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Eleven Defects and Their Reasons for Die Casting Parts(Part Four)

Source: Junying   Author: Junying   Posted: 2017-06-21 16:56:09   Hits: 16

7. Cold Shut
A. Defect Characteristic:
Poor filling conditions cause visible die casting defects on the die casting surfaces.

B. The main influence factors:
molten metal temperature
mold temperature
fast shot
pouring design

8. Cold Crack 
A. Defect Characteristic:
When the ejector pins push out die casts, die casts can not be separated from the molds successfully, resulting in bad influences.

B. The main influence factors:
alloy temperature
mold temperature
draft angles
mold hardness 

9. Netlike Burr
A. Defect Characteristics:
When crackings occur on the surfaces of the molds and cause netlike concave convex marks on die casts.

Solutions
long term practice-remake cavities and mold cores
short-term practice-grind cavities, mold cores and remove hot cracks.

10. Loose Structure
A. Defect Characteristic:
Filling conditions are poor, and filling the die casting materials by layers can cause loose inner structure of die casts.

B. The main influence factors:
mould temperature
ingates
filling time
releases agents

11. Inclusions
A. Defect Characteristic:
Molten alloy contains unnecessary metal and non-metallic objects.

B. The main influence factors:
graphite crucibles
filters

The reason of each defect is affected by different factors, so how to deal with all these causes in the actual production? When we need to solve the problems, do we adjust the machines or modify the molds first? It is recommended to solve the problems from simple to complex with steps as follows: 

Clean the parting surfaces, the cavities and the ejector robs; improve the paint and the painting techniques; increase mold clamping forces; increase the amount of metal melts. These measures can be carried out by simple operation.

Adjust the process parameters, pressure, injection speed, filling time, die-open time, pouring temperature, mold temperature, etc.

Change materials; choose aluminum alloy ingots with high quality; change proportions of new materials and foundry returns; improve smelting processes.

Modify the molds and the pouring systems; increase the ingates; add an overflow launder or a venf.