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Level 27

16 B - POWDER METALLURGY


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CONVENTIONAL PRESSING AND SINTERING
CONVENTIONAL PRESSING AND SINTERING consists of three steps: [1] Blending and mixing powders, [2] Compaction into desired shape, [3] Sintering - heating to cause solid state bonding. >>> BeaC Suck: BLENDING, COMPACTION, SINTERING.
Blending and mixing powders
MECHANICALLY MIXING DIFFERENT TYPES OF PARTICLES, in order to increase their qualities - small and big particles will minimize porosity, blending different elemental powders together will something nice as well, the powders mixed together in a rotating drum, rotating double cone, screw mixer, blade mixer, with an addition of some lubricants to reduce friction between particles, binders to help particles bind together after pressing, and deflocculants that inhibit agglomeration of powders during processing. >>> DuC Minge BaLD: DRUM, CONE, MIXER,,, BINDERS, LUBRICANS, DEFLOCCULANTS
Lubricants
REDUCE FRICTION BETWEEN PARTICLES and die wall during pressing, usually stearates of zinc and aluminum
Binders
HOLD UNSINTERED PART TOGETHER, allowing handling of unsintered parts.
Deflocculants
PREVENT AGGLOMERATION OF POWDERS thus increasing flow characteristics.
Compaction
COMPACTION OR PRESSING OF POWDERS INTO FORM, pressing the particles together so hard that some of them deform thus decreasing voids and increasing the compacted part's density, producing a "green compact" with "green strength", a compacted powder part strong enough to handle and move around. Pressing force for compaction of powder is the compaction pressure of the part multiplied by its area $F=p \cdot A$ >>> GREEN COMPACT SLOWLY MOVES SCORCHING FIRE.
Sintering
FUSES PARTICLES TOGETHER AT 70% TO 90% OF MELTING POINT TEMPERATURE, turning a collection of particles into one solid, strong metal part through diffusion and plastic flow, a process in which shrinkage also can occur due to the reduction of voids. The process occurs in three stages in a continuous furnace: [1] Preheat - burn of lubricants and binders, [2] Sintering - fuse particles together, [3] Cool down. PREHEATED BINDERS VACATE FUSED POWDER BLADE.
Sintering furnace
SINTERING FURNACES CONTROL THEIR ATMOSPHERE by having an inert gas, nitrogen-based, disassociated amonia, hydrogen, and natural gas in order to: [1] Protect from oxidation, [2] Provide reducing atmosphere to reduce oxides, [3] Provide carburazing atmosphere, [4] Remove binders and lubricants. >>> GAS FILLED FURNACE FEVERISHLY FRIES AND FUSSES OILY BLADES
Secondary operations
Secondary operations in powder metallurgy include: [1] Densification and Sizing, [2] Impregnation and Infiltration, [3] Heat treatment, [4] Finishing. >>> DoeS IckI HooF: DENSIFICATION AND SIZING,,, IMPREGNATION AND INFILTRATION,,, HEAT TREATEMENT AND FINISHING
Densification and sizing
During densification and sizing the sintered part is pressed to increase density and dimensional accuracy, sometimes machining the sintered part to give it features unattainable in a sintering process.
Impregnation
OIL OR POLYMER IMPREGNATES SINTERED PART, in order to make self oiling parts such as gears or bearings, or to seal the pores with polymer, so that nothing could get in.
Infiltration
MOLTEN METAL INFILTRATES POROUS SINTERED PART, sealing the pores and increasing the part's strength, drawing the liquid copper into an iron sintered part.
Heat treatment and finishing
SINTERED PART'S PORES CAN ABSORB SHIT DURING HEAT TREATMENT AND FINISHING. Sintered parts can go through heat treatment and coating processes, yet much care needs to be taken not to get anything into their pores, such as not heat treading with the use of salt baths, or entrapment of chemical solutions used in plating and coating. keep part clean during Finishing and heat treatment.
ALTERNATIVE PRESSING AND SINTERING TECHNIQUES
ALTERNATIVE PRESSING AND SINTERING TECHNIQUES use pressure, injection molding, powder rolling, powder extrusion, forging, combination of pressing and sintering, and liquid phase sintering to create sintered metal parts. PI REF CooL: PRESSURE, INJECTION,,, ROLLING EXTRUSION, FORGING,, COMBINATION, LIQUID_PHASE
Isostatic pressing
STRONG PRESSURE COMPACTS POWDER PART, pressing on it from all directions, applying pressure through a flexible mold. Two types exist: [1] Cold isostatic pressing and [2] Hot isostatic pressing.
Cold isostatic pressing
WATER OR OIL PRESS DOWN ELASTIC MOLD, pressuring the powder inside into a complex form usually unachievable with a regular mold, yet the dimensional accuracy is inferior to a regular process. INACCURATE WATER PRESSES FINE POWDER.
Hot isostatic pressing
HOT GAS PRESSES AND SINTERED POWDER THROUGH FLEXIBLE MOLD, pressing down upon it through a sheet metal mold, achieving compaction and sintering at the same time, an expensive process usually used in the aerospace industry.
Powder injection molding
INJECTION MOLDING MACHINE INJECTS POWDER MIXED WITH BINDER TO CREATE PART FOR SINTERING, heating up the polymer binder to injection temperature and injecting it into the mold, creating a complex geometry part removed from the mold, it's binder removed by solvent or heat, and finally it goes through the sintering and finishing processes, Mix with plastic, inject, Sinter >>> MIS: MIX, INJECT, SINTER
Powder rolling
Rolls compact powder into green strip, feeding it into sintering furnace only to be cold rolled and re-sintered afterwards. >>> RiSe CaR: ROLL, SINTER, COLD-ROLL, RE-SINTER.
Powder extrusion
MACHINE EXTRUDES HEATED CANNED POWDERS OR HEATED SINTERED BILLETS, thus achieving high degree of densification in the processes of powder extrusion.
Powder forging
Stupid machine forges sintered part
Combined pressing and sintering
Techniques that combine pressing and sintering: [1] Hot pressing - pressing and heating at the same time, a problematic process, since special mold and temperature control, [2] Spark sintering - pressing the part with punches that serve as electrodes, sending a high energy charge through the part, baking it into a sintered state.
Liquid phase sintering
In a two powder metal mix, the metal with lowest meting temperature melts and traps the other metal powder, sometimes producing an alloy by dissolving the particles in a process of prolonged heating. LIQUID PHASE SINTERS SOLID PARTICLES.
PM MATERIALS AND PRODUCTS
POWDER METALLURGY MATERIALS AND PRODUCTS are more expensive due to the cost of PM raw materials - additional energy required to reduce metal into powder form, thus PM processes are more competitive only at high rates of production and when producing specific, geometrically simple and preferably porous products.
Powder metallurgy materials
ELEMENTAL OR PREALLOYED POWDERS SINTER INTO PARTS AND BLADES. The elemental powders used to accomplish a mixture of materials impossible by regular alloying, the prealloyed powders use to make materials that can't be made by blending elemental particles, such as stainless steel. Most common materials used for powder metalurgy: Iron, Aluminum, Copper, Nickel, Stainless steel, High speed steel, tungsten, molybdenum, titanium, precious metals.
Powder metallurgy products
POWDER METALLURGY PRODUCES NET SHAPE OR NEAR NET SHAPE PRODUCTS, such as gears and bearings, sprockets and fasteners, electrical contacts and cutting tools, especially useful in applications where the parts have to be porous in order to absorb lubrication, such as gears and bearings.
Classes of powder metallurgy part designs
THE CLASSES OF POWDER METALLURGY PART DESIGN ARE: [I] Simple thin shapes that can be pressed from one direction. [II] Simple, thick parts - have to press from two directions. [III] Two levels of thickness - press from two directions. [IV] multiple levels of thickness - press from two directions, separate control for each level. >>> TiTi 2 Me: THIN, THICK, 2_LEVELS, MANY_LEVELS
Powder metallurgy part design considerations
PM part design considerations: [1] Economical for large quantities > 10,000. [2] Can make porous parts. [3] Unique metal blends possible. [4] Geometry must allow ejection - smooth vertical walls without side holes and side undercuts. [5] Can't screw on threads - only machine them afterwards. [6] Shallow chamfers and small fillets are easier to produce. [7] minimum wall thickness and hole diameter = 1.5 [mm] >>> MET PUC: MANY, EJECTION, THREADS,,, POROSITY, UNIQUE_BLENDS, SMALL_CHAMFERS