Accompany friends to pick up the car today. He opened the engine compartment cover and found that there were large traces of silica gel on the top of the shock absorber tower on the left and right sides of the engine room, which was very ugly. So he asked me, is this normal? Did you fix it later? I looked at it and told him it was normal. The traces like silica gel you see are actually welding sealant, which is a kind of process glue used in the manufacturing process of automobile body. As for why it is so ugly, it is a question of the skill and level of building a car.

So why do cars use this sealant? This will start with the manufacturing process of the body in white.

We removed all the parts and covers of the car, and the exposed metal frame was the white body of the car. It looks like a whole, but it is actually made up of 300~500 thin steel plates stamped into various shapes and then welded. However, not all welds are completely filled, which is time-consuming, laborious and costly, the welding process is not easy to control, and the deformation of the car body after welding is also large. Therefore, the general white body manufacturing does not adopt the full welding process, but spot welding. It is enough to weld a few points at the joint of two metal stamping parts with a welding machine, which can not only ensure the connection strength, but also save time and effort and cost. There are about 3000~6000 welding spots on the white body of an ordinary car.

But this welding method has a "sequela", because it is spot welding and there are only two sheet metal parts? Depending on several solder joints, there will be a large number of gaps at the joint, and external air, water and dust will enter the car through these gaps, causing pollution inside the car; In addition, these gaps rub and collide with each other, and air will vibrate when it flows through these gaps, which will also increase the noise of the car and seriously reduce the NVH performance of the car. Therefore, measures must be taken to seal these welds and improve the sealing performance of the car body.

How to seal it? The way that automobile engineers think of is to use all kinds of adhesives, also known as sealants. The adhesive is coated between two parts to be connected, and the same or different materials are firmly connected together by using the adhesive force of solid surfaces, so that a continuous sealing surface is formed on the mutually connected surfaces, thereby preventing the invasion of external harmful substances and improving the sealing performance of the car body. In addition, the gluing method can simplify the production process, save the use of materials, enhance the strength of parts, and have the functions of vibration reduction, noise reduction, heat insulation, corrosion prevention and rust prevention. It is beneficial to improve the safety and ride comfort of the car body and effectively improve the NVH level of the car.

So what kinds of glue are there? Where are they all used? How to apply? As we all know, the automobile manufacturing process is divided into four major processes: stamping, welding, painting and assembly. In addition to the stamping process, several other processes require different kinds of adhesives. The total amount of glue for a car is generally around 15 ~ 20kg. Let's talk about the use of glue in various processes.

1. Welding: Flanging glue, spot welding sealant, expansion glue, vibration isolation glue and structural glue are generally used in the welding process.

1, wrapping glue: wrapping glue is mainly used for doors, hoods, trunk lids and other parts. The edges of these parts need to be hemmed. If welding is used, pits will appear, which will affect the appearance quality. Using flanging glue can solve this problem well. Second-hand car dealers will look at the gluing state of this part when collecting the car, so as to judge whether this part is original or not.

2. Spot welding seal: Spot welding seal is mainly used at the joint of sheet metal parts. At the joint of two sheet metal parts, apply a layer of sealant in advance, and then weld, so that the weld will naturally seal after welding.

3. Expansion glue: Expansion glue is mainly used in various cavities of the car body, such as doors, hoods, A, B and C pillars. After BIW is manufactured, there will be many cavity parts. If these parts are not filled, cavity effect will be formed, which will lead to vibration or abnormal noise of the car. Injecting expansion glue into these cavities to form a support between the inner and outer plates can well weaken the cavity effect.

4. Vibration isolation glue: The vibration isolation glue is mainly coated on the inner side of the door, the top cover and the inner side of the side outer panel. These parts are characterized by large metal panel area, low strength and easy vibration. Sticking vibration isolation glue on these parts can improve the strength of the steel plate, reduce the vibration frequency and play a role in reducing vibration and noise.

5. Structural adhesive: Structural adhesive is mainly used for some structural parts that cannot be welded, such as the connection between the outer plate and the outer plate reinforcement. If welding is used, the surface quality will be affected and the bonding will be perfect. The bonding strength of structural adhesive is relatively high, and even some aluminum alloy bodies are completely bonded with structural adhesive.

Second, painting: in the painting process, weld sealant, PVC stone-proof coating, cavity wax injection, etc. Usually used. This process is set after phosphating and electrophoresis in white body and before painting.

1. Weld sealant: Weld sealant is mainly used for welds between sheet metal parts. After the welding of the body in white is completed, there will still be a big gap between the sheet metal parts, and there are also many corners and holes. Apply weld sealant to these parts, completely seal the weld and block the corners and holes, which can greatly improve the sealing performance of the car body and improve the NVH level of the car body. The traces similar to silica gel that we see in the engine compartment, trunk, wheel arch and other parts of the car are mainly this kind of weld sealant.

2. PVC stone-proof coating: PVC stone-proof coating is mainly used under the car body floor and inside the wheel arch. What we commonly call "chassis armor" is a PVC stone-proof coating. It can prevent the impact of stones on the car body floor and wheel arch during driving, and also has the functions of anticorrosion, waterproof, sealing and noise reduction.

Third, the final assembly: In the final assembly process, the main glue used is glass glue. The front and rear windshields, side triangular windows and other parts of the car are glued to it.

These are the main adhesives used in automobile manufacturing. Glue coating is a very important link in the automobile manufacturing process, which has a great influence on the vibration, noise and NVH level of the automobile. In the current automobile manufacturing process, gluing is generally done automatically by robots, and only the parts that individual robots can't reach are manually glued. Generally speaking, the original car is well glued, perfect and looks beautiful. Especially for Volkswagen, the gluing process is perfect, and the sealant applied to each part is very uniform and regular. However, some car companies have poor gluing skills and ugly gluing, such as Toyota. If there is an accident in the later stage of the car, the glue applied is generally not as good-looking as the original factory after the sheet metal repair, which is also a basis for judging whether a car has an accident.

This article comes from car home, the author of the car manufacturer, and does not represent car home's position.