The product cannot be poured in precision casting

The product cannot be poured in precision casting

In the production process of precision casting, many different problems will be encountered. Today, precision casting manufacturer Tianyao Metal will talk to you about the problems and solutions encountered in the production process of this product. A friend sent me a casting diagram and he said it was very difficult to dry. Although it has been tested multiple times, it still cannot be poured. I thought it wouldn't take shape if it couldn't be poured, but in reality, that's not the case. In fact, what he said about not being able to pour refers to the shrinkage of the casting, which causes water leakage after processing.

Casting pressure leakage indicates insufficient density of the casting, which must be due to shrinkage and porosity inside the casting. So, why do castings have shrinkage and porosity? Generally speaking, the internal shrinkage and porosity of castings are closely related to the structure of the castings themselves. For example, if the wall thickness of the casting is uneven and there are hot spots everywhere, it is not possible to use risers or gates for filling, or if the internal heat dissipation of the casting is uneven and local heat dissipation is poor, it can cause shrinkage and porosity in the casting. In fact, both of the above phenomena exist in this casting, and there are too many holes in the structural design of this casting. Of course, this is necessary for the functionality of the part itself. However, it is precisely because of this design that the hot spots of the casting are spread throughout the entire body of the casting. The casting needs to be filled and shrunk through a gate or riser to achieve densification, thereby achieving the goal of pressing without leakage, which is relatively difficult.

In addition, there are many places on the surface of this casting where a gate can be installed. However, due to the large number of holes on the casting, there is too much resistance to flow after designing the gate, and it is easy to cause the metal liquid to directly punch the core. This is a taboo in the pouring process design, so the casting forming is a problem, and there is no need to mention the layer of casting shrinkage. Therefore, it is relatively difficult to process and shape this casting using investment casting method according to the current design structure. Let's take a look at the two casting process designs in Figure 3 and Figure 4. The height of the casting is not small, with a size of about 250mm. Coupled with the vertical and horizontal distribution of holes in the middle of the casting, the first type of top pouring system appears to have many problems. Not to mention the oxidation of molten metal, but just the splashing of molten metal can easily cause cold shuts and inclusion defects on the castings, which will definitely greatly reduce the internal quality of the castings. The second option appears relatively reasonable compared to the first option, but the structure of the casting itself makes it impossible for the gating system design to fully function, and therefore, it cannot achieve the goal of casting density.

So, how should this precision casting solve the existing problems?

1、 Modifying the existing product structure does not mean changing the part structure, but rather changing the casting structure to make it more suitable for investment casting methods. For example, by plugging some holes and leaving a directional hole, the flow of molten metal is not obstructed, making it possible for the casting to shrink. Alternatively, it can be changed to an internal cold iron method and finally removed through processing.

2、 Adopting a bottom injection method for existing products to allow molten metal to smoothly enter the casting cavity, placing the largest surface on the lowest surface, and then adding a riser on the larger surface. When pouring to the top surface of the casting, switch to pouring from the riser to improve the filling and shrinking ability of the molten metal. Of course, if it could be supplemented by water cooling through the bottom hole, that would be the best thing.

From the above situation, we can see how important the structural processability of castings is. If these details can be handled well during contract negotiations in the early stage, it will benefit a lot from later production.

Precision machining