Hot forging is a method of plastically deforming metal materials using high temperatures, widely used to manufacture high-strength and high-toughness metal products. The hot forging process involves multiple steps, each critically affecting the final product quality. This article will provide a detailed introduction to each step of the hot forging process and delve into key techniques.

Process Flow

The hot forging process mainly includes the following steps: cutting, heating, forming, pre-forging, final forging, trimming and punching, correction, heat treatment, cleaning, correction, and inspection. These steps are introduced below.

Cutting

Cutting is the first step in the hot forging process, aimed at cutting the raw material into suitable blanks for forging. Common cutting methods include:

Sawing

Using a saw to cut the material to the required length, suitable for various metal materials.

Sharing

Using a shear machine for cutting, suitable for plates and strips.

Breaking

Breaking the material through mechanical force, commonly used for brittle materials.

Grinding wheel cutting

Using a high-speed rotating grinding wheel for cutting, suitable for harder materials.

Flame cutting 

Using high-temperature flames to cut materials, is suitable for thicker materials.

Heating

Heating is a crucial step in hot forging, aimed at increasing the material's plasticity and toughness. The main heating methods are:

Flame heating: Using high-temperature flames generated by burning gases, suitable for large-sized workpieces.

Electric heating: Using resistance heat generated by electric current passing through the material, with the advantages of fast heating and uniform temperature.

Forming

Forming is the process of preliminarily shaping the heated material, usually using open-die forging or closed-die forging. Open-die forging is suitable for large-sized and complex-shaped forgings, while closed-die forging is suitable for mass production of small to medium-sized forgings.

Pre-Forging

Pre-forging further shapes the formed material to improve its internal structure and mechanical properties. Pre-forging usually uses die forging to ensure the size and shape of the forging are close to the final product.

Final Forging

Final forging is the process of giving the pre-forged material its final shape, ensuring dimensional accuracy and surface quality. Final forging is usually performed on precision forging equipment, requiring high operational accuracy.

Trimming and Punching

Trimming and punching is the process of removing excess material from the forging and punching holes in it. This step usually uses special punching and shearing machines to ensure dimensional accuracy.

Correction

Correction is the process of adjusting the shape and size of the forging to ensure it meets design requirements. Correction usually combines mechanical and manual methods.

Heat Treatment

Heat treatment is a key step to improve the mechanical properties and internal structure of the forging. Common heat treatment methods include:

Full Annealing

Eliminates coarse and uneven structures and Widmanstätten patterns caused by forging, refines grains, removes residual stress, and reduces hardness.

Spheroidizing Annealing

Produces a spheroidized structure of carbides and ferrite, reducing hardness and making it easier to achieve a smooth machined surface and preventing deformation and cracks during subsequent quenching.

Isothermal Annealing

Shortening annealing time achieves uniform structure, and reduces hardness. It can also be used in large important forgings to diffuse hydrogen and prevent white spots.

Normalizing

Produces fine pearlite to improve the mechanical properties of the forging, suitable for machining.

Normalizing and High-Temperature Tempering

 Relieves stress produced during normalizing cooling increases plasticity and toughness.

Quenching and Tempering: Achieves good overall mechanical properties in the forging.

Aluminum and copper alloys usually undergo annealing after forging to eliminate work hardening and stress and to improve plasticity.

Cleaning

Cleaning removes oxidation and impurities from the forging's surface, usually through sandblasting, pickling, and other methods. The cleaned forging surface is smooth, facilitating subsequent processing and inspection.

Correction

Another correction ensures that the forging has not deformed after cleaning and that its dimensions and shape meet design requirements.

Inspection

Inspection is the final step in the hot forging process, involving the detection of dimensions, shapes, surface quality, and internal defects to ensure the forging meets design and quality standards. Common inspection methods include visual inspection, dimensional measurement, and non-destructive testing.

Hot forging is a complex and precise manufacturing technology that produces high-quality metal forgings through a series of scientifically rational process steps. The process parameters and operating methods of each step significantly impact the final product's performance and quality. Therefore, in hot forging production, it is essential to strictly control each process step to ensure every procedure meets design requirements, thereby producing high-quality forgings that meet customer needs.