Page 468 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

448 Chapter 17 Powder-Metal Processing and Equipment

ranges for CIP and other compacting methods in terms of the size
and complexity of a part are shown in Fig. 17.14. A typical applica-
HIP
0.6 tion is automotive cylinder liners.
In hot isostatic pressing (HIP), the container generally is
'e ' \ made of a high-melting-point sheet metal and the pressurizing
v0.4 \ medium is high-temperature inert gas or a vitreous (glass-like) fluid
cu \
_'JI \ (Fig. 17.15 ). Common conditions for HIP are pressures as high as
cn \ 100 MPa-although they can be three times as high--and temper-
0.2 "\ t PM atures of 1200°C. The main advantage of HIP is its ability to pro-
PF
duce compacts having almost 100% density, good metallurgical
Liv 2 PIM
bonding of the particles, and good mechanical properties.
0 r \_1 u
O 1 2 3 4 5 6 Consequently, it has gained wide acceptance in making high-quali-
Relative shape complexity ty parts.
The HIP process is used mainly to produce superalloy compo-
FIGURE |1.l4 Capabilities, with respect to nents for the aircraft and aerospace industries and in military, med-
part size and shape complexity, available from ical, and chemical applications. It also is used (a) to close internal
various PM operations. PF = powder forging. porosity, (b) to improve properties in superalloy and titanium-alloy
Source: Courtesy of the Metal Powder Industries castings for the aerospace industry, and (c) as a final densification
Federation. step for tungsten-carbide cutting tools and PM tool steels.
The main advantages of hot isostatic pressing are the following:

Because of the uniformity of pressure from all directions and the absence of
die-wall friction, it produces fully dense compacts of practically uniform grain
structure and density (hence, isotropic properties), irrespective of part shape.
Parts with high length-to-diameter ratios have been produced with very uni-
form density, strength, toughness, and good surface detail.
HIP is capable of handling much larger parts than those in other compacting
processes.
The limitations of HIP are as follows:
Wider dimensional tolerances are needed than those obtained in other com-
pacting processes
HIP requires higher equipment cost and production time than are required by
other processes
HIP is applicable only to relatively small production quantities, typically less than
10,000 parts per year.
Gas
End cap
Heating coils P

Pressure
Insulation cylinder Temperature

WOVKPIGCS High-pressure Part

End cap
1. Fill can 2. Vacuum 3. Hot isostatic press 4. Remove can
bakeout
Schematic illustration of hot isostatic pressing. The pressure and temperature
FIGURE l1.l 5
variation versus time are shown in the diagram.