Numerical Simulation Research In Continuous Induction Heat Treatment Of High Precision Rack Bar

Rack is one of the important parts of the automobile steering system.The heat treatment of rack bar is the key process in the rack manufacturing process.If there are quality issues in the heat treatment,the rack may be broken and the automobiles may lose their ability to control direction.This often leads to malignant traffic accidents or even car crash.As a result,the steering gear manufacturers have been paying high attention to the heat treatment of rack bar.Rack bar heat treatment technology also constantly improves with the development of the automobile industry.There are two types of rack bar heat treatment furnace,non-continuous heat furnace and continuous heat treatment furnace.On one hand,non-continuous heat treatment furnace includes box furnace and salt bath furnace.Its costly equipment occupies large area and requires high labor intensity.One the other hand,continuous heat treatment is based on induction furnace.Its equipment is simple and occupies small area.It has high heating speed,no heat storage,good continuity,high quality and efficiency.Comparatively,induction heating has significantly more advantages.In recent years,domestic and foreign induction heating technologies have made huge progress in improving product quality,enhancing equipment performance and increasing the degree of mechanization and automation.However,there are still deficiencies such as easy deformation,non-continuous production and high energy consumption in the domestic rack bar heating process.Luxury cars require the gear bar to undergo quenching and tempering using the induction heating technology,so as to achieve grain refinement and better performance.Since the finished rack experiences gear milling at 1 / 4D bar,the hardness and organization at 1 / 4D have to be guaranteed.Although it is difficult to determine the temperature at 1 / 4D of the rack bar in the actual measurement,a sound induction heating model can be built to estimate the surface temperature easily.Then the actual measured surface temperature can be used to verify the accuracy of the model and predict the temperature at 1 / 4D.It also plays a guiding role in the development of process requirements,practical technology and equipment.Hence,it improves the efficiency of development,lowers the design costs and solves problems created from inaccurate empirical data.The uniformity of rack bar temperature in the continuous induction heat treatment process and electrical efficiency of the heating are two key parameters in determining the reasonableness in the designs of the induction production line and the specifications of rack bar with diameter ranging from φ21 to 33 mm.Therefore,induction coils of different sizes are used in the heating,the resulting heating efficiency and surface temperature of the rack at 1 / 4D are then compared.The rack bar was transferred to the quenching spray room after heating.Continuous high-pressure water was sprayed to the surface of the rack bar using a ring-shaped water spray device.The quenching organization of the rack bar changed after a certain period of quenching spray.Under the impact of high-pressure water,the control of roller speed and circulation pressure indirectly affected the final organization of the quenched product,which directly led to bending deflection of the rack bar.In actual production,the process parameters of the quenching and cooling processes must be reasonably determined to achieve the desired organization,performance and straightness for a product.