Types of Casting Defects and How to Prevent Them in Your Products

Casting production is a complex multi-step process. The level of skill in each process varies greatly. The skills of the operator, quality management, and equipment all affect the final quality of the casting. If you want to know what are the various types of casting defects? What are the causes of casting defects, and how to prevent them? This guide will provide you with an overview of all casting surface defects.

Porous casting defects and causes

When the metal enters the gas during the casting process and solidifies, it will produce porosity. The most common gases that form porosity are nitrogen, oxygen, or hydrogen. Although the mold allows the gas to escape, many factors can cause the gas not to run. This results in a common casting surface defect in investment casting. There are three common casting defects related to porosity.

1. Pinhole casting defect


Pinhole casting defect is another term for stoma. Pinholes are the most prevalent metal casting defects, and they can be caused by any difficulties with the operating system. Pinhole casting defect are frequently visible to the naked eye near the surface of the casting or in clusters.

Casting and casting defects causes

  1. Sand with a high moisture content is used.
  2. Steel pouring from a damp ladle or inadequate gassing
  3. Molten metal absorbs hydrogen or carbon monoxide gas.

Measures

  1. By reducing the moisture content of the sand
  2. Increase the permeability of the sand
  3. Good fluxes and melting methods should be used
  4. By rapid solidification

2. Stomata


A larger hollow than a pinhole is called porosity in casting defects. They’re frequently located in the casting’s inside. Before machining, they are difficult to identify and require harmonic, ultrasonic, magnetic, or X-ray investigation.

Casting and casting defects causes

  1. There’s a lot of water in the sand.
  2. The sand has a low permeability.
  3. The sand grain is too small.
  4. Sand that has been too compacted
  5. Insufficient ventilation

Measures

  1. The moisture content of the sand must be controlled and maintained at the required level
  2. High permeability sand should be used
  3. Properly sized sand should be used
  4. Do not over-compact
  5. Adequate ventilation should be provided

3. Open Holes


Porosity in casting defects is harder to notice than open holes, which appear on the surface of the casting. A cracked aperture occurs on the casting’s surface in most cases. These flaws are generated by air trapped in the mold when the metal is poured.

Casting surface defects causes

  1. Poor venting of molds and cores
  2. Insufficient drying of molds and cores

Measures

  1. Dry and breathable sand to avoid openings
  2. Choose coarse sand. The coarser the sand, the better the permeability
  3. Make sure the mold and core are dry

Shrinkage Casting Defects and Causes

Because metal is less dense as a liquid than solid, it shrinks. During the chilling process, shrinkage problems are common. Alloy solidification shrinkage is typical, but uneven shrinkage causes casting surface flaws.
During the solidification process, shrinkage causes a depression in the casting. Shrinkage spaces have sharp edges instead of the smooth surface of gas voids. Voids are often found in conjunction with dendritic fractures or cracks. Large shrinkage voids might compromise the casting’s integrity and cause it to break under pressure. Casting defects can result from shrinkage in two ways.

1. Open Shrinkage Defects


A depression (also known as a depressed surface) or a hole forms on the surface of a cast product due to open shrinkage (also called a pipe). When metal shrinks unevenly, it sucks air into the mold in that location, resulting in flaws like these.

2. Closed Shrinkage Defects


Closed shrinkage faults, also known as shrinkage loosening, are flaws in the casting that cause closed shrinkage holes. Microscopic shrinkage, on the other hand, cannot be seen with the human eye.
Closed shrinkage faults are most commonly encountered near the tops of hot spots or isolated pools of hot liquid.

Metal casting defects causes

When the liquid metal temperature in the mold is not the same, shrinkage defects arise. Shrinkage flaws can occur if the metal is poured too hot into the mold or if the metal solidifies unevenly. When the mold design ignores the directional solidification pattern, uneven solidification is common.

Measures

Heat treating ferrous alloys to reduce residual tensions, in particular, helps prevent warpage. Straightening the casting between the quenching and aging processes prevents wattage in aluminum alloys. It also inhibits wattage, allowing for more consistent object cooling by ensuring that significant portions have more ribbed shapes, such as corrugations.

  1. Design of riser-based running (gating) systems to enable uninterrupted molten metal flow
  2. To increase local heat dissipation, insert internal coolers, heat sinks, or cooling coils.
  3. Lower casting temperature to limit the total volume deficit.

Mold material casting defects and causes

1. Cutting and Scouring


When liquid metal erodes part of the mold during pouring, and the sand does not have the thermal strength to withstand it, cutting and scouring occur. Cleaning and cutting appear as low bumps on the final surface that slant toward one end, where the molten metal flows in with greater power.

Casting defects causes

Cutting and tcouring can be puoduced by excessive metal flow through the gate due to high velocity molten metal flow.

Measures

  1. Improve the pouring system’s design
  2. Strengthen the mold and core
  3. Add binder to the finishing sand and core sand.

2. Fusing


When sand particles are fused with molten metal, this is known as fusing. On the casting surface, the fusion appears as a glass-like shell. It seems to be a thin, brittle, glassy crust that sticks tightly to the casting. This happens when some of the sand in the mold melts and merges with the casting.

Metal casting defects causes

  1. Clay or sand with low refractoriness
  2. Metal liquid with a high pouring temperature

Measures

The capacity of molding material to resist the temperature of a liquid so that it does not fuse with metal is known as refractoriness. The refractories of silica sand are the highest. To prevent fusion, we can improve the refractories of the molding material or lower the pouring temperature of the molten metal.

3. Metal penetration


Metal penetration is the leakage of liquid metal from the mold, resulting in incomplete or missing castings.

Foundry casting defects causes

  1. Use sand with low strength and high permeability.
  2. The use of a coarse or huge grit: the coarser the grit, the more severe the mental penetration.
  3. Inadequate mold removal
  4. Soft sand pounding

Measures

To avoid such casting defects, make sure the casting mold is well-designed. Before casting, inspect and replace any damaged molds.
High temperatures can cause excessive mold wear. For your molds, use high-quality raw materials that can withstand high temperatures.

4. Swelling


When the mold is too soft, the weight of the liquid metal pulls the sand outward, causing swelling faults. Swelling normally appears as a little, smooth hump on the casting’s vertical side.

Foundry casting defects causes

Expansion defects are usually caused by improper use of a mold or low-strength molds.

Measures

  1. To avoid such casting defects, make sure the casting mold is well-designed. Before casting, inspect and replace any damaged molds.
  2. High temperatures can cause excessive mold wear. For your mold, use high-quality raw materials that can withstand high temperatures.

5. Dripping

When sand falls into a metal casting while still wet, it drips. Drops appear on the top of the casting as uneven lumps. They happen when the mold isn’t strong enough, and sand gets into the liquid metal. Water drips can potentially contaminate the metal’s surface.

Foundry casting defects causes

  1. Sand with low strength
  2. Soft ramming
  3. Insufficient flux for molten metal
  4. Sand protrusions in the vault with insufficient reinforcing

Measures

  1. Sand with higher tensile strength is used.
  2. Provide a more difficult tamp.
  3. Can remove Impurities from molten metal if it is adequately fluxed.
  4. To reinforce sand protrusions, use nails or pliers.

6. Rat Tail


Rattails or veins can show as uneven lines or fissures in the casting when the surface of the mold sand buckles. Rat tails are most commonly found on the mold’s bottom surface, which is frequently covered in molten material. Buckling is a kind of rat tail that is more severe.

Die casting defects causes

  1. Poor expansion of sand
  2. A Hot pouring temperature
  3. Poor mold design

Measures

Making sure the mold has enough stamping to contain the molten metal is a good method to avoid these issues. Also, be sure the pouring metal doesn’t get too hot. If they don’t work, we can apply the above procedures to fix the problem.

  1. Adding combustible additives to sand
  2. Lower the pouring temperature of the metal
  3. The mold should also not be too hard

Metallurgical casting defects and causes

The subcooling temperature of the metal as it reaches the inside of the mold causes all defects in poured metal. Can generate These flaws by putting metal into a mold that isn’t hot enough. Even if the metal is poured at the correct temperature, a defective method can cause the metal to cool too quickly before entering the mold, or the mold section can be too thin, resulting in flaws. The tiny parts can harden and block other mold sections because of their light size.

1. Heat Crack/Cracking


Some cracks are visible without magnification, while others require it. Cracks appear after solidification when the casting cools.

Die casting defects causes

Hot ripping will occur if the solidified metal is not strong enough to resist the tensile tension during the solidification process.

Measures

  1. Improve mold design
  2. Modify the mold to improve foldability

2. Hot spots/hard spots


Hard spots are another name for hot areas. These flaws appear when particular casting sections cool faster than the surrounding area. This is because they cool faster than the surrounding material. As a result, stricter teams of the casting are formed. These can cause the tool to wear down and obstruct the machining operation. Challenging areas can block machining and lead to increased tool wear.

Metal casting defects causes

Hot spots are caused by improper cooling

Measures

  1. Correct cooling habits
  2. Consider changing the chemical composition of the metal

Casting defects and causes

The subcooling temperature of the metal as it reaches the inside of the mold causes all defects in poured metal. Simply running the metal when it is not hot enough can result in these problems even if the metal is poured at the correct temperature at the start. Later on, a faulty pouring mechanism may cause the metal to cool too much before entering the mold. Alternatively, the mold part could be overly thin, resulting in flaws.

1. Cold shut casting defect


A surface flaw is a cold shut casting defect. You’ll notice lines or fissures with rounded edges on the casting surface. When two molten metal streams meet at a temperature below their melting point, they do not fuse and solidify to produce a cold shut casting defect. As a result, it seems to be a fracture with a rounded edge. Defects in the casting can be observed with the naked eye.

Die casting defects causes

  1. Poor pouring system
  2. Low melting temperature
  3. Lack of fluidity

Measures

  1. Optimization of the pouring system
  2. Proper pouring temperature
  3. Improve the air permeability of the mold

2. Mis-Run


A mis-run occurs when molten metal hardens before filling the mold chamber, leaving a gap in the casting. The mold cavity is not completely filled with liquid metal.

Casting and casting defects causes

  1. Molten metal has a low fluidity.
  2. The fluidity of molten metal is reduced at low temperatures.
  3. Inadequate pouring system and too thin cross-section

Measures

  1. Optimize mold design and door control system design
  2. Increase metal flow
  3. Avoid the too thin cross section.

3. Slag Inclusion


Splashing during the pouring of liquids can cause solid pellets to develop. These bloblets become caught in the casting as they freeze. A cold shot is often spherical, teardrop-shaped, or pearl-shaped and is dispersed throughout the metal. Cinders and rattle are closely connected, and they frequently occur together. Usually, removing the crust reveals the rattail underneath.

Casting and casting defects causes

Slagging occurs when molten metal containing particles is poured into the mold cavity and solidifies

Measures

  1. Melt the metal with flux in v vacuum or inert atmosphere
  2. Use a special spoon for pouring metal from the bottom
  3. Adding ceramic filters to the pouring system

Casting shape defects and causes

Flaws in the casting form cause displacement or flying edges. Because shape faults usually require retooling the existing mold, they are the easiest to fix.

1. Displacement/Mismatch


When separate casting portions are misaligned, usually horizontally, mismatch, also known as offset, occurs. The top and bottom of the mold are not aligned, causing mold shift. Mold displacement is most commonly manifested as horizontal displacement. If vertical displacement occurs, the core, not the mold, is out of alignment.

Casting and casting defects causes

  1. During mold preparation, you did not align the upper and lower components properly.
  2. Misalignment of the sandbox
  3. Inattention to detail when installing the top cover on the resistance, resulting in misalignment

Measures

Check the installation and alignment of the matching plate pattern if you have an offset. Make sure you’re using the correct molding box and closing pins for the job.

2. Fly Edge


One of the most prevalent casting defects is flying edges. Casting fins, burrs, and flash are all terms for flying edges. Fly edges appear as extra material adhered to the casting, commonly in the form of flakes where the mold portions meet. A scrap that remelts and produces dross is known as a fly edge.

Casting defects causes

Cracks or holes on the core surface generate flying edges on the casting surface. Gaps might be caused by insufficient weight on the mold or poor sandbox clamping.

Measures

We can solve this problem by reassembling the mold and core. There should be enough weight on the top of the mold so that the two parts fit together tightly.
Flashing can range from slight to very severe. If it is not very severe, the manufacturer can remove the flash by breaking it off with a hammer or pliers and filing it to the parting line. However, this can be an expensive process.

3. Warpage


Warpage is a casting defect that occurs during or after solidification.

Casting defects causes

Different solidification rates in other areas frequently cause warpage. The adjacent walls are strained as a result of this. Warping is more likely in large, flat portions.

Measures

Cast iron parts can benefit from normalizing heat treatment to remove residual tensions. Aluminum castings may need to be straightened between the quenching and aging operations.

4. Honeycomb or spongy


This is an exterior flaw in which multiple small voids in the metal casting are immediately adjacent.

Casting defects causes

  1. In the suspension of molten metal, mechanically held debris and skin flakes produce it.
  2. Improper skimming in the ladle causes it.

Measures

  1. Stopped dirt and flakes from getting into the molten metal.
  2. Sand flushing is avoided.
  3. Proper skimming in the ladle to remove slag debris from the molten metal.

Conclusion

Casting quality management requires a thorough understanding of casting defects and their causes. To help your suppliers understand your quality standards, you should create specific fault tolerances and quality expectations before manufacturing.
Tolerances for defects vary depending on the product and the type of casting problem. Determining your tolerance for these casting faults will assist your vendors in understanding your expectations and avoiding future misunderstandings and quality difficulties.

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