Most of the automotive interiors are made of plastic parts. Automotive plastic parts have light weight, good chemical stability, good electrical insulation properties, excellent wear and wear resistance, good shock absorption and noise reduction.
With the widespread use of plastics in automobiles, especially the accelerated adoption of lightweight vehicles, the replacement of plastic parts in automobiles has become more and more extensive and mature, and the connection between plastics and design is particularly critical.
This article focuses on several common connections and design techniques for automotive plastic parts.
Basic distribution of automotive plastic parts
Common connection method for plastic
1.1 screwing
The use of self-tapping screws between plastic parts is a common screwing method. The advantage is that it can be repeatedly disassembled and assembled with great connection strength, but it takes time and requires additional assembly of parts and procurement cost of screws.
1) Self-tapping screws: Self-tapping screws are divided into expanded screw and cutting screw.
Threaded screw: Use the screw as a forming tool and squeeze it into the plastic hole to make it a thread shape. China's self-tapping screws standard is GB/T5280.
Cutting threaded screw: It has the function of "tap" or screw tapping. In the first few teeth of such a screw, a longitudinal cutting groove is opened. Plastic chips are produced during tapping. Provide sufficient chip depth for blind holes.
According to past experience, when the flexural modulus of the material is higher than 2758Mpa, the cutting thread is used, and when it is lower than 1379Mpa, the developed thread is used.
2) The design principle of the self-tapping screw BOSS column (Figure 1):
Figure 1 Design of self-tapping screw BOSS column
1.2 card connection
It is common to use the snap-on connection for automotive plastic connections. The advantage is that no tools or other accessory materials are required for assembly, and the components are assembled from one part to another using their own buckles.
Its shortcomings are in increasing the complexity of the mold of the part itself and increasing the cost of mold development.
1) Introduction of the card connection : The card connection can be divided into a detachable card and a permanent card.
2) Card connection design principle: insertion angle A=25-30 degrees, retention angle B=70-90 degrees, retention depth Y=1.0-2.0mm, buckle head length D=5-10mm, cantilever length L=4T- 10Tmm, buckle wall thickness T=1.5-3.5mm, insertion opening E>Y+T, buckle width W=5-25mm, non-positioning single side clearance C=2-4mm, installation clearance X=0.2-0.5mm.
as shown in picture 2.
Figure 2 card connection design
1.3 Bonding
Glue bonding is used in automotive rear wings and plastic back doors. Glue bonding is simple and can be used in almost all plastic assembly applications.
The disadvantage is that the surface of the product needs to be treated, for example, alcohol wipes the bonded surface. Solvent-based adhesives may cause contamination. Due to the long curing time of the adhesive, manufacturers generally use robotic glue instead of traditional manual glue to achieve high-volume production.
As shown in Figure 3.
Figure 3 Car tail rubber joint diagram
1.4 Welding
Welding can connect almost all thermoplastics, but the cost is higher. When the above three connection methods cannot be used, welding technology can be used.
Classification of welding methods: welding methods can be divided into hot plate welding, ultrasonic welding, vibration friction welding, laser welding and so on.
1) Hot plate welding method design principle: In principle, all thermoplastics can be connected by welding, except for thermoplastic materials which are unstable at high temperatures.
Generally welded, only the same thermoplastic material can be connected. Hot plate welding mainly relies on heating two mutually welded materials to achieve a state in which the materials are mutually fused, and then applying a certain pressure to achieve mutual welding effect.
2) Introduction of ultrasonic welding method: Ultrasonic plastic welding has many applications in the field of automotive plastic welding. It can weld the appearance parts of automobiles, such as plastic welding of automobile intake grille, plastic welding of headlights, bumper welding of automobile bumper, etc. Welding of a variety of automotive exterior parts, automotive interior parts are also useful for welding ultrasonic plastics, such as plastic welding of automobile dashboards, sound insulation cotton welding of automobile hoods, and sound insulation felt welding of automobile rear partitions.
3) Vibration friction welding: the workpiece will be welded, rubbed against each other under pressure, the energy is transferred along the fusion interface to generate heat and then melted, and then the cooling is completed under pressure, and the interface strength is equivalent to the strength of the body. In the connection process of the interior and exterior of the car, the glove box connection is the connection method.
4) Laser welding: Laser welding is the welding of infrared laser as the energy source. The laser is directly used as the welding heat source. The advantage is that the most accurate of all the welding methods, the heat is positioned to a minimum internal area, and there is no damage to the surface of the product. Any appearance such as flashing. The disadvantages are limited materials and high welding costs.
Conclusion
In order to simplify the design, improve the efficiency of production and reduce the procurement cost of parts, in the development of automotive interior and exterior products in the automotive industry in the past decade, automotive interior and exterior have been using the characteristics of plastic materials, integrating, modularizing and easy to manufacture. Unremitting efforts to install.
Modular or integrated design simplifies design, reduces error accumulation, reduces assembly time, and is easy to detect.
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