. The proposed process is as follows. The authors put a 3mm-thick A5083 aluminum alloy plate on a die and conducted friction stirring on its back surface. The material deformed and precisely filled grooves of the die due to high pressure and heat caused by friction stirring, to form a rib structure. This study investigates the forming conditions and the corresponding results, including the height limit of the rib structure. Results indicated that ribs even less than 1mm thick were successfully generated. For example, the maximum height of a 0.8mm-thick rib was 2.98mm with the offset pass. Greater groove width of the die resulted in higher rib generation. However, the height decreased for grooves wider than 2mm because of limitations of the deformable material volume. In the experiments, the maximum moment of inertia was obtained when a 3mm-thick, 4.29mm-high rib was fabricated. The moment of inertia was calculated as 7.1 times that of the original plate, provided that the ribs were fabricated at intervals of 10mm.

Low Height Ultra-thin Fin on A5083 Aluminum Plate Fabricated by Friction-stir Forming

Recent demands on miniaturization of an electronic apparatus have caused board-space constraints, and thermal management is getting increasingly difficult. Thermal management employing heat sinks is often compromised by the space constraints for a product design. Lower profile passive heat sinks having thin fins are among necessary solutions to these space limitations. Most such products have been generated by conventional or back pressure applied forging. However, thinness of its fin is limited, though a higher density of fins is more effective. This paper describes a new forming technology, friction-stir forming (FSF), to generate a low profile, ultra-thin fin. The suggested process is as follows. The authors put a material plate on a die and conducted friction stirring on its back surface. The material deformed and precisely filled narrow grooves of the die due to high pressure and heat caused by friction stirring. This study investigates the forming conditions and the corresponding results including the height limit of the fin. Consequently, we successfully generated low-profile, ultra-thin fins with 0.5mm thickness and less on 3mm-thick JIS A5083P-O aluminum plate.

Experimental Determination of the Effective Viscosity of Plasticized Aluminum Alloy 6061-T6 during Friction Stir Welding

Friction stir forming (FSF) refers the process variant of friction stir welding (FSW) where a joint is achieved through the creation of mechanical interlocking between two constituents by plasticizing one material through the use of the FSW process and in turn forcing said material to flow into the second material. In order to increase the understanding of material flow within this process, a method of quantifying the plasticity of flowing material during the FSF process is needed. A method is proposed in which a capillary hole is drilled into a backing plate used for FSW, and material is extruded through the capillary during processing. The flow of material is characterized and related back to an effective viscosity using the models that form the basis of a capillary rheometer. Initial testing shows promising agreements with CFD simulations of the FSW process (effective viscosity values within the range of 105 to 5×106 Pa-s). Furthermore, a promising initial agreement is shown when using effective viscosity values determined from the capillary method in a previously derived model that describes the infiltration for carbon fiber with plasticized aluminum produced by the FSW/FSF process.

Friction Stir Forming of Aluminum Alloy Gear-Racks

Friction-stir-forming (FSF) of gear-racks of JIS A5083 aluminum alloy is reported in this paper. We put a material plate on a gear-rack die and conducted friction stirring on its back surface. The material deformed and precisely filled the fine cavity of the die due to high pressure and heat caused by friction stirring. This study investigates the forming conditions and the corresponding results, including the material fill ratio in the tooth. It is thought that the deformation volume of the material is key for the fill ratio, and the shoulder diameter of the tool in a single-pass process or the path area in a multi-pass process affects it as well.

Friction stir forming for mechanical interlocking of insulated copper wire and Zn-22Al superplastic alloy

In this study, a novel method of friction stir forming (FSF) was conducted for mechanical interlocking of Zn-22Al superplastic alloy and thin copper wire insulated by polyimide. The potential development of a composite material capable of transmitting electrical energy or electric signals was studied experimentally, and it was concluded that FSF can successfully interlock insulated copper wire with Zn-22Al superplastic alloy. The authors suggest the possibility that FSF could join sheets of Zn-22Al alloy by pressure welding and superplastic forming and diffusion bonding (SPF/DB). Trials of FSF were carried out on a modified vertical milling machine. The results are discussed in terms of microstructure observations, hardness distributions, and temperature measurements.

Friction Stir Forming of A5083 Aluminum Alloy Gear-Racks with WC Particles Embedded in Tooth Surface

This paper proposes a new forming process for gear racks featuring a tooth-surface stiffening layer. The proposed process is as follows. First, a JIS A5083P aluminum alloy plate on which a surface modifier of WC particles and vaseline paste had been applied was put on a gear-rack die. Next, friction stirring was conducted on the back surface of the plate. The material then deformed and precisely filled the cavity of the die. WC particles were embedded into the surface of the aluminum alloy matrix due to high pressure and heat caused by friction stirring. The forming conditions and the corresponding results, including the distribution of WC perticles on the tooth surface, are investigated in the study. WC particles were embedded near the surface mechanically, and only a very few particles were observed inside the matrix. With an undefill condition, WC particles are concentrated on the rear surface of the tooth, which contacts the tail side of the die. In contrast, No significant particle density differences were observed among the profile of teeth with a fully filled condition in the die cavity.

Detailed thermal and material flow analyses of friction stir forming using a three-dimensional particle based model

The material point method is proposed as a framework to model friction stir forming. The flexibility of the method allows for the development of a fully coupled thermo-mechanical model which includes heat transfer processes due to plastic dissipation as well as frictional heating. A procedure is proposed to fully determine all numerical parameters from experimental data, thus eliminating the need for further calibration of the results. The model was used to gain insight into heat transfer mechanisms and material flow in friction stir forming of copper plates. Experimental verification of the results confirmed the predictive capability of the model. The predicted temperatures were in satisfactory agreement with thermocouple data while the material flow in the model compared reasonably well with experiments, thus providing a useful tool for analysing the complex physical mechanisms at play in friction stir forming.

Production of a Superplastic Vibration-Damping Steel Sheet Composite Using Friction Stir Forming

This study proposes a novel method of manufacturing composite vibration-damping steel sheet with Zn-22Al superplastic alloy using friction stir forming (FSF). Trials of mechanical interlocking of steel sheet with Zn-22Al superplastic alloy using FSF were carried out on a modified milling machine. The results are discussed in terms of residual microstructures and mechanical properties. We concluded that cladding steel sheet with Zn-22Al superplastic alloy using FSF results in superplastic forming and diffusion bonding.

摩擦攪拌成形(FSF)によるCFRP板とアルミニウム合金板の接合

This paper reports generation of the rivet-like joints between the CFRP and A5083P-O aluminum alloy plates with utilizing the friction stir forming (FSF) approach. The authors prepared a CFRP plate having a hole and put it on the mold having the cavity of the head of a rivet-like joint. Then we put a 3mm-thick A5083P-O aluminum alloy plate on them and conducted friction stirring on its back surface. Due to massive heat and compression force generated by the friction stirring, the rivet-like joint was generated without any additional fasteners.