Hitachi America Ltd., R&D

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ADSTEFAN

Dynamic Characteristics of Sleeve Behavior Analysis

SUMMARY

    Most of the Die Cast machines are transversely mounted, and cast parts by pouring the molten metal into a long transverse projection sleeve and force the molten metal into the mold through the movement of a plunger.  Usually, the fluid amount that is poured into the projection sleeve is 30%～60% of the sleeves capacity. If the acceleration of the plunger is not accurate, a mixture of air and fluid inside of the sleeve may form when the plunger is pushed towards the gate.  The fluid will cool down rapidly and start to solidify if the amount of fluid that is pushed out is too small, and a chill fracture phase may occur and provide bad influences to the product.


RESULTS OF SLEEVE BEHAVIOR ANALYSIS

    The part to be analyzed is equipped with a gate and a runner.  The sleeve has a diameter of 50mm and length of 250mm.  Analysis of the plunger movement from the beginning state, with an initial condition (time=zero), and having the sleeve 40% full, was conducted.  The plunger speed can be programmed to change using a multi step, but it was analyzed with a constant speed pattern.  The mesh pitch was 1.8mm, divided 254 ways in the X direction, 186 ways in the Y direction, and 254 ways in the Z direction, for a total of a 10,015,728 element mesh.

    Figure 1 shows the analysis results of when the plunger speed was 1.0m/sec.    From the results of the analysis, we can see that a wave is being created from the movement of the plunger.  The wave continues to move around inside of the sleeve, as if running through the surface of the sleeve.  Finally we can see that a large air entrapment is formed at the gate.  When the fluid reaches the runner its speed is accelerated, this is caused by the narrowing of the duct, and flows into the cavity mold.  In this analysis, the influence of the pressure provided inside the sleeve is not considered, air is simply pressed down.  In actuality, air mixes to a certain level with the fluid and flows into the runner.

                  
                   Figure 1 Results of Sleeve Behavior Analysis
 

    Considering the overall model of the Die Cast (product parts, gates, runners, sleeves) we were able to illustrate the fluid flow analysis, including the fluid projecting phenomenon of metal flowing from the smelter.  A well known fact is that during the casting in a Die Cast machine, for a relatively large mold clamping force, the quality of the product varies largely depending on the timing that the fluid is projected.  It is believed that when the fluid is poured into the sleeve, a wave occurs from the momentum of the fluid.  Inside the sleeve, fluid moves from the plunger side to the gate side and then falls back to the plunger side.  When the fluid is projected and the wave folds over, the air entrapment that occurs is more than normal. If the fluid is projected at the time of the folding of the wave, as if the fluid is catching up to the wave, the air entrapment that occurs is less than normal.  So from this we can see that in a large Die Cast machine, a long and thick sleeve is more likely to have a prominent flow phenomenon.

    Shown in Figure 2 and Figure 3 are the analysis results of a 0.5m/sec. plunger.   The temperature of the fluid is shown by the color coding scale on the left. Red represents a high element temperature level and blue represents a low element temperature level. After some travel, the fluid temperature decreases when it comes into contact with the sleeve base and it is seen that the a blue area spreads out. The spreading of the blue is believed to happen since the fluid mixes with the sleeve as the surface area becomes larger.  While the temperature lowers, the fluid moves to the gate side, hits the wall and rises up.  When the fluid hits the gate wall the direction of the fluid is changed and it moves on top of the fluid surface back towards the plunger side.
    At the same time the fluid projection finishes, the plunger starts to move.  Since the plunger is slower than before, the fluid movement is relatively mild inside of the sleeve and air entrapment has not occurred.  Fluid that has gone into the runner through the gate flows into the cavity.  At this point, the temperature of the fluid that has been projected is about 100 degrees lower than the initial temperature(680 degrees), and a phenomenon which cannot be avoided is re-created in a transverse Die Cast process.
 

                   
Figure 2  Results of Sleeve Behavior Analysis　　 　　　Figure 3 Results of Sleeve Behavior Analysis (Cut Section)

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Last modified: 01/22/08