Effect of film types on thermal response,cellular structure,forming defects and mechanical properties of combined in-mold decoration and microcellular injection molding parts

Different types of polymer films were used in the combined in-mold decoration and microcellular injection molding(IMD/MIM)process.The multiphase fluid-solid coupled heat transfer model was established to study the thermal response at the melt filling stage in the IMD/MIM process.It was found that the temperature distributed asymmetrically along the thickness direction due to the changed heat transfer coefficient of the melt on the film side.When polyethylene terephthalate(PET)films were applied,the temperature of the melt-film interface increased faster and to be higher at the end of melt filling stage in comparison with the application of polycarbonate(PC)and thermoplastic polyurethane(TPU)films.And the effects of film types on the cellular structure,forming defects and mechanical properties of IMD/MIM parts were also studied experimentally.The results showed that the film types had no obvious effect on the cells size in the transition layer and the mechanical properties of the parts.Under certain film thickness,the offset distance of core layer was the largest with PET film used,while the offset distance was the smallest with TPU film used.And similar results were found for the warpage of the parts.However,an exactly opposite change occurred for the thickness of film-side transition layer and the bubble marks on the surface of the parts.

Improving the process forming limit considering forming defects in the transitional region in local loading forming of Ti-alloy rib-web components

The isothermal local loading forming technology provides a feasible way to form Ti-alloy large-scale rib-web components in aerospace and aviation fields.However,the local loading process forming limit is restricted by forming defects in the transitional region.In this work,the feasibility of controlling forming defects and improving the process forming limit by adjusting die parameters is explored through finite element（FE） simulation.It is found that the common cavum and folding defects in the transitional region are significantly influenced by the fillet radii of left rib and middle rib,respectively.The cavum and folding defects can be effectively controlled by increasing the fillet radii of left rib and middle rib,respectively.The process forming limits considering forming defects in the transitional region are determined by the stepwise searching method under various die parameters.Moreover,the relationship between the process forming limit and die parameters is developed through the response surface methodology（RSM）.The developed RSM models suggest that increasing the fillet radii of left and middle ribs is effective to improve the process forming limit during local loading forming of rib-web components.The results will provide technical basis for the design of die parameters and the reduction amount,which is of great importance to control forming defects and improve the process forming limit in local loading forming of Ti-alloy large-scale rib-web components.

Multi-Point Forming Technology for Sheet Metal

Multi-point forming (MPF) is an advanced manufacturing technology for three-dimensional sheet metal parts. In this paper, the MPF integrated system is described that can form a variety of part shapes without the need for solid dies, and given only geometry and material information about the desired part. The central component of this system is a pair of matrices of punches, and the desired discrete die surface is constructed by changing the positions of punches though the CAD and control system. The basic MPF process is introduced and the typical application examples show the applicability of the MPF technology. Wrinkle and dimple are the major forming defects in MPF process, numerical simulation is a feasible way to predict forming defects in MPF. In conventional stamping, the mode to form sheet metal with blankholder is an effective way to suppress wrinkling; the same is true in MPF. A MPF press with flexible blankholder was developed, and the forming results indicated the forming stability of this technique. Based on the flexibility of MPF, varying deformation path MPF and sectional MPF were explored that cannot be realized in conventional stamping. By controlling each punch in real-time, a sheet part can be manufactured along a specific forming path. When the path of deformation in MPF is designed properly, forming defects will be avoided completely and lager deformation is achieved. A work piece can be formed section by section though the sectional MPF, and this technique makes it possible to manufacture large size parts in a small MPF press. Some critical experiments were performed that confirmed the validity of two special MPF techniques.

Forming Mechanism of Gaseous Defect in Ti-48Al-2Cr-2Nb Exhaust Valves Formed with Permanent Mold Centrifugal Casting Method

A method combining theoretical analysis with experiment is adopted and the flowing process of Ti-48A1-2Cr-2Nb alloy melt poured in a permanent mould during the centrifugal casting process has been analyzed. A mathematical model of the filling process is established and the forming mechanism of internal gaseous defect is summarized. The results of calculation show that the melt fills the mould with varying cross-section area and inclined angle. The filling speed of the cross-section is a function of filling time. The cross-section area is directly proportional to the filling speed and the inclined angle is inversely proportional to the filling speed at a given rotating speed of the platform. Both of them changes more obvious near the mould entrance. The gaseous defect can be formed in several ways and the centrifugal field has an important influence on the formation of the defect. In addition, the filling process in centrifugal field has been verified by wax experiments and the theoretical analysis are consistent with experimental results.

Hot spinning of cylindrical workpieces of TA15 titanium alloy

In order to form large-diameter thin-wall cylindrical workpieces of TA15 titanium alloy,tube hot spinning experiments of the alloy were conducted on a CNC hot spinning machine.The causes of some forming defects occuring in hot spinning,such as crack,pileup,bulge and corrugation,were analyzed and the corresponding measures were put forward to avoid spinning defects,based on which a proper process scheme of hot spinning of TA15 alloy was obtained and the large-diameter and thin-walled cylindrical workpieces were formed with good quality.The results show that spinning temperature has distinct influence on forming quality of spun workpieces.The range of spinning temperature determines the spinnability of titanium alloy and the ununiformity of temperature distribution near the deformation zone leads to the formation of bulge.The reasonable heating method is that the deforming region is heated to the optimum temperature range of 600-700 ℃,the deformed region is heated continuously and a certain length of undeformed region is preheated.With the thickness-to-diameter ratio(t/D) of spun workpiece reducing to certain value(t/D<1%),surface bulge and corrugation is rather easier to come into being,which could be controlled through restraining diameter growth and employing smaller reduction rate and lower temperature in the optimum spinning temperature range.