ME 355 Sp’06W. Li1 POWDER METALLURGY SUBMITTED BY : P MUKESH KUMAR TH SEMESTER MECHANICAL ENGINEERING C. V. RAMAN COLLEGE OF ENGINEERING

ME 355 Sp’06W. Li2 INTRODUCTION Competitive with processes such as casting, forging, and machining. Used when melting point is too high (W, Mo). reaction occurs at melting (Zr). too hard to machine. very large quantity. Near 70% of the P/M part production is for automotive applications. Good dimensional accuracy. Controllable porosity. Size range from tiny balls for ball-point pens to parts weighing 100 lb. Most are around 5 lb.

ME 355 Sp’06W. Li3 Basic Steps In Powder Metallurgy Powder Production Blending or Mixing Powder Consolidation Sintering Finishing

ME 355 Sp’06W. Li4 1. Powder Production (a)(b)(c) (a) Water or gas atomization; (b) Centrifugal atomization; (c) Rotating electrode Many methods: extraction from compounds, deposition, atomization, fiber production, mechanical powder production, etc. Atomization is the dominant process

ME 355 Sp’06W. Li5 Characterization of Powders Size of powders 0.1 um – 1 mm Sieve size quoted as mesh number Particle D = 15/mesh number (mm) 325 mesh  45 um

ME 355 Sp’06W. Li6 2. Blending or Mixing Blending a coarser fraction with a finer fraction ensures that the interstices between large particles will be filled out. Powders of different metals and other materials may be mixed in order to impart special physical and mechanical properties through metallic alloying. Lubricants may be mixed to improve the powders’ flow characteristics. Binders such as wax or thermoplastic polymers are added to improve green strength. Sintering aids are added to accelerate densification on heating.

ME 355 Sp’06W. Li7 3. Powder Consolidation Die pressing Cold compaction with 100 – 900 MPa to produce a “Green body”. Die pressing Cold isostatic pressing Rolling Gravity Injection Molding small, complex parts.

ME 355 Sp’06W. Li8 Friction problem in cold compaction The effectiveness of pressing with a single-acting punch is limited. Wall friction opposes compaction. The pressure tapers off rapidly and density diminishes away from the punch. Floating container and two counteracting punches help alleviate the problem.

ME 355 Sp’06W. Li9 4. Sintering Parts are heated to 0.7~0.9 T m. Transforms compacted mechanical bonds to much stronger metallic bonds. Shrinkage always occurs:

ME 355 Sp’06W. Li10 5. Finishing The porosity of a fully sintered part is still significant (4-15%). Density is often kept intentionally low to preserve interconnected porosity for bearings, filters, acoustic barriers, and battery electrodes. However, to improve properties, finishing processes are needed: Cold restriking, resintering, and heat treatment. Impregnation of heated oil. Infiltration with metal (e.g., Cu for ferrous parts). Machining to tighter tolerance.

ME 355 Sp’06W. Li11 Special Process: Hot compaction Advantages can be gained by combining consolidation and sintering, High pressure is applied at the sintering temperature to bring the particles together and thus accelerate sintering. Methods include Hot pressing Spark sintering Hot isostatic pressing (HIP) Hot rolling and extrusion Hot forging of powder preform Spray deposition

ME 355 Sp’06W. Li12 Process Capabilities Con’tionalHIPInjection Molding (IM) Precision IMPreform Forging MetalAllAll (SA, SS) All (Steel, SS)AllSteel, SA Surface detailBB-CBAA Mass, kg0.01-5(30) (e) Min. section, mm Min. core diam. mm Tolerance +/-% Throughput (pc/h) Min. quantity , , ,000 Eq. CostB-CAA-B A: highest, B: median, C: lowest

ME 355 Sp’06W. Li13 Design Aspects (a) Length to thickness ratio limited to 2-4; (b) Steps limited to avoid density variation; (c) Radii provided to extend die life, sleeves greater than 1 mm, through hole greater than 5 mm; (d) Feather- edged punches with flat face; (e) Internal cavity requires a draft; (f) Sharp corner should be avoided; (g) Large wall thickness difference should be avoided; (h) Wall thickness should be larger than 1 mm.

ME 355 Sp’06W. Li14 Advantages and Disadvantages 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. Very good material utilization. Limited part size and complexity High cost of powder material. High cost of tooling. Less strong parts than wrought ones. Less well known process.

THANK YOU