Powdered Metallurgy

Question 1

What is the objective of this lab?

Answer 1

Objective:
The objective of this lab is to demonstrate the process of making parts using powdered metals through direct pressing and hydrostatic pressing. Specifically, it focuses on:

Investigating the effect of varying tin content in a copper-tin alloy.
Examining the influence of part density on the final properties of the materials.

This will be done by compacting powder mixtures in molds, sintering them, and measuring various properties like hardness, density, and strength.

Question 2

What are the procedures of this lab? Part 1

Answer 2

1. Preheat Furnace
   Set the furnace to 1200°F and allow it to heat up.
2. Prepare Copper-Tin Mixtures
   Prepare 4 samples of copper-tin mixtures, each weighing approximately 9 grams. Prepare the following compositions:
   0% Sn (9 g Cu, 0 g Sn)
   15% Sn (17 g Cu, 3 g Sn)
   30% Sn (14 g Cu, 6 g Sn)
   45% Sn (11 g Cu, 9 g Sn)

For each sample:
a. Place an empty bottle on the scale and tare it.
b. Add the powder metals (Cu and Sn) into the bottle based on the required weight.
c. Close the bottle and mix the powders thoroughly.
d. Allow the powders to settle, then open the bottle.
e. Use a spatula to transfer the powder into the first crucible without creating a dust cloud.
f. Label each crucible with the percentage of tin using a permanent marker.
g. Carefully transfer the powder into a silicone rubber mold using a funnel. The mold should be filled to allow it to close when rubber bands are applied.

Question 3

What are the procedures of this lab? Part 2

Answer 3

3. Compact the Samples Using Cold Isostatic Press
   For each of the 4 mixtures:
   a. Connect the electric and air lines to the Cold Isostatic Press (CIP).
   b. Turn the ON/OFF switch to ON.
   c. Manually pull out the pin on the right side until it stops.
   d. Lift the cover using the 4-way valve handle and swing it out of the way.
   e. Place the molds in the aluminum ladle and submerge it gently in the water.
   f. Have the instructor check the water level for accuracy.
   g. Lower the cover, align it, and lower the 4-way valve.
   h. Insert the pin until the PIN-IN light appears.
   i. Close the SHUT-OFF valve and PRESSURE-RELEASE valve.
   j. Press the PUMP button to start the press and wait until the pressure reaches 30 kpsi (or instructor-specified pressure).
   k. Shut off the pump when the required pressure is reached.
   l. Slowly open the PRESSURE-RELEASE valve to reduce the pressure to below 1 kpsi, then fully open the PRESSURE-RELEASE valve.
   m. Remove the pin and raise the cover.
   n. Retrieve the ladle with the compacted samples.
   o. Repeat this process for the remaining molds.

Question 4

What are the procedures of this lab? Part 3

Answer 4

4. Press Samples Using the Metal Workbench Press
   For each sample:
   a. Raise the piston to the top position; ensure the punch is mounted.
   b. Zero the punch force strain gage voltage.
   c. Assemble the bottom die, cylindrical die, and bottom plug, then add the powder to the die.
   d. Carefully place the assembly in the base and rotate it to ensure it is seated properly.
   e. Lower the punch and record the pressure and punch force voltage when the top gauge reads its maximum pressure.
   f. Raise the punch and remove the die assembly.
   g. Replace the bottom die and plug, then insert the push rod into the cylindrical die.
   h. Lower the punch until the push rod is 0.1” above the die surface. Once the push rod falls, the coupon is out of the die.
   i. Raise the punch and remove the die.

Question 5

What are the procedures of this lab? Part 4

Answer 5

5. Carbon Powder Application
   a. Place each pair of green samples (same tin content) in a crucible.
   b. Cover each sample with about 1/8 inch of carbon powder.
6. Sintering
   a. Place the crucibles in the furnace in a prearranged pattern, ensuring they can be identified after heating.
   b. Sinter the samples at 1200°F (650°C) for 30 minutes.
   c. Shut down the furnace.
7. Cooling
   a. Once sintered, empty the contents of one crucible onto a steel sheet and remove the coupons.
   b. Place the coupons on aluminum strips to cool quickly, ensuring they are spaced apart to identify them later.
8. Post-Cooling Measurements
   Measure the diameter, length, and weight of each specimen.
   Measure the hardness using the L Rockwell scale at both the top and bottom of each specimen.
9. Equipment Clean-Up
   Ensure all equipment (Isostatic Press, Direct Press, Furnace, Balance, Hardness Tester) is properly cleaned and turned off.
   Store loose pieces in their correct locations, and make sure everything is returned to its designated space.

Question 7

Specific Things to Remember!

Answer 7

CIP pressure setting for this experiment = 30KPSI
Sintering Temp and time = 1200°F (650°C) for 30 minutes.
Why is rapid cooling done after sintering?
A: To lock in the material’s microstructure and prevent undesirable changes.
What measurements are taken after cooling?
A:
Diameter
Length
Weight

What equipment needs cleaning after the experiment?
A: Isostatic Press, Direct Press, Furnace, Balance, and Hardness Tester.
Why is the weight of each sample important?
A: It helps determine the density of the material after compaction and sintering.

What are the copper-tin mixture compositions?
A:
0% Sn (9 g Cu, 0 g Sn)
15% Sn (17 g Cu, 3 g Sn)
30% Sn (14 g Cu, 6 g Sn)
45% Sn (11 g Cu, 9 g Sn)

L Rockwell scale

Why is carbon powder applied to samples before sintering?
A: It prevents oxidation and ensures smooth sintering by reducing material sticking.