The idiom "Made to die" must have been no stranger to us. It now means to make a serious mistake. However, if you want to trace back to the source of the word, it actually refers to the meaning of casting into a large file, and the so-called casting, is one of the ways of metal processing, is the casting of liquid metal to fit the shape of the part In the cavity, after it is cooled and solidified, a metal processing method of a metal part blank having a certain shape, size, and performance is obtained.
Metal processing methods include a total of five: casting, plastic forming, cutting, welding and powder metallurgy, of which the oldest is the casting.
Traditional sand casting has a history of over 6,000 years. Until now, sand casting has accounted for more than 80% of all foundry parts due to its advantages of low cost, simple operation, and limited scale, etc. Accessories often need to be made by sand casting. It can be said that casting has always been inextricably linked with “big”.
And today's very hot additive manufacturing technology (often called 3D printing technology) is a breakthrough in manufacturing principles, it does not require any special auxiliary tools, and is not subject to batch size restrictions, can be directly from the CAD 3D model Rapidly transforming into a three-dimensional solid model, the product cost is almost irrelevant to the complexity of the parts. It is particularly suitable for the manufacture of complicated parts with fine internal structures, and the manufacturing flexibility is very high. A machine can be used to make various kinds of products. Various shapes of parts, and with the further development of technology, the accuracy of parts is also increasing.
So, what if you combine 3D printing technology with traditional metal processing technology? Let's start with the application of 3D printing technology in the foundry industry.
(A) The traditional sand casting is not only big, but also silly, black, rough
The traditional sand casting is really stupid, black and thick, and the four words never fall.
Silly is that the sand casting process requires a lot of labor.
Just like playing sand (of course not ordinary sand), foundry workers need to manually put one by one into the sand for casting, and then remove the pattern after compaction to make a sand pattern to simulate the shape of the part. Immediately afterwards, a core is squeezed out of the core box to simulate the inner cavity of the part. The sand mold and the sand core are used to form a cavity in the shape of a part. Finally, the liquid metal is poured into the cavity formed by the sand. .
If the parts are too large to move, the cranes in the workshop will be needed to help with the lifting during the casting... It can be said that the numerical control and automation technology has developed to the present, and sand casting has achieved very little automation.
“Big” refers to several other processing methods. Because casting is inexpensive and not precise, sand casting is often used to make some large blanks, and the machining continues to follow.
The "black" is because the workers' working environment is filled with black mud and sand dust, and it is impossible to clean the work day.
As for "coarse", since the principle of casting is cooling of metal liquid, the metal undergoes drastic state changes and the volume shrinks. In addition, the accuracy of the sand type is also difficult to control. In order to facilitate the removal of the pattern during sand molding, it is necessary to design. Some draft angles cause inaccurate manufacturing and are "coarse".
(B) 3D sand type printing makes operation simple, but efficiency and precision increase
The application of 3D printing in casting greatly changes the complexity of traditional sand casting processes, low automation, and low manufacturing precision.
The more complex the structure of the traditional sand casting parts, the more difficult the sand molds are made to be difficult. At this time, only the delicate design can make a required cavity for casting without interfering with each other, which greatly depends on the level of the workers.
In 3D printing, sand is stacked layer by layer, and then the resin is sprayed through the nozzle according to the shape of the cross-section of the part (for example, cold-formed furan resin, phenolic resin, etc.), and the sands can be bonded together through repeated sanding - selective The operation of spraying adhesive resin realizes an extremely complex geometry, and the operation can be simple and crude without any effort.
In addition, the 3D sand type printing technology does not require the production of molds and core boxes for the production of molds. At the same time, the sand molds can be manufactured automatically and with high precision, the process cycle is greatly shortened, and the manufacturing cost is reduced.
In addition, its appearance has also greatly improved the labor environment of workers, reduced the labor intensity, and greatly reduced the operational skills requirements of workers. However, the production efficiency has improved, and the silly and thick casting industry has become a “My Fair Lady”. ".
This kind of technology is extremely aesthetic. Although it lacks the craftsmanship of the handicraft industry, it is more efficient and accurate.
(3) China's 3D sand printers: large size, high efficiency and low cost
Due to these advantages mentioned above, the industry makes 3D sand type printers in the industry have a very broad application space in the foundry industry; but many previous printers have a small print space and cannot print large sand molds and cannot be used for casting such as ships. , Cylinder heads, crankshafts and other large parts of internal combustion engines for trains.
Before China achieved independent research and development, the imported 3D sand type printer was extremely expensive. The printing space provided by the German company was a 4m x 2m x 1m 3D sand type printer, which was the world's largest machine at the time and required approximately 2.3 million U.S. dollars; Another large-scale industrial 3D sand printer provided by another US company has a printing space of 1.8 meters by 1 meter by 0.7 meters. It also costs 1.3 million to 1.5 million dollars, which is not costly and not large enough.
Fortunately, at the beginning of 2016, China's independently-developed sand printer passed the test and was put into use. This machine is designed with two work boxes at the same time. The print space of a single work box is 2.2 meters by 1.5 meters by 0.7 meters. The price is RMB 6 million is the largest sand-type 3D printer in the world.
When using this 3D sand type printer to manufacture locomotive engine parts for CRRC, the number of laborers involved has reduced by more than half compared to conventional sand casting methods, and the production rate of engine cylinder head parts has increased from about 60% to 95%.
(4) Localization of more than just printers, key parts and raw materials
For sand type printers, the quality of the sanding directly affects the strength, surface quality, and sand size accuracy of the printed sand. Among them, the two main functions of the sander are to uniformly sand and scrape the lower sand surface.
In the same type of foreign products, there is a certain gap between the sanding plate and the sand surface of the sanding device. If the sanding device does not move accurately, the sand accumulated before the sanding plate will flow from the gap to the previously scraped sand surface to form a size. Small “hills”, though not directly recognizable by the naked eye, can affect the accuracy and surface quality of printed sand sizes. In addition, in the prior art sander, because the lower sand port is fixed, the amount of the lower sand is not easily adjusted, and it is not possible to adjust the amount of sand according to the type of sand and the real-time demand for sand coating.
The domestic large-scale 3D sand printer sander overcomes these technical difficulties. By setting the secondary scraping board in an ingenious way, the sand opening can be changed to a 2-8mm interval, which greatly improves the quality of the printed product.
Another important component of the sand printer is the print head, which affects the product's printing efficiency, print quality, and so on.
The objects printed by the casting printing apparatus are large, the single ink jet printing stroke is long, and the time for completing a round-trip printing task is longer. Since printing objects are layer by layer, it often takes a long time to print, and it takes even a dozen or tens of hours. At the same time, the print head device itself is heavily negative, resulting in the print head being easily deformed after a long period of operation, resulting in an inability to meet the requirements for printing accuracy and affecting the print quality of the product.
The above-mentioned German 3D sand type printer does not hesitate to reduce its size in order to reduce the weight of the print head, and it requires two reciprocations to cover the entire printing space, which reduces the printing efficiency.
The Chinese-made print heads have arrayed the nozzles. The area of a single print is large and the efficiency is improved accordingly; the continuity of printing is ensured by optimizing the ink supply system; after the long-term work of the print head, an additional adjustment stretching device is provided. The direction of the calibration, to ensure the accuracy of the print.
In addition to the localization of equipment, the sand used in the 3D printing process has also been independently developed. These sands are not ordinary sand, and their grain size, acid consumption value, and microscopic form must meet the corresponding printing requirements and cannot be realized. Prior to independent development, the cost remained high.
The substitution of domestically produced sand has reduced the cost by two-thirds. The curing agent has been independently developed and its cost has dropped to a quarter. The domestic resin has also fully met the printing demand.
The wave of smart manufacturing has swept the world, and new manufacturing methods represented by 3D printing are gradually entering ordinary Chinese factories, transforming the traditional labor-intensive manufacturing process into more and more intelligent, environmentally friendly, and high-efficiency, and also improving the Chinese manufacturing industry. Global competitiveness.