Turning High Performance into Reality
How does a product become the high performance leader for motion control for the most demanding applications in the world? It starts with innovative ideas of the product design experts. It is then proven using the most advanced simulation tools and testing methods available in the marketplace. Moog’s product design and testing are hidden assets that customers buy when they invest in best-in-class products.
While product design and testing may vary slightly among Moog’s core products, there are essential commonalities. To explore this, consider Moog’s core product range: Servovalves, Servo-Proportional Valves, Servomotors and Drives, Controllers, Pumps, and Electromechanical Actuators. Clearly the design and testing of a 92 gm. microvalve will be different from the process used for a 5,000 kg. manifold or a 432 kg. electromechanical actuator. What is common is the ability to ensure precision motion control by simulating product performance in complex control systems, and rigorous testing to verify performance in real world conditions.
Moog is profiling in this article two examples to demonstrate the complex role of product design and testing when creating performance-based products. The first example involves two types of simulation for Servo-Proportional Valves and the second addresses reliability testing for RKP Pumps. Similar examples are available for other products as well.
I. Simulation Tools used by Moog for Product Design of Servo and Proportional Valves
Simulation tools are an accepted way for engineers to understand and predict the behavior of a system. Moog is known for providing Servo-Proportional Valves that are exactly customized to provide the performance needed in a machine. Applying simulation to this product is a challenge and it involves the expertise Moog has gained in over 50 years in the business. In the section below, we will explore the details of valve simulation.
All of our simulation tool examples are based on the finite element method (FEM), where a spatial field is divided into finite elements. By giving these elements a specific physical property and applying the correct boundary conditions, an analysis of the physical behaviour of solid materials and even fluids can be performed. The only difference between determining stress and strain in a valve body made of ductile gray cast iron and determining the flow induced force on a spool are the governing equations.
A. Structural Analysis
During the design process it is useful to know how the structure (e.g. valve body) will react under the applied loads. One way Moog’s product designers obtain the answer is by using the software packages NASTRAN 4W and ANSYS to obtain detailed information about the deformations, stresses, and strains in the analyzed parts. These results can be used in further investigations such as estimation of fatigue limits or reducing stresses and deformation by modifying the actual geometry.
Figures 1 and 2 show typical applications of the FEM software looking at the deformation of a valve body.
B. Computational Fluid Dynamics (CFD)
A common application of CFD software (“Cfdesign“ from Blue Ridge Numerics) is to predict the steady state flow induced forces in hydraulic spool valves. The CFD-code is based on the following fundamental fluid equations:
- Momentum conservation
- Mass conservation
- Energy conservation
Flow force development is based on the momentum of the enforced redirection of the fluid jet and the change of hydraulic boundary conditions which accelerate the column of oil in the valve. The flow force can be divided into a steady-state and a transient part. Both parts have an effect on the moveable elements of a valve.
With the shown conservation equations and the actual software capabilities, the following states can be simulated:
- Internal/external flow
- Heat transfer (conduction, convection and conjugated)
To reach an optimal flow force compensation there are many possibilities. Substantially all of the possibilities can be reduced to the variation of the geometry. The aim of the geometry variation is the focusing of the jet of hydraulic oil close to the wall, so that there is nearly no loss of kinetic energy.
In the following design study the flow force could be reduced from 25 N to 9 N at a pressure drop of 320 bar by adding a compensation cone to the spool and a full angular scallop to the body.
C. Magnetic Analysis
Another specific example of the role of simulation in creating best-in-class products is the design of the linear force motor that drives the spool of Moog’s new High Flow Direct Drive Valve (DDV) (D634Pseries). In order to optimize the electromagnetic circuits a software package called Maxwell (from Ansoft) was used. By optimizing the geometry and characteristics of all of the parts involved in the magnetic circuit, Moog has nearly doubled the motor stroke, while maintaining the high driving force levels. The result is the addition of a higher flow capacity valve within the Moog Direct Drive Valve family, that also has the contamination tolerance and low power consumption requirements these valves are known for in the marketplace.
II. Stringent Reliability Testing for RKP Pump Products Allows for Reliable Customization.
Moog’s Radial Piston Pump (RKP) product line is well-known for reliability, low noise, and high performance. This is underlined by its strong reputation in the marketplace and an extended warranty of 10,000 operating hours or 24 months (whichever occurs first) when used with mineral oil.
As with Servo-Proportional Valves, a core advantage to RKP Pumps is Moog’s ability to customize the design to meet unique customer needs. When it is necessary to modify the design of single parts or subassemblies, replace one material with another, or to change the processes for heat treatment, testing is critical to product development. In all cases where a completely new design is created, it is necessary to investigate and document the implications of the modifications on function and lifetime.
Before an RKP Pump with new parts can be released into production and delivered to a customer, it undergoes a stringent fatigue test, where the pump load and displacement must change between zero and maximum in a period of one second. This procedure is repeated for at least 5,000 hours. The engineers that specialize in RKP Pumps have access to six different test rigs that are computer controlled for executing lifetime reliability tests. The tests are automatically generated and sensors for pressure, temperature, and leakage monitor the given range of parameters and allow a 24 hour operation. Moog also performs tests with fluids other than mineral oil, such as HFC fluid. The ability to handle other fluids is a key feature for the RKP Pump.
After a pump has passed the lifetime test it is disassembled. Visual inspection allows the engineers to decide whether a modified part or subassembly design is ready for customer’s application. This ensures that all customized products meet the same stringent requirements that the Moog RKP Pump is known for in the marketplace.
Excellence in product design is a combination of applying advanced technology and engineering expertise. The care that is used to ensure a Moog product is best-in -class starts with design and is carried through to manufacturing and global applications support. While simulation and testing are important components of the overall product design process, an intimate understanding of customers’ needs and application requirements is also a key part of Moog’s strategy. All of these things combined represent the reasons why Moog has earned its reputation as a world leader in the supply of high performance motion control products.
Matthias Finke is a Development Engineer at Moog GmbH in Germany where his main focus is on Finite Elements Method Simulation and Calculation. He received his degree in Mechanical Engineering from the University of Applied Sciences in Esslingen, Germany and wrote his Diploma Thesis using Moog as his topic. Dirk Becher is a Project Engineer, RKP at Moog GmbH, specializing in the design of piston pumps. He graduated with a degree in Mechanical Engineering from the University of Dresden, Institute for Fluid Power in Germany . He finished his Ph.D. in December 2003 with a thesis about the reduction of pulsation in axial piston pumps.
Dirk Becher is a Project Engineer, RKP at Moog GmbH, specializing in the design of piston pumps. He graduated with a degree in Mechanical Engineering from the University of Dresden, Institute for Fluid Power in Germany . He finished his Ph.D. in December 2003 with a thesis about the reduction of pulsation in axial piston pumps.