Solutions and precautions for defects in aluminum die casting

1. Net-shaped hairy fins (turtle cracks)

Appearance inspection: there are raised or depressed traces like mesh hair on the surface of the die-casting parts, which continue to expand and extend as the number of die-casting increases.
The causes are as follows: 1) Cracks on the surface of the die-casting cavity 2) The methods for solving and preventing uneven preheating of the die-casting mold are: 1) The die-casting mold should be annealed regularly or after a certain number of times, and should be annealed to eliminate the stress in the cavity 2 ) If there are cracks on the surface of the cavity, the molding surface should be polished to remove the crack layer 3) The preheating of the mold should be uniform

2, the cold partition appearance inspection: the surface of the die-casting has obvious, irregular, depressed linear patterns (both penetrating and non-penetrating), the shape is small and narrow, and sometimes the edge of the junction is smooth, and it is disconnected under the action of external force Possible.
The causes are as follows: 1) The two metal streams are butted against each other, but they are not completely fused and there are no inclusions between them. The bonding force between the two metals is weak. 2) The pouring temperature or the temperature of the die casting mold is low. 3) The runner position is not convection or flow. Long time passing 4) The solution and prevention of low filling speed are: 1) Properly increase the pouring temperature 2) Increase the injection rate than the compression short filling time, increase the injection speed 3) Improve the exhaust and filling conditions

3, shrinkage (dent) appearance inspection: There are smooth dents (like disks) on the surface of most of the thick parts of the die-casting.
The causes are as follows: 1) Improper design of the die-casting parts caused by shrinkage. The wall thickness difference is too large. The improper sprue position is low. The injection pressure is low and the holding time is short. The local temperature of the die-casting mold is too high. 2) The design of the cooling system is unreasonable. 4) The solution and prevention of excessive pouring temperature are: 1) The wall thickness should be uniform 2) The thickness transition should be eased 3) The correct location of the alloy liquid introduction and increase the cross-sectional area of the inner runner 4) Increase the injection pressure and extend the holding pressure Time 5) Appropriately reduce pouring temperature and die casting mold temperature 6) Local cooling for local high temperature 7) Improve overflow conditions

4, the appearance inspection of the impression: the trace left by the surface of the casting and the surface of the die-casting model cavity or the stepped trace on the surface of the casting.
The causes are as follows: 1. Caused by the ejector element 1) The end face of the ejector rod is worn 2) The length of the ejector rod adjustment is inconsistent 3) The splicing part of the die-casting model cavity is not well matched with other parts 2. It is caused by the splicing or moving part 1) Mosaic Partly loose 2) The loose part of the movable part is loose or worn 3) The side wall surface of the casting is formed by inserts that are inserted between the moving and fixed molds to solve and prevent the method: 1) The length of the top rod should be adjusted to an appropriate position 2) Fasten Inserts or other movable parts 3) Eliminate sharp corners during design, fit with clearance adjustment 4) Improve the structure of the casting so that the die-casting mold eliminates the interleaved mosaic form and improve the structure of the die-casting mold

5, the appearance inspection of the traces of adherents: small pieces and the metal or non-metal and metal substrates are partially welded, and the small pieces are peeled off under the action of external force. Some of the cast surface after peeling is shiny and some are dark gray .

The reasons are as follows: 1) There are metal or non-metallic residues on the surface of the die-casting mold cavity 2) The impurities are attached to the surface of the cavity during casting and the solution and prevention methods are: 1) The cavity of the cavity before die casting And the casting system should be cleaned to remove metallic or non-metallic adhesions 2) The casting alloy should also be cleaned 3) Select the appropriate coating and the coating should be uniform

6. Lamination (skin and peeling) appearance inspection or damage inspection: there are obvious layers of metal in the casting.

The reasons are as follows: 1) The mold is not rigid enough. During the filling process of the molten metal, the template produces jitter. 2) The punch appears during the injection process. 3) The improper design of the sprue system is solved and prevented by: 1) Strengthening the mold Stiffness, tighten the mold parts to make them stable 2) Adjust the cooperation between the injection punch and the pressure chamber to eliminate the crawling phenomenon 3) Design the inner runner reasonably

7. Friction ablation appearance inspection: the surface of the die-casting part has a rough surface at certain positions.
The causes are as follows: 1) Improper position direction and shape of the inner runner caused by the die casting mold (mold) 2) The cooling of the violent parts of the molten metal at the inner runner caused by the casting conditions is insufficient to solve and prevent the method: 1) Improving the position and direction of the inflow runner. Inadequate pouring. 2) Improving the cooling conditions, especially improving the erosion of the molten metal. 3) Adding paint to the ablated part. 4) Adjusting the flow rate of the alloy liquid so that it does not Cavitation generation 5) Elimination of alloy adherents on molds

8.erosion appearance inspection: There are pits or ridges in the local position of the die casting.

The causes are as follows: 1) Improper setting of the inflow gate 2) The methods for solving and preventing poor cooling conditions are: 1) The thickness of the inflow gate should be appropriate 2) Modify the position, direction and setting method of the inflow gate 3) Strengthen the cooling of the eroded parts.

9. Crack appearance inspection: Put the casting in alkaline solution, the crack is dark gray. The destruction and cracking of the metal matrix are linear or wavy, and the lines are narrow and long, and there is a tendency to develop under the action of external forces.
Reasons for cracks in aluminum alloy castings: 1) The iron content in the alloy is too high or the silicon content is too low; the content of harmful impurities in the alloy is too high, which reduces the alloy's plasticity; the aluminum-silicon alloy, aluminum-silicon-copper alloy contains zinc or copper Too high; too much magnesium in the aluminum-magnesium alloy 2) The mold retention time is too short and the holding time is short; where the wall thickness of the casting has drastic changes 3) The local tightening force is too large, and the uneven force during the ejection is solved And prevention methods: 1) Correct control of alloy composition, in some cases: pure aluminum ingots can be added to the alloy to reduce the magnesium content in the alloy; or an aluminum-silicon intermediate alloy is added to the alloy to increase the silicon content 2) increase Type (mold) with temperature; change the casting structure, adjust the core-pulling mechanism or make the force of the push rod 3) Increase the draft angle, use a strong release agent locally 4) Increase the mold retention time and increase the pressure holding time