Applications and defects of die castings

R-C (4)


Die casting can be made for die casting auto parts, die-casting car engine fittings, die casting, air conditioning accessories, die-casting cylinder of engine cylinder head casting, die casting valve rocker arm, die-casting valve bearings, electrical accessories, die-casting motor end cover, die casting, die casting, die casting, pump shell shell building parts, die-casting parts, die-casting fence parts, die-casting parts and so on, With the constant improvement of the level of domestic manufacturing equipment industry development, die-casting machine equipment level increased significantly, also can produce the types of parts are also constantly expanding, the precision of the die casting parts of, the complexity of the components has been larger ascension, believe in the near future, die casting will be better service to our production and life!


Flow mark

Other names: Stripes.
Characteristics: The surface of the casting presents local sag smooth lines consistent with the flow direction of liquid metal, which can be felt by hand. This defect has no development direction and can be removed by polishing.
Causes: 1. The traces left by the two metal flows not filling the cavity synchronously. 2, the mold temperature is low, such as zinc alloy die temperature is lower than 150℃, aluminum alloy die temperature is lower than 180℃, it is easy to produce this kind of defect. 3. The filling speed is too high. 4, paint dosage is too much.
Exclusion measures: 1. Adjust the cross-sectional area or position of the inner gate. 2. Adjust mold temperature and increase overflow groove. 3. Adjust the filling speed properly to change the flow pattern of the liquid metal filling cavity. 4, the use of thin and uniform coating.

Cold water lines

Other names: cold connection (docking), water pattern.
Characteristics: low temperature metal flow butt but not fusion and appear gap, irregular linear shape, penetration and not penetration of two kinds, under the action of external force has the trend of development.
Causes: 1. Low pouring temperature of liquid metal or low mold temperature. 2, alloy composition does not meet the standard, poor liquidity. 3. Liquid metal stock filling, poor fusion. 4, the gate is unreasonable, the process is too long. 5. Low filling speed or poor exhaust. 6, the specific pressure is low.
Exclusion measures: 1. Appropriately increase pouring temperature and mold temperature. 2, change the alloy composition, improve the fluidity. 3. Improve the pouring system, increase the speed of the inner gate, and improve the filling conditions. 4. Improve discharge conditions and increase overflow flow. 5, improve injection speed, improve exhaust conditions. 6, improve the specific pressure.


Other names: Tension, tension mark, adhesive scar.
Characteristics: ALONG the direction of demoulding, due to metal adhesion, mold manufacturing inclination is too small, resulting in strain traces on the surface of the casting, serious become strain surface.
Causes: 1. The casting inclination of the core and the wall is too small or backward. 2. The core and wall have pressure scars. 3. Alloy adhesion mold. 4. Casting ejection deviation, or core axis deviation. 5, the surface of the wall is rough. 6, paint often spray less than. 7, aluminum alloy iron content is less than 0.6%.
Elimination measures: 1. Correct the mold to ensure manufacturing inclination. 2, play light indentation. 3. Reasonably design the pouring system to avoid metal flow against the core and wall, and properly reduce the filling speed. 4, modify the mold structure. 5. Polish the surface. 6, the amount of coating is thin and uniform, can not leak spray paint. 7, appropriately increase the iron content to 0.6~0.8%.


Other names: indentation, indentation, breath-holding, edge collapse.
Characteristics: A concave part on a smooth surface of a casting, where the surface is naturally cooled.
Causes: 1. The structure design of the casting is unreasonable, and there are some thick parts and hot joints. 2. The shrinkage rate of alloy is large. 3. The cross-sectional area of the inner gate is too small. 4, lower than low. 5. The mold temperature is too high.
Exclusion measures: 1. Improve the casting structure, make the wall thickness slightly uniform, and gradually ease the transition at the joints with large thickness difference, so as to eliminate hot joints. 2. Choose alloys with small shrinkage. 3. Set the gating system correctly and increase the cross-sectional area of the inner gate appropriately. 4. Increase the injection force. 5. Adjust the heat balance conditions of the mold properly, adopt temperature control device and cooling, etc.

Air bubbles

Other names: bubbling.
Characteristics: Under the skin of the casting, the bubble formed by the swelling of the accumulated gas.
Causes: 1. The mold temperature is too high. 2. The filling speed is too high, and the metal flow is involved in too much gas. 3. The amount of paint is large, and the amount is too much. The volatile gas is wrapped on the surface of the casting before pouring. 4. Exhaust is not smooth. 5. Early mold opening. 6. The alloy melting temperature is too high.
Elimination measures: 1. Cool the mold to the working temperature. 2. Reduce the injection speed to avoid eddy current entrapment. 3. Select the coating with small air volume, thin and uniform dosage, and close the mold after burning out. 4. Clean and add overflow groove and exhaust duct. 5. Adjust the mold retention time. 6. Dressing melting process.


Other names: Air hole, air eye.
Characteristics: Regular shape, smooth surface holes formed by the gas involved in the die casting.
Causes: mainly caused by coil gas: 1. Improper gate location selection and guide shape lead to frontal impact and vortex of liquid metal entering the cavity. 2. Poor runner shape design. 3. The pressure chamber is not full enough. 4. The inner gate speed is too high, resulting in turbulence. 5, exhaust is not smooth. 6. The mold cavity is too deep. 7, too much paint, filling before burning. 8, the charge is not clean, poor refining. 9. The allowance for mechanical processing is too large.
Exclusion measures: 1. Select the location of the gate and the shape of the guide flow that is conducive to the gas removal in the cavity to avoid the overflow system on the parting surface being closed by the liquid metal. 2. The cross-sectional area of the nozzle of the straight runner should be as large as possible than the cross-sectional area of the inner runner. 3. Improve the filling degree of the pressure chamber, select a smaller pressure chamber as far as possible and adopt quantitative casting. 4, under the condition of good molding, increase the thickness of the inner gate to reduce the filling speed. 5. The overflow groove and exhaust passage should be set up at the last filling part of the cavity, and the overflow groove and exhaust passage should be avoided to be closed by metal liquid. 6. The exhaust plug is opened at the deep cavity, and the exhaust is increased by the inlaid form. 7, the amount of coating is thin and uniform, fill after burning, use the coating with small gas volume. 8, the charge must be handled clean, dry, strictly abide by the melting process. 9, adjust the pressure injection speed, slow pressure injection speed and fast pressure injection speed of the transition point. 10. Reduce pouring temperature and increase specific pressure.

Shrinkage cavity

Other names: eye shrink, void shrink.
Characteristics: Die casting in the process of condensation, due to internal compensation caused by irregular shape, rough surface holes.
Causes: 1. The casting temperature of alloy is too high. 2. The wall thickness of the casting structure is not uniform, resulting in hot joints. 3, the specific pressure is too low. 4, the overflow tank capacity is not enough, the overflow is too thin. 5. The filling degree of the pressure chamber is too small, the residual material (cake) is too thin, and the final filling can not play a role. 6. The inner gate is small. 7. The local temperature of the mold is high.
Exclusion measures: 1, comply with the alloy melting specifications, alloy liquid overheating time is too long, reduce the pouring temperature. 2, improve the casting structure, eliminate metal accumulation, uniform wall thickness, slow transition. 3, appropriate increase of specific pressure. 4. Increase the overflow tank capacity and thicen the overflow port. 5. Improve the filling degree of the pressure chamber and adopt quantitative pouring. 6. Properly improve the pouring system to facilitate good pressure transmission.

Decorative pattern

Features: THE SMOOTH STRIPES ON THE SURFACE OF THE CASTING, visible TO THE NAKED eye, but not felt by the hand, the color is different from the base metal grain, can be removed by rubbing 0# emery cloth a few times.
Causes: 1. The filling speed is too fast. 2, the amount of paint is too much. 3. The mold temperature is low.
Exclusion measures: 1, as far as possible to reduce the injection speed. 2, coating dosage is thin and uniform. 3. Increase the mold temperature.

The crack

Characteristics: The alloy matrix on the casting is destroyed or broken to form a fine filamentous gap, there are two kinds of penetrating and non-penetrating, there is a trend of development.
Cracks can be divided into cold cracks and hot cracks. The main difference between them is that the metal at the crack site of cold crack castings is not oxidized, while the metal at the crack site of hot crack castings is oxidized.
Causes: 1. The casting structure is unreasonable, shrinkage is hindered, and the rounded corners of the casting are too small. 2. The core pulling and ejection device will deviate during work, and the force will be uneven. 3, mold temperature is low. 4, mold opening and core pulling time is too late. 5, improper selection of alloy or harmful impurities are too high, so that the alloy plasticity decreases. Zinc alloy: Lead, tin, Cadmium and iron on the high side Aluminum alloy: zinc, copper and iron on the high side Copper alloy: zinc and silicon on the high side Magnesium alloy: Aluminum, silicon and iron on the high side.
Elimination measures: 1. Improve casting structure, reduce wall thickness difference and increase casting fillet. 2, modify the mold structure. 3, improve the mold working temperature. 4. Shorten the time of mold opening and core pulling. 5, strict control of harmful impurities, adjust the alloy composition, comply with the alloy melting specifications or re-choose the alloy brand.

Owe cast

Other names: insufficient pouring, unclear outline, incomplete corners.
Characteristics: The liquid metal does not fill the cavity, and there are incomplete filling parts on the casting.
Causes: 1, alloy flow caused by: (1) the metal liquid gas content is high, oxidation is serious, so that the fluidity decreases. (2) The alloy pouring temperature and mold temperature are too low. (3) The inner gate speed is too low. (4) Insufficient nitrogen pressure in the accumulator. (5) Low filling degree of pressure chamber. (6) The casting wall is too thin or the thickness is not properly designed. 2. Bad gating system causes: (1) improper choice of gate location, diversion mode and number of inner gate shares. (2) The cross-sectional area of the inner gate is too small. 3. Poor exhaust conditions cause: (1) poor exhaust. (2) too much paint, not burned out by drying. (3) The mold temperature is too high, the gas pressure in the mold cavity is high, and it is not easy to discharge.

Elimination measures: 1, improve the fluidity of the alloy: (1) adopt the correct melting process, eliminate gas and non-metallic inclusions. (2) Appropriately increase the alloy pouring temperature and mold temperature. (3) Increase the injection velocity. (4) Nitrogen is added to improve the effective pressure. (5) Quantitative casting is adopted. (6) Improve the casting structure and adjust the wall thickness appropriately. 2, improve the gating system: (1) The correct choice of gate location and diversion mode is beneficial to the use of multiple internal gates for ill-shaped castings and large castings. (2) Increase the cross-sectional area of the inner gate or increase the injection velocity. 3, improve the exhaust conditions: (1) add overflow groove and exhaust channel, deep concave cavity can be set up ventilation plug. (2) The coating is thin and uniform, and the die is closed after blowing dry and burning. (3) Reduce the mold temperature to the working temperature.


Other names: push rod impression, insert or movable block splice impression.
Characteristics: The convex and concave marks on the surface of the casting caused by the bumping of the mold cavity and the stitching of the pushing rod, insert block, movable block and other parts.
Causes: 1, push rod adjustment or end wear. 2. The mold cavity, slider splicing part and its moving part are not well coordinated. 3, putting area is too small.
Exclusion measures: 1. Adjust the putter to the correct position. 2. Tighten the insert or other moving parts to eliminate the improper concave and convex parts. 3, increase the putter area or increase the number.

Mesh burr

Other names: reticular marks, reticular patterns, cracked burrs.
Characteristics: A network of raised marks and metal spines on the surface of the casting due to thermal fatigue on the cavity surface of the die.
Causes: 1. The traces caused by mold cavity surface cracking, the heat conduction near the inner gate area is the most concentrated, the friction resistance is the largest, the erosion of molten metal is the strongest, the alternating cold and heat is the most dramatic, the most easy to produce hot cracking, forming cracking. 2. Improper mold materials or incorrect heat treatment process. 3. The temperature difference between cold and heat of the mold changes greatly. 4. The pouring temperature of the alloy liquid is too high, and the mold is not preheated enough. 5, the mold cavity surface roughness Ra is too large. 6, metal flow rate is too high and front scour wall.
Elimination measures: 1. Correct selection of mold materials and reasonable heat treatment process. 2. The mold must be preheated to the working temperature range before die casting. 3, as far as possible to reduce the alloy pouring temperature. 4, improve the surface quality of mold cavity, reduce Ra value. 5, insert regular annealing, eliminate stress. 6, the correct design of the pouring system, in the condition of good molding, as far as possible with a small injection speed.

Colored spots

Other names: Oil spots, black spots.
Characteristic: A spot on the surface of a casting that is different from the base metal, usually formed by coating carbides.
Causes: 1. The coating is not pure or the amount is too much. 2, paint containing too much graphite.
Exclusion measures: 1, the use of coating should be thin and uniform, can not be stacked, to use compressed air blown away. 2, reduce the graphite content in the coating or choose graphite-free water-based coating.


Characteristics: In the process of filling, due to the low temperature of the mold or the alloy liquid, the surface of the casting is formed under the condition of approximately underpressure.
Causes: 1. When filling, the metal disperses into dense droplets and impinges on the wall at high speed. 2. The thickness of the inner gate is small.
Exclusion measures: 1. Correct design of pouring system to avoid spatter of liquid metal, improve exhaust conditions, avoid excessive gas involved in liquid flow, reduce the speed of inner gate and increase mold temperature. 2. Adjust the inner gate thickness appropriately.


Other names: Slits.
Characteristics: Metal sheet appearing on the edge of the casting.
Causes: 1. The clamping force of the machine before injection is not well adjusted. 2, mold and slider damage, locking element failure. 3, mold insert block and slider wear. 4, the mold strength is not enough to cause deformation. 5. Sundries on the parting surface are not cleaned up. 6. 7, the injection speed is too high, the formation of pressure impact peak is too high.
Elimination measures: 1. Check the clamping force or pressurization, adjust the injection pressurization mechanism, so as to reduce the injection pressurization peak. 2. Check the damage degree of mold slider and trim to ensure that the locking element plays a role. 3. Check the wear and repair. 4, correct calculation of mold strength. 5. Remove sundries on the parting surface. 6. Correctly calculate and adjust the clamping force. 7. Adjust the injection speed appropriately.


Other names: septum.
Characteristics: There are obvious metal layers on the casting.
Causes: 1, mold rigidity is not enough, in the process of metal filling, the template jitter. 2. The pressure chamber punch is not well coordinated with the pressure chamber, and the forward speed of the pressure shot is not stable. 3. Improper gating system design.
Exclusion measures: 1. Strengthen the stiffness of the mold and tighten the mold parts. 2. Adjust the injection punch and pressure chamber to ensure good cooperation. 3. Reasonable design of inner gate.


Characteristics: The surface surface of the casting shows loose but not tight macroscopic structure.
Causes: 1. The mold temperature is too low. 2. The casting temperature of alloy is too low. 3, the pressure is small. 4, paint too much.
Elimination measures: 1. Increase the mold temperature to the working temperature. 2, appropriately increase the alloy pouring temperature. 3, improve the specific pressure. 4, coating thin and uniform.

Wrong side wrong button

Other names: Staggered seam.
Features: One part of the casting is staggered with the other part on the parting surface, resulting in relative displacement (the screw thread is called the wrong buckle).
Cause: 1, mold insert displacement. 2, mold guide wear. 3, two half die insert manufacturing error.
Exclusion measures: 1. Adjust the insert and tighten it. 2, replace the guide post guide sleeve. 3. Trim and eliminate errors.


Other names: Warp, warping.
Characteristics: The overall deformation of the casting does not conform to the design requirements.
Causes: 1, casting structure design is poor, causing uneven shrinkage. 2, early opening, casting rigidity is not enough. 3, casting inclination is too small. 4. Improper operation of casting picking. 5. Improper placement of the putter.
Exclusion measures: 1. Improve the casting structure to make the wall thickness uniform. 2. Determine the best opening time to strengthen the rigidity of the casting. 3. Enlarge the casting slope. 4. Take and put the casting carefully and gently. 5. Special box should be used for stacking castings, and the gate removal method should be appropriate. 6. Some deformed castings can be eliminated by shaping.


Characteristics: Welt on the surface of the casting caused by impact.
Causes: 1. Accidental injury in the process of gate removal, cleaning, correction and handling.
Exclusion measures: 1. Be careful when cleaning castings. Store and transport castings without stacking or hitting each other.

Hard spots

Other names: oxidized inclusion, slag inclusion.
Characteristics: There are small particles or lumps in the casting matrix whose hardness is higher than that of the metal matrix, which makes the processing difficult and the tool wear is serious. After processing, the casting often shows hard points with different brightness.
Cause: the alloy is mixed or precipitated with metal or non-metallic substances harder than the matrix metal, such as AL2O3 and free silicon.
1, alumina (AL2O3) : (1) aluminum alloy is not refined. (2) Oxide was mixed during pouring.
2, a complex compound composed of aluminum, iron, manganese, silicon, mainly formed by MnAL3 in the cold part of the molten pool, and then MnAL3