In order to increase the rigidity of the rack in the manufacturing process, there are many treatment methods, mainly through heat treatment. Heat treatment is a process of heating or cooling a metal material in order to obtain the required metal structure properties. With different cooling methods, different structures are obtained. Heat treatment is roughly divided into normalizing, annealing, quenching, tempering, surface hardening and so on. Effective use of heat treatment can give full play to the potential performance just now. So what are the common rack machining processes? The following is a step-by-step introduction to the relevant knowledge.

(1) Normalizing

Normalizing is a heat treatment method for refining steel grains and uniform internal structure. The purpose of normalizing treatment is to eliminate the internal stress generated during mechanical processing and the fibrous structure generated during plastic processing such as rolling.

(2) Annealing

Annealing is a heat treatment method for softening steel, adjusting crystal structure, removing internal stress, and improving cold rolling and machinability. According to the purpose of use, annealing is subdivided into complete annealing, spheroidizing annealing, stress relief annealing, intermediate annealing, and the like.

     ① Stress relief annealing

     The annealing treatment does not change the metal structure and eliminates the internal stress of the metal.

     ②Straightening and annealing

     In order to remove deformation such as warpage of the steel material, the steel material is subjected to annealing treatment while being loaded.

     ③ Annealing between processes

     In order to facilitate the processing of the next process, annealing processing is performed to soften the hardened material in the middle of the cold rolling process.

(3) Quenching

Quenching is a process in which the steel is heated at a high temperature and then rapidly cooled. Improve the hardness and strength of steel. According to the cooling conditions, it is divided into water quenching, oil quenching, vacuum quenching, etc. The quenched material must be tempered

(4) Tempering

Tempering is a heat treatment in which the steel is hardened and then heated to a certain temperature, and then cooled at an appropriate rate. The main purpose of tempering treatment is to adjust the hardness of the material, improve the toughness and eliminate internal stress. According to the different tempering temperature, tempering can be divided into low temperature tempering and high temperature tempering. The higher the tempering temperature, the hardness of the material decreases and the toughness increases. Quenching and tempering processing adopts high temperature tempering. The tempering treatment after the surface hardening treatment such as induction quenching and carburizing quenching is low temperature tempering.

(5) Quenching and tempering

Quenching and tempering is a heat treatment that combines quenching and tempering (high temperature) treatment to adjust the hardness/strength/toughness of steel. The hardness of the material after quenching and tempering treatment is the hardness in the general machining range.

The general quenched and tempered hardness is shown below.

S45C (carbon steel for mechanical structure) 200~270HB

SCM440 (alloy steel for mechanical structure) 230～270HB

(6) Carburizing and quenching

Carburizing and quenching is a heat treatment in which carbon is infiltrated into the surface of low carbon steel and then quenched. High hardness is obtained by infiltrating the surface layer of carbon. After quenching, it is tempered at low temperature to adjust the hardness. After the material is carburized and quenched, the hardness of the core will also increase to a certain extent, but it will not reach the level of the surface. If a carburizing agent is applied to a part of the material, the infiltration of carbon can be prevented and the purpose of preventing the hardness of this part from increasing. Surface hardness and depth of hardened layer are roughly as follows

Quenching hardness 55~63HRC (reference)

Effective hardened layer depth 0.3~1.2mm (reference)

The gear is deformed after carburizing and quenching, and the gear accuracy is reduced. In order to improve the gear accuracy, the gear must be ground.

(7) Induction hardening

High-frequency quenching is a quenching heat treatment in which steel with a carbon content of 0.30% or more is heated by induction to harden the surface of the material. After high-frequency quenching, the tooth surface and tooth top can get high hardness. However, the tooth root may not be hardened. Due to the deformation caused by induction hardening, the gear accuracy is generally reduced.

(8) Flame quenching

The heat source is surface heat treatment with an open flame. Mainly used when any surface or part of steel needs to be quenched.

(9) Nitriding

A heat treatment method in which nitrogen diffuses into the steel surface to harden the steel surface. Steels containing aluminum, chromium, and molybdenum can easily increase their hardness by nitriding. A representative nitrided steel is SACM645 (aluminum molybdenum steel).

(10) Whole piece quenching

The whole piece is quenched and heat treated by heating and rapid cooling. The surface core of the material achieves the same hardness.