Research On Cooling System Of Hot Forming Tools

Cooling system is the central and difficult point of designing hot forming tools. Settingup cooling system could intensify the heat transfer of hot forming blank during quenchingprocess and it is very important to improve the cooling performance of tools and guaranteethe quality of products. Typical cooling system of hot forming tools consists of diversiontank and cooling pipes. Research of cooling system concentrates mainly on factors ofcooling pipe’s diameter, pipe wall spacing, distance between pipe top and work piece and soon. But there is barely research on related parameters of diversion tank, shape andarrangements of cooling pipes, which leads to the lack of theoretical foundation in designingcooling system of hot forming tools.This paper utilized Gambit software to model cooling system of hot forming tools andcarried on simulation work with FLUENT computational fluid software to study factorswhich influences water flow in cooling system.Firstly, influence of diversion tank factors on water flow was investigated, andwater-entering along width direction was identified to get more even water velocitydistribution. Optimal value of distance between diversion tank’s inlet and cooling pipes(S) is20mm. Determination of diversion tank’s inlet diameter depends on cooling performance andstrength of tools. Reasonable values of length, width, height of diversion tank wererespectively investigated: L=90mm, W=25mm, H=50mm. Distinction of cooling systemwith whole-tank and split-tank was explained and homogeneity of water velocity distributionin cooling system with split-tank was optimized by setting appropriate ratio (7:5) of branchdiversion tank’s depth and main diversion tank’s depth.Secondly, influence of typical pipe shapes and arrangements on water flow was investigated: flow state of cooling water will change suddenly when flowing through cornerpositions or cross sections of sharp change, secondary flow which impedes fluid flow willoccur, so there will be local loss at mutational locations. For hot forming tools with bendingangle, increasing diameter (8mm increased to10mm) of cooling pipes with low flux willgreatly improve homogeneity of each cooling pipe.At last, a typical U-shape part’s hot forming tool was designed according to conclusionsfrom simulation and theory of fluid dynamics and heat transfer. Cooling performance undermulti-periods was studied by simulation. At the same time, heat balance water velocity(HBWV) was proposed according to the affect of water velocity on heat transfer coefficientand7m/s was determined to be HBWV of U-shape part’s hot forming tool under givenresearch condition. Finally, hot forming experiment of U-shape part was carried out, U-shapepart with good forming quality was obtained. And through microstructure observation,complete martensite transformation occured at typical locations on U-shape part and widthof martensite lath at side wall is larger than that at flange and bottom; microhardness ofbottom, flange and side wall is483.2HV,485.0HV,473.2HV, respectly.