Table of Contents 1 Introduction to Riveting 3 2 General Rivet Facts and Applications 4 3.1 Solid Shank Rivets 6 3.2 Special Rivets 8 4 Riveting Processes 10 4.1 Manual Process 10 4.2 Automated Process 12 4.3 Counter-sinking 13 4.4 Applying Special Rivets 14 References 17

List of Figures

Figure Number Figure Description Page Number 2.11 Riveted metal sheets under shear loads …………………………………. 3 2.12 AN270 Mushroom Head Rivet, AN426 Countersunk Rivet .…… 3 2.13 Before and after of rivet being set into a drilled hole …………... 4 3.11 Example of a Solid Shank Rivet ……………………………..……………... 5 3.12 Example of a rivet Identification Number …………………………….. 6 3.13 Examples of other Rivet heads …………………………………………….. 6 3.14 Markings on Rivet Heads ……………………………………………………… 7 3.21 Example of a friction lock rivet …………………………………………….. 8 3.22 Example of a mechanical lock rivet ………………………………………. 8 4.11 Example of a Rivet Gun ………………………………………………………… 9 4.12 Example of a Bucking Bar ………………………………………….…………. 9 4.13 A depiction of the riveting operation ………………………………….. 10 4.14 Example of Riveting in teams …………………………………….…….…. 10 4.25 Automated Riveter …………………………………………………….……….. 11 4.36 Countersinking Tool …………………………………………………….………. 12 4.47 Blind Rivet Guns ……………………………………………………………..…… 13 4.48 Example of how a Mechanical Lock rivet is applied ……………… 13

1 Introduction to Riveting

Rivets and riveting processes play a large role in the construction of aircrafts and other aerospace applications. The process of riveting is one which predates to the Bronze Age, but became heavily involved in the aerospace industry with mass aircraft production during World War one. The process of riveting itself is the joining of two surfaces together via a solid fastener, which is deformed into place. This process is required largely due to the fact that aircrafts are made up of a number of materials, which must be joined together in order to create the final piece. The rivets themselves come in various shapes and sizes, and vary according to their application on the structure. The method of application also greatly varies, from the traditional manned operation of riveting to the automated processes, depending on the type of rivet used and its area of application.

2 General Rivet Facts and Applications

Rivets are a special type of fastener which is applied by deforming them into place. Rivets are widely used in aircraft applications due to their ability to withstand static and dynamic loads, and corrosion resistivity if selected and set correctly. They’re ideal for aircraft use due to their ability to resist shear and bearing forces which affect the structure under for static and dynamic loads (Figure 2.11).

Figure 2.11: Riveted metal sheets under shear loads

Figure 2.12: From left to right; AN270 Mushroom Head Rivet, AN426 Countersunk Rivet
The two main types of rivets used are ‘mushroom head’ and countersunk rivets (Figure 2.12). Countersunk head rivets are commonly used for areas where smooth airflow is required, while mushroom head rivets are used everywhere else. When a rivet is driven into the hole, it will ‘swell’ to the size of the hole, creating is perfect fit (Figure 2.13). It is set into place by compressive forces acting on both ends, causing the rivet to deform.

Figure 2.13: Before and after of rivet being set into a drilled hole

3.Types of Rivets

As stated above, rivets are a solid fastener which must be deformed into place. The rivets themselves come in many different shapes, sizes, and designs depending on the application.
3.1 Solid Shank Rivets
The traditional rivet, also known as a solid shank rivet (Figure3.11), is the most widely used in aircraft construction.

Figure 3.11: Example of a Solid Shank Rivet These rivets are deformed into place by upsetting the shank end in order to form a ‘head’, setting it into place. The type of solid shank rivet to be used is selected based on its identification number (Figure 3.12). The identification number states the organization to which the rivets standard of quality conforms to, the type of rivet head, the material alloy, diameter, and length. Although there are many types of head designs (some examples shown in Figure 3.13), the two most commonly used are known as the AN470 ‘mushroom’ head and the AN462 countersunk head. Figure: 3.12: An example of a rivet Identification Number; Figure 3.13: Examples of other Rivet heads

The alloys these rivets consist of are typically made up of Aluminum alloys, with the exception of Corrosion-Resistant Steel and Monel rivets. The reason for this is due to aluminum being cost efficient, easily deformable for ease of application, and most aircraft structures consist of aluminum metal sheets (using similar metals for anti-corrosion purposes). The type of alloyed rivets are selected based on the application of the rivet; such as areas where high strength and shock resistance is required (2117 Aluminum Alloy), or applications of non-structural importance such interior furnishing, fairing, or baffles (1100 Aluminum Alloy). The heads of solid shank rivets are typically marked to indicate the type of alloy the rivet consists of (Figure 3.14).

Figure 3.14: Markings on Rivet Heads in order to indicate the type of alloy they are manufactured from

3.2 Special Rivets

The disadvantage to solid rivets is that in order to apply them, access of both sides of the sheet metal is required in most cases. This becomes difficult in large structures where access to the opposing side becomes difficult, if not impossible. Special rivets have been designed for these cases, where access to only one side is required in order to deform the rivet head. These special rivets, also referred to as blind rivets, consist of Friction Lock rivets and Mechanical Lock rivets. These rivets consist of a solid shank, which is pulled through the rivets in order to deform the other end into place. The major difference between the two rivets is that the shanks in Friction Lock (Figure 3.21) are held in place by friction, while in Mechanical lock rivets (Figure 3.22) the stem is mechanically locked into place. Figure 3.21: An example of a friction lock rivet; Figure 3.22: An example of a mechanical lock rivet, with a lock-ring

Friction lock rivets are seldom used in major repairs, due to the fact that the stems may fall out under vibration, considerably weakening the strength of the rivet. The stems in Mechanical Lock rivets on the other hand are mechanically locked into place, via a locking ring or collar. These rivets can be used to replace solid shank rivets in a repair, due to this locking mechanism which allows them to retain their integrity.

4 Riveting Processes

The method of application for both locking rivets and solid shank rivets are accomplished several ways.
4.1 Manual Process
The process of riveting itself is still done largely done manually, while some of it has moved onto automated processes within aircrafts. Traditionally, before automation of riveting process became available to aircraft manufacturers, riveting was done in pairs. One person would hold a rivet-gun, also known as an automated hammer (Figure 4.11), on one end of the structure, which another would hold a bucking bar (a small anvil) on the other (Figure 4.12). The person with the rivet gun would hammer at the head, while the end where the bucking bar was held would deform. The person holding the bucking bar would then communicate to the person with the rivet gun, telling them whether the shank end had formed properly or not. Figure 4.11: An example of a Rivet Gun; Figure 4.12: An example of a Bucking Bar

Figure 4.13: A depiction of the riveting operation

Figure 4.14: An example of two gentlemen riveting on the structure of an aircraft

4.2 Automated Process Automated riveting works in a similar fashion to manually riveting, where a rivet is placed in the hole, and hammered on the head end while the shank end is deformed into place by a bucking bar. In the automated process, the sheet metal with pre-drilled holes is fed into the machine. The machine will automatically feed a rivet into the hole, hold the shank end with a flat surface similar to a bucking bar, and hammer the head end in order to deform the rivet into place. The automated process is usually reserved for large sheet metal sections, before its assembly onto the final aircraft structure (Figure 4.25). The assembly portion is typically performed manually, as getting machines into the assembly areas would be difficult.

Figure 4.25: An automated riveter riveting the wing of an Airbus

4.3 Counter-sinking

Although the process of riveting for both mushroom head and countersunk rivets is similar, in the case of countersunk rivets, the sheet metal must first be prepared. The preparation for the countersunk rivet involves counter-sinking the hole diameter (shaving away metal) in order to compensate for the countersunk shape of the head. This is done using a countersinking tool (Figure 4.35).

Figure 4.36: An example of a countersink tool which is used to prepare a hole for a countersunk rivet

4.4 Applying Special Rivets

For blind rivets, a special tool is required depending on the type of blind rivet being used. For any blind rivet, the tool will typically consist of a mechanism which will allow the user to apply pressure to the head of the rivet, while pulling up the stem in order to lock the rivet into place (Figure 4.46). In the case of Mechanical Lock rivets, the tool must also put the locking mechanism into place (Figure 3.47).

Figure 4.47: Examples of Blind Rivet guns

Figure 4.48: An example of how a Mechanical Lock rivet is applied.

5 Summary

Riveting is an age-old process still widely used today. The reason for this is that it’s efficient, economical, and beneficial for aerospace applications. It still remains one of the biggest sheet metal joining operations up to date, due to its ease of application. With a wide variety of rivets to select from, and advances in the automation process, the applications become almost limitless. As this is a process which dates back to World War one, it still remains one of the biggest aerospace fastening operations to date.

References

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