Technical Sciences / 8. Metal Treatment in Machine-Building

Boldyrev А.А., Doctor of Technical Sciences, Professor Smolentsev V.P.

Voronezh State Technical University, Russia

Locating Mechanism of Rheological Medium Workpieces

with Controllable Physical and Mechanical Properties

At small series manufacture, broad assortment, and rather short periods of workpieces manufacture, amount and complexity of designed industrial equipment, including fastening devices, have great impact on conversion cost of items. For cutting costs of preproduction it is reasonable to use versatile accessories and appliances instead of special facilities.

At finishing stages of treatment cutting force declines dramatically, but more accurate installation of workpieces into operative position is required. That is why devices for workpieces fastening have to meet moderate requirements to rigidity and amount of holding force. Besides, power fastening methods may break the geometrical shape of delicate and thin-walled workpieces and cause disturbance of setting bases. This causes technical and economical premises for the use of versatile self-formable accessories with application of magnetic rheological liquids.

To ensure reliable fastening of workpieces from non-magnetic materials at treatment on magnetic benches, for example during grinding, we use fastening method based on rheological properties of ferrofluid [1].

During installation of workpiece on the bench, the fluid flows in front gap with destroyed structure. The switching on of electromagnetic coils causes magnetic field with induction , that directs ferromagnetic particles along force lines of the magnetic field with formation of chain structure, for destruction of which it is necessary to apply certain force.

Holding force of workpiece on the bench of machine-tool is defined by bonding force, operating in elemental layer of magnetic fluid with area :

Fig. 1. Rheological characteristics of magnetic fluid

at different magnetic induction B and average diameter of iron particles

d_ср=20 nanometers (dashed lines) и d_ср=100 nanometers (full lines)

Fig. 2. Relation of static limit of yield point in magnetic fluid

with magnetic induction at average diameter of iron particles:

d_ср=100 nanometers (curve 1) и d_ср=50 nanometers (curve 2)

. (1)

Transverse strain in layer of ferromagnetic rheological fluid is composed of two components, one of which () is conditioned by viscosity forces, the other () – by magnetic interaction between particles. It is deduced from experiments that in static mode the force preventing shift of workpiece is conditioned by static limit of yield point.

At application of magnetic filed:

, (2)

where – number of particles in volume unit;

– particle magnetic moment;

– distance between centres of particles.

Or on rearrangement:

, (3)

where – volume of ferromagnetic particle.

Intensity of stress can also be defined by rheological curve for magnetic fluid of given type (Fig. 1).

Yield stress grows with increase of induction of magnetic field operating in gap, this allows to control physical and mechanical properties of rheological fluid by change of current on control coil (Fig. 2).

As a result, disclosure of regulation mechanism for parameters of magnetic rheological fluid allows to work out modes, fixtures and tools and workpieces processing method in flexible structure manufacture with control of rheological media parameters.

Cited literature

1. Russian patent № 2312000, МПК B23Q 3/15. Method of Fastening of Workpieces from Non-Magnetic Materials and Device for its Implementation / А.S. Revin, А.V. Lisitsyn, V.P. Smolentsev. 2004136423/02: alleged 14.12.2004: published 10.12.2007 // Bulletin 34, 2007.

2. Smolentsev V.P. Application of Magnetic Rheological Fluids in Metal Processing / V.P. Smolentsev, А.А. Boldyrev // Non-Traditional Methods of Treatment: interacademic collection of scientific papers. Issue. 9. part. 3. Мoscow: Machine-Building, 2010. P. 120-129.

3. Magnetic Fluids in Machine-Building / D.V. Orlov, U.О. Mikhalev, N.К. Мyshkin et al.: under the general editorship of D.V. Orlov, V.V. Podgorkov. – Мoscow: Machine-Building. 1993.