Simulation of the casting and solidification process of the brake shoes intended for rolling stock

The paper presents the results obtained from the simulation of the casting and solidification process of the phosphorous cast iron brake blocks intended for rolling stock. The simulation of the casting and solidification process was carried out using the SolidWorks and Altair inspire cast programs. A S1 type brake shoe was chosen for this process. The solidification of phosphorous cast iron brake blocks is influenced by a number of constructive and technological factors. The simulation allows analysis of technological characteristics of casting and solidification of the alloy. The solidification process influences the micro and macrostructure of the parts, their compactness, mechanical strength, dimensional accuracy and surface quality.


Introduction
Brake shoes are component parts of the braking system of vehicles and towed rolling stock.In the case of passenger cars and limited-gauge locomotives, braking systems with shoes cast from cast iron or composite material are used [1], [2].The brake shoes used for towed rolling stock are manufactured in accordance with specific procedures and current legislation [2], [3]; these pieces are cast from phosphorous cast iron (type P10), where phosphorus has values in the range of 0.8-1.55%[4].
The process of making phosphorous cast iron is influenced by: -the quality of the ferrous raw material and auxiliary materials used in the production of cast iron; -chemical and thermal homogeneity of the melt; -the technological parameters of elaboration the liquid alloy and casting; -the technological parameters of casting the liquid alloy in the moulding.Currently, computer-aided design is used more and more frequently in various industries.Thus, with the help of the computer and using specialized programs [5][6][7][8][9], different fields of interest have taken on an ever greater scope.In this context, the Altair Inspire Cast Software [9] is highlighted, which is a tool for simulating the flow and solidification process for pressure cast parts.
To carry out the simulation process, it is necessary to create the 3D model in advance, this is done using the interactive graphic software Solidworks.Next, successively, the simulation parameters are established: the material from which the cast part is made, the direction of flow, the mold and the casting network.
With the help of these parameters, the software simulates the flow of the alloy, the solidification as well as the way of heat transmission through the mold during the cooling process.
The present paper refers to the simulation of the process of casting and solidification of the alloy cast in the mold.

Simulation of the cast iron casting and solidification process
To obtain the 3D model of the part, the CAD module of the SolidWorks software was used [8], [9].Thus, the modeling process has as its starting point the design of the S1 brake shoes; for them, the 2D sketch is made which then, through specific commands, is transposed to the 3D model.
In this way, the modeling result is represented by the two component elements of an S1 brake shoe, namely the cast iron part of the brake shoe and the reinforcing rail.Later, by means of the same software (Solid Works), the shoe -reinforcing rail assembly is made.Thus, Figure 1 shows a sequence during the realization of the 3D model in SolidWorks.

Figure 1. Shaping the body of the brake shoe
The 3D modeling in SolidWorks of the brake shoe also includes the stage of inscribing the various markings on the shoe (Figure 2), respectively the location and making of the of the liquid alloy gate runner (Figure 3).After making this 3D model of the part, Altair InspireCast simulation software will be used to perform a finite element analysis of the liquid alloy flow and solidification of the cast part.For this, the 3D model created in SolidWorks is imported, after which the material used in the brake shoe model is configured (chosen) so that it is consistent with industrial practice (phosphorus cast iron, type P10), according to the Figure 4.The alloy casting and solidification simulation program allows the choice of specific parameters (similar to industrial practice), respectively [10]: -establishing the casting position: vertical position; -establishing the casting method: gravity casting; -the material used to make the casting form (mold): casting sand; -casting technological parameters: casting speed, casting temperatures and simulation mode for the flow of the liquid alloy and its solidification.In general, the simulation results of the analyzed processes can be presented in the form of graphs or maps.In the present case, the temperature maps show the maximum values of the temperatures recorded when filling the form.According to the simulation, the mold filling process takes 4.35 seconds until the alloy casting is finished, the maximum temperature recorded being 1273 o C (Figure 5).From this moment, the cooling process begins, upon contact of the alloy with the mold (at ambient temperature).The module of the simulation program intended for the study of the solidification process of the liquid alloy indicates a visible decrease in the recorded temperatures, the duration of this process being 1.57 hours.Figure 6 shows a sequence from the alloy solidification simulation program, recorded after 6.28 min, when the temperature dropped to 1163.2 o C. In the solidification module of the simulation process, the solid fraction can be studied throughout the solidification of the parts, a fact that can indicate the areas where there is the possibility of the appearance of thermal nodes, which can lead to the appearance of defects in the cast part.
Also, a way to identify the inconveniences that may appear during the solidification process of the alloy in the mold, the Altair InspireCast simulation program uses a module designed to analyze the heat transfer mode between the liquid alloy and the casting mold [10].With the help of this module, the temperatures recorded in the form of casting are visualized, throughout the duration of the cooling process (Figure 7).All the results resulting from the simulation process provide information about temperatures and their distribution, porosities, the solidification process, mold behavior etc. which can be used in industrial practice to prevent the appearance of defects in cast parts.

Conclusions
The simulation of the solidification process of cast parts is technologically important, because it combines a series of process parameters, namely heat transfer, phase transformations, diffusion processes, volume variations, flow processes, local supply processes, etc.
The constructive factors of the cast part (geometry, dimensions) and the technological factors (nature of the alloy, casting temperature, type of mold, material of the mold, method of feeding the mold with liquid alloy, etc.) have a particular influence on the solidification of the cast parts.For this reason, the necessity of the simulation process and the comparison with the results obtained in the industry is important.
The use of software for the simulation of solidification at an industrial level became possible with the development of the calculation technique and led to obtaining concrete studies aimed at optimizing the forming and casting technologies.
The simulation of the process of casting and solidification of the liquid alloy brings the following advantages: -The possibility of anticipating the behavior of the metal alloy during the technological processes; -Optimizing process parameters according to the dimensions of the various cast parts; -Selecting the optimal technological options for casting and solidification taking into account the real conditions in the industrial practice;

Figure 2 .Figure 3 .
Figure 2. Placement of markings on the 3D model pf the part

Figure 4 .
Figure 4. Choosing the material in the simulation program

Figure 5 .
Figure 5.The result of the simulation process (filling the mold)

Figure 6 .
Figure 6.The result of the simulation process (alloy solidification)

Figure 7 .
Figure 7. Heat transfer in the mould