8 Particulation

Question 1

1. What are the three basic steps in the conventional powder metallurgy shaping process? (3)

Answer 1

(1) blending and/or mixing

(2) pressing

(3) sintering.

[What is the technical difference between blending and mixing in powder metallurgy?]

Blending

combining particles of the same chemistry but different sizes, while mixing refers to the combining of metal powders of different chemistries.

Pressing Step

powders are compressed into the desired shape to produce a green compact, which is completed in a press using a punch and die.

Sintering Step

green compacts are heated to bond the particles into a hard rigid mass, in which temperatures are below melting point.

Question 2

2. What are some of the advantages and disadvantages of PM methods?

Answer 2

Advantages of Powder Metallurgy (2MW)

1 Mass produce to near net shape, thus eliminating the need for subsequent machining

2 Wastes very little material, approximately 97%

(Powder Metallurgy can be made with a specified level of porosity, to produce porous metal parts)

Disadvantages of Powder Metallurgy (3HML)

1 High tooling and equipment costs

2 Metallic powders being too expensive

3 Limitations on part geometry because metal powders do not readily flow laterally in the die during processing.

Question 3

3. Why is the PM technology so well suited to the production of gears and bearings?

Answer 3

1 Because their geometric shapes are defined in two dimensions

2 there is a need for porosity in the part to serve as a reservoir for lubricant.

Question 4

4. List the basic steps in the TRADITIONAL ceramics processing sequence.

Answer 4

1 Preparation of raw materials

Loose powders surrounded by air

2 Shaping

Clay mixed with water as a general form of end product

3 Drying

Dry clay surrounded by air

3 Firing

Fired clay in the shape’s fully compact form

Question 5

5. List the basic steps in the new ceramics process sequence.

Answer 5

1 Preparation of starting materials

2 Shaping

3 Sintering

4 Finishing

Question 6

6. What are the functions of sintering in the production sequence to make NEW ceramic parts?

Answer 6

1 Bonding individual grains into a solid mass

2 Increasing density

3 Reduction of porosity

Question 7

7. How are WC-CO tools manufactured? Briefly describe each step.

Answer 7

WC-CO tools are manufactured through:
SINTERING

Here;
1- WC dissolves gradually in Co during sintering
(and in order to melt the melting point is reduced)

2 - Co flows and wets the WC particles during the liquid phase,

3 - thus dissolving the solid further.
(Molten metal also serves to remove gasses from the internal regions of the compact)

4 - This leads to the leftover WC particles rearranging into a closer packaging.

5 - As a result, there is significant densification and shrinkage of the WC-CO mass.