Diagnosis of Die Casting Product Defects
The die casting process is a complex process. The qualification rate of die-casting products is generally between 70% and 90%. The factors affecting die-casting products are as follows: the performance of the machine itself; various working parameters of the machine; the structure and performance of the die-casting mold (mold); the quality of the die-casting alloy And the skills of the operator. In order to improve die-casting production efficiency and product qualification rate, operators must have a certain ability to prevent and eliminate product defects.
01. Die casting product defect types, causes and solutions
(1) Flow marks and patterns
Appearance inspection: There are stripes on the surface of the casting that are consistent with the flow direction of the molten metal, and there are obviously visible lines that are different from the metal matrix in color and have no directionality, and there is no development trend.
1. The causes of flow marks are as follows, which should be corrected in time after the causes are found out.
(1) The mold temperature is too low.
(2) Poor runner design and poor position of the inner gate.
(3) The material temperature is too low.
(4) The filling speed is low and the filling time is short.
(5) The pouring system is unreasonable.
(6) Poor exhaust.
(7) The spray is unreasonable.
2. The pattern is caused by too much paint in the cavity or poor paint quality. The solutions and prevention methods are as follows:
(1) Adjust the cross-sectional area or position of the inner runner.
(2) Increase the mold temperature.
(3) Adjust the speed and pressure of the inner runner.
(4) Appropriate selection of paint and adjustment of dosage.
(2) Net-like hairy wings (cracked tortoise)
Appearance inspection: The surface of the die-casting parts has the same raised or depressed traces as net-like hair, which will continue to expand and extend as the number of die-casting increases.
The reasons are as follows:
1. There are cracks on the surface of the die-casting mold (mold) cavity;
2. The preheating of the die-casting mold (mold) is uneven.
The solutions and prevention methods are:
1. The die-casting mold (mold) should be annealed regularly or after a certain number of die-casting to eliminate the stress in the cavity.
2. If tortoise cracks have appeared on the surface of the cavity, the molding surface should be polished to remove the cracked layer.
3. The preheating of the mold (mold) must be even.
(Three) cold barrier
Appearance inspection: The surface of the die casting has obvious, irregular, and sinking linear lines (both penetrating and non-penetrating). The shape is small and narrow, sometimes the junction edge is smooth, and there is a possibility of disconnection under the action of external force.
The reasons are as follows:
1. The two metal streams are connected to each other, but they are not completely fused and there are no inclusions in between, and the bonding force of the two metal streams is very weak;
2. Pouring temperature or die casting mold (mold) temperature is too low;
3. The runner position is wrong or the flow path is too long;
4. Low filling speed.
The solutions and prevention methods are:
1. Appropriately increase the pouring temperature;
2. Improve the injection ratio and shorten the filling time and increase the injection speed.
3. Improve exhaust and filling conditions.
(4) Shrinkage (dents)
Visual inspection: There are smooth dents (like discs) on the most thick surface of the die casting.
The reasons are as follows:
1. Caused by shrinkage
(1) Improper design of die-casting parts with too large wall thickness difference;
(2) Improper runner position;
(3) The injection pressure is low and the pressure holding time is short;
(4) The local temperature of the die-casting mold (mold) is too high.
2. The cooling system design is unreasonable;
3. Opening (mold) is too early;
4. The pouring temperature is too high.
The solutions and prevention methods are:
1. The wall thickness should be uniform;
2. The thickness transition should be eased;
3. Correctly select the alloy liquid introduction position and increase the cross-sectional area of the inner runner;
4. Increase the injection pressure and prolong the pressure holding time;
5. Appropriately reduce the pouring temperature and die-casting mold (mold) temperature;
6. Partially cool the local high temperature;
7. Improve overflow conditions
(5) Imprint
Visual inspection: the traces left by the contact between the surface of the casting and the surface of the die-casting mold (mold) or the step marks appear on the surface of the casting.
The reasons are as follows:
1. Caused by ejector components
(1) The end face of the ejector rod is worn;
(2) The adjustment length of the ejector rod is inconsistent;
(3) The splicing part of the die-casting mold (mold) cavity does not fit well with other parts;
2. Caused by splicing or moving parts
(1) The mosaic part is loose;
(2) The movable part is loose or worn;
(3) The surface of the side wall of the casting is formed by the inserts with the movable and fixed molds interspersed with each other.
The solutions and prevention methods are:
1. The length of the ejector rod should be adjusted to the proper position;
2. Fasten inserts or other movable parts
3. Eliminate sharp corners when designing, and adjust it to fit the gap;
4. Improve the structure of castings so that the die-casting mold (mold) can eliminate the interspersed inlay form, and improve the structure of the die-casting mold (mold);
(6) Traces of adherents
Appearance inspection: small flakes and metal or non-metallic and metal base parts are welded, and the small flakes are peeled off under the action of external force. After the peeling, the surface of the casting is bright and some are dark gray.
The reasons are as follows:
1. There are metallic or non-metallic residues on the surface of the die-casting mold (mold) cavity;
2. When pouring, the impurities are first brought in and attached to the surface of the cavity.
The solutions and prevention methods are:
1. Before die-casting, clean the cavity pressure chamber and pouring system to remove metal or non-metal adherents;
2. Clean the cast alloy;
3. Choose the right paint, and the coating should be even.
(7) Delamination (skinning and peeling)
Visual inspection or damage inspection: There are obvious layers of metal in the casting part.
The reasons are as follows:
1. The mold (mold) has insufficient rigidity. During the liquid metal filling process, the template will shake;
2. The punch appears to crawl during the injection process;
3. Improper design of runner system.
The solutions and prevention methods are:
1. The reinforced type (mold) has rigidity, and the tightened type (mold) has parts to make it stable;
2. Adjust the cooperation of the injection punch and the pressure chamber to eliminate the crawling phenomenon;
3. Reasonably design the inner runner.
(8) Friction and ablation
Visual inspection: The surface of the die-casting part has rough surfaces in some positions.
The reasons are as follows:
1. Improper position, direction and shape of the inner runner caused by the die-casting mold (mold);
2. Insufficient cooling of the parts where the molten metal is scoured severely at the inner runner caused by the casting conditions.
The solutions and prevention methods are:
1. Improve the position and direction of the inner sprue where it is improper in pouring;
2. Improve the cooling conditions, especially the areas where the molten metal is violently scoured;
3. Add paint to the ablated part;
4. Adjust the flow rate of the alloy liquid to prevent cavitation
5. Eliminate the alloy adherents on the mold (mold).
(9) Erosion
Visual inspection: There are pitting or embossing in the local position of the die casting.
The reasons are as follows:
1. Improper setting of the inner runner position;
2. Poor cooling conditions.
The solutions and prevention methods are:
1. The thickness of the inner runner should be appropriate;
2. Modify the position, direction and setting method of the inner runner;
3. Strengthen the cooling of the eroded parts.
(10) Cracks
Visual inspection: Put the casting in alkaline solution, the cracks are dark gray. The destruction and cracking of the metal matrix are straight or wavy, with narrow and long lines, which have a tendency to develop under the action of external forces.
Causes:
(1) The iron content in the alloy is too high or the silicon content is too low; the content of harmful impurities in the alloy is too high, which reduces the plasticity of the alloy; aluminum-silicon alloy, aluminum-silicon-copper alloy contains too much zinc or copper; aluminum-magnesium alloy Excessive magnesium content;
(2) The mold retention time is too short, and the pressure holding time is short; there are drastic changes in the wall thickness of the casting;
(3) The local packing force is too large, and the force is uneven during ejection.
Solutions and prevention methods:
(1) Correctly control the alloy composition. In some cases: pure aluminum ingots can be added to the alloy to reduce the magnesium content in the alloy; or aluminum-silicon master alloy can be added to the alloy to increase the silicon content.
(2) Increase the temperature of the mold (mold); change the structure of the casting, adjust the core pulling mechanism or make the push rod force uniform;
(3) Increase the draft angle and use strong release agent locally;
(4) Increase mold retention time and increase pressure holding time.
Causes:
The alloy has a high content of aluminum and silicon; the mold (mold) temperature is low; the wall thickness of the casting changes drastically; the force is uneven during ejection and core pulling.
Solutions and prevention methods:
Pure magnesium is added to the alloy to reduce the content of aluminum and silicon; the temperature of the mold (mold) should be controlled within the required range; the structure of the casting should be improved to eliminate the cross-section with large thickness changes; the core and push rod should be adjusted to balance the force .
3. Cracks in copper alloy castings
Causes:
(1) The content of zinc in brass is too high (cold cracking) or too low (hot cracking); the content of silicon in silicon brass is high;
(2) The opening time (mold) is late, especially for castings with many cores.
Solutions and prevention methods:
(1) Ensure the chemical composition of the alloy, and the lower limit of the alloying elements: when the silicon brass is prepared, the content of silicon and zinc cannot be taken at the same time as the upper limit;
(2) Increase the mold (mold) tool temperature; appropriately control and adjust the mold opening (mold) time.
(11) Undercasting and unclear outline
Appearance inspection: The molten metal fills the cavity, the surface of the casting has irregular holes, depressions or irregular edges and corners, and the surface shape is natural liquid flow or similar to the liquid surface.
The reasons are as follows:
1. The width of the inner runner is not enough or the die-casting mold (mold) is poorly exhausted;
2. The alloy has poor fluidity;
3. The pouring temperature is low or the temperature of the die-casting mold (mold) is low, and the injection speed is low;
4. Insufficient injection pressure;
5. The dimensions of the corners of the die-casting (mold) cavity are unreasonable and difficult to fill;
6. The spray is unreasonable.
Solutions and prevention methods:
1. Improve the inner runner, improve the exhaust conditions, and appropriately increase the temperature of the die-casting mold (mold) and the pouring temperature;
2. Increase injection specific pressure and injection speed;
3. Pay attention to the position of the spray.
(12) Deformation
Visual inspection or measurement and marking: The casting is warped (bent) and exceeds the tolerance requirements of the drawing.
The reasons are as follows:
1. The casting structure is unreasonable, and the shrinkage of each part is uneven;
2. The mold retention time is too short;
3. The casting is skewed during ejection;
4. The castings are not rigid enough;
5. Unreasonable stacking or improper sprue removal method.
Solutions and prevention methods:
1. Improve the casting structure and make the wall thickness uniform;
2. Do not stack and store, especially large and thin castings;
3. Do not stack into the furnace during aging or annealing;
4. Plastic surgery can be carried out if necessary.
(13) Fins
Visual inspection: Excessive metal flakes protruding at the parting surface or movable part of the casting
The reasons are as follows:
1. The adjustment and operation of the machine before injection are inappropriate;
2. The die-casting mold (mold) and the sliding block are damaged, and the locking element is invalid;
3. Wear of inserts and sliders;
4. The die-casting mold (mold) is not strong enough to cause deformation;
5. The sundries on the parting surface are not cleaned up;
6. The lock type (mold) force is small.
Solutions and prevention methods:
1. Check the closing (mold) force and pressurization conditions;
2. Adjust the pressure boosting mechanism to reduce the peak pressure of injection pressure;
3. Check the die-casting mold (mold) strength and locking components;
4. Check the damage of the die-casting mold (mold) and repair it;
5. Clean the parting surface to prevent debris;
6. Increase the lock type (mold) force.
(14) Slag inclusion (slag hole)
Visual inspection or flaw detection and metallographic inspection: There are irregular bright or dark holes on the castings, and the holes are often filled with slag. In metallographic examination, it is dark black under a low-power microscope; bright and colorless under a high-power microscope.
The reasons are as follows:
1. There are slag inclusions in the metal or non-metallic residues in the cavity, which have not been removed before injection;
2. The molten slag on the surface of the molten metal has not been removed;
3. Pour molten slag and metal into the press chamber at the same time.
Solutions and prevention methods:
1. Carefully remove the slag on the metal surface;
2. Comply with metal smelting scooping process regulations.
(15) Hard point
Appearance inspection or metallographic inspection during machining or after machining: There are fine particles or blocks on the casting that are harder than the metal matrix, which causes serious tool wear and often shows different brightness after machining.
1. The causes of non-metallic hard spots and the solutions and prevention methods
(1) Non-metallic hard spots are produced due to the mixing of oxides on the surface of the alloy liquid. The solutions and prevention methods are as follows:
Do not scoop the oxide on the surface of the alloy liquid into the spoon during casting; remove the oxide on the surface of the cast iron crucible before coating
Paint; eliminate oxides on spoons and other tools; use paint that does not react with aluminum;
(2) Non-metallic hard spots are generated due to the mixing of reaction products of alloy liquid and paint. Should be used with aluminum alloy
Reactive paint.
(3) Compound compounds are produced in the molten metal, such as compounds composed of Al, Mn, Fe, and Si. It should be noted: in aluminum
When the alloy contains Mn, Fe and other elements, it should not be segregated; and keep it clean; use a dry degassing agent for degassing, but pay attention to compensation when the aluminum alloy contains magnesium.
(4) The aluminum-silicon alloy in the molten metal contains high Si; the aluminum alloy is poured in a semi-liquid state; silicon is free, or the aluminum-silicon alloy Si
It is higher than 11.6% and the content of Cu and Fe is also high. The solution and prevention methods are: when the aluminum alloy contains a lot of Cu and Fe, the Si content should be reduced to below 10.5%; the pouring temperature should be appropriately increased to avoid the precipitation of Si.
(5) Non-metallic hard spots are produced due to the impure metal ingots or the adhesion of oil stains, the smelting tools are not clean and foreign matter is entrained. answer
Pay attention to check the purity of metal ingots, strengthen the cleaning of raw materials and recycled materials, and do not stick foreign objects such as oil, sand, dust, etc.; pay attention to clean the crucible, rust and oxide on the smelting tool.
3. The causes of metal hard spots and the solutions and prevention methods:
(1) The undissolved silicon raw material is mixed to produce metallic hard spots. The solutions and prevention methods are:
1) Do not use silicon element powder when smelting silicon alloys;
2) When adjusting the alloy composition, do not directly add silicon element, but an intermediate alloy must be used;
3) The smelting temperature should be high and the time should be long to fully dissolve the silicon.
(2) Metallic hard spots are produced by mixing raw materials that promote the growth of primary silicon crystals. Pay attention to:
Reduce the casting temperature fluctuation range to keep it in a molten state; prevent the alloy ingot from solidifying the alloy when adding cold material; try to reduce the components that promote the easy growth of coarse-crystalline silicon.
(3). Metallic hard spots are produced by mixing crystalline substances that generate metal compounds. Pay attention to the following during production:
1) Reduce the temperature fluctuation range, and do not make the temperature of the alloy liquid too high or too low;
2) While controlling the impurity content of alloy components, be careful not to increase impurities;
3) The materials that can produce intermetallic compounds should be smelted at high temperature. In order to prevent the increase of impurities, they should be added in small amounts little by little.
4. The cause of segregation hard spots is due to the rapid cooling, which makes the components that are easy to segregate to become hard spots. Pay attention to the injection: After the alloy liquid is poured into the pressure chamber, it should be injected and filled immediately; it should not contain Ca as much as possible. , Mg, Na and other alloy components that easily cause quenching effect. Ca should be controlled below 0.05%.
(16) Brittleness
Visual inspection or metallographic inspection: The alloy grains are coarse or extremely small, which makes the castings easy to break or break.
The reasons are as follows:
1. The alloy is too hot or the holding time is too long;
2. Intense and too cold, too fine crystals;
3. Aluminum alloy contains too many impurities such as zinc and iron;
4. The copper content in aluminum alloy exceeds the specified range.
The solutions and prevention methods are:
1. The alloy should not be overheated;
2. Increase the mold (mold) temperature and reduce the pouring temperature;
3. Strictly control the alloy composition within the allowable range.
(17) Leakage
Through the pressure test, the die-casting parts leak or seep water.
The reasons are as follows:
1. Insufficient pressure;
2. The design of the gating system is unreasonable or the structure of the casting is unreasonable;
3. Improper alloy selection;
4. Poor exhaust.
The solutions and prevention methods are:
1. Increase the injection pressure;
2. Try to avoid post-processing;
3. Improve the gating system and exhaust system;
4. Use good alloys.
(18) Stoma
Visual inspection or flaw detection after anatomy: The stomata have a smooth surface and are round or oval in shape.
The reasons are as follows:
1. The distance of the first speed is too short, the first speed is too fast, and the gas is entrained in the material liquid;
2. The design of the runner is unreasonable;
3. The position of the inner gate is unreasonable;
4. Improper selection of parting surface;
5. Poor exhaust;
6. The material liquid has high gas content;
7. The material liquid has high impurity content;
8. Improper spray volume and position;
9. The mold temperature is too high;
10. The material temperature is too high;
11. The cooling system design is unreasonable;
12. The closing (mold) is too early.
The solutions and prevention methods are:
1. Use dry and clean additives to prevent the alloy from overheating and exhaust gas well, and improve the direction of metal introduction;
2. Reduce injection speed;
3. Under the condition of ensuring good filling, increase the cross-sectional area of the inner runner as much as possible;
4. The exhaust slot should be set reasonably and have sufficient exhaust capacity.
(19) Bubbles
Visual inspection or flaw detection after autopsy: There is gas accumulation near the surface of the casting, and sometimes bubbling is seen on the surface of the casting.
The reasons are as follows:
1. Caused by entrapped gas: cavity gas is not discharged and is wrapped in the casting; the gas generated by the coating is entangled in the casting;
2. Caused by alloy gas: There is a lot of gas absorbed in the alloy, and it will precipitate and stay in the casting during solidification.
The solutions and prevention methods are:
1. Improve the size and position of the inner runner and the exhaust duct of the overflow groove; improve the filling time and the flow rate at the inner runner; increase the injection pressure; set the core where the air hole occurs; use as little paint as possible;
2. Remove the gas and oxides in the alloy liquid; the charge should be managed well to avoid being polluted by dust and oil.
(20) Shrinkage cavity shrinkage porosity
Visual inspection or flaw detection after anatomy: the surface of shrinkage cavity is dark and not smooth, irregularly shaped holes, large and concentrated ones are shrinkage holes, and small and scattered ones are shrinkage porosity.
The reasons are as follows:
1. Shrinkage cavity is the cavity caused by insufficient internal compensation during the condensation process of die casting. Due to the high pouring temperature, low injection ratio, the structure of the casting has metal accumulation parts and the cross section changes drastically, and the inner runner is small. And produce
2. The temperature of the mold (mold) is too high;
3. The pressure holding time is short.
Solutions and prevention methods:
1. Change the structure of the casting to eliminate metal accumulation and large changes in cross section;
2. Lower the pouring temperature when possible;
3. Increase the injection pressure;
4. Appropriately improve the gating system to better transmit the pressure;
5. Lower mold temperature;
6. Improve the pressure holding time.
(21) Sticky mold strain
Visual inspection: The die-casting alloy adheres to the mold wall and produces strain marks, which will be torn in severe parts.
The reasons are as follows:
1. The alloy casting temperature is high;
2. The mold (mold) temperature is too high;
3. Insufficient or incorrect use of paint;
4. The surface of the mold (mold) is rough in some parts; the draft angle is too small or it is drawn upside down.
5. The runner system improperly uses the alloy frontal impact wall or core;
6. Improper use of mold (mold) materials or incorrect heat treatment process, insufficient hardness.
7. The iron content of aluminum alloy is too small (<0.6%). ZCuZn40Pb2 has low zinc content or segregation;
8. The filling speed is too high.
The solutions and prevention methods are:
1. Lower the pouring temperature;
2. The temperature of the mold (mold) is controlled within the process range;
3. Eliminate the rough surface of the cavity;
4. Check whether the paint variety or dosage is appropriate;
5. Adjust the inner runner to prevent the frontal impact of molten metal;
6. Check the alloy composition to make the iron (Fe) content of the aluminum alloy within the required range;
7. Check whether the material, heat treatment and hardness of the mold (mold) are reasonable;
8. Appropriately reduce the filling speed.
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