The structure of cylinder block casting is complex, and there are many internal cavities. For this kind of structure casting, the traditional casting process needs to consider the following points:
(1) The water cavity of the cylinder block is a relatively independent structure, and the sand core of the water cavity needs to be fixed to ensure the wall thickness of the casting. In traditional casting, the sand core is usually produced with the external mold or the main core after being molded separately. This production method has a large deviation in the size of the sand core. Because the sand core is long and thin, it is easy to deform and the production efficiency is very low.
(2) V-shaped cylinder belongs to 12 cylinder series, which has 6 internal gears and 6 cam cavities. In traditional casting, each internal gear and cam cavity must be formed with sand core respectively. This method will also bring quality risks such as size problem and sand inclusion, and the operation efficiency is low.
For the 3D printing process, the casting structure has a much smaller impact than the traditional process, and there are many options. A good core separation scheme has a great impact on the casting quality and on-site operation, The design of sand core separation scheme is shown in Figure 1.
It can be seen from Fig. 1 that according to this core separation scheme, the casting only needs five sand cores to be formed, of which five sand cores are used to form the overall structure of the casting, and the bottom sand core is easy to place the gating system.
From the structure of the whole cylinder block casting, the wall thickness of most parts of the casting is less than 15 mm. These thin wall cavity structures are not conducive to the design of the ingate position, which is easy to cause sand washing defects. The thicker position of the casting is between the cylinder ports of the casting. The wall thickness of this position is 60 mm, and the flow in the ingate at this position can avoid the risk of sand inclusion caused by direct core punching. In order to ensure that the gating system can play a better role in slag skimming, prevent the first strand of cold and dirty molten iron from entering the mold cavity, and reduce the flow rate of molten iron, the runner of gating system is arranged under the casting, and the form of open gating system and filter screen is adopted. The proportion of sectional area of gating system is Σ F straight: Σ F horizontal: Σ Fnet = 1: (1.5 ~ 2): (1.5 ~ 2), the size of filter screen is 100 mm × 100 mm × 25 mm SiC filter screen, pouring temperature 1 350 ℃.
In order to ensure the uniform feeding and temperature field of the casting, a special anti sand side riser for the foundation is specially designed. At the same time, an air outlet riser is also designed at the position of the bearing seat for the air outlet of the mold cavity, as shown in Figure 2.
In order to ensure the smooth mold filling, low flow rate, steady rise of liquid level, and prevent sand flushing and turbulence of molten iron, the simulation analysis of the designed gating system is carried out, and the simulation results are shown in Fig. 3. It can be seen that when the molten iron enters the mold cavity, the velocity of the ingate is very low, only 0.5 m / s, and the whole filling process of the casting is very stable, which meets the requirements of the process design.
The sand core design of 3D printing for cylinder block casting is shown in Fig. 4. It can be seen from Fig. 4 that only five sand cores are needed for the casting. The side appearance structure and riser of the casting are formed by the sand cores on both sides, the inner cavity structure and two end faces structure of the casting are formed by the integral sand core in the middle, and the cylinder appearance structure and gating system are formed by the two sand cores at the bottom, The sand cores are positioned by concave convex positioning table, which ensures the accuracy and efficiency of core setting.