A

Report on

Aluminium Jointings

(Building Construction and Materials)

Submitted by:

Kandarp Rajyaguru

2010UAR139

ALUMINIUM JOINTINGS

Using the opportunities provided by the extrusion process for creative designs gives strong, stable, rapid and effective joints. Whether it is for joining one extrusion to another or for joining an extrusion to another material.

There are many advantages to be obtained by joining several smaller extrusions to a larger unit. Handling is easier. Pressing, surface treatment and a large amount of the machining can be done on a more rational basis. Smaller extrusions can be produced with less material thickness, better accuracy and in many cases lower die costs.

The different types of jointing in aluminium are as follows:

1. Screw ports2. Tracks for nuts or bolt heads3. Snap fit joints4. Joining profile to profile5. Telescoping6. Latitudinal joining7. Hinges8. T-joints9. Corner joints10.Riveting11.End Caps

Screw ports

The screw port can be threaded in the normal way for machine screws

Most commonly, screw ports are used directly for self-tapping screws. In these cases, the screw ports will have projections to centre the screws.

Here, a component is being fitted by screwing through a port at right angles to the profile. In such cases, the port should have a shoulder.

Placing screw ports at corners saves material. To ensure that screw head does not protrude beyond the contours of the profile at outer corners, pay special attention to screw head diameter.

A screw port along the length of as profile facilitates "stepless fastening" , i.e. screw joints can be made at any point along the profile.

Upper joint: A hollow profile joined to another profile via a screw port. To avoid unwanted flexing in the joint, the screw is driven directly through the bottom of the hollow profile. A single screw is sufficient - the hollow profile's flanges stabilize the design. After step drilling, the hole through which the screw is introduced can be hidden using a plastic plug.

Lower joint : The same solution, but without a hollow profile. The U-profile has tracks for the insertion of, for example, a metal or foil laminate strip.

Solutions with special screws that fill the screw head clearance hole are common in, for example, the furniture industry.

One way of avoiding step drilling and visible holes is to replace the hollow profile with two snap-fit profiles. This solution is often used in handrails.

Tracks for nuts or bolt heads

Continuous tracks enable stepless fastening with no need to machine the profile.

If a standard bolt is too long, it is not always necessary to find a shorter bolt. The track for the nut can easily be designed/extruded.

Using special nuts/bolts, fastening can take place without having to slide the nut/bolt in from the end of the track. There are no accepted standards, but various solutions are available from screw and fastener manufacturers.

If a set c/c distance between the bolt holes is required, a flat bar with precut threads can be put in the track.

The profile can be stamped to fix fasteners longitudinally in position.

Snap-Fit joints

Aluminium's elasticity is highly suited to snap-fit joints.

These give far quicker assembly than, for example, screw or welded joints.

Snap-fit joints are widely used in a range of industries.

A permanent snap-fit joint. Dimensions and tolerances must be decided on a case-by-case basis. The length of the hooking arm should not be under 15 mm. In some cases, long hooking arms may have to be extruded pre-stressed. This can eliminate the need for special tolerances.

If a snap-fitting is difficult to assemble/disassemble, punching a section out of the hooking arm may be the solution.

Amongst other factors, the design of the joint is determined by whether or not it is to be openable. This joint can be opened using, for example, a screwdriver in the outer track.

Examples of snap-fit joints.

Plate A has a punched, rectangular hole. Mounting profile B is pushed into the hole until a snap-fit joint is formed. Lamella profile C is then pushed into profile B to form another snap-fit joint. Exploiting the space under the plate makes it possible to have sufficiently long hooking arms.

The hinge profile A (cut from a longer profile_ forms a snap-fit joint with main profile B. Punched hole C also provides longitudinal locking. Sufficient spring is generated in the hooking arm by springing the main profile at d.

Joining Profile to Profile

Longitudinal joining

Joining with a standard

Joining with a fluted, sprung profile in purpose-designed channels.

A sprung inner section that compresses to allow assembly. For easy entry, the inner profile (A) is believed and cut parallel to the main profiles. Tolerances are not critical in this solution. The result is a play-free joint.

Anchoring joined profiles by welding - the illustration shows solutions with a solid profile and a hollow profile respectively.

Longitudinal joining via asymmetrically located screw ports and a pre-drilled spacer. The profiles are turned so that the screws do not foul each other.

Longitudinal joining via longitudinal screw joints. A gap slightly longer than the length of the screw is milled in the screw port.

Longitudinal jointing using the spring and friction in a snap-fit design.

Telescoping

To ensure smooth silent operation, plastic components are often used in telescoping designs. This design features stepless height adjustment using a nut (a threaded flat bar could also be used) that runs freely in its track. Tightening the fasteners locks the height and removes any play in the joint.

Height adjustment where the inner profile has a fixed thread (blind rivet nut) and the outer profile has a punched or extruded channel.

Height adjustment where the outer profile has a fixed thread (blind rivet nut) and the bolt clamps the inner profile in position.

Where a play-free joint is essential (e.g. a single leg stand), plastic gauge blocks are used.

Plastic is often an excellent solution where components have to be able to slide. A plastic profile can be a part of a telescoping assembly.

Plastic wheels used part of the fastening in the outer profile serve as spacers and give smooth, play-free telescoping.

Telescope solution with stepless clamping.

Latitudinal joining

Larger cross-sectional areas can be economically created by joining a number of profiles together. This solution is often chosen because it is easier to machine smaller profiles individually rather than a single construction as a whole.

Mechanical joints, adhesive bonding, fusion welding and, as illustrated above, Friction Stir Welding. can all be used for latitudinal joining.

Using a flat bar, bracket or similar to join profiles together gives good flatness.

Latitudinal joining using screw ports.

Locking using a splined dowel pin.

Latitudinal joining with a snap-fit.

Latitudinal joining with a snap-fit.

Joining using an end plate that holds the sections together.

Joining by stamping

Latitudinal joining using dovetail tracks. Note the shape - to achieve acceptable precision, sharp-tipped corners must be avoided.

Hinges

A simple hinge - the ball's diameter should never be less than 5 mm.

If the hinge has a screw port, it can be easily locked longitudinally using plastic inserts and self-tapping screws.

Self-locking with approx. 180 degrees opening.

Both parts of this hinge are made from a single profile.

Three-part hinge made from a single profile.

Two-part hinge made from a single profile and with identical machining.

A longitudinally adjustable hinge.

T-joints

A simple T-joint using screw ports.

Screw ports used to join tubular and rectangular profiles.

To avoid flexing in the joint, the screws are driven directly through the inner wall. The outer clearance holes are plugged with standard plastic caps.

Fitting to a wall or another profile: The end fastener is cut from a longer profile and secured with screws.

A simple and stable soultion for T and corner jointing of square tubes.

In the furniture and interior decoration industry, special fasteners are used where joints must be easy to take apart. The fasteners often run in a nut track and there is this thus a stepless fit with the mounting profile.

A simple T-joint using nut tracks, right-angled brackets and bolts.

Corner joints

There are various types of brackets that are extremely suitable for corner joints where the strength and rigidity requirements are high. The brackets are usually cut from long aluminium profiles.

Brackets are usually designed to allow several fitting methods. The corner bracket above has both screw ports (for side screws) and channels for stamping.

A special machine or an excentric press is used in the stamping method of connecting profiles. The method is particularly common in long production runs.

In picture frames and other light constructions, the corner joint comprises two flat right-angled brackets, one of them with threaded holes.

This corner joint for square tubes uses self-tapping screws in the transverse screw ports.

A torsionally rigid joint using a single screw. As shown, one of the profiles has flanges. This type of corner joint is used in, amongst other things, TV stands.

This stable corner joint, which has precise angles and good design, involves relativelyeasy machining only.

These frame profiles have screw ports and, to give a snug fit, need only be cut at 90 degrees when used with the corner profile shown in the illustration. The flanges of the corner profile create channels for the fitting of an outer profile (free choice of radius). Plastic caps are used to cover the ends.

A corner joint that can be used in, for example, a table. The plate and joint combination represents a very stable solution.

Corner joint using pre-mounted bolts in two of the profiles. The bolts are tightened from above using a special tool.

Riveting

Examples of blind rivet nuts and press nuts.

In a long profile, it is often uneconomic to build extra thickness simply to provide longer threads. Using blind rivet nuts or press nuts, all that is required is a hole.

The bling rivet nut is fitted from the outside using a special rivet gun.

Press nuts: These are fitted from the back using, for example, an excentric press.

Sliding pop riveting in a longitudinal profile channel.

Pop riveting at the end of a screw port.

Self-punching rivets countersink and join in a single operation.

Riveting without rivets : This method, which is highly suitable for long runs, can join different materials of different wall thicknesses. A crimping press is used.

End Caps

Screws and screw ports are the most common method of securing metal or plastic end caps to box profiles.

If the main profile is long, it is more cost-efficient not to have screw ports in this but in a purpose-designed end cap. Slight displacement of the holes in the main profile (relative to the screw ports) ensures that a force is set up pulling the end cap into the main profile.

Channels in the main profile for the fitting of an end cap with a sprung arm.

An end cap with sprung arms - the cap is removable .

This plastic end cap is held in place by stamped catches in the profile.

Cast metal or plastic end caps are suitable for long runs where the shape of the main profile is complex or where a highly rounded end cap is required.

Two end caps can be held together using long screws or draw bars. Screw ports with adequate clearance are a suitable way of giding the screws. The result is one end cap with no visible screws. This is a good solution in, for example, fascias.