12 Common Questions and Solutions: Aluminium Die Casting

Aluminium Die Casting

Aluminum alloy high pressure die casting refers to the liquid aluminum alloy under high temperature and pressure, with a breakneck speed from the pressure chamber into the casting cavity, after cooling to form the casting method. Die casting has the advantages of high dimensional accuracy, good mechanical properties, and high production efficiency. It has broad application prospects in automobiles, motorcycles, internal combustion engines, electronics, instrumentation, and aerospace.

The liquid metal is in high temperature, high pressure, with breakneck speed from the pressure chamber into the casting cavity. The metal liquid in the flow process is quickly involved in the gas and the imbalance of casting process temperature. It causes the casting of porosity, shrinkage, burns, cold compartments, and other defects. This article introduces 12 common questions and solutions for aluminum die casting.

Table of Contents

1. Cold compartment problem

Appearance characteristics: die casting appearance has noticeable, irregular sagging linear texture (there are two kinds of penetration and non-penetration) shape is small and narrow, sometimes account for the smooth edge, there is a possibility of development under the action of external forces.

Cold compartment problem

Reason: Two or more strands of molten soup are too low in temperature and have marks when stacked. Metal bond is weak. Low pouring temperature or mold temperature. Poor flow of molten soup. Incorrect sprue position or too long flow line. Low filling speed and poor venting. Low-pressure injection ratio pressure. The metal liquid does not flow smoothly in the cavity.

Solution: Increase the pouring temperature appropriately, control at 640°-680°C (can be adjusted according to the product and aluminum material), and increase the mold temperature appropriately. Increase the pressure ratio and shorten the filling moment. Increase the punch’s speed during the die-casting machine’s commissioning process, and increase the cross-sectional area of the internal gate. Improve the exhaust filling conditions. Select a suitable alloy to improve the fluidity of a metal liquid. Improve the smooth flow of metal liquid in the cavity. Check whether the wall thickness is too thin (design or manufacture) and should fill the thinner area directly. Check whether the shape is not easy to fill. Too far away, closed areas (such as fins, bumps), blocked areas, rounded corners too small, etc., are not easy to fill, and if this happens, change to increase the sprue to supplement the cold separation area. And pay attention to whether there is a ribbed point or freezing point. Increase the slag bag in the cold isolation area. Increasing the exhaust or adding a vacuum device may be helpful.

2.Cracks Problem

Appearance characteristics: die casting appearance in a straight line or irregular shape narrowly varying texture, under the action of external forces have a development trend. Cracks include cold cracking and hot cracking. Cold crack: the metal at the crack is not oxidized. Hot crack: the metal at the crack is oxidized.

Cracks Problem

Reason: The alloy composition has a problem, which decreases the plasticity of the alloy. The mold temperature is too low. Casting wall thickness where there is a drastic change, shrinkage is blocked, shrinkage stress. Too long mold retention time, high stress. Uneven force during ejection.

Solution:

  1. Correctly control the alloy composition.
  2. Change the casting layout, increase the rounded corners, increase the slope of the mold release, reduce the wall thickness difference, and change or increase the ejector pin so that the ejection force is uniform.
  3. Check whether the mold is misaligned and deformed, and shorten the moment of mold opening or core extraction.
  4. Control the mold temperature (mold working temperature 130°C-200°C).
  5. Increase or shorten the closing time of the mold.

 

3.Porosity problem

Appearance characteristics: pinhole-like or larger pores occur in the castings, castings exposed after machining, or pores in the sealing requirements of high places. After the test leak, machine pressure often appears leakage phenomenon. Pores are generally smooth, round, or oval, sometimes isolated, sometimes clustered. It can be divided into hydrogen gas pores and rolled gas pores.

Porosity problem

Reasons:
(1) the formation of hydrogen gas pores: hydrogen gas pores are tiny, shaped like needles, and evenly distributed and can only be observed after the surface of the parts are machined. Due to the thin wall of die casting and fast solidification of metal liquid, sometimes hydrogen gas pores are difficult to be observed by naked eyes. Water vapor is the most important source of hydrogen gas, which may come from furnace gas, melting tools, aluminum ingots/recycled parts, oil-contaminated machine processing chips and wet refining agents, etc.
2) Formation of roll gas pores: The roll gas pores are round, clean inside, with a relatively smooth and shiny surface, and the rolling gas sometimes exists alone, sometimes clustered together. Volume gas generally occurs in the punch, sprue, and cavity.

Solutions:
(1) To form hydrogen gas holes, the solution is to refine with a GBF de-gassing and drossing device; check whether the release agent is sprayed too much and whether the concentration of the release agent is in the correct range.
The solution for the formation of rolled gas holes: choose the appropriate slow speed during the commissioning of the die-casting machine, check whether the flow channel turns are round and smooth and whether the cross-sectional area is gradually decreasing. Check whether the exhaust area is large enough, whether it is blocked, and whether the position is located in the last filling place to improve the exhaust. Checking whether the mold temperature is too low. Using the method of evacuation can effectively exhaust the gas entering the cavity.

4.Shrinkage Problem

Appearance characteristics: occur in the casting surface below the larger pores. Sometimes visible to the naked eye, sometimes detected by an X-ray machine.

Reason: Due to the molten metal filling, from the liquid phase into the solid phase, the inevitable existence of phase change shrinks. The solidification characteristics of die casting are cooled from the outside to the inside. When the casting local wall thickness is larger, the internal shrinkage is bound to produce shrinkage holes shrink loose problem. Put the thicker position of the product, due to the high temperature, cooling is relatively slow and the formation of sagging pores.

Solution: The product is in a thicker position to reduce the material. Die-casting machine commissioning process to increase pressure. Change the mold temperature, locally increase the cooling, spray release agent, and reduce the mold temperature. If the location of the shrinkage hole is in the sprue direction, can add new sprue to make up the shrinkage directly. Adopt the extrusion process, and add a new extrusion pin. When the shrinkage hole is in a semi-solid state, forcibly extrude to make up the shrinkage.

5. Deformation Problem

Appearance characteristics: the geometry of the die casting does not match the drawing, the whole deformation, or partial deformation, resulting in the dimensional tolerance of critical parts of the product does not meet the requirements of the drawing.

Deformation problem

6. Hairy edge problem


Appearance characteristics: The product’s appearance produces a thin sheet of excess material.
Reason: Insufficient clamping force. Poor mold closing. Insufficient mold strength produces sagging, and melt soup temperature is too high. The mold is not blown clean and is indented by excess material during the mold closing process.
Solution:

1. Check the clamping force of the machine.

2. Check the mold closing situation and whether the mold is sunken.

3. Check whether the mold material meets the requirements.

4. Check whether the casting pressure is too high during the commissioning of the die-casting machine. Control the temperature of molten soup at 740°C-780°C.

Hairy edge problem

7.Mold erosion, cracking problems

Appearance characteristics: mold burns, severe erosion. The product appears net-like hair-like raised or depression traces, with the number of die-casting increases and shall not expand and extend.
Reason: The filling speed is too high, impacting the mold, and causing mold damage and cracking.
Solution: Check the pressure injection ratio. The punch’s cross-sectional area and the internal gate’s cross-sectional area are generally controlled at 13-16 times. If it is too high, the width and thickness of the internal gate should be increased. Check if the mold material is by the regulations. Check if the mold has reached its design life. If it has, replaces the mold. In addition, you can also do special treatment to the mold local erosion serious position by doing the cloaking process. During the die-casting machine’s commissioning process, reduce the punch’s high speed appropriately.

8.Ripple Problem

Appearance characteristics: the product’s local organization is different, with apparent ripples.
Reason: The first layer of molten hot on the surface of the rapid cooling, the second layer of molten soup flowing through, failed to melt the first layer, yet there is enough fusion, resulting in different organizations.
Solution: Improve the filling mode and shorten the filling time.

9.Sticky Mold Problem

Appearance characteristics: the product as a whole or partially sticky in the mold cavity can not come out of the mold, divided into the sticky dynamic mold and sticky fixed mold.
Reason: The slope of the product out of the mold is not enough, the problem of ejecting, and the local temperature of the mold is too high.
Solution: Increase the angle of the product’s mold pulling. Mold new increases cooling, die-casting process local increase spraying replenishment water, reduce mold temperature. Mold to increase the ejector rod. Sticky fixed mold can be considered to add a new fixed mold top bar mechanism and a dynamic mold to increase the buckle.

10.Carbon Accumulation Problem

Appearance characteristics: the appearance of die castings is different from the color of the base metal spots
Reason: mold release agent or other impurities accumulate on the mold
Solution: Reduce the amount of release agent sprayed, increase the mold temperature, choose a suitable release agent, and use soft water to dilute the release agent.

11. Peeling problems

Appearance characteristics: blackening and peeling of die castings.

Reason: Poor filling pattern, causing overlapping of molten soup. Deformation of mold, entrapment of oxide layer.

Solution:

  1. Switch to high speed early, shorten the filling time and change the filling mode, gate position, and gate speed.
  2. Check if the mold strength is sufficient.
  3. Check whether the inclusions of oxidation had.

 

12.Under Casting Problem

Appearance characteristics: die casting appearance has to fill lack of parts or contour is not clear.

Solution: Improve the quality of metal liquid. Increase the pouring temperature or mold temperature. Improve die-casting injection ratio pressure and filling speed. Improve the inflow of metal liquid in the pouring system, and increase the overflow slot and exhaust slot in the under-cast part. Correct die-casting operation.

Conclusion

Aluminum die casting is one of the elements of die casting production. To produce excellent die castings, a well-designed die casting mold and die casting machine with superior process performance and a suitable performance alloy is also required in addition to reasonable part construction. Choosing the right die casting is the key to your product’s promise. V1DIECAST is your trustful partner, please feel free to contact us.

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