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

Die-casting production often encountered in the mold problems exist in the attention of the following points.

1、Pouring system, overflow discharge system

(1) For the requirements of the straight sprue of the mould on the cold chamber horizontal die-casting machine: ① The size of the inner diameter of the press chamber should be selected according to the required specific pressure and the fullness of the press chamber, meanwhile, the deviation of the inner diameter of the sprue sleeve should be appropriately enlarged by a few threads compared to the deviation of the inner 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 sleeve and the inner diameter of the press chamber, and the wall thickness of the sprue sleeve should not be too thin. The length of the gate sleeve should generally be less than the delivery range of the pressurised punch, so that the paint can be removed from the pressure chamber. ② The inner hole of the pressure chamber and the sprue sleeve should be finely ground after heat treatment and then ground in the direction of the axis, with a surface roughness ≤ Ra0.2μm. ③ The diverter and the concave cavity where the paint 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 the coating is introduced into the straight sprue, the volume of the effective length of the pressure chamber is shortened and the filling of the chamber can be increased.

(2) Requirements for the mould cross sprue: ① The entrance of the cold horizontal mould cross sprue should generally be located in the upper part of the pressure chamber above 2/3 of the inner diameter, so that the metal liquid in the pressure chamber will not enter the cross 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 have an enlarged cross-section, there will be a negative pressure when the metal liquid flows through, and it is easy to inhale the gas on the parting surface, increasing the vortex in the flow of the metal liquid to wrap the 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. The cross-sectional area of the horizontal 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 made with a slope of about 5°. The surface roughness of the cross sprue should be ≤ Ra0.4μm.

(3) Inside the sprue: ① The metal liquid should not be closed immediately after entering the mould, and the overflow and exhaust slots 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.. ②When choosing the location of the internal gate, make the liquid metal flow as short as possible. When using multiple internal gates, to prevent the convergence of several strands of metal liquid into the shape, mutual impact, thus producing 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 groove should be easy to remove from the casting and try not to damage the body of the casting. ②When 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 port 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): castings are often specified on the map is not rounded R2 and other requirements, we must not ignore the role of these unspecified rounded corners when opening the mould, must not be made into 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 in the place or due to filling is not smooth and various defects).

3, the slope of the mold: in the direction of mold release is strictly forbidden in the side concave caused by human beings (often test mold when the casting is stuck in the mold, with incorrect methods of processing, such as drilling, hard chisel, etc. to make local concave).

4, surface roughness: forming parts, pouring system should be carefully polished according to the requirements, should be polished in the direction of mold 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, the hardness of the mould forming part, aluminium alloy: HRC46 ° or so; copper: HRC38 ° or so; processing, the mould should try to leave a margin of repair, do size of the upper limit, avoid welding.

Technical requirements for die-casting mould assembly: 1. Requirements for parallelism between mould parting surface and template plane. 2、 The requirement of verticality of guide pillar, guide sleeve and template. 3、The plane of the moving and fixed mould insert on the parting surface is 0.1-0.05mm higher than that of the moving and fixed mould plate. 4、The push plate and reset lever are flush with the parting surface, generally the push lever is recessed into 0.1mm or according to the user's requirements. 5、All movable parts on the mould are reliable and free from crosstalk.

6、The positioning of the slider is reliable, and the distance between the core and the casting is maintained when the core is withdrawn, and the slider and the block are more than 2/3 of the matching parts after the mould is closed.

7、The roughness of the sprue is smooth and seamless.

8、Local clearance of the parting surface of the block when the mould is closed <0.05mm.

9、Cooling water channel is smooth, import and export signs.

10、Roughness of moulding surface Rs=0.04, no micro injury.