Isostatic pressing

Question 1

What is the first step to CIP?

Answer 1

~ a previously-formed part (uniaxially-pressed) is placed in a rubber (latex or neopreme) or polyurethane bag

~ the bag is evacuated around the part and sealed with rubber tape

Question 2

What is the second step to CIP?

Answer 2

~ the encased part is immersed in a fluid (water + oil to prevent corrosion)

~ the fluid is pressurized, which squeezes the part hydrostatically

~ the part may be removed from a reusable bag, or must be cut out

Question 3

What pressures are possible?

Answer 3

~ very high: 700 MPa, 100,000 psi (uniaxial reaches ~200MPa maximum)

~ in CIP, pressure is NOT DEPENDENT on the size of the part

Question 4

How fast do pressurization and depressurization occur?

Answer 4

~ pressurization can occur quickly

~ depressurization should be slower to minimize springback defects

Question 5

What is done for parts with internal cavities during the removal process (step 2)?

Answer 5

~ a mandrel made out of tool steel may be used

~ surface needs a good polish for release

Question 6

What happens during the dry bag process?

Answer 6

~ fluid fills the cavity between steel outer walls and rubber side walls, squeezing a powder compact radially

~ a continuous process for tubular shapes such as spark plugs

Question 7

What are pre-formed CIP bags used in? (dry bag process)

Answer 7

~ in which powder is loaded and vibrated

~ the isopressed part assumes the shape of the bag, but smaller

~ all directions are squeezed, including radial (dry bag)