Die Casting Defect Analysis
Time：2026-10-12 09:36:58 / Popularity： / Source：
I. Essence of Die Casting
Essence of die casting is to use a high-pressure injection head to fill a die casting mold cavity at extremely high speed and in a short time under high pressure, where it solidifies to obtain a casting.
Because it transforms molten alloy into a component that satisfies customer within a very short time, die casting process has very high requirements: it involves organic combination and comprehensive application of three major elements—die casting machine, die casting mold, and die casting alloy. These factors are closely related, influencing and restricting each other.
Main process parameters are: pressure, speed, time, and temperature. Selection and reasonable matching of these process parameters are crucial to ensuring the overall performance of die casting, directly affect production efficiency and mold life.
Because this production process is extremely complex, many die-casting companies in China have already adopted automation. Whether it's manual or automated operation, problems affecting product quality can still occur during production. Below, we describe some common defects in die-cast parts, hoping it will be helpful in your future work.
1. Common Appearance Defects - Cold Shut
Because it transforms molten alloy into a component that satisfies customer within a very short time, die casting process has very high requirements: it involves organic combination and comprehensive application of three major elements—die casting machine, die casting mold, and die casting alloy. These factors are closely related, influencing and restricting each other.
Main process parameters are: pressure, speed, time, and temperature. Selection and reasonable matching of these process parameters are crucial to ensuring the overall performance of die casting, directly affect production efficiency and mold life.
Because this production process is extremely complex, many die-casting companies in China have already adopted automation. Whether it's manual or automated operation, problems affecting product quality can still occur during production. Below, we describe some common defects in die-cast parts, hoping it will be helpful in your future work.
1. Common Appearance Defects - Cold Shut
| Defect Name | Characteristics and Inspection Methods | Causes | Prevention Methods |
| Cold Shut | Appearance Inspection: Casting surface has obvious, irregular, lower limit linear lines (both penetrating and non-penetrating), small and narrow in shape, sometimes with smooth edges. These lines may develop under external force. | 1. Two metal streams meet but are not completely fused, and there are no inclusions between them; bonding force between two metal streams is very weak. 2. Pouring temperature or die-casting mold temperature is too low. 3. Inappropriate alloy selection, poor fluidity. 4. Inappropriate gating position or excessively long runner. 5. Low filling speed. 6. Low injection pressure. |
1. Appropriately increase pouring temperature and mold temperature. 2. Increase injection pressure and shorten filling time. 3. Increase injection speed and increase cross-sectional area of ingate. 4. Improve venting and filling conditions. 5. Correctly select alloys to improve alloy fluidity. |
2. Common Appearance Defect Analysis - Scratches
| Defect Name | Characteristics and Inspection Methods | Causes | Prevention Methods |
| Scratches | A strip-shaped scratch mark appears on the surface of casting along mold opening direction, with a certain depth. In severe cases, it is a surface scratch. Another type is scratches caused by welding or adhesion between molten metal and mold, resulting in excessive or insufficient material in casting. |
1. Scratches on cavity surface 2. Insufficient draft angle or tilting during ejection 3. Deflection during ejection 4. Excessive pouring temperature or mold temperature causing alloy liquid to adhere 5. Poor performance of release agent 6. Iron content in aluminum alloy is below 0.6% |
1. Repair damaged areas on mold surface, correct draft angle, and improve surface finish 2. Adjust ejector pins to balance ejection force 3. Replace release agent 4. Adjust iron content of alloy 5. Lower pouring temperature and control mold temperature 6. Modify ingate to avoid direct impact on core and mold wall |
3. Common appearance defects - bubbles
| Defect name | Characteristics and inspection methods | Causes | Prevention methods |
| Bubble | Rales size of rice grains or larger on the surface of casting | 1. Alloy liquid is not filled too low in pressure chamber, which easily produces air entrapment; injection speed is too high 2. Poor mold venting 3. Solution is not degassed, and aluminum liquid temperature is too high 4. Mold temperature is too high, and metal solidification time is insufficient. Insufficient strength, premature mold opening and ejection of casting, causing it to expand under gas pressure. 5. Too much release agent. |
1. Adjust die casting process parameters, injection speed, and high-speed injection switching point. 2. Reduce mold temperature in defect area to reduce gas pressure. 3. Set up venting channels and overflow channels. 4. Adjust melting process. 5. Extend mold opening time. |
4. Common appearance defects - cracks
| Defect name | Characteristics and inspection methods | Causes | Prevention methods |
| Cracks | Casting surface exhibits straight or wavy lines, narrow and long, which tend to develop under external force. Cracks are of two types: 1. Cold cracks (the metal at crack is not oxidized); 2. Hot cracks (the metal at crack is already oxidized). | 1. Ion content in alloy is too high or silicon content is too low. 2. Content of harmful impurities in alloy is too high, reducing alloy's plasticity. 3. Aluminum-silicon alloys: Aluminum-silicon-copper alloys have excessive zinc or copper content; aluminum-magnesium alloys have excessive magnesium content. 4. Mold, especially core temperature, is too low. 5. Where casting wall thickness changes drastically, shrinkage is hindered. 6. Mold dwell time is too long, resulting in high stress and uneven force during ejection. |
1. Correctly control alloy composition. In some cases, add pure aluminum ingots to alloy to reduce magnesium content; or add aluminum-silicon intermediate alloys to increase silicon content. 2. Change casting structure, increase fillet radius, increase draft angle, and reduce wall thickness difference. 3. Change or increase ejection position to make ejection force more uniform. 4. Shorten mold opening time and core pulling time. 5. Increase mold temperature. |
5. Common appearance defects - deformation
| Defect name | Characteristics and inspection methods | Causes | Prevention methods |
| Deformation | Geometric shape of die castings Discrepancies with design drawings, overall or partial deformation | 1. Poor casting structure design, causing uneven shrinkage 2. Premature mold opening leading to insufficient casting rigidity 3. Improper ejector pin placement, resulting in uneven force during ejection 4. Improper method of gate removal |
1. Improve casting structure 2. Adjust mold opening time 3. Reasonably set ejector pin positions and numbers 4. Select appropriate gate removal methods |
6. Common appearance defects - flow marks and patterns
| Defect Name | Characteristics and Inspection Methods | Causes | Prevention Methods |
| Flow Marks and Patterns | Appearance Inspection: Stripes on casting surface aligned with direction of molten metal flow, with clearly visible, non-directional lines that differ from basic metal color and show no development trend | 1. Trace left by initial thin and incomplete metal layer formed by molten metal entering mold cavity, which is then filled in by subsequent molten metal. 2. Low mold temperature 3. Splashing caused by an insufficiently small cross-sectional area or improper position of ingate. 4. Insufficient pressure acting on molten metal. Painting: Excessive paint application. |
1. Increase mold temperature 2. Adjust cross-sectional area or position of ingate 3. Adjust speed and pressure of ingate 4. Select appropriate paint and adjust amount |
7. Common appearance defects - mesh-like hairline
| Defect name | Characteristics and inspection methods | Causes | Prevention methods |
| Mesh-like hairline | Appearance inspection: There are mesh-like hairline-like raised or recessed marks on the surface of casting, which continue to expand and extend with increase of die casting times | 1. Cracking on the surface of die casting mold cavity 2. Inappropriate die casting mold material or incorrect heat treatment process 3. Temperature difference between hot and cold molds 4. Too high a pouring temperature 5. Insufficient preheating of die casting mold 6. Rough surface of cavity |
1. Correct selection of die casting mold material and heat treatment process 2. Pouring temperature should not be too high, especially for high melting point alloys 3. Sufficient preheating of mold is necessary 4. Die casting mold should be annealed periodically or after a certain number of die castings to eliminate internal stress 5. Grind surface of formed part to reduce surface roughness 6. Reasonable selection of mold cooling method |
8. Common appearance defects - dents
| Defect name | Characteristics and inspection methods | Causes | Prevention methods |
| Dents | Appearance inspection: Dents appear on smooth surface of casting | 1. Significant differences in casting wall thickness lead to depressions, often occurring in thicker areas. 2. Localized overheating of mold, resulting in slow solidification of overheated portion. 3. Low injection pressure. 4. Gas trapped in cavity, unable to escape, and compressed between cavity surface and molten metal interface. |
1. Wall thickness of casting should be designed to be as uniform as possible. 2. Adjust local cooling of mold. 3. Increase injection specific pressure. 4. Improve venting conditions of cavity. |
9. Common appearance defects - under-casting, poor forming
| Defect Name | Characteristics and Inspection Methods | Causes | Prevention Methods |
| Incomplete Casting, Poor Forming | Appearance Inspection: There are insufficient pouring areas on the surface of casting, poor mold finding. | 1. Causes of poor fluidity: A. Gas absorption by alloy liquid, oxide inclusions, high iron content, resulting in poor quality and reduced fluidity. B. Low pouring temperature or low mold temperature. 2. Poor filling conditions: A. Specific pressure too low. B. Too much gas entrapment, increased back pressure in cavity, obstructed filling. 3. Poor operation, excessive paint, paint accumulation, gas cannot evaporate. |
1. Improve alloy liquid quality 2. Increase pouring temperature and mold temperature 3. Increase injection pressure and filling speed 4. Improve flow of molten metal in gating system, adding overflow channels and venting channels in under-cast areas 5. Correct die-casting operation |
10. Common appearance defects - burrs, flash
| Defect Name | Characteristics and Inspection Methods | Causes | Prevention Methods |
| Burrs, Flash | Appearance Inspection: Thin metal flakes appear on parting surface edge of casting | 1. Insufficient clamping force 2. Injection speed is too high, resulting in excessively high pressure impact peaks 3. Debris on parting surface is not cleaned properly 4. Insufficient mold strength causes deformation 5. Inserts and sliders are worn and not flush with parting surface |
1. Check clamping force and pressurization; adjust die-casting process parameters. 2. Clean cavity and parting surface. 3. Repair mold. 4. Ideally, use a closed-loop injection termination time system to achieve flash-free die casting. |
11. Common Appearance Defects: Discoloration, Spots
| Defect Name | Characteristics and Inspection Methods | Causes | Prevention Methods |
| Discoloration, Spots | Appearance Inspection: Spots on casting surface that are different in color from base metal | 1. Inappropriate release agent 2. Excessive release agent usage 3. Graphite from graphite-containing lubricant falling into casting surface |
1. Replace with high-quality release agent 2. Strictly control spraying amount and operation |
12. Common Appearance Defects: Excess Material, Raised Material
| Defect Name | Characteristics and Inspection Methods | Causes | Prevention Methods |
| Excess Material, Raised Material | Appearance Inspection: A raised or extra piece or spot is found on casting surface or inside hole compared to design drawing | 1. Mold material aging and chipping 2. Insert material aging and chipping 3. Localized mold compression causing mold deformation or chipping |
1. Change mold material 2. Change insert material 3. Add cooling system 4. Strictly require mold preheating 5. Improve operation methods |
13. Common appearance defects: Sticking to mold, missing material
| Defect name | Characteristics and inspection methods | Causes | Prevention methods |
| Sticking to mold, missing material | Appearance inspection: Compare surface of casting or inside of hole with design drawing. A piece or section is missing. | 1. High mold temperature 2. High pouring temperature 3. Improper operation method 4. Poor effect of release agent 5. Local pressure on mold causes deformation or undercutting of mold shape 6. Insufficient draft angle 7. Change in mold material |
1. Lower mold temperature 2. Lower pouring temperature 3. Add cooling system to corresponding part 4. Improve operation method 5. Repair draft angle of mold 6. Improve mold material |
14. Common appearance defects: Blind hole, broken needle
| Defect name | Characteristics and Inspection Methods | Causes | Prevention Methods |
| Blind Holes, Broken Pins | Visual Inspection: Shape of hole in casting is inconsistent with original shape of insert pin; hole is solid or partially solid. | 1. Aging and breakage of insert pin on mold. 2. Improper operation leading to insert pin breakage. |
1. Replace insert pin and improve its cooling system. 2. Improve operating methods to prevent collisions. |
15. Common Visual Defects: Delamination
| Defect Name | Characteristics and Inspection Methods | Causes | Prevention Methods |
| Delamination | Visual Inspection: Gaps, crack-like lines, with no development trend are present at parting surface of casting. | A thin layer of burr on mold parting surface is not cleaned in time; a crack-like line appears at corresponding parting surface of product during die casting. | Clean burr and residual debris on mold surface in time. |
16. Common Internal Defects: Porosity
| Defect Name | Characteristics and Inspection Methods Methods | Causes | Prevention methods |
| Porosity | Post-dissection inspection or flaw detection: Pores have smooth surfaces and are circular in shape. | 1. Improper alloy melt introduction direction or excessively high metal flow velocity causes spraying, prematurely blocking venting channel, or frontal impact on mold wall forming vortices that trap air. This type of porosity often occurs in areas with poor venting or deep cavities. 2. Due to unclean furnace charge or excessively high melting temperature, a large amount of gas in molten metal is not completely removed and precipitates during solidification. 3. Excessive gas generation or use of coating material, if not completely removed before casting, causes gas to be entrained into casting. This gas often appears as a dark gray surface. 4. Excessively high mold temperature. |
1. Use dry or clean furnace charge to reduce impurities. 2. Use vacuum die casting. 3. Improve metal introduction direction. 4. Reduce injection speed. 5. While ensuring good filling, increase cross-sectional area of ingate as much as possible. 6. Venting groove should be reasonably designed and have sufficient space. Sufficient venting capacity, using rapid cooling venting. 7. Select paint with low gas generation; spray thinly and evenly; close mold after paint evaporation. |
17. Common internal defects: shrinkage cavities, porosity.
| Defect Name | Characteristics and Inspection Method | Causes | Prevention Methods |
| Sinking cavities, porosity | 1. During solidification process, casting shrinks and cannot be compensated by molten metal, resulting in cavities. 2. Excessively high pouring temperature, unreasonable temperature field distribution in mold. 3. Low injection pressure. 4. Small ingate, premature solidification, unfavorable for pressure transmission and molten metal compensation. 5. Hot spots or drastic changes in cross-section in casting structure. 6. Insufficient molten metal pouring volume, too thin residue, unable to compensate for shrinkage. |
1. Lower pouring temperature to reduce shrinkage. 2. Increase injection pressure to improve density. 3. Modify ingate to improve pressure transmission and facilitate feeding effect of liquid metal. 4. Change casting structure to eliminate metal accumulation areas, ensure uniform wall thickness. 5. Accelerate cooling of thick sections. |
18. Common internal defects: Inclusions (slag porosity)
| Defect Name | Characteristics and inspection methods | Causes | Prevention methods |
| Inclusions (slag porosity) | Metal or non-metallic impurities mixed into casting. After machining, irregularly shaped points or holes of different sizes, colors, and brightness can be seen. | 1. Unclean furnace charge 2. Unrefined alloy liquid 3. Slag or oxides introduced when scooping liquid with a spoon for pouring 4. Graphite crucible or coating contains graphite flakes that mix into metal liquid |
1. Use clean alloy liquid, especially dirt on recycled charge must be cleaned thoroughly. 2. Alloy solution must be refined and degassed to remove slag. 3. When scooping liquid with a spoon for pouring, carefully spread liquid surface. Avoid mixing in slag and oxide scale 4. Clean mold cavity and pressure chamber 5. Replace release agent |
19. Common Internal Defects: Brittleness
| Defect Name | Characteristics and Inspection Method | Causes | Prevention Methods |
| Brittleness | Matrix metal grains of casting are too large or too small, making casting prone to breakage or shattering. | 1. Zinc and iron inclusions in aluminum alloy exceed specified range. 2. Overheating of alloy liquid or excessive holding time leads to coarse grains. 3. Rapid undercooling. |
1. Strictly control impurity composition in alloy. 2. Control smelting process. 3. Lower pouring temperature. 4. Increase mold temperature. |
20. Common Internal Defects: Leakage
| Defect Name | Characteristics and Inspection Method | Causes | Prevention Methods |
| Leakage | Die castings leak water or air during pressure tests. | 1. Insufficient pressure results in poor density of casting matrix. 2. Internal defects, such as porosity, shrinkage cavities, slag inclusions, cracks, and shrinkage porosity. 3. Poor design of gating and venting system. |
1. Increase specific pressure. 2. Take corresponding measures for internal defects. 3. Improve gating and venting system. 4. Perform impregnation treatment to compensate for defects. 5. Replace pressure chamber and punch. |
21. Common internal defects: Hard spots.
| Defect Name | Characteristics and inspection methods | Causes | Prevention methods |
| Hard spots | Machining process or post-machining appearance inspection or metallographic examination: Small particles or lumps with a hardness higher than metal matrix on casting, causing severe tool wear, often showing different bright spots after machining. | I. Non-metallic Hard Spots: 1. Oxides mixed in from surface of alloy liquid. 2. Reactants of aluminum alloy and furnace lining. 3. Foreign matter mixed in with metal material. 4. Inclusions. |
1. Do not scoop oxides from surface of molten alloy into ladle during casting. 2. After removing oxides from iron and crucible surfaces, apply a coating and clean residue at the bottom of furnace promptly. 3. Remove oxides from tools such as ladles. 4. Use furnace lining materials that do not react with aluminum. 5. Metal material should be clean and pure. |
22. Common Internal Defects: Hard Spots
| Defect Name | Characteristics and Inspection Method | Causes | Prevention Methods |
| Hard Spots | Machining process or post-machining appearance inspection or metallographic examination: Small particles or lumps with a hardness higher than metal matrix on casting, causing severe tool wear, often showing different bright spots after machining. | II. Metal Hard Spots: 1. Undissolved silicon element mixed in. 2. Primary silicon crystals. 3. Low aluminum liquid temperature and long standing time, Fe and Mn elements segregate, producing intermetallic compounds. |
1. Do not use silicon powder when smelting aluminum-silicon alloys. 2. When adjusting alloy composition, do not add silicon directly; an intermediate alloy must be used. 3. Increase melting and casting temperatures. 4. Control alloy composition, especially amount of Fe impurities. 5. Avoid segregation of elements such as Fe and Mn. 6. Si content in alloy should not approach or exceed eutectic composition; control amount of primary silicon in matrix microstructure of raw materials. |
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