A hydraulic pump directly coupled with a servomotor is an energy-efficient solution that delivers highly dynamic performance with double-digit energy savings typical. The press manufacturer Lasco Umformtechnik GmbH, a machine tool builder in Coburg, Germany, uses this servo-electric pump drive for solid and sheet metal forming presses.
“This drive system provides many performance advantages,” said Harald Barnickel, head of the Electrical Engineering Department at Lasco. “It provides substantial energy savings for companies operating our presses,” said Barnickel in describing the advantages of this forming press technology.
This manufacturer of systems for solid forming and sheet metal forming produces screw presses, forging hammers, forging and cross wedge rolls and complete plants that are used by the building materials industry to produce sand-lime products.
When Lasco was founded in 1863, the main focus was on the iron foundry. However, just a few years later, it began producing water turbines, followed by forging machines in 1880. Since then, the company has concentrated on producing machines for forming technology and has been active worldwide for many years.
“As a solution provider, we develop customized systems for optimized work piece transport within the press as well as for feeding and removing work pieces,” Barnickel said.
The company has a strong focus on continuous improvement in its processes and technology. The servo technology is a technological milestone, as demonstrated through Lasco’s implementation in a recently delivered deep drawing press with a press force of 800 tons for up to 40 strokes per minute.
The servo-electric pump control for presses, developed by Lasco Umformtechnik GmbH in Coburg, uses far less energy than conventional valve control systems, often well into the double-digit range, according to this press builder.
A Fast Controller
At the core of this solution is a servomotor, which directly drives the hydraulic pump. This drive is controlled by a drive platform.
A motion control system handles the complete path, velocity and position control of the axes—the controller and drive are both from the same manufacturer.
With a response time of 250 microseconds, up to 256 axes can be rapidly synchronized and precise axis motion and curve profiles are executed.
“The initial applications have demonstrated that this type of servo technology provides outstanding results,” said Barnickel. This applies to the closed-loop control performance, its energy efficiency and the application as a whole.
The challenge on the deep drawing press was to control the press force and press speed, based on a motion profile that could be set individually. The hydraulic force and, therefore, the press force can be adjusted at the servomotor by means of the torque. The plunger speed is controlled by the motor speed and by the volumetric flow rate of the pump. For the project described, axial reciprocating pumps with a fixed displacement per revolution were used.
Pump System Scalability
Four axial reciprocating pump systems were connected simultaneously for a maximum pressure of 250 bar supply to the pressure line for the press stroke of the plunger. Three additional pump systems are responsible for the return stroke of the press plunger.
“The possibility of scaling or adapting this kind of standard servo solution to the actual requirements is another advantage of this new technology that certainly cannot be underestimated,” Barnickel said.
The hydraulic oil tank of the deep drawing press holds about 2,377 gallons (9,000 liters). Because of a high flow rate of 16,000 liters per minute, filling valves are used for the fast downward motion of the plunger. The servo pumps provide the required flow rate for the actual pressing operation, with a speed of up to 100 millimeters per second.
In the past, high-precision control valves with zero overlap were required to obtain the precise traversing profiles. In this arrangement, this function is handled by the motion control system in conjunction with the servo pumps. Because of this new technology, the valve systems in the press can be reduced by up to 40 percent. The remaining valve technology is mainly needed to comply with machine safety specifications.
The drive unit for the pump control consists of servomotors, drives and motion control devices.
The new technology allows expensive, traditional valve systems to be eliminated, and energy efficiency has been significantly improved.
“In the past, the large cooling systems for the hydraulic oil had to be installed before the first test run at Lasco. Now, with the servo technology, significantly smaller units can be used, and they are not required until the press is actually operational at the customer’s facility,” said Barnickel.
One reason for this is that the oil is no longer forced through the narrow gaps at the control edges of the control valves, which means that these types of technology-related losses no longer occur. The press manufacturer sees efficiency improvements well into the double-digit range depending on the application, significantly reducing the end users’ electricity costs.