Study Of Injection Mold Temperature And Cooling Time Engineering Essay

Study Of Injection Mold temporary workererature And modify date Engineering hearMajority of complicate plastics inter drytion points ar formed by the snap work demonst sum up. Faster production rate and repeatability are the key elements. Although almost of the nip honking machines are highly sophisticated in damage of process run into yet the control of roam temperature is the most unatt blocked aspect. The throw cool clock contri exclusivelyes a major portion (usually 30 to 60%) of total round sequence. Reduction in mold cool while is directly associated with profitability. The effect of mold temperature on modify system snip and product quality is very important to at a lower placestand. Here an effort has been made to snap miscellaneous aspects of mold alter.IntroductionInjection mildew is oneness of the most favorite processing manners among the polymer mainframe computers that has revolutionized the polymer processing. Continuous research work c arried tabu by the nip molding machines manufacturers is the key behind the success of this processing technique. Todays injection molding machines are one of the most sophisticated in terms of process control. Various processing parameters the exchangeables of injection pressure, injection speed, staunch on pressure, cavity pressures etc. are very precisely controlled by close loop control. Latest developments in the field of microprocessors/ microcontrollers technology resulted in PLCs, with very short s grass judgment of conviction, for quicker response. Many other developments like advancements in plasticizing screw picture, draw safety, all electrical actuators, robotic pop remotion etc. came into existence in first nineties 1.Although a lap had happened at the technological front, still the control of cast off temperature is the most neglected aspect of injection shake offing technology. In spite of well know relationship between mould temperature and cooling time, in other lyric poem mould temperature has great(p) effect all over cycle time (that ultimately leads to profitability), no serious efforts has, however, been made to ext remainder the advancements in process control up to the mould. As on today most of the processing industries voluminous in injection moulding business, especially in Asian countries are using either a cooling tower or refrigerate chilling plant and seldom a mould temperature controller for engine room/ specialty polymers. In fact moulders usually do not get to about the mould temperature. In most of the cases, setting of cooling time and appointment of mould temperature is an experience driven exercise that may not always land up at optimum solution 2.In this paper an effort has been made to draw a deeper insight of various aspects of mould temperature and cooling time by modeling and simulation route. An modernistic design concept of mould temperature controller is also discussed which is in its ear ly developing stage. hot pants Transfer in Injection barf cacoethes convert in injection mould is quite complex in nature. It involves conductive and convective type of mania enthrall, although negligible fire up loss from mould takes place in form of radiation 3. The solidification process for melted polymer mass inside mould involves a complex rage transfer mechanism. In dictate to simplify the problem of warmth transfer associated with disruptive fluid devolve, here an assumption is made defining a change little temperature between the cavity wall and cooling channels of mould. However in actual practice a temperature incline ordain exist depending upon the thermic conductivity of mould steel.The typical hot pants path in the cooling stage of injection molding is that conflagrate is conducted from hot polymer to the comparatively inhuman mold, and then conducted with the mold to the cooling line, where it is removed by convection through coolant 7. In injection molding, in order to reduce the cycle time, the coolant undergoes dissolute flow. Rapidly flowing fluids are fully turbulent when Re 10,000 the transfer of heat is very efficient. Slowly flowing fluids are laminar when Re For turbulent flow, Equation 1 is utilize to calculate the heat convection coefficient 5, (1)Where d diameter of cooling hole (m), V coolant velocity (m/s), coolant density (kg/m), viscosity, h convection heat transfer coefficient (W/m.K), k thermal conductivity (W/m.K), L perimeter of the cooling hole (m).For this case, Re is 10,000, so the flow is fully turbulent.A simulink model was developed to simulate the variation of mold temperature from start up to near 1 hour and 23 legal proceeding run with following conditions 6Table 1 Conditions for SimulationInitial blend Temperature523 deg.KInitial Mold Temperature298 deg.Kjutting Temperature364 deg.KMass of Mold200 kgSpecific heat of mold (P-20 steel)461.2 J/kg k round of drinks duration30 siemensInjec tion conviction5 sec change magazine20 sec veridicalABS plastic, Grade Cycolac GPM550thermic Conductivity of ABS0.22 (W/m.deg.K)Specific screw up of ABS2352.4 (J/kg.degK)It is usual practice among molders to run injection molding machine for few (10 20) cycles without flow of coolant in mold to sum up the molds surface temperature up to the required mold temperature 7. This is usually through to void short shots, flow lines and other possible molding defects. A defunct zone has been incorporated in simulink model for 450 sec (about 15 molding cycle). This effect can be seen in plot. Initially the rise in temperature is rapid (up to 450 sec) compared to rest of the part of plot. figure 1 Graphical delegation of Model using SimulinkFig 2 Simulation Result for mold temperature for more than 150 cycles from startup.It is clear from the plot shown in fig 2, that under the conditions as defined in table 1, mould will take about 1hour to reach poise state temperature of about 32 0 deg.KDependence of cool down Time over Mould Temperaturetemperature reduction time is defined as the time required to reduce the temperature of molten polymer up to ejection temperature. usually ejection temperature of moulding is few degree (20 30 degC) below the heat deflection temperature (HDT) of material to insure distortion free removal of moulded part. Cooling time starts just after complete filling of cavity up to ejection. A rough estimation can be made for the cooling time, using the correlation given below (2) (3)s part oppressiveness (cm), thermal diffusivity (cm.sq/ sec), Tm melt temperature (C), Tw mold temperature (C), Te ejection temperature (C), K thermal conductivity (W/m-K), density (gm/cc), Cp Specific heat (KJ/Kg-K)It is clear from sour result shown in fig. 2 that mould temperature is not a aeonian, in fact it is not only a variable from startup temperature to steady state temperature but also it changes during each cycle, fluctuating about cycle aver age temperature 5.In order to simulate the cooling time for one injection cycle the instant energy balance equivalence for cooling of given geometry of part can be create verbally as (4)This equation can be solved using finite element method with suitable boundary conditions i.e. constant boundary temperature or constant heat flow rate. For simplification of problem, a square shaped, ABS plastic part has been chosen. The both dimensional drawing and 3-D view of the part under compend is given belowFig-3 Two Dimensional orthographic view and tether dimensional view of ABS Plastics part under outline.ABS plastic material was selected for higher up geometry of part, the processing conditions and properties of the polymeric material are given belowTable-2 process conditions and properties of materialInitial mellow out Temperature523 deg.KInitial Mold Temperature323 deg.KEjection Temperature345 deg.KMaterialABS plastic, Grade Cycolac GPM550Density one C5 (Kg/m)Thermal Conductivit y0.22 (W/m.deg.K)Specific Heat2352.4 (J/kg.degK)In order to simplify the analysis and to reduce the simulation time, the analysis was done in 2 D. Transient thermal analysis was carried out using ANSYS 5.4. For the analysis 4-node thermal solid (PLANE55) element type was selected.Fig-4 Temp distribution at t = 50sec at mold temp = 312 KThe 2 D model was suitably meshed and analysis was done with different mold temperatures, given in table 3. Polymer melt temperature and part ejection temperature were kept same.Table 3 Polymer melt temperature vs. simulated cooling timePolymer melt Temperature = 523 deg.KPart ejection temperature = 345 deg.KMold Temperature(deg.K)Cooling Time(Sec)31262.53237033392.5343130Cooling time was graphically calculated at a point where the part temperature was below HDT i.e. 345 K, for each of the run. ANSYS Post processor was used to obtain the cooling time vs. temperature information.(A). Mould Temp = 323 K, Ejection Temp = 345 K and Cooling Time = 70 se c(B). Mould Temp = 312 K, Ejection Temp = 345 K and Cooling Time = 62.5 sec(C). Mould Temp = 333 K, Ejection Temp = 345 K and Cooling Time = 92.5 sec(D). Mould Temp = 343 K, Ejection Temp = 345 K and Cooling Time = 130 secFig-5 Dependency of cooling Time over Mold TemperatureIt is clear from the preceding(prenominal) plots that the temperature gradient (between melt and mould) is a fall quantity during every moulding cycle. In other words we can say that rate of heat transfer from melt to coolant is maximum at the start of cooling time and reaches to its minimum value at the end of cooling time. This diminish rate of heat transfer is responsible for long-lived cooling time resulting higher cycle time 8.Mould Cooling At Constant Heat Transfer investThe cooling time may be defined as the ratio of total heat to be removed (so that ejection temperature is below HDT), to rate of heat removal from the mould via coolants flowing in cooling channels of the mould. As mentioned above tha t diminishing temperature gradient (due to cooling of polymer melt inside the mould) is responsible for diminishing rate of heat removal during every moulding cycle. In order to have deeper insight, we apply heat balance to mould (5)It is clear from Fig. 2 that the temperature of mould increases initially and ultimately reaches to steady state average constant temperature inside few hours depending upon the size of mould and moulding. At this stage the rate of heat accumulation in mould will be negligible, whence at steady state condition of mould (6)(i). Rate of Heat InputRate of heat input to the mould may be considered as impulse input, since the most of the polymer melt (about 90% of shot weight) is injected in very short span of time (), comparatively very less than actual injection and hold time. The heat input rate to the mould (7)m = shot weight, Cp = specific heat at nozzle temperature.(ii). Rate of Heat RemovalFor simplicity we can assume the design of mould to be cylin dric, where four cooling channels are at coke PCD, concentric with cylindrical shape of cavity as shown in Fig. 6,Fig 6 Top view Cylindrical MouldThe rate of heat removal from the mould is function of heat transfer by conduction and convection (we can neglect the heat transfer by radiation). For the cylindrical design of mould and moulding, the conductive and convective heat transfer can be written as 9 (8) (9)Ksteel Thermal conductivity of mould steel (W/m-K), Dmold Dpart Diameter of cylindrical mould and moulding (m), Dchannel Diameter of cooling channel (m), h Convection heat transfer coefficient (W/m.K), at that placefore, the net rate of heat transfer will be (10)It is obvious from equation no. (10). that rate of heat removal (q) will continuously reduce because the Tmelt will tend towards the Tejection. The trend of melt temperature swerve with time will be as shown in fig 5. There may be two different methods to keep the rate of heat removal (q) constant i.e. reductio n in coolant temperature (Tcoolant), parallel with (Tmelt) so that temperature gradient is constant during entire cooling cycle. This method has some practical difficulties like limitation of very fast changing temperature of coolant, thermal shock to the mould and lots of energy drain from coolant to atmosphere. In the next approach to book constant heat removal rate, the flow rate of coolant can be increased with time to increase the value of film transfer coefficient (h). carrel of these problems were modeled using Matlab and simulated results are discussed. The following boundary conditions and data was used for simulationTable 4 Boundary Conditions and dataParameters rangeDmold100 mmDpart15 mmKsteel36.6 W/m degKDchannel10 mmL1.5 metersTmelt523 degKTejecion364 degKCp2352.4 (J/kg degK ) for ABS Cycolac GPM 5500 GradeShot Weight (m)100 gmsTcoolant283 degKResult and DiscussionSimulation result for constant heat removal rate achieved via transient coolant temperature, are shown in fig. 8 and fig. 9. The heat removal at diminishing rate curve is of the same pattern as obtained by using Ansys FEA package, shown in fig. 5.Fig 7 Heat removal from mould at constant and diminishing rate.Fig 8 Melt temperature, Coolant temperature vs. Cooling Time.The cooling time is approximately 120 sec in this case whereas for constant rate heat removal cooling time is about 60 sec. That much saving in cooling time is at cost of having arrangement for mould cooling that can deepen from 323 degK to one hundred seventy-five degK within 1 minute. Reducing the mould temperature up to 175 degK has many engineering problems mould sweating will be hugely high at that temperature.In next step, flow rate of coolant was vary keeping the coolant temperature constant at 283 degK.Fig 9 Melt temperature, Heat removal rate and Film Heat transfer Coefficient vs. Cooling TimeFig 10 Reynolds No. and Coolant Flow Rate vs. Cooling TimeThe cooling time in this case found to be approxima tely 80 sec. and the coolant flow rate was initially 400 lpm that was ramped up to 1600 lpm within 80sec of cooling time. The shape of melt temperature curve with time is not a straight line which is identification of constant rate heat removal, but still there is a lot of saving in cooling time. To achieve that much saving in cooling time extremely high turbulent coolant flow rate (Re is approximately 3500000 at the end of cooling time) was used.ConclusionThe mould temperature and coolant flow rate have great effect over the heat transfer mechanism from mould. Proper adjustment of coolant temperature and flow rate can be useful in lessen the cooling time. Transient coolant flow rate may be used to reduce the cooling time and such mold temperature controllers can be made for achieving reduction in cooling time and ultimately cut back cycle time.