Hydrostatic Microextrusion of Steel and Copper

Journal Article · Wed May 04 04:00:00 EDT 2011 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.3589564· OSTI ID:21516762

Berti, Guido; Monti, Manuel ^[1]; D'Angelo, Luciano ^[2]

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1. University of Padua, DTG, Stradella San Nicola 3, I-36100 Vicenza (Italy)
2. University of Ferrara, Dept. of Engineering, via Saragat 3, 44100 Ferrara (Italy)

The paper presents an experimental investigation based on hydrostatic micro extrusion of billets in low carbon steel and commercially pure copper, and the relevant results. The starting billets have a diameter of 0.3 mm and are 5 mm long; a high pressure generator consisting of a manually operated piston screw pump is used to pressurize the fluid up to 4200 bar, the screw pump is connected through a 3-way distribution block to the extrusion die and to a strain gauge high pressure sensor. The sensor has a full scale of 5000 bar and the extrusion pressure is acquired at a sampling rate of 2 kHz by means of an acquisition program written in the LabVIEW environment. Tests have been conducted at room temperature and a lubricant for wire drawing (Chemetall Gardolube DO 338) acts both as the pressurizing fluid and lubricant too. In addition, billets were graphite coated. Different fluid pressures and process durations have been adopted, resulting in different extrusion lengths. The required extrusion pressure is much higher than in non-micro forming operations (this effect is more evident for steel). On the cross section of the extruded parts, hardness and grain size distribution have been measured, the former through Vickers micro hardness (10 g load) tests. In the case of the extrusion of copper, the material behaves as in microdrawing process. In the case of the extrusion of steel, the hardness increases from the core to the surface as in the drawing process, but with lower values. The analysis evidenced the presence of the external layer, but its thickness is about 1/3 of the external layer in the drawn wire and the grains appear smaller than in the layer of the drawn wire. The extruding force required along the extruding direction is higher (22-24 N) than the drawing force along the same direction (12 N): being the material, the reduction ratio, the die sliding length the same in both cases, the higher extrusion force should be caused by a higher tangential friction force and/or a higher redundant work of deformation and/or a different material behaviour. Which is the real mechanism is not clear at present, but surface layer grains in extrusion are more deformed than in wire drawing. For this reason the deformation inhomogeneity increases in extrusion and the material under the highly deformed surface layer should be subjected to lower strains, strain hardening and finally resulting in lower hardness.

• OSTI ID: 21516762
• Journal Information: AIP Conference Proceedings, Journal Name: AIP Conference Proceedings Journal Issue: 1 Vol. 1353; ISSN APCPCS; ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALLOYS
CARBON
CARBON ADDITIONS
CARBON STEELS
COPPER
DEFORMATION
DIES
DIMENSIONS
DRAWING
ELEMENTS
EXTRUSION
FABRICATION
FLUIDS
FRICTION
GRAIN SIZE
GRAPHITE
HARDENING
HARDNESS
IRON ALLOYS
IRON BASE ALLOYS
LAYERS
LUBRICANTS
MATERIALS WORKING
MEASURING INSTRUMENTS
MECHANICAL PROPERTIES
METALS
MICROSTRUCTURE
MINERALS
NONMETALS
PRESSURIZATION
RECRYSTALLIZATION
SIZE
STEELS
STRAIN GAGES
STRAIN HARDENING
STRAINS
SURFACES
THICKNESS
TRANSITION ELEMENT ALLOYS
TRANSITION ELEMENTS