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Fettling is a post-casting process in a steel foundry that involves cleaning, trimming, and finishing metal castings after they have been removed from the mold. This is an essential step in preparing the castings for their final use, ensuring they meet required specifications for surface quality, size, and shape.

Key Steps in Fettling:

1. Removal of Flash and Gates:

Flash refers to excess material that appears around the edges of a casting where the mold halves meet. Gates are channels through which molten metal enters the mold cavity.

During fettling, these unwanted parts are removed using tools like grinders, chisels, or cutting machines.

2. Surface Grinding and Cleaning:

After the flash and gates are removed, the casting often has rough or uneven surfaces. Fettling includes grinding and smoothing the surfaces to meet the desired finish and remove any imperfections, such as sand from the mold.

The process may involve abrasive grinding, polishing, or shot blasting to achieve the required surface quality.

3. Deburring:

Deburring is the removal of sharp edges or burrs from the casting. This is typically done using grinding wheels or manual filing.

4. Inspection:

After fettling, the casting is usually inspected for dimensional accuracy, surface defects, or any other issues that may require correction. Non-destructive testing methods like ultrasonic testing or dye penetrant testing may be used to check the integrity of the casting.

Real-Time Example:

Consider a steel gear cast in a foundry. After the molten steel is poured into the mold, the casting cools and solidifies. The casting may have unwanted features, such as gates where the molten metal entered the mold, and flash along the edges. Additionally, the surface might be rough due to sand stuck from the mold.

Step 1: The fettler begins by using a cutting tool to remove the gates, flash, and any other metal protrusions.

Step 2: The surface of the casting is then ground down using a grinder to smooth it out, removing any sand residue from the mold and creating a more polished surface.

Step 3: The fettler checks for any burrs on edges that could cause injury or interfere with the casting's function, using hand tools to smooth them out.

Step 4: The finished gear is inspected to ensure that it meets specifications, both visually and dimensionally. If required, additional testing might be done to ensure the gear's quality, such as checking for cracks or voids.