In recent years, energy conservation and emissions reduction has become the zeitgeist, automotive lightweighting is also the trend of The Times, in the two big background, aluminum alloy material used more widely in the car with the help of die-casting molding automobiles parts more and more. As the core parts of the car engine cylinder mostly adopts aluminum alloy and cast iron materials, including die casting aluminum alloy cylinder block has been more and more recognition, Japan and South Korea and the European and American car companies mostly use the die casting aluminum alloy cylinder block.
In the field of cylinder production, ordinary sand cast iron cylinder has the advantages of simple process, low cost, rigidity and heat resistance, but also has a disadvantage, which is that it is too heavy. Such as the block at the bottom of the crankshaft and at the top of the cylinder liner is split in two, the use of aluminum alloy and cast iron used above, you can kill two birds with one stone, both to reduce the quality of cylinder block and can keep the advantages of cast iron cylinder block again.
The lower cylinder block is the crankshaft part of the engine that has been divided into two parts. Because the cylinder block is thick wall parts, and the wall thickness is very different, it is very difficult to die casting. We draw on relevant experience at home and abroad, and develop a set of cylinder die casting technology for type 1.5T engine. The experiment is very successful.
1. Difficulties in die-casting of cylinder body under aluminum alloy.
The casting quality of the aluminum alloy is 8.4kg, the contour size is 382mm x 258mm * 67mm, the die casting quality is 11.1kg, the material is A380, and the average wall thickness is 7.2mm. Because the lower cylinder is connected to the crankshaft, cast iron inserts are also needed at the bottom.
The process of casting die casting is complex, and the difficulties are as follows:
First, the castings need to be placed in 5 castings of cast iron, and cast iron inlays are perfectly inlaid on top of aluminum alloy castings, which cannot be separated.
Second, the thickness of the wall thickness of the cylinder block is as thin as 2mm, the thickest thickness is 24mm, and the distribution is very uneven.
Thirdly, due to the large difference between the two sides, the liquid filling of aluminum alloy is very difficult, and it also tests its ability to make up.
Fourth, aluminum alloy castings are prone to porosity, shrinkage, crack, shrinkage and other defects, and quality control is difficult.
According to the experimental analysis, the main points of the die casting technology of the cylinder block are as follows:
First, the scientific design of cylinder body die casting gating system, for the thin wall cylinder under the middle place insert position, upper and lower parts for most of thick, so we choose one casting, thus, liquid aluminum can be made of bottom side feed, through the middle insert after arrived at the top.
Second, we use the tooth chill exhaust vacuum die casting, chill exhaust piece of tooth profile and share can be improved by vacuum machine two thin wall caused by insufficient liquidity problems, ensure the casting quality.
Third, for the improvement of cast iron and aluminum alloy liquid wetting degree of inserts, we conducted inserts preheating, such not only ensures the molding after iron and aluminum alloy are not isolated, also increases the liquid aluminum liquidity.
After the experiment, we obtained the dense inner structure of the cylinder body, and the appearance formed well. In the process of cylinder die casting, the scientific and reasonable technological parameters are the guarantee of the cylinder body with high quality. We believe that the following process parameters are the key influencing factors for casting molding:
First, die casting temperature. In the process of die casting, aluminum liquid temperature should be controlled well, because the temperature too high or too low can achieve good effect of casting, easily lead to high porosity and shrinkage, low is likely to cause a bad filling. Generally speaking, the liquid aluminum reasonable temperature should be between 650-665 ℃, and the temperature of the mold after spraying should be between 150-200 ℃.
Second, the setting temperature. When inserts of 120-140 ℃, liquid aluminum side of the overflow groove side, so that we can improve the internal quality.
Third, casting fast, slow pressure shooting speed and pressure. The fast and slow injection speed should be controlled at about 4m/s and 0.22m/s respectively, and the pressure is controlled at about 70MPa.
Fourth, aluminum liquid quality. As the base material of the casting, the quality of the aluminum liquid determines the quality of the casting. Therefore, to ensure the quality of the aluminum alloy, every aluminum solution must be refined and degassed to avoid contamination.
Casting defects and coping with aluminum alloy cylinder.
After the casting process, we tested the casting and found some internal defects such as shrinkage cavity, porosity and shrinkage. In order to improve the defects and improve the quality, we put forward the corresponding countermeasures. The main direction is as follows:
First, improve the overflow tank structure. The overflow tank has the function of excluding gas in the cavity, storing and mixing gas, and transferring shrinkage cavity. After repeated trial and study, we found that we can improve the shrinkage cavity, porosity and other defects by extending and adding the overflow tank. Due to the large shrinkage of the central part of the casting, if the overflow port is set on the flat surface, the filling pressure will be affected, so the vertical overflow port is usually chosen.
Second, optimize the mold cooling system. The shrinkage cavity of the casting will usually appear in the position of high local temperature or excessive wall thickness. Through the study, we found that the temperature on the two sides of the wall is high, which can easily trigger the shrinkage cavity. Due to the minimum point of cooling is initially tube diameter of 12 mm, not effective cooling of the above position, therefore, we to the cooling water pipe structure was improved, using the high pressure cooling equipment and the inner diameter of 4 mm stainless steel cooling tube. We will be on both sides of the casting mould core in central cooling to about 180 ℃, sharply reduce the phenomenon of shrinkage cavity and greatly improved the quality of castings.
Third, improve the separation of inlays. In view of the separation phenomenon between inlaid parts and aluminum alloy castings, we adopt the following measures: first, the inlaying parts are cleaned with the thinner to improve wettability; Secondly, the positioning hole inspection and appearance inspection of the inserts are carried out. Third, inserts for preheating test, the study found that when the temperature is above 120 ℃, can effectively solve the problem of separation of inserts.