Incremental improvements can only get you so far — sometimes you have to start over to rebuild better. Husky took that approach in advancing hot runner and injection molding technology, and it resulted in the Ultrashot system, which the company displayed for the first time at a trade show at Fakuma last week in Friedrichshafen, Germany. James Plumpton, Advanced Solutioning Team Leader for the Bolton, ON–based company, explained the thought process and the outcome to PlasticsToday from the Husky booth.
“As you make more parts in the same press, performance declines. Everybody in the hot-runner world, including us, has spent efforts fine tuning, trying to accommodate the variability,” said Plumpton. Rather than make incremental adjustments to improve performance, Plumpton’s team chose to eliminate the variation. It achieved that goal by distributing the injection control inside the hot runner.
“Normally, the injection unit controls all the filling, pressure, and impulse for all of the cavities inside the mold,” he explained. “There’s a large volume of melt between where you control pressure and where you actually need it, which is at the gate. The melt is compressible, especially when you have high pressure. So one of the things we tried to do is eliminate the variability that comes from compressibility and the volume of melt you have between where it is pressurized and where you need the pressure.” It’s a simple idea, he added, but the gains are huge. “Now we have pressure control very close to the gate.”
In a multi-cavity tool, the melt splits between channels, added Plumpton, and it doesn’t split evenly under normal circumstances. “A little hotter melt goes this way, and a little colder melt goes that way, and then you split it again,” he explained. “As you go up in cavitation, your performance gets worse. By cutting out the splits and controlling the pressure very close to the gate, you have a huge variety of gains."
Plumpton summarized the benefits as follows:
- The ability to scale cavitation without affecting performance, as noted above. “We can double the size of an eight-cavity mold and it will make 16 parts that are exactly identical.”
- Generating high pressure close to the gate. In a conventional system, a lot of pressure is lost on the way to the gate, said Plumpton. “You might generate 2000 bar at the injection unit and by the time it gets to the gate, it’s at 1200 bar. That’s wasted energy. And by generating much higher pressure at the gate, we can consider building parts that would not be considered injection moldable under other circumstances.”
The proof, as they say, is in the pudding, or in this case, a medical diagnostic chip. At the Fakuma booth, Husky demoed the Ultrashot system by molding a polycarbonate part similar to one that a customer is molding. It weighs approximately 0.56 g and is 0.5 mm thick with very thin webs that are challenging to fill, according to Husky. Moreover, the flatness of the diagnostic chip and the hole size are critical to its functionality.
The customer was molding the part using 3 X 2 cavity hot runners. Extreme pressure was needed to fill the cavities and very high melt and mold temperatures were required. The scrap rate was 5%. As demand for the part increased, the company would have had to make a major capital and footprint investment to satisfy its customer.
By investing in an Ultrashot system, the company was able to rapidly scale from a two- to eight-cavity tool, improve cavity-to-cavity part quality, consistency, and repeatability, and almost eliminate scrap, according to Husky. Bottom line? Ultrashot technology reduced part cost by 74%, said Husky.