11 November 2014
11 November 2014
RAMPF Machine Systems has unveiled a bonded lightweight carriage in a highly dynamic, multi-axis moving system at this year’s Motek trade fair in Stuttgart, Germany.
The company states the carriage features improved rigidity, significantly better damping, and low weight.
For the first time, RAMPF Machine Systems claims it has manufactured a carriage for a highly dynamic multi-axis system using aluminium foam sandwich panels that have been cut to size and bonded together.
According to RAMPF the carriage weighs 32% less than a comparable version made entirely of steel, while also delivering improved rigidity and significantly better damping. The acceleration of the three axes in this moving system that can be adapted for different applications is 8g on the X-axis, 3g on the Y-axis, and 13g on the Z-axis. Rigidity at the top of the carriage in the Z-direction has been measured at 50N/µm.
“As a result, this system is suitable for highly dynamic pick & place tasks and for soldering, bonding, measuring, dispensing, print, and laser applications,” says Dr. Utz-Volker Jackisch, Managing Director of RAMPF Machine Systems. “The carriage can even cope with the loads that occur when cutting wood, plastic, and aluminium.”
The lightweight aluminium foam carriage puts in an impressive performance. However, that’s hardly surprising given the mechanical properties of the material. The cellular structure absorbs vibrations, jolts, and sounds exceptionally well and, with its low weight, provides an ideal basis for the lightweight construction of machine bed components with optimum flexural strength and vibration damping. Assemblies made from metal foams also withstand high temperatures up to well over 100 °C, offer highly effective shielding against electromagnetic waves, and can be easily recycled .
At the moment, it is primarily aluminium foam that is used in mechanical engineering applications. This material is generally made using powder metallurgy processes, during which aluminium powder is mixed with a gas-generating blowing agent such as titanium hydride. Other additives are used mainly to stabilize the foam. The powder mixture is then compacted into semi-finished products using powder extrusion or axial hot press moulding and adapted to the component geometry in subsequent forming steps. When heated above the melting point of the metal, the gas released from the blowing agent foams the metal. The foam structure is then permanently solidified through cooling . “Aluminium foams expand to around five times the initial volume, and the foam densities are thus around 0.5 g/cm³,” says Steven Donner, who developed the carriage and works in the design/development department at RAMPF Machine Systems.
Cover plates made of aluminium have proved popular for composite structures with aluminium foam filling. This combination offers the following benefits:
· Durable metallic bonding of hybrid partners
· Damping of wall vibrations in intricate moving machine bed assemblies through the dissipation and reduction of vibrational energy thanks to minimal plastic deformation of the thin cell walls and friction of the crack surfaces in the cell walls 
· Reinforcement of intricate component structures and thus prevention of buckling in thin walls
Bonding is the joining technology used in lightweight construction
In additional to the lightweight material, further weight optimization was achieved based on the FEM calculation of equivalent cross bar rigidity and notch stress optimization according to Mattheck. The manufacturing process depicted in the following image features several innovative approaches:
The cuts were made from standard sandwich material (1100 x 2400 x 14 mm) with 1 mm aluminium top layer using five-axis water jet cutting. The advantages include:
· Optimal material utilization
· Chamfers for subsequent bonding are cut directly
· No coolants, thus minimal cleaning outlay prior to bonding
· Optimized costs compared to other processes
Selecting the smallest possible top layer thickness is essential to fully harness the lightweight construction potential of aluminium foam sandwiches. However, that removes the option of manufacturing a welded composite. “Bonding is the joining technology used in lightweight construction,” emphasises Jackisch. “The advantages are automation potential, savings on time and weight, and additional damping and rigidity.” When cut-offs of aluminium foam sandwiches are bonded, the open-walled pores ensure that the epoxy resin adhesive covers large areas for force distribution.
Compared to carriages or booms made of fibre composites, such as CFRP, bonded cut-off sections of aluminium foam sandwiches can generate cost savings of up to 100 percent with a similar weight. The outlay for manufacturing tools or fixtures is also reduced. The integral process is recommended for series components, with outer shells made to customer specifications foamed using the procedure detailed above. This brings further improvements in strength and lightweight properties.
Steven Donner developed the lightweight carriage made from aluminium foam. He works in the design/development department at RAMPF Machine Systems.
The moving system with a carriage made of aluminium foam sandwiches combines three different, very high-performance drive types within an integrated overall concept. The main bulk of the linear motor that drives the X-axis is integrated directly into the load-bearing machine structure made of natural hard stone. A belt axis with servo motor has been selected for the Y-direction. Due to the mass located near the X-carriage, the bending moment can be kept low. A simple step motor solution is used on the Z-axis by linking the guide and rack.
According to Zäh und Löhe , balanced dynamics and robust damping are among the trends in machine concepts for highly dynamic production technology. Alternative materials, such as aluminium foam in combination with high-performance bonding technology, can play an important role in fulfilling these requirements.
Photo provided by RAMPF
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