슬라이드 1

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1 Powder Metallurgy Powder metallurgy may be define as the art of producing metal powders and using them to make serviceable objects. Powder metallurgy principles were used far back in 3000 B.C. by the Egyptians to make iron parts. The use of gold, silver, copper, brass & in powders for ornaments was common during the middle age. Recently, materials with mechanical properties far better than those of conventional materials have been developed by improving heat-treatment, powder composition and processing methods to achieve higher densities. So powder metallurgy has become a manufacturing technique to produce considerably complex shaped components to exact dimensions at high rates of production with extremely low costs.

2 Powder Metallurgy TEXT : 분말재료및공정, 한국분말야금학회, (Powder Metallurgy & Particulate Materials Processing), Sub-Text : Powder Metallurgy Science, R. M. German, Metal Powder Industry, Instructor : Prof. Soon-Chul Ur of MSE (x5385) Grade Policy 1. Mid term exam: 40% 2. Term paper and presentation: 40% 3. Lecture attendance : 20%

3 Powder Metallurgy Introduction Characterization of powders Synthesis and Fabrication of powders Microstructure control of PM materials Pre-treatment of PM materials Compaction of PM materials Consolidation and sintering Full density processing Finishing and property measurement Application of PM materials Nano technology in PM materials

Powder Metallurgy (P/M) Method: Make fine metal powders and sort Mix powders to get alloy Iron alloys most common, also Bronze Compaction Powder is pressed into a

75 of Tm Particles bind together Part shrinks in size Density increases, up to 95% Strength ~ Density P/M (vs.

4 Powder Metallurgy (P/M) Method: Make fine metal powders and sort Mix powders to get alloy Iron alloys most common, also Bronze Compaction Powder is pressed into a green compact MPa Still very porous, ~70% density May be done cold or warm (higher density) Sintering Controlled atmosphere: no oxygen Heat to 0.75 of Tm Particles bind together Part shrinks in size Density increases, up to 95% Strength ~ Density P/M (vs. Casting): Mass produce small steel parts, net-shape Less waste Unusual alloys Range of densities, porosity (adv or disadv) Less energy use But: Smaller parts and less complexity (2.5D) P/M net-shape gears are common, save machining time

5 마이크로크기분말재료로부터부품을제조하는기술 ( 분말야금 /PM ) 통상적인분말야금법 : 원하는형태로분말성형 (pressing) 단단하고, 견고한성형체 (compact) 를얻기위하여가열에의하여입자를접합 (Sintering) - 원하는부품형상을얻기위하여제작된 punch와 die를사용하여유압식혹은기계식 Press에의하여수행되는작업 - 소결 : 금속의용융온도이하온도에서가열 ; non-melting process Press Sintering furnace

6 마이크로분말소재공정 (PM process) Metals Ceramics

7 나노 마이크로소재공학 마이크로소재공정

PM 소재를사용하는이유 경제성 (economic): 정밀도와비용절감, 소품종다량생산 ( 예 : automotive parts (bearing, valve seat, plugs, injector sensor, connecting rods, sprockets and etc) 독특성 (unique) : 차별화된특성및미세구조 ( 예 : 다공질필터,

8 PM 소재를사용하는이유 경제성 (economic): 정밀도와비용절감, 소품종다량생산 ( 예 : automotive parts (bearing, valve seat, plugs, injector sensor, connecting rods, sprockets and etc) 독특성 (unique) : 차별화된특성및미세구조 ( 예 : 다공질필터, 산화물분산강화터빈합금 (ODS superalloys), Cermet, 경사기능합금 (Functional Gradiented Materials; Ti-hydroxyapatite), 전기접점함금 (Cu-Cr), WC 등 유일성 (captive): 다른공정으로는만들기어렵거나불가능한공정, 분말성형 +( 저온 ) 소결 ( 예 : 초경재료, 고온재료, 폴리머등의난용해성소재, MoSi 2, TiB 2, MgB 2, amorphous alloy, and etc)

9 마이크로분말소재공정의차별점 주조공정 (casting) 을적용할수없는경우

10 마이크로분말소재공정의유일성, 경제성 Unique points Merits in economical view

melting process PM 에의해서만제조가가능한재료 - 예 : W (for filaments), Cermets( 내열합금 ) 등.

11 마이크로분말야금 (powder metallurgy : PM) 의장점 사용된원료분말중 97% 이상높은수율을갖는부품제조 (chip-less). 원하는기공을갖는다공질제품의제조가능. - 예 : 윤활제가함유된 bearing 또는 gear 미세조직, 화학적성분, 물리적성질이상대적으로균일한재질을얻을수있음 주조법 (casting) 에비하여낮은온도의공정 : non melting process PM 에의해서만제조가가능한재료 - 예 : W (for filaments), Cermets( 내열합금 ) 등. 최종제품형상에가깝게제조가능 (near net shape) 후가공공정감소. 미려한부품표면. 균질의마이크로미세조직 : 고강도, 내마모성합금제조에적합 단순형상부품의대량생산에적합 cost effective ( 최근, 복잡한형상부품의대량생산도가능해짐 )

12 마이크로분말야금의한계와단점 금속분말의가격이높다. ( 고비용제조단가, 취급, 보관, 운송등의영향 ) 상대적으로고가의제조장비필요 : press, 소결로, 혼합기 (mixer) 등 금속분말의경우보관이나취급에어려움. 예 : 분말의열화 (oxidation or hydration), fire and explosion 형상및크기의제약 : tooling and largest available press 금속분말의유동성이열악하여균질성형에어려움이따름. 분말의형상, 입도및입도분포를제어하는것은 PM 법에서매우중요하지 만항상용이한것은아님.

13 Powder Metallurgy Range of particle sizes Slightly porous appearance is common

14 Powder Metallurgy: Cermet cutting tools (Ceramic-Metal composite) Cermet cutting inserts for lathe Microstructure: ceramic particles in metal matrix Cermet-tipped saw blade for long life

15 Powder Metallurgy: Porous Metals Metal filters Oil-impregnated Porous Bronze Bearings

16 Powder Metallurgy: Connecting Rods Forged on left; P/M on right

17 Powdered Metal Transmission Gear Warm compaction method with 1650-ton press Teeth are molded net shape: No machining UTS = 1,000MPa 30% cost savings over the original forged part

18 Powdered Metal Turbine blade-disk ( blisk ): 1 piece!

19 Conventional Forging vs. Forging of Powdered Metal blank (2 nd op)

20 Basic Steps In Powder Metallurgy (P/M) Powder Production Blending or Mixing Compaction Sintering Finishing

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

22 Blending or Mixing Can use master alloys, (most commonly) or elemental powders that are used to build up the alloys o 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: o Desire to produce a homogenous blend o Over-mixing will work-harden the particles and produce variability in the sintering process

Compaction Usually gravity filled cavity

strong as finished part handling concern

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

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

25 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

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

27 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.

$Advantages of P/M Virtually unlimited choice of alloys, composites, and associated properties o Refractory materials are popular by this process Controlled porosity for self lubrication or filtration$

28 Advantages of P/M Virtually unlimited choice of alloys, composites, and associated properties o 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

29 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

Financial Considerations Die design must withstand 700MPa, requiring specialty designs Can be very automated o 1500 parts per hour not uncommon for average size part o 60,000 parts per hour

30 Financial Considerations Die design must withstand 700MPa, requiring specialty designs Can be very automated o 1500 parts per hour not uncommon for average size part o 60,000 parts per hour achievable for small, low complexity parts in a rolling press Typical size part for automation is 1 cube o Larger parts may require special machines (larger surface area, same pressure equals larger forces involved)

31 나노 마이크로소재공학 크기단위접두어의의미 CNT: carbon nano tube

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