Friction extrusion

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Friction extrusion is a thermo-mechanical process that can be used to form fully consolidated wire, rods, tubes, or other non-circular metal shapes directly from a variety of precursor charges including metal powder, flake, machining waste (chips or swarf) or solid billet. The process imparts unique, and potentially, highly desirable microstructures to the resulting products. Friction extrusion was invented at The Welding Institute in the UK and patented in 1991. It was originally intended primarily as a method for production of homogeneous microstructures and particle distributions in metal matrix composite materials. [1]

Contents

Description of the Process and Essential Process Variables

Figure 1. C-frame milling machine modified for friction extrusion. At left is an overview image and at right is a close up of the mechanical spindle which provides die rotation and the hydraulic cylinder that provides the extrusion pressure. Wire is extruded vertically through the hollow draw bar of the milling machine. This configuration corresponds to a direct extrusion with a rotating die: i.e. the charge (billet in this case) is pushed into the rotating die. Friction Extrusion Milling Machine.png
Figure 1. C-frame milling machine modified for friction extrusion. At left is an overview image and at right is a close up of the mechanical spindle which provides die rotation and the hydraulic cylinder that provides the extrusion pressure. Wire is extruded vertically through the hollow draw bar of the milling machine. This configuration corresponds to a direct extrusion with a rotating die: i.e. the charge (billet in this case) is pushed into the rotating die.

As in conventional extrusion processes, in friction extrusion, a shape change is enforced on the charge by forcing its passage through a die. However, friction extrusion differs from conventional extrusion in several key ways. Critically, in the friction extrusion process, the extrusion charge (billet or other precursor) rotates relative to the extrusion die. In addition, similar to conventional extrusion, an extrusion force is applied so as to push the charge against the die. In practice either the die or the charge may rotate or they may be counter-rotating. The relative rotary motion between the charge and the die has several significant effects on the process. First, the relative motion in the plane of rotation leads to large shear stresses, hence, plastic deformation in the layer of charge in contact with and near the die. This plastic deformation is dissipated by recovery and recrystallization processes leading to substantial heating of the deforming charge. Because of the deformation heating, friction extrusion does not generally require preheating of the charge by auxiliary means potentially resulting in a more energy efficient process. Second, the substantial level of plastic deformation in the region of relative rotary motion can promote solid state welding of powders or other finely divided precursors, such as flakes and chips, effectively consolidating the charge (friction consolidation) prior to extrusion. [2] Scrolled features on the face of the die aid material flow into the extrusion orifice which can lead to order of magnitude reduction in extrusion force compared to conventional extrusions of equivalent cross section. [3] Third, the combined effects of elevated temperature and large levels of deformation normally lead the extrudate to have a relatively fine, equiaxed, grain structure which results from recrystallization after the conclusion of deformation: desirable crystallographic textures may also be created by the process and formation of nanocomposite structures are also possible. [4]

Figure 2. ShAPE(tm) machine at Pacific Northwest National Laboratory capable of 100 ton linear force and 1000 ft-lb torque at 500 rpm. Friction Extrusion ShAPE Machine.jpg
Figure 2. ShAPE™ machine at Pacific Northwest National Laboratory capable of 100 ton linear force and 1000 ft-lb torque at 500 rpm.

Based on the foregoing, it can be said that the essential controlled parameters in friction extrusion are typically:

  1. The die rotation rate.
  2. The die geometry.
  3. The extrusion force normal to the die face or, the rate of die advance into the charge.

The corresponding response parameters include:

  1. The required torque and power.
  2. The extrusion temperature.
  3. The extrusion rate in force controlled extrusion or the extrusion force in rate controlled extrusion.
  4. The extrudate microstructure and properties.

Friction Extrusion Equipment

Figure 3. The friction extrusion process is highly scalable. The extrusion on the left has a 7.5mm diameter, the one on the right has a 50 mm diameter. These extrusions were performed on a TTI friction sir welding machine. Friction Extrusion Stir Welding.jpg
Figure 3. The friction extrusion process is highly scalable. The extrusion on the left has a 7.5mm diameter, the one on the right has a 50 mm diameter. These extrusions were performed on a TTI friction sir welding machine.
Figure 4. Typical die scroll geometries for making rod and tube. Dies are rotated such that the scrolls aid material flow toward the die opening. Friction Extrusion Dies.jpg
Figure 4. Typical die scroll geometries for making rod and tube. Dies are rotated such that the scrolls aid material flow toward the die opening.

In principle, friction extrusion can be performed on any machine which can produce the required rotary and linear motions between the die and charge. Examples include machines built for friction stir welding, milling machines modified to accommodate the extrusion forces, and purpose built friction extrusion equipment such as the shear assisted processing and extrusion (ShAPE™) machine at the Pacific Northwest National Laboratory. Figures 1-3 show examples of friction extrusion equipment and extruded products. Figure 4 shows typical friction extrusion dies designed for production of wire, rod and tube. Dies are rotated in the direction which enhances material flow toward the extrusion orifice during the process.

Strain in Friction Extrusion

In conventional extrusion, the strain imparted to the charge is loosely defined by the extrusion ratio. [5] The extrusion ratio is simply the cross-sectional area of the extrusion billet, A0, divided by the cross sectional area of the extrudate, Af. The extrusion strain is then e=ln(A0/Af).

In friction extrusion there is an additional strain component which will arise from the shearing motion of the rotating die as it contacts the charge. The strain produced by the rotation of the die results in redundant work as it does not accomplish a shape change. In order to investigate the strain due to shearing, studies have been performed with marker materials embedded in the material to be extruded. [6] After extrusion, these materials are detected by metallographic methods and provide insight regarding the way in which material flows during the extrusion process. Figure 5 shows an example of how the amount of shear strain changes with changing ratios of extrusion rate to die rotation rate. In the limit of very high extrusion rates, the friction extrusion process closely mimics the conventional extrusion process with respect to strain levels.

Figure 5. Distribution of AA2195 marker wire in an extruded 6061 wire. The marker was inserted into the billet at 1/3 of the billet radius prior to extrusion. The amount of shearing is a function of the extrusion rate relative to the die rotation rate: this ratio increases from a-h. Friction Extrusion Marker.jpg
Figure 5. Distribution of AA2195 marker wire in an extruded 6061 wire. The marker was inserted into the billet at 1/3 of the billet radius prior to extrusion. The amount of shearing is a function of the extrusion rate relative to the die rotation rate: this ratio increases from a-h.

Typical microstructure resulting from friction extrusion

Figure 6 shows the cross section and microstructure of a titanium wire produced by friction extrusion of Ti-6-4 powder. Notably, the cross section is fully consolidated and the transformed b microstructure indicates that extrusion likely occurred near 1000 °C (above the beta transus for the alloy). Figure 7 shows grain size and crystallographic orientation typical of thin walled tubing extruded from AZ91 melt spun flake. [7] Grains are refined to less than 5 mm and orientation of the (0001) planes are off-normal due to the rotational shear component. Figure 8 shows examples of friction extruded magnesium alloy tubes. Friction consolidation has also been used to refine grain size and preferentially orient texture in functional materials such as bismuth-telluride thermoelectrics [8] and iron-silicon magnets. [9] Examples of the effect of friction extrusion of microstructure have been reported for AZ31, [10] [11] [12] various aluminum alloys [13] [14] [15] [16] and pure copper. [17]

Figure 6. As extruded wire, overall cross section, and microstructure of a wire produced by friction extrusion of Ti-6-4 powder. Friction Extrusion Cross Section.png
Figure 6. As extruded wire, overall cross section, and microstructure of a wire produced by friction extrusion of Ti-6-4 powder.
Figure 7. Grain size and texture development in a friction extruded tube produced directly from AZ91 (magnesium alloy) melt spun flake. Friction Extrusion Texture.jpg
Figure 7. Grain size and texture development in a friction extruded tube produced directly from AZ91 (magnesium alloy) melt spun flake.
Figure 8. Friction extruded tubes of magnesium alloy ZK60 extruded from a cast billet using the ShAPE machine at Pacific Northwest National Laboratory. The extruded tubes exhibit desirable microstructure and crystallographic texture, which enhance their ductility and ability to absorb deformation energy compared to conventionally extruded tubes. Friction Extrusion Tubes.jpg
Figure 8. Friction extruded tubes of magnesium alloy ZK60 extruded from a cast billet using the ShAPE machine at Pacific Northwest National Laboratory. The extruded tubes exhibit desirable microstructure and crystallographic texture, which enhance their ductility and ability to absorb deformation energy compared to conventionally extruded tubes.

Potential of Friction Extrusion for Commercialization

  1. Creep resistant steel piping.
  2. Lightweight magnesium and aluminum structures.
  3. Materials with enhanced thermal properties.
  4. Recycling of aluminum machining waste and swarf.
  5. Nanocomposite functional materials.

Advantages and Disadvantages Relative to Conventional Extrusion

Advantages

  1. Potential for significantly lower power consumption and extrusion force compared to conventional extrusion due to rotational shear generating the necessary process heat and scroll features aiding material flow into the extrusion orifice. [3]
  2. Friction extrusion is capable of refining microstructure from powder/flake/chip (bottom-up) and solid billets (top-down). [2] [3] [7] [18]
  3. Enables extrusion of materials, such as Mg2Si which cannot be readily extruded by conventional means. [19]
  4. As a solid-phase process, friction extrusion can be done at low temperature thereby retaining nanoscale second phases and particles present in precursor material. Enables fabrication of bulk nanocomposite materials. [4] [7] [19] [20]
  5. Enables enhanced bulk properties, such as energy absorption in magnesium alloys. [19]

Disadvantages

  1. Extrusion rates competitive with conventional extrusion processes have yet to be demonstrated.
  2. Uniformity of microstructure and material properties are difficult to obtain in plane perpendicular to extrusion direction because the imposed strain is non-uniform. [6]
  3. Full range of process scalability has not been assessed.

Related Research Articles

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<span class="mw-page-title-main">Powder metallurgy</span> Process of sintering metal powders

Powder metallurgy (PM) is a term covering a wide range of ways in which materials or components are made from metal powders. PM processes can reduce or eliminate the need for subtractive processes in manufacturing, lowering material losses and reducing the cost of the final product.

<span class="mw-page-title-main">Extrusion</span> Process of pushing material through a die to create long symmetrical-shaped objects

Extrusion is a process used to create objects of a fixed cross-sectional profile by pushing material through a die of the desired cross-section. Its two main advantages over other manufacturing processes are its ability to create very complex cross-sections; and to work materials that are brittle, because the material encounters only compressive and shear stresses. It also creates excellent surface finish and gives considerable freedom of form in the design process.

<span class="mw-page-title-main">Friction stir welding</span> Using a spinning tool to mix metal workpieces together at the joint, without melting them

Friction stir welding (FSW) is a solid-state joining process that uses a non-consumable tool to join two facing workpieces without melting the workpiece material. Heat is generated by friction between the rotating tool and the workpiece material, which leads to a softened region near the FSW tool. While the tool is traversed along the joint line, it mechanically intermixes the two pieces of metal, and forges the hot and softened metal by the mechanical pressure, which is applied by the tool, much like joining clay, or dough. It is primarily used on wrought or extruded aluminium and particularly for structures which need very high weld strength. FSW is capable of joining aluminium alloys, copper alloys, titanium alloys, mild steel, stainless steel and magnesium alloys. More recently, it was successfully used in welding of polymers. In addition, joining of dissimilar metals, such as aluminium to magnesium alloys, has been recently achieved by FSW. Application of FSW can be found in modern shipbuilding, trains, and aerospace applications.

The stacking-fault energy (SFE) is a materials property on a very small scale. It is noted as γSFE in units of energy per area.

<span class="mw-page-title-main">Magnesium alloy</span> Mixture of magnesium with other metals

Magnesium alloys are mixtures of magnesium with other metals, often aluminium, zinc, manganese, silicon, copper, rare earths and zirconium. Magnesium alloys have a hexagonal lattice structure, which affects the fundamental properties of these alloys. Plastic deformation of the hexagonal lattice is more complicated than in cubic latticed metals like aluminium, copper and steel; therefore, magnesium alloys are typically used as cast alloys, but research of wrought alloys has been more extensive since 2003. Cast magnesium alloys are used for many components of modern automobiles and have been used in some high-performance vehicles; die-cast magnesium is also used for camera bodies and components in lenses.

<span class="mw-page-title-main">Plastic extrusion</span> Melted plastic manufacturing process

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<span class="mw-page-title-main">Aluminium alloy</span> Alloy in which aluminium is the predominant metal

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<span class="mw-page-title-main">Cold spraying</span> Coating deposition method

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<span class="mw-page-title-main">Equal channel angular extrusion</span>

Equal channel angular extrusion (ECAE) called also equal channel angular pressing (ECAP) is one technique from the Severe Plastic Deformation (SPD) group, aimed at producing Ultra Fine Grained (UFG) material. Developed in the Soviet Union in 1973 by Segal. However, the dates are not always consistent. In industrial metalworking, it is an extrusion process, The technique is able to refine the microstructure of metals and alloys, thereby improving their strength according to the Hall-Petch relationship. This process improves not only the strength but also other properties such as corrosion and wear resistance of alloys and compounds.

Semi-solid metal casting (SSM) is a near net shape variant of die casting. The process is used today with non-ferrous metals, such as aluminium, copper, and magnesium, but also can work with higher temperature alloys for which no currently suitable die materials are available. The process combines the advantages of casting and forging. The process is named after the fluid property thixotropy, which is the phenomenon that allows this process to work. Simply, thixotropic fluids flow when sheared, but thicken when standing. The potential for this type of process was first recognized in the early 1970s. There are three different processes: thixocasting, rheocasting, thixomolding. SIMA refers to a specialized process to prepare aluminum alloys for thixocasting using hot and cold working.

Severe plastic deformation (SPD) is a generic term describing a group of metalworking techniques involving very large strains typically involving a complex stress state or high shear, resulting in a high defect density and equiaxed "ultrafine" grain (UFG) size or nanocrystalline (NC) structure.

<span class="mw-page-title-main">Friction stir processing</span>

Friction stir processing (FSP) is a method of changing the properties of a metal through intense, localized plastic deformation. This deformation is produced by forcibly inserting a non-consumable tool into the workpiece, and revolving the tool in a stirring motion as it is pushed laterally through the workpiece. The precursor of this technique, friction stir welding, is used to join multiple pieces of metal without creating the heat affected zone typical of fusion welding.

<span class="mw-page-title-main">Food extrusion</span> Food processing method

Extrusion in food processing consists of forcing soft mixed ingredients through an opening in a perforated plate or die designed to produce the required shape. The extruded food is then cut to a specific size by blades. The machine which forces the mix through the die is an extruder, and the mix is known as the extrudate. The extruder is typically a large, rotating screw tightly fitting within a stationary barrel, at the end of which is the die.

Al-Ca composite is a high-conductivity, high-strength, lightweight composite consisting of sub-micron-diameter pure calcium metal filaments embedded inside a pure aluminium metal matrix. The material is still in the development phase, but it has potential use as an overhead high-voltage power transmission conductor. It could also be used wherever an exceptionally light, high-strength conductor is needed. Its physical properties make it especially well-suited for DC transmission. Compared with conventional conductors such as aluminium-conductor steel-reinforced cable (ACSR), all aluminium alloy conductors (AAAC), aluminium conductor alloy reinforced (ACAR), aluminium conductor composite reinforced ACCR and ACCC conductor that conduct alternating current well and DC current somewhat less well, Al-Ca conductor is essentially a single uniform material with high DC conductivity, allowing the core strands and the outer strands of a conductor cable to all be the same wire type. This conductor is inherently strong so that there is no need for a strong core to support its own weight as is done in conventional conductors. This eliminates the "bird caging", spooling, and thermal fatigue problems caused by thermal expansion coefficient mismatch between the core and outer strands. The Al-Ca phase interfaces strengthen the composite substantially, but do not have a noticeable effect on restricting the mean free path of electrons, which gives the composite both high strength and high conductivity, a combination that is normally difficult to achieve with both pure metals and alloys. The high strength and light weight could reduce the number of towers needed per kilometer for long distance transmission lines. Since towers and their foundations often account for 50% of a powerline's construction cost, building fewer towers would save a substantial fraction of total construction costs. The high strength also could increase transmission reliability in wind/ice loading situations. The high conductivity has the potential to reduce Ohmic losses.

6162 aluminium alloy is an alloy in the wrought aluminium-magnesium-silicon family. It is related to 6262 aluminium alloy in that Aluminum Association designations that only differ in the second digit are variations on the same alloy. It is similar to 6105 aluminium alloy, both in alloy composition and the fact that it is only really used in extrusions. However, as a wrought alloy, it can also be formed by rolling, forging, and similar processes, should the need arise. It is supplied in heat treated form. It can be referred to by the UNS designation A96162, and is covered by the standard ASTM B221: Standard Specification for Aluminum and Aluminum-Alloy Extruded Bars, Rods, Wire, Profiles, and Tubes.

The 6463 aluminium alloy is an aluminium alloy in the wrought aluminium-magnesium-silicon family. It is related to 6063 aluminium alloy, but unlike 6063 it is generally not formed using any processes other than extrusion. It is commonly heat treated to produce tempers with a higher strength but lower ductility. Like 6063, it is often used in architectural applications.

<span class="mw-page-title-main">DFM Guidelines for Hot Metal Extrusion Process</span>

Extrusion is a metal forming process to form parts with constant cross-section along its length. This process uses a metal billet or ingot which is inserted in a chamber. One side of this contains a die to produce the desired cross section and the other side a hydraulic ram is present to push the metal billet or ingot. Metal flows around the profile of the die and after solidification takes the desired shape.
Extrusion process can be done with the material hot or cold, but most of the metals are heated before the process, if high surface finish and tight tolerances are required then the material is not heated.

<span class="mw-page-title-main">Dissimilar friction stir welding</span>

Dissimilar friction stir welding (DFSW) is the application of friction stir welding (FSW), invented in The Welding Institute (TWI) in 1991, to join different base metals including aluminum, copper, steel, titanium, magnesium and other materials. It is based on solid state welding that means there is no melting. DFSW is based on a frictional heat generated by a simple tool in order to soften the materials and stir them together using both tool rotational and tool traverse movements. In the beginning, it is mainly used for joining of aluminum base metals due to existence of solidification defects in joining them by fusion welding methods such as porosity along with thick Intermetallic compounds. DFSW is taken into account as an efficient method to join dissimilar materials in the last decade. There are many advantages for DFSW in compare with other welding methods including low-cost, user-friendly, and easy operation procedure resulting in enormous usages of friction stir welding for dissimilar joints. Welding tool, base materials, backing plate (fixture), and a milling machine are required materials and equipment for DFSW. On the other hand, other welding methods, such as Shielded Metal Arc Welding (SMAW) typically need highly professional operator as well as quite expensive equipment.

References

  1. ↑ “Forming metallic composite materials by urging base materials together under shear” US patent #5262123 A, Inventors: W. Thomas, E. Nicholas, and S. Jones, Original Assignee: The Welding Institute.
  2. 1 2 Tang, W.; Reynolds, A.P. (2010). "Production of wire via friction extrusion of aluminum alloy machining chips". Journal of Materials Processing Technology. 210 (15): 2231–2237. doi:10.1016/j.jmatprotec.2010.08.010.
  3. 1 2 3 4 "Scaled-up fabrication of thin-walled magnesium ZK60 tubing using shear assisted processing and extrusion (ShAPE™)", S. Whalen, V. Joshi, N. Overman, D. Caldwell, C. Lavender, T. Skszek, Magnesium Technology, 315-321, 2017.
  4. 1 2 “Dispersoid distribution and microstructure in Fe-Cr-Al ferritic oxide dispersion-strengthened alloy prepared by friction consolidation”, D. Catalini, D. Kaoumi, AP Reynolds, G. Grant, Metallurgical and Materials Transactions A, v. 46, no. 10, pp. 4730–4739, 2015.
  5. ↑ “Manufacturing Processes for Engineering Materials, 5th ed.”, S. Kalpakjian and S. R. Schmid, ISBN   0132272717, pp. 307-314, 2008.
  6. 1 2 “Strain and texture in friction extrusion of aluminum wire”, X. Li, W. Tang, AP Reynolds, WA Tayon, CA Brice, Journal of Materials Processing Technology, v. 229 ,pp. 191-198, 2016.
  7. 1 2 3 4 “Microstructural evolution of rapidly solidified AZ91E flake consolidated by shear assisted processing and extrusion (ShAPE™)”, N. Overman, S. Whalen, M. Olszta, K. Kruska, J. Darsell, V. Joshi, X. Jiang, K. Mattlin, E. Stephens, T. Clark, S. Mathaudhu, Materials Science and Engineering A, 701, pp. 56-68, 2017.
  8. ↑ “Friction consolidation processing of n-type bismuth-telluride thermoelectric material”, S. Whalen, S. Jana, D. Catalini, N. Overman, J. Sharp, Journal of Electronic Materials, 45(7), pp. 3390-3399, 2016
  9. ↑ “Friction consolidation of gas-atomized Fe-Si powders for soft magnetic applications”, X. Jiang, S. Whalen, J. Darsell, S. Mathaudhu, N. Overman, Materials Characterization, v. 123, pp. 166-172, 2017
  10. ↑ J. Milner, F. Abu-Farha, “Microstructural evolution and its relationship to the mechanical properties of Mg AZ31B friction stir back extruded tubes”, Magnesium Technology, pp. 263-268, 2014
  11. ↑ “A numerical model for Wire integrity prediction in Friction Stir Extrusion of magnesium alloys”, D. Baffari, G. Buffa, L. Fratini, Journal of Materials Processing Technology,pp. 1-10, 2017
  12. ↑ “AZ31 magnesium alloy recycling through friction stir extrusion process”, G. Buffa, D. Campanella, L. Fratini, F. Micari, International Journal of Material Forming, 1-6, 2015
  13. ↑ “A preliminary study on the feasibility of friction stir back extrusion”, F. Abu-Farha, Scripta Materialia, 66, pp. 615-618, 2012.
  14. ↑ "Production of wire from AA7277 aluminum chips via friction-stir extrusion (FSE)", R. Behnagh, R. Mahdavinejad, A. Yivari, M. Abdollah, M. Narvan, Metallurgical and Materials Transactions B, 45:4, pp. 1484–1489, 2014
  15. ↑ "Microstructure evolutions and mechanical properties of tubular aluminum produced by friction stir back extrusion", M. Khorrami, M. Movahedi, Materials and Design, 65, pp. 74-79, 2015
  16. ↑ "Direct solid-state conversion of recyclable metals and alloys", V. Manchiraju, Final Technical Report DE-EE0003458, Oak Ridge National Laboratory, 2012
  17. ↑ "Microstructural characterization of pure copper tubes produced by a novel method – friction stir back extrusion", I. Dinaharan, R. Sathiskumar, S. Vijay, N. Murugan, Procedia Materials Science, 5, pp. 1502–1508, 2015
  18. ↑ Baffari, Dario; Reynolds, Anthony P.; Li, Xiao; Fratini, Livan (2017). "Influence of processing parameters and initial temper on Friction Stir Extrusion of 2050 aluminum alloy". Journal of Manufacturing Processes. 28: 319–325. doi:10.1016/j.jmapro.2017.06.013.
  19. 1 2 3 "High shear deformation to produce high strength and energy absorption in Mg alloys", V. Joshi, S. Jana, D. Li, H. Garmestani, E. Nyberg, C. Lavender, pp. 83-88, Magnesium Technology, 2014
  20. ↑ Catalini, David; Kaoumi, Djamel; Reynolds, Anthony P.; Grant, Glenn J. (2013). "Friction Consolidation of MA956 powder". Journal of Nuclear Materials. 442 (1–3): S112–S118. Bibcode:2013JNuM..442S.112C. doi:10.1016/j.jnucmat.2012.11.054.
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