Customer Successes

Hydraulic Cylinder Design Now Faster and More Exact



Rexroth Hydraudyne is a division of the Bosch Group, a German-based industrial company with activities ranging from automotive technology to broadband networks. Based in The Netherlands, Rexroth Hydraudyne provides large, specialized hydraulic cylinders to companies around the world. These cylinders serve to drive and control all kinds of mechanisms. One notable job involved the hydraulics for a tidal barrier — a door between an inland waterway and the sea — in the Hartel Canal, just 10 miles south of Rotterdam.

Engineers at Rexroth Hydraudyne use PTC Mathcad — a visual design environment that allows engineers from all industries to draw from a variety of data sources during the design phase of a product and document all mathematical formulas and calculations — to design the large industrial hydraulic cylinders. Although every cylinder is a custom product, the calculations that go into each one are highly standardized and optimized for maximum reliability. Ten years' experience with PTC Mathcad has brought considerable savings in production costs and more effective cooperation with industrial partners.

The in-house research and development department of Rexroth Hydraudyne is responsible for the engineering of all cylinders. "There are no second chances," says engineering manager Marc Moolenaar. "In most cases, we only make one cylinder for every job, so we can't test a prototype first. We're a real 'engineering-to-order' organization. It has to be right the first time. That means we make heavy demands of our technical calculations."

Used by more than 1.5 million engineers worldwide, PTC Mathcad lets engineers work with mathematical expressions using standard math notation — but with the added ability to recalculate, view, present and publish with ease, even to the Web. PTC Mathcad makes it easy for engineers to communicate the rationale that goes into their calculations, enabling design quality assurance and verification, as well as facilitating reuse of frequently performed calculation routines.

"In most cases, hydraulics are just one part of a greater entity," says Moolenaar. "A lot of companies are working together at once. And, of course, everyone is looking at our design data. Very often, the client will double-check our calculations. For instance, to make sure we've maintained the right procedures, standards and safety margins. So, the calculation and clarification are inextricably linked. With Mathcad we can provide the right documents every time. Mathcad plays a key role in the communication [process] with our industrial partners. The consistent and precise presentation of our calculations helps our clients to understand what we are doing. What they see is what they get. This is an invaluable advantage."

Situation Before PTC Mathcad

Rexroth Hydraudyne has been using PTC Mathcad since 1993. Two-thirds of the company's 16 design engineers use the package on a daily basis. Before the arrival of PTC Mathcad, engineers relied on tailor-made software from a vendor for their calculations. This proved to be a reliable; however, it was an inflexible solution. New cylinder types, new engineering standards or new applications always involved new software changes, which consumed time and human resources. The engineers needed a more flexible solution and found it in PTC Mathcad.

"It's easy to learn," says senior design engineer Kees van de Grint. "It can do almost anything, and it gives you the freedom to design your calculations according to your own needs. You simply start your calculations on an empty screen, just as you would on paper."

Through its self-documenting interface, PTC Mathcad allows engineers to combine formulas, text and interactive graphics in a single worksheet. Unlike most calculation packages, spreadsheets or programming languages, PTC Mathcad "whiteboard" interface accepts and displays natural mathematical notation using keystrokes or menu palette clicks, so no programming is required. The "live" interface allows engineers to change a variable or number and instantly recalculate the result as well as the two- and three-dimensional graphs.

"It's great having all this freedom," Van de Grint continues. "But if you want to have a uniform approach and consistent presentation, you have to organize that well within the department." In line with this, he started drawing up an engineering handbook three years ago. It takes the form of an electronic library within PTC Mathcad, which makes it easy to organize information. The methodology for the most important calculations is laid down there together with a standard text for clarification and for citing sources. All the user has to do is copy the appropriate passages or even complete calculations. After filling in some additional information about materials and the specific situation, PTC Mathcad does all the mathematics automatically, so the whole story is available immediately.

Results

"Even the drawings made by Intergraph SmartSketch, the integrated CAD system, are adapted automatically to the calculated measurements," Van de Grint says. "Introduction of the digital engineering handbook brought an increase in productivity at the engineering department. And, since you're always using the same tried-and-true formulas from the engineering handbook, the outcome is much more reliable." The digital engineering handbook in PTC Mathcad now consists of 165 core calculations and five templates.

The chance of errors is further reduced by the fact that users can enter data in the form they are provided. Whether engineers are using inches, millimeters or meters, PTC Mathcad automatically handles the measurement conversion process, which is often error prone when done manually. "It's extremely handy if you're working on the international market," says Van de Grint. "And, by checking the units you can quickly see if there are any errors in the formulas."

The Competitive Advantage

When designing a hydraulic cylinder, proper calculation of the shell is essential. Very often, it has to cope with enormous forces and pressures, so it's one of the most expensive parts of the cylinder. The more precisely an engineer calculates the optimum thickness for a shell, the less material will be needed. That can make a big difference in cost and in profit. "That's how we can make competitive offers," Van de Grint says.

"For this reason, we have included some highly detailed calculations in the handbook," Moolenaar adds. "We've thought long and hard about some of these formulas. But, afterward, you can keep using them the same way, again and again."

But there are times Moolenaar does not want those formulas exposed. "You can also make a part of your calculations inaccessible to others with PTC Mathcad. After all, we don't want to give away our trade secrets," he says with a smile. "Very often, we look at alternative constructions, for instance, with other mounting principles or other construction types. Of course, that's not exactly our job, but it can sometimes pay to intervene. In some cases, by employing even slightly different assumptions, the hydraulics can be made much cheaper. For instance, maybe you can manage with much less concrete. In a situation like that, you need very well-documented calculations. Otherwise you'll never get to make a change of that kind."

PTC Mathcad sometimes even helps to change the scope of a project. "PTC Mathcad gives us extreme flexibility to generate calculations," Van de Grint adds. "We can show our clients the detailed consideration of every design. We avoid unnecessary risks by using strict and proven design rules. Together, that makes it possible to meet every client wish."

About Bosch Rexroth AG

Bosch Rexroth AG, a 100-percent owned subsidiary of Robert Bosch GmbH, achieved sales of 3.62 billion euro in 2002 with approximately 25,500 employees. The company was formed in May 2001 by the merger of Bosch Automationstechnik and Mannesmann Rexroth and includes the products and services of the former brands of Bosch Automation, Brueninghaus Hydromatik, Indramat, Lohmann + Stolterfoht, Mecman, Refu, Rexroth Hydraulics and Star. Rexroth offers all relevant drive, control and motion technologies from mechanics, hydraulics, pneumatics, electronics as well as the associated services in about 80 countries.

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