Forging is a metal part that is formed by heating the metal to a certain temperature and then applying pressure in a mold to cause it to deform plastically, ultimately forming a metal part of the desired shape. To ensure the quality of forgings, a series of inspections and tests are usually required. The following are some of the commonly used inspection methods for forgings:
I. Forging quality inspection purpose and content
(1) The purpose of testing
In order to ensure that the general and specialized technical requirements of forgings meet the product design and use requirements.
(2) Test content
① The re-examination of forging raw materials
Forging raw materials must be selected in accordance with relevant national standards before going into production, the size, surface quality, chemical composition, high-fold organization, low-fold organization and mechanical properties of the re-examination of the project. Unqualified materials cannot be put into production; in the production of raw materials must be strengthened management, to avoid mixing materials.
② Forging process quality inspection
The forging process quality inspection refers to the raw materials from the beginning of the material, by forging, heat treatment and other forging process inspection. Inspection content mainly includes surface quality, geometric size and hardness of forgings.
The production process inspection is also known as follow-up inspection. It is the forging feeding, heating, forging, cooling, heat treatment and other processes to assess the credentials, to check whether it meets the requirements, what problems and how to deal with for finished product inspection for reference.
③ Forging product testing
Forging product testing is generally carried out by the enterprise quality inspection department according to the forging map, technical requirements and relevant standards. The main test content of the forging surface quality, geometry, hardness, mechanical properties, low-fold organization, fracture and non-destructive testing.
II. Finished product quality inspection includes the following items.
- a. Chemical composition test should be based on the results of the sample analysis and the value of the current standard.
- b. Appearance inspection of forgings’ appearance, shape, size, and defects should be in line with the forging diagram or relevant national standards.
- c. Low test with the naked eye or not more than 10 times the magnifying glass to check the surface of the forging or section of the macro-organization, also known as macro-organizational inspection. Its main methods are sulfur stamping, hot acid immersion, cold acid immersion and fracture.
- d. Microstructure inspection, that is, metallographic examination, this method is observed under an optical microscope, identification and analysis of forging microstructure state and distribution, but also shows the distribution of segregation and a number of compounds, and can be carried out on the grain size and non-metallic inclusions in the rating.
- e. Mechanical properties of the test, including hardness, determine the strength index and, plasticity index, toughness index for some important parts but also for persistence, creep and fatigue tests.
- f. Residual stress test in the forging production, due to uneven deformation, uneven temperature and uneven phase transition will cause internal stress, and part of the internal stress will eventually remain inside the forging. Therefore, for some important forgings, such as generator ring technical conditions, the residual stress shall be at most 20% of the yield point. g. Non-destructive testing is a non-destructive test of the forging process.
- g. Non-destructive testing is on the premise of not damaging the raw material and checking the internal quality of the forging method, also known as non-destructive flaw detection. It includes magnetic flaw detection and ultrasonic flaw detection.
III. Forging quality inspection methods
(1) Geometry and size inspection
- ① Visual method: the shape of forging dimensions, such as rounded corners, distortions, errors, etc., more serious, can be based on experience found by visual inspection.
- ② Gauge Inspection Method: that is, with the use of general-purpose gauges and special gauges on the geometry and dimensions of the forging inspection, it is the most intuitive, the most basic inspection method.
- ③ Sample inspection method: that is, with the pre-produced samples and local samples to detect the geometry and size of forgings. It is suitable for large quantities and more complex shapes of the forgings.
- ④ Line test: some complex shapes of forgings cannot directly use the gauge or sample plate for inspection, generally through the line to check the geometry and size of forgings.
(2) Surface quality inspection
When checking the surface quality of forgings, the commonly used method is visual inspection, such as cracks, inclusions, pits and other defects, which can be found by experience.
(3) Internal quality inspection
- ① Low inspection: 5-10 times or dozens of times through the magnifying glass to observe the forging cracks, white spots, inclusions, bubbles, shrinkage and other defects.
- ② High-fold inspection: with an optical microscope or electron microscope to observe the metallographic group of forgings.