What are the common problems encountered in die casting mould production?

Thu May 04 14:41:34 CST 2023

1. Pouring system, overflow discharge system

(1) The requirements for the straight sprue of the mould on a cold chamber horizontal die casting machine are

①The size of the internal diameter of the press chamber should be selected according to the required specific pressure and the fullness of the press chamber. At the same time, the deviation of the internal diameter of the sprue should be enlarged by a few threads compared to the deviation of the internal diameter of the press chamber, so as to avoid the problem of the punch jamming or serious wear caused by the different axis of the sprue and the internal diameter of the press chamber, and the wall thickness of the sprue should not be too thin. The length of the gate sleeve should generally be less than the feed stroke of the pressurised punch, so that the paint can be removed from the chamber.

② The bore of the pressure chamber and the gate sleeve should be finely ground after heat treatment and then ground in the direction of the axis with a surface roughness ≤ Ra0.2μmDie casting mould

③ The diverter and the concave cavity where the coating is formed, with a recessed depth equal to the depth of the cross sprue and a diameter matching the inner diameter of the sprue sleeve, with a 5° slope along the direction of release. When using the direct sprue of the coating introduction type, the volume of the effective length of the pressure chamber can be improved by shortening the volume of the pressure chamber.

(2) Requirements for the mould cross sprue

① The entrance of the horizontal sprue of a cold horizontal mould should be located above 2/3 of the inner diameter of the upper part of the pressure chamber, so that the metal liquid in the pressure chamber will not enter the horizontal sprue prematurely under the action of gravity and start solidifying in advance.

② The cross-sectional area of the cross sprue should be gradually reduced from the straight sprue to the inner gate, in order to expand the cross-section, there will be negative pressure when the metal liquid flows through, and it is easy to inhale the gas on the parting surface, increasing the flow of metal liquid in the vortex wrapped gas. Generally the cross section at the outlet is 10-30% smaller than at the inlet.

③ The horizontal sprue should be of a certain length and depth. The purpose of maintaining a certain length is to play the role of steady flow and guidance. If the depth is not enough, the metal liquid will be cooled down quickly, and if the depth is too deep, the condensation will be too slow, which will affect the productivity and increase the amount of furnace material.

④ The cross-sectional area of the sprue should be larger than the cross-sectional area of the internal gate to ensure the speed of the metal liquid into the mould. The cross-sectional area of the main sprue should be larger than the cross-sectional area of each branch sprue.

⑤ The bottom sides of the cross sprue should be rounded to avoid early cracks, and the second side can be sloped by about 5°. The surface roughness of the cross sprue should be ≤ Ra0.4μm.

(3) Inner sprue

① The metal liquid should not be closed immediately after entering the mould, and the overflow groove and exhaust groove should not be impacted on the core. The flow direction of the metal liquid into the mold as far as possible along the cast into the rib and heat sink, from the thick wall to fill the thin wall, etc..

② When choosing the location of the internal gate, make the liquid flow as short as possible. When using multiple internal gates, to prevent the confluence of several strands of metal liquid into the shape, mutual impact, resulting in vortex pack gas and oxidation inclusions and other defects.

③ Thin-walled parts of the inner gate thick parts to be appropriate smaller to ensure the necessary filling speed, the setting of the inner gate should be easy to remove, and not make the casting body has defects (eat meat).

(4), Overflow groove

① The overflow channel should be easy to remove from the casting and try not to damage the body of the casting.

② When opening an exhaust slot on the overflow tank, attention needs to be paid to the position of the overflow opening to avoid prematurely blocking the exhaust slot and making the exhaust slot ineffective.

③ should not be opened in the same overflow tank on several overflow or open a very wide and thick overflow port, so as to avoid the metal liquid in the cold liquid, slag, gas, paint, etc. from the overflow tank back to the cavity, resulting in casting defects.

2, casting rounded corners (including corner)

Casting drawings often indicate the requirements of the unspecified rounded corners R2, we must not ignore the role of these unspecified rounded corners when opening the mould, never make a clear corner or too small rounded corners. Casting rounded corners can make the metal liquid filling smoothly, so that the cavity gas sequence discharge, and can reduce the stress concentration, extend the service life of the mold. (Castings are also less likely to crack at this point or have various defects due to poor filling). For example, the standard oil pan mould has more clear corners, relatively speaking, the current Brother oil pan mould is the best open, and the heavy machine oil pan is also more.

3、 Slope of demoulding

In the direction of mold release is strictly forbidden to be caused by human side concave (often when the mold test castings stick in the mold, with the incorrect method of processing, such as drilling, hard chisel, etc. to make local concave)

4、 Surface roughness

Molding parts and pouring systems should be carefully polished as required, and should be polished in the direction of mould release. As the metal liquid enters the pouring system from the pressure chamber and fills the cavity, the whole process only takes 0.01-0.2 seconds. In order to reduce the resistance to the flow of the metal fluid and to make the pressure loss as low as possible, all need to flow through the surface with a high degree of finish. At the same time, the pouring system part of the heat and erosion by the poorer conditions, the poorer the finish is, the easier it is to damage the mould.

5、Hardness of the moulding part

Aluminium alloy: HRC46° or so

Copper: HRC38° or so

When processing, the mould should try to leave a margin for repair, to do the upper limit of the size, to avoid welding.