Introduction The injection molding process depends on the repeated production of parts according to the required specifications and quality.
Some changes are inherent, but this can be minimized for any given polymer, mold, and processing conditions.
Understanding and quantifying changes can improve process optimization and quality control.
With the development of more and more complex molding process
Assembly, fluid assist and Micro
In the successful production of high quality parts, proportional molding, control and repeatability become more important.
Several factors, including processor control technology, may affect the repeatability of the injection molding process (
Able to control screw position, speed, etc. )
, Melting temperature control, Mold temperature control, material consistency and batch change.
The direct effects of these factors are obvious;
The driving technology and control system of the machine determine the accuracy of the screw rotation, position and injection speed, thus controlling the melting preparation, injection and packaging stage of the circulation [1, 2].
Barreland nozzle temperature controller by using closed-
Integral Derivative of cyclic proportion (PID)
, The purpose is to ensure that the polymer maintains a consistent temperature in the cycle.
Mold temperature control during cooling and solidification affects the quality of parts [3, 4]
This may affect the strength of the crystals and parts and cause shrinkage or warping.
Minor differences between batches of the same nominal material were found to result in a significant change in [5]
Especially when the molding process runs in a narrow processing window.
Other factors affect the consistency of the molding process.
Servo hydraulic or electric injection molding machines perform sametask with different operating properties [6].
Electric machines are generally considered to be more precise than hydraulic systems and have proven to be more energy efficient, although increased flexibility of hydraulic machines may lead to more consistent products, currently, the cost of hydraulic machinery is much lower than that of electric machinery [7].
The performance of hydraulic and electric molds is studied in detail here, with special attention to energy consumption and efficiency.
The aging of the machine will also affect its accuracy and repeatability;
The development of control technology makes the microprocessor used in modern machines more and more complicated.
The improvement of the control technology makes the control of screw position, speed and rotation more accurate, and the partial repeatability is also improved.
Wear of mechanical parts can adversely affect the process performance, such as wear on screws or backrestflow valve.
This is more likely to have a longer term impact on process changes and can be monitored to determine when a mechanical part needs to be replaced.
Period during which all injection molding machines change during start-up-up [8].
This is due to the gradual heating of various mechanical components (
Screw, mold, nozzle, hydraulic oil)
In the first 10-
The mold runs 100 cycles to achieve the \"steady state\" condition of the cycle from one cycle to the other.
Preheating the mold to the operating temperature helps minimize the start-up effect, but some transient thermal effects are inevitable due to the input of energy during the molding process.
If the use of start
Up effects, such as the size of the machine and the type of molded polymer, can be identified and quantified, reducing the setting time.
At the beginning of a long production run (i. e. , several days)start-
When the amount of waste produced in the first cycle is compared to the total amount of waste produced, the up effect is generally considered insignificant.
Statistical process control to monitor changes (SPC)
Can be used for molded products [9].
However, this is a time-consuming and inefficient method of quality control that takes a long time from finding a fault to taking corrective action.
Now, the monitoring system is usually integrated into the molding machine, and many machine control processors are equipped with monitoring software.
Time map of various process parameters such as injection pressure and switching position.
This information improves understanding of machine performance and changes, but may not be directly related to part quality.
Therefore, some monitoring methods have been developed to measure some aspects of the thermal aging process more directly, such as melting temperature and pressure [10-12]
Cave pressure [13]
Tie the rod. 14, 15].
These methods provide a great deal of useful information about the process, but are often inappropriate or too expensive in a production environment, and the link to product quality is not well quantified.
The purpose of this work is to quantify the performance of 4 injection molding machines, different ages and techniques, and to form General parts from the same polymer using universal tools.
Special emphasis on inspection start-up using instrument forming machines and complex data acquisition systems-
Dynamic, repetitive and power consumption.
Four molding machines were used in the test equipment test, as shown below.
Detailed specifications are shown in Table 1.
Machine A: Cincinnati ACT30, servo electric forming machine, 30 Mt clamping force, microprocessor control (1989).
Machine B: Fanuc Roboshot, servo electric forming machine, 50 metricton clamping force, full microprocessor control (2000).
Machine C: Battenfeld CDK750, Servo Hydraulic forming machine, clamping force of 75 metric tons, full microprocessor control (1997).
Machine D: sandreessen Series 7, scale-
60 metric tons of clamping force, microprocessor control (1987).
Four molding machines provide different sample groups for performance comparison.
Two of the machines are servo motors and two hydraulic drives, which can be directly compared to these two technologies.
During the experiment, the two machines were relatively modern (
1 and 4 years old)
And the other two represent oldermachine technology (
12 and 14 years old)
Wear is more obvious.
In each case, the interchanging \"box\" tool insert allows the use of a universal mold tool on each machine.
This allows direct comparison of the ability of each machine to make the same parts.
Production of tensile test samples using tensile test Rod molds, standard en iso 527-2 [16].
General injection molding grade of high density polyethylene (
HD5050EA BP Chemicals)
Used throughout the experiment, molded parts as shown in the figure1.
Using the 6 KW Churchill Conair water temperature control unit, the mold temperature control is achieved at each half of the mold by continuously pumping water through the cooling channel.
Measure the weight of molded parts using aMettler BB244 balance and size (
Length, width and thickness)
Measuring with a special construction fixture where the spring-
Linear voltage displacement sensor loaded (LVDTs)
Signals are automatically sent to aPC.
Use the InstronSeries 9 tensile testing machine with 2 kN load cell to measure the tensile strength of the molded part. [
Figure 1 slightly]
Each molding machine has a high degree of instrument and computer monitoring.
During the molding test, the following
At a frequency of 50Hz, use in-
House monitoring software and Microlink 2000 data acquisition hardware.
The melt pressure thenozzle Reservoir is a measure of the hydraulic pressure to melt using Dynisco PT422 presuretransucer (
In the case of 2 Hydraulic Machines)
Measured with Dynisco Inc IDA 354 sensor, melt temperature thenozzle Reservoir is a J-measure of temperature monitoring using Dynisco Inc-
Thermocouple.
The position of the sensor relative to the nozzle is shown in the figure. 2.
Process Energy Measurement using Hioki 3-
Phase unbalanced load electric energy meter with Hall fixture is on the power supply of the machine.
This monitors power consumption and power factor ([lambda])
Instructions for process efficiency.
For a pure resistance load, the current in the circuit is exactly the same as the voltage ,[lambda]=cos(0)
= 1, the power used is a multiple of the voltage and current.
For pure inductive load, the current in the circuit causes the voltage to lag exactly 90 [degrees], [lambda]= cos(90)
= 0, when the current time is extracted from the supply, no useful work is done.
For circuits containing a mixture of inductance and resistance loads, the power factor is between 1 and 0, which is the exact value determined by the composition of the circuit.
Take the average value during the outeach molding process and calculate it according to the hourly power consumption. [
Figure 2:
Detailed experiments were carried out to simulate production from the beginning
Improvement of molding process.
In each case, the molding is monitored immediately-
Until 400 parts are produced.
The machine settings remain the same throughout the experiment.
Before molding, the mold tool is heated overnight to minimize the time required to stabilize the process.
The mold temperature control on each machine is implemented by an independent controller that continuously pumps water through a cooling channel of two and a half of the mold to set the temperature.
Each machine is set to perform the same molding in terms of injection size, injection speed, holding pressure, and packaging and cooling times.
Due to the different sizes of the 4 machines, it is difficult to ensure that all aspects of the molding process are the same in each case.
For example, the difference in the diameter of the screw affects the amount of energy input into the melt during the molding process.
In this case, the screw rotation speed of each machine is set to transmit the same specific energy per mass melting.
In addition, due to the different working capacity of each machine, it is necessary to run some machines at both ends of the processing range (e. g.
, Compared with Machine C, the maximum injection speed of machine A is 78% and the speed is 38%)
Achieve a common volume throughput during injection.
The melting temperature is 210 [degrees]
C. set the temperature on each machine and on the mold to 40 [degrees]C.
Table 2 shows a complete list of molding conditions.
Mid-range values were selected for package pressure and back pressure.
High Density Polyethylene (HDPE)
What is studied here is a general injection molding grade, which can be formed well under this condition and has a large processing window.
All of the above process measurements are monitored in the first 4 seconds of each injection cycle.
Each molded part is labeled and cooled after pop-up.
After 24 hours, the parts are weighed (
Including the gate and the gate part)
And measured the size.
The final 10 molded parts for each run are then mechanically tested to determine the maximum tensile strength.
Results The Machine compares the average results of the final 100 parts of each experiment (
Select to represent steady state forming conditions)
Overview in Table 3.
Nozzle temperature rise is defined as the difference between the melting temperature before injection and the peak temperature during injection.
The initial screw position is defined as the position of the screw before injection.
Average weight from 15. 51 to 15.
86g for 4 machines with a range of 2. 2%.
This highlights the difficulty of producing duplicate molded parts using different machines even under the same set conditions.
The average part size range between machines is small; 0. 48% long, 1.
Width 76%, 5.
Thickness 12%. Machine D (
1987 ratio-hydraulic)
Molded parts with the highest average part weight and length produced.
The existing stretch bar mold has been designed to the size of the required standard [16]
Contraction is not allowed;
Therefore, the width and thickness dimensions of some measurements are lower than the standard tolerances ([+ or -]0.
2mm on the width and thickness of the specimen).
Machine B produced smallestmean parts with 3.
The width of the sample shrinks by 6%, 7.
Thickness 25%.
The average shrinkage of all 4 machines is 2.
5% wide, 4. 8% inthickness. [
Figure 3 slightly]
Before injecting the nozzle, the melt consistency is quantified by the melting pressure and temperature measurements performed in the reservoir.
12 differences.
During the injection process of the two hydraulic machines C and D, a peak melting pressure of 5% was observed, while the peak injection pressure of the two servo motors was similar.
Figure 3 shows a comparison of the typical primary injection pressure distribution for 4 machines.
Although the injection speed was stable in each case, a significant difference in the injection profile was observed.
The injection speed was found to deviate from the set value.
Machine A reaches the injection speed closest to the set value (faster by 1. 1%)
Machine B and C are 8 respectively. 2% and 9.
It is 4% slower, and the Machine D is 37.
3% slower than the set value.
From table 3, the maximum melting temperature during injection is at least 10 higher than the set value [degrees]
C on all machines.
The temperature rose to 21. 4[degrees]C (machine B)
Occurs during the injection process, mainly due to the thermal insulation heating of meltreservoir during a 860 bar increase in pressure 0. 5 seconds.
Figure 4 shows the melting temperature of all 4 machines during one injection4.
These are closely related to the pressure distribution including Figure 1.
3. due to the increase of melting pressure, the temperature rises.
The average mold temperature of each machine is similar, close [degrees]
C. set the temperature above 40 【degrees]C.
In order to achieve the same lens size, the initial screw position of each machine is different, although for the hydraulic machine, the initial screw position is farther than the set position, because the screw bounces at the end of the plastic processing
Measure the tensile strength of the final 10 molded parts from each molding machine (i. e.
Part Number 391-400)
As shown in figure shown in5.
The maximum tensile load range is 0. 87 to 0.
93 kN, difference of 7%.
Based on the error bars of the 99% confidence intervals of each machine dataset, the combined variation levels of the tensile testing process and period are determinedto-
Change of circulation molding process.
Because there is no overlap in the calculated confidence intervals of each mold machine, the difference in tensile strength between the mold machines is determined to be statistically significant.
As shown in the figure, during the injection process, it is found that the maximum tensile load is most closely related to the melting temperature5.
It was observed that the tensile strength decreased linearly with the melting temperature, which may be related to the cooling effect of crystals in the cavity.
A bigger one-
Section gates are used on the mold tools used here to minimize the amount of orientation in the molded stretch bar.
This large lemmay affects the effect of cooling on the weight and tensile strength of the part by allowing the melt to be forced into the cavity during the filling phase.
For the narrow range of mold temperature measured here, the mold tool temperature seems to have no measurable effect on the tensile strength. [
Figure 4 slightly][
Figure 5 Slightly]Start-
During the transient period at the beginning of each run, check the dynamics of machine performance, production of parts 1-
50 is defined as \"start-up.
\"During this period, all 4 molding machines show transient behavior as the screw, mold tool, hydraulic and mechanical gradually heat to the equilibrium working temperature.
Figure 6 shows the change of part weight during start-up
Type C hydraulic machine tool, Mold temperature.
Part weight drop observed at the beginning
Rising cycle, which seems to be positively related to the tool temperature.
As shown in the figure, this relationship is observed for all 4 machines
7: the change of mold temperature seems to be the most important factor in the start-up
Even if the mold is kept at the working temperature overnight before each test.
The minimum machine A studied changes the tool temperature to A minimum during start-upup.
It seems, start-
Machine size and heat affect uplink transmission
Although the newer motor has a higher maximum clamping force and capacity, alogarithmic model is installed on the mold tool, with a hydraulic pressure of 16% and a servo power of 7%. [
Figure 9 omitted[
Figure 10 slightly]
The energy increase used to run the hydraulic injection molding machine is mainly due to the continuous induction load required by the hydraulic motor.
As shown in the power factor, the inductive load also reduces the efficiency of the hydraulic machine ([lambda])
Values shown in Table 3.
Machine B operated with [power factor]lambda]= 0. 98 (i. e.
Very efficient).
An old-fashioned electric machine is less efficient ([lambda]= 0. 70)
Due to the old technology, the servo motor with high inductance.
Two hydraulic machines with a power factor of less than 0.
5, this is typical for servo and proportional hydraulic machines.
Power factor correction equipment can be installed on the Servo Hydraulic Machine to improve the electrical efficiency of the process [17].
From the results reported here, the age of the molding machine seems to be the most important factor in determining the repeatability of the part.
This reflects the development of process control technology, thus improving the screw position and melting temperature control.
Mechanical wear may also be a factor as the two old machines studied here have been running (
Not continuous though.
In a research environment of more than 10 years
The quality of the parts formed here is more difficult to evaluate.
Since the original mold design ignores shrinkage, the part size is slightly lower than the state tolerance of this standard.
Although no target weight is set, the average weight of the parts produced by these two newer machines is the lowest.
The only part mass variable that can be directly compared is the tensile strength of the curved sample.
It was found that this was related to the melting temperature during the injection process, not to the age of the machine or to the mode of operation.
However, the part quality measurement does highlight the difficulty of copying the same molded parts from different molding machines even with the same mold cavity insert.
Bhogesara, etc. [18]
It was also found that setting up the same machine on different machines will produce different results, introducing the concept of \"Machine personality. [
Figure 11 omitted][
Figure 12:
Differences in machine technology (
Hydraulic or electric)were observed.
The most noteworthy is the repeatability of the screw position and fusion consistency during injection (
As shown in peak melting pressure and temperature). All-
The motor seems to control the process with a smaller change.
This may be due to the fact that the drive mechanism of the servo motor is more rigid, while some of the inherent \"flexibility\" in the servo and proportional hydraulic motor is related to the compression of the oil.
However, the repetitive changes in the process measured on the hydraulic machine did not result in a significant change in the quality of the part, as shown in the variable coefficients shown in Table 4.
The coefficient of variation at the screw position is 10 times. 3 and 3.
9 is higher than the machine and B respectively, but the weight of the part changes the least.
The weight of the machined parts changes the maximum (a factor of 2.
7 times higher than machine)
However, this does not indicate poor screw position control (15.
5 times higher than machine).
These findings are consistent with a previous study. 6]
The conclusion is that the mechanical repeatability of the motor is better, but not necessarily the partial repeatability is better. Start-
It was found that up transient is common in all injection molding machines.
In the first 1-production process, the weight of the part gradually decreases
There are 50 cycles in each case, most likely due to a gradual increase in the temperature of machine parts such as mold tools.
This transient effect seems to be related to the size of the machine, and the interference of small machines is minimal.
This confirms that gradual heating is the reason: the metal heated by the smaller machine is small in volume and therefore has less time to reach equilibrium.
There is no easy way to eliminate the transient from the beginningup--
This effect is inherent in polymer processing.
Whether to start is controversial.
Change is important.
During the production of thousands of parts, the transition change of the first 50 parts may be considered negligible.
However, for large molds or expensive polymers, any scrap produced may be critical.
Advanced mold temperature control technology such as mold tool cooling [19, 20]
May help reduce startup
Change up as it may be the development of automated \"experts\"
Line Control system]21].
For the 4 injection molding machines studied here, it is found that the age of the machine is the most important factor in determining the quality and repeatability of the parts. Modern (
Less than 4 years old during the experiment)
The performance of servo motor and Servo Hydraulic machinery is equivalent.
Performance differences between Machine technologies.
The servo motor exhibits a better machine control interface in screw positioning, but this does not necessarily shift to state-of-the-art repeatability.
The average energy consumption of the servo motor is found to be 3.
6 times less than hydraulic operation. Start-
During the molding process of the first 50 parts, all machines detect the rising transient, during which the quality of the parts is related to the mold temperature.
It is found that the size of the mold tool will affect the time when the mold temperature is stable after startingup.
It was found that during one injection, the tensile strength of the molded part decreased linearly with the melting temperature.
Sponsor of the contract: Polymer Science and Technology Research Center;
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International Research Center (IRC)
Bachelor\'s degree in Polymer Engineering, School of Engineering, design and technology, Bradford University, UKL. Kelly; e-mail: a. l. kelly@bradford. ac.
The UK delivered its first speech at the International Conference on Technology (ANTEC)
2001, paper 238.