Soldagem por Friction Stir: A Solid-State Metal Joining Process

 It is applied for using as a solid state welding that is based on friction with purpose to heat and weld the metals and their alloys.This piece explains how it works, why it is preferable to fusion welding, its major areas of usage such as automobile, aerospace, a brief update on modern developments in FSW, and various spin-off processes like Friction Stir Spot Welding . It aims to cover all the essential information about this important metal joining process.

Friction Stir Welding: A Solid-State Metal Joining Process

Friction stir welding (FSW) is a novel solid state joining process invented in 1991 at The Welding Institute, United Kingdom. Since its inception, it has greatly transformed a host of metal working industry sectors relying on metal joining techniques other than the fusion joining processes. In FSW, a non-consumable rotating tool is used to generate frictional heat below the melting point of the materials being joined. This heats and softens the metals allowing them to be forged together producing high quality defect-free joints.

Due to the absence of issues like solidification cracking and porosity, FSW produces stronger, more consistent welds than fusion alternatives. It has used not only limited to aerospace aluminium alloys but it is also used in automotive, marine, railway etc. These are the basic discussion of this article which include the principles of friction stir welding, advantages of friction stir welding, application of friction stir welding and new developments in friction stir welding. Its scope includes all aspects of this significant metal joining process.

Principle of Operation

The FSW is a novel process of joining materials with less heat input and without melting the base material. During this process, an electrically heated non-condusive electrode having a cylindrically shaped pin and a cylindrical shoulder being placed on two adjacent surfaces of the abutting members and moved from end to end of the work joint.

Generating Heat through Friction

As the pin of the FSW tool rotates and translates through the material, frictional heat is generated between the shoulder and pin surfaces contacting the workpieces. This heat causes the materials of the butting workpieces to soften without reaching their melting points. The pin then mechanically mixes the softened materials by breaking up the original bond structure and forging them together.

Forming a Uniform Weld

Behind the pin, the material cools and rapidly recrystallizes, resulting in a solid-state bond between the two original pieces. This leaves a uniform weld nugget devoid of any melting or solidification related defects typically seen in fusion welding.

Advantages over Conventional Welding

Excelentes propriedades mecânicas

The absence of melting and solidification associated defects gives FSW welds excellent mechanical properties equivalent or superior to the base material in the as-welded condition itself.

Improved Safety

Compared to fusion welding processes like gas metal arc welding, there are no fumes, splatter or ultraviolet radiation associated with FSW. This makes it a safer welding process.

No Filler Required

Since FSW is a solid-state process, it does not require any filler material like wire or flux, simplifying the process.

Easy Automation

The automated sequential nature of FSW lends itself very well to robotic and automated implementations in large volume manufacturing across various industries.

Operates in All Positions

Unlike some fusion welding processes, FSW can be performed on materials in flat, horizontal, vertical or overhead positions with equal effectiveness.

Good Weld Appearance

Typically friction stir welds have a flat, uniform appearance with minimal distortion compared to fusion welds.

Tool Design and Process Parameters

Importance of Tool Design

The tool design plays a critical role in determining the penetration depth, heat generation characteristics and ultimately the quality of the weld. Advanced tool designs help achieve higher depths and thicker section welds.

Tool Geometry Variations

Tool designs can vary the probe or pin profile (profiles range from simple cylindrical shapes to threaded or stepped pins), shoulder diameter and features to influence the material flow.

Process Parameter Effects

Process parameters like tool rotation and travel speeds, plunge depth, etc. significantly impact heat generation and material flow during welding. Yielding less energy and torque is preferred at slow speeds for thicker sections to penetrate deep while a high speed is applicable for thin gauge material. However, friction stir welding is one of the promising solid state joining techniques, which has several advantages compared to other fusion welding processes for different industries… Continuous advancements in tool designs and process parameters further enhance its capabilities.

Applications of Friction Stir Welding

Metal Matrix Composites

Joining Aluminum Matrix Composites

Fsw process was successfully utilized to weld metal matrix composites (MMCs) reinforced with hard ceramic particle like silicon carbide (SiC) and boron carbide (B4C). The method yields sound joints in Al matrix reinforcements SiC, and B4C particulates with mechanical characteristics that are comparable or superior to those of the base metals.

Improved Microstructure and Strength

MXY joints produced using FSW have a finer and more uniform distribution of reinforcements in the weld nugget compared to fusion welding techniques. This translates to higher joint strength approaching that of the base composite. The absence of liquation and resolidification defects in FSW prevents cracking and porosity issues often seen in fusion welds of MMCs.

Automotive and Aerospace Industries

Aircraft Wing and Fuselage Panels

Leading aircraft manufacturers extensively use FSW to join aluminum alloy panels for wings, fuselages and tail sections. Embraer uses the technique to fabricate wing skins and spars for its E-Jets. Boeing utilizes FSW on 747-8 panels manufacturing over 33 kilometers of welds.

Automotive Body and Chassis Parts

Structural auto components like Hoods, doors, rear body panels, suspension links are FSW joined by top manufacturers. Mazda uses the process on multiple models including its large truck Bongo. Ford employs FSW on aluminum bodies of F-150 pickup and Expedition SUV.

Marine and Transportation

Shipbuilding and Marine Vessels

Italian shipbuilder Fincantieri constructs superstructures, decks and bulkheads of ferries and cruise ships entirely from FSW bonded aluminum plates. Dockwise uses friction stir butt welds to join pontoon sleeves of heavy transport ships.

Subway and High Speed Trains

Metro trains in cities like Delhi, Mumbai and Sydney feature FSW joined aluminum body panels and underframes. Japanese Shinkansen bullet trains have structural parts and exterior skin made of friction stir welded aluminum alloys.

In summary, friction stir welding enables efficient and defect-free joining of various metals and alloys across diverse industries from aerospace and automotive to marine, transportation and electronics. Its applications continue expanding to new areas with ongoing process developments.

Metal Joining Challenges and Latest Advancements

Difficult-to-Weld Materials

Friction stir welding techniques are being explored to join materials traditionally considered difficult to weld.

Joining Steels and Titanium Alloys

Considerable research examines feasibility of FSW for joining high strength steels and titanium alloys which are challenging to fusion weld due to cracking. Preliminary studies show desirable strengths can be obtained in dissimilar steel-aluminum and titanium-aluminum welds.

Dissimilar Metal Joints

FSW is also investigated for joining dissimilar combinations like aluminum to copper, magnesium, and carbon fiber reinforced plastics. Successful zirconium alloy to steel welds demonstrate the versatility of the solid-state process.

Process Optimization Studies

Tool Design Improvement

Tool designs with threading, venting and advanced shoulder features are studied to improve joint penetration, heat flow and material mixing. Contoured pins help reduce defects in thick section welds.

Otimização de parâmetros

Research optimizes interdependent parameters like plunge force, rotation speed, travel speed and tool geometry. Thermal models coupled with experiments provide insights into defect prevention.

Microstructure Evolution

Studies examine factors governing stir zone grain size and structure. Tailoring cooling rate and tool features refines microstructure and mechanical properties of difficult alloy combinations.

Innovative Derivatives

Friction Stir Spot Welding

This development enables spot joining of sheet assemblies. It finds applications in automotive closures and body panels with advantages over resistance spot welding.

Friction Stir Processing

This technique modifes material properties by carefully controlled stirring action. Applications include property enhancement of metal matrix composites and fabrication of gradient nanostructures.

Friction Hydro-Pillar Processing

A hybrid of FSW and extrusion expands options for tubular and hollow component manufacturing from materials like aluminum, titanium and stainless steel.

Continued advancements are expanding friction stir welding applications to new frontiers of materials, designs and large volume manufacturing across industries.

Conclusão

In conclusion, friction stir welding has revolutionized metal joining since its invention in 1991. Originally developed as an alternative to fusion welding of aluminum alloys, it is now a mature technology being used across diverse industries for applications that were previously considered difficult using conventional techniques. The unique advantages of friction stir welding like excellent mechanical properties, reduced defects, safety, automation capability and ability to join a wide range of metal alloys have made it a preferred fabrication method. Continuous research aimed at understanding material flow behavior, optimizing process parameters and designing advanced tools is further enhancing the scope and productivity of friction stir welding. Innovative derivatives like friction stir spot welding and friction stir processing are also expanding its application potential to new manufacturing domains. With ongoing development efforts, friction stir welding and its variants will likely continue disrupting traditional manufacturing approaches and enable fabrication of advanced alloy combinations and component designs across industries in the future.

Perguntas frequentes

What are the major advantages of FSW over fusion welding?

It produces stronger, higher quality welds without defects like porosity or cracking. It’s also safer, more automated, operates in all positions and causes less distortion.

Is FSW limited to flat sheet or plate joining?

No, advances allow FSW of complex 3D shapes, tubular/hollow components, and dissimilar/multimaterial combinations. Spot welding tools enable panel assembly.

What factors affect weld quality?

Primary factors are tool design (pin/shoulder profile), rotation/travel speeds, plunge depth and pin force tailored for the material and thickness. Heat, material flow and joint strength are optimized.

Can other joining techniques replace FSW?

For many applications, no alternatives provide the same degree of consistency and mechanical integrity. However, some specialized fastenings may work where FSW tool access is limited.