Analysis on the uniformity of temperature field of direct heating mold for composite material curing process
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摘要: 针对复合材料固化成型工艺的直热模具温度场均匀性进行了研究。建立模具温度场和复合材料固化反应温度场的耦合传热学模型,并对该模型进行有限元建模仿真分析。针对影响模具表面温度均匀性的主要因素,即电加热管的间距和功率,设计正交试验优化,优化后模具表面最大温差为3.5℃,达到行业标准。此外,对影响温度场均匀性的其他因素,即加热管与模具的接触热阻、复合材料层合板厚度进行了探讨,接触热阻的存在使得模具表面最大温差达到7.24℃,模具加热到指定温度多用时800 s,降低了效率。研究层合板对模具温度均匀性的影响时发现未加入复合材料时模具表面最大温差为4.44℃,加入层合板耦合后最大温差为3.5℃;厚度为毫米级时,层合板对直热模具表面温度均匀性影响不大。Abstract: The uniformity of the temperature field of the direct heating mold of the composite material curing molding process was studied. A coupled heat transfer model of mold temperature field and composite material curing reaction temperature field was established, and finite element modeling and simulation analysis was performed on the model. In view of the main factors that affect the uniformity of the mold surface temperature, which are the distance and power of the electric heating tube, the orthogonal experiment was designed to optimize, and the maximum temperature difference of the mold surface after optimization was 3.5℃, which reached the industry standard. In addition, other factors that affect the uniformity of the temperature field, the thermal resistance of the contact between the heating tube and the mold, and the thickness of the composite laminate were discussed. The existence of contact thermal resistance makes the maximum temperature difference of the mold surface reach 7.24℃, and it takes 800 s to heat the mold to the specified temperature, which reduces the efficiency. When studying the effect of laminates on mold temperature uniformity, it is found that the maximum temperature difference on the mold surface without composite materials is 4.44℃; the maximum temperature difference after coupling with laminates is 3.5℃, and the thickness of the laminate is millimeter-level. The uniformity has little effect.
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表 1 干空气热物理性质
Table 1. Thermal physical properties of dry air
Temperature/℃ $\lambda /({10^2}{\rm{W}} \cdot {({\rm{m}} \cdot {\rm{K}})^{ - 1}})$ $v/({10^6}{{\rm{m}}^2} \cdot {{\rm{s}}^{ - 1}})$ ${P_{\rm{r}}}$ 20 2.59 15.06 0.703 60 2.90 18.97 0.696 90 3.13 22.10 0.690 Notes: $\lambda $—Thermal conductivity of dry air; $v$—Acceleration of dry air; ${P_{\rm{r}}}$—Prandtl Number. 表 2 M21预浸料的基本参数
Table 2. Basic parameters of M21 prepreg
ρc/(kg·m−3) Cc/(J·(kg·K)−1) hc/mm Vc/wt% kc/(W·(m·K)−1) 1580 926 0.184 ${V_{\rm{f}}}$=59.2
${V_{\rm{r}}}$=40.8${\lambda _{\rm{P}}}$=2.56
${\lambda _{\rm{T}}}$=1.48Notes: ρc—Density of M21 prepreg; Cc—Specific heat capacity of M21 prepreg; hc—Thickness of every piece of prepreg; ${V_{\rm{c}}}$—Volume fraction; ${V_{\rm{f}}}$—Volume fraction of carbon fiber; ${V_{\rm{r}}}$—Volume fraction of epoxy resin; kc—Thermal conductivity of M21 prepreg; ${\lambda _{\rm{P}}}$—Thermal conductivity of the prepreg along the fiber direction; ${\lambda _{\rm{T}}}$—Thermal conductivity of the prepreg perpendicular to the fiber direction. 表 3 结构钢的物性参数
Table 3. Physical parameters of structural steel
${\rho _{\rm{m}}}$/
(kg·m−3)${C_{\rm{m}}}$/
(J·(kg·K)−1)km/(W·(m·K)−1) 20℃ 120℃ 205℃ 7850 434 60.4 55.9 52.1 Notes: ρm—Density of structural steel; Cm—Specific heat capacity of structural steel; km—Thermal conductivity of structural steel. 表 4 加热管具体参数
Table 4. Heating tube specific parameters
L1/mm L2/mm L3/mm P1/W P2/W P3/W 33 66 40 300 300 300 表 5 正交实验前加热管设置
Table 5. Heating tube setting before orthogonal experiment
L1/mm L2/mm L3/mm P1/W P2/W P3/W 33 66 25 300 300 400 表 6 正交试验因素水平
Table 6. Orthogonal test factor level
Level Factor L1/mm L2/mm P1/W P2/W 1 35 70 350 250 2 39 66 300 300 3 43 62 250 350 表 7 正交试验方案及结果
Table 7. Orthogonal test plan and results
Test number Factor Maximum temperature
difference/℃L1/mm L2/mm P1/W P2/W 1 1 1 1 1 6 2 1 2 2 2 5.11 3 1 3 3 3 4.82 4 2 1 2 3 4.65 5 2 2 3 1 3.51 6 2 3 1 2 6.39 7 3 1 3 2 4.51 8 3 2 1 3 5.46 9 3 3 2 1 3.95 表 8 正交实验极差分析
Table 8. Orthogonal experiment range analysis
Variable Factor L1/mm L2/mm P1/W P2/W ${K_1}$ 15.93 15.16 17.85 13.46 ${K_2}$ 14.55 14.08 13.71 16.01 ${K_3}$ 13.92 15.16 12.84 14.93 Excellent level 3 2 3 1 R 2.01 1.08 5.01 2.55 Order C>D>A>B Notes: ${K_i}(i = 1,2,3)$—Sum of the i-th level test indicators of each factor, R—Extremely poor, that is, the difference between the maximum value and the minimum value of ${K_i}$ in each column. -
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