Hydraulic linear drive in punching machines and test stands
Custom hydraulic cylinder as a self-contained servo drive

The name CLDP stands for 'Closed Loop Differential Pump' from Voith in Rutesheim and is a servo drive with integrated pump. This hydraulic drive only needs to be mechanically, electrically and electronically connected and then operates maintenance-free for a period of 3 years or 20,000 hours. Voith supplies the complete package, the drive element of which uses a hydraulic cylinder from Herbert Hänchen GmbH. This means that both the user and the manufacturer of machines and plants can use high-performance hydraulics without their own hydraulic know-how - and this in a valveless system with optimum efficiency. "Especially when it comes to large forces, the hydraulic cylinder is clearly superior to the spindle drive. In addition to the easier handling of large forces, it has significantly less wear," explains Dipl.-Ing. Harald Branz, project manager responsible for sales at Voith. "And the valveless design enables unsurpassed energy efficiency." However, many customers are now shying away from hydraulics because they no longer have their own specialists. However, the cost-benefit ratio and the high power density of this technology are still unmatched. The CLDP is a high-performance device that the customer can use without any hydraulic expertise of their own.

Hänchen as a strategic partner
Voith therefore sought and found a strategic partner in Herbert Hänchen GmbH, based in Ostfildern near Stuttgart, whose hydraulic cylinders meet a wide range of requirements and who has decades of experience in manufacturing. "We were looking for a partner who could complement our system know-how with corresponding expertise in hydraulic cylinders," reports Branz. "Our core competence lies in short-stroke cylinders. Our manufacturing facilities are optimally geared to the series production of these cylinders. Hänchen has the right expertise for the CLDP and is not a competitor. We therefore jointly optimised the cylinder for the hydraulic linear drive in many areas and combined the strengths of both companies." Voith provides the basic specifications, which Hänchen implements. Stefan Hänchen: "We had many discussions in order to arrive at a joint product. The right engineers worked together at both ends." There were clearly defined processes on both sides as part of the joint development. Hänchen contributed with its cylinder know-how and Voith with its system know-how to the successful implementation of the project. The two companies have been working very closely together since mid-2015, and the geographical proximity of the companies is an additional positive effect. Branz and Hänchen are jointly convinced: "This partnership has a future and brings great advantages for our joint customers."

Hänchen's expertise lies in meeting the special requirements of Voith, which are necessary for the compact drive system:

• Hänchen hydraulic cylinders are known for their tightness, accuracy and durability.
• Hänchen has expertise in the use of materials, especially in seals and rods.
• Hänchen offers stick-slip-free hydraulic cylinders. Sealing combinations and manufacturing methods such as special honing processes play a special role here.
• Hänchen is flexible in design and manufacturing when it comes to dimensions.
• Hänchen is known as a specialist that implements customer-specific adaptations and special requests.

Actuators with a specially configured seal combination Servocop^® are now a core element of every CLDP. These cylinders can also be configured with millimetre precision for the bore. In this way, the cylinders can offer an exact area ratio of 1:2. Hänchen's manufacturing technology also makes it possible to produce the cylinders in a square block that contains the piping in the form of bores and at the same time is a mounting surface for the other elements of the CLDP. Hänchen offers a wide range of standardised cylinders that are built to a high standard and cover numerous applications and industries. In the end, it is the customer who benefits most from the broad knowledge gained. This makes Hänchen an ideal partner for series cylinders that are perfectly matched to the application. By fulfilling all these requirements, the cylinder offers an excellent price-performance ratio.

Seal combination Servocop^®
The seal combination Servocop^® operates largely stick-slip-free thanks to two seals, wiper ring and lip seal. It is extremely tight and does not require a leak oil circuit. All of these are properties that are essential for the closed, valve-free fluid circuit, as there is no provision for refilling fluid outside of the maintenance interval, which lasts for years. The system contains an accumulator solely to compensate for the fluid volume between the rod and cap side. The possible speed of the CLDP is up to 1.5 m/s at 250 bar system pressure. The Servocop^® seal combination was specially adapted to the requirements of Voith.

Application areas for the CLDP are bending, separating and forming machines as well as presses and synthetic material machines. In general, the drive is an alternative to the spindle drive with servo motor. Other important application areas are special machines, material handling and the food industry. The CLDP is now also used in the testing area. For all these and many other application areas, the CLDP offers the chance of a return to the great advantages of hydraulics - without your own hydraulic expertise.