In the high-pressure die casting process, the quality of the mold directly determines the precision, surface quality, and production efficiency of the casting. However, even experienced manufacturers inevitably encounter various mold problems, such as scratches, sticking, flash, cold shuts, and shrinkage. To help customers better identify and solve these common problems, we have summarized 25 common die casting mold problems and corresponding solutions, focusing on the actual application scenarios of high-pressure die casting molds to provide highly operable and practical technical solutions. As a professional high-pressure die casting mold manufacturer, Raidy mold factory is committed to creating die casting molds with long service life, high stability, and low defect rate for customers through scientific design and precision manufacturing.
1. Flow Marks
Other Names: Streaks
Characteristics: Smooth, locally sunken lines that appear on the surface of the casting in the direction of molten metal flow, perceptible to the touch. This defect has no tendency to develop and can be removed by polishing.
Causes:
① Marks left by the asynchronous filling of the cavity by two metal streams.
② Low high-pressure die-casting mold temperature, such as below 150℃ for zinc alloy molds and below 180℃ for aluminum alloy molds, easily leads to this type of defect.
③ Excessive filling speed.
④ Excessive coating application.
Exclusion measures:
① Adjust the cross-sectional area or position of the ingate.
② Adjust the mold temperature and increase the size of the overflow channel.
③ Appropriately adjust the filling speed to change the flow pattern of the molten metal filling the cavity.
④ Apply a thin and even coating.
2. Cold Shut
Other Names: Cold Joint
Characteristics: A gap that appears when two relatively cool metal streams meet but do not fuse. It presents as an irregular line, and can be either penetrating or non-penetrating. It tends to develop under external force.
| Causes | Exclusion measures |
| ① Low molten metal pouring temperature or low high-pressure die-casting mold temperature. | ① Appropriately increase pouring temperature and mold temperature. |
| ② Alloy composition does not meet standards, resulting in poor fluidity. | ② Change alloy composition to improve fluidity. |
| ③ Molten metal is poured in separate streams, leading to poor fusion. | ③ Improve the gating system and filling conditions. |
| ④ Inappropriate gate design, excessively long flow path. | ④ Improve overflow conditions and increase overflow flow rate. |
3. Scratches
Other names: scratches, marks, mold adhesion marks
Characteristics: Along the demolding direction, scratches are caused by metal adhesion and insufficient draft angle in the high-pressure die-casting mold, resulting in scratch marks on the surface of the casting. In severe cases, they are called scratched surfaces.
| Causes | Exclusion measures |
| ① Casting draft angle of the core and mold wall is uneven or there is a reverse draft angle. | ① Modify the mold to ensure the manufacturing draft angle. |
| ② Indentation marks on the core and mold wall. | ② Polish and remove indentations. |
| ③ Alloy adheres to the high-pressure die-casting mold. | ③ Rationally design the gating system to avoid metal flow impacting the core and mold wall, and appropriately reduce the filling speed. |
| ④ Casting ejection deviation or core axis deviation. | ④ Modify the structure of the high-pressure die-casting mold. |
| ⑤ Rough mold wall surface. | ⑤ Polish the surface. |
| ⑥ Paint is often not applied effectively. | ⑥ Apply paint thinly and evenly, avoiding missed areas. |
| ⑦ Iron content in the aluminum alloy is less than 0.6%. | ⑦ Appropriately increase the iron content to 0.6-0.8%. |
4. Dent
Other names: Shrinkage, depression, air pocket, edge collapse
Characteristics: A sunken area appearing on the smooth surface of the casting, with the surface in a naturally cooled state.
| Causes | Exclusion measures |
| ① The casting structure is poorly designed, with locally thick sections that create hot spots. | ① Improve the casting structure to achieve a more uniform wall thickness. At joints with significant thickness differences, the transition should be gradual to eliminate hot spots. |
| ② The alloy has a high shrinkage rate. | ② Select an alloy with low shrinkage. |
| ③ The cross-sectional area of the ingate is too small. | ③ Properly design the gating system and appropriately increase the cross-sectional area of the ingate. |
| ④ The specific pressure is low. | ④ Increase the injection force. |
| ⑤ The temperature of the high-pressure die-casting mold is too high. | ⑤ Appropriately adjust the mold’s thermal balance conditions, employing temperature control devices and cooling systems. |
5. Bubble
Other names: Bubbling
Characteristics: Bubbles formed by the expansion of accumulated gas under the surface of the casting.
Causes:
① The temperature of the high-pressure die-casting mold is too high.
② The filling speed is too high, and too much gas is drawn into the metal liquid flow.
③ The paint has a high gas release rate, excessive usage, and is not fully burned before pouring, causing volatile gases to be trapped on the surface of the casting.
④ Poor exhaust.
⑤ Mold opening too early.
⑥ The melting temperature of the alloy is too high.
Exclusion measures
① Cool the high-pressure die-casting mold to working temperature.
② Reduce the injection speed to avoid vortex entrapment.
③ Choose coatings with low gas generation, use thin and uniform amounts, and close the mold after burning out.
④ Clean and install overflow channels and exhaust ducts.
⑤ Adjust the mold retention time.
⑥ Refine the smelting process.
6. Porosity
Other names: Air holes
Characteristics: Relatively regular-shaped, smooth-surfaced cavities formed by gas trapped inside the die casting.
Causes:
Mainly caused by the wrapping gas:
① Improper selection of gate position and guide shape can cause the metal liquid to enter the mold cavity, resulting in frontal impact and vortex formation.
② Poor design of the sprue shape.
③ The pressure chamber is not fully filled.
④ The speed of the sprue is too high, causing turbulence.
⑤ Poor exhaust.
⑥ The position of the high-pressure die-casting mold cavity is too deep.
⑦ Too much paint, not fully burned before filling.
⑧ The furnace material is not clean and the refining is poor.
⑨ The machining allowance is too large.
Exclusion measures:
① Choose a favorable gate position and guide shape for gas removal in the mold cavity to avoid the metal liquid from sealing the overflow system on the parting surface first.
② The cross-sectional area of the nozzle of the sprue should be as larger as possible than that of the sprue.
③ Improve the filling degree of the pressure chamber, choose smaller pressure chambers as much as possible, and use quantitative pouring.
④ Under good molding conditions, increase the thickness of the sprue to reduce the filling speed.
⑤ Open overflow channels and exhaust channels at the final filling position of the mold cavity, and avoid sealing the overflow channels and exhaust channels with molten metal.
⑥ An exhaust plug is installed at the deep cavity, and the exhaust is increased by inlaying.
⑦ The amount of paint used is thin and uniform, filled after burning out, and the paint with low gas generation is used.
⑧ The furnace material must be cleaned and dried, and the smelting process must be strictly followed.
⑨ Reduce machining allowance.
⑩ Adjust the transition point between injection speed and fast injection speed. Reduce the pouring temperature and increase the specific pressure.
7. Shrinkage Cavity
Other names: Shrinkage void, shrinkage eye
Characteristics: Irregularly shaped, rough-surfaced pores caused by insufficient internal compensation during the solidification process of the die casting.
| Causes | Exclusion measures |
| ① The casting temperature of the alloy is too high. | ① Adhere to alloy melting standards, avoid overheating the alloy liquid for too long, and lower the pouring temperature. |
| ② The uneven wall thickness of the casting structure results in thermal joints. | ② Improve the casting structure, eliminate metal accumulation areas, achieve uniform wall thickness, and slow transition. |
| ③ The pressure is too low | ③ Appropriately increase the specific pressure. |
| ④ The overflow tank capacity is insufficient and the overflow outlet is too thin. | ④ Increase the capacity of the overflow tank and thicken the overflow port. |
| ⑤ The filling degree of the compression chamber is too low, and the remaining material is too thin, which ultimately makes the shrinkage ineffective. | ⑤ Improve the filling degree of the pressure chamber and adopt quantitative pouring. |
| ⑥ The sprue is relatively small. | ⑥ Properly improve the pouring system to facilitate good pressure transmission. |
| ⑦ The local temperature of the mold is too high. | ⑦ Cooling high-pressure die-casting molds in areas with high local temperatures. |
8. Patterns
Characteristics: Smooth stripes appearing on the surface of the casting, visible to the naked eye but not felt by hand, with a color different from the base metal. They can be removed by gently rubbing with 0# sandpaper.
| Causes | Exclusion measures |
| ① The filling speed is too fast. | ① Minimize the injection speed as much as possible. |
| ② Too much paint is used. | ② The coating dosage is thin and uniform. |
| ③ The temperature of the high-pressure die-casting mold is too low. | ③ Raise the mold temperature. |
9. Cracks
Characteristics: Fine, thread-like cracks form in the casting due to damage or breakage of the alloy matrix. These can be penetrating or non-penetrating, and tend to develop.
Cracks can be divided into cold cracks and hot cracks. The main difference is that in cold cracks, the metal at the crack opening is not oxidized, while in hot cracks, the metal at the crack opening is oxidized.
Causes:
① The casting structure is unreasonable, shrinkage is hindered, and the casting fillet is too small.
② The core pulling and ejection device deviates and experiences uneven force during operation.
③ The temperature of the high-pressure die-casting mold is low.
④ The mold opening and core pulling time is too late.
⑤ Improper selection of alloys or excessive harmful impurities can lead to a decrease in alloy plasticity.
Exclusion measures:
① Improve casting structure, reduce wall thickness difference, and increase casting fillet.
② Revise the mold structure.
③ Raise the working temperature of high-pressure die-casting molds.
④ Shorten the mold opening and core pulling time.
⑤ Strictly control harmful impurities and adjust alloy composition.
10. Incomplete Casting
Other names: Insufficient filling, unclear outline, missing edges and corners
Characteristics: The molten metal does not completely fill the mold cavity, resulting in incompletely filled areas on the casting.
Causes:
(1) Poor flow of alloy liquid causes:
① The alloy liquid has a high gas content and severe oxidation, resulting in a decrease in fluidity.
② The alloy pouring temperature and high-pressure die-casting mold temperature are too low.
③ The speed of the sprue is too low.
④ The nitrogen pressure inside the accumulator is insufficient.
⑤ The pressure chamber is not fully filled.
⑥ Improper design such as excessively thin casting walls or uneven thickness.
(2) Poor pouring system causes:
① Improper selection of gate position, diversion method, and number of inner gate strands.
② The cross-sectional area of the sprue is too small.
(3) Poor exhaust conditions cause:
① Poor exhaust.
② Too much paint, not dried and burned out.
③ The mold temperature is too high, and the gas pressure inside the mold cavity is high, making it difficult to discharge.
Exclusion measures
(1) Improving the fluidity of alloys:
① Adopt the correct melting process to eliminate gases and non-metallic inclusions.
② Appropriately increase the alloy pouring temperature and mold temperature.
③ Increase the injection speed.
④ Supplement nitrogen to increase effective pressure.
⑤ Quantitative pouring is adopted.
⑥ Improve the casting structure and adjust the wall thickness appropriately.
(2) Improve the pouring system:
① Correctly selecting the gate position and flow guide method is beneficial for using multiple internal gates for poorly shaped castings and large castings.
② Increase the cross-sectional area of the sprue or increase the injection speed.
(3) Improving exhaust conditions:
① Add overflow channels and exhaust ducts, and vent plugs can be installed at deep concave cavities.
② The coating should be thin and uniform, dried and burned off before closing the mold.
③ Reduce the mold temperature to the working temperature.
11.Imprint
Other names: push rod imprint, inlay or movable block splicing imprint.
Features: Protrusions and depressions on the surface of the casting due to impacts from the mold cavity and the splicing of parts such as push rods, inserts, and moving blocks.The marks left behind.
| Causes | Exclusion measures |
| ① The push rod is not properly adjusted or its end is worn. | ① Adjust the push rod to the correct position. |
| ②High pressure die castingMold cavity, slider assembly and its moving partsThe coordination of the moving parts is poor. | ② Secure the inserts or other moving parts.EliminateThe necessary uneven parts. |
| ③ The push rod area is too small. | ③Increase the area of the push rod or increase its number. |
12.Reticulated burrs
Other names: reticulated marks, reticulated patterns, cracked burrs
Features: Mesh-like raised marks and metal burrs on the surface of the casting, formed due to thermal fatigue on the surface of the mold cavity.
Causes:
① Cracks on the surface of the mold cavity, near the ingate areaThe heat conduction is most concentrated there.Frictional resistance is the greatest.Exposed to molten metalThe erosion is the strongest.The most dramatic temperature changes are between hot and cold.Most prone to thermal crackingshapeBecome cracked.
②High pressure die castingThe mold material is inappropriate, or the heat treatment process is incorrect.
③ The die-casting mold experiences large temperature variations due to heating and cooling.
④ The alloy liquid pouring temperature is too high, and the mold preheating is insufficient.
⑤ Surface roughness of die casting mold cavityRaToo big.
⑥ High metal flow rate and frontal scouring of the wall.
Exclusion measures
① Correctly select mold materials and reasonableHeat treatment process.
②High pressure die castingThe mold must be preheated to the working temperature before die casting.Use the temperature range.
③ Minimize the alloy pouring temperature as much as possible.
④ Reduce the pouring temperature of the alloy liquid and the mold.Preheat to the appropriate temperature.
⑤ Improve the surface quality of the die-casting mold cavity and reduceLowRaNumerical values, periodic annealing of inlays,Relieve stress.
⑥ Design the gating system correctly to meet the requirements.Under good molding conditions, as much as possibleUse a smaller injection velocity.
13.Colored spots
Other names: oil spots, black spots
Features: Spots on the surface of the casting that differ from the base metal are generally formed by coating carbides.
| Causes | Exclusion measures |
| ① The paint is impure or the amount used is excessivemany. | ① The paint should be applied thinly and evenly, without piling up, and should be applied using a compressed air compressor.The air was blown away. |
| ②The coating contains too much graphite. | ② Reduce the graphite content in the coating or choose a graphite-free graphite-based coating.material. |
14.Pockmarked
Features: During the filling process, due toHigh pressure die castingWhen the mold temperature or alloy temperature is too low, fine pitting-like distribution forms on the surface of the casting under near-under-pressure conditions.
| Causes | Exclusion measures |
| ① During filling, the metal is dispersed intoDense droplets, high-speed impactShape wall. | ① Correctly design the gating system to avoid molten metal splashing, and modify…Improve ventilation conditions to prevent excessive gas entrainment in the liquid flow and reduce the risk of internal gating.Increase the injection speed and raise the temperature of the high-pressure die-casting mold. |
| ②The thickness of the ingate is too small. | ② Adjust the thickness of the ingate appropriately. |
15. Flash
Other names: burrs
Characteristic: Thin metal flakes appearing on the edge of a casting.
Feature: Thin metal flakes appearing on the edge of the casting.
Causes:
① Adjusting the clamping force of the machine before injectionNot good.
②High pressure die castingMold and slider damaged, locking elementThe component is invalid.
③ Wear of mold inserts and sliders.
④ Insufficient mold strength causes deformation.
⑤ Debris on the parting surface was not cleaned properly.net.
⑥ The projected area is calculated incorrectly, exceeding the limit.Excessive clamping force.
⑦ Excessive injection velocity creates pressureThe impact peak is too high.
Exclusion measures:
① Check the clamping force or pressure increase, and adjust the injection press.This structure reduces the peak pressure of the injection boost.
②Inspect the mold slide for damage and repair it to ensure proper sealing.The components play a role.
③Inspect for wear and tear and repair accordingly.
④ Accurately calculate the strength of the high-pressure die-casting mold.
⑤ Remove debris from the parting surface.
⑥ Calculate and adjust the clamping force correctly.
⑦ Adjust the injection speed appropriately.
16.Layering
Other names: diaphragm
Feature: There are obvious metal layers in some areas of the casting.
| Causes | Exclusion measures |
| ① The mold rigidity is insufficient, during the molten metal filling process,Template generationShaking. | ①Strengthen the rigidity of the mold and tighten the mold components. |
| ② The injection punch and the pressure chamber are not well matched.The forward speed during compression is notsmooth. | ② Adjust the injection plunger and injection mechanism to ensure proper coordination.good. |
| ③ Improper design of the gating system. | ③ Design the ingate appropriately. |
17.loose
Characteristics: The surface of the casting exhibits a loose and non-compact macrostructure.
| Causes | Exclusion measures |
| ① The mold temperature is too low. | ① ImproveHigh pressure die castingThe operating temperature of the mold. |
| ②The alloy casting temperature is too low. | ② Appropriately increase the alloy pouring temperature. |
| ③ Low specific pressure. | ③ Increase the specific pressure. |
| ④ Too much paint. | ④ The coating is thin and even. |
18. Misaligned edge (misaligned fastening)
Other names: staggered seam
Feature: One part of the casting is offset from another part on the parting surface, resulting in relative displacement (for threads, this is called misalignment).
| Causes | Exclusion measures |
| ①High pressure die castingDisplacement of mold inserts. | ① Adjust the insert and tighten it. |
| ②High pressure die castingWear on mold guide components. | ② Replace the guide post and guide sleeve. |
| ③ Manufacturing error of the inserts in the two halves of the mold. | ③ Make adjustments to eliminate errors. |
19.Deformation
Other names: Twisted, Warped
Feature: Overall deformation where the geometry of the casting does not conform to the design requirements.
| Causes | Exclusion measures |
| ① Poor casting structural design leads to unevennessshrink. | ① Improve the structure of the casting to make the wall thickness uniform. |
| ② The mold was opened too early, resulting in insufficient rigidity of the casting. | ② Determine the optimal mold opening time to enhance the rigidity of the casting. |
| ③ The draft angle of the casting is too small. | ③ Increase the casting draft angle. |
| ④ Improper handling of the casting. | ④ Castings should be handled with care when handling them. |
| ⑤ Improper stacking or improper removal of the gate. | ⑤ Use special boxes for stacking castings and remove gates.It should be appropriate. |
| ⑥ Improper placement of the push rod. | ⑥ Some deformed castings can be eliminated through shaping. |
20.Bump
Characteristics: Scratches on the surface of castings caused by impact.
| Causes | Exclusion measures |
| Gate removal, cleaning, alignment, and handling.It was accidentally damaged during the transfer process. | Cleaning castings requires care.Storage and handling of castingsShould not be piled upTo prevent stacking or collisions, use specialized storage and transport containers. |
21. Hard Spots
Other names: Oxide inclusions, inclusions.
Characteristics: Small spots or lumps with a hardness higher than the metal matrix exist within the casting matrix, making machining difficult, causing severe tool wear, and often displaying hard spots of varying brightness on the finished casting.
Causes：
The alloy contains or precipitates substances harder than the base metal.Metallic or non-metallic substances, such as Al2O3and free siliconwait.
(1) Alumina (Al2O3)
① The aluminum alloy was not properly refined.
②Oxides were mixed in during casting.
(2) Complex composition of aluminum, iron, manganese and siliconCompounds, mainly composed ofMnAl3In the cooler part of the molten poolFormed, then with MnAl3For the core, make FePrecipitation,Silicon and other materials also participate in the reaction to form compounds.
(3) Free silicon incorporations
① Aluminum-silicon alloys have a high silicon content
②Aluminum-silicon alloy is cast in a semi-liquid state.There exists a gameSilicon.
Exclusion measures:
(1) Reduce unnecessary stirring during smelting.To prevent overheating and maintain the cleanliness of the molten alloy, when keeping the molten aluminum alloy at a constant temperature in the furnace for an extended period, it should be…Periodic refining to remove impurities.
(2) Aluminum alloys contain titanium, manganese, iron, etc.When refining aluminum alloys containing magnesium, it is important to avoid segregation and maintain cleanliness. Use a dry refining agent. However, when the aluminum alloy contains magnesium, it is necessary to supplement it.Compensation.
(3) When aluminum alloys contain a high amount of copper and iron,The silicon content should be reduced to10.5%Below, appropriately increase the pouring temperature to avoid…Silicon precipitation.
22. Brittleness
Characteristics: The base metal grains of the casting are too coarse or too fine, making the casting prone to breakage or shattering.
| Causes | Exclusion measures |
| ① The alloy liquid is overheated or the holding time is too long.long. | ① The alloy should not be overheated, and prolonged storage of the alloy should be avoided.temperature. |
| ② Excessive cooling leads to excessively fine crystals. | ②Increase the temperature of the die-casting mold and decrease the pouring temperature. |
| ③ The aluminum alloy contains too much impurities such as zinc and iron.many. | ③ Strictly control the chemical composition of the alloy. |
| ④ The copper content in the aluminum alloy exceeds the specified range. | ④ Ensure the crucible coating layer is intact and in good condition. |
23. Leakage
Characteristics: The die-casting part shows signs of leakage, such as water leakage, air leakage, or water seepage, after testing.
Causes:
① Insufficient pressure.
② The gating system design is unreasonable or the casting structure is unsuitable.reason.
③ Inappropriate alloy selection.
④ Poor exhaust.
Exclusion measures:
①Increase the specific pressure.
② Improve the gating system and venting system.
③ Select a good alloy.
④ Avoid processing as much as possible.
⑤ The castings are impregnated.
24. The chemical composition does not meet the requirements.
Characteristics: Chemical analysis revealed that the alloy elements in the casting did not meet the requirements or contained too many impurities.
Causes：
① The ingredients are incorrect.
② Raw materials and recycled materials were processed without analysis.It has been put into use.
Exclusion measures:
① The furnace charge should be chemically analyzed before it can be used.
② The furnace charge should be strictly managed, and new and old materials should be handled in accordance with certain regulations.Use in the correct proportions.
③ Strictly adhere to the smelting process.
④ Smelting tools should be coated with paint.
25. Mechanical properties do not meet requirements.
Characteristics: The mechanical strength and elongation of the cast alloy are lower than the required standards.
| Causes | Exclusion measures |
| ① The chemical composition of the alloy does not meet the standard.allow. | ① Strict control of chemical composition and impurities is required during ingredient preparation and melting.quantity. |
| ② The casting contains porosity and shrinkage cavities.Slag inclusions, etc. | ② Strictly adhere to the smelting process. |
| ③ Incorrect sample treatment methodwait. | ③ Prepare samples as required, and regularly inspect castings during production.Process testing. |
| ④ The casting structure is unreasonable, which restricts…The castings met the standards. | ④ Improve the structure of the casting. |
| ⑤ Improper smelting process. | ⑤ Strictly control the alloy melting temperature and casting temperature.Try to eliminateBesides the various factors that contribute to the formation of oxides in alloys. |
The stability and lifespan of die-casting molds not only affect production costs but also product quality and delivery time. By systematically understanding these 25 common mold problems and their solutions, companies can effectively reduce downtime, lower scrap rates, and significantly improve overall production efficiency.
If you are looking for a reliable high-pressure die-casting mold supplier, Raidy has extensive industry experience and mature mold development capabilities, providing you with a one-stop solution from design and manufacturing to after-sales optimization. Contact us for professional technical support and customized mold services to make your die-casting production more efficient and stable..
