CN114074397A

CN114074397A - High-pressure injection molding process of HFI nozzle

Info

Publication number: CN114074397A
Application number: CN202111359929.XA
Authority: CN
Inventors: 王友明
Original assignee: Wuxi Longsheng Technology Co Ltd
Current assignee: Wuxi Longsheng Technology Co Ltd
Priority date: 2021-11-17
Filing date: 2021-11-17
Publication date: 2022-02-22

Abstract

The invention discloses a high-pressure injection molding process of an HFI nozzle, which comprises the following steps: s1, increasing the material hardness of the injection molding product; s2, setting key parameters of the equipment through modular flow analysis and simulation; optimizing a high-pressure injection molding process, and locking process parameters by comparing the variation of the product size before and after injection molding under different limit working conditions; s3, injection molding; the injection molding is divided into five stages of material plasticizing, injection, pressure maintaining, cooling and demolding. The injection molding process at each stage is reasonably arranged, so that the injection molding defect can be avoided, the product precision and the production efficiency are improved, the high-pressure injection molding process is optimized, and the deformation of an injection molding piece is avoided.

Description

High-pressure injection molding process of HFI nozzle

Technical Field

The invention relates to the technical field of high-pressure injection molding methods of nozzles, in particular to a high-pressure injection molding process of an HFI nozzle.

Background

Natural gas engines typically employ an open combustion chamber, i.e., a spark plug directly ignites a mixture of fuel gas and air in the combustion chamber. One path of air inlet, namely fresh air and fuel gas are mixed by a mixer and then enter an air inlet pipe, and then enter each cylinder through an air passage of the cylinder cover. The gas is sprayed out from a natural gas nozzle, which is an actuating mechanism for adjusting the air intake flow of the engine.

In the production process of the natural gas nozzle, in order to achieve the purposes of local protection of a product and matching with a client plug, a high-pressure injection molding process is needed to wrap a pre-assembly body, and the product is guaranteed to have the characteristics of high temperature resistance, corrosion resistance, pressure resistance, smooth butt joint and the like.

However, the high-pressure injection molding process parameters are improperly set, so that the injection molded part is deformed, the movable iron core of the internal movable part moves unsmoothly, and the flow performance of the product is finally influenced. As shown in fig. 9, when the parameters of the high-pressure injection molding process are improperly set, the internal matching condition of the part is observed through cutting the product and CT scanning, and the deformation of the thin-wall part is found.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a high-pressure injection molding process of an HFI nozzle, which aims to solve the problems in the background art, optimize the high-pressure injection molding process and avoid the deformation of an injection molding part.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows.

A high-pressure injection molding process of an HFI nozzle comprises the following steps:

s1, increasing the material hardness of the injection molding product;

s2, setting key parameters of the equipment through modular flow analysis and simulation;

optimizing a high-pressure injection molding process, and locking process parameters by comparing the variation of the product size before and after injection molding under different limit working conditions;

s3, injection molding; the injection molding is divided into five stages of material plasticizing, injection, pressure maintaining, cooling and demolding.

Further optimizing the technical scheme, the key parameters of the equipment comprise: injection molding pressure, screw speed, pressure maintaining pressure, barrel temperature, mold cavity temperature, dryer temperature and mold locking force.

Further optimizing the technical scheme, the process of carrying out simulation comprises the following steps:

setting the temperature of the melt, performing pressure maintaining switching when the melt is filled to 90% of the volume of the cavity, setting pressure maintaining pressure according to the maximum injection molding pressure, and setting pressure maintaining time;

setting the cooling time of a product in a mold cavity and the temperature of mold cooling water;

and respectively carrying out simulation calculation on different injection molding time, and analyzing the influence of the injection rate on the cavity pressure and the fiber distribution on the surface of the product.

Further optimizing the technical scheme, in the step S2, the optimizing the high-pressure injection molding process comprises the following steps:

s21, detecting the diameter, roundness and cylindricity of the pipe under different injection molding pressures, and comparing the diameter, roundness and cylindricity of the pipe before and after injection molding;

s22, selecting injection molding pressure based on the step S21, and increasing the sample size;

and S23, tracking the moving smoothness of the movable iron core of the nozzle, and tracking the failure rate of the static flow and the dynamic flow of the subsequent flow detection station.

Due to the adoption of the technical scheme, the technical progress of the invention is as follows.

The injection molding process at each stage is reasonably arranged, so that the injection molding defect can be avoided, the product precision and the production efficiency are improved, the high-pressure injection molding process is optimized, and the deformation of an injection molding piece is avoided.

According to the invention, the key parameters of the equipment are set through mold flow analysis and simulation, so that the fact that the injection molding pressure required is larger when the injection molding time is shorter is obtained; in order to avoid product deformation caused by melt impact during injection molding, the melt filling time is properly increased to reduce the injection pressure, but after the injection time is increased to a certain degree, the material viscosity is increased due to heat dissipation of the melt, and the required injection pressure is also increased.

Drawings

FIG. 1 is a flow chart of the present invention;

FIG. 2 is a comparison of the dimensions of the product of the present invention before and after injection at an injection pressure of 110 MPa;

FIG. 3 is a comparison of the dimensions of the product of the present invention before and after injection at 100 MPa;

FIG. 4 is a comparison of the dimensions of the product of the present invention before and after injection at an injection pressure of 90 MPa;

FIG. 5 is a comparison of the dimensions of the product of the present invention before and after injection at an injection pressure of 80 MPa;

FIG. 6 is a comparison of the dimensions of the product of the present invention before and after injection molding at different injection pressures;

FIG. 7 is a graph comparing the properties of the inner tubes of the material of the injection molded product of the present invention with different hardness;

FIG. 8 is a schematic diagram of the high pressure injection molding process of the present invention with varying parameters;

FIG. 9 is a schematic view of the deformation of the injection-molded part caused by improper setting of the parameters of the high-pressure injection molding process.

Detailed Description

The invention will be described in further detail below with reference to the figures and specific examples.

An HFI nozzle high pressure injection molding process, shown in fig. 1 to 9, comprises the following steps:

and S1, increasing the material hardness of the injection molding product, thereby enhancing the high-pressure impact force. Referring to FIG. 7, it can be seen that the inner tubes of the injection molding materials with different hardness have different properties.

The technical indexes of the raw materials are as follows: carrying out heat treatment, stress relief and annealing on the raw materials;

hardness: 250 plus or minus 40 HV;

the inner diameter measurement of the sliding area of the movable iron core needs to be fitted with a minimum measurement circle, and the diameter measurement of the rest positions needs to be fitted with an average diameter circle.

And S2, setting key parameters of the equipment through modular flow analysis and simulation. The key parameters of the equipment comprise: injection molding pressure, screw speed, pressure maintaining pressure, barrel temperature, mold cavity temperature, dryer temperature and mold locking force.

1) The step S2 is performed in the injection simulation model, and the process of establishing the injection simulation model is as follows:

first, a three-dimensional model of the product and insert needs to be built for analysis of melt flow and filling, and at the same time, a gating system model needs to be built to verify whether the design of the gating system is reasonable.

In addition, the circulating water path of the mold is arranged on the metal frame outside the cavity, in order to accurately simulate the heat transfer process of the mold during injection molding, models of the metal frame and the circulating water path are established, and boundary conditions such as temperature and heat conduction coefficient outside the metal frame are set, so that the simulation model is close to actual experimental conditions as far as possible.

The product, insert and cavity in the simulation model can be created using mapping software UG10.0 and imported into the analysis protocol for Moldflow. The casting system and the cooling water channel of the model are obtained by establishing corresponding axes by UG10.0, leading the axes into the Moldflow and setting the section attributes. In addition, the metal frame in the model was built directly using Moldflow's nest guide commands.

2) Dividing grids and defining grid attributes:

the method comprises the steps that after a three-dimensional model of a research object is established, grid division is needed, the purpose of grid division is to disperse a calculation domain of injection molding simulation, and a simulation result of a given boundary condition is obtained by calculating an algebraic equation system formed by grid nodes.

The Moldflow can use a neutral surface mesh, a two-layer mesh, or a 3D mesh discrete model. The neutral surface mesh is a product neutral surface formed by triangular units instead of a product shape, and is suitable for simulating a thin-wall product symmetrical about a central plane. The double-layer mesh replaces a product model with a product surface shell consisting of triangular units, and is suitable for simulation of thin-shell products. The 3D grid is a discrete product model using tetrahedral units, can express a complete product structure, is suitable for simulation of any product shape, and has the highest calculation precision.

After the mesh division is completed, the attributes of the mesh need to be defined according to the materials of the parts of the model. The heat conduction coefficient (HTC) between each part can adopt a Moldflow default value during mould simulation, and the process setting in injection simulation software can be used as the process initial setting in an injection molding machine and can reflect the related rules of melt filling and solidification.

The process of performing simulation includes the steps of:

The process setting of PA66 injection molding simulation is shown in Table 1, the temperature of the melt is set to 290 ℃, when the melt is filled to 90% of the volume of the cavity, pressure maintaining switching is carried out, the impact of molten plastic on the insert is reduced, the pressure maintaining is set to 80% of the maximum injection molding pressure, the pressure maintaining time is 15s, the cooling time of the product in the cavity of the mold is set to 25s, and the temperature of the cooling water of the mold is set to 85 ℃. Meanwhile, the injection molding time of 0.5s, 1s, 2s, 4s and 8s is respectively subjected to simulation calculation, and the influence of the injection rate on the cavity pressure and the fiber distribution on the surface of the product is analyzed.

TABLE 1

Injection molding simulation process	Parameter setting
		Melting temperature	290℃
Pressure maintaining switch	90% fill volume
		Pressure maintaining pressure	80% fill volume
Dwell time	15s
		Cooling time	25s
Temperature of circulating water	85℃
		Time of injection	0.5,1,2,4,8s

The process parameters are locked by comparing the variation of the product sizes (inner diameter, roundness and cylindricity) under different limit working conditions before and after injection molding.

Step S2 includes the following steps:

and S21, detecting the diameter, roundness and cylindricity of the pipe under different injection molding pressures, and comparing the diameter, roundness and cylindricity of the pipe before injection molding and after injection molding.

The different injection pressures may be: 60MPa, 70MPa, 80MPa, 90MPa, 100MPa, 110 MPa.

Fig. 2 to 5 are graphs showing the comparison of the roundness dimensions of the product before and after injection molding at different injection pressures. In fig. 2 to 5: the lateral coordinates are times, "1" for the 1 st time, "2" for the 2 nd time, and so on; the vertical coordinate represents roundness/mm.

FIG. 6 is a comparison of the diameter dimensions of the product of the present invention before and after injection molding at different injection pressures. In fig. 6: the transverse coordinate represents injection pressure/Mpa; the vertical coordinate represents diameter/mm.

S22, the injection pressure (upper and lower limit tolerance) is selected based on the step S21, and the sample size is increased to determine the rationality of the current parameters.

S23, tracking the moving smoothness of the movable iron core of the nozzle, tracking the failure rate of static flow and dynamic flow of a subsequent flow detection station, reducing the optimized rejection rate from 1% to 0.01%, and reducing the internal cost.

S3, injection molding; the injection molding is divided into five stages of material plasticizing, injection, pressure maintaining, cooling and demolding. The final quality of the product can be influenced by the process setting of each stage, the injection molding defects can be avoided by reasonably setting the injection molding process of each stage, and the product precision and the production efficiency are improved.

1) Firstly, the proper temperature of the charging barrel is determined according to the melting temperature range provided by a material manufacturer, so that the melt can be smoothly filled.

2) In order to improve the production efficiency, the injection speed should be set to a large value within the range allowed by the stable flow of the melt and the injection pressure.

3) The holding pressure is usually slightly lower than the highest injection molding pressure in the injection molding stage, when the holding pressure is too high, the product has the defects of difficult demolding, flash and the like, and the shrinkage rate of the injection molding product with too low holding pressure is increased. The pressure holding time is related to the solidification rate of the gate, and the pressure holding process can be finished after the gate is completely solidified.

4) The lower packing that is unfavorable for the melt of mould temperature, the higher cooling efficiency that then can influence of mould temperature, and cooling time has similar influence to the process of moulding plastics, and the material is not completely solidified when cooling time is shorter, can take place to warp among the product drawing of patterns process, and the cooling time overlength can influence the efficiency of moulding plastics.

5) The main technological parameters in the demolding stage are the ejection stroke and the ejection speed of the ejector pin, and the product can be completely separated from the cavity by ensuring the ejection stroke of the ejector pin.

The high-pressure injection molding plastic particles of the invention are as follows: CM3001G 33.

As shown in FIG. 8, the injection pressure required is greater for a shorter injection time because the injection time is reduced, the flow rate of the molten plastic is increased, the flow resistance is increased, and a greater injection pressure is required to overcome the flow resistance of the melt. In order to avoid deformation of the product due to impact of the melt during injection molding, the melt filling time should be increased appropriately so that the injection molding pressure is reduced. However, when the injection molding time is increased to a certain extent, the viscosity of the material increases due to heat dissipation of the melt, and the required injection molding pressure also increases, so that it is necessary to determine an appropriate injection molding time according to the structure of the product. In addition, the required pressure maintaining pressure is increased in the pressure maintaining process, and the pressure of a cavity caused by pressure maintaining is increased to cause product deformation.

Claims

1. The high-pressure injection molding process of the HFI nozzle is characterized by comprising the following steps of:

s1, increasing the material hardness of the injection molding product;

2. An HFI nozzle high pressure injection molding process according to claim 1, wherein the equipment critical parameters include: injection molding pressure, screw speed, pressure maintaining pressure, barrel temperature, mold cavity temperature, dryer temperature and mold locking force.

3. The high pressure injection molding process of an HFI nozzle as claimed in claim 1, wherein the simulation comprises the steps of:

4. The high pressure injection molding process for an HFI nozzle as claimed in claim 1, wherein the step S2 of optimizing the high pressure injection molding process comprises the steps of: