U.S. patent application number 12/668282 was filed with the patent office on 2010-10-07 for forging mandrel for hot-forging tubular workpieces of metal.
This patent application is currently assigned to V & M DEUTSCHLAND GMBH. Invention is credited to Gerd Homberg, Rolf Kummerling, Pierre Lefebvre, Stefan Wiedenmaier.
Application Number | 20100251794 12/668282 |
Document ID | / |
Family ID | 39670381 |
Filed Date | 2010-10-07 |
United States Patent
Application |
20100251794 |
Kind Code |
A1 |
Wiedenmaier; Stefan ; et
al. |
October 7, 2010 |
FORGING MANDREL FOR HOT-FORGING TUBULAR WORKPIECES OF METAL
Abstract
The invention relates to a forging mandrel for hot-forging
tubular workpieces of metal, said mandrel comprising a mandrel body
and a mandrel bar, in which forging mandrel the mandrel body is
composed of a heat-resistant material. The forging mandrel
according to the invention is embodied here in such a way that the
mandrel body is provided, at least in the work zone, with a layer
which reduces the dissipation of heat into the mandrel body during
the forging process and adheres firmly to the mandrel body, wherein
the layer has a lower thermal conductivity than the material of the
mandrel body and has a thickness of at least 50 .mu.m.
Inventors: |
Wiedenmaier; Stefan;
(Aachen, DE) ; Kummerling; Rolf; (Duisburg,
DE) ; Homberg; Gerd; (Mettmann, DE) ;
Lefebvre; Pierre; (Bavay, FR) |
Correspondence
Address: |
HENRY M FEIEREISEN, LLC;HENRY M FEIEREISEN
708 THIRD AVENUE, SUITE 1501
NEW YORK
NY
10017
US
|
Assignee: |
V & M DEUTSCHLAND GMBH
Dusseldorf
DE
|
Family ID: |
39670381 |
Appl. No.: |
12/668282 |
Filed: |
June 25, 2008 |
PCT Filed: |
June 25, 2008 |
PCT NO: |
PCT/DE08/01067 |
371 Date: |
May 24, 2010 |
Current U.S.
Class: |
72/264 |
Current CPC
Class: |
B21J 13/00 20130101 |
Class at
Publication: |
72/264 |
International
Class: |
B21C 25/04 20060101
B21C025/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 10, 2007 |
DE |
10 2007 032 804.6 |
Claims
1.-6. (canceled)
7. A forging mandrel for hot-forging a tubular workpiece of metal,
comprising: a mandrel body made of heat-resistant material; and a
layer adhering firmly upon the mandrel body at least in a work zone
thereof, said layer being configured to reduce heat dissipation
into the mandrel body during forging and having a thermal
conductivity which is lower than a thermal conductivity of the
material of the mandrel body, said layer having a thickness of at
least 50 .mu.m.
8. The forging mandrel of claim 7, wherein the layer is an oxide
layer.
9. The forging mandrel of claim 7, wherein the layer is applied
onto the mandrel body through a flame-spraying process.
10. The forging mandrel of claim 7, wherein the layer is applied
onto the mandrel body through plasma spraying.
11. The forging mandrel of claim 7, wherein the thermal
conductivity of the layer is lower by at least 50% than the thermal
conductivity of the material of the mandrel body.
12. The forging mandrel of claim 7, wherein the mandrel body is
constructed in the form of a hollow body which is provided with an
opening on one side and includes an internal cooling device which
extends at least into the work zone.
13. The forging mandrel of claim 7, wherein the mandrel body has a
mandrel bar to allow displacement of the mandrel body within the
workpiece in axial and rotatable manner.
Description
[0001] The invention relates to a forging mandrel for hot-forging
tubular workpieces of metal according to the preamble of patent
claim 1.
[0002] Hot-forming of tubular workpieces, such as, e.g., seamless
steel pipes, is known from DE 10 2005 052 178 A1.
[0003] Starting from a block heated to forming temperature, this
method involves a first forming step in which a thick-walled hollow
block is produced through punching and then forged into a seamless
pipe by a radial forging process which uses a forging mandrel as
internal tool which is pushed into the hollow block and at least
two forging jaws of a forging machine to act on the outer surface
area of the hollow block. The hollow block is hereby turned and
shifted axially in clocked manner in the phase of the idle stroke
of the forging jaws.
[0004] The forging mandrel is exposed during the forging process to
significant thermal and mechanical stress, causing wear of the tool
surface and decreasing the service life of the forging mandrel.
Forging temperatures of above 1300.degree. C. may occur for
example.
[0005] In order to minimize wear caused as a result of thermal
exposure, it is known from DE 2825940 A1 to cool the forging
mandrel from the inside in order to accelerate heat dissipation
from the surface of the mandrel into the mandrel.
[0006] In order to increase wear resistance of the mandrel, it is
further proposed to surround the mandrel body with an outer jacket
of highly heat-resistant material, e.g. a nickel or cobalt base
alloy.
[0007] This forging mandrel suffers several drawbacks. On the one
hand, this forging mandrel is very complex and expensive to
manufacture. On the other hand, heat introduction into the mandrel
material is not diminished so that the shape stability of the
forging mandrel is reduced, when exposed to high temperature stress
and thus causes premature failure.
[0008] It is an object of the invention to provide a forging
mandrel for hot-forging tubular workpieces of metal, which forging
mandrel can be manufactured inexpensively and exhibits high wear
resistance while yet is of stable shape even when exposed to high
forging temperatures.
[0009] Starting form the preamble, this object is solved in
combination with the characterizing features of claim 1.
Advantageous refinements are the subject matter of sub-claims.
[0010] According to the teaching of the invention, the mandrel
material is made of heat-resistant alloy, with the mandrel body
provided at least in the work zone with a layer which lessens heat
dissipation into the mandrel body during forging and adheres firmly
upon the mandrel body and which has a thickness of at least 50
.mu.m.
[0011] The essential novelty of this invention resides in that the
layer which surrounds the mandrel body has a lower thermal
conductivity than the mandrel body so that heat introduction into
the mandrel body is significantly decreased to thereby realize a
significantly improved shape stability, even when exposed to high
forging temperatures.
[0012] The layer has hereby in accordance with the invention a heat
conductivity which is significantly lower than the one of the
material of the mandrel body, advantageously by at least 50%.
[0013] The layer on the mandrel body can be advantageously produced
according to the invention in a very cost-effective way through
oxidation or also through application of a respective layer, e.g.
through thermal methods.
[0014] Oxidizing the mandrel is advantageously applied when carbon
steels are involved, whereas high-alloy mandrel materials involve
application of the layer advantageously through thermal spraying
processes, such as, e.g., flame-spraying or plasma spraying.
[0015] The thermally applied layers may hereby contain zirconium
oxide, aluminum oxide, or iron oxide, for example.
[0016] It is hereby essential that the thermal conductivity of the
coating material is always significantly below the one of the
mandrel material.
[0017] In order for the layer to be able to exert a recognizable
effect with respect to a significantly reduced heat introduction
into the mandrel body, it is advantageous when the layer has a
minimum thickness of about 50 .mu.m.
[0018] The forging mandrel according to the invention has hereby
not only the advantages with respect to improved shape stability
but also with respect to a decrease of the abrasive wear. Tests
have shown the presence of a certain lubricating effect of the
layer material during forging to reduce the abrasive wear.
[0019] For selecting a suitable material for the mandrel body, it
is essential to suit the mandrel body to the material being forged
in such a way that fusion of forging mandrel and forging workpiece
is prevented.
[0020] The forging mandrel according to the invention has hereby
the beneficial effect that the layer acts upon the mandrel body as
a separation layer which opposes a fusion under forging pressure
and temperature.
[0021] As a certain heat introduction into the mandrel body cannot
be completely eliminated, it may be further prudent to provide the
mandrel body with an additional internal cooling in order to assist
the shape stability of the mandrel.
[0022] As an alternative, it may also be provided to cool the
outside of the mandrel body in phases of standstill. This can be
implemented in a much more cost-efficient manner than internal
cooling.
[0023] In order to limit the heat introduction into the mandrel
body to a minimum during the forging process, it may be further
prudent to move the mandrel in the workpiece during forging because
in this procedure constantly other work zones of the forging
mandrel surface come into engagement so that local heat
introduction is reduced.
[0024] The forging mandrel according to the invention will be
described in greater detail with reference to an illustration.
[0025] The forging mandrel shown in the sole FIGURE has a mandrel
body 1 provided with bevels 3, 4 and secured to a restraining bar
2. The restraining bar 2 is required to be able to move the forging
mandrel in axial and rotatable relationship in a tubular workpiece,
not shown here.
[0026] The forging mandrel 1 is made of heat-resistant steel which
is provided in accordance with the invention with a layer 5 which
reduces in the work zone the heat introduction into the mandrel
body 1.
[0027] The layer 5 has hereby a thermal conductivity which is
significantly lower than the one of the material of the mandrel
body 1 in order to reduce heat introduction and thus to ensure the
shape stability of the mandrel body 1, even when exposed to high
forging temperatures.
[0028] The mandrel body 1 is configured as solid body in the
present case; it is, however, also possible to provide the mandrel
body with internal cooling to dissipate as rapidly as possible
unavoidable heat introduction into the mandrel body 1 during
forging.
LIST OF REFERENCE SYMBOLS
TABLE-US-00001 [0029] No. Designation 1 Mandrel body 2 Restraining
bar 3, 4 Bevel 5 layer
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