LPDC casting X-ray inspection interpretation, differentiation and rejection criteria for porosity, slag inclusion, shrinkage, and hot cracks

LPDC casting X-ray inspection interpretation, differentiation and rejection criteria for porosity, slag inclusion, shrinkage, and hot cracks
X-ray inspection is a core quality control method for pressure bearing castings in automobiles and new energy industries. Many on-site personnel are unable to distinguish between air holes, shrinkage holes, and slag inclusions, leading to misjudgment and resulting in the scrapping of good products and the flow of defective products into the next process. At the same time, they do not know the root cause of defects and repeat the occurrence.
1、 Characteristics and size thresholds of various defect X-ray images
Pores: circular, elliptical, with smooth black edges, isolated or scattered; Single pore diameter ≤ 0.8mm, sparse dispersion is acceptable; Single pores ≥ 1.2mm or dense pores are generally rejected.
Shrinkage/looseness: Irregular, dendritic, sponge like dark areas with blurred boundaries, concentrated near the hot runner; If the continuous loose area exceeds 3mm, the pressure bearing parts shall be rejected directly.
Slag inclusion: irregular shape, rough edges, uneven grayscale, mixed with bright or dark spots; Oxidation slag belongs to high-risk defects, and most pressure bearing parts have zero tolerance.
Hot cracks: fine, serrated intermittent black lines extending along the joints and corners of the reinforcement; Pressure bearing parts and load-bearing parts with hot cracks shall be rejected.
Cold insulation: Gap like dark lines with fusion boundaries, often located at the end of the filling process and at the intersection of thin walls.
The defect map of Xinfeng Machinery is synchronized with the defect traceability list, and the X-ray defect can be directly identified as a melting, mold or process problem.
2、 Sampling, filming location, and rating standards for non-destructive testing
Key filming locations: near the sprue, thick hot spots, T-shaped joint ribs, flange sealing surfaces, and pressure bearing areas of the oil passage.
Batch sampling: full inspection of the first article of automotive parts, sampling according to AQL for mass production; 100% X-ray inspection of pressure bearing shell.
The defect rating is based on ASTM E155 standard, and is classified according to defect size, quantity, spacing, and location. The functional area standard is stricter than the non functional area standard.
If the same defect is close to the sealing surface or stress surface, the rating will be strict; Relax appropriately away from non appearance and non functional areas under stress.
3、 Differences in X-ray inspection standards for overseas customers
Southeast Asian customers have relaxed standards, allowing for infiltration and repair for small pores and looseness. After infiltration, re inspection is qualified and released.
Tier 1 in North America strictly adheres to ASTM E155, with zero tolerance for hot cracks and strip-shaped slag inclusions. The size and quantity of pores in functional areas are strictly limited, and infiltration cannot be used to conceal cracks.
European customers distinguish between safe and non safe areas, with drawings directly indicating the defect level of each area, and X-ray reports and castings bound and traced one by one.
Middle Eastern construction machinery thick walled pressure parts have large X-ray attenuation in thick sections and use high-energy radiation to strictly control continuous looseness and prevent pressure leakage.
4、 X-ray defect traceability chain
Smooth circular pores → Insufficient gas removal during melting, moisture in the recycled material, and water in the release agent;
Tree like loose shrinkage cavity → premature solidification of gate, insufficient pressure holding, and failure of sequential solidification;
Irregular and rough slag inclusion → inadequate slag removal, falling slag from the lifting pipe, and turbulent flow of aluminum liquid rolling slag;
Serrated fine line cracks → hot cracks, insufficient rounded corners in the structure, sudden changes in wall thickness, and concentration of shrinkage stress.
5、 Long tail traffic layout ideas
Low pressure casting X-ray inspection ASTM E155、 Interpretation of porosity and shrinkage in castings, aimed at quality engineers and explorers.
Keywords: LPDC casting X-ray inspection, ASTM E155 aluminum casting defect acceptance;
Category of questions: difference between porosity and shrinkage on X-ray film;
Comparison class: lean test vs X-ray inspection for pressure housing.
Suitable for quality inspection and pressure component quality control special pages.
6、 Common misconceptions in the industry
Misconception 1: Black spots on X-rays are all pores, and the morphology of shrinkage and slag inclusion images is completely different, with different root causes and rectification plans.
Misconception 2: As long as infiltration is used, all X-ray defects can be solved. Cracks cannot be sealed by infiltration, and leakage still occurs under pressure.
Misconception 3: Non functional area defects can be infinitely large, and defects near the stress boundary will still expand and fail.
FAQ
Q: Typical characteristics of pore X-ray?
A: Circular ellipse with smooth edges.
Q: What are the imaging features of shrinkage porosity?
A: Irregular tree branches with blurred boundaries.
Q: What is the standard for hot cracking of pressure parts?
A: Generally zero tolerance, reject directly.
Q: What are the key areas for X-ray imaging?
A: Hot section, sprue, sealing flange, and joint position of reinforcement.
Q: Do North American customers allow infiltration to cover up cracks?
A: Not allowed, cracks are considered fatal defects.
Q: What is the purpose of ASTM E155?
A: Standard for X-ray inspection rating of aluminum castings.
Q: What are the X-ray characteristics of slag inclusion?
A: Rough edges and uneven grayscale.
Q: Source of dense pores?
A: The hydrogen content in the aluminum liquid exceeds the standard.