Die Casting Design Considerations

Die-casting mold is one of the three major elements of die-casting production, the structure is correct and reasonable mold is the success of die-casting production conditions, and to ensure the quality of castings (under the machine pass rate) plays an important role. Because of the characteristics of the die-casting process, the correct selection of the process parameters is the decisive factor for obtaining high-quality castings, and the mold is the prerequisite for the correct selection and adjustment of the process parameters. The mold design is essentially a variety of factors that may occur in die-casting production Comprehensive reflection. If the mold design is reasonable, in the actual production of the problems encountered less castings under the pass rate is high. On the other hand, the mold design is unreasonable, the casting force of the casting mold is basically the same, and the pouring system is mostly in the fixed mold, and placed in the shot after the punch can not feed the production of irrigation die casting machine can not be normal production, The casting is always stuck on the mold. Although the mold cavity clean finish playing very light, because the cavity deep, still appear on the fixed mold on the phenomenon. Therefore, in the mold design, we must fully analyze the structure of the casting, familiar with the operation of the die-casting machine, to understand the die-casting machine and process parameters to adjust the possibility of mastering the filling characteristics in different circumstances, and consider the mold processing methods, Eyes and fixed form, to design a realistic, to meet the production requirements of the mold. At the beginning, it has been said that the filling time of the molten metal is extremely short, the specific pressure and the flow rate of the molten metal are very high, and the working conditions are extremely poor for the die-casting mold, and the impact of the alternating heat Role, have a great impact on the life of the mold. The service life of the mold is usually referred to by the careful design and manufacture, under normal conditions of use, combined with good maintenance under the natural damage, before the repair can not be repaired, the die-casting modulus (including die-casting production Of the number of waste).

The actual production, die failure mainly in three forms:

① thermal fatigue cracking failure;

② fragmentation failure;

③ dissolution failure.

There are many factors that cause mold failure, both external factors (such as the level of casting temperature, whether the mold is preheated, the amount of water spray coating, the size of the die-casting machine tonnage match, die pressure is too high, the gate too fast, Water is not synchronized with the die casting production, casting material types and composition of the height of Fe, casting size, wall thickness, paint type, etc.). (Including the mold quality of the material itself, the forging process of the blank, the rationality of the mold structure design, the rationality of the design of the pouring system, the internal stress generated during the machining of the mold machine (electric machining), the heat treatment process of the mold, including Various matching accuracy and finish requirements, etc.). If the mold appears early failure, you need to find out what internal or external causes, in order to improve the future.

① die thermal fatigue cracking failure die casting production, the mold repeatedly by the role of cold and hot, forming the surface and its internal deformation, involving each other and repeated the thermal stress, resulting in damage to the structure of the two structures and loss of toughness, causing micro-cracks And continue to expand, once the crack is expanded, there are molten metal liquid squeeze, coupled with repeated mechanical stress to accelerate the expansion of the crack. To this end, on the one hand die die must be fully warmed. In addition, in the die-casting process, the mold must be kept within a certain operating temperature range, so as to avoid early cracking failure. At the same time, to ensure that the mold before production and manufacturing within the internal problems do not occur. Due to the actual production, the majority of die failure is thermal fatigue cracking failure.

② fragmentation failure in the role of pressure, the mold will be the most weak in the initiation of cracks, especially the mold forming surface of the crossed traces or electrical processing traces are not polished light, or forming the angle will be the most First appear fine cracks, when the grain boundary there is brittle phase or grain coarse, that is easy to break. And the brittle fracture crack propagation is very fast, which is the fracture of the mold failure is a very dangerous factor. To this end, on the one hand where the mold surface scratches, electrical processing traces must be polished, even if it is in the casting system parts, must also be lighted. Also require the use of the mold material of high strength, good plasticity, impact toughness and fracture toughness are good.

③ molten failure has been mentioned earlier, commonly used die-casting alloys are zinc alloy, aluminum alloy, magnesium alloy and copper alloy, there are pure aluminum die-casting, Zn, Al, Mg is more active metal elements, Good affinity, especially Al easy bite mold. When the mold hardness is high, then the corrosion resistance is better, and the molding surface if the soft point, then the corrosion resistance. However, in the actual production, the erosion is only part of the mold, where the gate directly washed the site (core, cavity) prone to dissolution phenomenon, and the hardness of the soft side of the aluminum alloy prone to sticky mold. Die-casting production often encountered in the mold problems Note:

First, pouring system, overflow system

1, for the cold room horizontal die casting machine on the mold sprue requirements:

a. The diameter of the chamber should be selected according to the required specific pressure and pressure chamber filling degree. At the same time, the deviation of the inner diameter of the gusset sleeve should be appropriately enlarged by the deviation of the inner diameter of the compaction chamber, The inner diameter of the chamber is different from the shaft and the punch is stuck or the wear is serious. The wall thickness of the sprue can not be too thin. The length of the gusset should generally be less than the delivery of the plunger so that the paint is removed from the chamber.

b. The inner hole of the pressure chamber and the sprue sleeve shall be ground after the heat treatment and then ground in the direction of the axis, and its surface roughness ≤ Ra0.2μm.

c. Splitter and paint the formation of the cavity, the depth of the groove is equal to the depth of the runner, the diameter of the inner diameter of the sprue, along the stripping direction of 5 ° slope. When the coated inlet runner is used, the fullness of the pressure chamber can be increased by shortening the effective length of the press chamber.

2, for the requirements of the mold runner

① cold horizontal mold runner entrance should generally be located in the upper part of the upper part of the pressure chamber more than 2/3, so that the pressure chamber in the metal under the action of gravity into the runway prematurely, began to solidify in advance.

② cross-sectional area of the runner from the sprue to the gate should be gradually reduced, in order to expand the cross-section, the metal flow through the time there will be negative pressure, easy to inhale the surface of the gas, increase the flow of molten metal In the vortex wrapped up. The general exit section is 10-30% smaller than the entrance.

③ The runner should have a certain length and depth. Maintain a certain length of the purpose is to stabilize and guide the role. If the depth is not enough, the metal liquid cooling fast, the depth is too deep, because the condensation is too slow, both affect the productivity and increase the amount of back to the furnace.

④ cross-sectional area of the runner should be greater than the cross-sectional area of the gate to ensure that the metal liquid into the type of speed. The cross-sectional area of the main runner should be greater than the cross-sectional area of each branch runner.

⑤ the bottom of the runner should be rounded on both sides, so as to avoid early cracks, the two sides can make about 5 ° slope. The surface roughness of the runner site is ≤ Ra0.4μm.

3, the gate

① metal liquid into the type should not immediately close the sub-surface, overflow tank and exhaust tank should not be positive impact core. After the metal liquid into the flow as far as possible along the cast ribs and heat sink, from the thick wall to fill the thin wall and so on.

② When selecting the gate position, make the molten metal flow as short as possible. The use of multi-strand gates, to prevent the accumulation of several kinds of metal after the convergence of the liquid, the impact of each other, resulting in vortex charcoal and oxide inclusions and other defects.

③ thin-walled parts of the inner gate to be appropriate to make smaller, to ensure that the necessary filling speed, the gate should be set to facilitate the removal, and does not make the casting body defect.

4, overflow slot

① overflow tank to facilitate removal from the casting, and try not to damage the casting body.

② When opening the exhaust slot on the overflow tank, pay attention to the position of the overflow port, to avoid premature obstruction of the exhaust slot, so that the exhaust slot does not work.

③ should not be in the same overflow slot to open a few overflow or open a very wide and very thick overflow port, so that the molten metal in the liquid, slag, gas, paint and so on from the overflow tank to return to the cavity , Resulting in casting defects.

⑤ cast rounded corners (including corners) castings are often marked with no rounded corners R2 and other requirements, we should not ignore the open mold when the role of these fillets are not marked, never made clear or too small round angle. Casting fillet can fill the metal liquid smoothly, so that the cavity gas discharge, and can reduce the stress concentration, extend the service life of the mold. (Casting is not easy to appear in the cracks or fill due to fill a variety of defects). The standard oil plate mold on the clearance at the more, relatively speaking, the current brother of the oil plate mold to open the best, heavy oil pan is also more.

⑥ stripping slope in the direction of stripping is strictly prohibited people caused by the side of the concave (often try to die when the mold in the mold, with an incorrect way to deal with, drilling, hard chisel, etc. to the local concave).

⑦ surface roughness forming parts, pouring system should be required to seriously light, should follow the direction of hair removal. As the metal liquid from the pressure chamber into the casting system and fill the cavity of the whole process only 0.01-0.2 seconds. In order to reduce the resistance of the molten metal flow, as much as possible to reduce the pressure loss, need to flow through the surface of the high finish. At the same time, the gating system parts of the heat and erosion of the conditions worse, the worse the mold is easier to damage the mold.

5, the hardness of mold parts aluminum alloy: HRC46 ° about copper: HRC38 ° processing, the mold should try to leave the remaining capacity, do the size of the ceiling, to avoid welding.

Die-casting mold assembly of the technical requirements:

① mold parting surface and template plane parallelism requirements.

② guide column, guide sleeve and template vertical requirements.

③ sub-surface on the dynamic, fixed-mode inserts plane and moving sets of mold plate higher than 0.1-0.05mm.

④ push plate, reset rod and sub-surface is flush, the general putter concave 0.1mm or according to user requirements.

⑤ all the active parts of the mold activities are reliable, no sluggish pin pinless.

⑥ slider positioning and reliable, the core out of the casting and keep the distance, the slider and the mold after the mold with more than 2/3.

⑦ Sprue roughness is smooth and seamless.

⑧ joint mold when the sub-part of the local surface gap <0.05mm.

⑨ cooling waterway, import and export signs.

⑩ forming surface roughness Rs = 0.04.

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