Views: 0 Author: Site Editor Publish Time: 2021-09-23 Origin: Site
Forging parts refers to a workpiece or blank obtained by forging and deforming a metal blank. By applying pressure to the metal blank, it produces plastic deformation, which can change its mechanical properties. Forging parts are widely used in joints, valves, chains, mining equipment, food equipment, automobile and motorcycle accessories, environmental protection equipment, rail transit, and other fields.
Here is the content list:
l Features of forging parts.
l Disadvantages of forging parts.
l Quality inspection of forging parts.
1. Large weight range. Forging parts are as small as a few grams to as large as hundreds of tons
2. Higher quality than castings. Forging parts have better mechanical properties than castings, and can withstand large impact forces and other heavy loads. Therefore, forging parts are used for all important and stressed parts.
For high-carbide steels, forgings are of better quality than rolled products. For example, high-speed steel rolled products can only meet the requirements after being reformed for forging. Especially high-speed steel milling cutters must be forged.
3. The lightest weight. On the premise of ensuring design strength, forging parts are lighter than castings, which reduces the weight of the machine itself, which is of great significance for transportation, aircraft, vehicles, and astronautical equipment.
4. Save raw materials. For example, for a crankshaft with a deadweight of 17kg used in automobiles, when using rolled material for cutting and forging, the chips account for 189% of the crankshaft weight, while when using die forging, the chips account for only 30%, which also shortens the machining time by 1/6. Precision forging parts can not only save more raw materials but also save more machining man-hours.
5. High productivity. For example, using two hot forging presses to forge radial thrust bearings can replace 30 automatic cutting machine tools. When the upsetting automatic machine is used to produce M24 nuts, the productivity of the six-axis automatic lathe is 17.5 times.
6. Free forging has great flexibility. Therefore, forging methods are widely used in some repair factories to produce various accessories.
(1) Oxidation: The phenomenon in which the metal billet reacts with the oxidizing gas in the furnace to generate oxides when heated is called oxidation. The generation of oxide scale not only causes the burning of the metal but also reduces the surface quality and dimensional accuracy of the forging parts. When the depth of the oxide scale pressed into the forging exceeds the machining allowance, the forging parts can be scrapped.
(2) Decarburization: The phenomenon in which the carbon on the surface of the metal billet undergoes a chemical reaction with oxygen and other media during heating, resulting in a decrease in surface carbon is called decarburization. Decarburization will reduce the surface hardness and wear resistance. If the thickness of the decarburized layer is less than the machining allowance, it will not cause harm to the forging parts; otherwise, it will affect the quality of the forging parts. Using rapid heating, coating protective coatings on the surface of the blank, heating in neutral or reducing media can all slow down decarburization.
(3) Overheating: The phenomenon that the metal billet is heated by too high a temperature or the holding time at high temperature causes coarse crystal grains is called overheating. Overheating will reduce the plasticity of the blank and the mechanical properties of the forging parts. For this reason, it is necessary to strictly control the heating temperature and shorten the heat preservation time in the high-temperature stage as much as possible to prevent overheating.
(4) Overburning: The heating temperature of the metal billet exceeds the initial forging temperature too much, and the phenomenon of oxidation and melting of the grain boundaries is called overburning. After burning, the strength of the material is severely reduced, and the plasticity is very poor. Once forged, it will be broken into waste, which is irreparable. Therefore, it is necessary to strictly implement the correct operating specifications.
(5) Cracks: When heating large forging parts, if the furnace loading temperature is too high or the heating speed is too fast, the temperature difference between the core and the surface of the forging parts will be too large, causing excessive internal stress and causing cracks. Therefore, when heating large forging parts, it is necessary to prevent the furnace temperature from being too high and the heating speed from being too fast, and heat protection measures should generally be adopted.
(1) Geometry and dimensions: the general dimensions of forging parts are tested with steel rulers, calipers, templates, and other measuring tools; die forging parts with complex shapes can be accurately tested by scribing.
(2) Surface quality: If there are cracks, crushing, and folding defects on the surface of the forging parts, they can generally be found with the naked eye. Sometimes the crack is very small and the depth of the fold is not known, it can be observed after cleaning the shovel; if necessary, the flaw detection method can be used to check.
(3) Internal structure: Whether there are cracks, inclusions, looseness, and other defects inside the forging parts, the macroscopic structure of the forging parts section can be inspected with the naked eye or with a magnifying glass of 10 to 30 times. The commonly used method in production is acid etching inspection, that is, to cut samples from the forging parts that need to be inspected, and etch them with acid to clearly show the defects of the macrostructure on the section, such as forging streamline distribution, cracks and inclusions Wait.
(4) Mechanical properties: The test items of mechanical properties are mainly hardness, tensile strength, and impact toughness. Sometimes cold bending tests and fatigue tests can be done according to the design requirements of parts.
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