Visual judgment criteria for surface defects of castings

Visual judgment criteria for surface defects of castings
Visual judgment relies on three things: standard samples, limit templates, and lighting conditions. Missing one can make the judgment result vary from person to person.
Lighting is a prerequisite for judgment
The recommended illuminance for visual inspection is not less than 500 lux, and the recommended illuminance for appearance inspection is above 1000 lux.
The direction of light can also affect interpretation. Side light can expose irregularities, while positive light can mask shallow defects.
In the appearance requirements of the wheel hub mold, Xinfeng Mold will specify the inspection illumination and observation distance to reduce the judgment differences between the supply and demand sides.
The role of limit templates
The limit template is a physical object with a defect upper limit recognized by both parties. With it, judgment shifts from subjective to comparative.
The template should include the boundary states of various defects: allowable minor flow marks, unacceptable cracks, and acceptable repair marks.
The sample needs to be signed and confirmed by both parties, and regularly reviewed. After years of use, the sample itself will wear out and need to be updated.
Visual characteristics of common defects
Cold insulation has arc-shaped indentations with smooth edges, often appearing at the intersection of two streams of liquid at the distal end of the thin wall.
The strain is a strip-shaped scratch, with the direction consistent with the demolding direction, and the depth can be perceived by the nail.
Shrinkage is a local depression with a smooth surface, mostly located at the corresponding position of the hot spot.
Identification of cracks
Cracks are in the shape of thin lines, with sharp edges and often accompanied by oxidation color. The difference from the seam is that the seam has a regular direction.
Visual inspection reveals suspicious cracks, which need to be confirmed by penetrant testing or magnetic particle testing. Visual inspection cannot be used as the final determination of cracks.
The crack at the root of the spoke is the most dangerous, and this area should be 100% visually inspected and spot checked.
Judgment grading
Classify according to the number, size, and location of defects. The tolerance of the appearance surface, sealing surface, and stress surface is different.
The same defect may be deemed invalid on the exterior surface, but may be acceptable on non exterior surfaces. The grading standards should be included in the technical agreement.
Unclear grading can lead to different opinions during acceptance.
Record and Trace
Record the type, location, and quantity of defects in each batch. Defect distribution can infer mold or process problems.
Repeated occurrence of similar defects at the same location indicates that the mold needs to be repaired at that location.
Records should be accompanied by photos and marked with a scale. Only written description, unable to be reviewed later.
Consistency of inspector's judgment
Consistency comparison is required among multiple inspectors. The same batch of documents should be independently judged by two individuals, with a difference rate of less than 5%.
When the difference rate is high, retrain or revise the limit template. The criteria for judgment are not uniform, and there will always be disputes over acceptance.
Align with customer judgments
Conducting a limit sample confirmation with the customer before shipment can reduce disputes after arrival.
The limit template should be reviewed every two years, as material aging can cause changes in color and texture.
It is recommended to use neutral gray for the background color of the inspection table, as a white background will mask light colored defects.
The inspector conducts a visual and color vision review every six months, which is the basic condition for visual judgment.
Frequently Asked Questions
Question: What is the visual inspection illuminance?
Answer: Generally 500 lux, with an appearance of 1000 lux or more.
Q: Is it necessary to make a limit template?
Answer: It is recommended to do so to reduce differences in judgment.
Question: How to distinguish between cold insulation and shrinkage?
Answer: The edge of the cold insulation is smooth and has circular indentations, and the surface of the indentation is smooth.
Q: Can cracks be determined visually?
Answer: Suspected cracks need to be confirmed by penetrant or magnetic particle inspection.
Q: Is the standard for judging the appearance of the product the same?
Answer: Different, judged according to the classification of the surface area.
Q: Do defect records need to be accompanied by photos?
Answer: Yes, and mark the scale for easy review.
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