Powder metallurgy processes – Forming articles by uniting randomly associated metal particles – Consolidation of powders
Patent
1986-10-22
1988-09-13
Jones, David
Powder metallurgy processes
Forming articles by uniting randomly associated metal particles
Consolidation of powders
264113, 264 84, 425355, 425405H, 425 1, 419 8, B22F 700
Patent
active
047708492
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to the addition of an extra element into the path of stress waves present during the working or compaction of solid phase materials.
BACKGROUND ART
It is well established that materials can be shaped or compacted by impacting them with either a hammer or piston or punch or similar, e.g. see U.S. Pat. No. 4,255,374 issued Mar. 10, 1981, to Bo Lemcke et al and assigned to Institut Cerac S.A. The operation of this type of equipment is described in greater detail below.
OBJECT OF THE INVENTION
It is an object of the present invention to modify the propagation of stress waves in a material which is being dynamically loaded so as to gain greater control over the way in which the material is loaded compared to prior techniques. Other objects and advantages of the invention will hereinafter become apparent.
NATURE OF THE INVENTION
The invention provides a method of dynamically loading materials such as solid materials, or powders of solid materials, wherein the material is loaded in a support means and is impacted by a means generating a stress wave therein, characterised by the provision of an impedance means between the material and the means generating a stress wave, the impedance means being effective to cause reflection of stress waves within the material being dynamically loaded.
The invention also provides an apparatus for dynamically loading materials such as solid materials, or powders of solid materials, comprising a support means wherein the material is loaded, and a means generating stress waves therein characterised in that an impedance means is provided between the material and the means generating stress waves.
The impedance means may be applied directly to the means which generates stress waves or it may be located adjacent the material being stressed.
The purpose of the impedance means is to modify the propagation of stress waves by either nature of stress wave reflections in the materials being worked, or both.
In the present specification the term `solid phase` merely denotes a solid phase as distinct from a liquid or gas phase. Typical materials include metals, plastics, and ceramic. The term `high shock impedance` merely implies that an impedance mismatch exists.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic of an apparatus of a type to which the invention may be applied.
FIG. 2a is a wave diagram setting out the characteristic stresses to be encountered in a material being worked in the apparatus of FIG. 1.
FIG. 2b graphically shows the pressure experienced by a powder under impact.
FIGS. 3 and 4 show two ways in which the invention may be applied in the working of powders.
FIGS. 5aand 5b show wave diagrams corresponding to the situation arising in operation of the apparatus of FIGS. 3 and 4 respectively.
FIGS. 6a and 6b show the pressure variations arising in the material being worked in the apparatus of FIGS. 3 and 4 respectively.
DESCRIPTION OF PREFERRED EMBODIMENTS
For simplicity in the subsequent description, the invention will be described in terms of its application to the dynamic compaction (consolidation) of powdered materials but in principal it could also be applied to other processes utilizing stress waves caused by the impact of one body on another.
One method of dynamic powder compaction that lends itself to simple description of the invention utilizes a gas driven piston which is fired into powder constrained in a die (FIG. 1). On impact, an initial shock wave is formed in the powder. This is a compressive stress wave across which there is an abrupt increase in pressure. This propagates through the powder compressing it. Simultaneously there is a compressive stress wave formed in the piston which propagates back into the piston away from the piston/powder interface. This and subsequent wave behaviour is illustrated in FIG. 2.
In the apparatus of FIG. 1, a piston 10 is fired down a launch tube 14 at a powder 11 contained in a die insert 12 in a die block 13. The piston 10 is propelled by a high pressure gas
REFERENCES:
patent: 1951174 (1934-03-01), Simons
patent: 3065073 (1962-11-01), Hug
patent: 3084398 (1963-04-01), Swed
patent: 3356496 (1967-12-01), Hailey
patent: 3657917 (1972-04-01), Chelminski
patent: 4049367 (1977-09-01), Tominaga et al.
patent: 4255374 (1981-03-01), Lemcke et al.
patent: 4384834 (1983-05-01), Wichoud
Jones David
University of Queensland
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