FRICTION WELDING

Friction Welding Lesson Objectives When you finish this lesson you will understand: Continuous Drive Friction Welding & Applications Variables Effecting Friction Welding Variations of friction Welding Process Dissimilar Materials Welded Inertia Welding Process & Applications Learning Activities View Slides; Read Notes, Listen to lecture Do on-line workbook View Video Keywords: Friction Welding, Inertia Welding, Forging Pressure, Orbital Friction Welding, Linear Friction Welding, Angular Reciprocating Friction Welding, Radial Friction Welding, Friction Stir Welding

The friction welding process is a solid state welding process where heat is imparted to the work pieces by mechanical means via the frictional rubbing of the mutual pieces together under a load and accompanied by deformation of the parts.

Definition of Friction Welding Friction welding is a solid state joining process that produces coalescence by the heat developed between two surfaces by mechanically induced surface motion. In the general case, one part is held fixed while the other is rotated. When the two parts are brought into contact, the frictional heat generated breaks down the surface asperities under the action of the load, and surface material is plastically moved out of the interface, carrying with it any surface oxide and contamination into the outside “flash” material (gray in this figure). This flash material may or may not be subsequently machined off depending upon the final use of the part.

Examine the Friction Weld Video on the Web Page Link to Friction Welding Video

Categories of Friction Welding Continuous drive Inertia There are two types of friction welding variations, continuous drive friction welding and Inertia Welding. The first uses a continuous drive motor while the other uses inertia energy stored in a flywheel to impart the frictional energy into the weldment.

Continuous Drive Friction Welding One of the workpieces is attached to a rotating motor drive, the other is fixed in an axial motion system. One workpiece is rotated at constant speed by the motor. An axial or radial force is applied. Workpieces Non-rotating vise Motor Chuck Spindle Hydraulic cylinder Brake In continuous “direct drive” friction welding, one workpiece is attached to a rotating motor drive unit as shown above. The other workpiece is clamped in a non-rotating axial drive unit. The two workpieces are gradually brought together with one rotating and the other still. When they make contact, heat is generated at the interface due to friction. Additional axial force is applied. The axial force is raised to a final constant value and held for a predetermined time, or until a preset amount of upset takes place. The rotational driving force is disconnected, and the rotating workpiece is stopped by the application of a braking force. The axial force (forging force) is maintained or increased for a predetermined time after rotation ceases.

Continuous Drive Friction Welding The work pieces are brought together under pressure for a predeter-mined time, or until a preset upset is reached. Then the drive is disengaged and a break is applied to the rotating work piece. Workpieces Non-rotating vise Motor Chuck Spindle Hydraulic cylinder Brake Continuation of previous slide

Linnert, Welding Metallurgy, AWS, 1994

Friction Welding Variables (Continuous Drive) Rotational speed Heating pressure Forging pressure Heating time Braking time Forging time

AWS Welding Handbook

AWS Welding Handbook

AWS Welding Handbook

Equipment Direct Drive Machine Courtesy AWS handbook

Questions

Friction Welding Process Variations

AWS Welding Handbook

Friction Welding Joint Design Continuous Drive Friction Welding Joint Design The joint face of at least one of the work piece must have circular symmetry (usually the rotating part). Typical joint configurations shown at right. Rod Tube Rod to tube Tube to disc Rod to plate Tube to plate

Orbital Friction Welding AWS Welding Handbook

Angular Reciprocating Friction Welding AWS Welding Handbook

Linear Reciprocating Friction Welding AWS Welding Handbook

Radial Friction Welding Used to join collars to shafts and tubes. Two tubes are clamped in fixed position. The collar to be joined is placed between the tubes. The collar is rotated producing frictional heat. Radial forces are applied to compress the collar to complete welding. + F F F F F Radial friction welding is used to weld collars to shafts and tubes. For the radial friction welding of tubes, the two tubes are clamped firmly. The collar to be joined is placed between them. The collar is rotated producing frictional heating. When heated enough by friction, radial forces are imposed along the periphery of the collar. These forces compress the collar to produce the weld. An internal expanding mandrel is often used to support the tube walls. F

Friction Surfacing AWS Welding Handbook

Friction Stir Welding Parts to be joined are clamped firmly. A rotating hardened steel tool is driven into the joint and traversed along the joint line between the parts. The rotating tool produces friction with the parts, generating enough heat and deformation to weld the parts together. Butt welds Unlike conventional friction welding, the parts to be joined by friction stir welding are not rotated. The parts are clamped firmly in a restraining device. A rotating tool traverses along the joint line. During rotation, the tool generates frictional heating, deformation, and welding along the joint line of the workpieces. Butt joints, corner joints, T joints, and fillet-butt joints can be welded by friction stir welding. Overlap welds

Friction Stir Welding Clamping force clamping force Step -1 Step -3

T-section ( 2- component top butt) Friction Stir Welding 900 Corner welds T-section ( 2- component top butt)

Friction Stir Welding Fillet butt welds

Questions

Friction Welding Applications Continuous Drive Friction Welding Applications Frequently competes with flash or upset welding when one of the work pieces to be joined has axial symmetry. Used in automotive industry to manufacture gears, engine valves, and shock absorbers. Used to join jet engine compressor parts.

Friction Welded Joints Applications Friction Welded Joints Friction Welded Joint Friction Welded Automotive Halfshaft Courtesy AWS handbook

Friction Welded Joints Applications Friction Welded Joints Camshaft Forging Friction Welded To Timing Gear. Cross Section of Aluminum Automotive Airbag Inflator. Three Welds Are Made Simultaneously Courtesy AWS handbook

Friction Welds Applications A Jet Engine Compressor Wheel Fabricated by Friction Welding Inertia Welded Hand Tools Courtesy AWS handbook

Dissimilar Metals – Friction Welded Aluminum to Steel Friction Weld

AWS Welding Handbook

Photomicrograph of Aluminum (top) to Steel (bottom) AWS Welding Handbook

Friction Weld Tantalum to Stainless Steel Note: mechanical mixing AWS Welding Handbook

Continuous Drive Friction Weld of Titanium Pipe Ti-6Al-4V-0.5Pd 246 mm diameter 14mm wall thickness No shielding used This is an example of continuous drive friction welding of a titanium alloy for use in offshore applications. Although there was considerable “flashing” observed, both the weld center and the heat affected zone were free from defects, and very little (if any) change in hardness was noted across the weld. Center HAZ Froes, FH, et al, “Non-Aerospace Applications of Titanium” Feb 1998, TMS

Radial friction weld of Ti-6Al-4V-0.1Ru The radial Friction Welding process offers the cost effective production of high quality welded titanium alloy risers offshore. The present study evaluates the metallurgical and mechanical properties of RFW welded titanium pips (9mm thick, 170mm outside diameter). The microstructural features of the weldments have been investigated by optical microscopy. The mechanical properties of the welded joints were characterized by micro hardness tests, conventional tensile and micro flat tensile tests. The microstructural investigations showed a fine transformed microstructure in the weld region (incl. HAZ). The tensile test results revealed higher weld region strength compared to the pipe material due to the observed fine transformed microstructures in this region. The weld ductility of the higher strength weld and HAZ regions remains high due to a process induced beta gain refinement by recrystallization. Properties in Weld Better than Base Metal Froes, FH, et al, “Non-Aerospace Applications of Titanium” Feb 1998, TMS

Linear Friction Weld Repair of Fan Blades Turbine Fan Compressor Combustor This is a process for joining a base for an airfoil to a disk for an integrally bladed rotor stage in a gas turbine engine The process includes bringing the root surface into contact with a recessed surface in the rim and linear friction bonding the two. Walker, H, et al, “Method for Linear Friction Welding and Products made by such Method” US Patent 6,106,233 Aug 22, 2000

Friction Welding for Mounting Ti Alloy Rotor Blades Shielding Gas & Induction Pre-heat Weld Nub Force This invention is directed to a friction welding process for mounting blades of a rotor for a flow machine. A plurality of oblong welding surfaces “nubs” are provided at a circumferential surface of a carrier and are respectively welded to a surface of the blade. The welding temperature is obtained by external induction heating which is protected by shielding gas flow and the pressing application of oscillating friction relative motion between the blade and the carrier. Linear Friction Weld Schneefeld, D,et al. “Friction Welding Process for Mounting Blades of a Rotor for a Flow Machine”, US Patent 6,160,237 Dec 12, 2000

Friction Welding Connector to Imbedded Window Wires Silver Based Ceramic Paint Wire Conductor Glass An automotive body glass comprising (a) a laminated glass with (b) conductive leads on or in the glass and having one or more conductive lead terminals, (c) an ultra thin pad of noble metal deposited onto a small zone of the glass in connection with a terminal, has a terminal clip connected to the noble zone using friction welding. White, D et al, “Friction Welding Non-Metallics to Metallics”, US Patent 5,897,964 Apr. 27, 1999

Friction Stir Welding – Tool Design Modification Hard Tool Tip Buried in Work Piece Metal Flow Force A modification in the tool design is recommended in this patent where a tip with ridges is buried beneath the surface during friction stir welding at a slit angle to the perpendicular. This forces metal flow and good weld mixing and results in improved friction stir welding. Travel Speed Midling, O, et al, “Friction Stir Welding” US Patent 5,813,592 Sep. 29, 1998

Friction Stir Welding – Automation Moving Device Elevation Platform and fixture device Friction Stir Welder This friction stir weld system has a base foundation unit connected to a hydraulically controlled elevation platform. The base unit may be connected to a movable support in order to provide mobility to the system. Mobile Support System Ding, R. et al, “Friction Stir Weld System for Welding and Weld Repair”, US Patent 6,173,880 Jan 16, 2001

Questions

Inertia Welding

Inertia Welding Process Description Inertia Drive Inertia Welding Process Description One of the work pieces is connected to a flywheel; the other is clamped in a non-rotating axial drive The flywheel is accelerated to the welding angular velocity. The drive is disengaged and the work pieces are brought together. Frictional heat is produced at the interface. An axial force is applied to complete welding. Spindle Workpieces Non-rotating chuck Hydraulic cylinder Flywheel Motor Chuck In inertia friction welding, one of the workpieces is connected to a flywheel, and the other is connected to a non-rotating axial drive system. The flywheel is accelerated to a predetermined rotational speed, storing the required rotational kinetic energy. The drive motor is disengaged and the workpieces are brought together. This causes the faying surfaces to rub together under pressure. The kinetic energy stored in the rotating flywheel is dissipated as heat through friction at the weld interface as the flywheel speed decreases. An increase in friction welding force (forging force) may be applied before rotation stops. The forge force is maintained for a predetermined time after rotation ceases to complete the weld.

Inertia Welding Where E = Energy, ft-lb (J) I = Moment of Inertia, lb-ft2 ( kg-m2) S = Speed, rpm C = 5873 when the moment of inertia is in lb-ft2 C = 182.4 when the moment of inertia is in kg-m2 Eu = Unit Energy, ft-lb/in2 (J/mm2) A = Faying Surface Area

Inertia Welding Variables Inertia Drive Inertia Welding Variables Moment of inertia of the flywheel. Initial flywheel speed. Axial pressure. Forging pressure.

Linnert, Welding Metallurgy, AWS, 1994

Inertia Welding Machine Equipment Inertia Welding Machine Courtesy AWS handbook

Linnert, Welding Metallurgy, AWS, 1994

Questions

Homework

A Few Specific Examples

Super-speed (750 SFM) Inertia Welding of Jet Turbine Components In this example, rather large diameter components are made from nickel base superalloy materials for various jet engine components. Typical forms of welding locally melt the parent material and are not useful for welding superalloys in view of the attendant change in microstructure thereof which significantly reduces their high temperature strength capability. In addition, the forging temperature range can be a low as 200F thus precise control of inertia welding variable must be maintained. Problems Melting Destroys Properties Low (200F) Forging Temp Range – Need Precise Control Ablett, AM et al, “Superspeed Inertia Welding”, US Patenmt 6,138,896, Oct. 31, 2000

Super-speed (750 SFM) Inertia Welding of Jet Turbine Components Control Parameters Workpiece Geometry (size) Applied Weld Load Contact Stress) Initial Contact Speed (surface velocity Unit Energy Input (moment of inertia, radius of gyration) Because of the large diameter parts, the surface speed is greater than most ordinary inertial welding applications and this further necessitates precise control of the weld parameters. The controllable parameters are listed above. Through experimentation, the working equations listed here have been defined as relationships between these parameters. As an example, a unit energy input E of 50,000 ft-lb/sq. in, and the contact area of 67.9 sq. in., a required rotary speed from the equation of 99.8 RPM is calculated which is within the operational limit of the specific welding machine with all the flywheels installed obtaining a maximum flywheel inertia of 2,000,000WK2. Correspondingly the initial contact speed requires 1880 SFM which is substantially greater than the 400-750 SFM range according to conventional practice. Where E = unit energy input W = flywhel weight K = radius of gyration RPM = initial rotation SFM = contact speed D = diameter A = contact area Ablett, AM et al, “Superspeed Inertia Welding”, US Patenmt 6,138,896, Oct. 31, 2000

Titanium Engine Valve Inertia Weld Titanium Aluminides Titanium Alloy or Titanium Borides (Brittle at RT) Titanium Alloy (Ductile) This example provides a titanium engine valve fabricated with discrete head and stem portions joined by inertia welding. The joint is located well up on the valve stem so that it iw not exposed below the valve guide. The head portion consists of a cast or forge heat trated titanium intermetallic compound. However the stem portion which is not directly exposed to the hostile environment of the combustion chamber, may be fabricated with mill anneal conventional titanium alloy rod stock. The valve is much less expensive to manufacture without sacrificing any mechanical or environmental characteristics in the portions of the valve subjected to high stress or those portions subjected to high temperatures. Jette, P , Sommer, A., “Titanium Engine Valve”, US Patent 5,517,956 May 21, 1996

Hot Inert Shielding Gas Inertia Welding of Magnesium and Aluminum Wheels for Motor Vehicles Inertia Weld Hot Inert Shielding Gas Wheel Spider Aluminum Magnesium Mg AM60 Mg AE42 Mg AM60 Mg AZ91 Mg AE42 Mg AZ91 This is a process for manufacturing a wheel for a motor vehicle, in which a wheel spider and a rim ring are connected with one another by means of inertia friction welding. At least one of the wheel parts consists of a magnesium alloy. The controlling of the speed of the start of the friction and compression process takes place as a function of physical characteristics of the magnesium alloy. Welding parameters determined by the lower-deforming alloy or the alloy with higher melting point Separautzki, R,et al, “Process for Manufacturing a Wheel for a Motor Vehicle” US Patent 6,152,351 Nov 28, 2000

Similarities between Continuous Drive and Inertia Drive In both methods, welding heat is developed by frictional heat and plastic deformation. Both methods use axial force for upsetting purpose. In both methods the axial pressure may be changed (usually raised) at the end of rotation.

Differences between Continuous Drive and Inertia Drive Inertia drive One of the workpieces is connected to the flywheel. Rotational speed decreases continuously to zero during the process. Kinetic energy of the flywheel dissipates through friction and plastic deformation producing heat. Continuous drive One of the workpieces directly connected to a rotating motor drive. Rotational speed remains constant until the brake is applied. Rotational energy of the workpiece dissipates through friction and plastic deformation, producing welding heat.