Servo Press Assembles Fine and Large Parts at the Same Time
IEF-Werner GmbH was approached by a user to provide a single press that allows crimping, i.e.joining through plastic deformation, of both very fine metal parts and thick, massive components to form a single subassembly. The automation specialist based in Furtwangen, Germany, was able to meet this requirement with a machine from its aiPRESS servo press series which features a pressing force of 12 kilonewtons. This solution provides the required force and very high accuracy. Users only need one system, which allows them to save investment costs and provides high-quality and reproducible joining in less time.
Manufacturing companies have to respond to customer orders with increasing flexibility to remain competitive. New products or product versions being brought to market at shorter intervals than ever before increases the demands made on machinery. The systems have to process materials that differ significantly in terms of structure, size, or thickness. However, new systems are expensive, and once they have been set up, they have to be utilized to full capacity. A user in medical engineering was faced with the issue that components quite different from each other needed to be deformed to produce a subassembly, and that different pressing forces were required for the same. The subassembly consisted of very small metal parts on the one hand and thick, massive components on the other. “This task required a press that enables two process steps to be performed at high accuracy,” explains Frank Neugart, Product Manager for servo presses at IEF-Werner GmbH. Moreover, this flexible solution had to be large enough to meet the requirements of future orders which would likely involve an even higher force. This was a reasonable approach, particularly with regard to streamlining machinery. Both process steps involved the crimping of components.
“Servo technology enables the process to be controlled such that the required offset is reached with an accuracy of a few micrometers.” Frank Neugart, Product Manager for servo presses at IEF-Werner GmbH
Engineers at IEF-Werner took a close look at the task and delivered a machine of the aiPRESS series of servo presses which features a pressing force of 12 kilonewtons.
“This series enables high-precision joining processes to be performed in an automatic and reproducible way,” explains Frank Neugart.
"The systems are designed flexibly and can be integrated in assembly lines as well as manual work places. The servo technology has significant advantages in this application. This technology enables the operators to set parameters such as speed. Depending on the required precision, very short cycle times can be implemented, because the driving force acts on a spindle,” says Frank Neugart.
A massive and torsion-resistant C-frame made of tool steel forms the base of the press. The system eliminates deformations, bending, or setting processes that affect the force-transmitting parts during the pressing process through mechanical decoupling of the measuring system and compensates for them through the servo control.
The drive train consists of a precision spindle, a servo motor, and a quill guide that enable lateral forces to be fully absorbed. With the aiPRESS, a precision guide keeps the drive train precisely on track through the entire duty stroke. “Positioning errors resulting from the deflection of a quill can be excluded,” says Frank Neugart. A configuration system allows the drive train to be adapted to the required force range. Thus, the servo drive always works under optimum operating conditions. The user can adapt process factors such as feed force, traverse speed, positioning time, and accuracy to the specific application.
“To enable both process steps to be implemented precisely, we fitted the aiPRESS with a piezoelectric force sensor that has two scalable operating ranges,” explains Frank Neugart.
“They ensure accurate measurement through parameter switching in the sensor.” IEF-Werner cooperated closely with HBM Test and Measurement (HBM) to implement this sub-range calibration.
Piezoelectric sensors are real alternatives to sensors based on strain gauges, particularly when a very large measurement range is required. Piezoelectric force transducers allow the acquisition of force ranging from few newtons to many kilonewtons. Provided that the required calibration has been made, a single sensor can be used in different force ranges.
IEF-Werner uses the CFTplus/25kN piezoelectric force transducer from HBM. The sensor has been pre-stressed and calibrated and is ready for immediate use. A gallium phosphate crystal makes up the core of the CFTplus sensor with 25 kN capacity. The material offers the advantage that it achieves twice the sensor sensitivity than the frequently used quartz. Drift and noise are low, which significantly increases the usable measurement range. The sensor is connected to the CMD 600 charge amplifier using particularly noise-free cables. CMD 600 has two programmable parameter sets, an extremely high bandwidth, as well as a very low drift – optimal prerequisites for use in demanding measurement tasks.
IEF-Werner, in cooperation with the user, developed a special pressing process that can also be used for other applications. During the joining process, the pressing punch, driven by a servo motor, initially moves quickly downward to bring the components into contact. Then the process slows down. In general, the system measures the pressing force and the position of the components to be joined. Due to its special design, the aiPRESS crimps the fine metal parts at a force of maximum 3,000 newtons, with an accuracy of less than ±15 newtons. “Usually 500 to 600 newtons at the most are used with such components,” says Frank Neugart. “This enables us to guarantee a high-quality joining process.” In the second process step, the servo press crimps the more massive parts at 6,000 newtons, with an accuracy of less than ±30 newtons.
To make the setup and control concept as ergonomic and user-friendly as possible, the IEF developers have equipped the aiPRESS graphical user interface with their own operating system for pressing processes. The aiQ-CONTROL is at the core of the operating system. This force-path monitor graphically represents the pressing process and monitors its progress. The monitor provides different functions such as envelope curves, windows, and force-path barriers. It enables users to keep an eye on interrelated measured quantities at any time.
In addition, aiLIGHT smart process visualization is provided; it is based on energy-efficient 4-color LED technology. It uses the reflective properties of the materials to interact with the operator through light-color codes. All required information is provided: Bright white light supports setup or the insertion of a component. Blue light signals that components are being pressed. When the result is OK, the LED lights green. NOK is signaled by red light. The integrated red-light function at the top of the press also signals the quality of the pressing result and is clearly visible from all directions. Thus, no information needs to be retrieved from the user interface to evaluate the pressing result; the operator does not have to look away from the current task to view pressing curves. This allows convenient and focused operation without any distractions and increases work efficiency.
Another important aspect in the development of IEF-Werner’s series of servo presses was energy-efficient operation: In one-shift operations, the entire system only needs as much energy as a usual 60-watt light bulb. A vacuum or pressure air supply is integrated directly in the quill of the aiPRESS series. Hence, the tool does not need any supply cables from outside. The whole series covers a force range from 200 newtons to 30 kilonewtons.
A further advantage of the aiPRESS series, especially in this project, is: “All open and visible parts are made of stainless steel. If the plant stands in a clean room, the work area can be cleaned completely,” says Frank Neugart. Moreover, if users need a higher force for future orders, they can reconfigure the press by scaling the force ranges up to 12 kilonewtons, and easily adapt it to the changed demands.
IEF Werner offers a broad product line of sophisticated automation components for tasks ranging from dynamic traversing with highest precision to powerful movement. For more than 35 years, the company has produced specialized automation systems for various branches of industry such as automotive, medical, electrical, and precision engineering, as well as the semiconductor and food industry.
For more information about the aiPRESS series of servo presses, please visit www.aipress.de/en
Images: IEF-Werner GmbH