POWDER METALLURGY NAMEENROLLMENT NO. MANANI RAVI D PATIL YOGESH R HADIYA FORMAL B CHOUDHARI KULDEEP PATEL VIKAS

Definition of Powder Metallurgy Powder metallurgy may defined as, “the art and science of producing metal powders and utilizing them to make serviceable objects.” OR It may also be defined as “material processing technique used to consolidate particulate matter i.e. powders both metal and/or non- Metal’

POWDER METALLURGY: Powder metallurgy is a forming and fabrication technique consisting of three major processing stages. First, the primary material is physically powdered, divided into many small individual particles. Next, the powder is injected into a mold or passed through a die to produce a weakly cohesive structure (via cold welding) very near the dimensions of the object ultimately to be manufactured. Finally, the end part is formed by applying pressure, high temperature, long setting times during which self-welding occurs.

The process of P/M is the process of producing metallic parts from metallic powders of a single metal, of several metals or of a combination of metals and non-metals by applying pressure. The powders are mixed mechanically, compacted into a particular shape and then heated at elevated temperature below the melting point of the main constituent.

Importance of P/M: The methods of powder metallurgy have permitted the attainment of compositions and properties not possible by the conventional methods of melting and casting. Powder metallurgy is an alternative, economically viable mass production method for structural components to very close tolerance. Powder metallurgy techniques produce some parts which can’t be made by any other method.

Process of Powder Metallurgy: The process of P/M in general consists of a series of steps/stages to form a final shape. These stages are shown by a simple flow sheet diagram. Powder Production Powder Characterization & testing Mixing - Blending Processing - Compacting Sintering Operation Finishing Operations Finished P/M Parts

Powder Production Atomization the most common Others – Chemical reduction of oxides – Electrolytic deposition Different shapes produced – Will affect compaction process significantly

Blending or Mixing Can use master alloys, (most commonly) or elemental powders that are used to build up the alloys – Master alloys are with the normal alloy ingredients Elemental or pre-alloyed metal powders are first mixed with lubricants or other alloy additions to produce a homogeneous mixture of ingredients The initial mixing may be done by either the metal powder producer or the P/M parts manufacturer When the particles are blended: – Desire to produce a homogenous blend – Over-mixing will work-harden the particles and produce variability in the sintering process

Compaction Usually gravity filled cavity at room temperature Pressed at ksi Produces a “Green” compact – Size and shape of finished part (almost) – Not as strong as finished part – handling concern Friction between particles is a major factor

Isostatic Pressing Because of friction between particles Because of friction between particles Apply pressure uniformly from all directions (in theory) Apply pressure uniformly from all directions (in theory) Wet bag (left) Wet bag (left) Dry bag (right) Dry bag (right)

Sintering Parts are heated to ~80% of melting temperature Transforms compacted mechanical bonds to much stronger metal bonds Many parts are done at this stage. Some will require additional processing

Sintering ctd Final part properties drastically affected Fully sintered is not always the goal – Ie. Self lubricated bushings Dimensions of part are affected

Die Design for P/M Thin walls and projections create fragile tooling. Holes in pressing direction can be round, square, D-shaped, keyed, splined or any straight-through shape. Draft is generally not required. Generous radii and fillets are desirable to extend tool life. Chamfers, rather the radii, are necessary on part edges to prevent burring. Flats are necessary on chamfers to eliminate feather-edges on tools, which break easily.

Advantages of P/M Virtually unlimited choice of alloys, composites, and associated properties – Refractory materials are popular by this process Controlled porosity for self lubrication or filtration uses Can be very economical at large run sizes (100,000 parts) Long term reliability through close control of dimensions and physical properties Wide latitude of shape and design Very good material utilization

Disadvantages of P/M Limited in size capability due to large forces Specialty machines Need to control the environment – corrosion concern Will not typically produce part as strong as wrought product. (Can repress items to overcome that) Cost of die – typical to that of forging, except that design can be more – specialty Less well known process

Limitations of P/M Process There are numbers of limitations of Powder Metallurgy process as given below: (i)In general, the principal limitations of the process are those imposed by the size and shape of the part, the compacting pressure required and the material used. (ii)The process is capital intensive and initial high costs mean that the production ranges in excess of 10,000 are necessary for economic viability (cost of dies is very high). (iii)The configuration of the component should be such that it can be easily formed and ejected from a die, undercuts and re-entrant angles can not be molded (when using conventional pressing and sintering) and have to be machined subsequently.

(iv) The capacity and stroke of the compacting press and the compacting pressure required limit the cross-sectional area and length of the component. (v) Spheres cannot be molded and hence a central cylindrical portion is required. (vi) Sintering of low melting point powders like lead, zinc, tin etc., offer serious difficulties.

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