Straight cooling channels are the most common method of controlling part temperature in injection molding process. However, straight cooling channels are not enough to manage temperature uniformity of the parts. In this work, a numerical study is conducted to decrease cycle time and cost of the injection molded parts by using conformal cooling channels. For this purpose, the commercial injection molding simulation program Moldflow is used. The governing physical equations for injection molding were derived and presented. The assumptions of the model were checked for simple geometries by comparing analytical results and numerical results of Moldflow. Then, the effect of conformal cooling channels is investigated for injection molding of a half cylinder shell part. It was seen that conformal cooling channels cools part faster and more uniform than straight cooling channels without corruption on the surface appearance. Finally, a real life case study was presented. For this purpose, a refrigerator shelf that is manufactured by the Ar&ccedil / elik Company was studied. The process was simulated using actual process parameters and simulation results were compared with production results. Then, the process was simulated using conformal cooling channels and compared with production results. It is seen that the cycle time of the refrigerator shelf was decreased considerably while preserving surface quality appearance.

This study focuses on the cycle-averaged mold temperature of additively manufactured injection molding tooling and how it is affected by conformal cooling channels. This was done by producing a benchmark mold out of Digital ABS produced by Stratasys, an acrylic based photopolymer, which was then used to produce injection molded parts until tool failure. Another, more cost-effective material, High Temp Resin produced by Formlabs, another acrylic based photopolymer, was also tested but yielded very little success. Then the mold design was altered by adding conformal cooling channels and again tested by producing injection molded parts while tracking the mold temperature. This experimentation was then compared to an injection molding cooling channel model in order to validate the model for use with additively manufactured tooling with conformal cooling channels for use in injection molding. The benchmark Digital ABS mold was able to produce 66 shots in the injection molding machine before complete mold failure. The Digital ABS mold had a cycle-averaged mold temperature of about 155°F. The High Temp Resin mold was able to produce 3 shots before complete mold failure. The High Temp Resin material is much more brittle, and the mold design did not take into account how brittle the material was. The Digital ABS mold with conformal cooling channels had a cycle-averaged mold temperature of 111°F. This is significantly lower than without cooling channels and has a high potential for improving tooling life. The cooling channel model predicted the cycle-averaged mold temperature to be 116°F. This proved to be a very good model and can be used as a design tool when choosing cooling channel geometry and position in additively manufactured tooling. This research shows the potential that conformal cooling channels have to help improve additively manufactured tooling life for injection molding. As shown in other research done, the ability to maintain the mold below 120°F significantly improves the life of additively manufactured tooling. The results of this study demonstrate the effectiveness of conformal cooling channels in controlling mold temperature. It should be researched further, but the use of conformal cooling channels has the potential to produce more production or prototype parts with additively manufactured tooling for injection molding.

The U.S. Evolutionary Power Reactor (EPR) is a new, large-scale pressurized water reactor made by AREVA NP Inc. Surrounding the core of this reactor is a steel wall structure sitting inside called the heavy reflector. The purpose of the heavy reflector is to reduce the neutron flux escaping the core and thus increase the efficiency of the reactor while reducing the damage to the structures surrounding the core as well. The heavy reflector is heated due to absorption of the gamma radiation, and this heat is removed by the water flowing through 832 cooling channels drilled through the heavy reflector. In this project, the temperature distribution in the heavy reflector was investigated to ascertain that the maximum temperature does not exceed the allowable temperature of 350 C, with the intent of modifying the flow distribution in the cooling channels to alleviate any hot spots. The analysis was conducted in two steps. First, the flow distribution in the cooling channels was calculated to test for any maldistribution. The temperature distribution in the heavy reflector was then calculated by simulating the conjugate heat transfer with this flow distribution as the coolant input. The turbulent nature of the flow through the cooling channels made the calculation of the flow distribution computationally expensive. In order to resolve this problem, a simplification method using the "equivalent flow resistance" was developed. The method was validated by conducting a few case studies. Using the simplified model, the flow distribution was calculated and was found to be fairly uniform. The conjugate heat transfer calculation was conducted. The same simplification method used in the flow distribution analysis could not be applied to this calculation; therefore, the computational cost of this model was reduced by lowering the grid density in the fluid region. The results showed that the maximum temperature in the heavy reflector is 347.7 C, which is below the maximum allowable temperature of 350 C. Additional studies were conducted to test the sensitivity of the maximum temperature with change in the flow distribution in the cooling channels. Through multiple calculations, the maximum temperature did not drop more than 3 C; therefore, it was concluded that the flow distribution in the cooling channels does not have significant effect on the maximum temperature in the heavy reflector. / Master of Science

Liquid methane is becoming an increasingly attractive rocket propellant due to its high performance characteristics and potential to support in-situ resource utilisation. Methane, however, when heated, can thermally decompose in a process known as pyrolysis. In regeneratively cooled rocket engines, the solid carbon products from the pyrolysis reactions are deposited on the walls of the cooling channels. This increases the thermal resistance of the channel walls, resulting in higher wall temperatures. In turn, this can facilitate cracking and crack propagation, presenting a potential problem in rockets, especially for future reusable designs. It will therefore be necessary to inspect the state of the cooling channels between flights. The carbon layer also changes the catalytic properties of the surface, affecting the onset temperature of methane pyrolysis, and thus impacting the pyrolysis behaviour during subsequent flights. It is possible to clean the channel using a mixture of gaseous oxygen and ozone, however, preliminary testing has indicated that not all the carbon is removed within a reasonable time frame. An experimental facility exists which can control the thermal and flow conditions in straight test channels to replicate the conditions seen in methane rocket nozzle cooling channels. The purpose of this project is to develop a system to quantitatively assess the amount of carbon deposition in these test channels after methane pyrolysis has occurred within them, and following ozone cleaning. The developed system is an optical method which uses a borescope to capture images within the coked channel. These images are then run through bespoke image processing software to determine the proportion of the inner channel wall that is coked. The software has been developed and a provisional mechanical setup has been designed. Initial validation tests have been conducted to assess the accuracy of the software used in conjunction with the borescope and camera. The results indicate that the system is capable of quantifying coke in a metal channel with an error of 1.489%±0.232% or less. / Flytande metan är på väg att bli ett mera attraktivt raketbränsle på grund av sina högprestanda-egenskaper samt potential för att stödja resursanvändning, in situ. Hursomhelst så kan metan, då uppvärmt, termiskt brytas ned i en process kallad pyrolys. I regenerativt kylda raketmotorer så utfälls de solida kolprodukterna från pyrolysen på väggarna av kylkanalerna. Detta höjer den termiska resistansen hos kanalens väggar vilket resulterar i högre väggtemperaturer. Detta kan, i sin tur, leda till spricktillväxt som väcker ett potentiellt problem med raketer, speciellt för framtida återanvändningsbara designer.Det kommer därför vara nödvändigt att inspektera skicket av kylkanalerna mellan flygningar. Kollagret förändrar också de katalyserande egenskaperna av ytan, vilket har en inverkan på begynnelsetemperaturen av metanpyrolys, som påverkar hur pyrolysen beter sig för följande flygningar.Däremot är möjligt att rena kanalerna genom att använda en blandning av syre i gasform, och ozon. Preliminära tester indikerar på att inte allt kol är borttaget inom en rimlig tidsram. En experimentell anläggning finns, som kan kontrollera tillstånd för värme och flöde i raka testkanaler för att replikera tillstånden som setts i kylkanaler i dysor för metanraketer. Syftet med detta projekt är att utveckla ett system för att kvatitativt bedöma mängden koldeposition i dessa testkanaler efter att pyrolys av metan har skett i dem, följt av ozon-rening. Det utvecklade systemet är en optisk metod som använder ett boroskop för att fånga bilder inuti den kanalen med koks. Dessa bilder körs genom ett skräddarsytt bildprocesseringsprogram för att bestämma proportionerna av den inre kanalväggen med koks. Mjukvaran har utvecklats och en provisorisk mekanisk anordning har utformats. Initiella valideringstester har genomförts för att bedöma noggrannheten av mjukvaran som använts i samband med boroskopet och kameran. Resultaten indikerar på att systemet är kapabelt att kvatifiera koks in en metallkanal med ett fel på 1,489%±0,232% eller mindre.

In der Arbeit wurde der stationäre wie instationäre Wärmetransport in exemplarischen Werkzeuggeometrien untersucht. Im Ergebnis konnten Wärmedurchgangswiderstände und instationäre Verläufe charakteristischer Temperaturen (Mitteltemperatur, Werkzeugwand- und Kanalwandtemperatur) in Abhängigkeit der Wand- und Kanalabstände sowie der Strömungsgeschwindigkeit bestimmt werden. Daraus wurden Auslegungsgrundlagen in Form von Gleichungen zur Bestimmung des Formfaktors der Wärmeleitung sowie der zeitlichen Verläufe der Werkzeugwandtemperatur, der Kanalwandtemperatur und der Wandtemperatur-inhomogenität erarbeitet. Dabei zeigt sich eine gute Übereinstimmung zwischen den Gleichungen sowie experimentellen und numerischen Daten. Die Gleichungen erweitern den Wissenstand zur Auslegung von Temperierkanälen von Werkzeugen in variothermen Prozessen.

Additive manufacturing can bring several advantages in tooling applications especially hot working tooling as high pressure die casting. Printing of conformal cooling channels can lead to improved cooling and faster solidification, which, in turn, can possibly result in better quality of the cast part. However, few studies on advantages of additive manufactured tools in high pressure die casting are published.The aim of this study was to investigate and quantify the effect of conformal cooling on microstructure and mechanical properties of high pressure die cast aluminum alloy. Two tools each consisting of two die inserts were produced with and without conformal channels using additive manufacturing. Both tools were used in die casting of aluminum alloy. Aluminum specimens were then characterized microstructurally in light optical microscope for secondary arm spacing measurements and subjected to tensile and hardness testing. Cooling behavior of different inserts was studied with a thermal camera and by monitoring the temperature change of cooling oil during casting. Surface roughness of die inserts was measured with profilometer before and after casting.Thermal imaging of temperature as a function of time and temperature change of oil during casting cycle indicated that conformal insert had faster cooling and lower temperature compared to conventional insert. However, thermal imaging of temperature after each shot in a certain point of time showed higher maximum and minimum temperature on conformal die surface but no significant difference in normalized temperature gradient compared to the conventional insert.The average secondary dendrite arm spacing values were fairly similar for samples from conventional and conformal inserts, while more specimens from conventional insert demonstrated coarser structure. Slower cooling in conventional insert could result in the coarser secondary dendrite arm spacing.Tensile strength and hardness testing revealed no significant difference in mechanical properties of the specimens cast in conventional and conformal die inserts. However, reduced deviations in hardness was observed for samples cast with conformal insert. This is in agreement with secondary dendrite arm spacing measurements indicating improved cooling with conformal insert.Surface roughness measurement showed small wear of the inserts. More castings are needed to observe a possible difference in wear between the conventional and conformal inserts.Small observed differences in cooling rate and secondary arm spacing did not result in evident difference in mechanical properties of the aluminum alloy but the variation in properties were reduced for samples cast with conformal cooling. Future work may include more accurate measurement of cooling behavior with a thermocouple printed into the die insert, casting of thicker specimen for porosity evaluation and fatigue testing and longer casting series to evaluate the influence of conformal cooling on tool wear.