Adapter molding and heat transfer analysis

In this paper, we investigated the excessive thermal stress caused by the difference in the coefficient of thermal expansion of the material during the molding process of the adapter. It has led to the bulging phenomenon during the high and low-temperature tests. We analyzed the heat transfer mechanism of the adapter during the high and low-temperature tests by using finite element simulation. We then analyzed the causes of the bulging phenomenon. We successfully solved the bulging problem by using the method of heating up the foamed adapter together with the mold for curing, which provided a new idea for adapter molding.


Introduction
The adapter studied in this paper is installed between the missile and the launch box.It provides support for the missile and provides damping for the missile when the launch box is subjected to shock or vibration.It guides the missile during launch.It seals the missile gas flow in the launch box and plays an extremely important role in the storage, transportation, loading, unloading, and launch of the missile [1][2][3][4][5].The commonly used cushioned cartridge adapter has high efficiency in space utilization, a simple manufacturing process, easy installation, etc. [6][7][8].The cushioned adapter mostly consists of two parts: a bearing base and a buffer layer.
In this paper, the heat transfer mechanism of the adapter molding process is studied by the finite element method.The causes of the bulging deformation of the adapter during the high and lowtemperature tests are analyzed.The method of heating and curing the foamed adapter together with the mold is adopted.It successfully releases the excessive thermal stress generated by thermal expansion and solves the bulging problem, providing a new method for adapter molding.

Adapter structure, molding process, and test
The adapter is an important part of the missile cold launch system, which mainly plays a supporting, fixing, and balancing role for the bullet during the transportation and storage after the missile is loaded into the launch tube.The adapter is mainly composed of a base, adapter layer (NBR), sleeve, and spring.The external dimension is 320×200×60 mm.The structure of the adapter is shown in Figure 1, where the base is made of patterned rubber composite plate (hereinafter referred to as patterned rubber plate) / polyurethane foam/positioning pin seat co-curing molding, the sleeve, spring, and adapter layer are external parts; the base and adapter layer are glued together by LD01.The spring and the sleeve are   The base is mainly composed of a positioning pin holder, polyurethane foam, and a patterned rubber composite plate.The structure is shown in Figure 3.The supporting situation of each part is shown in Table 1, in which the positioning pin holder structure is cylindrical with a supporting ear structure.The structure is shown in Figure 4.The main process of the base is to fix the positioning pin holder and patterned rubber composite plate on the mold.Then, the polyurethane raw material isocyanate Suprasec5005 is poured, and combination resin AP0301-SF is poured into the mold after mixing by a two-component high-pressure foaming machine.The mold is locked in a -5~50℃ environment for more than 2 h.It is then de-molded after the trimming and inspection process in the warehouse.High and low-temperature storage tests are conducted.It is found that the front adapter, front adapter-m, rear adapter, and rear adapter-m at high temperature +65 ℃ after 12 h appeared bulging.After the test, the appearance of the adapter was inspected.It was found that the adapter bulge was mainly located at the face of the patterned rubber-plastic composite board and the small end bevel.After dissection, the internal foam of the adapter appeared to be separated from the metal parts between the positioning pin seat and the internal foam separation of the bulge in two cases.The anatomical situation is shown in Table 2. Anatomical results show that the bulge on the surface of the patterned rubber composite plate is mainly located in the buried parts of the adapter.The location of the adapter bulge is shown in Figure 5 and Figure 6 (red circle parts) below.
Table 2. Summary of problem products and anatomy.

Finite element model
The adapter was modeled, and finite element meshing was performed using Abaqus with tetrahedral cells.The cell number is 538034.The finite element model is shown in Figure 7.

Material parameters
Table 3 shows the performance parameters of the materials used.Table 3. Material performance parameters.

Constraint and loading case
Figure 8 shows the loading and constraint schematic for this working condition.In Figure 8, the adapter applies thermal convection boundary conditions to all surfaces with a convective heat transfer coefficient of 20 W/m 2 ꞏK.In Figure 8, the z-direction constraint is at point 1, the solid support constraint is at point 2, and the y-direction constraint is at point 3.Because the thermal emissivity of foam and aluminum alloy is too small, the effect of thermal radiation is not very large.Hence, it is ignored here.

Mechanical Analysis
The adapter consists of a positioning pin holder/polyurethane foam/patterned rubber sheet/adaptation layer, which contains three materials in total.Due to the different thermal conductivity of the three materials, there are differences in the surface and internal temperature fields of the polyurethane foam during the warming process.The simulation was carried out according to the condition that the air is heated up to 65℃ at a rate of 1 ℃/min starting from 20℃.The results are shown in the figure below, where the temperature decreases from the red area to the blue area in order.The results show that when the air temperature reaches 65℃, due to the low thermal conductivity of polyurethane foam, patterned rubber composite plate, and adaptor layer, the surfaces of base polyurethane foam, patterned rubber composite plate, and adaptor layer are heated quickly.The temperature is close to the air temperature.The positioning pin seat has high thermal conductivity and fast heat transfer.The temperature of the whole positioning pin seat is uniform but lower than the air temperature.This indirectly provides a heat source for the interior of polyurethane foam to heat it.Therefore, the temperature inside the base is higher near the positioning pin seat, and the heating effect gradually decreases along the direction of the lug axis.The temperature of the parts is farther away from the base surface, and the positioning pin seat is lower.The lowest temperature point is on the polyurethane foam near the patterned rubber plate.The maximum temperature difference is up to 40℃ and is distributed in a stepped manner.
When the surface temperature of the adapter is heated to 65℃, due to the large temperature difference inside the adapter, the temperature of the polyurethane foam near the locating pin holder is higher.The temperature of the polyurethane foam at the part far from the locating pin holder is lower, and the expansion is smaller.The temperature of the beveled surface of the polyurethane foam in the adapter is higher.The foam expands along the beveled surface, while the temperature of the surface near the patterned rubber sheet is lower.The expansion is smaller, resulting in the tendency of the product to warp away from the beveled surface.The displacement cloud diagram is shown in Figure 11.The displacement trend diagram is shown in Figure 12.The displacement increases from red to blue in order.

Solution
In order to suppress the thermal stress, the curing process was improved by directly heating the mold in the oven at 65℃ for 6 h without curing at room temperature after casting.The mold is used to resist the thermal stress caused by thermal expansion.The problem of bulging after the heating of the adapter oven was successfully solved.

Conclusion
In this paper, we analyzed the cause of the bulging problem caused by the conventional adapter molding method through the finite element method.This is mainly due to the excessive thermal stress caused by the difference in the coefficient of thermal expansion, which is between the metal used in the adapter and the polyurethane foam during the curing at room temperature.It is also due to the bulging phenomenon caused by the release of the mold.In response to this analysis, the method of curing the foamed adapter together with the mold at elevated temperatures successfully released the excessive thermal stresses.It provided a new method for the adapter molding process.
.1088/1742-6596/2713/1/012075 2 glued together by mechanical structure.The adapter molding process flow chart is shown in Figure2.The double dotted line area is the base molding process.

Figure 2 .
Figure 2. Flow chart of adapter production.

Figure 3 .
Figure 3. Schematic diagram of the base structure.

Figure 4 .
Figure 4. Schematic diagram of the structure of the positioning pin holder.

Figure 5 .
Figure 5. Diagram of the location of the bulge.

Figure 6 .
Figure 6.Diagram of the package location.

Figure 9 .
Figure 9. Temperature distribution of the adapter profile.

Figure 10 .
Figure 10.Polyurethane foam profile temperature distribution

Figure 11 .
Figure 11.Displacement cloud of polyurethane foam after heat (Arithmetic results trend magnified 100 times).

Figure 12 .
Figure 12.Schematic diagram of the displacement trend of the adapter base after heat.Due to the difference in expansion amount in each area inside the polyurethane foam, stress concentration is generated at the support lug and the sloping surface.The stress cloud diagram is shown in Figure13and Figure14.Due to the low degree of maturation, the mechanical properties of the product have not yet reached the maximum.The thermal stress and the material's stress exceed the strength of the polyurethane foam itself to form cracks.The gas gathers at the cracks.The gas expands after being heated to form a bulge.The bulge part gradually pulls off the bottom surface of the positioning pin seat and the part of the positioning pin seat.In serious cases, the positioning pin seat and the bottom surface of the positioning pin seat are completely detached.The diagram of the bulging situation in each stage is shown in Figure15.

Figure 13 .
Figure 13.Stress distribution in the adapter profile

Figure 14 . 15 .
Figure 14.Stress distribution in the polyurethane foam profile.

Table 1 .
Summary of base parts.
NumberName Materials and Sources 1 Patterned rubber composite panel Nitrile rubber over PTFE film, purchase 2 Positioning pin holder Aluminum 2A12-T4, strip processing 3 Polyurethane foam Polyurethane foam