The design of the insulation layer and energy consumption optimization of the injection mould for the motor commutator

The injection molding of the motor commutator requires a long-term high-temperature operation, which poses a problem of high energy consumption. The heating zone is located behind the mold, and there is thermal radiation and convection during heating, resulting in uneven temperature distribution. To solve the above problems, an automatic lifting and insulation mechanism is proposed. An insulation frame is built with an aerogel insulation layer inside. It is connected up to the upper table of the machine, moving up and down during processing, and connected down to the crank slider mechanism. Simulation software analyzes its insulation and temperature distribution and, through experimental verification, compares the temperature distribution and energy consumption of injection molds before and after the installation of insulation mechanisms. The experimental and simulation results show that using the automatic lifting insulation layer design scheme can effectively reduce energy consumption, improve temperature distribution unevenness, and increase the yield rate.


Introduction
Commutators are one of the core components of electric motors, and new energy vehicles have a great demand for motors [1].At present, industrial production of commutators is achieved through hightemperature die-casting of molds, which consumes a huge amount of energy [2].There is an urgent need to transform traditional high-energy consumption production methods.Domestic and foreign enterprise engineers and scholars have proposed various solutions for optimizing the energy consumption of injection molds.Bai et al. [3] recommended a series of correction coefficients to convert into the thermal resistance required for insulation structures in order to obtain the insulation layer thickness required for the mold to achieve the desired insulation effect.Zhou et al. [4] used the test scheme of economic thickness, double-profiled materials, and composite insulation structure for the oil steam pipeline to reduce the heat loss.They confirmed that the aerogel felt insulation structure can effectively reduce the thickness of the insulation layer and improve the pipeline layout efficiency.The insulation structure design of the motor commutator molding mold is mostly focused on patents, such as the utility model patent for the "mold insulation structure" of Zhengtai Electric Co., Ltd.[5].It covers the insulation board and is fixed and connected to the outer wall of the mold with a simple structure.Kunshan Nengshengyuan Energy saving Equipment Co., Ltd. has disclosed an industrial mold insulation structure [6], which is equipped with an insulation sleeve on the outer side of the heating chamber and an insulation layer inside the mold column to prevent excessive temperature reduction and ensure smooth injection molding.The above article and patent's insulation and energy-saving solutions can only be applied to the outer side of molds with simple structures, and the material's insulation performance is average.In this paper, aiming at the mold with complex structure and frequent movement in actual production [7], an automatic lifting mechanical structure is designed.The aerogel insulation layer with excellent thermal insulation performance is added to reduce the heat exchange between the high-temperature mold and the lowtemperature external environment, improve the uneven temperature distribution, and achieve the purpose of energy saving and improving the yield.

Mold die-casting process flow and principle
The research object of this article is an injection molding die-casting machine for a new energy vehicle commutator mold in a certain enterprise.The machine places the upper mold, middle mold, feeding, and lower mold in sequence between the upper and lower bottom plates.Heating rods are inserted into the upper, middle, and lower molds.After being powered on, the injection mold is heated using the principle of resistance heating.Contact thermocouples are installed in each area to control heating on and off as the temperature changes.

Energy consumption issues in injection molds
At present, a certain enterprise uses a resistance heating mold method, which has the following problems: Firstly, the working temperature of injection molds is high and needs to be maintained between 170ႏ and 240ႏ.High-temperature molds will generate a radiation heat transfer to the surrounding air, causing the working environment temperature to increase gradually.The workshop needs to use fans to cool down, resulting in secondary energy waste.At the same time, in order to maintain the specified working temperature of the mold, the resistance heating source needs to work frequently, resulting in serious heat loss; Secondly, the heating rod is horizontally inserted into the back half of the mold, and the front half can only be heated by metal heat conduction, resulting in insufficient melting of the front material during temperature control and an increase in defect rate [8].

Structural design of insulation layer
The insulation layer is drawn using SOLIDWORKS and is assembled onto the injection mold, as shown in the 3D diagram below.

Thermal simulation comparative analysis
In this paper, Fluent in ANSYS is used for simulation [10].The mold material is low-carbon steel, and the thermal insulation material is aerogel felt.The eight holes on the back of the 3D model mold simulate the 580ႏheating rod.Steady-state thermal simulation is used to simulate the temperature distribution in the processing phase.During post-processing, the thermal insulation mechanism is hidden to make the temperature cloud more intuitive.3, the surface temperature of the mold is higher after adding an insulation layer, and the insulation structure retains most of the heat.
In the post-processing, the thermal energy of the injection mold after heating was also calculated.The heating power of molds without an insulation layer is 2.08×106 W/m 3 ; with an added insulation layer, the heating power of the mold is 1.56×10 6 W/m 3 .Ș indicates the insulation efficiency of the insulation layer.

Protocol
Based on the above analysis results, an insulation prototype is built and experimented.The experiment is divided into mold testing with and without an insulation layer, conducted at room temperature of 25ႏ, and the electricity consumption and temperature during the heating and processing stages are measured separately.An electricity meter is installed to measure electricity consumption.A thermocouple is installed to measure the temperature at the monitoring point, as shown in Figure 4.

Comparison of experimental results
The experimental results are divided into two stages: heating and processing, and the experimental data with and without insulation layers are compared.The heating time and total electricity consumption are measured during the heating stage, and the results are shown in Table 1.The experiment in the processing stage is conducted over three days, twice a day, from 8 am to 11 am and from 1 pm to 4 pm.The electricity consumption during the processing stage is measured every three hours and the average hourly electricity consumption is calculated.The results are shown in Table 2.
Table 2 The experiment showed that after the installation of the insulation layer, the heating stage shortened the heating time by 33.33%, reduced the electricity consumption by 27.97%, and reduced the electricity consumption by 26.32% in the processing stage.The insulation efficiency in the result is 25%.
The experimental temperature measurement with and without insulation layer is shown in Figure 5.

Conclusions 1)
The insulation mechanism designed in this article can operate stably on the machine without affecting processing and production and has good reliability.
2) The finite element thermal simulation obtained an ideal insulation efficiency of 25% and a uniform temperature distribution, which was verified through temperature measurement experiments at multiple locations.
3) By analyzing and comparing the experimental results, it was found that the installation of an automatic lifting structure with an insulation layer and a compression-resistant insulation board can reduce heating time by 33% and electricity consumption by 28% during the heating stage and reduce electricity consumption by 26% during the processing stage.This verified the reliability of the simulation results and proved that the insulation mechanism has a good insulation effect.
4) The experiment has limitations and did not consider the impact of adverse weather on insulation performance.Only a few temperature points can be measured, and the overall temperature field cannot be obtained.

Figure 2 .
Figure 2. 3D drawing of the injection mold and insulation mechanism.The insulation layer consists of a heavyweight and pressure-resistant insulation board on the top and a lightweight insulation layer with a mechanical structure on the side, consisting of three layers: upper, middle, and lower.The middle insulation layer is designed to move along with the movement of the upper workbench, and the upper and lower insulation layers are respectively fixed on the upper and lower machine countertops.The guide rail and slider are drawn as standard parts.Adjustable screws and fisheye joints are used to connect the double support columns and two connecting rods.The upper and lower countertops are blocked from heat transfer by installing mold-specific insulation boards with excellent compression resistance[9].

Figure 3 .
Figure 3. Temperature distribution diagram of molds: (a)without insulation layer; (b) with insulation layer.Comparing Figure3, the surface temperature of the mold is higher after adding an insulation layer, and the insulation structure retains most of the heat.In the post-processing, the thermal energy of the injection mold after heating was also calculated.The heating power of molds without an insulation layer is 2.08×106 W/m 3 ; with an added insulation layer, the heating power of the mold is 1.56×10 6 W/m 3 .Ș indicates the insulation efficiency of the insulation layer.

Figure 5 .
Figure 5. Temperature curve diagram: (a) the front of the mold; (b) the back of the mold.

Table 1 .
Comparison table of experimental results during heating stage.

.
Comparison table of experimental results during the processing stage.