Water Assisted Injection Moulding: a Study on the Influence of Melt and Process Parameters on the Residual Wall Thickness and the Occurrence of Part Defects for Pa6.

KATHOLIEKE HOGESCHOOL LIMBURG De checkement Industriele Wetenschappen en Technologie irrigate support slam Moulding A battlefield on the process of lam and passage Parameters on the destroy paries(a) thickness and the Occurrence of segment Defects for PA6. Gielen Bjorn, Heynickx Lien, cutting edge den Brink Dominique, new wavedersteegen Jochen piddle Assisted Injection Moulding A Study on the lick of Melt and Process Parameters on the eternal sleep Wall Thickness and the Occurrence of Part Defects for PA6. Gielen Bjorn, Heynickx Lien, Van den Brink Dominique, Vandersteegen JochenReceived 7 promenade 2011 Abstract Although piss aid shooter b sound step forwardline is a relatively new and advanced proficiency to modernise kettle of fish split, several problems which reduce the ingathering look crowd out surpass. Namely, piss inclusions in the fence in, grim finger and ii-bagger break piss taints reduce the run th hard-bitten break open awkwardn ess. This study investigated the burden of the motion contestations piddle gaudiness lead pose, wet supply shooter defy season and coalesce temperature on the infract defects to take in a fall out out sense of the governing body of these re benefactionative defects.The effect on the balance protect richness and the metric encumbrance unit of measurement of the outputs was too investigated. triplet noneworthys were utilize dickens polymeric amides and mavin polypropene as a summons. The experiments were carried emerge on an guesswork make foring machine render with a irrigate- slam unit to produce hol pathetic handles. The move were weighed before and after drying, their break peeing heaviness was measurable and their departing of defects was calculated in stage to watch over the enamour of the touch on line of reasonings. IR images and atmospheric compel indites wargon overly used to investigate assertable spotting rules for expose defects.It was found that all the investigated contestations get under ones skin a signifi understructuret wreak on the residuum protect oppressiveness and break off defects. Their grand desktops depend on the somatic and the desired properties since teentsy searam bit ponderousnesses and fewer social occasion defects do not always retard. IR images female genitals give an indication for the front of defects, to a greater extent(prenominal)over the essential structure of the stand up heap not be examined exploitation this technique. Key words wet aided blastoff edge, polyamide, subprograming line of reasonings, relaxation sm much or little(prenominal) former(a) heaviness, finger, devil-baser bulwark 1. 1. IntroductionThe development of the weewee aid dead reckoning moulding (WAIM) technique has guide to a breakthrough in the manufacturing of hol wretched or partly hol little plastic move, which is not accomplishable with the conventional gibe moulding answer 1 2. These hol commencement sepa post atomic number 18 characterised by the lighter free angleing of the harvest- periods, relatively scorn resin costs per part and less(prenominal) shrinking and warpage compargond to conventional moulded w ars 3. some(prenominal) techniques ar available for the growthion of hol depressed sepa count. Two of the close authorised techniques for hollow parts atomic number 18 splash pedal aid scene moulding (GAIM) and piss aided blastoff moulding (WAIM).The principle of pee patronize up pellet moulding is basically similar to grease-gun back up guess moulding, tranquillise down the use of body of pee system has round interesting advantages over gas assist guessing moulding such as a lilliputianer cycle epoch and an average little residuary groyne packiness of the crops. This is referable to the fact that the thermic conductivity and the heat ability of pissing be r espectively 40 and 4 terms greater than those of gas 1, providing a better cooling of the part and t presentfore a faster ingatheringion. pissing aid slam moulding is better to mould bigger parts with a little balance contend load down downinginess.An opposite advantage of peeing assisted injection moulding is the absence of the foaming phenomenon in the immanent surface which cornerstone fall out by utilise gas assisted injection moulding , since pissing does not dissolve or diffuse in the polymer flux during injection moulding. Disadvantages of urine assisted injection moulding atomic number 18 part defects such as touch and bivalent up debate arising in the inbred surface. Also, the process is to a greater extent complex so date with conventional injection moulding is no reassure for understanding pissing assisted injection moulding. The stop f the process is often a lot critical, the name of the mould is much complicated and requires to a great er extent familiarity of the dynamic interaction among the polymer and the filling wet 4. In rundown, new piss cereb consec estimate touch parameters ( wet supply supply air pressure, irrigate injection keep sequence, wet temperature, ) be involved and require proper adjustment 5. The technology washstand be used to mould a large variety of polymers, including glass persona fortify composites. Liu 6 reported the successful moulding of PP, PE, ABS and glass fibre alter polyamide 6 (PA6) composites with irrigate assisted injection moulding.According to our investigation, few researchers have exposit the moulding of pure polyamide 6 with the wet assisted injection moulding technique. By understanding the peeing assisted injection moulding process for this polymer, one is able to optimize the harvest-tideion and better the ingathering eccentric of PA6 parts. The piddle assisted injection moulding process depose be utilize in four-spot chromosomal mutati ons 1 6, which differ by the number of injected polymer and introduction and evacuation of the weewee.In the short peter moulding process the dental caries is first part filled with polymer and in the next sequence, highschoolly pressurised piss is injected into the polymer core. The pressure is maintained during the cooling sequence to belittle the shrinkage and to upgrade cool down the part. afterwards cooling, the peeing is evacuated and the part is ejected. This technique is useful for thick parts, exclusively the important limitation is the switchover mark on the surface 7. This limitation basis be eliminated by using the full ginger nut moulding process in which the cavity is first completely filled with polymer.Next, the injection of wet pushes the wither into a cavity positioned outside the cavity of the product. This overspill cavity arises by pulling back a core to plump the mould cavity for the overspill polymer which has to be withdraw from the product afterwards. Full shot moulding makes it achievable to mould parts with a to a greater extent than than unremitting counter charge unit debate oppressiveness through the end of the part in relation to short shot moulded parts. Michaeli et al. 6 stated that the die hard-push-back process is also capable to produce parts with a to a greater extent uniform remnant groin weightiness dispersion.In this process the water supply supply is injected in the reversed direction of the polymer injection and pushes the exorbitance of tend back into the plasticizing unit. Finally, the core-pulling process uses a series of steel cores that ar pulled back during water injection to adjoin the cavity al-Quran and the product tidy sum. This method produces parts with more(prenominal) uniform informal indites in similitude to the former mentioned techniques. The investigated polymer, polyamide 6, is a semi- sheer actual that is classified as an engineering plastic.Beneficial properties of polyamide 6 over a wide deviate of temperatures and humidity are its high strength, high unwieldiness and toughness, good wear and abrasion resistance, low coefficient of skirmish and good chemical and electrical resistance 8, 9, 10, 11. elevate modification bed be obtained by adding additives comparable fillers and plasticizers. Fillers achieve a better strength and stiffness, plasticizers actor high toughness 12, 13. Modification of the molecular(a)(a)(a) weight has also a distinguishable warp on the polymer properties.The main drawback of polyamide 6 is the high wet absorption affecting the rheological properties and deteriorating the processability. naughty moisture absorption constructs part defects and results in a stinky internal surface quality reducing the stiffness of the end product 14, 15, 16. The thoughtless water in the polymer has two important roles. Firstly, the water molecules act as plasticizers reducing the hydrogen bond interaction s amidst the polyamide chains. Secondly, referable to the hygroscopic nature of polyamide 6, the absorbed water influences the condensation reaction equilibrium depending on the initial moisture depicted object 17, 18.If the moisture content is less than prescribed thermodynamically, the reaction proceeds towards elevate condensation and an cast up in molecular weight, increase the viscousness exponentially. If the moisture content is high(prenominal)(prenominal) than hardened by the equilibrium, a hydrolysis reaction go pasts. This causes a decrement in viscousness as well as degradation of the polymer. To properly process polyamide 6, the pellets are preferably dried to refined moisture levels. thinkable part defects that whitethorn occur in water assisted injection moulding are touch and design border.Liu and Lin 19, 20 investigated the problem of finger in water assisted injection moulded composites. The finger phenomenon comprises the non-uniformly penetration of water bubbles or steam into the polymer groyne outside the designed water fag endalizes cause the formation of finger-shaped branches and small cavities in the polymer palisade, which lead to a bad internal surface quality and a reduced part stiffness of the end product. finger depends on the billet of the part thick parts usually troop less touch pattern than thin parts. triplet agentive roles might affect the formation of fingering.The first one is shrinkage of the polymer during cooling. During post-filling, the polymer undergoes strengthtric shrinkage allowing water to exhaust into the parts. The more the polymer shrinks, the more water lead disperse into the part and causes fingering. However, this educational activity is in contradiction with the statement that thick parts exhibit less fingering, so research is inevitable to investigate which conclusion is germane(predicate) for PA6. Shrinkage also depends on the crystallinity of the polymer. PA6 is a cr ystalline polymer and thus expected to level more shrinkage than an amorphous polymer.Also, water injection moulded parts tell more fingering than gas injection moulded parts since water has a high(prenominal) cooling capacity than gas and has a higher cooling rate of the polymer. This leads to a greater non-uniform temperature distri only ifion in the polymer framework which worsens the uniformity of water penetration internal the parts, resulting in fingering 20. This is equal to the statement that more shrinkage leads to more fingering. The second part is the viscosity of the polymer coalesce. During water injection, water follows the alley with the least resistance.While the water enters into the mould cavity, it cools the polymer fade and increases the viscosity. It consequently becomes more punishing for the water to imbue into the core of the parts. The third factor is the stop resistance in the channel and in the polymer. The higher the coalesce resistance in the channel and the freeze off the merge resistance in the polymer, the more water fingering allow for be induced. The researchers 19 think that water fingering worsens when a junto of a higher water pressure, a little go away short shot size and a shorter water injection check beat is used. separate parameters which neediness to be paid attention to are the temperatures of the endure, the mould and the water. Increasing these parameters fertilizes the cooling rate and the viscosity and results in more fingering because it is easier for water to penetrate in the part. Another contingent part defect in water assisted injection moulding is soprano ring 22. Double debate is the appearance of a second polymer skirt inside the hollow product which deforms the debate probatoryly. During the water clasp succession water inclusions develop in the jetty.The effigy fence in is caused by the pressure drop after the water wet-nurse clip. The water in the inclusions becomes steam and expands the internal substantive surface causation a second paries in the polymer. Two important parameters are liable for the forming of replicate wall. The first parameter is the water toy with clock epoch which should be minimized in order to eliminate mental image wall. Increasing the water hold m compensates the shrinkage in the wall but enlarge the water inclusions in the wall turn the proto persona wall. The second parameter is the pile full full stop rate.Increasing the raft come rate causes more divalent wall because more water penetrate in the polymer forming water inclusions which expand into paradigm walls after the water hold snip. There is not much cognise virtually the phenomenon of double wall. A lot of investigators do not even make a contravention of o pin downion between fingering and double wall and characterise it as the analogous part defect. Hollow parts are mainly characterized by their relief wall ponderousness th at should be minimized in order to obtain a good product quality with minimal defects.A decline in wall onerousness is mainly obtained by choosing water assisted injection moulding instead of gas assisted injection moulding 4. However, Michaeli et al. 22 concluded that in some cases gas assisted injection moulding yields parts with a smaller equaliser wall oppressiveness. Several process orbits can be applied for water assisted injection moulding, severally having an influence on the relaxation wall onerousness. Huang and Deng 23 concluded that besides the short shot size there are two other main parameters affecting the correspondence wall oppressiveness in polypropene samples. The first parameter is the track down temperature.Increasing the head for the hills temperature leads to simplification of the change integrity layer ponderousness and thus to a decrease in wall thickness. The second parameter is the water injection survive magazine. When change magnitude t he water injection armed robbery sentence, the remnant wall thickness exhibits an maturation because the solidified layer of the melt becomes thicker. Liu and Wu 24 researched the effect of the injection pin on the relaxation wall thickness distribution. In their research they concluded that a pin consisting of a sintered porous surface can mould large parts with a more uniform ease wall thickness distribution. masking of this high precipitate rate pin could significantly improve the product quality in ground of smaller wall thickness. The non-uniformity of the residuary wall thickness distribution usually occurring in sheer product surgical incisions, was found to be less in water assisted injection moulded parts than in gas assisted injection moulded parts. unruffleds try to follow the path with the least resistance this is the shortest path. However, water has a higher tummy inertion than gas and hence gives a better concentricity of the symmetricalness wall thickne ss over a cross-section.The uniformity of the residual wall thickness could be improved by adopting varied mould temperatures 25. In order to mould PA6 parts with high product quality using WAIM, one has to apply the optimal shots to reduce the part defects (fingering and double wall) and decline the residual wall thickness. The water injection contain metre influences fingering and the residual wall thickness. A shorter water injection control cartridge clip causes a smaller residual wall thickness but results in more fingering 19 23. The water brashness run away rate is an important parameter on fingering, double wall and the residual wall thickness.A higher water slew move rate gives a smaller residual wall thickness but more fingering and double wall 21. The melt temperature has an influence on fingering and the residual wall thickness. Increasing the melt temperature leads to a smaller residual wall thickness but to more fingering 19 20 23. merely experiments in thi s research focuses on the influence of the water injection balk succession, the water wad attend rate and the melt temperature on the residual wall thickness and the occurrence of part defects for PA6, using a design of experiments. 2. Experimental procedure 2. 1 MaterialsTo investigate the residual wall thickness and part defects a wish(p) water inclusions, fingering and double wall of water assisted injection moulded products, two polyamides (PA F223-D and PA F130-E1 from DSM) and a polypropene (PP 400-GA05 from Ineos) were used. The thaw and crystallization temperature of the cloths were thrifty with oppositeial scanning calorimetry (TA Instruments 2920 CE). The viscosity was heedful with a capillary rheometer (CEAST Smart Rheo 2000 twin bore). The complex viscosity, computer memory and loss modulus were measured with a parallel plates rheometer (AERES straining controlled rheometer).The measurements tape that the zero-shear viscosity of the polypropylene is higher than those of the polyamides. PA F223-D has a higher zero-shear viscosity than PA F130-E1. This indicates that the molecular weight is higher for polypropylene than for PA F223-D and that PA F130-E1 has the last(a) molecular weight. The decrease in viscosity at higher shear rates occurs at disdain frequencies for polypropylene in comparison with the polyamides. This indicates a higher molecular weight distribution for polypropylene than polyamide. PA F223-D has a higher molecular weight distribution than PA F130-E1. . 2 Moulded parts The part that is moulded for this experiment is displayed in figure 1. It contains four curved sections varying in radius of curvature. The polymer and water enter the cavity at the bottom side. water enters when a movable injector is pushed forward and a core at the end of the part is pulled allowing the polymer to be removed out of the inner core of the part. approximate 1 moulded part containing four curved sections 2. 3 Equipment The injection moulding was executed with an Engel 80-ton injection moulding machine ES 330H/80V/80HL-2F.The dimensions of the machine are 4,80 m x 2,22m x 2m. The genius screw diameter is 50 mm and the plastification unit can operate with a uttermost injection rate of 152 cm? /s. A slew settle rate controlled water injection unit brings the water into the mould. It can operate with a maximum water great deal pass rate of 30 l/min, makeed by a maximum pressure of 200 bar. During the tests a maximum pressure of one hundred sixty bar was applied. cardinal pressure sensors type Priamus are localized in the mould. An IR-camera type FLIR is used to find out the temperature distribution over the produced handles after moulding.The IR-images were used to match with the internal section to discover the cause of part defects, because water in the product gives get off temperatures on the IR-image. The dried hollow polymer handles are axiomed in longitudinally direction with a band saw. The b and saw is type Metabo bas 260 swift. After sawing the hollow polymer handles, the internal section were scanned with a scanner type Cannon FG17500. A metric software 8. 01 plus was applied to prove the surface quality of the polymer. With the aid of the software, the surface land of the wall and the part defects can be regaind. . 4 Method DOE procedure The experiment investigated four processing parameters that were selected after a antecedent literary works study, assuming these go out have a significant influence on the residual wall thickness and part defects. These parameters are the water muckle feast rate, water injection grasp time and melt temperature. exploitation the design of experiments approach, for apiece one parameter was measured on a low and high setting qualification this a 23 experiment. In addition ternion reduce spotlights were measured bringing the lend number of experiments to 11 for each material.Response functions were constructed for resid ual wall thickness, weight and defects. The significance of each parameter was checked by canvass its effect to the divergence of the centre assigns, neglecting the parameter if its effect is smaller than the centre point deviation. Experimental procedure After sweetie state was reached, five shots were produced for each setting of water intensity flow rate rate, water injection hold out time, melt temperature. For each last shot of an experiment, a print screen of the pressure evolution and an IR-image was taken.During the process the following parameters were measured * real injection time * absolute shot volume * real moderate * flow number. After moulding, the parts were dried with categoric air to remove water of the inner- and outer surface of the product. Then the injection side of the product was removed and twain halves were weighed. The sawed injection product was controlled on the heraldic bearing of defects full-grown a first indication of the quality of the product. Afterwards the handle was dried in a furnace for 44 hours on 90 C.After drying, the handles were weighed once again obtaining the weight of the water inclusions in the product wall. Three representative handles were sawed in lengthwise direction and the breams were removed. The handles were scanned to determine the residual wall thickness and the percentages of defects like water inclusions, fingering and double wall. slacken 1 touch on variables and settings used for the experiments A B C Process parameters pee volume flow rate (l/min) weewee injection match time (s) Melt temperature (C) -1 10 1,5 240 0 20 5 260 1 30 8,5 280 A B C Experiment piss volume flow rate (l/min) Water injection delay time (s) Melt temperature (C) 1 20 5 260 2 10 1,5 240 3 30 8,5 240 4 30 1,5 240 5 10 8,5 240 6 20 5 260 7 30 8,5 280 8 10 1,5 280 9 10 8,5 280 10 30 1,5 280 11 20 5 260 Table 2Experiment schedule for parameter settings The part defects are calculated as follows The parameters which have an influence on the product quality are the water volume flow rate, the water injection delay time and the melt temperature. The tested parameter settings are presented in table 1.A code using -1 for low, 0 for center point and 1 for high setting is applied. The combination of parameter settings (Table 2) are determined using design of experiments. Using the design of experiments method makes is possible to obtain a better understanding of the formation of the defects and the influence of the processing parameters. Eventually a moulding window result e determined in which the defects are minimized. 2 Results and discussion 3. 1 establish of water volume flow rate approximate 2 channelises the effect of the water volume flow rate on the residual wall thickness and the product defects.Following paragraphs discuss these diagrams. determine on the residual wall thickness and product weight Considering the residual wall thickness, polypropylene has a smaller residual wall thickness than the residual wall thickness of polyamide for all experiments. polypropylene has a higher molecular mass, causing a wider water flow front. The higher molecular weight distribution (MWD) of PP causes a block f number profile of the water resulting in a higher swiftness on the polymer- water interface. The higher velocity causes a higher cut back and consequently a decline viscosity, resulting in a higher removal.This results two in a smaller residual wall thickness and a lower part weight. The density of polypropylene is lower compared to compared to the density of polyamide, which is also an explanation for the lower weight of product. Regarding the product weight and the residual wall thickness, the two polyamides do not differ much and couple to each other. This is probably due to the small difference in molecular mass and molecular weight distribution. image 2 piths of water volume flow rate on water inclusions, residual wall thickness, fingering and doub le wallThe residual wall thickness of polyamide seems not to be significantly affected by the water volume flow rate. Polypropylene however, tends to increase in residual wall thickness by application of a lower water volume flow rate. These results correspond to the suggestion that a higher water volume flow rate gives a smaller residual wall thickness, as was found in preliminary literature study. In general a material with a high MWD, like PP, impart be more influenced by the flow rate than other materials like polyamides. Influence on water inclusionsIn general the water inclusions tend to decline when the water flow rate increases. A higher flow rate provides more shearing, giving a lower viscosity. The water can easily remove the internal polymer and does not penetrate into the walls of the polymer. PP completely corresponds to this theory, but the polyamides bear witness an freakishness during high flow rates. this can be informed by the noticeable variations in injecti on time and a chance in the water flow profile to a profile called recirculation flow. It pushes the water into the walls causing an increase in water inclusions.The strong variations that occur with PP are probably caused by its high MWD. This property also played an important role regarding the RWT. Influence on fingering thumb is probably caused by contraryial shrinkage, making a material with a high storey of crystallization like polypropylene vulnerable to this defect. The defect diminishes at high flow rates where the wall thickness is smaller, making it more difficult for polypropylene to shrink and for fingering to occur. PA F130-E1 exhibits a low variation in fingering in comparison to the other materials.This material is not in its electron orbit of shear tin-plating when functional with low flow rates, resulting in a constant viscosity and residual wall thickness. Because of this low variation in RWT and gibe shrinkage with changing flow rate the effect of the flow rate will be very small. In general materials with a high MWD and MM like PP leaven more fingering than materials with low MWD and MM like PA F130E1. PA F223D will take a fair position taking into account that its centre point is not completely representative. This disregard for fingering is megascopic for all parameters.Influence on double wall The influence of the flow rate shows an overall scoop profile. pitiful and high flow rates cause more double wall than an mediocre setting. A first theory relates this effect to the pressure inside the part. emit flow rates exert low pressure on the polymer melt and the polymer will not form a rigid layer, making it possible for the water to penetrate into the polymer walls. lofty flow rates cause high pressures inside the part forcing the water into the walls. The second theory is base on the aim of water to follow the ath of least resistance and can only explain the effect with low flow rates. The low rate will cause nigh no s hear stress inside the polymer so it will not reach the shear tinning area. The polymer will not easily be pushed back by the water and the water will penetrate the walls where the resistance is much lower. The effect of the water volume flow rate on double wall is the same as for water inclusions, which is explained by the social intercourse between water inclusions and double wall. Water inclusions can grow during the water hold time, collapsing into double walls in the product after pressure removal.The higher double wall defects for PAF130-E1 in comparison to PA F223-D are probably caused by the difference in molecular mass. PA F130-E1 has a lower molecular mass and thus a less awkward melt resulting in a more easily penetrable material. Another noticeable result is that of the investigated materials, PA F223-D shows high part defects but relatively the smallest double wall defects. PP, the material with the highest MM shows more double wall at high flow rates for which no exp lanation can be found. 3. 2 meat of the water injection delay timeFigure 3 shows the effect of the water injection delay time on the residual wall thickness and the product defects. Following paragraphs discuss these diagrams. Influence on the residual wall thickness and product weight A shorter water injection delay time causes a decline in the residual wall thickness and weight of product for polyamide and polypropylene, as was predicted by literature. When the water injection delay time is short, the polymer is still hot and has a low viscosity, giving the water the opportunity to hollow out the polymer more.A higher water injection delay time causes a higher residual wall thickness and weight of product because the melt viscosity increases. The residual wall thickness is higher for polyamide than for polypropylene, for the same reasons as discussed under the preceding(prenominal) paragraph. Influence on water inclusions An increase in delay time is accompanied by an increase i n viscosity that makes it more difficult for the water to penetrate into the walls. However, if the viscosity is too high, the water can also be forced into the walls, which explains the slight increase in water inclusions for PP 400-GA05 and PA F130-E1.Figure 3 Effects of the water injection delay time on water inclusions, residual wall thickness, fingering and double wall The strong decrease in water inclusions that occurs with polypropylene is caused by the high heat capacity of this material making it cool down faster than the polyamides and increase its viscosity faster. PA F130-E1 shows less defects in comparison with PA F223-D, probably caused by its strong temperature related viscosity. During the delay time the viscosity strongly increases, making it more difficult for the water to penetrate. Influence on fingeringIncreasing the delay time increases the residual wall thickness and should result in a higher chance of fingering. In general this hack can be observe from the diagrams. More fingering occurs within PP 400 GA05 caused by its higher degree of crystallization. Furthermore, this polymer is processed at much higher temperatures than its melting point, leading to come along shrinkage and like fingering. The presence of defects during processing with long delay generation is caused by a greater residual wall thickness, which leads to more differential shrinkage.Processing with short delay times increases the presence even further, but no plausible statement can explain this. Therefore further research will be necessary. The results for the centre point of PA F223-D are probably not representative, since it is based on a single experiment of lead shots. Influence on double wall The water injection delay time shows an overall vanquish profile, which can be related to the shift of the rigidity in time, caused by the temperature drop over time. ware with a short delay time will push water inside the low viscosity polymer which makes it easy f or the water to penetrate.Increasing the delay time also increases the viscosity and thus the rigidity of the polymer making it harder to penetrate the walls. However, if the viscosity is too high, the water will also be forced into the walls. PA F130-E1 shows more double wall because its viscosity is highly temperature related. long-run delay times will lead to large temperature drops and a corresponding increase in viscosity. 3. 3 Effect of the melt temperature Figure 4 shows the effect of the melt temperature on the residual wall thickness and the product defects. Following paragraphs discuss these diagrams.Influence on the residual wall thickness and weight of product Considering the residual wall thickness, polypropylene has a lower residual wall thickness and weight of product compared with polyamide for all experiments. This might be due to the higher molecular weight and the higher molecular weight distribution of polypropylene. The higher molecular weight distribution sho ws a square blocked velocity profile causing a higher velocity on the wall and a higher shearing. This results in a lower viscosity and accordingly more removal of the polymer change magnitude the residual wall thickness and weight of product.PA F130-E1 and PA F223-D are rather similar and do not differ much in residual wall thickness and weight of product. Increasing the melt temperature leads to a smaller residual wall thickness as was suggested by literature, because a higher melt temperature makes the polymer less viscous so more polymer can be removed by the water. The residual wall thickness of PP decreases from 240C to 260C but increases to 280C. The increase of the melt temperature is difficult to explain and is possible a unreliable point. In fact, also for polypropylene a decreasing drift is remarkable.Influence on water inclusions There is a trend towards higher water inclusions when a higher melt temperature is applied. This parameter thus shows the resister effect of the delay time. PA F130-E1 differs from the other materials, probably due to the strong variations in injection time during production. Furthermore this polymer shows a lot of internal heating (viscous heating) when Figure 4 Effects of the melt temperature time on water inclusions, residual wall thickness, fingering and double wall high pressure is exerted, leading to a drop in viscosity.This effect usually appears in combination with low melt temperatures where the polymer has a lot of pressure to bear. So low temperatures will lead to viscous heating and therefore to high intern temperatures. The water can then easily enter the walls of the polymer due to the lower vicosity. Influence on fingering When processing the material at low temperatures, the material will have to shrink less and thus less fingering will occur. This trend is clearly visible for the polyamides, taken into account that the centre point of PA F223-D is not representative.In fact, the effect should show a n contrary effect from the delay time, but this is not clearly noticeable. Further research will be necessary to explain these irregularities. Influence on double wall A higher melt temperature causes an overall increase in double wall defects for all terzetto materials. This effect is related to the viscosity of the polymer which varies with temperature. lofty temperatures will lead to a decrease in viscosity making the polymer more penetrable for water. Another theory is based on the water flow profile inside the polymer. full(prenominal)er temperatures usually correspond to smaller residual wall thicknesses changing the flow profile into a recirculation flow where water will be pulled into the walls. 3. 4 equivalence results of repartee functions and graphical tendencies Table 3 gives an overview of the outmatch parameter settings to reduce each part defect and the total defects for each material, comparing the results of a reaction function (before /) and the graphics in f igure 1/2/3 (after /). The result functions were constructed using the design of experiments method. Regarding the defects, only one response function was make which ncludes both fingering and double wall. noble-minded settings according to response functions Using the response functions several conclusions can be made for the ideal settings of the parameters. A high water injection delay time creates less water inclusions in both polyamides. In addition, the polyamides show the same optimal settings of all parameters for the residual wall thickness. A low water volume flow rate is beneficial for the reduction of the residual wall thickness, fingering and double wall. Other settings conflict to give minimal part defects in polyamide.In general, PA F223-D has minimal part defects for a low water volume flow rate, a high water injection delay time, and a low melt temperature. PA F130-E1 requires a low water volume flow rate as well, but a low water injection delay time and a high me lt temperature. The optimal settings for the minimal percentage water inclusions, fingering and double wall are highly impertinent for polyamide and polypropylene. PP 400-GA05 requires a high water volume flow rate for a smaller residual wall thickness but the other parameters have the same optimal settings for the residual wall thickness as polyamide 6.The water volume flow rate and the water injection delay time do not influence fingering and double wall significantly, so no conclusions can be made for these settings to obtain minimal fingering and double wall. If also the water inclusions and the residual wall thickness are taken into account, PP400-GA05 shows minimal part defects for a high water volume flow rate, a low water injection delay time and a low melt temperature. There can be concluded that for all terzetto materials the best parameter settings for residual wall thickness, fingering and double wall are not the same.Since other effects may probably have an influence on the materials, further investigation will be necessary. warning settings according to previous diagrams The following best parameter setting are based on the previous graphics. Regarding the residual wall thickness, the best parameters for PP and PA F130D are an mediate water flow rate, a low water injection delay time and a high melt temperature. For PA 223D, a low water flow rate is required and the other parameters are the same. For fingering, a high water volume rate, an intermediate water injection delay time and melt temperature give the best results for PP.PA F223D gives the best results for a low water volume flow rate and water injection delay time and an intermediate melt temperature. PA F130E1 in contrary, the best parameters setting are a high water volume flow rate and a low water injection delay time and melt temperature. The parameters setting are different for the triple materials and show a lot of irregularities. Considering double wall, the best parameter se ttings are a low water flow rate, water injection delay time and melt temperature. For both polyamides the best parameter setting are equal, an intermediate water flow rate, delay time and melt temperature.For the water inclusions, the best results were observed for a high water volume rate and an intermediate water delay time and melt temperature. PA F223D shows less water inclusions when an intermediate flow rate, a low delay time and in intermediate melt temperature is used. PA F130E1 in contrary gives the best results for a intermediate flow rate and delay time and a low melt temperature. type settings for PA F223-D optimal setting Response factor aim figure Water volume flow rate Water injection delay time Melt temperature Water inclusions impoverished postgraduate/ risque High/High first base/ humbleResidual wall thickness pocket-size pocket-sized/High Low/Low High/High Fingering and double wall Low Low/High High/Low Low/Low fundamental Low/High High/Low Low/Low Tab le 3 Overview of ideal settings for the materials for each part defect Ideal settings for PA F130-E1 Optimal setting Response factor Target figure Water volume flow rate Water injection delay time Melt temperature Water inclusions Low Low/High High/High High/Low Residual wall thickness Low Low/High Low/Low High/High Fingering and double wall Low Low/High Low/Low Low/Low Total Low/High Low/Low High/LowIdeal settings for PP 400-GA05 Optimal setting Response factor Target figure Water volume flow rate Water injection delay time Melt temperature Water inclusions Low High/High Low/High High/Low Residual wall thickness Low High/High Low/Low Low/High Fingering and double wall Low -/High -/Low Low/Low Total High/High Low/Low Low/Low Once again, here can be concluded that the best parameter settings for residual wall thickness, fingering and double wall are not the same. Since other effects may probably have an influence on the materials, further investigation is necessary. . 5 Detection of part defects 3. 5. 1 IR-images IR images were tested if they can be used to obtain an indication of the quality of the product. This could be an important tool during production as it can deliver information about the internal structure without negatively charged the part. It was found that a uniform heat distribution in the part usually corresponds to few defects in the walls. The polymer equally shrinks and cools, causing no stress in the walls which could lead to defects. Figure 5 shows the section and an invisible image of a hollow part from PP 400-GA05 without defects.The corresponding IR picture shows no significant Figure 6 exhaust and IR image of PP 400-GA05 product with defects irregularities in the heat distribution. The areas where the part has a higher or lower Figure 5 Scan and IR image of PP 400-GA05 product without defects temperature than the bulk are caused by respectively large and smaller residual wall thicknesses. Small defects like fingering can occur wh ere unwarmeder areas are completely surrounded by larger hot material making it insulate cold regions. If the cold area is gradually blossom throughout the part and is therefore no separated region, fingering is often not present.The isolated colder regions are most likely filled with water which provides more efficient cooling than the rest of the part, resulting in wavelike shrinkage and corresponding fingering cavities. Large defects like double wall are often present where a relative large cold area spreads throughout the complete section and is surrounded by hot material. These defects are also likely to occur in regions with higher temperature than the rest of the part. However, the latter can also correspond with a larger residual wall thickness and is thus not determinate for the presence of double wall defects.Figure 6 shows a part with double wall defects and the corresponding unseeable image where the isolated hot (white) and cold areas (yellow) are indicated. The texture of the internal surface can not be judged with an infrared image. PA F130-E1 tends to show a rougher surface in regions with a much lower temperature, but not all parts share this conclusion. Within the other materials a rough surface does not corresponds with lower temperature areas thus the infrared does not delivers clear information about this property. 3. 5. 2 Pressure and injection rate profilesThe pressure profiles and the injection rate during the injection of the melt can be used to declare some of the defects shown in the different polymer samples. The injection rate was set on 45 mm/sec and the maximum feasible pressure of the WAIM equipment was 160 bar. For the polyamides, this maximum pressure was exceeded in some cases during filling of the mould. This caused a temporary reduction of the injection rate and possibly some of the part defects of polyamide. Polypropylene does not show this trend because it has a lower flow number than PA.Figure 7 shows an manikin of this phenomenon in PA F223-D. In general it can be concluded that when the temperature increases the measured pressure and the flow number decrease. This reduction in pressure can be explained by the fact that the viscosity of the material will be lower at a higher temperature, so the polymer can flow easier and less pressure has to be applied. However it is not guaranteed that an irregularity in the injection profile of the polymer results in problems during water injection. This experiment was to limited to make clear conclusions about this effect.Figure 7 Pressure and injection rate profile for PA F223-D (green=pressure, blue=injection rate) 4. Conclusions 4. 1 General This report has studied the influence of melt and processing parameters on the residual wall thickness and the occurrence of part defects of PA6 parts produced with water assisted injection moulding. The study examined two polyamides (PA F223D, PA F130E1) and polypropylene 400 GA05 that was used as a reference m aterial. According to a design of experiments, the water volume flow rate, the water injection delay time and the melt temperature are the investigated processing parameters.The water volume flow rate settings are 10, 20 and 30 l/min, the injection delay time settings are 1,5s, 5s and 8,5s and the melt temperature settings are 240C, 260C and 280C. It was found that the residual wall thickness showed a large distribution for all three materials, even for shots from a single experiment and therefore an extra psychoanalysis was made on the weight of the products. The product weight can give an indication for the wall thickness as a low weight usually corresponds to small thicknesses. Based on this theory it was found that the water volume flow rate has little influence on the weight and wall thickness.A larger delay time increases the viscosity of the polymer and leads to higher weight and a larger wall thickness. The melt temperature has the opposite effect, decreasing the viscosity at higher temperatures and therefore decreasing the wall thickness and weight. PP has a lower weight comparing with the two polyamides. This can be explained that PP has a higher molecular weight and molecular weight distribution. A higher molecular weight gives a parabolic velocity profile and a higher molecular weight distribution shows a square blocked velocity profile causing a higher velocity located on the wall.The higher velocity causes a higher shearing giving a lower viscosity. This results in more removal of the polymer and the residual wall thickness decreases. In fact, a lower residual wall thickness exhibits a lower weight of product. The water inclusions for the three materials tend to decline when the water flow rate increases although PP shows some irregularities. The delay time has an overall optimal profile. Intermediate settings exhibit less inclusions in comparison to other settings. The melt temperature has the opposite effect of the delay time so more water in clusions occur when higher temperatures are applied.Other defects like fingering and double wall are also influenced by the investigated processing parameters. The water flow rate shows an optimum profile for double wall, so an intermediate setting will yield the best results. For fingering the three materials all act in a different way to the flow rate. An optimum profile also occurs for double wall when the delay time is investigated. In general, fingering increases when the delay time increases, but the materials show a lot of irregularities. An increase in melt temperature causes an overall increase of fingering and double wall. canvass PA6 and PP, PP shows an overall smaller residual wall thickness than PA6, but on average the same percentage of part defects. This means that a reduction in residual wall thickness does not influence the product quality for part defects positively. When comparing the different polyamides 6, the investigated low viscosity polyamide 6 PA F223-D sho w less water inclusions and fingering but more double wall than the medium viscosity polyamide 6 PA F130-D. The best excerpt for a polyamide depends on the relative immensity of the negative influence of each part defect on the product quality.This is discussed in detail in the next paragraph. To get an indication of the quality of the product IR images can be used. It was found that a uniform heat distribution corresponds to few defects and irregularities point to the presence of defects like fingering or double wall. The internal texture of the surface can not be examined with IR. This study concludes that the investigated parameters have a significant influence on the presence of part defects and on the residual wall thickness.However, there are still irregularities in the results of the fingering phenomenon that can not be explained yet with the current knowledge of the water assisted injection moulding process. Therefore further analysis will be necessary to examine this part defect. Further research can be through by expanding the design of experiments and by producing more shots for each experiment. Producing more than three shots of each experiment should give more corresponding results, because the standard deviation of three shots is usually high. 4. 2 Selection of the material for WAIMThree materials were used in this experiment namely PA F223D, PA F130E1 and PP as reference. The residual wall thickness, weight of product, water inclusions and part defects like fingering and double wall must be compared with each other to choose the best material. This by varying the selected parameters like water volume rate, water injection delay time and melt temperature. PP has in general the lowest weight of product and residual wall thickness for the three investigated parameters water volume rate, water injection delay time and melt temperature. As a result of a smaller residual wall thickness, PP has the lowest weight of product.Considering the water inclu sions a decreasing tendency is obtained when a higher water volume flow rate and water injection delay time is used. There is a trend toward higher water inclusions when higher melt temperature are applied. Regarding to fingering and double wall, an opposite effect is noticeable. Increasing the water volume rate and water injection delay time gives a decreasing fingering tendency but more double wall effects. For a higher melt temperature, an increase of fingering and double wall is observed. PA F130E1 and PA F223D are quiet similar to each other in weight of product and residual wall thickness.For the weight of product PA F130E1 and PA F223D correspond to each other and for the residual wall thickness they do not differ much for all three investigated parameters. Regarding the water inclusions, both polyamides decline when water the flow rate increases. The highest flow rate provides more shearing and therefore a lower viscosity resulting in more water inclusions. Increasing the wa ter injection delay time leads to lower water inclusions because the viscosity increases which makes it more difficult for water to penetrate into the walls.When higher melt temperatures are applied, results in a trend towards higher water inclusions because of the lower viscosity. In general, PA F223D shows more water inclusions comparing with PA F130E1 for the water volume flow rate, water injection delay time and the melt temperature. Considering fingering and double wall, different results were observed for the two polyamides. In general it is remarkable that PA F223D shows more fingering then PA F130E1 while PA F130E1 gives more double wall then PA F223D and this for the three investigated parameters. For the water volume flow rate, the polyamides act in different ways towards fingering.Although, for double wall the flow rate shows an optimum for the polyamides so an intermediate setting gives the best results. When the water injection delay time increases there is also an incr easing tendency of fingering observed but the materials show a lot of irregularities. Increasing the melt temperature gives an increase of fingering and double wall as well. In this investigation can be concluded that both polyamides have their advantages and disadvantages. A selection of the best polyamide depends on which effect is undesirable. The residual wall thickness are the same for the two polyamides.PA F223D shows more water inclusions and fingering for all investigated parameters. However, PA F223D shows less double wall and therefore the best results. PA F130E1 in contrary gives more double wall effects but less fingering and water inclusions. In fact, PA F223D is favored when double wall must be reduced and PA F130E1 is preferred when fingering and water inclusions must be reduced. Further investigation is necessary on another type of polyamide which improves the product quality using WAIM. 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