CN1595404A - Digitalized design method of rubber product extrusion die - Google Patents

Abstract

The invention discloses a digital design method of a rubber product extrusion die. Three steps are added between the die design and die processing of the original trial and error method, that is, the computer-aided engineering analysis of the die and the judgment whether the analysis result is There are three steps to meet the design requirements and modify the die design. The computer-aided engineering analysis of die is the key step of the present invention, mainly comprises: select suitable melt constitutive equation, obtain the parameter in the constitutive equation according to the rheological experiment fitting of rubber material; Utilize computer-aided design technology to establish geometry Model, perform grid division, and determine boundary conditions; select finite element numerical methods and calculation parameters, perform solution calculations, and perform deformation and stress analysis on the calculation results to determine whether the required die shape meets the design requirements. In this way, the design of the die is completed under the finite element environment, which can reduce the number of corrections of the die and improve the yield of rubber products. At the same time, the design of the extrusion die of rubber products does not rely on experience.

Description

Digital Design Method of Extrusion Die for Rubber Products

Technical field:

The invention provides a mold design method, in particular to a digital design method of a rubber product extrusion die.

Background technique:

In the prior art, the design and processing of the rubber product extrusion die adopts the trial and error method (see Figure 1), which consists of the following steps: die design (S1), die processing (S2), product trial production (S3 ), checking whether the shape of the product meets the design requirements (S4), and correcting the die (S5). Since S1 is carried out based on experience, it needs to be repeated many times from S3 to S5, so the product trial production time is too long and the cost is high; the unreasonable S1 will also make it difficult to improve the production yield.

In 1997, Xifeng Shangxiu and others used the finite element method (FEM) to simulate thermal shrinkage deformation of plastic products, and invented a metal mold design method for resin containers taken out of the metal mold before the resin was fully cooled (Chinese patent application number: 97190340.9 ). This technology only considers parameters such as thermal conductivity and linear expansion coefficient of the material, and is mainly used for the analysis of blow molding process of plastic products. Since this technique does not involve extrusion characteristics such as outlet expansion and wall surface slippage, it cannot be used to analyze the extrusion molding process of rubber products.

In 2002, Takahashi Shohei developed an auxiliary method for mold component design with computer-aided design (CAD) technology (Chinese patent application number: 02140024.5), and provided standard component data for professional manufacturers such as the mold body and mold accessories, etc., built into the mold design In the auxiliary system, it is a shape symbol with various attributes based on the processing standards (size, material, processing method, etc.) of a professional manufacturer. This technology provides design data with CAD intermediate files, and selects the mold body and mold parts that can be used. This technology is a special case of the application of CAD technology, and does not involve the design of extrusion dies for rubber products.

Invention content:

The present invention is made in view of the existing problems and deficiencies in the prior art, and its purpose is to provide a design method for the extrusion die of rubber products. The shape of the product manufactured by this method has the ability to compensate for the distortion caused by extrusion deformation shape. Another object of the present invention is to provide a die design method that does not rely on experience for extrusion die design.

Based on computer-aided design (hereinafter referred to as CAD) and computer-aided engineering (hereinafter referred to as CAE) technology, the present invention proposes a brand-new mold digital design method according to the characteristics of extrusion molding of rubber products, so as to obtain the required product shape and simultaneously obtain High-performance products with reasonable internal structure. Compared with the original technology, the computer-aided engineering analysis of the die is added, and the CAD/CAE technology is integrated.

For a better understanding of the technical solution of the present invention, the specific implementation is further described:

Figure 1 shows the process of designing the extrusion die of rubber products using the trial and error method. There are 5 steps in total, namely, die design (S1), die processing (S2), product trial production (S3), and checking whether the product shape conforms to Design requirements (S4) and correct die (S5). Fig. 2 is the digitized design process of the rubber product mold of the present invention, compared with the trial and error method shown in Fig. 1, between S1 and S2, has increased die CAE analysis (S6)-judging whether the analysis result meets the design requirement (S7 )-correction die design (S8) three steps, wherein S6 is the key step of the present invention. S6 can be described in detail in Figure 3, mainly including 7 steps, which are as follows: set the mathematical model parameters (S61), first select the appropriate fluid constitutive equation according to the rheological properties of the rubber material, and then select the appropriate fluid constitutive equation according to the rheological experiment of the rubber material Fit the parameters in the constitutive equation; use CAD technology to establish a geometric model (S62) according to the design drawings of the product; establish a physical model (S63), import the geometric model into the FEM interface, perform grid division, and determine the boundary condition type; Solving and calculating (S64), selecting the appropriate finite element numerical method and calculating parameters, and performing solving and calculating; result analysis (S65), performing post-processing analysis on the calculated results, and performing deformation analysis and stress analysis; analyzing on the basis of S65 , judging whether the required die shape meets the requirements (S66), if the requirements are met, the calculation ends; if the requirements are not met, the calculation parameters are corrected (S67), and S64-S66 is repeated until the design requirements are met.

Adopting the invention can not only shorten the new product development period and reduce the production cost, but also can optimize the extrusion production process and improve product performance and quality. The invention can be used for the research and development of new products of rubber products, and can also be used for the improvement of the performance of existing products, to find out the reasons for the defects in the products in the processing process, and to propose measures to improve the structural design and processing technology, which is an effective and fast extrusion method. Design method of export die.

Description of drawings:

Figure 1 is a flow chart of the design process of rubber product extrusion die trial and error method

Figure 2 is a flow chart of the digital design process of the extrusion die of rubber products

Figure 3 is a flow chart of the CAE analysis process of the extrusion die of rubber products

Figure 4 is a diagram illustrating a two-dimensional geometric model of a rubber product

Figure 5 is a diagram illustrating the three-dimensional finite element analysis model and boundary conditions

Figure 6 is a graph of the shape of the extrudate predicted according to the extrusion die

Figure 7 is a mold shape diagram designed according to the shape of the product

Detailed ways:

Through the following examples, to further illustrate the present invention's substantive characteristics and remarkable progress, but not limit the present invention

the scope of the invention.

Example 1

Referring to Fig. 3, it is illustrated that the present invention calculates the shape of the extrudate according to the geometric shape of the mold, and determines the deformation law of the extrudate.

1 Establishing a mathematical model (S61)

Usually rubber melt can be simplified as a viscoelastic incompressible fluid, and its flow governing equation can be expressed as

Mass Conservation Equation:

·v=0

Momentum Conservation Equation:

$\mathrm{<span\; class="notranslate">\; Re</span>}\frac{\mathrm{<span\; class="notranslate">\; dv</span>}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; \&dtri;</span><span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; \&dtri;</span><span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; f</span>}$

Where v is the velocity, Re is the Reynolds quasi-number, p is the pressure, f is the body force, and τ is the deviatoric stress when the viscoelastic fluid flows.

fluid constitutive equation

The rubber melt can be represented by the Phan-Thien-Tanner (PTT) model of the differential viscoelastic constitutive equation. The PTT model is derived from the network theory, and it contains two nonlinear terms at the same time: F _c (τ, D) and F _d (τ).

F _c (τ, D) = ξ(D·τ·D ^T )

In the formula, D is the deformation rate tensor, which can be expressed as $\mathrm{D.}=\frac{1}{2}(L+L^T),$ L is the velocity gradient tensor, which can be expressed as L=v.

The introduction of F _c can describe the non-affine deformation of the polymer melt, where 0 ≤ ξ ≤ 2 has an impact on the slippage of macromolecular coils, which can lead to shear thinning of the melt, ξ=0 and ξ= 2 represent the upper and lower satellite derivatives respectively, and ξ=1 is the co-transmission number.

F _d (τ) is related to the rate of melt coil formation and unentanglement, and it has two forms:

$\mathrm{<span\; class="notranslate">\; PTTa</span>}<span\; class="notranslate">\; :</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{\frac{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}{\mathrm{<span\; class="notranslate">\; G</span>}}\mathrm{<span\; class="notranslate">\; tr</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; )</span>}$

$\mathrm{<span\; class="notranslate">\; PTTb</span>}<span\; class="notranslate">\; :</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}{\mathrm{<span\; class="notranslate">\; G</span>}}\mathrm{<span\; class="notranslate">\; tr</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&tau;</span>}<span\; class="notranslate">\; )</span>$

where ε mainly affects the steady-state extension, resulting in a decrease in the extensional viscosity. The difference between PTTa and PTTb is that PTTa can predict the extensional thinning characteristics of the melt at the extension rate, while PTTb can only obtain a plateau of infinite extensional viscosity.

2 establish the geometric model of die (S62)

Because the cross-sectional shape of the product is relatively complex, firstly use CAD to establish a two-dimensional geometric model. Figure 4 is a two-dimensional CAD geometric model of rubber products.

3 Establish a physical model, perform grid division, and set boundary conditions (S63)

The 2D CAD geometric model is imported into the finite element, and the finite element mesh is divided to obtain the 3D finite element analysis model, as shown in Figure 5. The analysis model is divided into two areas: SD1 is the extrusion die area, and SD2 is the extrudate area.

In the analysis, four types of boundary conditions are set:

The first boundary condition is the inlet flow, assuming that the flow at the entrance of the die is fully developed, such as

Q ₀ =5000m ³ /s.

The second boundary condition is the wall surface of the extrusion die, assuming there is no slip on the surface, so it can be set as: normal velocity v _n =0 and tangential velocity v _s =0.

The third boundary condition is the extrudate free surface, satisfying v·n=0, where n is the surface normal vector.

The fourth boundary condition is the outlet. For viscoelastic fluids, it can be set as normal force f _n =0 and tangential force f _s =0, and a tensile velocity can also be added, such as v _x =0, v _y = 0 and v _z = 58 m/s.

5 Model Solving (S64)

The numerical simulation in the solution area is carried out by the finite element numerical method, and the Galerkin correction method is used. The calculation parameters adopt the evolutionary algorithm (Evolution) to solve the nonlinear problem caused by the free surface.

6 Calculation result analysis (S65)

Figure 6 shows the shape of the extrudate predicted according to the extrusion die. The shape of the extrudate is smaller than that of the extrusion die under the action of stretching.

Example 2

Referring to FIG. 3, the present invention is illustrated to calculate the die geometry according to the desired extrudate shape (ie, product shape).

The geometry of the mold is calculated according to the shape of the extrudate, and the calculation process is basically the same as that of Example 1. The calculation steps of Example 1 are S61-S65, and the calculation steps of Example 2 are increased by S66 and S67. Calculation step S66 is to judge whether the required die shape satisfies the design requirements according to the calculation results. If the requirements are met, the calculation ends; if not, the calculation parameters are corrected (S67), and S65 is repeated until the design requirements are met. Figure 7 shows the calculated die shape from the shape of the extrudate.

Since the calculation purposes of Embodiment 2 and Embodiment 1 are different, their grid reset areas are different, and the area settings are shown in Figure 5.

(1) In Example 1, the shape of the extrudate is predicted according to the extrusion die, the position of the die area is determined, and the position of the extrudate area is uncertain, so only the extrudate area is re-meshed place.

(2) In embodiment 2, the geometry of the mold is calculated according to the shape of the extrudate. Since the positions of the die and the extrudate are uncertain, it is necessary to carry out the two regions of the extrudate area and the die area. Grid reset.

Example 3

The setting mathematical model parameters (S61) in Fig. 3 illustrates the method for determining the constitutive model parameters of different rubber materials.

In order to determine the constitutive model parameters, the following rheological experiments are required:

(1) Capillary rheometer experiment: used to determine the relationship between shear rate and viscosity in the high shear rate range;

(2) Rotational rheometer experiment: used to determine the relationship between shear rate and viscosity in the low shear rate range;

The parameters in the constitutive model can be obtained by fitting the rheological experimental data of the rubber material. Table 1 shows the material parameters of the PTT model of EPDM and SBR, which can be used to simulate the rubber extrusion process. Fig. 6 and Fig. 7 are calculation results obtained by using the PTT model according to the material parameters of EPDM in Table 1.

Table 1 unit EPDM SBR Shear viscosity (η ₁ ) Pa.s 2400000 2800000 Relaxation time (λ) the s 3.16 2.1 Material constant (ε) 0.008 0.006 Material constant (ξ) 0.99 0.87 Viscosity ratio (r) 0.2 0.3

Example 4

The effect of the digital design process of the rubber product mold of the present invention is illustrated with reference to Fig. 2 . Compared with the trial and error method shown in Fig. 1, the design method of the present invention adds die computer-aided engineering analysis (S6) between S1 and S2, judges whether the analysis result meets the design requirements (S7) and corrects the die design (S8) Three steps.

Embodiment 2 has illustrated the step of calculating the geometric shape of the mold according to the shape of the extrudate, on this basis, it is judged whether the analysis result meets the design requirements (S7), if the requirements are met, the calculation ends, if not, then the die design is corrected ( S8), repeating S6 until the design requirements are met.

Carry out extrusion die processing (S2) of rubber products according to the calculation results, and then carry out product trial production (S3) and modify the die (S5) until the shape of the product meets the design requirements. Table 2 is a comparison of the effects of the die design and the trial and error method carried out by the present invention.

Table 2 Die correction times (times) Die manufacturing time (days) Die debugging cost (10,000 yuan) Comparison method (trial and error method, Figure 1) 6 18 12 Design method of the present invention (Fig. 2) 2 6 4 difference 4 12 8 Difference/trial and error method×100 67 67 67

As can be seen from Table 1, by carrying out the die design of the present invention, the number of die correction times, the die manufacturing time and the die debugging cost are all reduced by 67% compared with the trial and error method, the product development cycle is shortened, the cost is reduced, and the product quality is improved. Competitiveness.

Claims (2)

1. the digitalized design method of rubber extrusion neck ring mold, it is characterized in that than having increased by three steps between the mouth mould design of original try and error method and mouthful mould processing, promptly whether computer-aided engineering analysis, the discriminatory analysis result of mouthful mould meet design requirement and revise mouthful three steps of mould design, wherein the computer-aided engineering analysis of mouthful mould comprises seven steps, be that mathematical model parameter is set successively, elder generation is according to the rheological characteristics of elastomeric material, select suitable fluid constitutive equation, obtain parameter in the constitutive equation according to the rheological experiment match of elastomeric material again; Utilize Computer-aided Design Technology to set up geometric model according to the design drawing of product; Set up physical model, geometric model is imported in the finite element interface, carry out grid dividing, determine the boundary condition type; Select suitable finite element numerical method and calculating parameter, find the solution calculating; Result of calculation is carried out reprocessing analysis, carry out deformation analysis, stress analysis; Judge whether mouthful mould shape of asking meets the demands; Carry out the calculating parameter correction.

2. the digitalized design method of rubber extrusion neck ring mold as claimed in claim 1, it is characterized in that mouthful mould shape does not comprise because of extruding expands and distortion that tractive force causes or comprise because of extruding the distortion that expansion and tractive force cause.

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