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Computer aided design of three-dimensional casting process tooling

introduction

computer aided design of casting process tooling is one of the important aspects of the application of computer technology in the casting field. With the maturing of 3D modeling theory and practical technology, 3D casting process tooling CAD system will become the mainstream of casting process tooling CAD system with reliable and stable operation. Foreign cad/cae/cam technology has been widely used in mold manufacturing. In China, mold cad/cae/cam technology started late, and the application of mold cad/cae/cam technology is still in its infancy. Some powerful domestic mold manufacturing enterprises have gradually begun to apply cad/cae/cam technology in mold design and manufacturing, and initially achieved good economic benefits. Relying on the integration of cad/cae/cam technology, traditional design and manufacturing help people live a more comfortable and healthy life. They plan and develop the separated tasks as a whole, realizing a high degree of integration of information processing

this paper studies and develops a CAD system of casting process tooling, expert-cad. It uses solid edge, a mid-range modeling software, as the modeling platform, and mainly aims at the disa vertical boxless modeling process design of ductile iron parts. Solid edge is an excellent feature modeling software developed by Intergraph company. It was merged by EDS Unigraphics in 1998. The merged solid edge modeling kernel will adopt Parasolid modeling engine, and its function and performance are expected to reach a new level

The main functions of expert CAD system include: general casting process parameter design, practical riser system design, constant pressure and equal flow gating system design, template layout design, etc. The developed auxiliary modeling module can reflect various numerical results generated by the process design calculation module to the three-dimensional casting model. Advanced database technology is used to store and manage the design results of each process design module and various standard data required by the design1 design of casting process parameters

the purpose of the design of casting process parameters is to transform the three-dimensional product model into a three-dimensional casting model, including the design of machining allowance, draft angle, casting shrinkage and minimum casting hole. The design process is divided into two steps. First, query the standard process parameter database to get the appropriate casting process parameter values, and then use the modeling function of solid edge or the developed auxiliary modeling function to reflect the casting process parameters on the three-dimensional casting model. Figure 1 is the query user interface for draft angle design

Figure 1 draft angle design user interface

2 practical riser system design

2.1 practical riser design principle

the riser system design of ductile iron castings adopts the practical riser design method. Ductile iron in the solidification process has to go through three stages: liquid shrinkage, graphitization expansion and secondary shrinkage. The secondary shrinkage occurs when the solid rate is very high, and it is difficult to achieve effective feeding with traditional risers. The design principle of the practical riser is to use the riser to compensate the liquid shrinkage of the key partition of the riser, and make full use of the internal pressure generated by the graphitization expansion of the key partition to compensate the liquid shrinkage of the thicker and larger partition or its own secondary shrinkage. According to the difference of mold strength and casting wall thickness, the practical riser system design methods can be divided into three categories. Figure 2 is the classification diagram of practical riser system design method. Disa process adopts green sand molding, and the mold strength is low. Only the design method of pressure control riser system and the design method of direct practical riser system can be selected. The two methods are mainly different in the utilization of graphitization expansion. The control pressure riser is suitable for medium wall thickness parts, and the expansion of the casting is relatively large. In order to prevent the mold from being crushed, part of the expansion is released by allowing some liquid metal to return to the riser, and the internal pressure generated by the appropriate residual expansion is used to compensate for its own secondary shrinkage; The direct practical riser is suitable for thin-walled parts, and the graphitization expansion is used to compensate for the liquid shrinkage of the thicker and larger body and its own secondary shrinkage

Figure 2 classification of practical riser design methods

2.2 split volume, modulus calculation

key modulus is an important parameter for practical riser system design. The calculation of split volume and modulus is the basis for determining the key split and then the key modulus. The super-cad system has developed the function module of split volume and modulus calculation, which can make full use of the three-dimensional modeling information of the split to accurately calculate the volume, surface area and modulus. The processing of non heat dissipation surface adopts a convenient and intuitive interactive way. Figure 3 is the user interface for calculating the 2# split volume and modulus of Hub Castings. Figure 4 shows the block division and modulus calculation results of castings. Figure 5 is the fringe diagram of the split modulus volume share relationship drawn according to the system and the calculation results

Figure 3 split modulus calculation user interface

Figure 4 casting block and split modulus calculation results

Figure 5 casting split modulus volume share fringe pattern

2.3 riser system design program implementation

based on the above practical riser design principle, the control pressure riser system and direct practical riser system design modules are designed respectively. The module integrates the riser system size calculation function and the riser 3D model generation function in the 3D modeling software solid edge. The key split modulus required for size calculation comes from the 3D model in solid edge. After the size calculation is completed, the appropriate standard riser can be automatically matched and added to the casting model. The design results can be stored in the process project database through the user interface. The process item database takes a process design version of a part as a process item, and manages the process design results uniformly. It supports multi version design

the two standard riser series recommended by disa process are spherical and cylindrical risers respectively. The riser neck section shapes include circle, trapezoid, square, rectangle, triangle and regular hexagon. Figure 6 is the hub casting model with the addition of a cylindrical riser system

Figure 6 designs the hub casting model of the riser system

3 gating system design

disa vertical parting gating system design, which is based on disa process design specifications. In order to ensure stable pouring and simultaneous filling, the design method of constant pressure and equal flow is adopted. The selection of runner, sprue and sprue cup shall be carried out according to disa process standard

the gating system design module is parasitic on the modeling platform solid edge, which realizes the real three-dimensional design. The workflow of the system is as follows: first, the casting model that has finished the process parameter design and riser design is split along the parting surface to generate a three-dimensional model of the pattern. In the assembly environment of solid edge, the three-dimensional model of the shape is installed on the disa standard template, and the layout of the template is designed, so as to make it look like beautiful hardwood and have no impact on the environment. Then, use the auxiliary tools provided by solid edge to measure the distance from each ingate to the sprue cup (i.e. static pressure height). Take the measured results as the input of the ingate design module, calculate the ingate area, and check the shape of the ingate so that the turbulence coefficient does not exceed a certain range. Calculate the area of the sprue and transverse sprue, and match the standard sprue series. Finally, the three-dimensional model of the gating system design results is added to the casting model, and the three-dimensional template layout model is generated

3.1 plane parting

separate the casting models along the parting surface in order to obtain the three-dimensional model of the pattern in disa process. In the gating system design module, the three-dimensional model of the pattern is used for the design of template layout

3.2 ingate design and verification

the design principle of ingate in constant pressure and equal flow gating system is to make the cavities at different heights fill and fill at the same time. The difference of static pressure height leads to the difference of pressure and speed, so the ingate area at different height is different. The design calculation formula is:

pouring time t means the time required to fill the cavity connected with the ingate, rather than the time required for the whole pouring process. In disa process, in order to meet the needs of continuous pouring, the pouring time should be determined according to the molding speed of the machine. The calculation formula is:

t=t1-t2-t3 (2)

where: T1 - the time required to produce a mold (s)

t2 - mold transfer time, generally about 2S

t3 - time required for molten metal to fill the gating system

after obtaining the area of the ingate, the specific shape of the ingate should be designed and checked to meet the requirements of stable mold filling, because the shape of the ingate has an important impact on the flow resistance and flow state of liquid metal. The flow state of molten metal is quantitatively evaluated by calculating the turbulence coefficient, so as to check the specific geometric size of the ingate. The calculation formula of turbulence coefficient re is:

where: G - casting weight (kg)

t - pouring time (s)

p - perimeter of cross section (CM)

experience shows that when the turbulence coefficient re> 13800, the liquid is in a completely turbulent state, which should be absolutely avoided in the design of the ingate. The shape of the ingate in the system is set as Generalized Trapezoid (rectangle is also included). The design and verification module of the ingate allows users to repeatedly try the size of the turbulence coefficient under the same area, different heights and the ratio of the upper and lower bottom, until satisfactory design results are obtained. The design results are stored in the process project database

3.3 design of sprue and runner

the runner and runner in disa process adopt standard trapezoidal sprue. The geometric parameters of the standard sprue have been entered into the casting process database. The area of sprue and transverse sprue is calculated according to the following formula

sprue:

fs=1.1 × (n1.f1+n2.f2+... +nk.fk) (4)

runner:

fr=1.1 × Ns.fs (5)

where: N1, N2... NK - the number of ingates at each height connected with the sprue

f1, F2... FK - ingate area at each height

ns - number of sprues connected to the runner

after obtaining the sprue and runner areas, the program compares the areas with the standard sprue Series in the casting process database, and automatically matches the appropriate standard sprue

4 template layout design

first, under the part design environment of solid edge, the three-dimensional models of ingate, sprue and runner are automatically generated according to the calculation results. The method adopted is to modify the variable table in the corresponding 3D standard part modeling file established in advance, and obtain the 3D model of each gating system with appropriate size through size driving

then, assemble the gating system and pattern together in the assembly environment of solid edge to generate a three-dimensional template assembly model. Figure 7 is a three-dimensional model of the template assembly of the wheel hub. In the engineering drawing environment of solid edge, the generated 3D template assembly model can be easily converted into 2D engineering drawings. Through the process database query, the design size of each process can be obtained, and the process card can be automatically generated

Figure 7 wheel hub casting template layout three-dimensional mold

5 conclusion

with solid edge as the modeling platform, the casting process tooling CAD system expert-cad based on three-dimensional modeling is developed, which can carry out the process tooling design of disa vertical parting box free modeling for ductile iron parts. The main functions include the design of casting process parameters (machining allowance, draft angle, etc.), and the reflection of the design results to the three-dimensional model of the casting, the calculation of casting split modulus, weight, volume and the drawing of split modulus volume share diagram, the practical riser design of ductile iron parts, the design of vertical parting gating system, template design, etc. Design generated three

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