Conformal cooling takes new twist
Published: June 13th, 2011
The holy grail of molding is the rapid cooling of molds, and while several techniques have been tried (and some have failed) conformal cooling of molds is making some headway.
Mold cooling is at the heart of molding-cycle optimization and part quality, which means that mold manufacturers need to understand mold cooling, molding cycle optimization and be up on the latest cooling technologies. "Mold manufacturers need to be concerned about cycle time if they want to help their customers maintain a competitive edge, improve efficiencies, productivity and profits in order to compete on a global basis," said Bob Beard of Robert A. Beard Associates Inc. His mantra was given in a webinar for the American Mold Builders Association, and it's something he preaches often to various groups.
As a "mold-cooling guru," Beard is familiar with the many technologies that have been developed over the past couple of decades to reduce cycle times and improve both quality and profitability. Beard noted that using high-thermal conductivity metals such as beryllium copper and aluminum has helped molders achieve cycle reductions of 20% or more. Of course, aluminum isn't suitable for every mold application.
While optimizing the choice of mold material may represent 50% of available cycle reduction, Beard said that the other 50% "is analyzing and optimizing how the cooling lines are connected to the plant cooling system." Beard's "enhanced cooling" analysis is the first step toward improving cooling in mold/molding systems. "By taking an engineering systems approach," Beard said, "cycle times can be reduced by 20% or more on existing molds. Measuring and optimizing water flow to ensure that turbulent flow is truly present in the mold-cooling system, and by changing the process, significant cycle reductions can be achieved."
Conformal cooling isn't new technology, however there are several new approaches to conformal cooling that have been introduced of late that promise to improve this technology. Beard commented that from a "theoretical dynamic heat transfer standpoint, conformal cooling would or should, always produce a faster cycle time than conventional mold-cooling techniques." However, he added, "no one has developed a working, cost-effective commercial process for injection molding that is being sold on the open market."
Evolution of a Technology:
A few years ago, FloodCooling Technologies LLC, filed for a patent on "Brazed Aluminum Laminate Mold Tooling." From research, it appears that the patent was issued on March 4, 2008. While FloodCooling Technologies still owns the intellectual property, a subsidiary company ThermaForm LLC, based in Troy, MI, developed the technology called ThermaBlocks, in blowmolds for rigid packaging applications. That seems to be the ideal niche for this technology, said Cole Clark, whose father, J. Thomas Clark, founded the company and serves as ThermaForm's CEO.
FloodCooling's technology was originally tried with steel injection molds through Fast4M, a subsidiary of FloodCooling (now out of business) and there were some problems with leaking, according to a couple of people familiar with the brazed lamination technology. Possibly, it was due to the high heats and pressures of the injection molding process that caused some failures.
"I think that early on, the process wasn't refined enough and there were some problems with trying to use the laminated brazing technology with steel injection molds," Cole Clark said in an interview with PlasticsToday. "Since I've been working with the company, we've had no failures or leaking using the brazed aluminum lamination technology in blowmolding for rigid plastic packaging applications."
The ThermaForm patented process uses laminated construction which results in 3D conformal cooling channels and yields a homogeneous 6061-T6 Aluminum block called ThermaBlock. The company performed testing at Wayne State University in Detroit to validate the process used in blow molds. The braze layer is an AISi alloy, and the ThermaBlock increases turbulent flow and cooling channel surface area, which increases corrosion resistance of the mold material and improves mold life.
In November 2009, ThermaForm and Uniloy North America performed joint tests using two conventional molds from Uniloy and two molds from ThermaForm that applied ThermaBlocks for an "apples-to-apples" comparison. The testing was done to understand the relation of varying cooling supply pressures and resulting flow rates. In both cases, the ThermaForm molds performed better than the Uniloy molds in all tests.
A year ago, Uniloy and ThermaForm implemented an exclusive licensing agreement between the two companies. Uniloy is currently the exclusive worldwide source of molds containing ThermaForm's ThermaBlocks for reciprocating screw blowmolding machines, according to Uniloy's information. "Our implementation of ThermaForm's technology will have significant, positive impact on the operations and economics of all Uniloy reciprocating screw molding machine operators," said Dave Skala, VP and GM or Uniloy in a statement in May 2010. "Running molds containing ThermaForm's ThermaBlocks will give our customers a real advantage in the marketplace - in terms of speed, efficiency and quality."
- Product: 100g 96 oz. Industrial Container
- Objective: To improve cooling of the neck to allow for reduction in cycle time and maintain quality.
- Solution: Retrofit of ThermaForm's ThermaBlock to existing production mold assembly
- Machine: automated 6 head reciprocating screw blow molding machine (mold, cool, trim and leak test) at the customer's site.
- Results: 20 degree F reduction in neck temperature vs. standard block; cycle time decreased until neck temperature raised to a maximum acceptable level; cycle time reduced from 10.0 seconds to 8.0 seconds while maintaining quality - a 20% productivity improvement.
"The ability to remove heat (energy) efficiently from a mold allows for an improved process window for customers to analyze and address various obstacles in the blow molding cycle," said Clark. "The majority of machines today have the ability to operate at faster cycle times than are currently used, but through-put is dictated by mold performance and resulting product quality, which means most machines are not being fully utilized."
Uniloy North America's Skala added that ThermaForm's success with the ThermaBlock "represents a long-sought breakthrough. Machines with molds containing ThermaBlocks can now operate at or near their true capacity, and new machines can be designed to take advantage of the improved cooling."
Cole said that ThermaForm currently has working prototypes with three of the largest rigid plastics packaging companies in the world, in Europe and the U.S. A large mold is running in Mexico blowmolding 5-gallon water jugs. "We're trying to get more production success," he noted. "We can do fairly large size molds and our only limitation is the furnace size."
New laminated technology for injection molds
Steel injection molds for components requiring conformal cooling can benefit from a new technology that started out in semiconductor and aerospace applications, but found its way into the mold manufacturing arena.
Die-Bond LLC, a Chandler, AZ-based company that developed an industrial laminate bonding process that its parent company, Refrac Systems, claims is better than brazing and eliminates the leaking problems that have been prevalent in other brazed laminate processes that have been tried. Norman D. Hubele, president and founder of Refrac Systems and of Die-Bond LLC, notes that while the company has no direct experience using aluminum for making injection molds, his experience has shown that "aluminum is almost impossible to diffusion bond directly, but rather requires a fairly expensive chemical bonding aide that helps mitigate the oxide layer formation that prevents good bonding in the aluminum containing systems." Plus, he added, it costs about $25/sf of bonded material per side.
Die-Bond uses a vacuum hot pressing and Liquid Interface Diffusion (LID) bonding technology, originally developed for the aerospace industry. Hubele expanded the process to accommodate the manufacture of production parts for the semiconductor, chemical, biomedical, and ultimately the plastic mold industries.
Several years ago, Refrac began working with some mold manufacturers to develop a more efficient process to bond mold inserts together. With the formation of Die-Bond, mold manufacturers who incorporate conformal cooling channels into molds to allow the mold to be cooled more efficiently, now have access to Die-Bond's proprietary technology. Die-Bond's process minimizes the potential for leakage and post-braze warpage problems that can occur in molds assembled using conventional vacuum brazing.
"With Die-Bond's LID bond process to bond in conformal cooling lines, moldmakers can easily get the cooling exactly where they need it to improve molding cycle times," comments Hubele.
Tech Mold Inc. is one of the few mold manufacturers that have caught onto Die-Bond's LID process for creating conformal cooling channels. Vince Lomax, vice president for Tech Mold, based in Tempe, AZ, said, "As the demand for faster cycles, greater consistency part-to-part, and higher quality expectations continue, the moldmaker must find ways to try and address those challenges."
One of the factors that impacts all of these is cooling. "Obviously you cannot eject the part that is not fully solidified and if ejected prematurely the part will have more post molding distortion and/or inconsistent shrinkage," Lomax stated. "So, it makes perfect sense that the colder you can get your mold the more successful you will be with addressing those three issues."
Conventional methods for mold cooling involves drilling holes as close to the molding geometry as possible. However, noted Lomax, this method "does not and cannot address the many complex part geometries we see in molds today, making it difficult - and often impossible - to drill the cooling lines close enough to cool the cavity steel in a uniform manner."
Conformal cooling has been developed to help address this problem of cooling cavity steel consistently and adequately and at the same time preserve mold integrity. For this reason, Tech Mold has embraced conformal cooling technology in many of the molds it builds. "By definition, conformal cooling is conforming and contouring the water channels to cool the cavity in a more effective and uniform manner, regardless of part geometry," said Lomax.
Tech Mold has used the Die-Bond LID process in several applications over the past year. In one instance, Tech Mold was approached by a customer with three molds that molded a very critical part with very stringent quality requirements. The geometry of the part dictated very thin steel coring that was almost impossible to adequately cool. The previous molds were built using a copper-based material to facilitate cooling. Although copper materials are superior for improving cooling, the cycle time still did not meet the customer's target, and unfortunately as a result of the softer material, those molds also required a lot of maintenance, Lomax explained. After reviewing the history, Tech Mold made the decision to accept the challenge and build a 64-cavity mold which would run enough product for the customer to shut down the three older molds.
"Obviously we planned to employ conformal cooling to cool the thin steel cores," said Lomax. "Our philosophy with respect to cooling is that a little bit of water in the right place is better than a flood of water circling through the base of an insert and really not effectively getting to the heat source. Using Die-Bond's LID conformal cooling process as seen in Figure 1, we were able to get a small spiral water circuit up inside the thin web of steel."
Die-Bond's LID bonding process allows small mold inserts, such as the ones that Tech Mold's customer had, to be hardened under high pressure, reducing the risk of warping during the "quenching" operation used during normal vacuum brazing operations. The results are more consistent yields.
"With Die-Bond's LID bond process to bond in conformal cooling lines, mold makers can easily get the cooling exactly where they need it to improve molding cycle times," comments Hubele.
Tech Mold has used other conformal cooling methods in the past but has had some leaking issues in the laminated steel. "We have not experienced those same leaking issues with Die-Bond's LID bonding process," said Lomax. "The primary difference is that other methods rely heavily on two elements for bonding - gravity and temperature. Die-Bond's technology raises the bar for laminated conformal cooling channels using temperature, pressure and a special bonding material. The key here for injection molds, I believe, is the pressure."
Lomax admitted that it was a "difficult application" for conformal cooling, "but it paid off in spades," he added. "We paid a premium for choosing conformal cooling, however we were able to reduce the cycle time over the existing molds by 30% and even at this reduced cycle, part consistency and quality was also improved. And, in this business we know that he who puts more parts in the box at the end of the day wins."