Friction Stir Incremental Forming Research Articles

Heat-assisted friction stir incremental sheet forming of thermoplastics

Incremental sheet forming (ISF) has been attracting increasing interests for customised manufacture of thermoplastics, but the application in high-performance and hard-to-form thermoplastics is still a challenge. This paper develops a new heat-assisted friction stir incremental sheet forming (HAFS-ISF) process to form polyether ether ketone (PEEK) and polymethyl methacrylate (PMMA, acrylic). Flexible heating tapes and tool rotational friction heat the thermoplastic sheet on both bottom and top surfaces, which maintain the sheet material at high temperature and reduce the through-thickness temperature gradient. Results are given for the effect of key parameters on forming temperature, force, accuracy and thickness distribution. Spindle speed has the most significant effect on all the studied aspects, followed by the pre-heating temperature, while feed rate and step size have less effect. With lower spindle speed of 100 rpm, the through-thickness temperature gradient is improved. Compared with PEEK parts, more uniform forming temperature and smaller forming force can be observed for PMMA parts. But the material brittleness causes worse formability, and the severer twist and stretching effect affect the forming accuracy of PMMA parts. Forming accuracy, fracture and twist are discussed by developing analytical models. The model for forming accuracy considers the initial bending effect and springback. The fracture is discussed by modelling the stress triaxiality and equivalent strain distribution under contact. While the model for twist considers effect of the applied torque on shear strain energy and continuous accumulation of twist along the tool path. By comparing analytical models and testing observations, the effectiveness of the models is confirmed to understand the underlaying mechanisms and to address a few challenges.

Pore form and size dependence on plastic joining characteristics of resin/metallic foam by friction stir incremental forming

A metallic foam specimen was plastically joined with a resin (polymethyl methacrylate, PMMA) sheet by applying friction stir incremental forming (FSIF) process. In FSIF process, a rotating flat-ended (no probe) rod tool was pushed vertically and fed horizontally against the resin sheet which was placed on the foam. The tool operation heated frictionally the resin and deformed incrementally to the resin, while the tool operation did not deform plastically to the cellular matrix of the foam. Due to the plastic flow of the heated resin, the bottom of the resin was interlocked mechanically to the pores near the top surface of the foam. In this study, the relationship between the pore morphology (form and size) and the joining characteristics (joinability, flow thickness of the resin, and joining strength) was investigated using commercial open-cell nickel and closed-cell aluminum foams. According to the experimental investigations, the foam with small size and low depression angle of the surface pore showed better results in relation with the joining strength and the (flow thickness of the resin)/(depth of the surface pore).

Tool and formability multi-response optimization for ultimate strength and ductility of AA8011 during axial compression

Friction stir incremental forming is a dieless forming process achieved through the severe plastic deformation of sheet metals by localized heat through tool friction with sheet metal. Tool rotation contributes significantly to determining the local heat generation and deformation of the sheets. In this study, a novel attempt was made to improve the desired surface quality with minimum tool wear using three different tool coatings. To identify the optimal parameters, process factors such as spindle speed, step size, and table feed were considered with two response parameters forming force and surface roughness. A total of 27 experiments based on a full factorial design were performed. During this optimization using TOPSIS, parameters are selected based on which FSIF parts should attain the minimum forming force and surface roughness. Based on the results obtained, the titanium nitride coating in the tool enhanced the surface roughness and increased the maximum formability. This study provides an optimal parameter setting for AA8011 and an understanding of the friction stir effect during the incremental forming process.

Plastic Joining of Metallic Foam/Resin by Local Friction Heating and Compressive Characteristics of Joined Metallic Foam/Resin

Friction stir incremental forming (FSIF) process was applied to join a metallic foam with a resin sheet for fabrication of porous metal–nonporous resin composite. In this process, a rotating rod-shaped tool was vertically pushed and horizontally fed against the sheet on the foam. The sheet was frictionally heated and incrementally deformed by the rotating tool, while the cellular matrix of the foam was not plastically deformed. The bottom of the sheet was mechanically interlocked to the pores of the foam by plastic flow of the frictionally heated sheet. In this study, (1) the joining characteristics of an open-cell type nickel foam and a polymethyl methacrylate (PMMA) sheet and (2) the compressive characteristics of the nickel foam/PMMA sheet specimen were introduced.

Friction stir incremental forming of polyoxymethylene: process outputs, force and temperature

ABSTRACT Despite good creep and fatigue durability, high resistance against chemicals and good surface finish, Polyoxymethylene (POM) has been sidelined in incremental sheet forming (ISF) literature due to its low formability at room temperature. This paper addresses the issue by deploying a cost-effective friction-induced heat at the tool-sheet interface. This work demonstrates a combined experimental, analytical, and numerical approach to investigate the effects of elevated temperature in ISF of POM. For this purpose, the formability of POM was first experimentally investigated under the interactive effects of the process parameters. Employing the membrane analysis approach, the stress state in the FSISF process was defined. The tool-sheet contact area was calculated as a function of toolpath and the relevant process parameters. The Johnson-Cook plasticity model was calibrated based on several universal mechanical tests at various temperatures and rates. Embedding the stress state, contact area, and the material model inside an algorithm developed by adopting the Finite Difference Method, force, friction-induced heat, and temperature at the tool-sheet interface were evaluated. Simulation results were validated by experimental outcomes. A threshold boundary for the maximum allowable tooltip temperature was established to avoid heat-induced defects while ensuring the sheet formability.

Improvement of Forming Limit in Height with Alternating Tool Path in Penetrating Tool Friction Stir Incremental Forming

Improvement of Forming Limit in Height with Alternating Tool Path in Penetrating Tool Friction Stir Incremental Forming

Plastic joining of open-cell nickel foam and polymethyl methacrylate (PMMA) sheet by friction stir incremental forming

Friction stir incremental forming (FSIF) process was applied to join a commercial open-cell type nickel foam with a polymethyl methacrylate (PMMA) sheet for fabrication of porous metal–nonporous resin composite. In this process, a rotating rod-shaped tool was vertically pushed and horizontally fed against the sheet on the foam. The sheet was frictionally heated and incrementally deformed by the rotating tool, while the cellular matrix of the foam was not plastically deformed. The sheet with a thickness of 1.0 mm was joined with the foam under FSIF conditions of rotation rate faster than 2000 rpm and feed rate slower than 60 mm/min. The joining strength between the foam and the sheet was investigated by performing tensile test. The joining strength was obtained over the fracture strength of the foam. The joining mechanism of the foam and the sheet was discussed from the microscopic observation of the foam–sheet interface and the temperature change in the sheet. It is concluded that the sheet was mechanically interlocked (anchored) to the porous structure of the foam by the plastic flow of the heated and softened PMMA into the surface pores of the foam.

Mathematical temperature model of sheet metal in friction stir incremental forming

Friction stir incremental forming (FSIF) is a practical forming technology for hard-to-form materials without additional devices or changes to the equipments. Temperature of sheet metal has an important influence on its formability in FSIF. Rosenthal model with line heating source used frequently in welding was developed to predict the temperature of sheet in this work. The relationship between the effective thermal power and the processing parameters was obtained using central composite response surface experimental method, with AZ31B magnesium alloy as the experimental material. On the basis of this relationship, the temperature model was established. Furthermore, the comparison between calculation results and experimental results show that the developed temperature model can be used to predict the temperature of sheet in FSIF. In addition, the influence of processing parameters on temperature of sheet metal was analyzed based on this model.

Effect of tool path on defect formation in penetrating tool friction stir incremental forming

Effect of tool path on defect formation in penetrating tool friction stir incremental forming

Friction Stir Incremental Forming of AA7075-O Sheets: Experimental Investigations on Performance Evaluation of Formed Parts

A comprehensive performance of formed parts by AA7075-O sheets was studied in friction stir incremental forming (FSIF). Various tool rotation speeds were set to form two typical parts (truncated funnel and pyramid frustum). The formability, surface quality, tensile strength, micro-hardness and thickness distribution of the formed parts were investigated. Results show that the formability generally increases as tool rotation speeds increase. On the contact surface, variation trends of the surface roughness are different in horizontal direction (parallel to tool path) and vertical direction (perpendicular to tool path). However, the surface roughness on the non-contact surface is almost not affected by tool rotation speed. Furthermore, mechanical properties including tensile strength and surface micro-hardness in formed parts are obviously enhanced compared to those of the initial sheet, of which the hardness values begin to fall down gradually after rotation speed reaches 3000 r/min. As for thickness measurement, more uniform thickness distribution of formed parts can be obtained at relative high tool rotation speeds. In general, parts formed at high rotation speed have a better comprehensive performance except the mechanical property.

Formability of titanium alloy sheets by friction stir incremental forming

This paper investigates the behavior of titanium formability when forming under localized friction heating, caused by high tool rotation. In accordance with planned experiments, different process conditions at various tool rotations, feed rates, and step-down sizes were investigated. The experiments were carried out on 1 mm thick Ti6Al4V alloy sheets, using an 11 mm diameter, ball-ended tooltip. The rotational speeds were designed to create sufficient thermal effect, while maintaining high lubricity at the forming interface. Moderate tool rotational speed (2000 rpm) tends to improve formability, reduce the forces, and lower the rate of tool wear. The experimental procedures are presented, and an extensive discussion of the results is reported.

Formation of skin surface layer on aluminum foam by friction stir powder incremental forming

To improve strength–mass relationship of a closed-cell type aluminum foam, friction stir powder incremental forming (FSPIF) process was applied to form nonporous skin surface layer on the foam surface from aluminum powder. In this process, the powder was supplied to the surface pores of the foam, and then, the powder and the cell wall near the foam surface were incrementally pressed by a rod-shaped tool without rotation (incremental hammering (IH)) and incrementally stirred by the tool at a very high rotation rate (friction stir incremental forming (FSIF)). The skin layer with a maximum thickness of 1.4 mm was formed on the foam surface without deforming the porous structure of the inside of the foam under the forming conditions, a tool rotation rate of 8000 rpm, a tool feed rate of 60 mm/min, and a total forming depth of 10 mm. The formation mechanism of the skin layer from the powder was investigated by microscope observation. Due to combination of sandwich structure and increase of bulk density, the specific plateau stress and the plateau end strain of the foam specimen with the skin layers were improved up to 1.2–1.6 times greater in a uniaxial compression test.

Relationship between Defect Formation, Tool Temperature and Revolutionary Pitch in Friction Stir Incremental Forming Process Using Penetrating Tool

Relationship between Defect Formation, Tool Temperature and Revolutionary Pitch in Friction Stir Incremental Forming Process Using Penetrating Tool

Friction stir incremental forming of AA7075-O sheets: investigation on process feasibility

Abstract Friction Stir Incremental Forming (FSIF), as a simple and effective hot incremental forming technology, has attracted increasing attentions from researchers in recent years. In FSIF, frictional heat generated by tool rotation on the interface between tool and workpiece is utilized to soften localized deformation zone, thus enhancing material formability. In order to facilitate the development of FSIF, a comprehensive analysis of process feasibility is needed for the performance evaluation of formed parts. In this work, FSIF has been employed to process 7075-O aluminum alloy sheets (a kind of hard-to-form light alloy materials) for assessing the formability, surface quality, tensile strength and micro-hardness of two typical parts (truncated funnel and pyramid frustum). Experimental results show that the formability generally enhances with the help of local frictional heating as tool rotation speeds increase. On the tool-sheet contact surface, surface roughness shows a different trend of variation in horizontal (parallel to tool path) and vertical directions (perpendicular to tool path). Furthermore, mechanical properties including tensile strength and surface micro-hardness in formed parts are obviously enhanced compared to the initial sheet, of which the micro-hardness values begin to fall down gradually when the tool rotation speed is greater than 3000 rpm.

Improvement of Forming Limit and Accuracy in Friction Stir Incremental Forming with Multistage Forming

Abstract To improve both forming limit and forming accuracy in friction stir incremental forming, multistage forming was carried out. JIS: A5052-H34 aluminum alloy sheets with a size of 100 mm × 100 mm × 0.5 mm were employed for specimens. The sheets were formed into a frustum of conical shape and forming limit was evaluated by the formable minimum wall angle without fracture. The formable minimum wall angle by single- and two-stage friction stir incremental forming was 70 ° and 72 °, respectively. When the wall angle was set to 70 ° and the sheets were formed by single- and two-stage forming, the formed shape by two-stage forming was closer to the objective shape than that by single-stage forming. The deformation of the sheet was shearing in single-stage forming, but that was two axis stretching in two-stage forming

摩擦攪拌インクリメンタル加工による発泡金属への緻密層形成

摩擦攪拌インクリメンタル加工による発泡金属への緻密層形成

Friction Stir Incremental Forming of Preformed Sheets with Improving Bending Stiffness

To improve forming accuracy in friction stir incremental forming of sheet metal, embossed sheets were used for specimen. A5052-H34 aluminum alloy sheets were formed by a hemispherical tool made of high speed steel with a diameter of 6 mm. A pitch and height of embossed dots were set to 10 mm and 5 mm, respectively. The embossed sheets were formed into a frustum of conical shape with a height of 20 mm and a wall angle of 20° by friction stir incremental forming. When an embossed sheet was formed, the droop at the flange was reduced and formed height became closer to the ideal one. When the embossed direction was set to downward and the sheet was formed, the embossed dots were disappeared after forming.

Excellent Formability of Light Metals Sheets by Friction Stir Incremental Forming

The results about friction stir incremental forming of light metals sheets from the beginning of development to the latest in the author’s laboratory are introduced. Comparison of formability by the conventional single point incremental sheet metal forming and friction stir incremental forming for magnesium alloys, aluminum alloys and titanium sheets were introduced. Effect of tool rotation direction, multistage forming and double side forming are also introduced.

貫通式ツールによる純アルミニウム板の摩擦攪拌インクリメンタルフォーミング

Friction stir incremental forming is a forming method of sheet metals which has combined incremental forming with friction stir welding and has a higher formability than incremental forming. But it still cannot form concave-convex shape. To solve the problem, a new forming process which combined friction stir incremental forming with bobbin tool friction stir welding, called friction stir incremental forming using penetrating tool, was developed. A simple and practical penetrating tool was designed and friction stir welding experiment was carried out as preliminary experiment. A1050-O sheet with thickness 2 mm was used as specimens. Welding parameters were found and sheets were welded successfully. Forming in one direction by friction stir incremental forming using penetrating tool was also carried out. The cross-sectional shape was measured by using a laser displacement meter and formed depth was 4 mm.

摩擦攪拌インクリメンタルフォーミング法における成形形状測定結果を利用した成形性向上

In friction stir incremental forming, formed shape becomes a little smaller than objective one due to springback. To improve forming accuracy, tool path was modified by experimentally obtained calibration equation. A5052 aluminum alloy sheets which size was 150 mm x 150 mm x 0.5 mm were employed for specimen. A hemispherical tool with a diameter of 6 mm was used. The tool was rotated at 10000 rpm and moved at 3000 mm/min and sheets were formed into a frustum of conical shape which height of 20 mm and wall angle of 25 °. Distance from the edge of blank holder to start position of forming was changed and errors of initial diameter of a frustum of cone, forming height and bottom diameter were measured. Errors of wall angle and overall shape were measured due to springback. By modification of tool path, errors of initial diameter, forming height, bottom diameter and wall angle were improved from 7.62 mm to 0.23 mm, 4.76 mm to 0.16 mm, 2.27 mm to 0.27 mm and 1.09 ° to 0.12 °, respectively.