Plastics processing goes green
Injection molding machines produce plastic products by melting and injecting material, most commonly plastic, into a preformed mold. Advantages of this method over alternative manufacturing methods include minimal finishing requirements and the ability to recycle and melt scraps for reuse. With an increase in packaging and various household items made from plastic, injection molding machine production has grown steadily.
Milacron LLC is the largest manufacturer of injection molding machines in the Western Hemisphere, particularly known for its medium to large sized injection molding machines. Products manufactured by these machines range from automotive parts to surgical instruments to consumer goods such as cutlery, bucket lids and cell phone housings.
With a focus on energy conservation, Milacron developed a line of servo pump injection molding machines. The energy savings and lower maintenance advantages offered by using a servo pump rather than traditional hydraulic machine methods made it an easy decision for the company to make the move. In researching an automation partner to maximize productivity of its medium and large sized servo pump machines, Milacron required a company that was as committed to delivering cutting-edge technologies as it was. "We have worked closely with B&R for more than 15 years and decided to partner with them on this project because of their advanced motion control technology," explains Brian Bish, Milacron’s global hydraulic machine product manager.
Speed and torque, along with duration of pressure, were important factors in determining which products to use on the Milacron line of servo pump injection molding machines. These large machines are designed to run for extended periods of time – 24/7 operation – therefore, reliability and sustainability are essential design features. Additionally, the machines must be flexible in their power supply requirements.
The ACOPOSmulti servo drive system from B&R meets these criteria. The modular design of the ACOPOSmulti allows users to easily expand drives to accommodate any machine size and reduce cabinet space. Each of Milacron’s servo pump machines uses multiple, modular drives with the number of pumps determined by the individual machine specification. This flexibility offers easy assembly and reduced wiring due to the use of an integrated DC bus connection.
The DC bus remains at a constant level regardless of the input voltage, leaving the performance of the servo motors unaffected by variations in voltage supply. It also regenerates energy normally wasted in heat back onto the grid, reducing the customer’s energy bills and allowing Milacron to create a highly "green" machine.
The "field-weakening" technique featured on the ACOPOSmulti enables the B&R amplifier to alter the speed-torque curve of the motor. This allows the system to run the motors at a higher speed while maintaining the same torque output.
The intelligent cooling concept behind the servo drive design enables Milacron to select the appropriate cooling method for each machine; in this case the feed-through option was chosen. Using this solution, minimal heat is generated within the control cabinet. Thermal waste is dissipated through external heat exchangers into the surrounding environment, thus eliminating the need for fans or air conditioning within the control unit. As a result, less maintenance and lower costs are incurred than with traditional servo drives. The servo system only delivers hydraulic oil as needed and avoids unnecessary generation of heat, substantially reducing oil cooling requirements. In turn, the service life of the hydraulic components and oil are enhanced. The system also reduces the number of hydraulic valves used in the control circuit.
The servo pump control loop executed on the ACOPOSmulti itself produces quick response times independent of the control system. The B&R closed loop control also considerably improves the cycle consistency and repeatability compared to traditional methods. Simple parameterization facilitates reduced commissioning times. These benefits result in higher machine productivity and increased precision to ensure consistent high quality of the manufactured products.
The communication backbone of the servo pump injection molding machine is Ethernet POWERLINK. Without this real-time, deterministic network standard, it would not be possible to achieve the synchronization and precision required in Milacron’s application. POWERLINK also offers diagnostics reporting and assists in reducing maintenance delays.
By using B&R products, Milacron was able to take advantage of energy regeneration, improved performance, space savings and simple assembly. These overall benefits culminate into highly efficient machines, offering up to 70 percent energy savings in comparison to their hydraulic counterparts. "Sustainability and energy cost reduction are an integral part of our product development culture," comments Bish, "and B&R technology helps us achieve our energy goals while improving system compatibility and performance."
In late 2012, Milacron introduced the Maxima G Servo series of medium and large sized servo pump injection molding machines. "The overwhelming response to our new line of machines has been incredible. Customers continue to report increased productivity and reduced energy costs," Bish adds. "We didn’t expect anything less as we handpicked B&R for its deep experience in optimizing industrial plastics processes."