Numerical Simulation Of The Formation Of Transverse Welds And Optimization Of Pipe Moulds During Extrusion Of Molybdenum Alloy Pipe Rods

Due to the high specific intensity,good corrosion resistance,high thermal conductivity,can be surface-treated and easy recycling,etc,aluminum extrusion profiles is widely used in civil construction and transportation industries.With the progress of economic development and extrusion technology,the demand for aluminum profiles and production is growing.Rapid development of finite element technology and computers technology,making the extrusion die design that based on simulation and virtual extrusion gradually become the mainstream of the industry.In this paper,numerical simulation techniques was used to study the formation of the transverse weld in the process of "billet-to-billet" aluminum bar extrusion and the effects of the die angle on the length of transverse weld.Then study the effects of the porthole die structure on the length of transverse weld in OPC tube further,achieve the purpose that shorten the transverse weld in the OPC tube by optimize the die structure.The main findings are as follows:Numerical simulation techniques was used to study the formation of the transverse weld in the process of "billet-to-billet" extrusion and the effects of the die angle α on the length of transverse weld.The research indicates that: The metal flow quickly at the entrance of the die when the die angle is 30°,make the residual material from the former billet can quickly flow out of the die.Therefore,the finished bar contains a short transverse weld.Reference study the transversely welds in the bar further analysis the effects of the entrance angle α₂ of the welding chamber on the transverse weld length in the OPC tube.The results show that: Within a certain range,when the angle of α₂ increases,the metal in the welding chamber flow faster.while the α₂ is in the weld between 45 ° to 60 ° the metal flow rate in the welding chamber achieve the fastest.If using the porthole die that with the α₂ 45 ° 60 °,which transverse weld in the OPC tube will be relatively short.Study the effect of porthole die with the butterfly welding chamber on extrusion process by finite element simulation method,the results show that: Use the porthole die with the butterfly welding chamber can reduce or even eliminate the dead zone in the welding chamber,which help to shorten the transverse weld in the tube.Use butterfly welding chamber also can reduce the extrusion load without compromising the welding quality.Extrusion simulation with a porthole die that have a optimized small cavity,the simulation results show that: When using the optimized porthole die to have a "billet-to-billet" extrusion the amount of metal in the die reduces,so the length of the transverse weld will be shortened in the extruded tube,and the extrusion load only about 900 MPa,the hydrostatic pressure in the welding chamber is between 66 MPa 183 MPa which is meet the welding requirements.But the porthole bridge and the position of the edge of the porthole on the small-cavity die will bear larger stress,and these two positions easy to crack.The results of the practical extrusion of the traditional porthole die and optimized small-cavity die show that: the length of transverse weld extruded by the new die is about1800 mm,while the old die of this length is approximately 5500 mm,the former is only 1/3 of the latter.