Gravity Casting Process Research Articles

Numerical Simulation Analysis on Shrinkage and Porosity of ZL101A Alloy Mechanism Box

The Shrinkage and porosity of ZL101A alloy mechanism box prepared by sand gravity casting process was investigated. The solidification process was simulation analysis by using InteCAST software and the original casting process was optimized based on the above simulated results. The results showed that the shrinkage and porosity defects’ position of ZL101A alloy mechanism box were accurately predicted by the analysis procedure which was from liquid distribution to shrinkage formation and then to Niyama shrinkage porosity. The shrinkage and porosity of the ZL101A alloy mechanism box prepared by optimized process were clearly reduced and the distribution of them was reasonable. Keywords: InteCAST software;ZL101A; Mechanism box; Shrinkage and porosity; Numerical simulation

Confluence weld in an aluminum gravity casting

In aluminum engine housing castings, made by gravity casting process, a confluence weld defect can occasionally be found on their top flat surface. To understand the formation of the defect, three types of runner systems were designed in this study. At the top flat surface of the aluminum casting, the location of the confluence weld, where two filling fronts of the aluminum melt merge, could be determined by the velocity difference of the two fronts. The greater the difference, the further the weld location was away from the center of the top surface. The movement of the front was detected by a time-logger and indirectly filmed by a camera in the casting experiments. The filling profile was simulated by computational modeling. Two forms of the weld could be characterized by the velocity difference. In single-gating experiment, the difference was greater than that in double-gating experiment and the defect was more prominent. In all runner systems, the mechanical properties of the castings containing the confluence welds were examined by four-point bend test. Weibull probability plots were used to assess the fracture mechanisms for the three runner systems.

Effect of Ni on eutectic structural evolution in hypereutectic Al–Mg 2Si cast alloys

The aim of this work is to investigate the eutectic structural evolution of hypereutectic Al–20% Mg 2Si with Ni addition under a gravity casting process. Three-dimensional morphologies of eutectic phases were observed in detail using field emission scanning electron microscopy, after Al matrix was removed by deep etching or extraction. The results show that Al–Mg 2Si binary eutectic gradually evolves into Al–Mg 2Si–NiAl 3 ternary eutectic with the increase of Ni content, and flake-like eutectic Mg 2Si transforms into rods. The ternary eutectic presents a unique double rod structure that rod-like NiAl 3 and Mg 2Si uniformly distribute in Al matrix. Further, the high temperature (350 °C) tensile strength of the alloy increases by 23% due to the eutectic structure evolution, and the mechanism of structural evolution was discussed and analyzed in terms of the detailed microstructural observations.

Feeder growth: a new method for automatic optimal feeder design in gravity casting processes

The optimal feeder design in gravity casting processes is considered. The design problem is formulated as an additive, growth-like, evolutionary topology optimization problem. The initial design of the presented method is a casting part which is placed in a suitable environmental mould box. The method is composed of three stages: determining the feeder-neck connection point on the casting surface, constructing the feeder-neck and the feeder growth. During the growth stage, the feeder topology is changed gradually until satisfying some predefined criteria. The design of multiple feeders is also considered in this work. In the presented method, feeders are designed in a descending order of their sizes. The success of the proposed method is supported by an illustrative example.

Application of fuzzy PID self-adaptive controller in pressurisation control system of counter gravity casting

Good counter gravity casting process control is very important to the production of high quality light metal parts. However, due to uncertain dynamic properties, large delay and interactive influencing factors, this kind of process control is quite complex and it is hard to build a precise mathematic model to describe its characteristics. PID control dose not depend on mathematic model, but once the parameters are given, it cannot regulate itself and cannot get satisfied control effect. In order to satisfy the higher control performance requirement, fuzzy logic control is introduced, which is used to revise three coefficients of PID controller. It can greatly overcome the defects of conventional parameter fixed PID algorithm and get a good self-adaptive ability. Compared with the commonly used classical PID controller, the proposed fuzzy PID controller shows excellent robustness against system parameter variations and external disturbances in the counter gravity casting machine.

Familial Risk Of Kidney Cancer

Gravity and centrifugal investment casting processes of low-pressure turbine blades with high Nb–TiAl alloy were simulated by Procast software. Actual blade components were poured by vacuum induction suspended furnace with Ar protection. The experimental verification indicated that the simulation results were in good agreement with the experimental results. Comparative results had shown that the surface of centrifugal casting blade was more complete than that of gravity casting one. In gravity casting process, molten metal filled the thinnest trailing edge at last, resulting in the generation of misrun defects. Furthermore, the shrinkage porosity and crack defects of gravity casting were much more and dispersive. The internal and external quality of centrifugal casting was much better than that of gravity casting. Microstructures from edge to center of gravity casting blade had no significant change. The microstructure for centrifugal casting blade is finer than that for gravity casting blade, however, a large number of dentritic γ segregation appeared in the blade edge of centrifugal casting, which resulted from the fast cooling rate of centrifugal casting surface.

Plaster casting process for prototyping of die casting based on rapid tooling

Rapid prototyping (RP) combined with a gravity casting process can provide a suitable substitute with steel tool die casting for prototyping metal casting. Due to differences between die casting and gravity casting, there are several drawbacks in RP simulated die casting. This paper is concerned with the development of a new plaster die casting process that combines pressurization and vibration for prototyping of die castings, and with a plaster die casting machine that has a structure similar to that of a die casting machine. The machine utilizes an oil cylinder for pressurization and a magnetic actuator for vibration. A rapid prototyped pattern is made by the laminated object manufacturing (LOM) process to prepare a plaster mold. In the process, a plunger in the developed machine simultaneously pressurizes and vibrates the molten metal to fill the plaster mold completely and to facilitate the creation of nuclei in the molten metal, respectively. The developed machine has produced a prototype of an end clutch cover with remarkable improvement in mechanical properties.

Influence of variations in alloy composition on castability and process stability. Part 1: Gravity and pressure casting processes

The influence of variations in alloy composition on the fluidity of three different light metal alloys was investigated. The aluminium alloys AlSi9Cu3 (A380) and AlSi7Mg (A356) as well as the magnesium alloy AZ91 were cast into spiral fluidity test dies at their upper and lower compositional tolerance limits. The test results show significantly varied behaviour, which is explained by microstructural features and heat content. In alloy AlSi7Mg at the upper compositional limit the formation of intermetallic phases in the interdendritic liquid physically blocks the flow and leads to short flow length compared with the same alloy with low iron and manganese content. Alloy AlSi9Cu3 at the upper compositional limit is very close to eutectic composition and flows significantly better than the alloy at the lower tolerance limit. The intermetallic phases are formed simultaneously with the matrix during eutectic solidification and do not block the flow. In the magnesium alloy the intermetallic phase is incorporated in the primary magnesium phase and does not hinder the flow. A higher content of alloying elements increases the flow length owing to a higher heat content of the melt.

Filling polyhedral molds

In manufacturing industry, finding an orientation for a mold that eliminates surface defects and ensures a complete fill after termination of the gravity casting process is an important and difficult problem. We study the problem of determining a favorable position of a mold (modeled as a polyhedron) such that, when it is filled, no air pockets and ensuing surface defects arise. Given a polyhedron in a fixed orientation, we present a linear time algorithm that determines whether the mold can be filled from that orientation without forming air pockets. We also present an algorithm that determines the most favorable orientation for a polyhedral mold in O( n 2) time. A reduction from a well-known problem indicates that improving the O( n 2) bound is unlikely for general polyhedral molds. We relate fillability to some well known classes of polyhedra. For some of these classes of objects, an optimal direction of fillability can be determined in linear time. Finally, for molds that satisfy a local regularity condition, we give an improved algorithm that runs in time O(nk log 2 n log log( n k )) , where k is the number of venting holes needed to avoid air pockets in an optimal orientation.

ＡＺ９１マグネシウム合金の機械的性質に及ぼす凝固組織の影響

An AZ91 alloy was preparded by a gravity casting process with either constant grain size or constant cooling rate. The as-cast alloys show good mechanical properties with decreasing dendrite arm spacing (DAS) or grain size. These phenomena are possibly explaned by the fact that cracks do not easily propagate in the brittle eutectic Mg17Al12 compounds due to the fine compounds. The ultimate tensile strength (UTS), 0.2% proof stress (PS) and elongation (Ef) at fracture of the T6 treated alloys increase with decreasing grain size. But the UTS and Ef of the alloy remain almost constant with decreasing DAS, while the PS increases with decreasing DAS. These phenomena in the T6 treated alloys are explained by assuming that (1) the stress concentration at a grain boundary is higher with larger grain size, (2) the density of grain boundaries which act as obstacles during crack propagation is higher with smaller grain size and (3) the homogenization is easily achieved in a shorter solution heat-treatment time with a small DAS.

Geometric and computational aspects of gravity casting

In the manufacturing industry, finding an orientation for a mould that eliminates surface defects and ensures a complete fill after the termination of the gravity casting process is an important and difficult problem which has not previously been investigated formally. The paper initiates the study of the gravity casting process from a geometric perspective and presents an optimal θ( n log n) time algorithm that solves this problem in 2D given an object of size n. The paper also characterizes the object shapes (modelled as simple polygons) that can be 1-filled and relate fillability to well known classes of polygons. For certain classes of objects, an optimal direction of fillability can be determined in linear time.

A foundry-based experimental investigation into the effect of die coats in the gravity casting process

An experimental investigation into air gap development and heat transfer at the casting-die interface is described. The experiments were carried out on a shaped casting under foundry conditions and the effect of different die coat thicknesses was investigated. The experiments show the complex mechanical contractions which take place, the restraining/supportive effect of the tooling and its effect on heat transfer. The die coat is seen to be most influential in reducing heat loss early in the transient, the heat-transfer coefficient being independent of die coat thickness on development of the air gap. These trends are similar to those encountered in laboratory experiments, although for this shaped casting the heat-transfer coefficients in the early phase are notably larger.