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Volume 07 - Powder Metal Technologies and Applications Part 10

Tham khảo tài liệu 'volume 07 - powder metal technologies and applications part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | of the available volume inside the container a considerable amount of shrinkage occurs. The science art of designing a container must account for the packing density and the symmetry or lack thereof to achieve an acceptable part. During the initial production of a particular component preproduction trials and or iterations of the full-size shape may be necessary to determine the shrinkages empirically. However this iterative approach is frequently costly and time consuming. Through the years HIP P M part manufacturers have employed engineering intuition and previous experience to develop the starting can design. At this time other approaches are being developed and used namely empirical and continuum mechanics fmite element modeling. Some of these are briefly described here. Empirical Models. A large percentage of the HIP P M compacts produced are either simple or hollow cylinders. An empirical model for these shapes was developed several years ago Ref 26 by analyzing dimensional data from before and after HIP for a variety of cylindrical shapes. To eliminate the effects of the HIP cycle alloy systems and container thickness the analysis focuses on cylinders made from nickel-base alloys consolidated in similar HIP cycles with a certain can thickness range. Best fit curves were generated for axial and radial shrinkage as a function of aspect ratio length to diameter and surface area ratio area of cylindrical component to area of the lateral ends as shown in Fig. 13. Based on these data a computer program was generated to provide either the starting container dimensions to make a finished near-net shape or predict post-HIP dimensions given a specified starting container Ref 26 . Fig. 13 Normalized shrinkage on solid cylinders normalized shrinkage actual shrinkage isotropic shrinkage . Source Ref 20 Engineering Models. One promising approach to perform a direct process simulation via the use of computer models is to combine a constitutive model of continuum mechanics