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Multistage injection molding process

Modern injection molding products have been widely used in various fields. The shape of the products is very complex and they are used
 
The properties of the polymers are also very different. Even for products of the same material, due to the number of sprue systems and parts
 
Different shapes and different parts require the flow (speed and pressure) of the filling melt, otherwise it is necessary to
 
It affects the rheological properties of the melt at this position or the crystallization orientation of the polymer, as well as the apparent quality of the product
 
Quantity. In an injection process, when the screw pushes the melt into the mold, it is required to realize the difference in different positions
 
With the same injection speed and different injection pressure, the injection process is called multi-stage injection.
 
The digital dial type injection molding machine is relatively backward, with only one or two stages of injection, one stage of pressure maintaining and one stage of fusing
 
control
 
degree
 
Law to improve
 
Development and production
 
Low speed is used in the initial stage of injection, high speed is used in cavity filling, and filling is close to
 
Use low-speed injection method at the end. Through the control and adjustment of injection speed, the system can be prevented and improved
 
The appearance of products such as burr, spray mark, silver bar or scorch mark, etc.
 
The multi-level injection control program can be based on the structure of the runner, the form of the gate and the structure of the injection part,
 
To set multi-stage injection pressure, injection speed, pressure maintaining pressure and glue melting mode reasonably is beneficial to improve plasticizing effect
 
Improve the quality of products, reduce the defect rate and prolong the service life of mould / machine.
 
By controlling the oil pressure, screw position and screw speed of injection molding machine with multi-level program, we can seek for improvement
 
The appearance of the mold is not good, and the corresponding measures of shrinkage, warpage and burr are improved, so as to reduce the injection molding parts of each mold every time
 
The size of is not uniform.
 
Effect of multilevel control
 
Forming condition effect
 
Injection speed
 
Prevent air / flow lines in the gate area, sharp corner flow marks, and
 
Collapse of the core to prevent burring.
 
Secondary pressure reduces internal stress and prevents shrinkage.
 
The stability of screw revolution measurement
 
Stability of back pressure measurement
 
 
 
However, many injection technicians are still used to the past injection method and do not know how to find it
 
Find the location and method of multi-stage glue injection, so that the machine with multi-stage glue injection function can not play its advantages.
 
1、 To set up a multi-level injection program:
 
It is more scientific to set at least three or four stages of injection for general plastic parts. The flow passage of the water inlet is
 
The first section and the gate are the second section, and the product is glued to the 90% Left and right are the third section, and the rest are the third section
 
Four paragraphs (also known as the last paragraph).
 
For simple structure and low appearance quality requirements of plastic injection, three-stage injection procedure can be used.
 
But more than four segments are needed for injection molding of complex structure, multiple appearance defects and high quality requirements
 
Glue injection control procedure.
 
Set up several injection procedures, which must be based on the structure of the runner, the form / position / quantity / size of the gate
 
Scientific analysis and reasonable setting of injection molding parts structure, product quality status and mold exhaust effect.
 
2、 Selection method of multi-stage injection position:
 
One . calculation weight method
 
Total weight = weight of all parts + weight of flow passage
 
During injection, the injection volume is the total weight, and the injection position of one section is the injection volume of the flow channel; the injection volume of two sections is the injection volume
 
The glue position is the product dispensing 90% The third segment is the last segment.
 
Two Debugging observation method
 
According to my own preliminary estimation, set the pressure / speed at the location of injection to zero, and observe the actual situation
 
The position of the rubber, and then fine-tuning according to the actual situation, until you find the position you want to choose.
 
The following is an illustration of the relationship between the product and the multi-level control program
 
Fig. 1: according to the different speeds set in the process conditions, the injection screw is subject to multi-level speed conversion (cutting
 
Replace).
 
Figure 2 is the multi-stage injection process selected based on the analysis of product geometry: due to the
 
The mold cavity is deep and the wall is thin, which makes the mold cavity grow and narrow. When the melt flows through this part, it must
 
Pass quickly, otherwise it is easy to cool and solidify, which will lead to the danger of filling the mold cavity. High speed injection should be set here.
 
However, high-speed injection will bring a lot of kinetic energy to the melt, which will produce a lot of inertial impact when the melt flows to the end,
 
In this case, it is necessary to slow down the flow rate of the melt, reduce the filling pressure and maintain the normal flow rate
 
The said holding pressure (secondary pressure, follow-up pressure) enables the melt to supplement the melt into the cavity before the gate solidifies
 
The shrinkage of the body requires the multi-stage injection speed and pressure in the injection process.
 
In Figure 2, the screw metering stroke is set according to the product material consumption and buffer. Injection screw from position
 
" Ninety-seven ”To“ Twenty ”It is the thin-walled part of the filling product, and the high-speed value is set as Ten , the purpose of which is
 
High speed mold filling can prevent the melt from cooling for a long time and the flow stops; when the screw moves from the position
 
" Twenty ”→“ Fifteen ”→“ Two ”And set the corresponding low speed Five Its purpose is to reduce the melt flow rate and
 
Kinetic energy of impact die. When the screw is in“ Ninety-seven ”、“ Twenty ” 、“ Five ”When the,
 
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