7 Discoloration and spots
(1) characteristics:
There are different colors and spots on the casting surface.
(2) Causes:
① Improper mold release agent; ② excessive amount of mold release agent, local accumulation; ③ graphite in the lubricant containing graphite falls into the surface of casting; ④ irregular solidification caused by low mold temperature and low metal liquid temperature.
(3) Treatment method:
① Replace the high-quality release agent; ② strictly control the spraying quantity and spraying operation; ③ control the mold temperature and keep the heat balance; ④ control the metal temperature.
8 Reticuloptera
(1) characteristics:
The surface of die casting has the mark of net hair like bulge or depression, which expands and extends with the increase of die casting times.
(2) Causes:
① The surface of die casting die cavity is cracked; ② the material of die casting die is improper or the heat treatment process is incorrect; ③ the temperature difference between cold and hot of die casting die is large; ④ the pouring temperature is too high; ⑤ the preheating of die casting die is insufficient; ⑥ the surface of die cavity is rough.
(3) Treatment method:
① Properly select die-casting mold materials and heat treatment process; ② pouring temperature should not be too high, especially high melting point alloy; ③ mold preheating should be sufficient; ④ after the mold is manufactured, carry out low temperature long aging treatment or chemical oxidation treatment on the surface; ⑤ Polish part of the surface to reduce the surface roughness Ra value, ra0.8-ra0.4; ⑥ reasonably select mold cooling method; ⑦ avoid No strong cooling of the die surface.
9 IEI depression
(1) characteristics:
Dents appear on the smooth surface of the casting.
(2) Causes:
① The difference of casting wall thickness is too large, and most of the depressions are produced in the thick wall; ② the mold is partially overheated, and the overheated part is slow to solidify; ③ the injection ratio is low; ④ the cavity gas cannot be discharged due to the high temperature of the mold, and is compressed between the cavity surface and the metal liquid interface.
(3) Treatment method:
① The design of casting wall thickness should be as uniform as possible; ② mold local cooling adjustment; ③ increase injection specific pressure; ④ improve cavity exhaust conditions.
10 Under cast
(1) characteristics:
The surface of the casting has insufficient casting parts; the outline is unclear.
(2) Causes:
① Causes of poor fluidity; ② alloy liquid inhales and oxidizes inclusions, with high iron content, so that its quality is poor and the fluidity is reduced; ③ pouring temperature is low or mold temperature is low; ④ filling conditions are poor; ⑤ specific pressure is too low; ⑥ too much gas is involved, the back pressure of mold cavity becomes high, and filling is blocked; ⑦ poor operation, excessive coating spraying, coating accumulation, and gas volatilization are not lost.
(3) Treatment method:
① Improve the quality of the alloy liquid; ② increase the pouring temperature or mold temperature; ③ increase the specific pressure and filling speed; ④ improve the flow guide mode of the metal liquid in the pouring system, and open the overflow slot and exhaust slot at the under cast part; ⑤ check whether the capacity of the die casting machine is sufficient.
11 Casting burr flash
(1) characteristics:
Sheet metal appears on the edge of parting surface of die casting.
(2) Causes:
① Mold locking is not enough; ② injection speed is too high, resulting in high pressure impact peak; ③ sundries on parting surface are not cleaned; ④ mold strength is not enough to cause deformation; ⑤ wear of inserts and sliders is uneven with parting.
(3) Treatment methods: ① check the die closing force and pressurization, adjust the die-casting process parameters; ② clean the cavity and parting surface; ③ trim the die; ④ it is better to use the closed injection end time control system, which can realize the die-casting without flash.