GB2558668A

GB2558668A - Fabrication method

Info

Publication number: GB2558668A
Application number: GB1700811.1A
Authority: GB
Inventors: Brewer Jon
Original assignee: Avdel UK Ltd
Current assignee: Avdel UK Ltd
Priority date: 2017-01-17
Filing date: 2017-01-17
Publication date: 2018-07-18
Also published as: GB201700811D0

Abstract

A method of mounting a nut 2 to a sheet material 18 is disclosed in which a nylon screw 14 may be inserted into the nut 2 in order to sandwich the sheet material between the nut and the screw whilst an epoxy resin 22 cures hard. The nylon screw 14 is not susceptible to bonding with the epoxy resin 22 and also serves to prevent ingress of epoxy resin 22 to an internal thread of the nut 2.

Description

(54) Title of the Invention: Fabrication method

Abstract Title: Method of mounting a nut to a sheet or plate (57) A method of mounting a nut 2 to a sheet material 18 is disclosed in which a nylon screw 14 may be inserted into the nut 2 in order to sandwich the sheet material between the nut and the screw whilst an epoxy resin 22 cures hard. The nylon screw 14 is not susceptible to bonding with the epoxy resin 22 and also serves to prevent ingress of epoxy resin 22 to an internal thread of the nut 2.

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

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FIG.2

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FIG.6

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FIG.9

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FIG.10(d)

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FIG.11(a)

FIG.11(b)

FABRICATION METHOD

The present invention relates to a novel fabrication method and also to products manufactured using this method.

Methods of fabrication wherein one component is bonded or otherwise connected or coupled to another are known. Techniques for coupling components to one another can include welding, screwing, riveting, gluing, swaging, curing or the like. Each technique will be chosen for its own particular properties either to best fit with the manufacturing application, or else with the environment in which the finished assembled product will be used. For example, use of bare metals in damp or humid environments may mean avoiding welding or screwing, as rusting of the components, or even the weld material, may ensue.

In the field of carbon fibre component connection, for example, often gluing is the preferred coupling technique between component parts, as use of a curable or settable glue obviates the need for high coupling forces, and hence localised high pressures, to be applied between those components during assembly. If high forces (such as caused by high torque applied between a nut and a screw or between a rivet head and its setting mandrel) are used, there is the propensity for damage to be caused to the carbon fibre layers or filaments, which could compromise the structural integrity of the composite material forming the carbon fibre component. In certain fields, such as aviation or automotive assembly, the potential for structural compromise of components is not acceptable.

Considering, as an example, the automotive assembly industry, taking a car body panel fabricated from carbon fibre and desiring to form therein a threaded insert to serve as an anchor point for subsequent component mounting is a common occurrence. The technique of simply mounting of a threaded insert onto the surface of a panel may be unsuitable as the joint robustness may be unduly limited by the adhesive bond strength alone when subject to tensile and peeling loads. In contrast using a threaded insert with a through-hole in the panel means the insert can be positioned on the opposite face of the panel such that the mating screw clamping force helps compress the bonded interface between insert and panel thus providing relatively higher resistance to external loadings such as tension, bending loads and torque applied to the mating screw.

In such an example, the starting point for coupling the threaded insert to the carbon fibre body is to bore or drill a suitable mounting hole into the body. It is to, or within, this mounting hole that the threaded insert is to be coupled. Importantly, the coupling of the threaded insert must be a permanent process such that removal of the insert is not possible (or, if it is possible, only with physical deformation of the body). For a carbon fibre body, the preferred coupling agent is gluing.

Glue is normally applied to either or both the hole in the body and the threaded insert before bringing the two together. Once in contact, the insert should be held steady relative to the body until such times as the glue has set. This setting or curing process can be accelerated by, for example, exposure to ultra-violet radiation, or by heating. In any event, an issue of concern is to ensure that the body and the insert do not move relative to one another until the glue has set, as otherwise it is possible the glue material may spread into areas of the body or the insert where it should not be. This can be either an annoyance (such as when glue spreads over the surface of the body making it no longer smooth), or a problem (such as when glue is set within the insert thread). Where the glue used is an epoxy adhesive, once it has set, its removal may cause structural damage to the body material or even the integrity of the coupling between the body and the insert.

Unintended movement of the insert during curing may also create subsequent assembly issues as the thread of the anchor may be misaligned with the body relative to its intended position. Even minor movements of the individual inserts may accumulate across the whole structure to generate problems when later assembling large mating components such as car body panels. So the desire to avoid the problems or annoyances is an aim of the present invention.

In addition to avoiding the aforementioned problems, in the case of a manually-applied insert, it is desirable to avoid the hands of the worker being exposed to any glue. Not only is this distracting for the worker, but it can be a potential safety hazard, depending on the chemical composition of the glue employed. So it is another aim of the present invention to avoid the possibility of the worker coming into contact with glue.

Also, it may be desirable under certain circumstances for the worker, having installed the insert and whilst waiting for the glue to harden/cure, to be able to handle the body without compromising the bond between the insert and the body. For example it is common to want to install the insert but then transfer the whole panel to an oven to cure the adhesive. It is, therefore a further aim of the present invention to allow this.

According to the present invention, therefore, there is provided a method for mounting a fastening anchor to a material substrate comprising:

providing a material substrate to which a fastening anchor is to be mounted, which material substrate is formed with a through-hole therein;

providing a fastening anchor for mounting to the substrate via the through-hole, the anchor having an internal screw thread;

applying bonding agent to either or both of the substrate and/or the fastening anchor;

mounting the fastening anchor to the substrate via the through-hole;

providing a plastics screw having an external screw thread and a screw head;

inserting the screw into the fastening anchor screw thread thereby to sandwich the substrate between the plastics screw head and the fastening anchor until the bonding agent has set, and;

removing the plastics screw from the fastening anchor after the bonding agent has set.

By employing a plastics screw, the ability of any bonding agent to adhere/bond thereon is obviated, as the smooth plastics surface of the screw resists any permanent adherence of such bonding agent. This means that the plastics screw helps prevent ingress of bonding agent to the internal screw thread of the fastening anchor when the plastics screw is inserted therein. Also the presence of the plastics screw in the fastening anchor provides for manual handling of the substrate (via the plastics screw) without the possibility of any disturbance of the bonding agent until it has set/been cured. A further advantage of this fabrication method is that the plastics screw, when in engagement with the fastening anchor, effectively sandwiches the material substrate between the plastics screw and the substrate.

Preferably the plastics screw is inserted into the fastening anchor in advance of mounting the fastening anchor to the substrate.

Advantageously the bonding agent includes solid particles to space the fastening anchor from the substrate when mounted thereto. And the solid particles may be of known, predetermined dimensions thereby to control the spacing between the fastening anchor and substrate. The solid particles may comprise glass beads.

The bonding agent may comprise or include epoxy resin. And the material substrate may comprise carbon-fibre reinforced plastics.

The plastics material of the plastics screw can include or comprise one or more of: a nylon,

PTFE or PEEK. These materials from which the plastics screw may be formed all exhibit low surface energies, low porosity and have non-polar or non-functional surfaces. Because these materials have no functional sites or surface roughness onto which the bonding agent may effectively attach itself, then the plastics screw resists any adherence to bonding agent. This means removal of the plastics screw after the bonding agent has set/cured may be achieved by a low-torque manual process easily carried out by a worker without the need for any specialist tools.

Suitable choice of clamping torque may be applied whilst the bonding agent sets/cures.

According to a preferred embodiment removal of the screw from the fastening anchor after 10 the bonding agent has set can is one of: mechanical, thermal or chemical removal. The thermal removal of the screw may comprise melting the screw from the fastening anchor. This can be achieved by suitable choice of curing temperature to eventually exceed the melting point of the plastics screw such that the plastics screw melts entirely and flows out of the fastening anchor thread. The chemical removal of the screw may comprise corroding the screw from the fastening anchor. A suitable acid or alkali could be used for this purpose.

Advantageously the fastening anchor includes a spigot. Such a spigot may protrude from a flange of the anchor. And the spigot may have an outer diameter smaller than the diameter of the hole in the substrate. The spigot may assist with alignment between the nut and the holing the substrate.

Preferably the bonding agent is a glue, more preferably an epoxy adhesive.

Advantageously the fastening anchor is an internally-threaded nut, preferably of metal.

The material substrate may be formed from carbon fibre, particularly carbon fibre reinforced plastic and may have a circular hole formed therein for mounting the nut thereto.

The present invention will now be described, by way of example only and with reference to the accompanying drawings, of which:

Figure 1 shows a perspective view of a threaded nut in accordance with the present 5 invention;

Figure 2 illustrates schematically the nut of figure 1;

Figure 3 shows the nut of figure 1 and a nylon screw in accordance with the present 10 invention;

Figure 4 illustrates schematically a side view of the nut of figures 1-3 and the material substrate to which the nut is to be mounted;

Figure 5 shows a side perspective view of the nut mounted to the substrate;

Figure 6 shows a plan view from above (the front of the substrate) of the nut mounted to the substrate;

Figure 7 shows a plan view from below (the rear of the substrate) of the nut mounted to the substrate;

Figure 8 shows a side view of the nut mounted to the substrate with the nylon screw inserted into the nut;

Figure 9 shows a view from below of the nut mounted to the substrate with the nylon screw inserted into the nut of figure 8;

Figures 10 (a)-(d) show the nut and screw coupling in an alternative assembly method to those of the previous figures and;

Figures 11(a) and (b) illustrate schematically the bonded nut in a CFRP panel and the bonded nut securing an L-section bracket after mounting, respectively.

Referring firstly to figures 1 and 2, there is shown a fastening anchor, in this example a stainless steel threaded nut 2. The nut has in internal screw thread 4 formed within an annular projection 6, which projection 6 emanates from a flange 8. The flange 8 is of a diameter larger than that of the annular projection 6. On its obverse face, the nut 2 has a further, smaller annular projection, here spigot 10, the purpose of which will be explained below.

The screw thread 4 is able to engagingly cooperate with a mating screw thread 12 formed on a plastics screw, in this example nylon screw 14 shown in figure 3. The nylon screw 14 has a knurled head 16 which is adapted to be able to be grasped, held and rotated manually by a fabrication worker, as will be explained in more detail below. If desired, to permit for ease of rotation, the knurled head 16 may have formed therein a slot 17 (see Figure 10), of any suitable shape or form, to accommodate a mating screwdriver bit.

Reference now also to figure 4 illustrates how the nut is mounted to a substrate, in this example, a sheet of carbon-fibre reinforced plastics (CFRP) such as is utilised in the automotive industry for use in motor vehicle body panels or the like. In this example, the CFRP is provided as a sheet 18 and has formed therein, by known means, such as drilling, a round mounting hole 20. It is within the mounting hole 20 that the nut 2 will be placed. In order to place the nut 2 the rear side of its flange 8 is coated with a bonding agent, in this example a glue in the form of an epoxy resin (in this example SikaPower® 490C) 22. Preferably the epoxy resin 22 is a two-part adhesive. Alternatively, or additionally the epoxy resin 22 may be spread on the inside of the hole 20. This permits a flexible approach to bonding the nut 2 to the sheet 18, in that either or both of the nut and the sheet 18 may have the resin 22 applied thereto. Issues such as ease of access may dictate this choice.

It is preferred, although not essential, that the resin 22 contain glass beads of known, constant diameter. This ensures a known, controlled spacing of the flange 8 from the surface of the sheet 18. This is achieved by use of a consistent bond line thickness of the resin 22 as the sheet 18 and nut 2 are pressed together, as will be appreciated by those skilled in the art.

As the nut 2 is pressed into the hole 20 of sheet 18, the spigot 10 leads. Use of the (rear) spigot 10 to lead insertion of the nut 2 into the hole 20 ensures accurate alignment of the nut with the hole 20 and, hence, sheet 18. Specifically, it ensures a normal entry of the spigot such that it is concentric with the hole 20, when both the spigot 10 and the hole 20 are circular in cross-section. Whilst it is possible for the hole 20 and spigot 10 to be shapes other than circular (such as square or hexagonal), for ease of manufacture, circular shapes are preferred.

It should be appreciated that the fit of the spigot 10 within the hole 20 provides positive resistance to lateral movement of the nut under loads that might otherwise (should the nut 2 have been mounted upon the surface of the sheet 18) shear the bonded interface between nut and sheet. The diameter of the spigot 10 is less than that of the hole 20.

Reference also now to figures 5 and 6 show the nut 2 inserted into the hole 20 with the resin 22 visible on both the front face 24 and rear face 26 of the sheet 18. If desired, it is possible for the assembly worker to insert a threaded rod (not shown) into the nut 2 screw thread 4 to aid insertion of the nut 2 into the hole 20. An advantage of adopting such a technique is to avoid the chance of the worker touching the resin 22. Should that happen, either the resin 22 could be spread to parts of the nut 2/ sheet 18 where it is not wanted, or the worker's hands could become contaminated with hazardous chemicals. Both of these scenarios are best avoided.

Insertion of the nut 2 into the hole 20 may also be accomplished by automated means such as a robotic arm or pick-and-place unit.

Once the nut 2 has been inserted into the hole 20 and before the resin 22 cures, the nylon screw 14 is wound into screw thread 4 from the front side 24 so as to sit within the nut 2, as shown in figures 8 and 9. Insertion of the nylon screw 14 in this manner is temporary until such time as the resin has cured. As stated above, choice of a plastics material for the screw 14 is as a result of its relatively (compared to the stainless steel nut 2) waxy outer surface, to which the resin does not form a good chemical bond (either when cured, or not). Placement like this of the nylon screw 14 achieves a novel, dual purpose. Firstly it permits, via head 16, clamping of the sheet 18 between the nylon screw 14 and nut 2, thereby ensuring no relative movement may occur between the sheet 18 and nut 2 until the resin 22 has cured. Secondly, its presence within the screw thread 4 prevents ingress of any resin 22 thereto, which could otherwise prevent the subsequent use of the screw thread 4, as insertion of any further screws would be prevented by the presence of cured resin therewithin. Any resin which does, even inadvertently, contact the nylon screw 14 can be easily removed, as there is no strong chemical bond, as has been mentioned above.

A further advantage of insertion of the nylon screw 14 into the nut 2 while the resin 22 cures is that this permits immediate handling of the composite assembly without fear of any relative movement between the sheet 18 and nut 2 which could otherwise jeopardise the integrity of the bond therebetween.

Curing of the resin 22 is achieved in any known manner and is not, itself, relevant to the current invention. In this example, however, the resin is heated in an oven at 140°C for 30 minutes until set. Once the resin 22 has cured, removal of the nylon screw 14 is easy, requiring little torque and being readily achievable manually. The slot 17 in the head 16 may aid use of a screwdriver, or the like, if desired.

Those skilled in the art will appreciate that the nylon screw 14 may already be fitted inside the screw thread 4 when the nut 2 is inserted into the hole 20 of sheet 18. Such is illustrated with reference to Figures 10(a)-(d). The head 16 of screw 14 in this example is be distal to spigot 10 in this initial assembled condition and thus allow a worker to fit the nut 2 by handling only the screw head 16 thereby minimising the risk of resin 22 contacting their hands. The nylon screw 14, after fitting the spigot 10 into the hole 20 of sheet 18, as above, is then removed and refitted into the opposite end of the nut 2 via the hole 20 in the sheet 18. This procedure may obviate the desire to use a separate rod to mount the nut 2 in the hole 20 that has been described above. It also permits the screw 14 and nut 2 to be delivered by a supplier as a single assembled item and thereby reduce logistical complexity for the user.

Once nut 2 has been inserted into hole 20 and resin 22 cured, the mounted nut 2 serves, via its internal screw thread 4, as an anchor point for subsequent component mounting. For example and with reference now to Figures 11(a) and (b), the anchor point may be used to secure metal assemblies such as a pedal-box unit 28 or steering column mounting bracket 32 onto the CFRP bulkhead 27 of a motor car using high tensile screws or bolts to engage the screw threads 4 of each nut 2. The nut flange 8 being positioned on the opposite surface of the CFRP bulkhead 27 to the metal assembly provides resistance to pull-out forces being applied to the metal assembly. Equally the adhesive bonding of nut flange 8 plus the mechanical engagement of spigot 10 to the CFRP bulkhead 27 ensure excellent resistance to lateral movement of the combined metal assembly.

Those skilled in the art will appreciate that any method of curing or hardening the bonding agent will suffice. Although the examples of thermal and ultra violet curing have been given, the particular method by which the agent is set is not material to the present invention.

Furthermore, it will also be apparent that only if the head 16 of the plastics screw 16 is of larger diameter than the hole 20 in sheet 18 will the screw 14 be able to used to sandwich, under load, the sheetl8 between its head 16 and nut 2 (as, for example shown in figure 8 or 11).

Claims

1. A method of mounting a fastening anchor to a material substrate comprising: providing a material substrate to which a fastening anchor is to be mounted, which material substrate is formed with a through-hole therein;

mounting the fastening anchor to the substrate via the through-hole;

providing a plastics screw having an external screw thread and a screw head;

2. A method according to either claim 1 wherein the plastics screw is inserted into the fastening anchor in advance of mounting the fastening anchor to the substrate.

3. A method according to either claim 1 or claim 2 wherein the bonding agent includes solid particles to space the fastening anchor from the substrate when mounted thereto.

4. A method according to claim 3 wherein the solid particles are of known, predetermined dimensions thereby to control the spacing between the fastening anchor and substrate.

5. A method according to either claim 4 or claim 4 wherein the solid particles comprise glass beads.

6. A method according to any one of the preceding claims wherein the bonding agent comprises epoxy resin.

7. A method according to any one of the preceding claims wherein the material substrate comprises carbon-fibre reinforced plastics.

5

8. A method according to any one of the preceding claims wherein the plastics material of the screw includes or comprises one or more of: a nylon, PTFE or PEEK.

9. A method according to claim 1 wherein removal of the screw from the fastening anchor after the bonding agent has set can is one of: mechanical, thermal or chemical removal.

10 10. A method according to claim 9 wherein thermal removal of the screw comprises melting the screw from the fastening anchor.

11. A method according to claim 9 wherein chemical removal of the screw comprises corroding the screw from the fastening anchor.

12. A method according to any one of the preceding claims wherein the fastening anchor includes a spigot.

13. A method according to claim 12 wherein the spigot has an outer diameter smaller than 20 the diameter of the hole in the substrate.

Intellectual

Property

Office

Application No: GB 1700811.1 Examiner: Peter Macey