A recent news report brushed the screen, and China needs to import a large amount of high-end bolts every year. With the development of China's manufacturing industry today, it is really difficult to understand the need for such simple things as imported bolts. As a pseudo-expert in the machinery industry (the automobile is also regarded as the machinery industry), A-Gump will analyze the reasons for everyone.
First of all, it should be emphasized that bolts look simple, but high-end bolts are really not simple. This starts with the technical requirements for bolts in high-end applications.
The technical requirements for bolts for high-end applications are as follows: 1. Corrosion resistance requirements, measured by the hours of salt spray resistance test, generally require more than 720 hours; 2. Strength requirements; 3. Tightening torque consistency requirements.
Corrosion resistance requires electroplating coatings. Generally, zinc-aluminum coatings, zinc-iron coatings, and zinc-nickel coatings are required according to the requirements of salt spray experiments. Strength requirements require the use of high-quality steel and a stable heat treatment process. The tightening torque consistency requirement is more complicated and is a combination of various factors: first, the consistency of the raw material and the stability of the heat treatment process are required to make the hardness and metallurgical organization of the bolt after heat treatment consistent; second, the stability of the key dimension of the bolt is required In general, the tolerance is required to be controlled at the level of 0.01 mm; finally, the consistency of the electroplated coating is required. Not only the thickness of the coating is stable, but the composition of the coating is also consistent. It is easier to reach certain targets, but it is more difficult to meet all the targets, not to mention that mass production can also meet all performance targets.
Specific to the specific manufacturing process of bolts. For bolt manufacturing, it is necessary to purchase wire rods with standard diameters from steel mills, and then perform drawing processing to obtain wire rods with specific diameters. There is no problem in China in this respect. Domestic Baosteel and other enterprises can provide high-quality raw materials, and the drawing molds and processes are also very stable.
The next step is the cold heading process of bolts. This process requires a cold machine. Generally, a bolting machine with 5 stations is required to manufacture bolts. The first station is to break the wire according to a specific length. It is necessary to accurately control the length of the blank. The next few stations are progressively formed bolts (except for threads). These processes need to control the critical dimensions such as length, diameter, etc., and the tolerance needs to be controlled at the level of 0.01mm. In addition to the stability of the cold head machine, this process requires particularly high cold heading molds. After all, all dimensions are guaranteed by the mold. The domestic situation is that the molds can basically be domestically produced, but the high-end cold machine is basically monopolized by Dutch Nedschroef, American National Machines, and manufacturers in Germany and Japan. The domestic and Taiwanese coldheaded machines basically monopolized the low-end market.
The third process is thread rolling. Threading the thread with a tooth plate on a thread rolling machine is also a key process, and the requirements for the stability of the machine and the thread rolling plate are also quite high. The high-end thread rolling machine market is basically monopolized by Europe, America and Japan, and the low-end market is occupied by Chinese and Taiwanese manufacturers. The domestic high school, low school and fish dragon of the thread rolling board are basically mixed.
The thread rolling board usually needs to be used in pairs
The next step is heat treatment. The heat treatment of bolts generally uses a continuous continuous heat treatment furnace, which is suitable for the needs of mass production. Generally need to go through these stages: cleaning and degreasing, quenching, cleaning and tempering. The heat treatment process is of great importance to the mechanical properties of the bolts. The temperature stability of the entire process is very high. The high-end market is basically occupied by foreign countries, and domestic brands occupy the low-end market.
The last is the surface treatment, usually electroplating. The thickness control and composition control of the plating layer not only affect the anti-corrosion effect, but also directly affect the consistency of the tightening torque. There are some professional electroplating manufacturers in China that can meet the requirements of the specifications.
Finally, back to the question, why are high-end bolts imported in large quantities? In fact, although many domestic equipment can not meet the manufacturing needs of high-end bolts, but these manufacturing equipment can be imported, many domestic manufacturers use imported equipment in large quantities, the equipment is not bad, the process is also very stable, and can fully manufacture high-end bolts. Moreover, many foreign high-end bolt companies have also set up factories to produce in China, and their equipment and process level are the same as abroad. So why do many applications prefer to import rather than using domestic bolts? Take the automobile industry as an example. The automobile industry is the industry with the most imported high-end standard parts in China.
Automated bolt tightening machines are commonly used in modern automobile assembly lines, which not only automatically monitor the tightening torque, but also monitor the number of tightening turns and angles at the same time. The purpose is to prevent safety problems caused by bolt tightening problems. The setting of bolt tightening torque requires a lot of testing and verification. Since a large number of domestic OEMs do not master the core technology, this part of the test verification work is basically done abroad. When conducting test verification work abroad, bolts produced abroad are generally used. After the verification of all the tests is completed, it only needs to be used for domestic production.
Multi-axis bolt tightening machine
Some people may ask, is it not enough to switch directly to domestic bolts when the vehicle is domestically produced? The problem is not so simple. Once the bolt tightening machine of the vehicle assembly line has completed the parameter setting, there are only two possibilities to switch to the domestic bolt when the vehicle is domestically produced:
Domestic bolts can fully meet the existing tightening machine parameter settings without any changes. It is almost impossible. The reason is that there are too many parameters that affect the tightening torque. Domestic bolts need to be exactly the same as those of foreign bolts. This is no longer a problem of process stability, but requires complete replication, which is impossible.
Re-test the tightening torque using domestic bolts. This possibility is also very small. First of all, the authority to change joint venture OEMs is basically in the hands of foreign parties. People simply do not have the will to do this. Secondly, even with this will, the price is very high. To re-test the torque test, it is necessary to stop the entire assembly line, and it is not impossible to stop for an hour or two, but in days. In the end, it is not worth the loss. Because the bolts are standardized and automated mass production, the production cost abroad is not much different from the domestic one. Switching to domestic production will not save much money. Considering the test verification cost of the switch, the cost performance is too poor. Basically, no one wants to do this.
The import of large quantities of standard parts such as bolts does not reflect problems in China's standard parts manufacturing industry, but reflects that many high-end industries in China are still in the hands of the West, and China does not have the right to speak. In comparison, domestic normal companies started to use domestic bolts for torque test verification at the beginning of the assembly line, and it was basically impossible to test imported bolts.
Of course, the lack of domestic high-end bolt manufacturing equipment still needs attention. After all, China cannot stay in the low-end industry forever, and climbing to the high end of the value chain is an inevitable choice.