A Servo Electric Press is a system that uses a linear actuator controlled by an AC or DC servo motor to deliver linear motion, similar to a press cylinder. Servo presses utilize ball or roller screws to offer precise control over speed, position, and force. Though a servo press isn't necessary for all applications, it can be ideal for some. In this blog post, we'll take a look at a few advantages and disadvantages of a servo press, and when this type of press might be the best choice for your application.
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A servo motor is typically an AC brushless electric motor that uses either an open-loop or closed-loop motion control system. Open-loop control systems do not incorporate any feedback in operation ' these systems simply follow directions from the controller without reading output or sending data back to modify input.
Conversely, a closed-loop system, that's more commonly used today, is controlled by motor feedback signals that make it possible to make micro adjustments to positioning, speed, and torque automatically as needed. As commands are being sent to the motor, a sensing device called an encoder sends positional, speed, and directional data back to the control system based on output. Torque feedback is also sent back to the control system which helps measure the force exerted by the linear actuator. This allows a servo press to be able to work with great precision, accuracy and control. Servo presses have many advantages as an option for industrial production.
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The positional feedback system within the servo motor press creates a highly accurate operation. The system has the ability to make very fine adjustments to meet the needs of the process. This is ideal for jobs with tight tolerances, or those working with very expensive materials.
Servo presses not only operate with a high level of accuracy, but their operation is steady and repeatable. Even as loads on the motor change, the controls can adjust accordingly to achieve the desired results. If the demands on the press frequently change, a servo electric motor is optimally designed to meet these needs.
The closed loop control system allows the press to operate with a very high degree of control. Though these presses can operate quickly, and with great power, they can also be carefully and precisely adjusted. The actuator's positional feedback provides an incredible degree of control to the speed and position of the actuator.
Even operating with high accuracy and control, the servo electric press does not sacrifice power. These types of presses can work with delicate materials and highly precise processes as well as very tough materials requiring a great deal of force.
Many high-powered motors are also very loud which require your operators to have hearing protection when in their proximity. A servo motor press is electrically powered, and produces very minimal noise only during the press cycle.
A servo motor press can work very quickly, up to speeds of around 300mm/s. The feedback loop system allows the motor to adjust itself as needed, without interfering with the pressing process. When it's important to produce components or complete jobs quickly and with great efficiency, a servo motor press may be ideal.
Though servo motor presses have many advantages, there are also some disadvantages. It's important to balance these factors to find the right press for your needs.
As previously discussed, the servo motor operates smoothly, accurately, quickly, and can produce a great deal of power. However, this optimal performance comes at a cost. Servo electric presses tend to come with higher initial costs to most other types of presses, including full hydraulic options.
Servo motors are more expensive generally because they use more complex construction and components. This also means they have more expensive parts and are difficult to maintain. While most presses have a range of issues that can be addressed with in-house maintenance, servo press components will most likely need to be sent back to the factory for repair. Extra components, emergency maintenance and off-site maintenance can be costly and time-consuming.
The high power output offered by servo machinery also comes with high power supply. Most servo press machinery requires either 480 or 240V of electricity, which increases potential safety risks for an operation compared to low or no voltage options like pneumatic presses.
Servo presses can perform a range of applications and can offer advantages for jobs with very tight tolerances, where precision and accuracy are an extremely high priority such as in medical device or aerospace manufacturing. Servo actuators are used outside of assembly to control the function of many products, like robots, drones and other electronics. With such precise operation from a closed-loop feedback system, servo actuators are even used to control the function of several vehicles in operation, like controlling steering motion or the speed of aircraft, submarines and automobiles.
If this level of precision and functionality isn't essential for your applications, you may be needlessly overspending. It's helpful to have details about your applications to choose a press, including the materials you're working with, the dimensions of the workpiece, and the type of operation you're conducting. This will help you get the right amount of force for your press, and get the right type of press.
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There are many different types of presses to choose from for your application. Finding the right design and configuration requires some careful consideration and planning. If your process requires a great deal of accuracy, precision, and smooth operation, a servo press might be ideal for you. However, many of these complex processes can also be performed with a force and distance monitoring air over oil press for a fraction of the cost and there may be a range of pneumatic, hydropneumatic and even hydraulic options that could provide the capabilities you need with a higher return on investment.
Save Your Tooling
Tool-life improvements, like so many other advantages inherent in servo presses, arise from slide-motion control. Controlling punch velocity during forming reduces tool-wearing heat generation arising from friction, not to mention the probable increase in scrapped bad parts. And, slide motion tied to a particular application helps ensure minimal stress on die components, reducing the likelihood of tool breakage and resulting costly downtime. In general, the ability to reduce the touching speed of the tool to a workpiece will extend tool life and avoid high impact loads. In addition, optimized slide motion reduces the chances of vibrations occurring in the work material, which, again, can impact tool life and part quality.
And, servo presses, with programmable slide motion, can form parts at lower tonnages than more static mechanical presses. This also aids tool longevity.
Part recipes with customized motions and slide velocities enable more work to be performed in fewer die stations. This can lower tool-build and -maintenance costs. As servo presses continue to become commonplace, more tool designers and builders are creating dies specifically to take advantage of the technology. More and more operations can be fitted into servo-press tooling, leading to greater productivity gains while further reducing the need for out-of-press secondary processes.
Getting the most out of tooling in servo-press operations'and out of the servo press itself'means optimizing. Of course, experimenting and refining, which leads to optimized job programming, is a tough sell when testing must occur on the shop floor. That's why some metalformers opt for servo presses as tryout equipment. Besides self-optimization, servo-mechanical presses can mimic the actions of traditional hydraulic and mechanical presses, making them ideal as tryout machines.
In one case, seeing the trend toward common use of servo presses, a toolbuilder decided to replace an offline-for-repair 400-ton mechanical press with a 330-ton servo model. While the immediate goal was to use the new press to make adjustments to traditional tooling, ultimately the servo press would serve as an R&D project leading to new press-specific tooling and new ways to leverage servo-press technology.
The press also simulates press rates provided in the toolbuider's customer quotes. This has helped reduce final tryout time in customers' presses.
Servos Serve Up Success for Ohio Metalformer
One company taking advantage of servo-driven-press technology is Automation Tool & Die (AT&D), Valley City, OH. In , after researching the technology and seeking to prove out the advertised advantages related to part quality and process productivity, it purchased an Aida DSF-N2- 330-ton direct-drive ServoFormer. The two-point straightside press can produce at speeds from 1 to 100 strokes/min., and features a 102-in. (left-to-right) bed and 25.6-in. die height.
With the ServoFormer, unlike flywheel mechanical presses, excess energy through the nonworking portion of the press stroke is stored in capacitors. As the press idles, power consumption is minimized. This regenerated-energy design lowers operational costs and conserves electricity, according to Aida officials. Reported results include lower operating costs as compared to mechanical and hydraulic presses'30-percent savings in kWh and as much as a 70-percent reduction in peak load.
Encoders located at the motor and the crankshaft provide redundancy to help ensure against unintended motion that affects part quality and possibly damages tooling and press components.
Bringing a servo-mechanical press inhouse allowed AT&D to assess the technology's performance, which would determine whether the company would migrate to higher-tonnage servo-driven units. Satisfied that the press delivered more rapid production of higher-quality parts while extending tool life, in , AT&D again went the servo route. This time, it opted for a 700-ton Aida DSF-M2- straightside press, featuring a 168-in (left-to-right) bed and speeds to 75 strokes/min.
Offering infinitely programmable stroke and velocity profiles, AT&D can program constant velocity for forming applications or use standard programs to ease setup and operation. Programming technology enables increased production rates at shorter stroke lengths, according to Aida officials. Similar to the 330-ton servo press, the 700-ton press also benefits from capacitor-stored energy. In addition, both presses feature automated coil-feed lines from Dallas Industries.
Look for more details on AT&D's servo-press path and its other forward-looking initiatives, including the embrace of Internet of Things (IoT) technology, in a future issue of MetalForming. MF
See also: Dallas Industries, Aida-America Corp.