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OCR for page 19
Appendix A
HIP Casting Consolidation Technology
Hot isostatic pressing (HIP) is a generic name for materials
processing at high temperature and pressure. The earliest applications
of HIP include powder metallurgy and consolidation of carbides. This
study examines the development and diffusion of the concept of HIP
casting: hot isostatic pressing for the purpose of closing porosity in
castings.
The following technical and market structure conditions underlie
the technology transfer process.
Techn ical Conditions
1. Alcoa holds the earliest patents for HIP casting, with
applications to aluminum castings. (See the chronology at the end of
the appendix.) This work preceded the efforts of Air Force
contractors and subcontractors and established the concept of HI P
casting explored by Battelle, General Electric, and Howmet.
2. The concept of HIP casting is the dominant attribute of the
technology to be transferred. Conferences and technical reports
resulting from private research and the AFML have been important
contributions to the diffusion of the concept.
3. Current HIP casting equipment (which embodies the concept) is
similar to the autoclave technology used for powder metallurgy and
carbide production at the time of early HIP casting development.
Modif ications of such equipment are necessary for HIP casting. Powder
metallurgy uses lower temperatures and protects the materials in an
envelope; the proximity of HIP casting temperatures to melting and the
exposure of parts require closer temperature and environmental
controls. Necessary operating changes are minor.
4. HIP casting researab was first undertaken to lower rework and
scrap rates for cast parts. In many cases HIP casting has also
improved material properties and increased the uniformity of batches of
cast parts. These added benefits have been an incentive to specify
HIP-cast components during the design of new products.
5. In some cases, improved investment casting techniques,
directional solidif ication, single crystal castings, or use of forgings
are technical alternatives to HIP casting. In other cases, however,
practical technical alternatives do not exist.
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6. Technical questions about the design and process control for
large pressure vessels have so far limited the size of BIP autoclaves
and so limit the size of HIP-cast parts. One of the largest HIP
facilities, installed by Pratt and Whitney in 1975, is an 80-incb high
cylindrical chamber with an inside diameter of 46 inches. These size
restrictions tend to make HIP casting of large components
f~nancially--if not teabnically--infeasible at the present state of the
art.
Market Structure Conditions
1. In the aircraft engine supply market (where the HIP casting
applications under study have been developed), the important
participants are engine buyers, their contractors, and the contractors'
parts suppliers. Primary engine buyers include defense and commercial
users of jet and gas turbine engines. General Electric and Pratt and
Whitney have been the important engine suppliers for this study. Parts
suppliers are foundries, notably Howmet Turbine Components Corporation,
Precision Castparts Corporation (PCC), and TRW.
2. Adoption of HIP casting technology teas a double meaning. A
parts supplier becomes an adopter by purchasing HIP casting equipment.
A contractor adopts the technology by specifying HIP-cast components in
its designs. When a contractor becomes an adopter, the parts supplier
may invest in HIP casting facilities, find an outside HIP casting
service (see conditions ~ 3 and $4 below), or forgo bidding on the
spec i f fed part .
3. Development of other HIP technologies created sources of HIP
casting capacity for contractors and parts suppliers. Because of their
earlier research in powder metallurgy and cemented carbide, Battelle
and Industrial Materials Technology (IMT) were the major sources of HIP
capacity during the development of HIP casting. More recently Battelle
has avoided that role, but IMT and other firms provide HIP casting job
shop services to parts suppliers. When Howmet acquired production
facilities, it began to provide job shop service to other parts
suppliers; TRW, for example, sends part of its HIP casting business to
Howmet. Thus, parts suppliers can choose between in-house and outside
HIP casting operations.
4. The availability of outside HIP casting services enables parts
suppliers and contractors to experiment with the technology and adopt
it gradually. As their technical experience and customer demand
increase, firms may then choose to invest in their own HIP casting
capacity. ~
5. Much of the present demand for HIP-cast aircraft engine parts
is for after-market components. Lead times for introducing new
processes to aircraft engine production can be quite long. Adoption of
new technology for full-scale production awaits a new generation of
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engines because of testing requirements and because of the structure of
contracts between engine builders and engine users. Pratt and Whitney
has specified titanium castings using HIP for both original equipment
and after-market components in the F-llO program.
The Air Force Materials Laboratory (AFML) became involved in HIP
casting when General Electric Evendale offered the AFML laboratory
evidence of feasibility in 1971. The AFML saw HIP casting as a generic
manufacturing technology, beneficial to all users of castings but not
likely to be developed quickly by industry. Proponents of HIP casting
in the AFMD, convinced that the potential benefits were great,
advocated and won funding for General Electric's work in 1972 through
the Manufacturing Technology program. The AFML hoped to demonstrate
the efficacy of HIP casting and to provide sufficient process
specifications to allow adoption by parts suppliers.
While General Electric pursued its research in Evendale, Helmet
began to develop its own HIP casting process without AFML funding.
Both companies can be considered originators of the technology.
General Electric
The Technical Systems and Materials Division of General Electric
(GE) produces jet engines for aircraft, industrial, and marine
applications as well as electronics and materials for space, defense,
medical, communications, and computing applications. General Electric
has a matrix organization, with Engineering, Manufacturing, Project
Management, and Quality Control divisions in each of its plants. Two of
the aircraft engine plants were included in this case study: a
facility in Evendale, Ohio, primarily producing large commercial
engines, and a facility in Lynn, Massachusetts, producing small
military engines as well as combustors, nozzles, and frames for use in
other plants. Researchers at GE Schenectady Materials and Processes
Laboratory in the Gas Turbine Products Division carried out early HIP
casting research and presented a paper to the Seven Springs Conference
of the American Institute of Mining, Metallurgical, and Petroleum
Engineers (AIME) in 1972. HIP casting development under the AFML
contract was the responsibility of a group working in the Engineering
Division of GE's Evendale Plant.
General Electric does much of i ts Techn ica1 Systems and Mater ials
business as a direct government contractor. The firm has years of
exper fence in R&D and production pro jects for the government and
continues to seek government contracts. Evendale, located close to the
AEML in Dayton, Ohio, follows a policy of using Air Force f unds for
risky R&D that it might not otherwise undertake. Within GE, design and
manufactur ing considerations are tightly coupled, but managers in the
Manufacturing Technology Operation believe that product design
considerations ultimately drive decisions related to production
processes .
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Changes from wrought to cast turbine blades and the increasing
blade tip speeds of the supersonic transport program fostered General
Electric's initial interest in HIP casting. During 1969 and 1970
General Electric obtained laboratory confirmation of the technical
feasibility of such techniques. In 1972 they acquired Air Force funds
for development of a prototype. Evendale looped to use HIP-cast parts
by persuading the foundries that supply cast engine components to adopt
HIP casting techniques.
In 1974 General Electric completed its first AFML contract in HIP
casting, an investigation of its application to aluminum and
superalloys. That year the firm received another AFML contract, to
obtain data for titanium and three other superalloys.
Howmet Turbine Components Corporation
Howmet believes itself to be the largest supplier of turbine blades
to the U.S. aircraft industry. A wholly owned subsidiary of Pechiney
Ugine Kuhlmann of France, Howmet specializes in the production of
investment castings used in the hot section of gas turbine engines. In
addition, Howmet produces its own air and vacuum melted alloys,
manufactures ceramic products for its casting operations, precision
machines and coats its finished castings, and produces titanium ingot
for the aerospace industry. Howmet facilities in Whitehall, Michigan,
include a research center and HIP casting facilities. A materials
research and development (R&D) group at the Technical Center was
responsible for preproduction HIP casting research.
Howmet is well established as a supplier to government contractors
but prefers not to involve itself extensively in government R&D
projects. Managers at Howmet believe that requirements to justify and
generalize federally funded researob force contractors to undertake
additional work that does not benefit them. They prefer to retain
maximum control over the nature and duration of R&D projects. Howmet
has an aggressive R&D program for its own purposes and considers itself
to be the leading supplier of high-technology cast higb-temperature
engine components.
In 1965 owlet researchers began to investigate applications of HIP
for closure of porosity in titanium- and cobalt-based alloy castings.
The research was completed in 1967, with positive results for
titanium. A Howmet team investigating techniques for elimination of
microshrinkage attended a conference of the AIME in 1972. There they
heard a presentation on HIP casting given by workers from GE
Schenectady. After the conference Howmet researchers recovered the
results of earlier Howmet research and initiated development using
powder metallurgy facilities at Industrial Materials Teabnology (IMT)
and, later, at Battelle.
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By 1974, with about 3750, 000 invested in R&D, Bowment was HIP
casting several of its customers' parts and considering purchase of its
own HIP casting facilities. Howmet continued to monitor General
Electric's work while developing HIP casting technology to production
readiness . Howmet developed casting preparation procedures, post-EIIP
heat treating routines for restoration of material properties, and
established process tolerance for a wide variety of its customers'
alloys.
Adoption of HIP casting in the aircraft engine industry occurs in
two ways. First, contractors attracted by the potential cost ravings
and materials properties resulting from the technique may place orders
for HIP cast parts with their subcontractors. These orders may be for
experimental work, development, after-market components, repairs, or
production. Second, parts suppliers may decide that demand justifies
the purchase of HIP casting equipment. Parts suppliers that have not
adopted the technology may employ the services of outside HIP casting
f acilities such as those of IMT and Battelle. The decision to adopt
frequently follows a period of using outside HIP casting services.
Parts Suppliers
Howmet Turbine Components Corporation
Howmet, at the completion of its HIP casting development project,
had to decide whether to continue to subcontract for HIP casting or to
acquire its own equipment. Investment costs were f irst estimated in
1974 as $1 million. In 1975 Howmet tried to organize a joint venture
with two of its major customers to share the ri sks and profits of TIP
casting equipment. Howmet presented evidence on the improved and more
uniform properties of HIP~ast components. The firm's customers, whose
analyses focused on projected rework and scrap cost savings, declined
to join Howmet in investing in HIP casting.
After hesitation, Mowmet decided to assume the risks of investment
alone. Approval was given for purchase of a pressure vessel from
Automation, Inc., and a furnace designed and produced by Battelle. In
making this decision, Howmet let commitment to technological leadership
be the deciding factor. Full production began in 1977, with the
largest order placed by GE Evendale. In 1978 Howmet built another
furnace under license from Battelle at a cost of $80, 000.
At present Howmet's titanium casting division augments demand for
HIP casting of engine components. Howmet also offers HIP casting
services to other parts suppliers.
2. TRY
TRW is a major competitor to Howmet in the turbine blade market but
not in titanium. Researabers at TRW first considered purchasing HIP
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casting facilities in 1972, when General Electric' s work in the area
became widely available. Like other parts suppliers, T]W's options
included improvements in casting processes and contracts for outside
H IF services .
Volume was the primary consideration for TOW. They found that
requests for airfoil HIP castings were too limited to support the
expense of in-house equipment. TRW lacks the titanium work available
to the Howmet HIP casting operation and was not interested in providing
a HIP casting service to other parts suppliers. On this basis, TOW has
elected not to purchase HIP casting equipment. Bowmet and IMT do much
of the HIP casting work for TRW.
Recently, TRW has approved the purchase of a small HIP casting unit
for research and development. The company reviews annually its
decision not to purchase HIP casting equipment for production.
Precision Castparts Corporation
Precision Castparts Corporation ~ PCC) is a supplier of large
aluminum and superalloy investment castings (e.g. structural components
for large gas turbine engines) and engine airfoils. It began supplying
HIP-cast components before 1976 but does not have its own HIP casting
capacity. PCC sends its large components from its Portland, Oregon,
location to Crucible, a Pittsburgh-based foundry. Industrial Materials
Technology HIP casts PCC' s sma' 1 components in a Portland facility that
depends on PCC' s business .
Precision Castparts Corporation's decision not to adopt HIP casting
by purchasing equipment is based on its customers' demand. GE Evendale
is at present PCC's largest user of HIP-cast parts. Pratt and Whitney
is in the process of evaluating several substantial commitments to HIP
castings from PCC. Fiat, MTU (Germany), and a mix of smaller customers
provide the balance of the demand. PCC and IMT are both prepared for
the eventual acquisition by PCC of IMT's Portland facility. PCC is
also considering the purchase of equipment suitable for large
structural HIP castings if sufficient demand develops.
Engine Builders: GE Lynn
Engine builders provide the demand for HIP castings which drives
the investment decision of the part suppliers. Within GE, the demand
entails technology transfer from engineering materials researab to
engineers responsible for the design and production of specific engine
programs.
Material processing innovations at GE are often developed during an
ongoing engine production program but not fully adopted until a later
engine goes into development. The transfer of HIP casting to GE's Lynn
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Aircraft Engine operations, still in process, seems to fit this
pattern . At present, GE Lynn is in the early stages of adopting the
techniques first developed by the Engineering Division materials R&D
group in E`rendale in 1972-74.
Three obstacles have slowed adoption of HIP casting at Lynn.
1. Equipment Availability -- until recently HIP casting was
available only from Battelle (which wished to avoid production
cost itments) and IMT. Growth of IMT' ~ capacity and Howmet' s new
operations suggest that when GE Lynn is ready to adopt fully HIP
castings, production capacity will be available.
2. Engineering Confidence -- Materials engineers require full
documentation of materials properties at the operating conditions of
the engine in question. Though Evendale teas supplied verification of
materials properties at some temperatures, these temperatures are not
necessarily the same as those for which current engine components are
designed. Development of materials data, especially low and high cycle
fatigue and stress rupture properties, will be carried out in Lynn.
Adoption requires operating experience with HIP-cast parts. At
present, HIP casting is becoming an unapproved repair procedure. Once
this is accomplished, HIP-cast parts will be verified with at least 150
hours of factory engine use.
3. Contract Cost Controls -- HIP casting can add $200-$300 per
engine in foundry costs that are subject to the scrutiny of project
cost accountants. Offsetting savings in rework and ship time are
included in overhead and are not as readily visible to cost
controllers. Further, GE's customers already have a workable contract
and are only gradually being educated to the benef its that justify what
appears to be an expensive change in production techniques.
Introduction of HIP casting through the design and development of
new engines avoids these obstacles. During development designers can
take full advantage of improvements in materials properties afforded by
HIP casting and gain engine use verification of materials properties
during engine testing. GE is very likely to specify HIP~ast
components for future engines, though GE engineers expect to continue
their efforts to improve conventional casting techniques as well.
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HIP Casting Chronology
1967 : Alcoa, working with Battelle, patents the concept of HIP
casting for aluminum.
1965-67 : Howmet performs research on HIP castings of titanium- and
cobalt-based alloys.
1971-72 : GE offers evidence of feasibility to the AFML. Mowmet,
after hearing a report from GE, recovers past research
and begins R&D.
1974 : GE completes its first AFML contract, reporting success
in densification of Rene'80 and Ti-6 Al -4V castings.
1975 : Hbwmet commits to capital investment in HIP casting
facilities.
1976 : Testing, development, experimental, and after-market use
of HIP-cast components.
1977 : H~wmet begins full production.
1978 : Howmet invests in additional production capacity.
1980 : GE completes its second AE?ML study, Manufacturing
Methods for Low Cost Turbine Engine Components of Cast
Superalloys. n
26
Representative terms from entire chapter:
hip castings
