Chapter 15

Before pressing and sintering in the conventional PM sequence, the powders are blended and/or mixed. Blending refers to which one of the following: (a) air is largely removed from the powders, (b) ceramic powders are intermingled with the metal powders to create cermets, (c) powders of different chemistries are intermingled, or (d) powders of the same chemistry but possibly different sizes are intermingled?

Powders of the same chemistry but possibly different sizes are intermingled

Which of the following statements are correct in the context of metallic powders (three correct answers): (a) porosity + packing factor = 1.0, (b) packing factor = 1/porosity, (c) packing factor = 1.0 - porosity, (d) packing factor = porosity, (e) packing factor = bulk density/true density, and (f) packing factor = true density/bulk density?

porosity + packing factor = 1.0, packing factor = 1.0 - porosity, packing factor = bulk density/true density

Which one of the following most closely typifies the sintering temperatures used in powder metallurgy: (a) 0.5 Tm, (b) 0.8 Tm, or (c) Tm, where Tm = melting temperature of the metal on an absolute scale?

0.8 Tm

After pressing in the press and sinter PM sequence, the work part is called which one of the following: (a) green compact, (b) pressed piece, (c) software, or (d) unsintered work?

Green compact

In the water atomization process for producing metallic powders, particle size is controlled largely by the velocity of the fluid stream; higher speeds create larger particles: (a) true or (b) false?

False

Repressing refers to a pressworking operation used to compress a sintered part in a closed die to achieve closer sizing and better surface finish: (a) true or (b) false?

False

The conventional process for producing parts in powder metallurgy is to simultaneously press and sinter metallic powders in a closed mold: (a) true or (b) false?

False

Which of the following processes combines pressing and sintering of the metal powders (three best answers): (a) hot isostatic pressing, (b) hot pressing, (c) metal injection molding, (d) pressing and sintering, and (e) spark sintering?

Hot isostatic pressing, hot pressing, spark sintering

Which of the following design features would be difficult or impossible to achieve by conventional pressing and sintering (three best answers): (a) outside rounded corners, (b) side holes, (c) threaded holes, (d) vertical stepped holes, and (e) vertical wall thickness of 1/8 inch (3 mm)?

Outside rounded corners, side holes, threaded holes

Powder metal part shaping operations are generally considered to be net shape or near net shape processes: (a) true or (b) false?

True