Riveting Techniques PDF

Riveted Joints Lap Joints In general, three types of riveted joints are used in the manufacture and repair of aircraft: Lap joints Flush joints Joggle joints. In a lap joint, the skins are riveted together so that there is a distinct step or chang...

Riveted Joints Lap Joints In general, three types of riveted joints are used in the manufacture and repair of aircraft: Lap joints Flush joints Joggle joints. In a lap joint, the skins are riveted together so that there is a distinct step or change in levels. The skins are not on the same plane, but are stacked. Lap joints This type of joint is not good for aerodynamic smoothness as the skin edges disrupt airflow during flight. For this reason, it is generally used on light aircraft where aerodynamic smoothness is not a concern. A lap patch is an example of where lap joints are used. Lap patch 2023-11-16 B1-07d Maintenance Practices Page 13 of 335 CASA Part Part 66 - Training Materials Only  Flush Joints Flush joints are used to obtain aerodynamic cleanliness between two skins. The skins are both riveted to the same substructure, which puts them on the same plane. Flush joints The substructure can be longerons, bulkheads, formers, etc. A separate metal piece called a doubler may also be used as the substructure. Flush patches are an example of a flush joint. Aerodynamic smoothness is maintained by tying the skin and an insert the same thickness as the skin together by riveting a doubler under the skin and insert. Flush patch 2023-11-16 B1-07d Maintenance Practices Page 14 of 335 CASA Part Part 66 - Training Materials Only  Joggle Joints A joggle joint is a combination of flush and lap joints. One skin is joggled to accommodate the other and produce one smooth side. Joggle joint Another use for joggle joints is when fitting doublers over other internal structure. Rather than trying to pull the doubler against the skin with rivets, a joggle is formed to allow the two pieces of metal to be on the same plane. Joggle joint with doubler 2023-11-16 B1-07d Maintenance Practices Page 15 of 335 CASA Part Part 66 - Training Materials Only  Strength of Joints Strength of Joint Factors The factors that govern the strength of a joint are: Plate specification of such a material and gauge as to successfully withstand tensile and bearing loads. Rivet specification selected to withstand shear loads; when the specification is not given, use a rivet of the same material as the plate and a diameter 2.5 times the thickness of the plate. Rivet spacing determined to give the joint optimum strength characteristics. Rivet Sphere of Influence The sphere of influence of a rivet is the area in which the closed rivet maintains the plates in close proximity, and this is approximately 5 times the diameter of the fastener, or 5D. When the pitch of rivets is 4D, the sphere of influence of each rivet overlaps, providing a fluid-tight joint. Rivet sphere of influence 2023-11-16 B1-07d Maintenance Practices Page 16 of 335 CASA Part Part 66 - Training Materials Only  Rivet Positions The position of the rivets relative to one another and the edge of the sheet material is important. They must not be too close together as an excessive number of holes weakens the joint. If they are too far apart, there are too few to take the load, causing leakage in pressurised areas. Rivets must not be too near the edge of the sheet as they tear through the material when the joint is under load. These conditions, modified for practical reasons, determine the rivet spacing and pattern. Typical minimum distances are: Pitch – the distance between rivets in a row measured from centre to centre, 3D minimum. Land – the distance between the rivet centre and the edge of the material, 2D minimum. Spacing – the distance between adjacent rows of rivets, 3–4D minimum. Where D = rivet shank diameter. Rivet position 2023-11-16 B1-07d Maintenance Practices Page 17 of 335 CASA Part Part 66 - Training Materials Only  Pitch Circle Diameter Pitch circle diameter is the diameter of a circle which is dictated by the pitch of a number of rivets of a given size. It is used to determine the diameter of circular repairs. Pitch circle diameter (PCD) Rivet Layout Single Row A single-row layout is used chiefly on attachment and lightly stressed joints. Rivet layout single row 2023-11-16 B1-07d Maintenance Practices Page 18 of 335 CASA Part Part 66 - Training Materials Only  Multiple Row A multiple-row layout is common for watertight joints and in places of high stress where thick gauge plate is used. Rivet layout multiple row Staggered Riveting A staggered layout is used as an alternative to multiple rows in watertight joints, circular patches, etc. Staggered riveting will equal 75% of the rivet pitch. Rivet layout staggered riveting 2023-11-16 B1-07d Maintenance Practices Page 19 of 335 CASA Part Part 66 - Training Materials Only  Riveting Tools and Procedures Clearance If the hole is too small, the protective oxide coating on the rivet will be shaved off its shank. It may also cause buckling of the sheet metal as the rivet is driven. Clearance Holes should be deburred after drilling using special deburring tools, which are available in a variety of styles. If a deburring tool cannot be sourced, use a larger diameter drill bit to achieve similar results. Deburring tool 2023-11-16 B1-07d Maintenance Practices Page 20 of 335 CASA Part Part 66 - Training Materials Only  Deburring using large drill bit 2023-11-16 B1-07d Maintenance Practices Page 21 of 335 CASA Part Part 66 - Training Materials Only  Solid Riveting Tools Solid rivets can be closed by hand using appropriate snaps, sets and dollies. This technique is usually confined to bench work. On aircraft structures, reaction riveting using pneumatic riveting guns is normally performed. Tools Set (also known as a draw tool) – a hollow punch used to draw the metal sheets together and bring the preformed rivet head against the metal surface Snap – a form of punch with a recess at one end, the same shape as the rivet preformed head Dolly – a metal block with a recess the same shape as the preformed head of the rivet, used to support the preformed rivet head, which should fit squarely into the dolly. Riveting tools are available in different sizes and shapes to accommodate the various rivet sizes and head forms. When the appropriate actions of drilling, countersinking, dimpling, deburring, cleaning and adjusting have been completed, the work to be riveted should be assembled, sealant applied and mating surfaces brought tightly into contact by use of skin grips or clips, care being taken not to damage the skin surface. It is important that no gaps are present between layers, as this prevents correct formation of the rivet and reduces shear strength. Riveting may stretch thin sheets slightly, particularly with minimum rivet clearances, and this should not be allowed to accumulate by riveting, for example, straight along a line of rivets. The correct sequence of closing rivets can only be obtained by experience, and with each type of joint, the order of riveting may vary slightly. Draw tool and snaps 2023-11-16 B1-07d Maintenance Practices Page 22 of 335 CASA Part Part 66 - Training Materials Only  Clamps, Fasteners and Skin Pins Tools come in a variety of shapes and sizes to hold sheets together for ease of riveting. C-clamps or Cleco edge clamps are used to hold skins together for drilling. Skin clip or pin Wing nut fastener 2023-11-16 B1-07d Maintenance Practices Page 23 of 335 CASA Part Part 66 - Training Materials Only  CLECO fasteners C-clamps or CLECO edge clamps 2023-11-16 B1-07d Maintenance Practices Page 24 of 335 CASA Part Part 66 - Training Materials Only  Rivet Cutters If the correct length of rivets is not available, use rivet cutters to shorten longer rivets. Rivet cutter The length of a rivet is determined by adding 1.5D to the material thickness. After driving, the tail/shop head should be 0.5D high and 1.5D wide. Formed rivet dimensions 2023-11-16 B1-07d Maintenance Practices Page 25 of 335 CASA Part Part 66 - Training Materials Only  Microstop Countersinker If flush rivets are to be used, then the holes need to be countersunk to accommodate the rivet heads. A microstop countersinking tool is used to accurately countersink the material. Microstop countersinker Microstop countersinker set too deep Do not countersink too far – the hole will be enlarged and the metal will shear across the head instead of the shank. When using thin material, a countersinker may enlarge the hole in the top skin, which weakens the riveted joint. 2023-11-16 B1-07d Maintenance Practices Page 26 of 335 CASA Part Part 66 - Training Materials Only  Hand Riveting If the job is small or can be done away from the aircraft, hand riveting may be convenient. When solid rivets are closed with a hand hammer, the preformed head should be supported in a dolly and a hollow set or draw tool used to ensure the sheets are drawn together. The tail is then driven using a flat snap to form a reaction head with a thickness of 0.5D. If a round or snap head is required on the shank end, the tail should first be partly formed with a flat snap, then finished with a suitably shaped snap. The rivet should never be hit directly with the hammer. Use of draw tool The rivet head sits in the bucking bar recess and the rivet is drawn through the material with a draw tool and hammer. A hand set or punch is then used to form the shop head. Acceptable standards for hand-driven rivets are the same as for other methods. 2023-11-16 B1-07d Maintenance Practices Page 27 of 335 CASA Part Part 66 - Training Materials Only  Hand riveting 2023-11-16 B1-07d Maintenance Practices Page 28 of 335 CASA Part Part 66 - Training Materials Only  Pneumatic Rivet Guns Aircraft solid rivets are often driven with pneumatic rivet hammers or guns. They use compressed air to drive a piston back and forth, applying a hammering action to the rivet snap. The air pressure required to operate the hammers is around 80 lb/in2. The rivet snaps are held in the gun with a spiral retaining spring made of heavy gauge steel wire. This type of spring allows the snap to have the full travel required without being driven out of the gun. It is extremely important that anyone operating a rivet gun is aware of the dangers associated with compressed air and pneumatic tools. Careless use of a rivet gun can result in a snap being driven from the gun with such force that it inflicts serious injury to persons or damages equipment. Retaining springs have been known to fail to hold the snap, so the rule is to always handle rivet guns with care. CAUTION: DO NOT PLAY WITH RIVET GUNS. A rivet must be driven with as few blows as possible to minimise the work hardening of the rivet but not over drive it, which results in an unacceptable tail. For this reason and because of the inaccessibility of many rivets, several types of rivet gun are available. For larger rivets that are relatively accessible, a slow, hard-hitting, long-stroke gun is required. Some of these guns deliver only one blow each time the trigger is pulled. For work with small rivets in thin skins, a light, fast-hitting rivet gun is often most suitable. Pneumatic rivet gun 2023-11-16 B1-07d Maintenance Practices Page 29 of 335 CASA Part Part 66 - Training Materials Only  Pneumatic rivet gun - cutaway Squeeze Riveting The squeeze method is used to install large quantities of rivets along an easily accessible edge. C-yoke squeezer 2023-11-16 B1-07d Maintenance Practices Page 30 of 335 CASA Part Part 66 - Training Materials Only  Alligator-yoke squeezer This method offers a few advantages: Produces uniformly sized shop heads Reduces installation time Can be done with two types of guns: C-yoke and alligator yoke. Bucking Bars (Dollies) The shop head is formed by the bucking or vibrating action of a bucking bar when the rivet gun is activated. Bucking bars (dollies) 2023-11-16 B1-07d Maintenance Practices Page 31 of 335 CASA Part Part 66 - Training Materials Only  They come in many different sizes and shapes for different applications. The driving face of the bar is machined smooth and polished so that no marks are left on the rivet tail. Typical shapes of bucking bars Bucking bar alignment 2023-11-16 B1-07d Maintenance Practices Page 32 of 335 CASA Part Part 66 - Training Materials Only  Using the Rivet Gun Prior to installing rivets, the gun needs to be adjusted for correct pressure/hammer. This is achieved by actioning the gun against a piece of wood. Adjust the airflow to the gun so it will indent the wood but not shatter it. Using the rivet gun Place a rivet in the hole and hold the gun against its head with enough pressure to keep the rivet against the skin. Hold the bucking bar flat and square against the rivet’s tail. Pull the trigger to form the rivet. Use the fewest blows possible so the rivet will not work harden, which may cause cracking. 2023-11-16 B1-07d Maintenance Practices Page 33 of 335 CASA Part Part 66 - Training Materials Only  Using the rivet gun Rivet Sets (Snaps) Ensure that the snap used is the correct size for the rivet. One that is too small will mark the rivet head. One that is too big will mark the skin. Rivet set fit 2023-11-16 B1-07d Maintenance Practices Page 34 of 335 CASA Part Part 66 - Training Materials Only  Rivet Inspection After the rivets have been closed, they should be inspected to ensure they are tight and fully formed. Rivet heads must not be deformed or cracked, and the surrounding area should be free from distortion and undamaged by the riveting tools. Rivets which are obviously not performing their function should be replaced, but replacing rivets that are only slightly below standard might do more harm than leaving them in position, particularly in thin materials. Before rejecting such rivets, the strength requirements of the particular joint and the effectiveness of the rivets in question should be considered. When a flushness tolerance is specified for countersunk rivets, this is normally checked before riveting is commenced; however, milling solid rivet heads may sometimes be permitted after riveting to obtain a uniform protrusion. In this case, protective treatments must be re-applied after milling. Good rivets - countersunk and universal Rivet inspection Manufactured head must be flat against the metal. Rivet should be uniform in height with adjacent rivets. Shop heads should be concentric. Shop head finish size should be as illustrated above. 2023-11-16 B1-07d Maintenance Practices Page 35 of 335 CASA Part Part 66 - Training Materials Only  Faults The following illustrations show some of the faults which may be found with solid rivets. Any cracks in the rivet head are not normally acceptable. If snap heads are formed on the tail of the rivet, a number of further faults may occur. These include a ‘flash’ round the rivet head if the shank was too long and a small head, possibly accompanied by snap marks on the skin, if the shank was too short. Countersinking too deep Countersinking too deep – incorrectly set countersink tool. Holes out of line Holes out of line – skins incorrectly drilled. High shop head High shop head – rivet too long or rivet not driven enough. 2023-11-16 B1-07d Maintenance Practices Page 36 of 335 CASA Part Part 66 - Training Materials Only  Clinched shop head Clinched shop head – bucking bar held at angle. Flattened shop head Flattened shop head – rivet too short or hit too hard. Uneven shop head Uneven shop head – bucking bar held on angle. 2023-11-16 B1-07d Maintenance Practices Page 37 of 335 CASA Part Part 66 - Training Materials Only  Skin bulged Skin bulged – holes not lined up or rivet hammered too hard for thin skin. Swelling between sheets Swelling between sheets – parts not properly held together, or chips between sheets. Open head Open head – rivet snap not held straight. 2023-11-16 B1-07d Maintenance Practices Page 38 of 335 CASA Part Part 66 - Training Materials Only  Burr under head Burr under head – not deburred correctly. Cut shop head Cut shop head – dolly did not cover entire end of rivet. Cracked shop head Cracked shop head – hard rivet or hit too long. 2023-11-16 B1-07d Maintenance Practices Page 39 of 335 CASA Part Part 66 - Training Materials Only  Skin marked by oversize rivet set Skin marked by rivet set – set head is too big for rivet. Skin marked by rivet set not aligned Skin marked by rivet set – set not centred on head of rivet. 2023-11-16 B1-07d Maintenance Practices Page 40 of 335 CASA Part Part 66 - Training Materials Only  NACA Riveting You may be required to install a rivet with a flush shop head due to interference from adjoining parts or disruption of air flow. This method is known as the NACA (National Advisory Committee for Aeronautics) flush riveting technique. The skin is countersunk and the rivet installed from inside the structure. NACA riveting - countersunk The rivet is driven to fill the countersink. NACA riveting - driven A micro-shaver is then used to mill the excess material from the shank and obtain a flush surface. 2023-11-16 B1-07d Maintenance Practices Page 41 of 335 CASA Part Part 66 - Training Materials Only  NACA riveting - milled If a gap under the rivet head is suspected after installation, use feeler gauges to confirm. No gap is allowed, and the rivet will have to be replaced. Feeler gauge If a gap is found under the head of an old rivet, the rivet may have cracked and separated inside the component. It will have to be replaced. 2023-11-16 B1-07d Maintenance Practices Page 42 of 335 CASA Part Part 66 - Training Materials Only  Gap under head of old rivet Team Riveting When riveting, hearing protection is essential. When riveting hearing protection is essential 2023-11-16 B1-07d Maintenance Practices Page 43 of 335 CASA Part Part 66 - Training Materials Only  Team riveting Communication is essential when team riveting. The person on the bucking bar is in control. They inform gun operator when to rivet, whether the rivet is good or bad, and whether the rivet needs more hammering. The gun operator’s job is to place the rivet into the hole, hold the gun straight and firm on its head, and do what the dolly operator instructs. It may not be possible to communicate by voice. The riveting team must devise a way of communicating. For example: One tap with dolly – rivet Two taps with dolly – good rivet Three taps with dolly – bad rivet. 2023-11-16 B1-07d Maintenance Practices Page 44 of 335 CASA Part Part 66 - Training Materials Only  Team riveting communication 2023-11-16 B1-07d Maintenance Practices Page 45 of 335 CASA Part Part 66 - Training Materials Only  Dimpling Tools The three types of dimpling are: Coin dimpling Radius dimpling Hot dimpling. Coin Dimpling A male die fits through a hole in the metal, and a coining ram in the female die puts pressure on the underside of the hole, forcing the male die into the female die and contouring the skin to the shape of the coin. Coin dimpling Coin dimpling offers the following advantages: It gives the hole sharply defined edges. Both the top and bottom of the dimple are formed at 100°, so multiple sheets can be stacked and dimpled. It provides a tighter fit but leaves a sharper bend around the rivet head, making the skin prone to cracking. 2023-11-16 B1-07d Maintenance Practices Page 46 of 335 CASA Part Part 66 - Training Materials Only  Nesting of dimples Radius Dimpling In radius dimpling, a cone-shaped male die is forced into the recess of a female die with either a hammer or a rivet gun. Radius dimpling 2023-11-16 B1-07d Maintenance Practices Page 47 of 335 CASA Part Part 66 - Training Materials Only  A flush rivet may be used as a die. In this case, a sharp blow hits the male die, forcing the metal into the female die and forming a dimple. A dimple formed in this way does not have parallel sides as its lower side angle is greater than 100°. Therefore, this method is not good for stacking. Radius dimpling is done because the equipment is smaller than what is needed for coin dimpling. Radius dimpling Hot Dimpling Magnesium and harder aluminium alloys need to be heated before dimpling because they are brittle and will crack if they are not. The equipment required is similar to that for coin dimpling, except that an electric current heats the dies, then the metal is positioned. The dies are operated to just touch the metal, allowing dwell time for sufficient heat to soften the metal before dimpling. The dwell time is automatically controlled to avoid destroying the metal’s temper and is adjustable. 2023-11-16 B1-07d Maintenance Practices Page 48 of 335 CASA Part Part 66 - Training Materials Only  Rivet Removal Rivet removal has been split into a five step process as follows. Rivet removal - Step 1 Centre punch the exact centre of the manufactured head. Rivet removal - Step 2 Drill through the head. Rivet removal - Step 3 2023-11-16 B1-07d Maintenance Practices Page 49 of 335 CASA Part Part 66 - Training Materials Only  Knock the head off with a cape chisel. Rivet removal - Step 4 Break the head off using a centre punch and a tipping motion. Rivet removal - Step 5 Back-up the sheet and punch the rivet out with a pin punch. 2023-11-16 B1-07d Maintenance Practices Page 50 of 335 CASA Part Part 66 - Training Materials Only  Hi-Loks The collar of a Hi-Lok rivet is installed onto a pin with a spanner/socket while the pin is prevented from moving with an Allen key. The wrenching part of the collar snaps off when the rivet reaches the preset torque. Removal procedure: Remove the collar with lock pliers and tap the pin out. Split the collar with a small chisel and tap the pin out. Drill off the pin head and tap the pin out. Hi-Lok installation 2023-11-16 B1-07d Maintenance Practices Page 51 of 335 CASA Part Part 66 - Training Materials Only