Study On Material And Its Near-Net-Shape Technology Of Ductile Cast Iron For Medium And Large-scale Punching Dies

The die and mould are important technical equipment for fabricating different product in manufacturing owing to the function of shaping the raw material. An efficient application in die and mould is in favor of guaranteeing production quality, of improving productivity and of reducing cost.With the development of economy, the demand for medium-sized and large-scale thin steel plate and aluminum plate used for auto, for underground and for carriage augment sharply and therefore the need for corresponding punching die increase. In addition, the key problem is how to improve manufacture efficiency and reduce cost under the precondition of fine quality and well applicability of die.At present, the advanced industry countries adopt alloy cast iron as the raw and processed materials of large-scale punching die. In Our country these punching die mostly need import. For example, FAW Mould Co.,Ltd. import the punching die from Japan. One of the main reasons for this is that the quality of die materials and forming technics for die can't satisfy demand. The development of mould industry need high technology and thus the key point is die material. If select materials are improper, the die will invalidate prematurely. In addition, the costly die materials are not in favor of the economic profit because technology rapidly progress. Therefore, it is necessary to select appropriate die and use corresponding surface treatment technology to prolong its longevity. Large-scale punching die is generally assembled by forging mould steel alloy formerly which is limited by high cost, complicated working procedure, long manufacture cycle, and low precision, leading to high production cost and low precision. Therefore, the exploitation for nodule cast iron which has the character of high quality, long longevity, and independence episteme property right is significant. Also this measure can aid promoting industrialization, rising agora competition capacity, increasing economic benefit and social benefit.In this study, a new type of high strength nodule cast iron with better obdurability and fine wear resistance was fabricated by optimizing alloy component. The longevity is similar to the import. The high strength Cu-Sb alloyed nodule cast iron was prepared by lost foam process and then was optimized by orthogonal experimental method. The effect of Cu,Sb element on microstructure and properties of nodule cast iron was investigated on system. The relationship between microstructure and property was forecasted by BP neural networks method and reasonable mathematics model was educed. The casting defects such as crack, porosity and shrinkage hole in the process of mold filling and solidification for middle-scale or large-sized pressing mould were nicely predicted by casting simulation using Procast software. Some innovative results have been obtained in the work. The major research efforts of the present study are as follows:Firstly, the better chemical component which was optimized by orthogonal experimental method is (by wt.%)C:3.70, Si:2.4, Mn:0.7, P:0.027, S:0.012. The high strength alloyed nodule cast iron was synthesized by adding Cu and Sb in to common nodule cast iron using lost foam process. The optimal alloy component is (by wt%) Cu:0.5, Sb:0.02. This material fill up the gap for large-sized punching dies in our country.The microstructure of nodule cast iron was observed. The effect of Cu and Sb element on microstructure and solidification of nodule cast iron was studied. The results indicated that the number of the graphite sphere and pearlite content increase when Cu contents go up. The number of pearlite increase with increasing Sb element. The Cu and Sb elements not only decrease pearlite lamellar distance but also minsh size of graphite sphere. When element contents reach 0.5 for Cu, 0.02 for Sb (by wt. %), the pearlite content reach 97 (by wt.%) and the graphite sphere of which diameter is about 16-25μm is round and lamellar distance of pearlite is about 0.35μm.The ferrite can't be observed around the graphite nodule.The structure of Cu and Sb alloy nodule cast iron is characterized by un-slippery sphere. Secondly, the experimental results of mechanical properties indicated that Cu and Sb element can improve strength and hardness of nodule casting iron, whereas decrease elongation rate. When Cu and Sb content are 0.5 wt % and 0.02 wt % respectively, the various mechanical properties is as follows: the strength is 785 MPa, the hardness is 280HB, the elongation rate is 3% and the fatigue strength is 333.6 MPa. Therefore nodule casting iron has preferable synthesis mechanical performance.Thirdly, the mathematics model on the relationship between such as pearlite content and chemical element, mechanical property and chemical component, weight loss, friction coefficient and pearlite, nodularity in Cu-Sb alloyed nodule casting iron were initially established under lost foam condition using BP neural networks method. These formulas are given as follows: Fourthly, the wear behavior under different operating conditions was studied. As a result, under dry friction condition, the weight loss and the friction coefficient for Cu-Sb alloyed nodule cast iron was less than that of the common nodule cast iron and decreased with increasing pearlite content. The wear weight loss and friction coefficient of the Cu-Sb alloyed nodule cast iron was decrease to 65% and 56% respectively than common nodule cast iron, when pearlite content is 97%. These illustrate increasing pearlite content can improve wear-resistance of nodule cast iron. When applied load and wear time rise, wear weight loss and friction coefficient increase for both two nodule cast iron, but the increasing range for alloyed nodule cast iron is less than common nodule cast iron. The morphology of the worn wear surfaces and the wear debris indicated that the glide wear behavior for both nodule cast irons were abrasive, oxidation, adhesion and stripped wear. The abrasive wear happen when load is low, while oxidation, adhesion and stripped wear take place when load is high. The lamellar pearlite in nodule cast iron prevent from oxidation and adhesion wear, which lead to not important wear degree in wear surface of alloyed nodule cast iron.Under abrasive friction condition, the weight loss of the Cu-Sb alloyed nodule cast iron was less than that of common nodule cast iron and decreased with increasing pearlite content. The wear-resistance of the Cu-Sb alloyed nodule cast iron increased up to 62% than common nodule cast iron, when pearlite content is 97%. The wear weight loss of nodule cast iron increase when applied load and abrasive granularity increase. But the increasing range for alloyed nodule cast iron is less than common nodule cast iron. The abrasive wear behavior of nodule cast iron is plough wear under abrasive wear condition. Lamellar pearlites effectively bear part of load and prevent from abrasive inrushing into matrix metal, resulting in a higher wear-resistance of alloyed nodule cast iron than that of common nodule cast iron.Fifthly, the numerical simulation method was adopted for first time to analyze the pouring system and the process of mold filling and solidification in middle-sized and large-scale pressing mould under lost foam condition using Procast software. The values of vacuum negative pressure and pouring temperature identified by numerical simulation method were 0.07MPa and 1450℃, respectively. This simulation result is in agreement with practice result which was gained by practical test adopting double sides pouring system.Finally, the medium-sized and large-scale punching dies with alloyed nodule iron were successfully fabricated for the first time in our country using lost foam process; these dies have fine mechanical properties, which are confirmed by experiment. The tensile strength, hardness, elongation rate and pearlite content reach 710 MPa, 230-280HB, 3-5% and 90%, respectively. The Shrinkage hole and shrinkage porosity aren't observed in mould by no-destructive test. Consequently, the moulds meet the drawing requirements thoroughly and are able to replace overseas production.