Die casting mold is a method of casting liquid die forging, a process completed on a dedicated die casting die forging machine. Its basic process is: metal liquid is firstly filled into the cavity of the mold at a low or high speed. The mold has a movable cavity surface. It is forged under pressure as the metal liquid is cooled, which eliminates shrinkage and shrinkage of the blank. The loose defect also makes the internal structure of the blank reach the forged broken grains. The comprehensive mechanical properties of the blank have been significantly improved. Die-casting molds Die-casting molds are the three major elements of die-casting production. The so-called die-casting process is an organic and comprehensive use of these three elements, which can stably and efficiently produce qualified castings, even high-quality castings that have an appearance, good internal quality, and dimensions that meet the requirements of the drawing or agreement.
Die Casting Die Alloy
The alloys used in die castings are mainly non-ferrous alloys. As for ferrous metals (steel, iron, etc.), due to problems such as mold materials, they are currently rarely used. Among non-ferrous alloy die castings, aluminum alloys are more widely used, followed by zinc alloys. The following briefly introduces the situation of die-casting non-ferrous metals.
(1) Classification of die-casting non-ferrous alloys Blocked shrinkage Mixed shrinkage Free shrinkable lead alloys ----- 0.2-0.3% 0.3-0.4% 0.4-0.5% Low-melting alloy tin alloy zinc alloy -------- 0.3 -0.4% 0.4-0.6% 0.6-0.8% Aluminum silicon series--0.3-0.5% 0.5-0.7% 0.7-0.9% Die-casting non-ferrous alloy aluminum alloy aluminum copper series aluminum magnesium series --- 0.5-0.7% 0.7-0.9% 0.9-1.1% high melting point aluminum-zinc magnesium alloy ---------- 0.5-0.7% 0.7-0.9% 0.9-1.1% copper alloy
2 (2) Recommended casting temperature of various die-casting alloys Type of alloy Average wall thickness of casting ≤3mm Average wall thickness of casting> 3mm Simple structure Complex structure Simple complex structure
Aluminum alloy Al-Si series 610-650 ℃ 640-680 ℃ 600-620 ℃ 610-650 ℃
Aluminum and copper series 630-660 ℃ 660-700 ℃ 600-640 ℃ 630-660 ℃
Al-Mg series 640-680 ℃ 660-700 ℃ 640-670 ℃ 650-690 ℃
Aluminium-zinc series 590-620 ℃ 620-660 ℃ 580-620 ℃ 600-650 ℃
Sm-Zn alloy 420-440 ℃ 430-450 ℃ 400-420 ℃ 420-440 ℃
Sm-Mg alloy 640-680 ℃ 660-700 ℃ 640-670 ℃ 650-690 ℃
Copper alloy ordinary brass 910-930 ℃ 940-980 ℃ 900-930 ℃ 900-950 ℃
Silicon brass 900-920 ℃ 930-970 ℃ 910-940 ℃ 910-940 ℃
* Note: ①The casting temperature is generally measured by the temperature of the molten metal in the holding furnace.
②The casting temperature of zinc alloy should not exceed 450 ℃ to avoid coarse grains.
Die casting mold design process
1. According to the materials used in the product, the shape and accuracy of the product and other indicators, process analysis of the product, and order the process.
2. Determine the position of the product in the mold cavity and perform the parting surface; analysis and design of the overflow system and the pouring system.
3. Design the core assembly method and fixing method for each activity.
4. Design of core pulling distance and force.
5. Design of ejection mechanism.
6. Determine the die casting machine, design the mold base and cooling system.
7. Check the relevant dimensions of the mold and die casting machine, and draw the process drawings of the mold and each component.
8. The design is completed.
Common problems and treatment methods of die-casting molds
1). Cold lines:
Reason: The temperature at the front of the molten soup is too low, and there are traces when they overlap.
1. Check if the wall thickness is too thin (designed or manufactured). Thinner areas should be filled directly.
2. Check if the shape is not easy to fill; it is not easy to fill if the distance is too far, closed areas (such as fins, protrusions), blocked areas, and rounded corners are too small. And pay attention to whether there are ribs or cold spots.
3. Reduce filling time. Ways to reduce filling time: ...
4. Change the filling mode.
5. Methods to increase mold temperature: ...
6. Increase molten soup temperature.
7. Check alloy composition.
8. Increasing the escape airway may be useful.
9. Vacuuming may be useful.
Reason: 1. Shrinkage stress.
2. Forced to crack when ejected or trimmed.
way of improvement:
1. Increase rounded corners.
2. Check for hot spots.
3. Pressurization time changes (cold room machine).
4. Increase or decrease mold closing time.
5. Increase draft angle.
6. Increase ejector pin.
7. Check whether the mold is dislocated or deformed.
8. Check alloy composition.
Reason: 1. Air is trapped in the molten soup.
2. Source of gas: during melting, in the material tube, in the mold, release agent.
1. Appropriately slow.
2. Check whether the runner turns smoothly and whether the cross-sectional area gradually decreases.
3. Check whether the area of the escape airway is large enough, whether it is blocked, and whether it is located at the last filling place.
4. Check if the release agent is sprayed too much and if the mold temperature is too low.
5. Use vacuum.
Cause: Due to the sudden decrease in pressure, the gas in the molten soup suddenly expands and impacts the mold, causing mold damage.
勿 Do not change the cross-sectional area of the flow path quickly.
5). shrinkage cavity:
Cause: When the metal solidifies from a liquid to a solid, the space it takes up becomes smaller. If there is no metal supplement, shrinkage pores will be formed. It usually occurs at slower solidification.
1. Increase stress.
2. Change the mold temperature. Local cooling, spray release agent, reduce mold temperature ,. Sometimes it just changes the position of shrinkage holes, not shrinks them.
Reason: 1. Poor filling pattern causes overlapping of molten soup.
2. The mold is deformed, causing the molten soup to overlap.
3. Including oxide layer.
1. Switch to high speed early.
2. Reduce filling time.
3. Change the filling mode, gate position, gate speed.
4. Check whether the mold strength is sufficient.
5. Check whether the pin mold device is in good condition.
6. Check for inclusion of oxide layers.
Cause: The first layer of molten soup is rapidly cooled on the surface, and the second layer of molten soup flows through and fails to melt the first layer, but there is sufficient fusion, resulting in different organizations.
1. Improve filling mode.
2. Reduce filling time.
8). Pore caused by poor flow:
Cause: The molten soup flows too slowly, or is too cold, or the filling mode is poor, so there are holes in the solidified metal joint.
1. With the improvement of cold lines.
2. Check if the temperature of the molten soup is stable.
3. Check whether the mold temperature filling is stable.
9). Holes on the parting surface:
Reason: It may be shrinkage or stomata.
1. If it is a shrinkage hole, reduce the thickness of the gate or the inlet thickness of the overflow well.
2. Cooling gate.
3. If it is a blowhole, pay attention to the problem of exhaust or gas.
Reason: 1. Insufficient clamping force.
2. Defective mold clamping.
3. Insufficient mold strength.
4. The temperature of the molten soup is too high.
Cause: Shrinkage occurs below the surface of the pressing part.
1. The same method to improve shrinkage.
2. Local cooling.
3. Heat the other side.
12). Carbon deposits:
Reason: Release agent or other impurities accumulate on the mold.
1. Reduce spraying amount of release agent.
2. Increase the mold temperature.
3. Choose the right release agent.
4. Use soft water to dilute the release agent.
Cause: The gas is rolled under the surface of the casting.
way of improvement:
1. Reduction of air volume (same air hole).
2. Cooling or preventing low mold temperature.
14). Sticky mold:
Reason: 1. Zinc accumulates on the surface of the mold.
2. The molten soup impacts the mold, causing damage to the mold surface.
1. Reduce mold temperature.
2. Reduce the surface roughness.
3. Increase the draft angle.
5. Change the filling mode.
6. Reduce gate speed