DE102018101845A1 - Blind-flow screw connection of materials - Google Patents

Abstract

It is a two-part mechanical fastener comprising an elongate body having a bore slidably supporting a mandrel adapted to engage the body. The fastener body has one or more protuberances on its outer surface. In one aspect, the protuberances form a thread. The fastener is configured to form and penetrate an opening in a stack of two or more workpieces. To secure the workpieces in the stack of workpieces and form a robust connection, the fastener body is deformed by the mandrel, thereby expanding the body so that a body end engages one surface of the workpiece stack and the one or more protuberances with the walls of the opening be engaged. Methods of using such a fastener to fasten non-ferrous or polymer-based sheet-like workpieces together are disclosed.

Description

TECHNICAL AREA

The technical field of this disclosure relates to mechanical fasteners and methods for using such fasteners to secure together two or more layers of materials that may be similar or dissimilar in structure and / or composition.

INTRODUCTION

Automotive vehicles, including automobiles and light trucks, use a wide variety of materials, including steel sheets having a tensile strength of from about 300 MPa to over 800 MPa, non-ferrous alloys such as cast and kneaded aluminum and magnesium alloys, and polymers including reinforced polymers. A vehicle body or structure results from the assembly of many parts and components that are robustly secured together and arranged so that the assembled components can cooperate to accommodate the loads applied to the body or structure. The extensive range of potential materials requiring attachment makes mechanical fasteners an attractive option, as mechanical fasteners can be adapted to interconnect and secure a variety of components from a wide range of materials of similar or dissimilar materials.

SUMMARY

A two-part fastener is disclosed wherein each part is made of a ferrous material to form a structural bond between two or more layered workpieces. Suitable workpieces include cast and forged aluminum and magnesium alloys and polymer based workpieces such as filled polymers and particulate and fiber reinforced polymers, including woven fibers.

The fastener includes a hollow, elongated, cylindrical or conical body having a pivot axis. The fastener body has a length, first and second ends, a bore of generally uniform inner diameter, and an outer surface. The fastener body terminates at the first end in an annular cap having an inner diameter equal to the diameter of the body bore and an outer diameter sized to project beyond the outer surface of the body.

The outer surface of the body may have one or more outwardly extending protruding features circumscribable by a circle centered on the body axis and having a diameter smaller than the outer diameter of the annular cap. The fastener may also include a mandrel positioned within the body bore, having a shaft sized to slidably engage the bore, and an end projecting out of the bore, a mandrel head sized to engage with engages the opposite end of the mounting body. The fastening element can be rotated about the axis of rotation. When a rotating fastener is brought into contact with a workpiece, the mandrel head can be adapted to frictionally engage and heat the workpiece, or to cut and mechanically remove workpiece material.

In one aspect, the protuberances may be threaded. In other aspects, the protuberances may be continuous or segmented ridges or isolated, equi-dimensional, or different sized isolated features.

The fastener described above may be used to join two or more workpieces to a clamped stack of workpieces by rotating the fastener about the fastener pivot axis as the fastener is advanced to the upper surface of the upper workpiece of the workpiece stack in a butting area. The rotating fastener is advanced into initial engagement with the surface of the workpiece stack and can be selectively held in contact with the workpiece surface while rotating for a time sufficient to frictionally heat the workpiece. The rotating fastener is then advanced further into the workpiece stack until the opposite end of the fastener penetrates and extends beyond the lower outer surface of the workpiece and the underside of the fastener cap contacts the outer surface of the upper workpiece. When this occurs, both the rotation and the feed of the fastener are adjusted.

Then, a continuously increasing force is exerted on the mandrel along the fastener axis in a direction that promotes engagement of the mandrel head and the body opposite end while supporting the body of the fastener such that the mandrel head engages the body end and deforms the body end and collapses until the mandrel shaft breaks and thereby the workpieces attached to each other.

In one embodiment, the bonding process may be performed while preheating the workpiece stack using resistance heating, induction heating, or laser heating.

list of figures

• 1 Figure 4 is a representative embodiment of a first aspect of a fastener having an externally threaded body and a mandrel having a head that is smaller than the diameter of the smaller diameter thread;
• 2 is another representative embodiment of a first aspect of a fastener having an externally threaded body and a mandrel having a head that is smaller than the diameter of the smaller diameter thread;
• 3 shows a disassembled embodiment of a threaded fastener as shown in FIGS 1 and 2 is shown;
• 4 illustrates a method of using the fastener of 1 . 2 and 3 to bond a stack of workpieces consisting of two superimposed elements with glue applied to the mating surface;
• 5 illustrates a method of using the fastener of 1 . 2 and 3 to bond a stack of workpieces consisting of two superimposed elements with glue applied to the mating surface;
• 6 illustrates a method of using the fastener of 1 . 2 and 3 to bond a stack of workpieces consisting of two superimposed elements with glue applied to the mating surface;
• 7 illustrates a method of using the fastener of 1 . 2 and 3 to bond a stack of workpieces consisting of two superimposed elements with glue applied to the mating surface;
• 8th illustrates a method of using the fastener of 1 . 2 and 3 to bond a stack of workpieces consisting of two superimposed elements with glue applied to the mating surface;
• 9 illustrates an alternative mandrel head geometry;
• 10 illustrates another alternative mandrel head geometry;
• 11 illustrates yet another alternative mandrel head geometry;
• 12 Figure 4 illustrates a representative embodiment of a second aspect of a fastener in which the fastener body has webs extending outwardly;
• 13 Figure 4 illustrates a representative embodiment of a second aspect of a fastener in which the fastener body has co-sized, co-molded protuberances;
• 14 Figure 4 illustrates a representative embodiment of a second aspect of a fastener in which the fastener body has variably shaped protuberances;
• 15 shows in plan view a heating and clamping device for carrying out a further embodiment for connecting a workpiece stack consisting of two superimposed workpieces with adhesive applied to the mating surface;
• 16 shows in sectional view a heating and clamping device for carrying out a further embodiment for connecting a workpiece stack consisting of two superimposed workpieces with adhesive applied to the mating surface;
• 17 shows in plan view a heating and clamping device for carrying out a further embodiment for connecting a consisting of two superimposed workpieces workpiece stack with adhesive applied to the mating surface and for illustrating the operation of a heating and clamping device; and
• 18 shows in sectional view a heating and clamping device for carrying out a further embodiment for connecting a consisting of two superposed workpieces workpiece stack with adhesive applied to the mating surface and for illustrating the operation of a heating and clamping device.

DETAILED DESCRIPTION

Exemplary two-piece male threaded fasteners, which are a first aspect 10 . 10 ' are in the 1 and 2 shown and disassembled form 10 "in 3 ,

Referring first to 3 includes the fastener 10 " a body 12 " and a thorn 14 " that a spike shaft 27 " and a thorn head 28 " includes. The mandrel shaft 27 " slides slidably into the hole 16 " in the corpus 12 " , When in the fasteners 10 . 10 ' ( 1 . 2 ), the spines can 14 . 14 ' temporarily against relative sliding or against relative rotational movement with the body 12, 12 'by the elongated bore engagement features 18 " be secured, as in 3 shown. The carcasses 12 . 12 ' . 12 " have external threads 20 . 20 ' . 20 " with a major diameter of 2 mm to 10 mm and a crest-root dimension of 0.3 mm to 2.5 mm, extending from an annular cap 22 . 22 ' . 22 " located at one end of the carcasses 12 . 12 ' . 12 " located, to an opposite end of the cabinet 24 . 24 ' . 24 " extend. The carcasses 12 . 12 ' . 12 " For example, a generally conical outer surface that tapers from the annular cap end to the opposite end may be attached to the body 12 " or a generally cylindrical outer surface as shown on the carcasses 12, 12 '. Suitably, the annular cap 22 for example, have an outer diameter which is 2-5 times the diameter of the body at the position immediately adjacent to the cap.

The thread pitch on the carcasses 12 . 12 ' . 12 " can be coarse, as with the fastener 10 " or fine as in the fastener 10 or with an intermediate distance, as in the fastener 10 ' , Although the examples shown have a fixed pitch along the body length, a variable pitch thread can also be used. Suitable thread pitches include 0.2 mm to 4 mm. Many thread variants are known to those skilled in the art of fasteners, including, but not limited to, UNC, UNF, BSW, BSF, metric, and BA. The carcasses 12 . 12 ' . 12 " can contain any of these threads as well as other non-standard or unrecognized thread variants.

The carcasses 12 . 12 ' . 12 " may be any suitable length, provided that it is sufficient to penetrate and extend from a stacked array of workpieces, each generally in sheet form, as further described below.

The spines 14 . 14 ' . 14 " are generally noticeably longer than the carcasses they occupy, with the waves 27 . 27 ' . 27 " cover most of their length. The waves 27 , 27 ', 27 "can have latching features like 26 on the shaft 27 (please refer 1 ) and 26 'on the shaft 27 ' ( 2 ), which allow a reliable transmission of a tensile force (F- see 1 . 2 ) to pull the mandrel out of the carcass. The mandrel shafts 27 . 27 ' , 27 "have a generally uniform, bore lubricious cross section and terminate in a mandrel head 28 . 28 ' . 28 " with a cross-sectional dimension that is larger than the dimensions of the respective holes 16 . 16 ' 16 ", so the spines 28 . 28 ' . 28 " when applying the tensile force "F" ( 1 . 2 ) with the opposite body ends 24 . 24 ' . 24 " their respective carcasses 12 . 12 ' . 12 " interfere.

The holes shown 16 . 16 ' . 16 " are cylindrical and sized to have corresponding cylindrical mandrel shafts 27 . 27 ' . 27 " take up. It will be understood, however, that holes and shafts may have alternative cross-sections, including polygonal, oval, and star-shaped, provided that they have a complementary shape and are dimensioned to be slidably intermeshed. Non-cylindrical bore and shaft cross-sections can engage in a disturbingly rotating manner, thereby obviating the need for features such as those in Figs 3 Shaft projections shown 18 " , and prevent relative rotation of the spine and the body.

Each of the thornheads 28 . 28 ' . 28 " is as a cylinder with a flattened end 29 , 29 ", 29", however, as described in more detail below, multiple shapes may be used 3 the example shown serves as a rejuvenation 30 " in addition, the mandrel head diameter 28 " smoothly to the shaft diameter 27 " to convict. When applying a force "F"', as in the 1 . 2 is shown, the mandrel head is used to drill the hole 16 " at the opposite end 24 " progressively and evenly expand to the opposite end 24 " to spread and enlarge its diameter when the mandrel head gradually into the hole 16 " is advanced.

The use of such a fastener s is in the 4 . 5 . 6 . 7 and 8th shown. In 4 is a two-layer stack of sheet-shaped workpieces 32 and 34 , possibly with at their abutment surfaces 33 . 35 arranged adhesive 36 , firmly clamped together under suitably distributed opposed clamping pressures P, around the workpiece abutment surfaces 33 . 35 in the joining zone 100 at least to bring in contact. The fastener 110 that is essentially the same as the one in 1 shown fastening element, but with coarser threads 121 on the body 120 and with a more rounded headboard 129 is mounted in a machine (not shown), which can perform both a rotational and a longitudinal movement, at least attached to the mandrel shaft 114. The machine may include a gripping device such as a chuck or a collet having latchable features 126 the wave 127 of the thorn 114 engaged come and also with the annular cap 122 either frictionally or mechanically (not shown) may engage to hold the fastener 110 securely. The machine then turns the fastener in one direction 40 while at the same time the fastener in one direction 38 is advanced to the now rotating fastener in the direction of the joining zone 100 to press in the area 129 of the thorn's head 128 with the area 31 of the workpiece 32 in the joining zone 100 comes into contact.

An intervention of the surface 129 of the thorn's head 128 with the area 31 of the workpiece 32 leads to a friction heating in the joining zone 100 , For materials such as non-ferrous alloys and polymers, including reinforced polymers, such heating, initially at about room temperature or 20-25 degrees Celsius, reduces their strength, makes them less resistant to penetration, and makes them more flowable. Thus, the advancement of the fastener 110 in first the workpiece 32 and then optionally the adhesive 35 and finally the workpiece 34 as it is in 5 is shown to proceed with less pressurization along the direction 38 than if the workpieces had remained at room temperature.

In one embodiment, when the fastener is initially applied to the surface 31 of the workpiece stack, the advancement is temporarily stopped and the fastener is rotated at high speed to maximize friction heating, resulting in a dwell time. Then, the rotational speed of the fastener is slowed down and advancement of the fastener is re-initiated so that advancement and rotation of the fastener into the clamped workpieces is coordinated to increase the pitch of the thread 121 to replicate. Thus, the fastener may generally be "screwed" into the softened, flowable workpieces with some displaced workpiece material being the screw thread 121 and excess displaced material is expelled from the openings in the workpieces created by the leading fastener

With continued advancement, 6 , the fastener penetrates 110 in the workpieces and brings the bottom 123 the annular cap 122 in engagement with the surface 31 of the workpiece 32 and causes the spike head 128 and the opposite end 124 of the body 120 the surface 37 of the workpiece 34 penetrate and extend beyond them, as in 6 shown. The length of the body is expedient 120 selected to make sure the section of the carcass 120 that is under the workpiece surface 37 extends, is in the range of 2-5 mm.

After the fastener 110 has completely engaged both workpieces, as in 7 shown, and while the clamping pressure P continues on the workpieces 32 . 34 is maintained, the rotation is 40 and advancing in the direction of the arrow 38 interrupted and a traction "p" is on the shaft 127 ( 4 . 5 ) of the fastener mandrel 114 exerted and an opposite reaction force "p" is applied to the annular cap 122 applied. The force "p" due to the interaction between the bore 16 " and the spike head 28 " ( 3 ) on the thorn 114 is exercised initially spreads the opposite end of the body 24 " ( 3 ) and this collapses and this body section 120 extends under the surface 37 ( 6 ). The spread and / or collapsed section 112 of the body 120 now has a larger diameter than the original exposed end diameter and the same sized hole in the workpiece 34 caused by the penetration of the opposite end 124 ( 6 ) was caused. Thus, the collapsed portion becomes 112 the surface 37 of the workpiece 34 mediate capture while the annular head 122 the area 31 of the workpiece 32 mediating captured to the workpieces 32 and 34 securely connect with each other.

As the force "p" continues to increase (and corresponding reaction force), the exposed workpiece end will continue to collapse and deform until the mandrel shaft 126 breaks and the remaining portion 114 ' of the thorn 114 with the collapsed body section 112 and the remaining, undeformed body section 212 comes into contact ( 8th ). If the optional adhesive layer 36 can be optionally hardened in the workpiece stack to develop a complete joint strength.

In the in the 4 - 8th illustrated embodiment, two workpieces were joined together. In the described / illustrated method, the type and composition of the workpieces was not addressed. It should be understood, however, that any workpieces that significantly soften at temperatures below the softening temperature of the ferrous fastener may be bonded by such a method. Non-ferrous alloys of aluminum and magnesium satisfy this requirement as well as thermoplastic polymer-based workpieces, whether reinforced or not, so that any combination of workpieces of these compositions can be suitably joined using the method described. It can also be seen that the method is not limited to just two Workpieces is limited, and that with a suitable choice of the length of the fastener body, a plurality of workpieces with or without adhesive can be connected to each other at their respective mating surfaces.

Alternative mandrel designs can be used. Some additional, non-limiting examples are in the 9 . 10 and 11 shown and include an ellipsoid 228 , a cone 328 and a ball 428 with an outwardly extending blade-like feature 440 , These mandrel head designs can heat, soften, and displace workpiece material (s), or, in some cases, also cut and mechanically remove a portion of the workpiece material (s). For example, the ellipsoid 228 and the flattening 29 ( 1 ) serve primarily to soften and displace the material. The ball-with-blade construction, in 11 is shown cutting and softening the workpiece material with the rotating blade-like feature cutting a small central hole and the rotating ball friction heating the remaining material. Geometric modifications can be made to this illustrated head design to modify its behavior. For example, the conical head 328 be modified with grooves extending along the axis of the fastener to induce a larger cutting action as needed. The choice of mandrel may be influenced by the workpiece material (s). For example, it may be preferable to use a mandrel head construction for fiber reinforced composites that predominantly displaces material rather than cutting to minimize any distortion of the reinforcing fibers.

Each of the spine head designs 228 and 328 is shown to have a tapered feature 130 , which engages in the body bore and allows a generally uniform expansion of the body when pulling out the mandrel, passes to the mandrel shaft diameter. Alternatively, the geometry of the head may be such as to provide a gradual engagement of the head with the bore, such as in FIG 11 shown ball 428 so that no taper at the connection of mandrel head and mandrel shaft must be introduced.

For a suitable fastener performance, the diameter "d" ( 9 ) of the mandrel head is equal to or smaller than the smaller diameter "D" of the thread at the opposite end 224 be. (In general, the mandrel head is symmetrical about the axis of rotation of the fastener and thus the area of the mandrel head workpiece contact is circular and may be characterized by a diameter "d".) This ensures that the resulting cylindrical cavity remaining after the Material has been moved or removed during the penetration of the rotating fastener, a diameter equal to or smaller than the smaller thread diameter on the diameter of the fastener body. Thus, at least a portion of the displaced, heated and softened material can be "packaged" as the fastener advances into the threads, or the fastener can be threaded into the workpiece stack. Upon cooling, the now stronger, previously softened material will engage the fastener body to improve joint strength. In general, the ratio of the diameters d / D may be in the range of 0.7 to 1.

Similar practices relating to the rotation and advancement of the fastener may be followed when using the fasteners with more irregular workpiece engaging features as shown in FIGS 12 . 13 and 14 shown fasteners 70 . 70 ' . 70 " are shown. Each of these fasteners has outwardly extending protruding features 78 . 78 ' , 78 "on the body 82 on. The protruding features may be continuous and extend in a continuous band around the circumference of the body or may be local and appear as isolated, spaced-apart features. The protuberances can vary in number, shape and size. For example, in 12 prominent features 78 sharp, pointed lands analogous to the thread-like features discussed above may be continuous or segmented and may be uniformly sized as shown; In 13 are the salient features 78 ' uniformly large, isolated and rounded and generally resemble small hills; and in 14 are several prominent features 78 " shown with different shapes and sizes. In these fasteners, however, the dimension d, the maximum dimension of the mandrel head 76 greater than the diameters D, D ', D''corresponding to the diameters of the circumscribing circles 80 . 80 ' . 80 "Match that on the rotation axis 90 of the fastener are centered. In some cases, it may be appropriate to use only a single protuberance instead of the plurality of protuberances shown.

When the fasteners 70 . 70 ' . 70 " rotated into a workpiece stack and advanced, as described above, the size of the hole in the workpieces, by the friction effect of the mandrel head 76 is generated, larger than it for receiving the mounting carcasses 82 . 82 ' . 82 " is required. Thus, the Feed rate of the fastener into the workpieces not by the necessity that the protuberances engage in the softened material, are determined cooperatively. Instead, the fastener may be advanced into the workpieces at any desired speed, subject to only the machine limitations of applied load and feed rate. Once the thorn 74 is fully inserted, ie when the bottom of the cap 72 When it touches the upper surface of the uppermost workpiece, it can be withdrawn and broken as described above around the fastening body 82 to expand and compress and the protuberances 78 , 78 ', 78 "into engagement with the walls of the hole just formed in the stack of workpieces 12 . 13 and 14 The ratios d / D, d / D ', d / D "shown are each in the range of 1.02 - 1.05, the degree through which the mandrel passes 74 on the mounting carcass 82 minimizes deformation experienced, which ensures good engagement of the mounting body with the workpieces, but higher ratios of up to 1.2 also provide an acceptable holding force.

In this aspect, the retraction of the spine 74 be firmly coordinated with the achievement of full penetration of the fastener in the stack of workpieces and the elimination of the rotation of the fastener or synchronized. This will be the deformation of the mounting carcass 82 while the area surrounding the hole in the workpieces is still at an elevated temperature, thereby reducing the load on the drive protuberances 78 . 78 ' . 78 " engages with the workpiece stack, is reduced. It may be convenient to use high speed rotation and limited feed rate of the fastener to expand by expansion the amount of heated area of the workpiece stack to further facilitate engagement of the protuberances with the workpiece stack. It should be understood that in this aspect, not the entire range of mandrel head designs shown and described may be suitable, and that only mandrel head designs that place emphasis on friction rather than cutting are most appropriate for this aspect.

In another embodiment, which is applicable to both aspects, the upper workpiece can be externally heated. Such heating is complementary to frictional heating and serves to reduce the cycle time for the attachment of the fasteners by reducing the amount of frictional heating and thus reducing dwell time or time while the rotating mandrel head is in a fixed position in frictional interference with the workpiece surfaces is maintained and generates heat. In one aspect, which is suitable for use on metallic or electrically conductive workpieces, is a combination clamp / combiner 50 with an annular, electrically non-conductive body 52 , the two independent electrically conductive segments 54 . 54 ' contains, in 15 in plan view and in 16 shown in sectional view. As in 16 shown exercises the clamp / conductor 50 Pressure on the surface 31 of the workpiece 32 ' (opposite clamp or carrier not shown), on a on the workpiece 34 positioned electrically conductive workpiece, and optionally between the workpieces 32 ' and 34 applied adhesive 36 out. The electrical wires 56 , 56 'are each with ladders 54 . 54 ' connected. As shown, DC power is provided, with each of the lines 56 and 56 ' is connected to an electrical source (not shown) and has opposite polarities, but alternating current would be equally well suited.

In operation, as in the plan view in 17 and in the sectional view in 18 shown, the current flows 58 from the electrode 54 through the workpiece 32 ' to the electrode 54 ', thereby inducing resistance heating in one region 60 in the workpiece 32 '. If a fastener 210 with its axis generally collinear with the axis of the annular bracket / conductor 50 is positioned in the in the 4 - 8th advanced manner, it encounters a heated, softened area 60 and therefore requires less frictional heating to penetrate and extend through the workpieces.

The specific example shown is exemplary and representative only of the external heating mode. As further examples, induction heating using an annular disk centered on the axis of the fastener may also be suitable for conductive workpieces and laser heating, where an externally focussed laser may be applicable to a wide range of workpieces including electrically conductive workpieces, such as polymer-based workpieces. If necessary, the efficiency of such a laser-based heating system can be improved by applying an absorption-enhancing coating to the workpiece.

The above description of the exemplary embodiments and specific examples are merely descriptive in nature; They are not intended to limit the scope of the following claims. Each of the terms used in the appended claims should be understood in its ordinary and general meaning, unless expressly stated otherwise in the specification.

Claims (10)

A fastener for forming a structural connection between two or more layered workpieces, the fastener comprising: a hollow, elongated body having a rotation axis, a length, first and second opposite ends, a bore having an inner surface and an outer surface, the body terminating at the first end in an annular cap having an outer diameter, the outer surface of the body having one or more outwardly extending protruding features, wherein the protruding features are rewritable by a circle centered on the body axis, the circumscribing circle having a diameter smaller than the outer diameter of the body annular cap, and a mandrel having a shaft terminating in a head, the mandrel extending along the body axis, the shaft slidably engaging the inner surface of the body, and the head disposed outside the body at the second end, the mandrel having a larger diameter Length as the body length, wherein the mandrel has a head which is dimensioned so that it interferes with the opposite second end of the body interfering. Fastener after Claim 1 wherein the protuberance is a thread having a pitch, a large diameter and a smaller diameter, the thread diameter defining the rewritable diameter and the mandrel head being characterized by a diameter greater than the body bore but smaller than the smaller diameter thread the opposite end of the mounting body. Fastener after Claim 2 wherein the thread pitch is uniform. Fastener after Claim 2 wherein the mandrel head is adapted for frictional engagement with the surface of a workpiece when the fastener is rotated in contact with a workpiece surface, and wherein the mandrel head additionally has features for cutting the workpieces. Fastener after Claim 1 wherein the protruding feature is continuous or local. Fastener after Claim 1 wherein the mandrel head is adapted for frictional engagement with the surface of a workpiece when the fastener is rotated and brought into contact with the workpiece during rotation, the mandrel head being characterized by a diameter greater than the diameter of the circumscribing circle, and wherein the protuberances are offset outwardly from the fastener axis when the mandrel head is forced into engagement with the body. A method of joining two or more workpieces using a mechanical fastener with a rotation axis, the method comprising: forming a layered stack of workpieces, the stack having an upper workpiece with an upper surface and a lower workpiece, applying pressure on the upper and lower workpieces of the stack to clamp the workpieces, rotating the fastener about the fastener rotation axis as the fastener is advanced to the upper surface of the upper workpiece of the workpiece stack into an abutment region, wherein the fastener comprises: a hollow, elongate, cylindrical or conical body having a body axis coincident with the axis of rotation of the fastener, a length, first and second ends, a bore of generally uniform inner diameter and an outer surface, the body at the first end e in an annular cap having an inner and an outer diameter, wherein the inner diameter of the annular cap is equal to the carcass bore, wherein the outer surface of the fastener body has one or more outwardly extending, protruding features, wherein the protruding features are rewritable by a circle centered on the body axis of rotation, the circumscribing circle having a diameter smaller than the outer diameter of the annular cap, and a mandrel having a shaft terminating in a head, the mandrel extending along the body axis, wherein the shaft is slidably engaged with the body inner surface and the head is positioned outside the body at the opposite body end, the mandrel having a length greater than the body length, the mandrel having a head sized to he with the opposite end of the ko rpus interferes, continuing advancement of the fastener into the workpiece stack until the opposite end of the fastener penetrates and extends beyond the lower workpiece outer surface and the lower surface of the fastener Fastener cap the outer surface of the upper workpiece contacts interrupting both the rotation and advancement of the fastener, and applying a continuously increasing force to the mandrel along the fastener axis in a direction that promotes engagement of the mandrel head and the body opposite end the body of the fastener is supported so that the mandrel head interferes with the body end to deform and collapse the body end until the mandrel shaft breaks to separate a portion of the mandrel shaft from the fastener. A method of joining two or more workpieces using a mechanical fastener Claim 7 wherein the protuberance is a continuous thread having a pitch, a large diameter and a small diameter, and wherein the feed rate and rotation of the fastener into the workpiece stack cooperate to correspond to the thread pitch and wherein the mandrel head is characterized by a diameter larger than the body bore but smaller than the smaller diameter thread at the opposite end of the mounting body. A method of joining two or more workpieces using a mechanical fastener Claim 7 in which the workpiece stack is heated externally. Method for joining two or more workpieces using a mechanical fastener according to Claim 7 wherein the rotating fastener is advanced in stages, a first stage during which the rotating fastener is initially brought out of contact with the workpiece stack into contact with the workpiece, a second stage in which, when the mandrel head is an upper surface contacting the upper workpiece of the workpiece stack, stopping the feed, and holding the mandrel head in contact with the upper surface to heat and soften at least the upper workpiece of the workpiece stack and a third stage in which the rotating fastener is advanced again; to drive the rotating fastener into the stack of workpieces.

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