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Techniques and Technical Infrastructure

Techniques

Friction Stir Welding (FSW)

Friction Stir Welding

Friction stir welding (FSW) is a solid state joining process, which was developed and patented in 1991. And represent’s one of the core competences where Hereon has taken an international leading position. Such processes allow to a very high degree of freedom to weld similar and dissimilar materials, which can not be treated by any other method.

The process runs below the melting temperature of the workpiece material the heat is generated through friction and shear forces between Tool and material to be welded. The joint is built by rotational and transversal motion of the FSW tool along the abutting edges of the workpiece. It consists of the shoulder and the probe, which generate the needed heat and to stir the workpiece material, respectively create the weld joint.

Principles of the process
The steps during friction stir welding can be described as followed.
1. The tool starts to rotate and moves toward workpiece
2. The probe gets into contact and begins to plunge into the workpiece. Hereby friction and shear forces (plastic work) generate heat which plastizises (softens) the workpiece below the shoulder and around the probe
3. The tool travels in the direction of the abutting edges. Hereby the plastizised material is stirred around the tool joining the to plates
4. Tool moves out of the workpiece. The materials cool down, the weld is build and an exit hole is left

The main process parameter are the rotational speed, the welding speed and downward force (pressure) of the FSW tool.

FSW Welding Technologies are of interest of the aircraft, aerospace, automotive, locomotive, shipbuilding industry were the advantages of the process (e.g.: high joint strength, low distortion, weight neutrality and process automatisation, no material addition, no shielding gas for Aluminum and Magnesium no fume) are beneficial. In comparison to conventional fusion welds, FSW has many advantages such as: lower temperatures required to weld, environmentally clean process, low distortion and residual stress, greater weld strength, little or no porosity, little or no post weld repair, no solidification cracking, no welding fumes, improved corrosion resistance, no need for consumables and no spatter.

Stationary Shoulder Friction Stir Welding (SSFSW)

Ssfsw

A variant, or more correctly a development, of the conventional FSW have been obtained with the use of a stationary shoulder, originally in the case of titanium weldments. The main difference between the two technologies is due to the mechanical separation between the shoulder and the probe, allowing for the shoulder not to be rotating as shown in.

Differently from conventional FSW, where the major of the heat, necessary in order to obtain the joining, is generated by the friction between the shoulder and the top surface of the material, in case of SSFSW the shoulder has just the function to retain the plasticised material in the correct position, giving a small contribution to the heat generation. Due to this the heat is distributed more uniformly throughout the thickness of the material leading to a more homogenous crystallographic structure.
Aditional Adwantages of the SSFSW are:

  • Produces welds with a excellent surface finish
  • Lower distortion due to the uniform heat input
  • Low Energy input and reduced volume of material affected by the weld
  • T Joint = Corner Joints to weld reenforcements to a Panel, Aircraft Skin Stringer Profiles

A solution in order to reduce weight in modern aircraft is the use of welding technologies to replace rivets in skin-stringer joints.

Bobbin Tool Friction Stir Welding (BT-FSW)

BT-FSW

The Bobbin Tool variant uses a two-shoulder tool system and avoids the need of a backing plate while eliminating roots defects by full penetration of the material. Further advantages are low process forces and distortion due to a symmetrical heat input. This set-up allows welding of hollow structures like extrusions, pipes or tanks.

The machine set-up is identical to FSW and the tool consists of an upper and a lower shoulder.

Friction Stir Processing (FSP)

FSP

Friction stir processing (FSP) is a derivative of friction stir welding (FSW) and is a processing method to locally modify the microstructure and texture of a given material. Using appropriate processing parameters, the resulting material properties can be tuned to fit a specific purpose i.e. homogenization and refinement of an as-cast microstructure, or alteration of the microstructure in such ways that enhanced strength or ductility can be reached.

Principles of the technique
The tool is prepositioned at the initiation site which is to be processed (a). Consequently, the tool in set under rotation and introduced into the material (b). Via friction, the material beneath the tool is heated up and plasticized. Once a sufficient plasticization is reached, the translation motion is started (c) and the process zone created. Finally, the tool is retracted from the sample sheet (d).

Potential Applications
Grain refinement / Homogenization:
Friction stir processing can be used to homogenize an as cast microstructure locally, so that connection parts or sealing surfaces can easily be improved. The final microstructure unusually incorporates small, recrystallized grains without the occurrence of pores. The processed material usually has a higher strength compared to the base material.

Friction Spot Joining (FSpJ)

Goushegir Technique Description

Since its introduction in 2009, Friction Spot Joining (FSpJ) has shown high performance in producing polymer-metal hybrid structures. Therefore, this technique is being investigated to join lightweight alloys such as aluminium and magnesium with high performance engineering thermoplastics and composites. For this reason a friction spot welding / joining machine (RPS 100) is employed. Briefly, the metallic partner is plasticized and deformed due to the generated frictional heat and applied force. A metallic nub is created which is inserted into the composite. Simultaneously, a thin layer of polymer matrix is molten, and displaced around the joining area. The joint is formed after consolidation of the polzmeric molten layer. These are the two main phenomena responsible for joining mechanisms.

The term "joining" is used to differentiate spot joints where a sharp interface is present (minimal or absent atomic or molecular diffusion), such as in hybrid polymer-metal joints, while "welding" is used for joints without a discontinuous transition between joining partners (presence of diffusion mechanisms), such as "polymer-polymer" or "metal-metal" spot welds.

Read more about principles of Friction Spot Joining (PDF) (328 KB)

Friction Spot Welding (FSpW)

FSW Hereon

Friction Spot Welding or also known as Refill Friction Stir Spot Welding is a solid-state welding process developed and patented by Helmholtz-Zentrum hereon GmbH. The process was developed as an alternative to riveting or resistance spot welding to produce similar and dissimilar overlap joints.

Refill FSSW uses a non-consumable tool consisting of three independent movable parts, including a stationary clamping ring and two rotating parts of the sleeve and the probe, as presented in Figure 1. The principles of the Refill FSSW are presented in Figure 2 and 3. First, the process starts with the clamping ring moving downwards to fix the workpiece for the rest of the process. Sleeve and probe start to rotate under a pre-set speed. Following that, in the sleeve plunge variant the sleeve plunges downwards into the workpiece while the probe is simultaneous retracted. The rotating sleeve generates frictional heat plasticizing the workpiece material. The downward movement of the sleeve forces the softened material into the cavity left by the probe. When a pre-determine plunge depth is reached, the rotating pin and sleeve move back to their initial position, pushing the material back into the joint to refill the keyhole left by the retracting sleeve. At the interface between the refilling plasticized material and the surrounding workpiece, metallic bonding is created by diffusion processes over the interface. In probe plunge variant as shown in Figure 3, the rotating probe plunges into the materials while the probe is simultaneous retracted. Finally, the tool is retracted from the surface, leaving a spot weld without a keyhole, as presented in Figure 3. Additionally, the Refill FSSW is also an excellent technique for closing keyhole, such as in conventional friction stir welding, by applying plug material.

This technique has successfully been used to produce overlap joints in different materials in similar and dissimilar joint configuration, such as aluminum-aluminum, magnesium-magnesium, aluminum-steel, magnesium-steel, aluminum-titanium, and magnesium-titanium.

Friction Riveting (FricRiveting)

Blaga Technique Description

Friction Riveting (Fricriveting), is an innovative joining technique for polymer-metal hybrid structures, developed and patented by the Helmholtz Zentrum Geesthacht in Germany. In this process, polymeric parts are joined by a metallic rivet; the joining is achieved by mechanical interference and adhesion between the metallic and polymeric joining partners. During the process, a rotating cylindrical metallic rivet is inserted into a polymeric base plate. Due to the local increase of temperature, a molten polymeric layer is formed around the tip of the rotating rivet. The local temperature increases leading to the plasticizing of the tip of the rivet. While the rotation is being decelerated, the axial pressure is increased, the so called forging pressure is applied and the plasticized tip of the rivet is being deformed and anchored in the polymeric plate. The technology is adequate to produce overlap riveted joints between metal-polymer, metal-composite and composite-composite connections.

Read more about principles of Friction Riveting (PDF) (74 KB)

Injection Clinching Joining (ICJ)

Abibe Technique Description

Injection Clinching Joining (ICJ) is a new joining process for hybrid structures, composed of one thermoplastic-based partner and a metallic or thermoset partner. The principle of the process is to produce joints through heating and deformation of a thermoplastic element (such as a cylindrical stud) integrated in the polymeric partner, which is previously inserted in a through hole (cavity) of a metallic/thermoset component, therefore creating a rivet from the structure itself. Spot joints created by ICJ process are tight and with good mechanical anchoring due to the cavity profiles on the metallic partner. ICJ is a potential technology for secondary and tertiary structures in automotive and aircraft applications.

Read more information about principles of ICJ (PDF) (242 KB)

Ultrasonic Joining (U-Joining)

Eduardo Techniques

Ultrasonic joining (U-Joining) is a new direct assembly technique developed by Helmholtz-Zentrum Hereon (patent EP 3 078 480 A1). U-Joining uses ultrasonic energy to join fiber-reinforced thermoplastics to surface-structured metallic parts, for instance produced by metal injection molding (Hereon’s patent EP 2 468 436 B1). Ultrasonic vibration and pressure create frictional heat at the materials interface, which softens the composite matrix and allows the reinforcement (structured on the surface of the metallic part) to penetrate the composite. As a result, a metal-composite hybrid joint with improved out-of-plane strength is achieved.

Read more information about principles of U-joining (PDF) (261 KB)

AddJoining

Addjoining Aa2024 Cf-pa6

The AddJoining concept (German patent application number DE 10016121267.9) uses a new and unique approach to produce complex hybrid parts, by combining the principles of joining and polymer additive layer manufacturing (ALM) to produce layered metal-polymer hybrid structures. This is an important contribution to the state-of-the-art in additive manufacturing. AddJoining has potential to overcome the main limitations of production time of state-of-the-art manual lamination techniques, allowing for the production of future composite-metal layered structures with high-specific strength (Rm/density), tight dimensional and damage tolerances.

Read more information about principles of AddJoining (PDF) (1,1 MB)

Technical Infrastructure

T805 Bobbin tool FSW Roboter System

140617 Wmp Www T805 Bbt FSW Roboter System Foto


Flexistir Bobbin Tool FSW System

140617 Wmp Www Flexistir Machine Foto Frontal

Six axes controlled by motors for movement
One manually adjustable axis
Two independently controllable spindles

Double shoulder FSW tool (Bobbin tool, BT)
- up to 20Nm per spindle
0-2000 u min^-1
- up to 4kN splitting force

Single shoulder FSW steel welding head:
- up to 80Nm
- up to 40kN axial force

Measurement and control
- of the axial force
- the rotational speed

Measurement
- axial force
- forces in the plane
- torque on the spindle
- split force


Hereon Portal FSW System

140701 Wmp Www Gantry Maschine Foto Iso

Axial forces up to 60 kN
Lateral forces up to 15 kN
Forces in feed direction up to 20 kN
Welding speed adjustable between 0.1 and 4 m/min
Speeds between 200 and 6000 rpm
Maximum uninterrupted welding length 2500 mm

Measurement and control
- of axial force
- of the speed

measurement
- forces in the plane
- of the torque on the spindle


T9000 FSW Roboter System

140617 Wmp Www T900 Robgant Maschine Foto Frontal Fischauge

Electric drive
Speed up to 6000 rpm
Axial forces up to 60 kN
Radial forces up to 20 kN
dimension of working space 6m x 2m x 0,8m

Measurement and control
- of axial force
- the rotational speed

Measurement
- of the forces in the plane
- of the torque on the spindle


Hereon RPS 100 Friction Spot Welding System

140630 Rps100 Wmp Www Foto Frontal

Electr. drive
Speeds between 500 and 3000 rpm
Max. Point diameter 12mm
Max. Welding depth 10mm

Measurement and control
- of axial force
- the rotational speed
- the feed path of pin and sleeve


Hereon RPS 200 Reibpunktschweiß System

140617 Wmp Www Rps200 Maschine Foto Perspektivisch

Welding tool stroke: 10 mm
Welding force: 35 kN
Torque: 60 Nm (90 Nm for 15 s)
speed of the tool elements: 3300 rpm
working surface: 1000 mm x 500 mm
mass: 4,7 t
stroke of the welding head: 300 mm
clamping force: 40 kN

Measurement and control:
- torque on the pin
- torque on the sleeve
- clamping force
- penetration force of the pin
- penetration force of the sleeve
- displacement of pin
- displacement of sleeve
- temperature


Friction Surfacing Machine RAS - Henry Loitz Robotik (HLR)

140617 Wmp Www Ras Maschine Foto Perspektivisch

Electric spindle drive
Electric linear drives
Spindle arbor hole: 30 mm

Axial force up to 60 kN
Up to 6000 rotations per minute
Torque up to 200 Nm
Axial travel up to 500 mm
Travel speed up to 20 mm/s

Force or displacement control
Surveilled cooling circuit
External shielding gas supply
Modular tool holder

Control/measurement of:
- Forces
- Feed rates
- Rotation
- Torque
- external temperature measurement
- Video process monitoring system


RSM Friction Rivet System (small)

Rsm 400

Pneu./ Electr. drive
Speeds between 6000 and 24000 rpm
Axial forces up to 15 kN
Feed path max. 50 mm

Measurement and control
- of the axial force
- the speed
- of the feed path (in preparation)


Friction Rivet System (big)

140617 Wmp Www Fricriveting Maschine Foto Perspektivisch

Automated three-axis control concept with four degrees of freedom

Spindle: RSM 410 Harms & Wende
- up to 21000 u min^-1
- axial force up to 24 kN
- torque up to 20Nm

Tool changer for 20 rivets
working surface 1000 x 1500 mm

Sensors:
- 3D piezoelectric force sensors
- measurement of X, Y and Z forces
-Torque measurement

Integrated position sensors


Scanning Electron Microskope (SEM) FEI Quanta 650 FEG

140617 Wmp Www Sem Quanta 650 Foto Frontal

High resolution Schottky field emission microscope

Vacuum Modes:
High vacuum, HiVac (10^-2 to10^-4 Pa)
Low vacuum, LoVac (10 to 200 Pa)
Extended vacuum mode, ESEM (10 to 4000 Pa)

Acceleration voltage : 200 V to 30 kV

Control stage: eucentric position

Analytical systems: simultaneous electron backscatter diffraction (EBSD) and energy dispersive X-ray spectroscopy (EDS) spectrometer

Auxiliary systems: control camera, fast loading

External systems: 24h emergency power supply, antimagnetic frame, vibration damping table

Miscellaneous: beam slowing, concentric solid-state backscatter detector (CBS)

Friction Surfacing (FS)

Friction Surfacing (FS) by V. Fitseva 2016

The Friction Surfacing (FS) process is a solid-state joining / deposition process. FS involves a rotating (ω) consumable stud, which is applied onto a substrate under axial load (Fz). The rotation of the rod and the axial load result in frictional heat being generated between the stud tip and the substrate surface, which plasticizes the stud tip. A relative traverse movement (vd) between stud and substrate is superimposed, where the plasticized rod material is then deposited on top of the substrate surface. As a byproduct, a flash at the tip of the stud forms. Main applications and areas of interest for the FS process are:

- Surface modification of materials
- Repair of worn parts
- Deposition of different metallic combinations and metallurgical incompatible materials
- Additive manufacturing of structural parts

Depicted in Figure 1 are the main components and process parameters of the FS process.

Figure 1 – Schematic of the friction surfacing process showing a) positioning of the rotating stud on top of a substrate surface, b) bringing the rotating stud tip in contact with the substrate surface under axial force, creating frictional heat and therefore plasticizing the stud tip, c) superimposing a relative traverse movement and thus depositing stud material on the substrate surface and d) lifting off the rotating stud at the end of the process.

Hybrid Friction Diffusion Bonding (HFDB)

 Schematic of the standard hybrid friction diffusion

The standard HFDB process was developed for joining thin sheets on to thin sheets as well as thin sheets on to thicker substrates. HFDB introduces energy in the form of frictional heat, as well as elastic and plastic deformation, into the joining area by moving a non-consumable rotating tool relative to the work piece for linear welds or keeping the tool stationary for spot welds while at the same time exerting pressure on the joining area.

The HFDB tool creates frictional heat and deformation by means of rotational (ω) and translational movement (v) as well as axial (normal) force (F). The friction partner, aka the upper layer, becomes partially plasticized and deformed. Diffusion processes in the joining area then join the friction partner and the joining partner. Depending on the material combination and geometry (e.g. thickness) of the friction and joining partners, the process can be repeated over the joining area.

Depicted in Figure 2 are the main components and process parameters of the standard HFDB process:

Schematic of the standard hybrid friction diffusion process showing 1) HFDB tool, 2) friction partner, 3) joining area and 4) joining partner (left), detailed view of the HFDB tool friction area (right)

Friction Extrusing Machine FE 100

Friction Extrusion Machine FE 100

Machine Dimensions
Length in the X : 2300 mm
Length in the Y: 1300 mm

Z-axis (Extrusion axis)
Drive: Hydraulic
Control mode: Closed loop force control or position control
Stroke: 508 mm
Max force: 1000 kN
Max Velocity: 305 mm/min

Two-Speed Spindle
Speed Range: 0-1000 RPM
Max Torque: 3561 Nm
Clear hole through spindle: 75 mm

Additional Feature : Water cooling and shielding gas (i.e. argon)

Capability
• Friction extrusion of different feedstock form: Bulk, machine chip and powder
• Friction extrusion of different feedstock material:
Aluminum and its alloys (similar and dissimilar) / Magnesium and its alloys