Die casting (die casting) is a kind of metal casting process, its characteristics is the use of mold cavity on the molten metal apply high pressure, similar to plastic injection molding. Die casting is particularly suitable for manufacturing a large number of small and medium-sized castings, so die casting is a variety of casting process in the most widely used one. Compared to other casting techniques, die casting has a flatter surface and higher dimensional consistency. However, non-standardized operation and parameters can also produce a large variety of defects.
I. Flow marks and patterns
Appearance inspection:
There are streaks on the surface of the casting that are consistent with the direction of the flow of the metal liquid, and there are clearly visible non-directional lines that are different from the color of the metal substrate, and there is no development trend.
The causes of flow marks are as follows:
1) Mold temperature is too low;
2) Poor sprue design and poor location of the inner gate;
3) Too low material temperature;
4) Low filling speed and short filling time;
5) Irrational pouring system;
6) Poor exhaust;
(7) spray unreasonable.
Second, reticulate hairy fins (cracks)
Appearance check:
Die casting surface with mesh hair like raised or depressed traces, with the die casting number of times and constantly expand and extend.
Produces the cause as follows:
(1) die-casting mold cavity surface cracks;
(2) die casting mold preheating is not uniform.
Third, cold segregation
Appearance check:
Die casting surface has obvious, irregular, sagging linear pattern (with penetration and not penetrate two kinds of) shape is small and narrow, sometimes the intersection edge is smooth, under the action of external force has the possibility of disconnection.
The reasons are as follows:
(1) two streams of metal butt each other, but not completely fused and no inclusions exist in between, the two streams of metal bonding force is very weak;
(2) The pouring temperature or die casting mold temperature is low;
3) Incorrect location of sprue or flow path is too long;
(4) low filling speed.
Fourth, shrinkage (dent)
Appearance check:
Comparatively thick aluminum castings, most of the surface has a smooth dent (like a disk dish).
Produce the following reasons:
(1) caused by shrinkage die casting design improper wall thickness difference is too large; sprue location improper;
Pressure injection ratio pressure is low, holding pressure time is short; die-casting mold local temperature is too high.
(2) cooling system design is unreasonable;
(3) Open the mold too early;
4) pouring temperature is too high.
5. Marks
Appearance check:
The casting surface and die casting mold cavity surface contact left by the trace or casting surface appears on the step trace.
Produce the following reasons:
(1) caused by the ejector element top rod end surface is worn; top rod adjustment length is not consistent;
Die casting mold cavity splicing part and other parts are not well coordinated.
(2) by splicing or movable part caused by the splicing part of the loose; movable part of the loose or wear; casting side wall surface, by the movable and fixed mold interspersed with each other by the formation of the inserts.
6. traces of adhesion
Appearance check:
Small flakes and metal or non-metallic and metal base partially fused, under the action of external forces peeling off small flakes, peeling off the casting surface some shiny, some dark gray.
Produce the following reasons:
(1) in the die-casting mold cavity surface metal or non-metallic residues;
(2) pouring first brought into the impurities attached to the cavity surface.
7. delamination (skinning and flaking)
Appearance inspection or damage inspection:
There are obvious layers of metal in the casting locally.
Produce the following reasons:
(1) mold rigidity is not enough in the liquid metal filling process, the template produces jitter;
2) Creeping phenomenon of the punch in the process of compression injection;
(3) Improperly designed sprue system.
8. friction ablation
Appearance check:
Die casting surface in some positions to produce rough surface.
Produce the following reasons:
(1) by the die casting type (mold) caused by the location of the inner sprue direction and shape is improper;
(2) by casting conditions caused by the inner sprue at the metal liquid scouring intense parts of the cooling is not enough.
9. erosion
Appearance check:
Die casting localized position has pockmarks or convex lines.
Produce the following reasons:
(1) the location of the inner sprue is not set properly;
2) Poor cooling conditions.
10. Cracks
Appearance check:
Put the casting in alkaline solution, the crack is dark gray. The destruction and cracking of the metal matrix is in a straight line or wave line, the grain is narrow and long, and there is a trend of development under the action of external force.
The causes are as follows:
(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 plasticity of the alloy; aluminum-silicon alloy and aluminum-silicon-copper alloy contain too much zinc or copper; aluminum-magnesium alloy contains too much magnesium;
(2) The time of leaving the mold is too short, and the pressure holding time is short; where there is a drastic change in the wall thickness of the casting;
(3) The local packing tightness is too large, and the force is uneven when ejecting.