ME 151 chapter 18 T.W.G.

55) What are some of the ways that the binder can be removed from metal injection molded parts?

solvent extraction, controlled heating to above the volatilization temperature, or heating in the presence of a catalyst that breaks the binder down into removable products.

43) What are some benefits of high-temperature sintering? Sinter hardening? microwave sintering?

-High-Temp. Sint.- Enables the use of less costly materials. -Sint. Hardening- integrates strengthening heat treatment. -Micro. Sint.- uniformly heats the whole part, reducing processing time and energy consumption to as little as twenty percent of traditional processing.

6) What are the four basic steps that are usually involved in making products by powder metallurgy?

1- Powder Manufacture 2- Mixing or blending 3- Compacting 4- Sintering.

37) What are the three stages associated most P/M sintering operations?

1- Preheat, burn-off, or purge stage. 2- High-temperature stage. 3- Cool down stage.

30) Describe the four classes of conventional powder metallurgy products.

1- Simplest and easiest to compact, single-level parts, are thin and can be pressed from one side. 2- Thicker parts, but still single level, that require being pressed from two sides. 3- Double level parts that require being pressed from two sides. 4-Multi-level and require two or more pressing motions.

15) What is apparent density, and how is it related to the final density of a P/M product?

A measure of a powder's ability to fill available space without the application of external pressure. Low apparent density means that a large fraction of unfilled space leading to non-uniform density of the final product.

33) What is a reasonable compacted density? How much residual porosity is still present?

Around eighty percent. (80%)

8) What is the most common method of producing metal powders?

Atomization.

4) What are some of the primary market areas for powder metallurgy products

Automotive, aerospace, nuclear, aircraft turbines, household appliances, recreational tools, hand and power tools, hardware items, office equipment, industrial motors, hydraulics, advanced composites, electronic components, magnetic materials, metalworking tools, and a variety of biomedical and dental applications.

9) What are some of the other techniques that can be employed to produce particulate materials?

Chemical reduction of particulate compounds, Electrolytic deposition, Pulverization or grinding, Thermal decomposition of particulate hydrides or carbonyls, Precipitation from solution, and Condensation of metal vapors.

7) What are some of the important properties and characteristics of metal powders to be used in P/M?

Chemistry, purity, particle size, size distribution, particle shape, and the surface texture.

31) What is isostatic compaction? For what product shapes might it be preferred?

Compacting a sealed, flexible mold, then immersed in pressurized gas or liquid applying pressure to all sides of the material. It is best suited for a large part with complex shapes.

17) How do the various powder properties relate to the method of powder manufacture?

Each form of powder manufacturing excels in at least one or the other while falling short in another category.

34) What types of materials are used in compaction tooling?

Hardened tool steel and in some cases, cemented carbides may be employed.

51) Describe the spray-forming process and the unique feature that enables production of a high-density, fine-grain-size products?

Harmless gas propels molten droplets that are in a semi-solid state which flatten upon impact. Freezing occurs quickly and and the resultant product is a uniform chemistry.

23) What are some of the objectives of the compaction operation?

High product density and the uniformity of that density throughout the product.

12) What are some of the unique properties of amorphous metals?

High strength, improved corrosion resistance, and reduced energy to induce and reverse a magnetization.

50) What are some of the other methods that can produce high-density P/M products?

High-temperature metal deformation process, ceracon process, and the in-situ compaction(or spray forming).

14) Why is flow rate an important powder characterization property?

If flow rates are poor, it can lead to non-uniform die filling and non-uniform density and properties in the final product.

38) Why is it necessary to raise the temperature of P/M compacts slowly to the temperature of sintering?

If raised rapidly, it would produce high internal pressure from any entrapped air in closed pores or volatilizing lubricants and would result in swelling or fracture of the compacts.

5) Which metal family currently dominates the powder metallurgy market?

Iron and low-alloy steels.

22) Why might mixing or blending be performed under wet conditions?

It enhances particle mobility, reduce dust formation, and lessen explosion hazards.

19) How does the addition of a lubricant affect compressibility? Green strength?

It improves compressibility at the expense of green strength.

1) What type of product would be considered to be a prospect for powder metallurgy(P/M) manufacture?

Small intricate parts of high precision.

53) In the MIM process, what is done to enable metal powder to flow like a fluid under pressure?

The addition of ultra-fine spherical-shaped metal, ceramic, or carbide powder with a low-molecular-weight thermoplastic or wax material in a mix that is around sixty percent powder.

39) Why is a protective atmosphere required during sintering? During the cool down period?

The compacted shapes tend to have ten to twenty-five percent residual porosity and some of the internal voids are connected to exposed surfaces. At elevated temperatures, rapid oxidation would occur and significantly impair the quality of inter-particle bonding.

32) What is the benefit of warm compaction?

The metal responds better to the applied pressures, resulting in improved properties both in the as-compacted state and after final processing.

13) Why is powder metallurgy a key process in producing products from amorphous or rapidly solidified materials?

The need for high cooling rates along with ultra small dimensions. Also because much of the ribbon material is further fragmented into powder.

60) Why can the original compaction tooling not be used to perform repressing?

The shrinkage of the piece from sintering.

16) What is green strength, and why is it important to the manufacture of high-quality P/M products?

The strength of the pressed powder immediately after compacting. Good green strength means superior mechanical properties and fracture resistance, smooth surfaces, sharp corners, and intricate details.

47) What are some of the attractive properties of hot-isostatic products?

They emerge at full density with uniform, isostatic properties that are often superior to others processes. Also, since compaction and sintering occur simultaneously, it is great for reactive and brittle materials.

26) Describe the movement of powder particles during uniaxial compaction.

They move primarily in the direction of the applied force.

59) What is the purpose of repressing, coining, or sizing operations?

To restore or improve dimensional precision after a piece has been warped or distorted from non-uniform cool down.

35) How do the common sintering temperatures compare to material melting points?

Usually they are around seventy to eighty percent of the materials melting temperature and in some cases for refractory metals, near ninety percent.