The casting process design involves the process design of the part itself, the design of the gating system, the design of the feeding system, the design of the vent, the design of the chill system, the design of the special casting process, etc.
The process design of the part itself involves the design of the machining allowance of the part, the selection of pouring position, parting surface, the selection of casting process parameters, the dimensional tolerance, the shrinkage rate, the draft angle, the amount of correction, the negative parting number, etc.
The pouring system is a channel that guides the molten metal into the mold cavity. Whether the pouring system is designed reasonably or not has a great impact on the quality of the castings, which can easily cause various types of casting defects, such as: insufficient pouring, cold isolation, sand washing, Casting defects such as slag inclusions, inclusions, sand inclusions, etc. The design of the gating system includes the selection of the type of the gating system, the selection of the position of the inner gate, and the determination of the cross-sectional dimensions of each component of the gating system. In addition, the choice of gating system is also very important, so how can we choose the correct gating system?
For mechanized assembly lines and mass production, in order to facilitate production and help ensure the quality of castings, the inner runner is generally set at the parting surface of the casting mold. According to the casting position of the casting blank and the selection of the parting surface, the inner casting The channel opening at the parting surface of the mold belongs to the “middle injection” gating system. Liquid metal will inevitably contain a certain amount of “slag” during the pouring process. In order to improve the slag retaining ability of the pouring system, it is suitable to adopt a “closed” pouring system.
In the casting process, the design of the casting process has a great influence on the quality of the cast product, but the choice of the gating system selection method cannot be ignored.
The design of the feeding system is a reasonable design of risers and subsidies to compensate for the liquid and solid contraction of the casting during the solidification process to obtain a sound casting.
The vent hole is used to discharge the gas in the cavity, improve the filling capacity of the molten metal, eliminate the supercooled molten metal and scum filled into the cavity first, and can also be used as a sign to observe whether the cavity is full.
Matters needing attention during the use of the wooden mold: Check whether the geometrical size of the casting has been deformed before using the wooden mold; put the wooden mold in the sand box, put the sand evenly, and balance the sand to prevent unevenness in softness and hardness. ,
Be careful when you hit the sand. Leave the wood mold about 2mm away. Don’t use sand rams to damage the mold. After the molding is completed, you must first walk around the wood mold when lifting the mold, but try not to beat with iron to prevent damage to the model.
When the mold is about 1mm away from the sand mold, gently lift it out with your hand or with a special tool. When the mold is in use, it is easy to bond to the sand, especially the water glass sand casting, which will damage the mold greatly. The mold release agent should be applied before the sand box; it is easy to come out when the model is out of the mold. If the model is found to have sand sticking, the cavity of the sand mold needs to be repaired, and the miscellaneous sand in the cavity should be cleaned up, and the casting of the sand core is required , After checking that the sand core is intact, put it into the cavity, put on the top and bottom core irons, and prepare the chassis. Pay attention to the two box marks or the locks on the chassis.
Another point for sodium silicate sand casting is to use CO₂ gas to solidify the sand in a timely and uniform manner, and to dry the filled cavity with an open flame. Complete the chassis, add tightening screws and pressure box.
Disadvantages of sand casting: The mold should be appropriately increased in the inclination used when drawing the mold. On the bamboo slips, there is a heavy weight and time-consuming machining. The runner system is easy to flush sand, and the cavity is unevenly soft and hard, which will cause local sand sticking, and cleaning time is time-consuming.