The post-production inspection processes required for making close-die steel forging parts

Post-production inspection is crucial for ensuring the quality and integrity of close-die steel forging parts. The following are the typical post-production inspection processes involved in the production of high-quality close-die steel forging parts:

1. Visual Inspection

• Purpose: To check for surface defects such as cracks, folds, laps, or excessive scale.

• Method: Inspect the forged part under adequate lighting. A magnifying tool or a microscope may be used for fine detail inspection.

• Criteria: Parts should be free from visible surface defects. Surface finish quality can also be assessed here.

2. Dimensional Inspection

• Purpose: To verify that the forged parts meet the specified dimensions.

• Method: Measurement tools such as calipers, micrometers, height gauges, or CMM (Coordinate Measuring Machine) are used.

• Criteria: All critical dimensions (diameters, lengths, thicknesses) must fall within the specified tolerances.

3. Non-Destructive Testing (NDT)

NDT techniques are employed to detect internal defects without damaging the part.

• Ultrasonic Testing (UT): Used to detect internal cracks, voids, or inclusions.

• Magnetic Particle Inspection (MPI): Detects surface and near-surface defects in ferromagnetic materials.

• Dye Penetrant Inspection (DPI): Identifies surface cracks or porosity.

• X-ray or Radiographic Inspection: Detects internal defects and porosity in thick or complex parts.

4. Hardness Testing

• Purpose: To ensure the material's hardness meets the required specifications.

• Method: Hardness tests such as Rockwell, Brinell, or Vickers are used.

• Criteria: The hardness values should meet the material grade specifications and the application requirements.

5. Tensile Testing

• Purpose: To measure the material's tensile strength, elongation, and other mechanical properties.

• Method: A sample of the forged material is pulled in a tensile testing machine until it fractures.

• Criteria: The results should meet the specified mechanical property requirements, such as yield strength and ultimate tensile strength.

6. Impact Testing (Charpy V-Notch)

• Purpose: To evaluate the material's toughness, particularly its ability to withstand impact at low temperatures.

• Method: A Charpy impact test is performed, where a sample is struck by a pendulum hammer.

• Criteria: The material should have an adequate impact toughness for the intended service conditions.

7. Grain Flow Analysis

• Purpose: To assess the directional properties of the material and ensure the forging process has produced a favorable grain flow.

• Method: The grain flow can be analyzed using methods like acid etching or microstructural examination.

• Criteria: Proper grain flow should follow the part's geometry to ensure optimal mechanical properties and reduce weak spots.

8. Metallographic Inspection

• Purpose: To analyze the microstructure of the forged material.

• Method: The sample is polished, etched, and then examined under a microscope.

• Criteria: The microstructure should reveal uniform grain structure, minimal porosity, and no signs of undesirable inclusions or segregations.

9. Straightness and Flatness Measurement

• Purpose: To ensure the part is free from warping or distortion.

• Method: Parts are checked using gauges, dial indicators, or flat surfaces.

• Criteria: The part must meet the tolerance specifications for straightness and flatness.

10. Surface Finish Testing

• Purpose: To verify the surface texture and finish, which can affect the part's performance and fit.

• Method: Surface roughness is measured using profilometers.

• Criteria: The surface finish should meet the specified roughness (Ra) values, which depend on the application requirements.

11. Chemical Composition Analysis

• Purpose: To verify the material's chemical composition against the specifications.

• Method: Spectrometry or other chemical analysis methods are used to determine the element levels.

• Criteria: The composition must match the required alloy grade and pass any relevant quality standards.

12. Visual and Functional Testing of Complex Features (e.g., Threads, Holes)

• Purpose: To check the functionality and integrity of special features like threads, holes, and keyways.

• Method: Functional checks like thread gauging, hole dimension checking, and flow testing are performed.

• Criteria: All features must conform to functional requirements.

13. Heat Treatment Monitoring

• Purpose: To ensure the forging part has undergone the correct heat treatment process to achieve the desired mechanical properties.

• Method: Verification of heat treatment parameters such as temperature, time, and cooling rate, using thermocouples or other temperature monitoring systems.

• Criteria: The part must meet the required hardness, tensile strength, and toughness as per the heat treatment specifications.

14. Final Inspection and Quality Certification

• Purpose: To provide an overall assessment and ensure all the previous checks are completed.

• Method: A final audit of the part’s compliance with design specifications is conducted.

• Criteria: All documented requirements must be met, and the part is ready for shipping or assembly.

Conclusion

These inspection processes, when properly executed, ensure that close-die steel forging parts meet high standards of quality, durability, and performance. The specific testing methods and their frequency may vary depending on the application, material type, and criticality of the part in its end-use.