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Modern hydraulics: Six advanced capabilities for stamping presses

The need to form more complex shapes and to work with high-strength materials drives stampers to adopt advanced technology

Figure 1
Advanced hydraulics and intelligent drive systems are now available to help metal formers tackle more challenging projects that involve new metal alloys that can be difficult to form.

By virtue of its speed, force, and power density, hydraulics technology has long been used as a core drive system in stamping presses. Yet stamping press manufacturers are under pressure to deliver more sophisticated performance.

Operators need presses that can provide greater precision; produce more complex shapes and parts; and operate with increased productivity, cost control, and energy efficiency. Many machine designers may not be aware how the latest electrohydraulic control technology has significantly advanced the performance and intelligence of modern hydraulics to achieve those objectives.

Two areas in particular are driving the demand for better hydraulics technology in stamping presses. One is the need to improve precision for increasingly complex shapes stamping presses produce. For example, in the automotive industry, doors, quarter panels, fenders, and other components feature complex, rounded surfaces that require sophisticated hydraulics and controls to achieve accurate and high-volume fabrication.

The industry also is seeing a movement to greater use of higher grades of steel, steel alloys, and aluminum to fabricate parts (see Figure 1). These materials react differently to forming processes, which in turn require better hydraulic control to handle the formability challenges.

Advanced hydraulics and intelligent drive systems now are available to provide greater precision and improve stamping press productivity and product quality. Some of the capabilities of this versatile drive technology may come as a surprise.

Micrometer Precision

Electrohydraulic axis controllers close the control loop decentrally, similar to electric servo drives, and harmonize the target/actual position in real time within milliseconds. The precision of the movement solely depends on the measuring system used. In stamping presses, hydraulic drives can reliably position axes to within a few micrometers of precision.

One way to achieve this precision is through the use of more powerful and accurate measuring system technology. Transducer electronics have been dramatically improved, with digital transducers being free of electrical noise interference present in older analog devices. Combined with the right digital hydraulic controller, transducer electronics achieve and sustain a much higher level of control over motion sequence parameters such as speed, velocity, and force. This equals much greater control over the quality and precision of the part being produced.

Compact and Powerful

It is often difficult to place electromechanical drives with sufficient performance in tight machine spaces. Unlike hydraulic drives, they also generate significant heat. This is one of the key advantages that hydraulics continues to provide for stamping presses. Because power generation is decentralized in the hydraulic power unit and is connected to the actuator via lines or pipes, machines can generate great forces even with minimal construction space (see Figure 2).

Even for older-model stamping presses, dramatic improvements in power density can be achieved by retrofitting them with modern electrohydraulic technology, which is compact yet delivers hydraulic pressure up to 5,000 pounds per square inch.

This kind of retrofitting also can add a level of sophistication to stamping press cushioning functions. Synchronization of the speed, velocity, and force parameters of the cylinders driving the cushioning axis now can be more sophisticated for shaping an asymmetrical part, enabling older presses retrofitted with the latest hydraulics to produce higher-quality, higher-value products.

Figure 2
This amount of space can accommodate electrohydraulics that can deliver high levels of pressure in a stamping press.

On-demand Energy Efficiency

Some of the most important advances in hydraulic stamping presses involve technologies that operate more intelligently, such as variable-speed hydraulic pump drives. In these systems, software combines the best characteristics from electronic and hydraulic products. The decentralized intelligence in the electronic control device coordinates the rotational speed of the hydraulic pump drive on demand as the stamping press requires power, or reduces it to zero to save energy in idle mode.

In comparison to traditional constant-speed drive systems, energy consumption of hydraulic power units is reduced by up to 80 percent. This can offer significant savings for older facilities and stamping presses, extending their service life while reducing energy consumption. Those savings can help justify the investment in a hydraulic system controls upgrade.

Balanced Drive Physics

Fluid technology is not always inherently linear. Drive software for hydraulic actuators takes these characteristics into consideration and harmonizes them automatically. Pre-programmed hydraulic function blocks, like synchronization and position-dependent braking, provide the software foundation for efficient hydraulic controller programming.

Hydraulic motion control components have been specifically engineered to take full advantage of modern electrohydraulics and variable-speed pump drives. They provide intelligent, high-performance control for these pump systems as well as systems controlled with traditional proportional valves.

They typically feature advanced control software packages tailored to the unique demands of hydraulic system properties (see Figure 3). For example, the software compensates for factors such as fluid compressibility and nonlinear system dynamics. Hydraulic-specific algorithms for proportional valve and variable-speed pump drives allow for smooth transitions between position control and force control, the generation of smooth motion trajectories, and multiaxis synchronization. These features reduce system shock and impact on tooling, provide improved dynamics and accuracy, and boost energy efficiency and press productivity.

Open and Easily Integrated

Real-time Ethernet protocols are used more and more in modern machines to integrate all actuators and peripherals together. This trend also includes stamping press operations.

One key driver in this area is quality control and process data capture for both diagnostic purposes and to document quality processes for end-user parts customers. Hydraulic controls platforms not only need to tell a valve what to do, they also need to capture data such as valve position and cylinder delivery force and then communicate that information from the press to higher-level management and quality control systems.

Modern motion controls for hydraulic drives support all common protocols such as Sercos, EtherCAT, Ethernet IP, PROFINET RT, Powerlink, and VARAN. Their software is also based on open standards including IEC 61131-3 and PLCopen. With this support, they are an ideal match for the increasingly integrated and technology-overlapping infrastructure of modern production environments and provide stamping press operators with competitive advantages as they work with customers who need “smart factory” machine-to-machine communication and data sharing. This is especially important as machines incorporate Industrial Internet of Things and Industry 4.0 concepts.

Plug-and-Play Modularity

Ready-to-install servo-hydraulic axes have an integrated fluid loop and are driven by the same electric servo drives as electromechanical versions (see Figure 4). Many hydraulic axes are now available as complete self-contained systems, to which engineers can simply connect power and communication cables for assembly and start-up. Everything else (for example, the parameterization values determined from simulations) is already stored in the drive software and supports the plug-and-play philosophy.

For stamping press operations, a modular, self-contained hydraulic axis—comprising cylinder, motor, pump, and manifold—could provide an efficient, easily integrated way to upgrade secondary systems, such as tooling used to punch holes on parts that are being simultaneously formed. It also could be a cost-effective method for handling systems that move source metal into presses or remove finished parts.

About the Authors

Jeffrey Grube

Press Group Manager

2315 City Line Road

Bethlehem, PA 18017

610-694-8300

Jens Schmitt

Manager, Stamping Presses

2315 City Line Road

Bethlehem, PA 18017

610-694-8300