Sat Apr 29 22:31:38 CST 2023
The control of die casting die surface temperature is very important for the production of high quality die castings. Uneven or inappropriate die casting mould temperatures can also lead to dimensional instability of the casting, distortion of the ejector casting during production, defects such as heat stress, mould sticking, surface depressions, internal shrinkage holes and heat bubbles. When the mould temperature difference is large, the variables in the production cycle, such as filling time, cooling time and spraying time, etc. have different degrees of impact.
1). Cold streaks:
Cause: The temperature at the front end of the molten soup is too low and there are traces when the phase is stacked
1. check whether the wall thickness is too thin (design or manufacture), the thinner areas should be filled directly. 2. Check whether the shape is not easy to fill; too far away, closed areas (such as fins (fin), bumps), blocked areas, rounded corners are too small, etc. are not easy to fill. And pay attention to whether there are ribbed points or cold spots . 3、Shorten the filling time, shorten the filling time method. 4、Change the filling pattern. 5.Methods to increase the mould temperature. 6、Increase the temperature of the molten soup. 7.Checking alloy composition. 8．Increasing the air escape channel may be useful. 9. Adding a vacuum device may be useful.
Cause: 1. Shrinkage stress. 2. Cracking by force during ejection or rimming
Improvement methods: 1:
1. increase the rounding angle 2. check for hot spots 3. change the pressurisation time (cold chamber machine) 4. increase or shorten the closing time 5. increase the extraction angle 6. increase the ejector pin 7. check the mould for misalignment and deformation 8. check the alloy composition
3). Air holes:
Causes: 1. Air entrapped in the molten soup 2. Sources of gas: during melting, in the material tube, in the mould, release agent
Improvement methods: 1: 1. slow down properly 2. Check that the runner turns are rounded and that the cross-sectional area is not decreasing 3. check that the escape zone is large enough, that it is not blocked, and that it is located at the last filling point 4. check that the release agent is not oversprayed and that the mould temperature is not too low 5. Use vacuum
Cause: The sudden decrease in pressure makes the gas in the molten soup suddenly expand and impact the mould, causing damage to the mould.
Do not change the cross-sectional area of the flow channel rapidly
Cause: When the metal solidifies from the liquid state to the solid state, the space occupied becomes smaller, if no metal replenishment will form a shrinkage hole, usually occurs in the slower solidification
Improvement methods: 1:
1. increase the pressure
2. Change the mould temperature. Local cooling, spraying release agent, lowering the mould temperature, etc. Sometimes only the location of the shrinkage is changed rather than eliminating it.
Causes: 1. poor filling pattern, resulting in overlapping of melt 2. Deformation of the mould, resulting in overlapping of the melt 3. Inclusion of oxide layer
Improvement methods 1. Switch to high speed earlier 2. Shorten the filling time 3. Change filling pattern, gate position, gate speed 4. check that the mould strength is adequate 5. check if the pinning device is good 6. Check for inclusions of oxide layer
Cause: The first layer of molten soup cools rapidly on the surface, and the second layer of molten soup flows through and fails to melt the first layer, but there is enough fusion, resulting in different organization
Improvement methods: 1: 1. improve the filling pattern 2. Shorten the filling time
8). Holes caused by poor flow:
Causes: The molten soup flows too slowly, or is too cold, or has a poor filling pattern, resulting in holes in the solidified metal joint
Improvement methods: 1: 1. Same method as for cold pattern 2. Check that the melt temperature is stable 3. Check that the mould temperature is stable.
9). Holes in the parting surface:
Cause: Possible shrinkage or air holes
Improvement methods: 1: 1. If it is a shrinkage, reduce the thickness of the sprue or the thickness of the inlet of the overflow well 2. cool the sprue 3. If it is a hole, pay attention to the problem of venting or coiling
Causes: 1. Insufficient clamping force 2. Poor mould closing 3. Insufficient mould strength 4. Too high temperature of molten soup
Cause: Shrinkage occurs below the surface of the pressed part
Improvement methods: 1．Same method as for improving shrinkage 2. Local cooling 3．Heat the other side
12). Carbon build-up:
Cause: Release agent or other impurities accumulate on the mould.
Improvement methods: 1: 1. Reduce the amount of release agent sprayed 2. Increase the mould temperature 3. Select a suitable release agent 4. Use soft water to dilute the release agent
Cause: Gas rolls under the surface of the casting
Improvement methods: 1、Reduce the gas roll (same as air hole) 2. cool or prevent low mould temperature
14). Sticky mould:
Causes: 1. Zinc build-up on the mould surface 2. The molten soup strikes the mould, causing damage to the mould surface
Improvement methods: 1: 1. Reduce the mould temperature 2. Reduce the roughness of the scribing surface 3. Increase the extraction angle 4. Coating 5、Change the filling pattern 6. Reduce gate speed