Failure Analysis Of Die Casting Machine Punch And Development Of Austempered Ductile Iron Punch

Die casting machine punch is a key component on pressure transmission in thecasting production. It with 2×106kN/mP2P specific pressure and 100m / s high-speedimposing on the liquid metal which filled casting cavity model access to high-qualitydie castings. Die casting machine punch's working environment is very bad which lifeis very low, while it has 1-2 working times that has to be replaced. So the materialwaste is serious. The domestic factory uses the coating of carbon steel punch, its lifehas 6-7 work-times, but its price is expensive. The QT600-3 punch works only onework-time. The abroad uses Beryllium Bronze as the punch's material which life has1-2 million times. But beryllium bronze is expensive, toxic, rarely used internally. Sothe study that how to improve the wear resistance of the punch has an importanttheoretical and practical value.Austempered ductile iron as a new engineering material, its excellent wearresistance HThas caused the extensive concernTH. Austempered ductile iron is made fromthe bainite (no carbide ferrite) + austenitic + spherical graphite, the organization ofaustenite content from 5% to 40%.First, in the process of wear,the austenitic phaseproduced plastic deformation which leaded to the relaxation of stress concentrationthat was from crack, and ferrite was surrounded by toughness of austenitic thatprevents the expansion of cracks and improves the wear resistance of materials.Second,in the process of wear ,austenite transformed to martensite which increased hardness significantly, and improved the wear resistance of materials. Third, thegraphite of austempered ductile iron played a HTsolid lubricantTH role under dry friction andthe bad conditions of lubrication. Thus, if the punch was made of austempered ductileiron material ,it will be a very important theoretical and practical value.Byexperimental study ,this paper analyzed the failure mechanism of punchsystematicly,and used austempered ductile iron as punch ,it made the life of punchimprove nearly three times. Main research content in this paper is as follows:1. Failure analysis of die casting punchThrough the failure analysis of punch drew the following conclusions:(1)Punch inthe process of reciprocating motion, Molten aluminum embedded in the gap veryeasily between the punch and cylinder that formed debris after molten aluminumbecame solidification which was effect of cutting on punch, this is the main reason forfailure Punch.(2) Punch worked in the conditions of thermal cycles and cycle ofstress ,it is easy to produce thermal fatigue, pearlite decomposition that resultedg indecreased matrix hardness, surface cracks,which has accelerated the wear ofpunch.(3)Wear of punch surface has also been affected by aluminum alloy corrosion,the aluminum of punch surface repeatedly in the role of friction and heat , acombination of iron and aluminum produced brittle hardware intermitallic compound.In the condition of repeated friction and heat stress field, punch would have a crack oreven intermitallic compound would fall off which become HTwear particleTH and cutsurface that accelerated the punch of wear.2. The preparation for material of cast ductile iron punch1) In the isothermal treatment of the large castings.In in order to ensurehardenability need to join the large number of expensive alloying elements (Ni,Mo, Cu, etc.)But the punch of size and surface's HTpropertiesTH decide theperformance.In order to reduce production costs, the author considered thecomposition of low-alloy design.HTAccording to practical situationTH of ductileiron ,components were optimized to identify ductile iron components: C3.6%Si2.4% Mn0.4% Cu0.7% Mo0.3% Ni0.4%.2) The second composite inoculation can improve the shape of graphite, increased nuclear capability, and promote precipitation of the large number of smallspherical graphite,futher mprove the comprehensive performance of ductile iron.Through experiments that the best composite inoculant: Si- Ba-Ca-Al-compositeinoculant + 0.3% Sb0.02%.3. The effect of isothermal heat treatment process on material of austemperedductile iron punch1) The overhigh HTaustenitizingTH temperature makes carbon-rich austenitic and bainitethat formed in the course of isothermal heat treatment process becomebigger ,which will influence the mechanical property of austempered ductile iron.By orthogonal design optimization that the best austenitic temperature for 920℃.2) The overlong HTaustenitizingTH time also makes carbon-rich austenitic and bainite thatformed in the course of isothermal heat treatment process become bigger ,whichwill influence the mechanical property of austempered ductile iron. By orthogonaldesign optimization that the best austenitictime for 90min.3) Isothermal processing time on the mechanical properties of austempered ductileiron impact is very close, When isothermal time is short ,austenite only HTprecipitateTHlittle bainitic ferrite, austenite will change into martensite and retained austeniteafter cooling. When isothermal time is long, carbon-austenitic will break downinto ferritic and carbide, the last organization are ferrite and carbides. Byorthogonal design optimization that the best isothermal heat treatment time for60min.4. Research for material of austempered ductile iron punch's wear behaviorThrough experiments proved that the friction in different conditions, isothermalheat treatment tempeture for 350℃has the best wear resistance, isothermal heattreatment process: austenitic temperature for 920℃, austenitic time for 90 min,isothermal heat treatment temperature for350℃, isothermal heat treatment time for 60min. It compared with ordinary wear ductile iron reduced by 60%, Because theaustempered ductile iron'has the best combination of strength and toughness under theisothermal temperature is 350℃,the strength and toughness is a major factor that decide wear resistance.5. Industrial test of Austempered ductile iron punchBy test of installation in DongFang non-ferrousdie casting Co., Ltd. It showedthat austempered ductile iron material as punch to enhance the punch of theanti-friction properties played a very significant role which made service life of punchincreased nearly twice on the basis of the original.