Application of Huck Rivets on Aluminum Alloy Bus Body

This paper introduces the characteristics and classification of Huck rivets, explains its practical application on the body of aluminum alloy passenger cars, and analyzes its production efficiency and lightweight results.

In the production of modern aluminum alloy bus bodies, riveting , bolting and welding are the main three connection methods.

When the aluminum alloy structure body is welded, not only the skeleton deformation is easily caused, but also defects such as pores, undercuts, cracks, and unmelting are easily generated, the process technology is difficult, and the professional skill of the operator is required to be high.

According to the relevant information, the man-hours for correcting the welding deformation of aluminum alloys account for about 20% of the total working hours of the car body.

The bolted body has poor precision, low production efficiency, difficult torque detection, and the body structure is easily deformed under vibration or alternating load, so that the bolt connection is loose.

The riveted body has no stress deformation, no need for correcting process, no need to detect torque process, simple process technology, low requirements for operators' professional skills, and energy saving, pollution reduction and green environmental protection in the manufacturing workshop.

At present, many domestic bus manufacturers have also developed all-aluminum riveted body, such as Shenlong SLK6109, Hager KLQ6762, Shenwo SWB6108, Jingang ZJG6140 and so on.

Although the advantages of riveting technology are obvious, due to its structural design, mechanical properties, working space and other aspects, its application on aluminum alloy body can not completely replace welding.

Huck rivets features and classification

The Huck rivet consists of two parts: a nail rod and a nail sleeve. The nail rod further includes four parts, a nail head, a locking groove, a broken neck groove, and a tail section (gun groove), as shown in FIG.

Figure 1 Structure of the Huck rivet

Different from the traditional bolts, the tightening force is generated by the torsion rotation. The special ring groove locking and ring groove breaking technology are used. Under the external tension, the tensile nail rod extrusion nail sleeve is plastically deformed, and the deformation base is used to clamp the substrate. Reliable tight connection, as shown in Figure 2.

Figure 2 Pull and displacement curves

The structure has high clamping force and high shear resistance, which fundamentally solves the problem that the ordinary fastener is loose under vibration conditions. At the same time, it has higher precision, higher production efficiency, excellent vibration resistance and fatigue resistance.

A large number of Huck rivets are used in many construction, automobile, railway, ship, and aerospace structures that require bolting or welding at home and abroad to reduce the proportion of bolting or welding applications.

At present, Huck rivets applied to the body of aluminum alloy passenger cars are divided into two types: double-sided blind rivets and single-sided blind rivets .

Double-sided blind rivets are first placed from the back of the substrate with rivets and then riveted from the front side of the substrate; single-sided blind rivets are rivets from the front side of the substrate and riveted from the front side of the substrate.

According to the structure, Huck rivets can be divided into three types: ring groove rivets, wire drawing blind rivets and Hackcomb rivets, which are also called Huck Bolt, Magna-Lok and Huck BOM in foreign countries.

Huck Bolt, also known as Huck Bolt , consists of two separate parts, a nail sleeve and a nail rod, and is a double-sided blind rivet.

The ring groove rivet utilizes the principle of Hooke's law, through the special equipment of the rivet, under the action of the unidirectional tension, the nail rod is stretched and the nail sleeve is pushed. After the structural member is pressed, the smooth inner nail sleeve is pressed to the nail. The rod groove forms a 100% interference fit between the nail sleeve and the nail rod. After the design clamping force is reached, the nail rod breaks the neck groove and completes the riveting, as shown in FIG.

The ring groove rivet has high shear resistance, high tensile strength and large riveting range (rive thickness 3.5~30 mm), but in the narrow working space, the operation is not as convenient as single-sided blind rivet.

Figure 3 Ring groove rivet riveting principle

The brushed rivet (Magna-Lok) is a single-sided blind rivet. Unlike the ring groove rivet structure, under the action of the unidirectional tension, the shank is stretched upwards, so that the thicker end of the shank enters the nail sleeve. The nail sleeve is gradually squeezed and thickened to fill the nail hole, and the annular groove on the nail rod is pressed into the annular boss of the nail sleeve after the structural member is pressed, and the nail is broken after the design clamping force is reached. The slot is broken and the riveting is completed, as shown in Figure 4.

The wire drawing rivet has low cost and convenient operation, but the mechanical properties are poor. The shearing and tensile strength are 0.8 times and 0.7 times of the ring groove rivet, respectively, and the riveting thickness range is small (the riveting thickness is 1.5~16 mm).

Figure 4: Principle of drawing and rivet riveting

Huck BOM is a single-sided blind rivet. It not only has the structural characteristics that the ring groove rivet never looses , but also has the advantage of drawing the blind rivet on one side, and under the action of one-way tension, pull Stretch the nail rod and push the nail sleeve to deform the tail end of the nail sleeve to form the head end. After the structural member is pressed, the smooth inner nail sleeve is pressed into the nail rod groove to make the nail sleeve and the nail rod become 100%. After the fit, after the design clamping force is reached, the nail rod breaks the neck groove and completes the riveting, as shown in Fig. 5.

The Huckbohm rivet has high mechanical properties, and the shear and tensile strength are 1.6 times and 1.3 times that of the ring groove rivet, respectively. It can replace the ring groove rivet in the structure with narrow working space, but the procurement cost is too high. 3 times the ring groove rivet.

Figure 5 Hackerbohm rivet riveting principle

Huck rivet on aluminum body

The aluminum alloy profile has a high specific strength. Although the modulus of elasticity is low, it has good extrusion properties, and can obtain a member with a complicated cross section, which can structurally compensate the rigidity of a single component of the aluminum alloy body.

At the same time, Huck rivet has high clamping force, high shear resistance and never loosening. During the riveting process, as the tensile force increases, the broken neck groove first breaks beyond the yield limit of the material and breaks. There is no plastic deformation, and the shank of this structure is allowed to be made of a high-strength material, thereby improving the joint strength between the various components of the aluminum alloy body.

Huck rivets combined with 6061-T6 aluminum alloy profiles have been widely used in foreign countries.

The 14 m airport shuttle bus designed by a bus company was improved on the basis of the original mature steel body, and it was improved to 80% of the aluminum alloy riveted structure, and 20% of the argon arc welded structure, as shown in Fig. 6.

Figure 6 Six skeleton structure of a passenger car

The front and rear surrounding frames of the aluminum alloy body are curved according to the curved structure, the joints are not perpendicular to each other, the connecting parts are difficult to design, and the riveting cannot be applied. The argon arc welding is used; the roof frame and the side frame of the body are all riveted with Huck rivets. The chassis skeleton is not modified, and it is still welded by Q345B ordinary rectangular steel pipe; the body is assembled in five pieces, and the body and chassis are assembled by Huck rivets.

At the same time, combined with UG finite element analysis, the contact analysis of the rivets in the combined area is established one by one, fully simulating the horizontal bending, emergency braking, emergency turning, ultimate torsion and other working conditions of the riveted body, and the strength of the rivets is checked one by one to ensure the aluminum The riveting strength and rigidity of the alloy body frame meet the requirements for use.

After the design optimization, the aluminum alloy body frame has a total of 1232 ring groove rivets, 1748 wire drawing rivets, and 96 Huckbohm rivets. When the car body is actually manufactured, a Huck rivet riveting time is 3~8s, and the aluminum profile is cut. The total working time of the six-piece skeleton assembly is 80 h, and the production efficiency is nearly three times higher than the total working time of the steel body welding frame of 230 h (including 16 h correct welding deformation working hours).

The steel body weighs 2 t (excluding the chassis skeleton), the curving quality is 12.5 t, the aluminum alloy riveted body frame weight is 920 kg; the curb weight is 11 t, the skeleton weight loss is 54%, the vehicle weight reduction is 12%, and the lightweight effect is remarkable.

In 2014, the prototype passed the load test, steering performance test, structural static stress test, structural dynamic stress test, wind stability test, 5 000 km reliability test, etc. The results show that the aluminum alloy riveted body structure is stable and the body performance Safety. The product has been operating safely at Shanghai Pudong Airport for 4 years.

Conclusion

At present, under the background that the aluminum alloy welding technology is immature, the welding deformation is large, and the cost of the process equipment is too high, the riveting technology is simple and efficient to operate, and the internal stress is not eliminated, and the Huck rivet is used as a high clamping force and high resistance. The shearing force and the never-relaxed joint structure can partially replace the welding, which is inevitably widely used in the passenger car manufacturing industry in China.

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