How Servo Motors Enhance Press and Metalworking Applications

The precision control and programmable flexibility inherent in servo technology transform traditional press operations, enabling manufacturers to optimize cycle times, reduce material waste, and maintain consistent part quality. By replacing conventional motor systems with servo-driven alternatives, facilities can adapt quickly to changing production requirements while maximizing operational efficiency and worker safety across the entire manufacturing line.

This article examines the compelling advantages that servo motors offer for press operations and their associated material-handling systems.

What Is Servo Press Technology?

Servo press technology refers to the use of servo motors and drives to control a press’s motion, rather than relying on spinning flywheels or pressurized fluid. Servo press technology is operated via programmable, computerized systems, which gives engineers direct control over each phase of the press stroke. This allows for faster cycles in a more adaptable production line as well as better part quality.

Servo vs. Mechanical & Hydraulic Presses

Mechanical presses can be fast and reliable. However, their motion profiles are fixed by the machine’s physical design. In other words, what you build is what you get.

Hydraulic presses offer more force control and adjustability, but what you gain in flexibility you lose in cycle speed and energy efficiency.

Servo presses, meanwhile, combine the speed of mechanical systems with the flexibility of hydraulic systems.

With their programmability and energy recovery capability, servo systems are increasingly a practical (and optimal) choice for OEMs building modern servo-mechanical machinery.

Benefits and Considerations of Servo Motors in Press Machinery

Servo motors have established themselves as the optimal choice across numerous industrial machinery applications.

In metal forming, stamping, and bending operations, integrating servo motors into press systems delivers substantial performance gains. Ancillary equipment, including front-of-line destackers and end-of-line conveyors, similarly achieves enhanced throughput and improved safety by implementing servo systems.

Motor Shaft Performance

Presses often require a high degree of precision and repeatability. Servo motors provide closed-loop feedback, allowing for accurate positioning and torque control at the motor shaft.

While induction motors can be fitted with encoders (referred to as “vector motors”), they come with a hefty price premium and exhibit notable limitations, particularly at 0 rpm, necessitating additional forced air cooling.

In metal bending applications with precise angles, precise positioning becomes imperative. A drive’s ability to accurately control torque is paramount when precise force control is required.

Servo motors excel in synchronizing multiple motor axes, a requirement in scenarios such as transfer press applications where several motors must work together. KEB F6 VFDs have an internal positioning module that delivers outstanding motion control performance and reduces system expenses, mainly when a PLC does not require a motion controller add-on.

When coordinated motion with camming is required, an external controller such as KEB’s C6 Compact 3 embedded controller is ideal. The most straightforward integration occurs via a real-time fieldbus protocol like EtherCAT.

Fast Cycle Times

Machines are often evaluated by how many parts they can make during a given period. Therefore, there is always a desire to reduce cycle times. During the machine cycle, the motors accelerate and decelerate quickly. Servo motors are ideal for fast cyclic applications and offer advantages over induction motors.

However, choosing the lowest inertia is not always the correct answer. It’s crucial to align the servo motor’s inertia with the load inertia. KEB provides a range of servo motor products tailored to various inertia requirements. This alignment between motor and load inertia ensures the most effective system response.

For example, KEB’s DL3 motors are suitable for low-inertia applications, while the DL4 is for large power, and the TA servo motors are more appropriate for medium-inertia applications seen on many presses.

High-Speed Press Capabilities

Every millisecond of cycle time matters in high-speed press applications. Servo motors for high-speed presses must have the capability to accelerate and decelerate in sync with their load in order to hit fast, repeatable cycles. This all comes down to inertia matching.

A complementary servo motor will respond cleanly, where a poorly matched motor may overshoot or lag. KEB’s DL4 and TA servo motors each target a different inertia profile, so engineers can match the right motor to their specific press without overbuilding the system.

Energy-Efficient Servo Motors

Metalforming and stamping represent energy-intensive processes, often necessitating substantial power due to the nature and scale of the materials involved. These operations typically require powerful motors, and at high duty cycles, a significant amount of energy is consumed.

Consequently, the ongoing electrical energy operating costs over the machine’s lifespan tend to exceed the initial machine acquisition cost.

In contrast, servo motors are more energy-efficient than their induction-motor counterparts. Motor efficiency improves with both motor types as motor power increases. Notably, Permanent Magnet (PM) servo motors can outperform induction motors by several percentage points in larger sizes. While this might appear modest, the cumulative effect of this enhanced efficiency translates into substantial energy savings throughout the machine’s operational life.

Servo Motors – Part of the Safety Solution

As mentioned, lowering cycle times is always desired. Therefore, robotics are increasingly being used to manage the infeed and outfeed of material to the press.

In addition to reducing cycle times, another compelling rationale for deploying robots is the inherent safety risks associated with operating presses and similar machinery by humans. These motorized applications often expose operators to hazards such as cutting, crushing, pinching, burning, etc.

To address these safety concerns, the industry is increasingly adopting Performance Level (PL) components. KEB servo motors, for instance, offer SIL2/PLd motor encoders, which can be further assessed using a safety controller or a safe motion drive, thereby enhancing the overall safety and reliability of the machinery.

Motor Feedback Options

Servo motors rely on shaft feedback to precisely regulate position, torque, and velocity. KEB servo motors offer a range of encoder technologies to cater to diverse application requirements. The standard feedback option for servos is the resolver, known for its robust, shock-resistant performance.

However, some applications might require more precision so an absolute encoder might be used that can provide extremely fine resolution (e.g. >500,000 counts per motor revolution). These absolute types can be selected in single-turn and multi-turn variants.

The multi-turn encoder allows the motor shaft position to be known even in the case of a loss of power or machine restart, meaning the machine does not need to “rehome” during a power cycle. This is especially interesting for critical machinery that could experience frequent power cycles or changeovers.

High Overloads

Presses are machines that require high overloads during the machine cycle. This is where servo motors excel, as they can deliver peak torque levels ranging from 350% to 500% when required. In contrast, depending on their design, induction motors may reach only 200% of peak torque (breakdown torque). The superior peak torque capabilities of servo motors contribute to a more space-efficient overall configuration, greatly enhancing the machine’s overall design.

Choosing a Servo Motor for Your Press

Your application’s inertia and power requirements will help determine which servo motor is best for your situation. KEB offers two servo motor families for press applications:

• DL4: Delivers high torque despite its compact size. Great for applications with large power demands.
• TA: Provides high dynamic torque while also suitable for precise positioning and powerful driving in medium-inertia applications.

Early on in the motor browsing process, it’s also worth thinking about encoder selection. Resolvers are standard due to their durability and shock resistance. But, for applications requiring finer resolution or position retention, absolute encoders are available in single- and multi-turn variants.

Integrating the Full System

A complete servo system for press application will bring together four primary elements: servo motor, drive, controller, and fieldbus. When all these components come from the same supplier, integrating them is simpler, and there’s less risk of compatibility issues.

KEB supplies the full stack for servo press applications, offering OEMs a single supplier from the start. KEB’s servo families pair with the F6 VFD or S6 servo drive for motor control, the C6 Compact 3 for multi-axis coordination, and EtherCAT for real-time fieldbus communication.

Summary

Servo motors offer many benefits for machine performance, especially in demanding applications like stamps and presses. The performance improvement comes from various factors, including superior motor shaft performance, a more compact package, and better inertia and motion control system optimization. Over the years, the cost premium associated with servo systems has reduced, and they are increasingly economical considering their advantages.

Contact a KEB engineer to discuss incorporating servo motors into your application.