Dry Pressing and Isostatic Pressing Questions and Answers

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the mechanism. Under load the compact is elastically strained and the die holds it; as it is pushed clear the constraint is removed one section at a time and the stored energy is released as springback. If the compact relaxes faster than its weak green strength can accommodate, it laminates or cracks - which is why ejection is done slowly and why a tapered die exit helps.

Answer: B

Elastic recovery makes the part marginally larger than the die cavity, which must be allowed for in tooling design. Excessive springback is a warning that laminations or end capping may follow. Springback is measured and used as a warning as well as an allowance.

Answer: C

Correct answer: False

The compact springs back on ejection, expanding by a few tenths of a per cent to a per cent as the elastic strain is released. The die must therefore be cut undersize by that allowance, which is determined by trial for each powder and binder system - and the springback is the same phenomenon that causes ejection cracking when it happens too abruptly.

Answer: D

The first two are correct. The third has the direction wrong, since elastic recovery makes the ejected compact slightly larger than the cavity that formed it. Tooling is sized from the measured recovery of that powder.

Answer: A

Green density rises steeply at first and then flattens, while stored elastic energy and the risk of lamination keep growing. The working pressure is chosen near the knee of that curve rather than at the capacity of the press.

Answer: B

Beyond a point the density gain is negligible while end capping, laminations and die wear all increase. Pressure is optimised against the powder and the shape rather than simply maximised. The knee of the density curve is where the working pressure sits.

Answer: C

Three points on a base of 55 is about 5.5 per cent. Doubling the pressure for so modest a gain illustrates why very high pressures are rarely worth the tooling and the defect risk they bring. Press capacity is rarely the binding constraint in practice.

Answer: D

Lower wall friction means a smaller density gradient and less force needed to eject the part. Excess lubricant, however, can weaken the green body and leave residue that must burn out cleanly. Lubricant type is chosen for its burnout behaviour as well as its slipperiness.

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives both costs. Lubricant reduces die wall friction and eases ejection, but it also comes between the particles and prevents them bonding, so the green strength falls; and every trace of it must be burnt out in firing, which takes time in the schedule and can cause bloating if it is trapped. It is therefore applied to the wall in the smallest quantity that works.

Answer: B

Anything deep or re-entrant suffers badly from density gradients and cannot be ejected from a simple die. Complex or elongated parts go to isostatic pressing or to another route entirely. Shape complexity is what usually decides between the forming methods.