Question

1. What is significance of powder shape in relation to density and strength of the powder metallurgy parts?
2. What is significance of metallic powder flow rate, density and green strength?
3. Graphite can be used as a lubricant in the metallic powder; what is advantage of using the graphite in addition to providing lubrication?
4. Describe isostatic compaction method, and identify its advantage over conventional powder pressing method?
5. Define liquid phase sintering, and explain it.
6. What is sinter brazing?
7. Identify one application of powder metallurgy which is based on impregnation.
8. List one application of powder metallurgy parts that utilizes infiltration.
9. Would you be able to make undercuts in the metallurgy parts through the powder metallurgy process? Explain.
10. Define sizing, and explain why it is performed?
11. Which environment would you recommend while performing a sintering process, and why? Oxidizing, reducing, or neutral
12. Identify at least one problem associated with using carburizing environment while sintering the plain carbon steel sprockets.
13. Identify at least one problem associated with using oxidizing environment while sintering plain carbon steel gears?
14. Search literature and identify at least one application of powder metallurgy to manufacture tools using composite materials.
15. Metallic sheets can be manufactured through rolling process using either plate or metallic powder as starting material; identify one drawback and one comparative advantage in each case.

Answer 1

ANSWER 1

Powder metallurgy is one of the oldest practices which are still used to produce objects. It comes under the category of metal forming process. Shape of poder decides most of the things in powder metallurgy. To achieve high porosity spherical shape particles are required and to produce high strength coarse particles are needed.

ANSWER 2

Flowability of metallic powder depends upon how fine the particles are, more fineness, more fluidity, coarse particles resist fluidity. Green strength is the ability to withstand large amounts of forces during compaction. Density of powder particles depends upon how close grains are, grains of perfect spherical sizes have more gaps(voids) in between so they are less dense compared to coarse grains who have close arrangements.

ANSWER 3

Graphite has one of the marvellous properties, it can be used as lubricants between two surfaces having relative motion to avoid wear and tear, it can be used with dry as well as between wet surfaces.Graphites molecules have unique feature of having flowability because of loose bonding among molecules which allows slippery behaviors and this is used as lubrication.

ANSWER 4

ISOSTATIC COMPACTION

As the name suggests, iso means the same and static compaction means - pressure application. To achieve uniform pressure from all the directions metal powders are packed inside a special bag and then put deep inside fluid it ensures uniform pressure application from all the directions, although there are some variations but they are so too small to do anything.This method is excellent in achieving the uniform density over conventional methods.

ANSWER 5

LIQUID PHASE SINTERING

Sintering is the process achieved after the compaction process. After compacting metal powders are heated in a controlled environment. Liquid phase sintering is used when multiphase components are needed to be sintered.Liquid phase sintering enhances density and must have wetting property.,

ANSWER 6

Sinter brazing is a way of joining two different parts using filler material which has a low melting point than the other two parts . When filler material melts it makes joint

ANSWER 7

One of the best applications of powder metallurgy impregnation process is in Porous metallic bearings which are oil impregnated.,These bearings are made up of large pores which allows oils to be soaked. These bearings are used in areas where frequent lubrication is not possible. More the porosity more will be lubrication absorbing capacity which enables for high speed applications in extreme conditions.

ANSWER 8

In the infiltration process low melting point liquid alloy is made to go inside pores using capillary action. The major application is copper infiltrated steel products and copper infiltrated ferrous alloy products, products made by infiltration have better mechanical properties,higher densities etc.

ANSWER 9

No, undercuts are not preferred using powder metallurgy generally but there are few exceptions Sometimes it is not possible to make undercuts during the compaction stage and they are made using secondary machining operations later.

ANSWER 10

Sizing is nothing but squeezing action performed to achieve desired thickness. They are done to bring uniformity on parts sometimes and pressure involved is kept below that was used during the compacting process..Sizing refines surface

ANSWER 11

Types of products produced sintering depends upon its environment.Some products require carburizing, some require neutral or some require oxidising environment but out of these sometimes vacuum is also preferred since vacuum sintering has no scope of contamination.