NL2028068B1

NL2028068B1 - Apparatus for friction stir applications and method for manufacturing such an apparatus

Info

Publication number: NL2028068B1
Application number: NL2028068A
Authority: NL
Inventors: Bernard Lind Jesper; Cornelis Bor Teunis
Original assignee: Univ Twente
Priority date: 2021-04-26
Filing date: 2021-04-26
Publication date: 2022-11-03
Also published as: WO2022231423A1

Abstract

A friction stir extrusion apparatus for extruding material, comprising a housing, a transport screw and a feeder, the housing comprising a body with a round cavity and extending along a rotational axis and having an input opening for a material feed and an output opening for extruded 5 material, the transport screw having helical ridges along its length is arranged within the cavity and adapted for rotating inside the cavity, the feeder adapted for feeding the material feed to the input opening, wherein a ﬁrst portion of the cavity is tapered towards the output opening and the transport screw is 10 tapered along the ﬁrst portion of the cavity, and a ﬁrst gap perpendicular to the rotational axis and a second gap parallel to the rotational axis between the helical ridge of the transport screw and the inner wall of the cavity are each constant and non-zero along the ﬁrst portion. 15 [ﬁg lA]

Description

Apparatus for friction stir applications and method for manufacturing such an apparatus Field of the invention The present invention relates to a friction stir extrusion apparatus for extruding material. Also, the invention relates to a printing apparatus for printing solid-state material. Furthermore, the invention relates to a method for extruding material. Background Additive manufacturing (AM) or 3D printing provides new routes to manufacturing of parts with complex shapes, new and/or integrated functionalities, with short time to market, and adaptable to individual needs/requirements.

In AM, a feed material is deposited layer-by-layer on a substrate to create a 3D object.

For 3D printing of metals, it is known to use either powders or wires as feed material. When using powder as a feed material, deposition may take place by a fusion process, in which the powder is controllably melted locally and fused with the substrate. A high energy beam (laser beam or electron beam) is controlled to heat powder particles in a predefined pattern to induce local melting and subsequent solidification. Powder based additive manufacturing allows complex and highly detailed designs. Porosity and microstructure are however difficult to control. Also, due to melting, alloying elements may be lost due to evaporation from the melt pool which affects application for metal alloys such as a number of high strength Al alloys.

An alternative approach is layer-by-layer deposition based on friction surfacing or friction stir welding of wire material. The wire maternal is forced against the substrate while simultaneously at the contact area between wire and substrate friction is created. As a result, the wire material 1s softened and fused with the surface of the substrate. Friction stir based additive manufacturing may sutfer from reduced reproducibility and variation of tolerances.

Also, methods and devices are known in which feed material 1s compacted and extruded using an Archimedes screw. Patent application US2010/0285165 describes a screw extruder for continuous extrusion of materials with high viscosity. Patent US 8,875,976 describes a system for continuous feeding of filler material for friction stir welding, processing and fabrication. Such a system includes friction-based fabrication tooling comprising a non-consumable member with a throat and a consumable member disposed in the throat, wherein consumable filler material is capable of being introduced to the throat in a continuous manner during deposition using frictional heating and compressive/shear loading of the filer material onto the substrate.

It is an object of the present invention to overcome or mitigate one or more of the disadvantages from the prior art. Summary of the invention The object is achieved by a friction stir apparatus for extruding material, comprising a stationary housing, a transport screw and a feeder, the housing comprising a body provided with a round cavity defined by an inner wall and extending along a rotational axis and having an input opening to the cavity for a material feed and an output opening for extruded material; the transport screw being provided with one or more helical ridges along its length and at least partially arranged within the cavity with a longitudinal axis of the transport screw coinciding with the rotational axis of the cavity and adapted for rotating inside the cavity; the feeder adapted for feeding the material feed to the input opening, wherein at least a first portion of the cavity is tapered towards the output opening and the transport screw is tapered along at least the first portion of the cavity and a first gap perpendicular to the rotational axis and a second gap parallel to the rotational axis between a major diameter of the at least one helical ridge of the transport screw and the mner wall of the cavity are each constant and non-zero along at least the first portion.

During operation of the apparatus, (metallic) material is entered through the feeder in the cavity between the inner wall thereof and the transport screw. By providing a gap between the inner wall and the major diameter of the transport screw, the material is exposed to a plastic deformation and brought in softened state (i.e., the material is brought to a temperature above its recrystallisation temperature) while transported towards the output opening. Due to the work on the material while passing the housing, the temperature of the material is high enough for deposition, no additional friction heating on the substrate is required during the deposition. Since the plastic deformation is predominantly controlled by the rotation of the transport screw, the deposition process is highly reproducible.

According to an embodiment, a diameter of an end of the transport screw at the output opening is smaller than an opening diameter of the output opening. This arrangement provides an advantageous setup for additive manufacturing in which the softened material is output at the output opening and deposited on a substrate or previously deposited material. If the substrate is controllably moved relative to the output opening, the softened material can be deposited in a predetermined pattem, allowing to build a structure corresponding with the pattern.

According to an embodiment, the apparatus comprises a die that is either integrated with or mounted on the output opening of the stationary housing, the die having an opening smaller than the opening of the output opening.

In this embodiment, the opening of the die may have any shape, for example, circular, rectangular, elliptical, etc.

The arrangement of the friction stir apparatus with a die provides an advantageous setup for extrusion of the softened material.

Also, the invention relates to a printing apparatus for printing solid-state material, comprising a print head consisting of a friction stir extrusion apparatus as described above.

Moreover, the invention relates to a method for extruding material by a friction stir extrusion apparatus as described above, comprising: feeding material into the input opening by the feeder; forcing the material from the feed to the output opening by rotating the transport screw inside the cavity so as to bring the material in a softened state while passing between the transport screw and the inner wall of the cavity, and outputting the material in the softened state at the output, wherein the plastic deformation comprises forcing the material to propagate through a first portion of the cavity between the inner wall and the transport screw in which the inner wall of the cavity is tapered towards the output opening and the transport screw within the cavity is tapered along at least the first portion of the cavity in such a manner that the material is plastically deformed while passing between the transport screw and the inner wall of the cavity, and wherein a first gap perpendicular to the rotational axis and a second gap parallel to the rotational axis between a major diameter of the at least one helical ridge of the transport screw and the inner wall of the cavity are constant along at least the first portion of the cavity.

Advantageous embodiments are further defined by the dependent claims.

Brief description of drawings The invention will be explained in more detail below with reference to drawings in which illustrative embodiments thereof are shown.

The drawings are intended exclusively for illustrative purposes and not as a restriction of the inventive concept.

The scope of the invention is only limited by the definitions presented in the appended claims.

Figures 1A, 1B show a cross-sectional view of a friction stir apparatus according to an embodiment of the invention; Figure 1C shows a detail of a friction stir apparatus according to an embodiment of the invention; Figure 2 shows a cross-sectional view of a friction stir apparatus according to an embodiment of the invention; Figure 3 shows a cross-sectional view of a friction stir apparatus according to an embodiment of the invention; Figure 4 shows a cross-sectional view of a friction stir apparatus according to an embodiment of the mvention, and Figures SA, 5B show a perspective view of an output opening according to an embodiment of the apparatus.

Detailed description of embodiments Figure 1A, 1B show a cross-sectional view of a friction stir apparatus according to an embodiment of the invention.

According to an embodiment, the friction stir apparatus 100 comprises a stationary housing 110, a feeder 120 and a transport screw 130.

The housing 110 is a body provided with a round cavity defined by an inner wall 112, internal in the body, and which extends in the body along a rotational axis R. At least a first portion of the cavity is tapered along the rotational axis.

Additionally, at the relatively wider diameter of the cavity, the housing 110 is provided with an input opening 114 for entry of feed material, which is positioned substantially perpendicular to the rotational axis, and is in communication with an entry portion of the cavity.

Further, at the relatively smaller diameter of the cavity, the housing has an output opening 116 that is positioned at an end face of the housing and centred with the location of the rotational axis R.

The feeder 120 is connected to the input opening and adapted for feeding the material feed to the input opening 114 of the housing 110. According to an embodiment, the feeder comprises a tube with one end configured for receiving the feed material and the other end connected to the input opening.

According to an embodiment, the feeder is configured for feeding material having a shape of wires, granules, chips (turnings, filings, shavings) and/or fines.

The transport screw 130 is at least partially arranged within the cavity with a longitudinal axis of the transport screw coinciding with the rotational axis R of the cavity such that the transport screw can rotate inside the wall 112 of the cavity. The transport screw is coupled with a drive (not shown) preferably having a controllable rotational speed.

The transport screw 130 is provided with one or more helical ridges 132 along its length which during operation engage with feed material entered at the input opening 114 and drive it towards a tip end 131 at the level of the output opening 116.

As shown in Figure IC, the transport screw 130 is tapered conformally with the shape of the cavity, in a manner that at least in the tapered region of the cavity, a non-zero and constant gap is present between the inner wall and the transport screw; i.e. a first gap gl,134 perpendicular to the rotational axis R and a second gap g2.136 parallel to the rotational axis R between a major diameter D of the at least one helical ridge 132 of the transport screw 130 and the inner wall 112 of the cavity. By the presence of such a gap gl, g2 the transport screw is not an Archimedes screw which provides transport of material within the space in between the helical ridges, but is a tool that is adapted to transport material and at the same time deform the material. By the gap a space is created for material outside of the helical ridge (i.e. outside of the space between the helical ridges and the central body of the screw): the apparatus is provided with a volume within the cavity in which material from the feeder is plastically deformed while it is transported towards the output opening. As a result, the material can be brought into the softened state when reaching the output opening. This has the benefit the material can be deposited on a substrate substantially without additional frictional heating on that substrate. 5 In an embodiment, the apparatus comprises means for adjusting the size of the gap by adapting the axial position of the transport screw relative to the cavity.

According to an embodiment as shown in Figure 1A, a diameter of the tip end 131 of the transport screw at the output opening is smaller than an opening diameter 118 of the output opening. This allows an unhindered flow of the softened material from the output opening on a substrate below the output opening. As explained below in more detail the arrangement of Figure 1A is suitable for additive manufacturing to create a 3D structure from the softened material.

In an embodiment, the apparatus comprises a sample table 140 on which a substrate 150 can be placed. The table 140 is moveable relative to the output opening of the apparatus, which allows the printing of extruded material on the substrate according to a pattern imposed by the movement of the table. The movement of the table is in at least a direction parallel to the rotation axis R and a direction perpendicular to the rotation axis. The movement can be controlled by a suitable drive mechanism coupled to the table 140 (not shown).

The vertical distance between the output opening and a surface of the substrate 140 can be set such that it substantially corresponds with a thickness of the layer 130 that is to be printed/deposited on the surface.

In Figure 1B an altemative embodiment is shown in which a die 116 is provided that is either integrated with or mounted on the output opening 118 of the stationary housing. The die 116 has an opening area smaller than the area of the opening of the output opening. In this arrangement the apparatus is suitable for extrusion of the softened material. The opening area of the die 116 can have anv shape: for example, circular, elliptical, rectangular, etc.

Figure 2 shows a cross-sectional view of a friction stir apparatus according to an embodiment of the invention.

In this embodiment, the cavity comprises a first exit portion 1101 that is tapered towards the output opening, similar as described above with reference to Figures 1A, 1B. Additionally, at the side of the input opening the cavity comprises a second entry portion 1102 that is substantially cylindrical. The transport screw is positioned in the cavity and has at least one helical ridge which preferably extends along the entering and end portions. The shape of the transport screw 130 is conformal with the shape of the cavity, with a cylindrically shaped portion 1302 that extends in the cylindrical portion 1102 of the cavity and a tapered portion 1301 that extends in the tapered portion 1101 of the cavity, such that at least in the tapered region of the cavity, the non-zero and constant gap is present between the inner wall and the transport screw.

In an exemplary embodiment the transport screw 130 has a length of 23.5 mm with a cylindrical and a conical section with lengths of 7 mm and 16.50 mm, respectively. The helical ridge is manufactured according to ISO metric screw thread of a 20 mm bolt with a 2.5 mm pitch. The helical ridge from the cylindrical section 1302 is continued on the conical section 1301. The conical section 1301 has a total taper angle o of 40 degrees.

The inner wall 112 of the cavity comprises a cylindrical section with a diameter of 21 mm and a tapered/conical section that conforms with the shape of the transport screw. The current setup is designed with a vertical gap 136, g2 that can be set between 0 mm and 15 mm.

In an example. using this set-up, the vertical gap is set between about 3 and 4 mm, which corresponds to a first horizontal gap 134, gl between the inner wall and the major diameter of the screw of about 1 and 1.5 mm (perpendicular to the rotation axis) while the vertical gap 136, g2 is between 3 and 4 mm, see fig IC.

Experiments with aluminium alloy AA6060T6 as feed material show that at values of the vertical gap between 3 to 4 mm the volume of the aluminium leaving the output opening is predominantly determined by the volumetric supply rate provided through the feed opening and not by the rotation rate of the transport screw. At these conditions the rotation of the screw appears no longer directly coupled to the transport of the material through the apparatus. Changes of the rotation rate can lead to changes in the temperature of the material present in between the screw and the inner wall and the material leaving the output opening providing additional means to control the process temperature.

From the experiments it was observed that a rotation rate between 300 rpm and 600 rpm worked well with a value of the vertical gap between 3 mm to 4 mm while the volumetric supply rate could be varied between about 10 mm?/s and about 110 mms.

Figure 3 shows a cross-sectional view of a transport screw 135 according to a further embodiment of the invention.

In this embodiment, the transport screw 135 is similar to the transport screw as shown in Figure

2. in which the transport screw 135 has a cylindrically shaped portion 1302 that extends in the cylindrical portion of the cavity and a tapered portion 1301 that extends in the tapered portion of the cavity. Additionally, the transport screw is provided at the tip end 131 which is on level with the opening of the output opening 118 of the cavity 110, with a protruding portion 1303 mounted on the tip end and which protrudes outside the output opening. The protruding portion 1303 can have a same diameter as the tip end 131 of the tapered portion 1301, but alternatively the diameter of the protruding portion is smaller. The protruding portion 1303 can be either cylindrical or tapered. The protruding portion 1303 is provided with a thread along at least a portion of its length, which thread can have a same pitch as used on the cylindrical and tapered portions 1301, 1302. Alternatively, the pitch of the thread on the protruding portion 1303 can be different, preferably smaller.

When in this embodiment the friction stir apparatus is extruding material on a substrate, the protruding portion is configured to contact or penetrate the surface of the substrate which causes local deformation and softening of the substrate material, similar to the prior art stir welding mechanism. Also, any surface layer on the substrate such as an oxide layer will be removed by the interaction between the protruding portion and the surface. As a result, the local deformation and softening causes an improved adhesion and mixing of the extruded material with the substrate. Figure 4 shows a cross-sectional view of a friction stir apparatus according to an embodiment of the invention.

In Figure 4 the feeder 120 is shown in some detail. The feeder comprises a feeder tube (or channel) through which the feed material, preferably as wire, is transported to the input opening 114 of the cavity. The feeder is positioned substantially horizontal, but may show a downward slope towards the cavity. The inclination angle may vary between 0° and about 25°.

In an embodiment, a selection is made with respect to the location where the feeder brings the material into contact with the transport screw. Apparently, when during operation the feed material comes in contact with the tapered portion, more or less constant conditions occur over time, which is a preferred situation. In this case, the feeder tube should be oriented substantially towards the tapered portion of the cavity.

Additionally, in an embodiment, the feeder tube 120 is provided with cooling means 122. The cooling means are arranged in proximity to the housing 110, in order to absorb any heat that is generated by the work performed by the apparatus on the feed material in the cavity.

In this embodiment, the feeder is provided with mechanical means for feeding material towards the cavity in the housing, for example, such means comprise a hydraulic cylinder. If the temperature near the feeder tube exit towards the housing becomes too high, plastic deformation of the feed material inside the feeder tube may cause such high frictional forces with the feed tube wall that the feed material gets stuck inside. To avoid this. the cooling prevents local overheating of the feed material close to the entry (i.¢., the input opening 114) of the feeder tube. In an embodiment, the cooling means comprises a cooling channel that is in contact with the feeder tube and in which a cooling fluid is circulated.

Additionally or altematively, the apparatus may comprise one or more thermal devices 115, 117 that locally heat or locally cool the housing (and/or if present the die).

For example, a cooling device 115 may be arranged in proximity to the output opening or output opening 116 to prevent that the temperature of the softened material at the output opening becomes too high. A heating device 117 may be arranged closer to the input opening for pre-heating. Other arrangements of cooling and/or heating devices are conceivable as well.

Figures SA. 5B show a perspective view of an output opening according to an embodiment of the apparatus.

In Figure 5A, 5B embodiments of end plates 160, 162 comprising an output opening are shown in a position when mounted below the die of the friction stir apparatus.

Figure 5A shows an output opening in a “flat” arrangement 160. During operation, extruded or printed material from the output opening is deposited on a substrate that is positioned under the output opening. The printed material can spread out freely without lateral geometrical restrictions based on the ability of the material to deform under the local thermo-mechanical conditions employed.

Figure 5B shows an output opening in an arrangement 162 with two guiding elongated ridges 164 extending parallel on opposite sides of the output opening 116. The guiding ridges 164 create a printing/extrusion channel 1161 into which material from the output opening is extruded/printed on a substrate during operation. The guiding ridges limit the spread of the printed material on the substrate to substantially the width between the guiding ridges. This arrangement allows printing/deposition of line shaped layers with substantially a same width as the width between the guiding ridges. In an alternative arrangement the output opening is arranged with a single guiding ridge to provide a guiding edge along which softened material can be deposited.

The friction stir apparatus according to the invention as described above can be used for additive manufacturing (3D printing) of materials that can undergo plastic deformation within the volume between the transport screw and the inner cavity. Within temperature limits for the housing (and if present the die) and the transport screw and taking into account the melting point of a feed material, many metals, metal alloys and metal matrix composites can be printed. Without any limitation such materials comprise at least light metal alloys, aluminium and aluminium-based alloys, magnesium and magnesium alloys, and soft metal alloys such as copper-based alloys but the skilled in the art will appreciate that other metals or alloys can be printed depending their material properties and the characteristics of the apparatus, in particular the materials of which the apparatus is constructed.

The use of a feeder tube allows the use of metal wire or metal rod in a (semi)continuous fashion, next to the use of metal-based chips, grains or fines.

Also, the invention envisages the application of two (or more) feeders connected to the cavity in the housing which would allow a mixing of two (or more) materials shortly before the extrusion process.

The mvention has been described with reference to some embodiments. Obvious modifications and alterations will occur to others upon reading and understanding the preceding detailed description.

Itis intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims.

Claims

Conclusions

A friction stir extrusion apparatus for extruding material, the apparatus comprising a stationary housing, a screw conveyor and a feeder, the housing comprising a body having a circular cavity defined by an inner wall of the body and extending along an axis of rotation and having an inlet port to the cavity for feed material and an outlet port for extruded material: wherein the lead screw has one or more helical ridges along its length, is disposed at least partially within the cavity with the longitudinal axis of the lead screw coincident with the axis of rotation of the the cavity and is arranged to rotate within the cavity: wherein the feed device is arranged to feed the feed material to the input opening, wherein at least a first portion of the cavity tapers towards the output opening and the lead screw is tapered along at least the first part of h olte, and a first gap perpendicular to the axis of rotation and a second gap parallel to the axis of rotation are arranged between an outer diameter of the at least one helical edge of the lead screw and the inner wall of the cavity. both of which are constant and non-zero along at least the first part.

The apparatus according to claim 1, wherein a diameter of a tip of the screw conveyor at the level of the outlet opening is less than a diameter of the opening of the outlet opening.

The apparatus according to claim 1 or 2, wherein a second portion of the cavity at the entry opening of the cavity is cylindrical and a diameter across the at least one helical edge of the lead screw is constant in the second portion of the cavity.

The apparatus according to any one of the preceding claims, wherein the lead screw comprises a projection extending beyond the output opening, the projection having a thread on a periphery of the projection.

The apparatus according to any one of the preceding claims 1 or 2 or 3, wherein the outlet opening is provided at a bottom of the cavity and coincides with the location of the axis of rotation, at a level below the tip of the lead screw with a third gap , non-zero, parallel to the axis of rotation between the tip of the lead screw and a level of the output port.

The apparatus according to any one of the preceding claims 1, 3 or 5, further comprising: a die either integrated with or mounted on the output opening, the die having a smaller opening than the opening of the output opening.

The apparatus according to any one of the preceding claims 1-6, wherein the delivery device comprises a tubular channel having a distal end communicating with the insertion port and a proximal end configured to receive the delivery material.

The apparatus according to claim 7, wherein the supply device comprises a cooling device for cooling the feed material.

The device of claim 8, wherein the cooling device is disposed in or on the distal end of the tubular channel.

The apparatus according to claim 8 or claim 9, wherein the cooling device is a cooling channel for containing a cooling fluid and the cooling channel is in thermal contact with the tubular channel.

The device according to any one of the preceding claims 7-10, wherein the tubular channel extends substantially perpendicular to the axis of rotation of the cavity.

The apparatus according to any one of the preceding claims 1-11, further comprising: a thermal device for controlling the temperature in a first region of the housing adjacent the input opening and an input portion of the first portion of the cavity and/or or in a second region of the housing.

The apparatus of claim 12, wherein the thermal device is configured for heating in the first region.

The apparatus according to any one of the preceding claims 1-13, further comprising: an additional thermal device for controlling the temperature in a second region of the housing adjacent the exit opening of the cavity.

The apparatus according to claim 14, wherein the additional thermal device is arranged for cooling in the second region.

The apparatus according to any one of the preceding claims 1 - 15, further comprising: a movable table for holding a workpiece in proximity to the output opening, the table being movable in at least two orthogonal directions relative to the output opening .

A printer apparatus for printing solid material, comprising a print head comprising a friction stirrer extruder according to any one of the preceding claims 1 - 16.

A method of extruding material through a friction agitation extruder according to any one of the preceding claims, comprising: feeding feed material into the feed port by means of the feed device; driving the material from the feed device to the discharge opening by rotating the screw conveyor within the cavity to soften the material by plastic deformation as the material passes between the screw conveyor and the inner wall of the cavity, and performing the material in the softened state from the exit port, the plastic deformation comprising applying force to the material to move through a first portion of the cavity between the inner wall and the screw conveyor, the inner wall of the cavity being provided to taper to the exit opening and the screw conveyor within the cavity is tapered along at least the first portion of the cavity such that the material is plastically deformed as it passes between the screw conveyor and the interior wall of the cavity, with a first gap perpendicular to the axis of rotation and a second gap parallel to the axis of rotation between and an outer diameter of the helical edge of the lead screw and the inner wall of the cavity of constant size. non-zero, are along at least the first part of the cavity.

The method according to claim 18, wherein a diameter of an end of the screw conveyor at the output opening is smaller than a diameter of the opening of the output opening, the method further comprising: additive manufacturing by applying the softened material from the output opening on a substrate or surface.

The method according to claim 18, wherein a mold is either integrated or mounted on or at the output opening, the mold having an opening with a smaller size than the diameter of the output opening, the method further comprising: additive manufacturing by extruding the softened material from the opening in the mold.