Correlation and difference between plastic machine process and mold flow analysis data

Time:2022-12-28 08:35:01 / Popularity: / Source:

Abstract: This paper focuses on analysis of Moldflow software, compares data analyzed by software with process parameters debugged on on-site injection molding machine. Combination of software legends, then complete some unpredictable flaws in data correlation.
In connection between practice and theory, following parameters are mainly confirmed and error calculated: maximum clamping force, deformation, gate gas mark, weld line position, etc.

1 Introduction

With continuous implementation of intelligent manufacturing, simulation analysis is becoming more and more important in proportion of production. Difference analysis between simulation analysis and actual production is particularly important. Process parameters automatically generated in simulation analysis are rarely used in actual commissioning or production. Many analysis software companies are also looking for a balance between analysis parameters and actual parameters. Whether it is moldflow or moldex 3D, they are looking for a solution that can directly convert analyzed process into actual production.
Before actual mold opening, CAE analysis report is mostly used as a judgment value. In many cases, product company will confirm theoretical state that appears in CAE analysis report, and adjust it according to theoretical state. When actual product is close to theoretical product, product company will confirm that it can meet production conditions.
How to make actual product close to theoretical product analyzed by CAE, how to know process parameters of product from CAE report, how to adjust it to make product and theoretical value same when there is a problem, can only be obtained by mutual communication and cooperation between on-site process, technicians and CAE analysts.
In this paper, moldflow is used as product analysis software to compare equipment status, tonnage, deformation, gas marks, weld line position, pressure difference between analytical parameters and actual parameters, conducts verification through actual verification to find difference and adjustment methods.

2. Problem description

In actual production, there are various errors that lead to differences between glue flow and analysis in actual product. This includes more than equipment-related errors. In actual debugging of product, various problems always occur when process adjustment is carried out according to data analyzed by CAE, which makes results unsatisfactory.
When setting injection pressure, according to recommended pressure value given by CAE, it was found that product finally stopped due to insufficient pressure, resulting in an incomplete product. What's more, in product that needs pressure balance, the whole product cannot maintain pressure balance and hold mold, which is difficult to come out, resulting in mold being disassembled for maintenance.
mold flow analysis 
Figure 1 Easy to hold mold products
When CAE estimates tonnage of equipment, sometimes tonnage of equipment is too small, and qualified products cannot be produced on budgeted equipment, and sometimes it will lower production equipment when equipment is scheduled, it is still able to produce qualified products. When budgeting for equipment tonnage, what conditions are used as a judging criterion? Pure clamping force or interference from other factors? What is difference between analyzed clamping force and actual error?
mold flow analysis 
Figure 2 Clamping force analysis diagram
Deformation of CAE is very important for pre-analysis. As a plastic product, degree of deformation is directly related to material, and how to avoid or reduce deformation, early analysis plays an extremely important role. Pre-deformation of many products is planned in advance by CAE to complete confirmation of product deformation. But sometimes actual production is contrary to CAE, how to explain these deformation problems?
mold flow analysis 
Figure 3 Deformation analysis
Gate gas marks are difficult to analyze in CAE analysis, and they always surprise you inadvertently. According to experience, gas marks may appear, and every time gate gas marks appear, it is a difficult problem to solve. How to interpret gate air marks from CAE report and how to adjust gate air marks?
mold flow analysis 
Figure 4 Difficult to analyze gas marks
Weld line is the most accurate value analyzed in CAE. Number of existing lines is almost same as analysis report. However, there is always a slight difference between direction of weld line and direction in analysis report during injection molding. Why are these differences caused?
mold flow analysis 
Figure 5 Weld line analysis
Do parameters appearing in CAE analysis report have a guiding role in actual process, where are parameters related to each other, how to obtain useful and instructive parameters for process from CAE analysis report?
mold flow analysis 
Figure 6 Recommended process parameters

3. Analysis of problems and differences

3.1 Equipment status and pressure loss

First of all, in actual debugging or production, difference in equipment status will cause errors. For example, oil temperature of injection molding machine will cause pressure of oil pump to be unstable, and process parameters will have a small deviation in unstable state. Oil temperature will have a relatively stable fluctuation range value after injection molding machine equipment runs stably for a period of time, and debugging is carried out under this range value.
Secondly, when screw is pushed forward, there will be a pressure loss. There is a certain loss between set pressure of injection molding machine and actual pressure on product. This loss is a necessary loss and cannot be avoided by artificial means. It will rise or decrease in a certain proportion according to number of gates and wear degree of screw.
As shown in Figure 7, adding a sensor to mold of product integrated barrel to confirm actual pressure does have a large pressure gap between setting of injection molding machine and injection molding machine. There is also a certain error between CAE analysis and actual pressure. As shown in Figure 8, moldflow analyzes data and pressure difference obtained by actual pressure sensor. After comparison, difference ratio is still relatively large, so a parameter is required for optimization.
mold flow analysis 
Figure 7 Sensor display pressure vs. press set pressure
mold flow analysis 
Figure 8 moldflow analysis pressure and sensor position

3.2 Equipment tonnage verification

Clamping force analysis in CAE is calculated based on projected area and pressure of product. Demand for clamping force here is relatively accurate, it is calculated from theoretical injection pressure and projected area. Base pressure P0 is obtained from flow length ratio and wall thickness, then multiplication coefficient K is confirmed according to different materials, as shown in Figure 9 below. By multiplying these two values, cavity pressure P= P0*K is obtained, which is used as basic value for tonnage calculation. Calculated equipment tonnage is then obtained using product of projected area (S) and cavity pressure (P). Clamping force F=P*S= P0*K*S.
Projected area S: the largest area observed when mold is opened and closed
Cavity pressure P: maximum pressure for product filling
Clamping force F: minimum pressure required when product is formed
mold flow analysis 
Figure 9 Material names and multiplication constants
In actual verification, according to comparison between clamping force analyzed by CAE and clamping force of injection molding machine, whether clamping force can reach standard is confirmed by whether clamping force will exceed value during injection. Clamping force requirement is rarely lower than actual clamping force. However, when high packing pressure of some products occurs, clamping force exceeds analytical clamping force.
Verification process of clamping force is as follows:
Set clamping force → confirm whether clamping force changes during injection and pressure holding → lower clamping force if there is no change → minimum clamping force (clamping force does not change at the end, and change in clamping force should be less than 20)
Set clamping force → confirm whether clamping force changes during injection and maintaining pressure → change and increase clamping force → minimum clamping force (clamping force does not change at the beginning, and change in clamping force should be less than 20)
In actual test, product is an observation window screen, and material is transparent ABS. CAE analysis of clamping force is shown in Figure 10 below for calculation of 680T. According to experience analysts gave a budget of 700T for clamping force.
However, during actual verification, 680T clamping force was slightly abundant during production. After several times of clamping force adjustment, it was found that actual clamping force of the entire product was around 600T. When clamping force of equipment was set to 580T, after the holding pressure is provided according to CAE and the injection setting is completed, the clamping force rises to about 610T and stagnates. When clamping force is 620T, there is not much change in dynamic injection, and minimum clamping force is determined to be 600T. At the same time, it is also confirmed that clamping force budget of moldflow software meets requirements of mold, and is generally too high, such as Figure 11.
mold flow analysis 
Fig. 10 CAE analysis of clamping force
mold flow analysis 
Figure 11 Comparison of actual setting clamping force
It can be seen that in software or calculation, clamping force can basically meet clamping force in actual production. Because actual contact area of 3D product in cavity is larger than contact area in real mold, that is, value of S in formula is larger than contact area in actual production, and calculated clamping force can meet needs of product.
Clamping force is measured according to actual measurement, and there is no other interference factor. Main difference of clamping force error calculated at present is accuracy of volume S of cross-sectional area and cavity pressure P value. Secondly, it is pressure requirement during molding. This value varies greatly within analysis range, and it needs to be debugged according to value of analyzed product.

3.3 Analysis of deformation and warpage difference

Plastic products will be deformed due to material shrinkage during production, because deformation caused by post-shrinkage is unavoidable. In CAE analysis, a plan will be proposed for deformation of product to inform deformation direction and deformation size of product. However, there will always be some differences in actual production and CAE data analysis, such as product analyzed in Figure 12, and difference analysis is performed on this product.
analysis of Moldflow software 
Figure 12 Vertical beam products
analysis of Moldflow software 
Figure 13 Product deformation analysis
As shown in Figure 13 above, deformation of single-mode product is used as analysis point during analysis. When mold is actually opened, it is made into one mold and two cavities, one left and one right. As shown in Figure 12, deformation trend of two-mode product should be same as the analysis. Deformation of single-mode products is same, but in actual production, deformation of two-mode products is not same, but one is heavier and the other is lighter, as shown in Figure 14:
analysis of Moldflow software 
analysis of Moldflow software 
analysis of Moldflow software 
Figure 14 Actual deformation of product
In actual deformation, it is confirmed that deformation trend of left and right cavities is slightly different. Reason for different deformation of such a product with multiple pieces is basically caused by unbalanced flow of cavity. Short-shot verification is performed on the cause of difference to confirm whether flow of two cavities is balanced. Short-shot verification is shown in Figure 15 below.
analysis of Moldflow software 
Figure 15 Product gate short shot verification
Result is shown in Figure 15. Two ends of cavity are left and right (sky side product is non-operation side). Product on non-operation side is filled slower than product on operation side, and weight difference is about 3g. Operating side of three gates is faster than non-operating side, so gate on non-operating side is slightly widened with a file, flow of two-cavity product is balanced, then deformation trend of two-cavity product is completely consistent, which is compared with theory.
It is concluded that deformation of product is mainly due to inconsistency between theory and actual situation caused by unbalanced internal pressure of product. Under theory, there is a certain gap between flow of product and error during actual mold processing. If the biggest factor of gap is found, it can be infinitely approached to theoretical deformation. Cause of imbalance is usually flow imbalance of gate and machining error of cavity. Adjustment method is to correct source of error through size of gate.

3.4 Interpretation of gate air marks

Gate air marks are also a difficult normative discovery problem in CAE analysis. In many cases, products are given according to analyst's experience whether there will be air marks. In analysis report, most of warning words that gate gas mark may appear at the first gate will also appear. However, it has always been difficult to confirm appearance of gate gas marks. After analysis report and exploration in actual mass production, I found some tips for observing gas marks in advance, which are organized and shared here.
analysis of Moldflow software 
Figure 16 Prompt gas marks in the analysis report
analysis of Moldflow software 
Figure 17 Contour analysis
Therefore, adjust density of contour lines to shorten display time of contour lines, and you can see chaotic area of contour lines. Speed of contour lines is uneven near intersection. Some areas are fast, and some areas are slow, forming an obvious pulling phenomenon. Considering reason for formation of gas marks, it is caused by too fast speed. From unstable contour line, it can be reported that speed here has a rapid change. Therefore, contour line can be used as a basis for judging gate gas marks. Contour map is shown in Figure 18 below:
analysis of Moldflow software 
analysis of Moldflow software 
Figure 18 Observation after contour line encryption
Distribution of gas marks on actual product is shown in Figure 19. It can be seen from figure that contour disorder area is consistent with area where gas marks are generated, so it can be confirmed that contour turbulent area and gate gas mark area are an overlapping area. It can be confirmed that contour disorder area and gate gas mark area are same. overlapping area. On the other hand, check whether contour lines in other areas are also disordered to verify whether gas marks can be confirmed by disorderly pulling of contour lines.
analysis of Moldflow software 
Figure 19 Actual position of gate air mark
Verify whether contour line can confirm air marks or flow marks through other positions. As shown in Figure 20, product will produce gas marks after passing through surface structure in actual production. This structure is particularly prone to gas marks, distance between structure and gate is very close, and inlays to increase exhaust gas have not been very good.
analysis of Moldflow software 
Fig. 20 Gas marks appearing over surface structure
Pushing back to over-gate position shown in moldflow report, it can be found that contour of product does not fluctuate at this position, and there is no significant change in the area without air marks at the back. Therefore, causes of trapped gas marks and flow gate gas marks are not same. One may be caused by flow rate of material, then pure gas cannot be discharged, , as shown in Figure 21.
analysis of Moldflow software 
Figure 21 Picture of above gas marks

3.5 Analysis of Weld Line Position Gap

Weld line is actually a general term for this kind of problem in workshop. In moldflow analysis, weld line are separated. Fusion line means that fusion angle of material flow is greater than 135°, and fusion line is that fusion angle of material flow is less than 135°. The smaller angle, the more obvious fusion line. In actual production, there is not much difference between fusion line. Fusion line is shown in Figure 22 below: fusion line is fusion line, fusion line may disappear.
analysis of Moldflow software 
In actual product (Fig. 23), length of welding line is longer than analyzed welding line. Affected by different injection speeds, length of welding line is not fixed. However, number and position of weld lines correspond to analysis results. Therefore, analysis of weld line is quite accurate in CAE, length and depth are difficult to confirm, but it is not much different from actual situation.
analysis of Moldflow software 
Fig. 23 Weld line of actual product
By comparing two phases, number of welding lines is same, and positions are roughly same. But the only difference may be that weld line of product can be bent when analyzed, while actual weld line always runs straight. Because in actual mold, position of exhaust groove has some effect on flow direction of plastic, so that material will travel towards position of minimum pressure value with the shortest stroke, so it will basically be a straight weld line.
If position deviation is found to be large, adjust switching time of sequence valve to adjust. Because in CAE analysis, gate is opened to confirm weld line after material flows through a certain point. In actual production, gate switch is generally controlled by time or measurement position, which is different from theory.

3.6 Correlation between analytical parameters and actual parameters

When CAE software analyzes, there will be some parameters input such as material, pressure, injection time, etc. These theoretical parameter settings are related to actual parameter settings. Many mold debugging is not carried out according to process parameters analyzed by CAE, or it is not known where to find set process parameters, resulting in no unity between practice and theory. Figure 24 below will tell you how to find process parameter settings of injection molding machine from CAE report.
First of all, we must understand five elements of injection molding machine process, which are position, pressure, time, speed, and temperature. Select important parameters from five elements, and find important parameters from analysis report.
Position: screw position and metering position of injection molding machine.
Pressure: Peak pressure and holding pressure required for injection.
Time: dwell time.
Speed: Injection speed.
Temperature: mold temperature and material temperature.
analysis of Moldflow software 
Figure 24 Input condition options in moldflow
As shown in figure above, almost all analysis software will require input of material properties, mold and melt temperature. Among these parameters, there are actual injection parameters: mold temperature and material temperature. As clearly stated in Figure 24 above, mold surface temperature is 45 degrees and melt temperature is 228 degrees. Because temperature of screw does not directly contact melt, temperature of melt zone of screw can be set slightly higher than melt temperature by 3-5 degrees.
At the same time, tell melt temperature range, lower it by 30 degrees as temperature of screw pressing area, and finally set a blanking port temperature. In this way, temperature parameters can basically be confirmed. Mold temperature is calculated according to purpose of runner to take away heat. Water flow temperature needs to be 10-15 degrees lower than cavity temperature to set mold temperature machine to complete mold temperature setting.
analysis of Moldflow software 
Figure 25 Parameters entered in moldflow
Figure 25 tells us a holding time and holding pressure set at the beginning. In actual injection molding, this parameter is also extremely important, just as holding time and holding pressure in pressure element and time element written earlier change can be found. This value is an important basis for comparison between actual and theoretical, and this value will not change in software.
Injection pressure is also required, and this value is interpreted from CAE analysis. Figure 26.
analysis of Moldflow software 
Figure 26 Analyzed injection pressure
According to setting of injection time of product, theoretically required injection pressure is obtained. However, according to actual pressure loss, it cannot be set according to pressure of theoretical analysis. An empirical value is required here to combine theoretical and practical pressures. Meanwhile, last required parameters remain actual metering and screw position.
When product generates product 3D drawing, theoretical weight of product can be calculated according to drawing, and theoretical measurement of product can be calculated through theoretical weight of product. Due to frequent calculations, I wrote a small algorithm for calculation, as shown in Figure 27 below. Weight is calculated by actual screw diameter, preset value of speed is set at the same time, equipment pressure and speed are matched.
analysis of Moldflow software 
In this way, all process parameters can be collected, and a first trial process algorithm verification can be carried out.

4. Summary of differences and practical solutions

(1) Problems of equipment status and pressure loss mainly focus on movement loss of equipment oil temperature and pressure.

Equipment oil temperature: Oil temperature of injection molding machine is an important basis for ensuring a stable production of injection molding machine. Hydraulic oil of injection molding machine will be viscous at low temperature, and will become thin when temperature is too high. Power of injection molding machine, especially hydraulic injection molding machine, is almost all provided by carrier oil of oil pump, so energy error between too high and too low temperature is very large. Maximum power of oil pump motor speed of injection molding machine is a rated power. When oil temperature fluctuates, corresponding fluctuations are required to obtain corresponding power. Therefore, oil temperature is an important influence of state differences.
Movement loss of pressure: All movements will have energy loss during process of injection. Energy is lost in process of injection, through gate, through nozzle, etc., and you should pay attention to loss of pressure when setting injection pressure.
Movement loss of equipment oil temperature and pressure is mainly compensated by setting pressure, so that a stable injection can be performed and mold can be better verified.

(2) Calculation of equipment tonnage

Calculated tonnage of equipment is slightly higher than actual clamping pressure, but in mold manufacturing industry, clamping force is not fixed, so it may be necessary to increase clamping force as much as possible to ensure stability of mold state. Considering that analysis is carried out in a completely ideal state, there will be deviations in practice, so clamping force will be high. At the same time, size of projected area S (see above) is generally larger than actual area, so tonnage calculation can be completely budgeted according to data analyzed by CAE, which can meet requirements.

(3) Differences in deformation and warping

Multi-cavity deformation and warping, major reason is that difference between actual and theoretical values is due to unbalanced glue discharge from gate, and reason for unbalanced discharge of glue is inconsistent wall thickness of two cavities caused by processing error. Actual product needs to be cut open for measurement. If it can be corrected by gate, gate will be corrected first, and judgment of wall thickness of product needs a little search.

(4) Gate gas mark solution

It is difficult to solve gate gas mark solution. First, adjust gate on CAE analysis, so that contour line has a uniform entry at gate position, and try to avoid occurrence of gas marks in advance. When adjusting process, slow down feeding speed, let material enter product smoothly, and finally realize disappearance of gate gas marks. High mold temperature is also very effective in adjusting air marks.
For gas marks of trapped air, it is necessary to clarify cause of problem first, because gas in closed structure cannot be discharged, and material along flow turns out from inside together, so when adjusting such gas marks, it should be mainly to increase exhaust gas. .

(5) Position and length difference of welding line

Weld lines in CAE analysis are weld lines and bonding lines, but length of lines in actual production is almost difficult to be consistent with analysis. In actual production, main factor affecting depth of weld line is exhaust. In the case of good exhaust, two strands of glue forming weld line can quickly collide with each other, temperature is high, a good strength can be achieved, and it can even be covered up in the case of electroplating or painting. Another mitigation method is to increase mold temperature as much as possible, keep fluidity of glue in a good state, try to reach state of bonding line in analysis, and finally successfully hide or reduce welding line.

(6) Analysis parameters and actual parameters

Error value between the two is difficult to confirm, but according to logic of normal production, try to increase pressure to ensure injection speed, then slowly adjust pressure downward to find a suitable value. Analysis parameters have a guiding role for actual debugging, especially one-piece barrel as shown in Figure 1, products that are easy to hold mold, deep cavity or mold whose ejector mechanism is not easy to adjust, necessity of the first full state is very high.
Therefore, some algorithms of CAE and actual connection will be a kind of demand of mold companies and even mass production manufacturers in the future. Whether it is injection molding machine analysis that MOLDEX 3D has started now or experience calculation of each craftsman, it is prototype of the first trial process algorithm.

5 Conclusion

In the case of product confirmation, CAE's front-end analysis has played a great guiding role in actual production and mold opening. Whether it is from budget of equipment tonnage or inference of welding lines, it has an important guiding role.
However, other problems will always occur in actual production of product, which is slightly different from state of previous analysis. At this time, experience of craftsman is needed to adjust parameters to achieve effect of previous budget. Function of process is to accurately determine what is factor causing this deviation. For example, inconsistency of deformation can be confirmed in time due to unbalanced flow of gate, so as to adjust mold or process, and even gate temperature in a targeted manner.
At the same time, feedback to front-end analysts and processing personnel during debugging, then consider unavoidable problems in subsequent analysis, and remind processing personnel to pay attention to accuracy of special points, so that role of process can be maximized. At the same time, analysis of CAE It will also become more and more accurate, linking front-end design with back-end production, and gradually improving the first-time pass rate of mold. At the same time, the first trial process algorithm is slowly forming a prototype, which will definitely shine in trial production of molds in the future.

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