With requirements for lightweight vehicles, engines are becoming more integrated and structures of die-casting parts are becoming more and more complex. Emergence of dense oil passage holes makes die-casting production more difficult. This type of oil channel has dense holes and long oil channels. In actual production, core pulling jamming and breakage often occur, causing production line to stop and causing large losses. Therefore, based on production experience, a core-pulling quick-change guide mechanism for die-casting molds was designed, which has good practical application results and provides a reference for solving problems such as die-casting core-pulling jamming and breakage. While optimizing core-pulling quick change, it also serves as a guide for long core-pulling, ensuring smooth extraction of castings and improving reliability of mechanism.
Graphical results
Shell of an engine chain cover has a special structure. There are many dense oil passage holes on fixed mold side, length exceeds conventional core pulling. If these oil passage holes are not die-cast, mold structure will be simple and production will be stable, but wall thickness will be thicker and it is easy to produce hot spots, which will lead to exposure of gas shrinkage holes during subsequent machining and cause gas leakage between oil passage holes, resulting in defective products. If a multi-axis core-pulling structure is used for production, problems of stuck long core-pulling and quick-change core-pulling sleeves need to be solved. After analysis and research, a core-pulling quick-change guide mechanism was adopted. Core pulling position and specific parameters of product are shown in Table 1 and Figure 1. It can be found from Table 1 that core-pulling lengths in Area 1 and Area 2 are longer and conventional core-pulling structures are used, which may easily cause mechanism failure during production process.

Table 1 Core pulling parameters at different locations in the chain cover shell

 

Figure 1 Multi-axis core-pulling area of chain cover housing

 

Figure 2 Conventional core-pulling structure
1. Oil cylinder 1 2. Oil cylinder bracket 3. Core-pulling needle seat 4. Core-pulling needle sleeve quick change plate 5. Product 6. Oil cylinder 2 7. Coupling 8. Guide rail 9. Core-pulling needle 10. Core-pulling needle cover

 

Figure 3 Core-pulling needle insertion state

 

Figure 4: Core-pulling needle withdrawn state
It can be found from Figures 3 and 4 that matching section between needle sleeve and core-pulling needle is only 30mm (if matching section is longer, it will easily cause core-pulling needle to get stuck in needle sleeve. According to experience, general length of matching section is 25 to 30mm. ), when core-pulling needle pulls away from product, straight section of core-pulling needle separates from mating section of needle sleeve. Since matching section between core-pulling needle and core-pulling needle seat is short and there is a gap, and core-pulling needle is long, core-pulling needle is in a sinking state under influence of gravity. After shell is taken out and core-pulling needle is inserted into core-pulling needle sleeve again, core-pulling needle is easily stuck between mating section and avoidance section of core-pulling needle sleeve. In order to solve problem that core-pulling needle is easily stuck between mating section and avoidance section of core-pulling needle sleeve, so that core-pulling needle can smoothly enter mating section of core-pulling sleeve, it is necessary to solve problem of core-pulling needle sinking due to gravity when it is pulled out of core-pulling needle sleeve. Therefore, it is assumed that when core is pulled out of shell, a guide hole is needed in the middle of core needle to form a preliminary guiding effect in the middle of core needle. The best position for this guide hole is on core-pulling needle sleeve quick-change plate (see Figure 5), therefore, a positioning hole 0.2mm larger than one side of core-pulling needle body is designed on quick-change plate, so that core-pulling needle will not sink before entering core-pulling needle sleeve, allowing it to enter core-pulling needle sleeve smoothly.

 

Figure 5 Core pulling guide hole

 

Figure 6 Split quick-change guide quick-change plate

 

Figure 7 Schematic diagram of working principle of quick change plate

 

Figure 8 Actual mold diagram
This core-pulling quick-change guide mechanism has a simple structure and is suitable for various multi-axis long core-pulling structures. Length and position of core-pulling forming are different and need to be designed accordingly according to actual situation. This can not only extend life of core-pulling mechanism, save production and maintenance time, but also improve stability of mechanism.