Variable speed hydraulic drive
Reducing cycle times and energy consumption while at the same time increasing repeatability has become an imperative task for all injection molding machine manufacturers. Woojin Plaimm has teamed up with B&R to develop the latest in cutting-edge injection molding technology. The innovations that resulted from this collaboration are likely to revolutionize Woojin’s future strategy.
Woojin Plaimm has reduced the energy consumption of its injection molding machines by around 50% with a sophisticated mechatronic solution integrating servo and hydraulic technology. Demonstrating a keen understanding of customer requirements, these new hybrid machines provide extremely accurate position control at high speeds with almost no mechanical shock during acceleration or deceleration.
"Looking at our specified performance targets, we saw that there was a limit to how far we could get by simply increasing servo pump control speed," explains Injun Jung, R&D director at Woojin. "Instead, we decided to completely redesign the hydraulics as well as the toggle structures we had previously been using."
Woojin’s goals for the redesign were clear. The new machines would have to provide fast acceleration and precise positioning. Key performance parameters would include the response time for hydraulic output and the amount of hydraulic oil that passes to the real axis from the controller.
Integrating the new solution with POWERLINK would also play a key role in the project’s success. Since Woojin’s founding in 1985, the Incheon-based company has spent 28 years perfecting the production of injection molding machines and currently holds more than 40% of the Korean market. By combining its expert design with POWERLINK, Woojin is now able to offer its customers cutting-edge injection molding machines.
With support from B&R, Woojin redesigned its machines to achieve injection response times as fast as 60 ms and clamp response times as fast as 90 ms. By recalculating and redesigning the hydraulic system, including the hydraulic block, valve, pipe and oil tank, they were able to minimize the time it takes for oil to pass from the hydraulic pump to the valve after going through the pipe.
To improve the acceleration of the clamp axis, Woojin developed a new toggle structure that can deliver its maximum performance at any position. This new toggle structure has a longer movement stroke than the previous system and has reduced mold plate deflection while also minimizing the mechanical oscillations that occur during acceleration and deceleration. This newly developed toggle system guarantees high precision and constant acceleration, regardless of the user’s system settings.
Minimizing hydraulic delay through optimizing hydraulic components also helped maximize responsiveness. By selecting the optimal motor and using the optimal control algorithms for the respective machine function (clamp movement or injection), they were able to increase hold time to nearly 5 times what was possible with previous machines.
In order to improve repeatability and reduce energy consumption, Woojin replaced its existing hydraulic and servo pumps with new servo pumps connected to the control panel via POWERLINK. "We were already using B&R products on our electric molding machines, so applying their integrated automation system was very easy," says Mr. Lim, sales manager at Woojin, citing his company’s confidence in B&R as a decisive factor early in the project. "We believe that the new solution with integrated POWERLINK will remove the limitations of the previous system and offer greatly enhanced capabilities."
Servo pumps used in the past had been connected to the controller via an analog output, which had severely limited the ability to obtain information from the servo drives. POWERLINK allows them to send and receive massive amounts of data with a network cycle time of 400 µs. This increased performance allows for more extensive control and ensures faster response times with real-time monitoring of torque, speed, current and temperature of the motors.
With the Automation Studio Hybrid Drive Control library (AsHDC), optimized flow and pressure settings can be transferred to drive via POWERLINK. Having these functions packed into a library for B&R’s servo pumps makes the technology very easy to use and has enabled Woojin to reduce the control accuracy of injection and clamp unit down to 100 µm and speed up clamp opening times to as fast as 0.84 seconds.
In addition to speed and precision, energy efficiency is also a top priority for injection molding machines. "We have redesigned all of the hydraulic components to minimize the energy generated during movement of the clamp and developed a library that maintains the optimal pressure," explains Mr. Jung. "As a result, the performance of the machine has improved tremendously." Woojin has also taken advantage of B&R’s newly released X20AP energy measurement module to monitor and analyze energy consumption in real time.
Competitive edge through mechatronic optimization
The newly developed machine was exhibited at the KOPLAS exhibition in Korea. "Visitors really took notice of the fast and accurate position control and that there was no mechanical oscillation during deceleration," recalls Mr. Jung. While it has traditionally been believed that the key to a good machine is specialized know-how, Jung points out that today’s best technology must combine and optimize mechanical, control and hydraulics systems into a fully integrated solution in order to compete. "We have witnessed once more that a mechatronic approach to development has been a key to these improvements, and with B&R as a partner, this approach was a huge success."