U.S. patent application number 10/878042 was filed with the patent office on 2005-04-28 for precision-forging parts manufacturingprocess.
This patent application is currently assigned to SNECMA MOTEURS. Invention is credited to Beignon, Dominique, Bouillot, Bertrand, Cougnaud, Camille, Lepetit, Marc, Plazanet, Jean-Claude, Valery, Lionel.
Application Number | 20050086783 10/878042 |
Document ID | / |
Family ID | 33484693 |
Filed Date | 2005-04-28 |
United States Patent
Application |
20050086783 |
Kind Code |
A1 |
Beignon, Dominique ; et
al. |
April 28, 2005 |
Precision-forging parts manufacturingprocess
Abstract
The present invention relates to a precision-forging parts
manufacturing process including the manufacture and development of
a first forging tooling equipment (20, 30), the forging of the
parts with said tooling equipment, whereas the parts have a
determined excessive thickness, and their finishing treatment, The
method is characterised in that it also includes the realisation of
a digital model of the surface of the first tooling equipment, the
forging of parts, the rehabilitation of the tooling equipment or
the manufacture of new tooling equipment from the digital model,
after forging a determined number of parts. In particular, the
parts are subjected to a finishing treatment directly after
forging, said treatment including mechanic polishing. The invention
applies to the forging of blades for turbo machines.
Inventors: |
Beignon, Dominique;
(Herblay, FR) ; Cougnaud, Camille; (Santeuil,
FR) ; Lepetit, Marc; (Sannois, FR) ; Bouillot,
Bertrand; (Paris, FR) ; Valery, Lionel;
(Taverny, FR) ; Plazanet, Jean-Claude;
(Argenteuil, FR) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
SNECMA MOTEURS
Paris
FR
|
Family ID: |
33484693 |
Appl. No.: |
10/878042 |
Filed: |
June 29, 2004 |
Current U.S.
Class: |
29/407.04 |
Current CPC
Class: |
Y10T 29/49769 20150115;
B21K 3/04 20130101; B21K 5/20 20130101; B23P 15/24 20130101; B23P
15/02 20130101 |
Class at
Publication: |
029/407.04 |
International
Class: |
B21D 031/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 23, 2003 |
FR |
03 09000 |
Claims
1. A precision-forging parts manufacturing process including the
manufacture and development of a first forging tooling equipment
(20, 30), the forging of the parts with said tooling equipment,
whereas the parts have a determined excessive thickness, and their
finishing treatment, characterised in that it also includes the
realisation of a digital model of the surface of the first tooling
equipment (20, 30), the forging of parts, the rehabilitation of the
tooling equipment or the manufacture of new tooling equipment (20,
30) from the digital model, after forging a determined number of
parts.
2. A method according to claim 1 wherein the parts are subjected to
a finishing treatment directly after forging, said treatment
including mechanic polishing.
3. A method according to claim 1 wherein the finishing treatment
also comprises chemical machining.
4. A method according to claim 1, wherein the forged parts are
controlled to determine at what time new tooling equipment (20, 30)
should be rehabilitated or manufactured.
5. A method according to claim 1 wherein the adjustment of the
tooling equipment manufactured (20, 30) includes a. digital
acquisition of the position of a determined number of points on the
surface of the tooling equipment manufactured, b. the comparison of
the position of the points with the digital model, and c. possible
correction of the surface of the tooling equipment.
6. A method according to claim 5, wherein the points of the surface
are acquired by contact free optical measurement.
7. A method according to claim 5, wherein the points are acquired
digitally using mechanical means.
8. A method according to claim 1, followed by elimination of said
excessive thickness of the parts by abrasion.
9. A method according to the previous claim wherein abrasion is
performed using a belt mounted on a wheel which is pressed against
the surface of excessive thickness.
10. A method according to the previous claim wherein the quantity
of matter to be eliminated is determined by selecting the machine
parameters; pressure of the wheel against the surface, forward
speed of the belt and displacement velocity of the wheel.
Description
[0001] The present invention concerns the field of precision
forging of metal parts and in particular of complex and
awkward-shaped parts, such as large-sized blades for turbo
machines.
[0002] For manufacturing metal parts, forging techniques are
preferably implemented when they should absorb significant loads
during operation. Such is the case for compressor blades or
turbo-jet engine blowers for which the internal loads are generated
notably by the vibrations and the centrifugal forces to which they
are subjected.
[0003] Forging consists in deforming plastically a block of metal
by imparting shocks or applying a pressure. The process is
generally composed of several steps, while forming successive
blanks, which come gradually closer to the finished part. If
required, the forging of the part is completed by a calibration
phase leading to more accurate shapes.
[0004] For compressor blades, for example made of titanium, an
operating mode comprises the steps of upsetting, extrusion and
stamping, out of bars.
[0005] Before the upsetting phase, the metal bars are prepared by
undergoing an enamelling operation. It is a glass-based coating
whose purpose is to facilitate the flow of matter into the tooling
equipment. It also serves as thermal insulation while maintaining
the temperature during the transfer from the oven to the press and
while preventing any thermal shocks when the part contacts the
tooling equipment. Its function also consists in protecting the
part against oxidation. According to a preferred embodiment, the
coating is sprayed electrostatically on the parts before loading
into the oven.
[0006] In parallel, the internal surface of both shells or
upsetting tools are lubricated. The upsetting phase consists in
pushing the end of the bar, raised to a temperature ensuring good
ductility, by means of a punch towards the inside of the cavity
formed by both shells. When the shape of the part requires so, the
upsetting is performed in several successive steps in suitable
tools. For example, this process may be appropriate to form the
feet of compressor blades as well as, if needed, the fins.
[0007] Between each upsetting step, the enamel coating, which has
warped, as well as the scale generated, must be eliminated using
appropriate baths, before building a new coat of enamel.
[0008] According to the type of part, for compressor blades for
instance and not for blower blades, the upsetting is preceded by an
extrusion step. Such step consists in stretching the metal slug
through a die whereof the profile corresponds to that to be
realised.
[0009] Once the parts have been preforged thus, they are forged
into given shapes by stamping dies.
[0010] This mechanical forging operation consists in elaborating a
part by forcing a blank thereof to fill in, by imparting shocks or
by applying pressure, a print engraved in a stamping die
corresponding to the shape of the part to be obtained. In the case
of titanium, its yield stress depending highly on temperature, the
forging is performed in hot condition up to a certain limit imposed
by the structural evolution of the material which alters the
mechanical properties thereof.
[0011] For a compressor blade or a blower blade, a known shaping
operation includes two stamping operations:
[0012] A predefinition stamping which preforms the foot, and the
fin if required, and starts to crush the blade by turning the bar
from a rounded shape into a flattened shape.
[0013] A finishing stamping operation, which completes the forging
cycle with displacement of matter and brings the part as close as
possible to its final geometric form before machining.
[0014] The stamping operations are carried out on hydraulic or
screw-type presses whereof the stamping dice are pre-heated. Under
such conditions, the forging time is relatively short to avoid too
rapid cooling down of the part and excessive heating of the
stamping die by thermal conduction between the part and said
stamping die inasmuch as the temperature of the tooling equipment
differs from that of the part. Besides, by reason of the high level
of stresses to which it is subjected by contacting the part, a
lubricant is applied to the engraving of the stamping die to slow
down the cooling process of the part, for easier flow of matter and
to reduce the forging loads.
[0015] Once the part has been forged, it is machined and polished
to final sizes. Such operation is made necessary by reason of the
excessive thickness remaining after forging. In fact, the engraving
of the stamping die is determined in order to keep the excessive
thickness of the part. After forging, machining and polishing
enable to give the finished part the precise shape and the surface
condition requested.
[0016] For parts made of titanium, notably, polishing is an
important operation. Its purpose is to eliminate the defects
resulting from the forging operation and which are liable to give
rise to developing cracks.
[0017] The present invention relates first of all to the
development of tooling equipment which are the stamping dice and
the shells introduced above. There is a need, indeed, to improve
these operations which have a negative contribution to the global
economy of this technique.
[0018] The time required for the realisation of the tooling
equipment, according to the conventional method, is rather long
since successive retouching operations are compulsory.
[0019] Indeed, the print of the stamping die has not rigorously the
shape and the sizes of the raw forging part to be obtained. It
departs therefrom by "corrective terms" which compensate for
elastic-plastic deformations of the tooling equipment during the
forging cycle. We do not know exactly how to forecast such
corrective terms and it is therefore necessary to retouch the
stamping die further to the measurements taken on the test pieces
obtained. In so-called "precision" forging, excessive thicknesses
are small, for example 0.8 mm, so that the finished part may be
obtained by polishing the raw part using a grinding belt or, if
needed, notably if the part is made of titanium, by the combination
of chemical machining and grinding belt polishing. Such is the case
for the airfoil part of blades.
[0020] Developing a precision forging stamping die is consequently
a long-winding and costly process, since it calls for numerous
retouching operations, interlaced with forge-testing of parts.
[0021] Retouching cannot be performed rapidly since it requires
forging tests with each time the steps of heating and assembling
the tooling equipment on the press, the realisation of a few parts,
the calibration and the control of these parts. Besides, tests
parts are generally not usable; they are wasted in most cases.
During the testing and retouching operations, it should be noted
that means such press, stamping die conveyor belt, control
instruments, are unavailable for production.
[0022] It should also be noted that, according to this conventional
method, it is practically impossible to obtain two identical pieces
of tooling equipment, either stamping dice or shells.
[0023] This lack of accuracy in the definition of the tooling
equipment translates by a lack of regularity in the products
manufactured by means of said tooling equipment.
[0024] Once the stamping has been adjusted, i.e. once the raw
forging test parts obtained have the shape and the sizes required,
such stamping die can be put into service in order to manufacture
series parts. The stamping die degrades gradually in operation, and
it becomes necessary, for example after 1000 to 5,000 parts as the
case may be, to rehabilitate the stamping die or to use
another.
[0025] The rehabilitation of a degraded stamping die consists,
according to a first method, in reloading the zones wherefrom
matter has been torn off and in machining and polishing a new
print. According to a second method, the print is reconstructed
completely by machining, after having eliminated the nitrided layer
and removed a thickness of several millimetres of matter. This
technique is designated as rewashing. The rehabilitation of a
stamping die or the manufacture of a new stamping die require the
same adjustments as the initial stamping die. They are consequently
also long and costly.
[0026] Finishing by abrasive belt polishing on a five or six-axis
type machine is well suited to complex-shaped parts such as blade
airfoils. Unlike a machining operation, for example by milling,
abrasive belt finishing removes, at each pass, a pre-established
thickness of matter, said thickness increasing with the speed of
the abrasive belt and the pressure exerted by the belt on the part,
said thickness decreasing with the forward speed of the belt with
respect to the part. The shape and the sizes of the part after an
abrasive belt pass depend therefore directly on the shape and the
sizes of the part before said pass.
[0027] This does not cause any problem with the first parts
produced from the stamping die, since they are all identical.
However, as the forging continues, degradation of the stamping die
can be noticed (wear, plastic deformation, etc.)
[0028] Parts are sampled for regular checking purposes. When the
sizes of the part reach a defined degradation threshold, the
tooling equipment is rehabilitated or new tooling equipment is
manufacture. The parts obtained with the new stamping dice or the
rehabilitated stamping dice may require several finishing passes,
separated by measurements, so that they are rigorously identical to
the parts obtained with the first stamping die. This similarity in
results is particularly important in the case of blade sets on a
turbo-jet engine rotor stage.
[0029] The problem to be solved is to reduce the finishing cost and
to obtain rigorously identical parts although they may have been
forged with different stamping dice. It also consists in avoiding
wasting parts because they do not meet the specifications, which in
the case of precision forging is an important criterion for
validation of the process.
[0030] According to the present invention, this problem can be
solved with a precision-forging parts manufacturing process
including
[0031] the manufacture and development of a first forging tooling
equipment,
[0032] the forging of the parts with said tooling equipment,
whereas the parts have a determined excessive thickness, and
[0033] their finishing treatment,
[0034] This method is characterised in that it also includes the
following steps
[0035] the realisation of a digital model of the surface of the
first tooling equipment,
[0036] the forging of parts,
[0037] the rehabilitation of the tooling equipment or the
manufacture of new tooling equipment from the digital model, after
forging a determined number of parts.
[0038] Advantageously, the parts are subjected to a finishing
treatment directly after forging, said treatment including mechanic
polishing.
[0039] In particular when the parts are made of titanium, the
finishing treatment comprises a combination of mechanical polishing
and of chemical machining.
[0040] Chemical machining consists of chemical dissolution of the
titanium alloys. Matter removal is conditioned by the soak time of
the parts.
[0041] The method according to the invention is remarkable in
that:
[0042] a) The first stamping die is in particular adjusted so that
the raw forging part has an excessive thickness liable to be
removed by a mechanical polishing and/or chemical machining
operation in a single pass or at least without resorting to
significant manual retouching operations.
[0043] b) When the first stamping die is adjusted, the position of
a determined number of points on the surface of the print is
acquired digitally and a model of said surface is digitalised.
[0044] c) The manufacture if new exchange stamping dice includes a
finishing machining operation so that the digital model of their
print is identical to the digital model of the print of the first
stamping die.
[0045] Preferably, polishing is automated thanks to abrasive belts.
Advantageously, a machine exhibiting a contact wheel system driving
an abrasive belt is used. This type of machine advantageously
enables controlling the removal value and the surface condition
requested, on the basis of simple machine parameters such as the
load exerted by the contact wheel on the part, the running speed of
the belt on the contact wheel as well as the relative displacement
velocity of the wheel with respect to the part to be processed.
[0046] This process enables to master the excessive thickness
removed and to reduce considerably the number of successive
finishing stapes after forging. The geometry of the part as well as
its finishing surface condition are ensured, with a minimum of
manual retouching operations, let alone, no such retouching
operation at all.
[0047] Other features and advantages will appear in the following
description of the method of the invention with reference to the
figures whereon
[0048] FIG. 1 represents a stamping die,
[0049] FIG. 2 an upsetting shell,
[0050] FIG. 3 a belt polishing machine.
[0051] As can be seen of FIGS. 1 and 2, the tooling equipment
involved in the forging method of the invention, regardless whether
it includes a blade forging stamping die 20 or an upsetting shell
30, is complex in shaped with, additionally:
[0052] warped and twisted zones, highly bent,
[0053] very little bent,
[0054] deep and narrow, for example a depth of 100 mm with a width
at the bottom of 20 mm,
[0055] composed of planes, cylinders, cones and fillets between
surface portions,
[0056] and significant variations in altitude between both sides of
the tooling equipment.
[0057] The stamping die degrades gradually by wearing the print,
notably, and by plastic deformation. When the degree of degradation
reaches a pre-established threshold and that renewal of the tooling
equipment is considered necessary, said equipment is rehabilitated
or new tooling equipment is manufactured on the basis of
information saved on the tooling equipment adjusted previously.
Continuity of the method is thereby ensured.
[0058] After having adjusted first tooling equipment to the final
sizes, a digital model of such tooling equipment is realised. The
means of implementation of this digital model of the tooling
surface are known by themselves and available on the market.
[0059] The items most frequently used in the industry are contact
sensors that can be found on three-dimensional measuring machines
(MMT). Because of the spherical shape of their ends, such sensors
provide results which ought to be subjected to a radius correction
calculation.
[0060] Among the contact free sensors, the most current ones are
those based on optical techniques with one or several laser sources
or laser free optical techniques. Both use the measuring principle
based on trigonometry and more particularly on triangulation.
[0061] In the case of a technique with laser sources, the part is
illuminated by a coherent light source, a laser beam generally, and
one or several CCD (charged coupled device) type cameras observe
the scene from an angle which is different generally from that of
the emission. After a calibration phase of the cameras, the
coordinates of the points of the object are deduced from those of
its picture on the CCD array of the camera.
[0062] In the case of a laser free technique, the principle is
based upon the projection, onto the part, of a regular grid, a
fringe network, then the calculation of the superficial points of
the object by triangulation.
[0063] Once the sensor has been selected, one should define the
3D-digitialisation strategy which consists in
[0064] finding one or several positions of the sensor(s) which
enable realisation of the digital model of all the surfaces of the
part to be accessed,
[0065] choosing a density of the cloud of points according to the
task to be performed then, from said result, such as rapid
prototyping, surface reconstruction or visualisation.
[0066] For all forging tooling equipment, a precision of
acquisition of the order of 0.02 mm, for instance, is required.
[0067] If needed, according to the complexity of the geometry of
certain portions of the surface, the geometry of the surface
follows a reconstruction stage. Such operation may be carried out
by data-processing means known to the man of the art.
[0068] First of all, the cloud of points obtained by digitalisation
is collected. According to the quality of this cloud of points, it
may be necessary to apply a filter thereto whereof the purpose is
to attenuate the multiple small local variations, while eliminating
aberrant points, measuring errors, etc.
[0069] Reconstruction is performed on the basis of this processed
cloud:
[0070] For the reference zones (planes, cylinders, spheres), the
shape is reconstructed automatically.
[0071] Failing which, a surface is reconstructed which covers "at
best" a selection of points delineated by its boundaries. The
latter may be boundaries of elements which have already been
reconstructed, curves plotted on the cloud of points, theoretic
elements. Upon completion of the reconstruction of each square, the
software enables analyses over the reconstructed surface (maximum
deviation, maximum distance between the boundaries of two adjacent
squares . . . ). This analysis enables the operator to modify the
reconstruction parameters (mathematic definition parameters,
surface tension, boundary curvature . . . ).
[0072] When the digital model is performed, it is saved under a CAD
file format to be importer into the CAM environment in order to
generate the manufacturing strategy, then a digital programme on a
machining tool, for example a UHS high-speed type machining
tool.
[0073] This programme is then used for the manufacture of new
tooling equipment, stamping dice, so that they are rigorously
identical to the perfect initial tooling equipment.
[0074] In the case of "rewashed" or new tooling equipment,
verification is conducted by comparison between the CAD model of
the perfect tooling equipment and the cloud of points derived from
digitalisation of the tooling equipment manufactured.
[0075] There is described thereunder a finishing method after
abrasion forging by means of a six-axis type polishing machine.
[0076] The geometry of the part is controlled by a
multidimensional-type technique and the thicknesses and the
geometrical shapes are re-balanced over the whole blade by
combination of weak point masking using an adhesive tape and
chemical machining.
[0077] Then the excessive thickness of matter is removed and the
final surface condition of the blade, requested on the plane of
definition, by automated polishing on six-axis polishing machines.
There is described below the method according to the FIG. 3 showing
a six-axis type commercial machine.
[0078] The machine comprises a frame 1 with a parts support 2, a
compressor blade for example, which is held horizontal along its
main axis, by means of a mechanic or hydraulic flanging device. A
first engine 4 ensure rotational position (rotational axis U) of
the part around its main axis. A second engine 6 ensures
displacement of the support of the part along a translation axis
(x). A third engine 8 drives the abrasive belt mounted on a contact
wheel 10 and stretched by a system of rollers.
[0079] The rotational axis of the wheel 10 is moreover positioned
in translation along both axes (y and z) perpendicular to the first
axis x and in rotation along both their associated rotational axes
V and W.
[0080] The contact surface of the wheel is held constantly in
tangential position in relation to the surface of the part.
[0081] According to an embodiment, a wheel of 25 mm in width with
120 mm in external diameter is used. Superficially, grooves have
been provided on sufficiently rigid coating; for its Shore hardness
is 65.
[0082] The polishing operation consists in moving the part along
the axis x and rotating said part around its axis. The wheel is
held constantly in tangential contact with the surface of the part.
The wheel is subjected to a pressure determined by the pressure
exerted by a cylinder, a belt velocity determined in order to
remove a controlled quantity of matter taking into account the
infeed of the part with respect to the wheel.
[0083] Once the part has exited the polishing machine, it is ready
for machining the foot and, if needed, the fin with a blade which
meets the geometrical as well as the surface condition
requirements.
* * * * *