U.S. patent application number 15/073271 was filed with the patent office on 2017-09-21 for recovery heat treatment of highly strained components.
The applicant listed for this patent is FORD GLOBAL TECHNOLOGIES, LLC. Invention is credited to Nia R. Harrison, Andrey M. Ilinich, Stephen Kernosky, S. George Luckey, JR..
Application Number | 20170268086 15/073271 |
Document ID | / |
Family ID | 59751652 |
Filed Date | 2017-09-21 |
United States Patent
Application |
20170268086 |
Kind Code |
A1 |
Ilinich; Andrey M. ; et
al. |
September 21, 2017 |
RECOVERY HEAT TREATMENT OF HIGHLY STRAINED COMPONENTS
Abstract
A method of recovery heat treatment of a workpiece includes
contacting at least a portion of the workpiece with a fluid heated
to a temperature sufficient to heat the at least a portion of the
workpiece to a predetermined temperature range in a predetermined
time period. The method may be implemented as a first step of a
two-stage recovery heat treatment or annealing process, followed by
a second step of heating the at least a portion of the workpiece to
a final target temperature by another annealing process.
Inventors: |
Ilinich; Andrey M.; (Novi,
MI) ; Luckey, JR.; S. George; (Dearborn, MI) ;
Harrison; Nia R.; (Ann Arbor, MI) ; Kernosky;
Stephen; (Livonia, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FORD GLOBAL TECHNOLOGIES, LLC |
Dearborn |
MI |
US |
|
|
Family ID: |
59751652 |
Appl. No.: |
15/073271 |
Filed: |
March 17, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C21D 1/607 20130101;
C22F 1/04 20130101; Y02P 10/253 20151101; Y02P 10/25 20151101; C21D
1/34 20130101; C21D 1/42 20130101; C21D 1/58 20130101; C21D 1/60
20130101 |
International
Class: |
C22F 1/04 20060101
C22F001/04; C21D 1/607 20060101 C21D001/607; C21D 1/58 20060101
C21D001/58; C21D 1/60 20060101 C21D001/60; C21D 1/42 20060101
C21D001/42; C21D 1/34 20060101 C21D001/34 |
Claims
1. A method of recovery heat treatment, comprising contacting at
least a portion of a workpiece with a fluid heated to a temperature
sufficient to heat the at least a portion of the workpiece to a
predetermined annealing temperature range in a predetermined time
period.
2. The method of claim 1, wherein the workpiece comprises an
aluminum alloy.
3. The method of claim 2, wherein the aluminum alloy is selected
from the group consisting of an AA6082 aluminum alloy, an AA6061
aluminum alloy, an AA6063 aluminum alloy, an AA6111 aluminum alloy,
an AA6022 aluminum alloy, an AA6016 aluminum alloy, an AA5754
aluminum alloy, or an AA5182 aluminum alloy.
4. The method of claim 1, wherein the workpiece is a bent and/or
pre-formed vehicle frame rail or a formed sheet metal
workpiece.
5. The method of claim 1, including contacting only a formed
portion of the workpiece with the fluid.
6. The method of claim 1, wherein the fluid is a liquid.
7. The method of claim 1, wherein the fluid comprises a finely
divided particulate solid.
8. The method of claim 6, wherein the liquid is selected from the
group consisting of an oil, a lubrication oil, a quenching oil, a
heating oil, a synthetic oil, a semi-synthetic oil, a mineral oil,
water, a water-oil emulsion, a polymer water, oil based solutions
and emulsions, a molten salt, an alkali salt, and combinations
thereof.
9. A method of recovery heat treatment of a workpiece, comprising:
heating at least a portion of the workpiece to a first,
intermediate temperature range in a predetermined time period; and
heating the at least a portion of the workpiece to a second,
annealing temperature range in a predetermined time period.
10. The method of claim 9, wherein the workpiece comprises an
aluminum alloy.
11. The method of claim 10, wherein the aluminum alloy is selected
from the group consisting of an AA6082 aluminum alloy, an AA6061
aluminum alloy, an AA6063 aluminum alloy, an AA6111 aluminum alloy,
an AA6022 aluminum alloy, an AA6016 aluminum alloy, an AA5754
aluminum alloy, or an AA5182 aluminum alloy
12. The method of claim 9, wherein the workpiece is a bent and/or
pre-formed vehicle frame rail or a formed sheet metal
workpiece.
13. The method of claim 9, including contacting the at least a
portion of the workpiece with a fluid heated to a temperature
sufficient to heat the at least a portion of the workpiece to the
first, intermediate temperature range.
14. The method of claim 13, including contacting only a formed
portion of the workpiece with the fluid.
15. The method of claim 13, wherein the fluid is a liquid.
16. The method of claim 13, wherein the fluid comprises a finely
divided particulate solid.
17. The method of claim 15, wherein the liquid is selected from the
group consisting of an oil, a lubrication oil, a quenching oil, a
heating oil, a synthetic oil, a semi-synthetic oil, a mineral oil,
water, a water-oil emulsion, a polymer water, oil based solutions
and emulsions, a molten salt, an alkali salt, and combinations
thereof.
18. The method of claim 9, including heating the at least a portion
of the workpiece to the first, intermediate temperature range by
one or more heating elements.
19. The method of claim 18, wherein the one or more heating
elements are infrared heating elements.
20. The method of claim 19, including heating the at least a
portion of the workpiece to the second, annealing temperature range
by an induction annealing process.
Description
TECHNICAL FIELD
[0001] This disclosure relates generally to the metal forming field
and, more particularly, to a method for recovery heat treatment of
a workpiece to provide for enhanced formability and to reduce
defect-related or strain-related splits during processes of
bending, pre-forming, hydroforming, secondary forming, drawing,
redrawing, restriking, stamping, flanging, etc. of the
workpiece.
BACKGROUND
[0002] Hydroforming is a term applied to metal forming in which the
metal is formed against a die by internal fluid pressure. This may
be done with an internal fluid pressure with an applied axial load
to a tube or in the case of sheet metal with a one-sided die in
which the sheet metal is formed by a bladder/diaphragm. Tube
hydroforming typically uses conventional, single action hydraulic
presses with high ram forces.
[0003] In one example, hydroformed aluminum closed or "boxed" rails
may be used to form the frame rails, A-pillar roof rails, etc. of a
vehicle structure. This type of part may be made with structural
(porthole) or seamless extruded tubes. Structural tubes have better
wall and diameter dimensional tolerances and are more efficient to
extrude but have lower formability for bending, pre-forming, and
hydroforming processes. As a consequence, structural tubes can
typically only be used to form less challenging component shapes in
hydroforming processes. Seamless tubes can have significantly
higher formability which has made them the preferred material for
hydroforming parts having complex cross-sectional geometries, such
as A-pillar roof rails and frame rails. However, seamless tubes are
relatively expensive compared to structural tubes. This is because
seamless tubes are less efficient to extrude relative to structural
tubes due to low output one-out extrusion process and seamless
press cycle time limitations. Seamless tubes also have wall and
diameter dimensional tolerances that can be at least twice that of
structural tubes.
[0004] When using a multiple stage approach to hydroforming various
bending/pre-forming steps may occur prior to the final hydroforming
of the part. During these initial deformation stages much of the
material formability can be exhausted leaving little plastic strain
capability for the hydroforming process itself. For example, during
hydroforming processes used in manufacture of workpieces such as
vehicle boxed frame rails, splits can occur in highly strained
areas of the workpieces. Such splits are potentially linked to
other aggravating factors, one non-limiting example being galling
occurring during bending and/or pre-forming processes, and result
in unusable or inadequate workpieces and attendant cost of
materials and labor in fabricating new workpieces. While to some
extent controllable, such defect-related splits are difficult to
eliminate completely.
[0005] One way to mitigate the influence of these local defects and
improve formability is to apply a recovery heat treatment between
stages of the hydroforming process. However, conventional recovery
heat treatment processes such as induction annealing, while
effective, have limited applicability to certain vehicle components
such as boxed frame rails due to their size and complex geometries.
Therefore, to solve this and other problems the present disclosure
is directed to recovery heat treatment processes to alleviate
defect-related splits such as are encountered during workpiece
bending, pre-forming, and/or hydroforming processes, and to improve
overall formability of workpieces. Advantageously, the described
process allows use of less expensive structural tube extrusions for
fabricating workpieces such as frame rails, roof rails, A-pillar
rails, and the like.
SUMMARY
[0006] In accordance with the purposes and benefits described
herein, in one aspect a method of recovery heat treatment or
annealing is provided, comprising contacting at least a portion of
a workpiece with a fluid heated to a temperature sufficient to heat
the at least a portion of the workpiece to a predetermined
temperature range in a predetermined time period. The workpiece may
comprise a metal or alloy for example an aluminum alloy such as a
6xxx or a 5xxx aluminum alloy. Such aluminum alloys include without
intending any limitation an AA6082 aluminum alloy, an AA6061
aluminum alloy, an AA6063 aluminum alloy, an AA6111 aluminum alloy,
an AA6022 aluminum alloy, an AA6016 aluminum alloy, an AA5754
aluminum alloy, or an AA5182 aluminum alloy. The workpiece may be a
bent and/or pre-formed vehicle boxed frame rail, front rail, or
roof rail. Alternatively, the workpiece may be a pre-formed sheet
metal body inner or outer panel, or structural component.
[0007] In embodiments, the method includes a step of contacting the
at least a portion of the workpiece with a fluid heated to a
temperature sufficient to heat the at least a portion of the
workpiece to a predetermined annealing temperature range in a
predetermined time period. In embodiments, the method may include
contacting only a bent portion of the workpiece with the fluid. In
embodiments, the fluid may be a liquid, and the workpiece may be
fully or partially immersed therein.
[0008] In another aspect, a method of recovery heat treatment or
annealing of a workpiece is described, comprising a first step of
heating at least a portion of the workpiece to a first,
intermediate temperature range in a predetermined time period. In a
next step, the at least a portion of the workpiece is heated to a
second, annealing temperature range in a predetermined time period.
The step of heating to a first, intermediate temperature range of
the at least a portion of the workpiece may be accomplished with a
suitable heat source. In embodiments, the at least a portion of the
workpiece may be heated to the intermediate temperature by a heated
fluid substantially as summarized above. In other embodiments, the
heat source may be one or more heating elements. In embodiments,
the step of heating the at least a portion of the workpiece to a
final target temperature may be accomplished by an induction or
other suitable annealing process.
[0009] In the following description, there are shown and described
embodiments of the disclosed recovery heat treatment processes. As
it should be realized, the processes are capable of other,
different embodiments and their several details are capable of
modification in various, obvious aspects all without departing from
the devices and methods as set forth and described in the following
claims. Accordingly, the drawings and descriptions should be
regarded as illustrative in nature and not as restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The accompanying drawings incorporated herein and forming a
part of the specification, illustrate several aspects of the
presently described methods and together with the description serve
to explain certain principles thereof. In the drawings:
[0011] FIG. 1 illustrates a workpiece received in a channel coil
for purposes of a prior art induction annealing process;
[0012] FIG. 2A depicts in flow chart form a representative method
for hydroforming a rail workpiece including a recovery heat
treatment process according to the present disclosure;
[0013] FIG. 2B depicts in flow chart form a representative method
for forming a planar workpiece including a recovery heat treatment
process according to the present disclosure;
[0014] FIG. 3 depicts the recovery heat treatment process of FIG.
2;
[0015] FIG. 4 depicts in flow chart form a representative method
for hydroforming a rail workpiece including a two-stage recovery
heat treatment process according to the present disclosure; and
[0016] FIG. 5 depicts a heating element arrangement suitable for
accomplishing the two-stage recovery heat treatment process of FIG.
4.
[0017] Reference will now be made in detail to embodiments of the
disclosed methods, examples of which are illustrated in the
accompanying drawing figures.
DETAILED DESCRIPTION
[0018] Preliminarily, the description that follows described
recovery heat treatment processes primarily in the context of a
hydroforming process for a pre-strained metal rail workpiece.
However, it will readily be appreciated that the described recovery
heat treatment processes apply equally to pre-strained planar
workpieces such as sheet metal. In turn, the described recovery
heat treatment processes apply equally to other metal-forming
processes, including without intending any limitation processes of
metal bending, pre-forming, secondary forming, drawing, redrawing,
re-striking, stamping, flanging, and others.
[0019] One known process for recovery heat treatment for
pre-strained metal workpieces is induction annealing, which uses
alternating current flowing through an induction coil to create an
electromagnetic alternating field which, in turn, induce Eddy
current to heat a workpiece. The process requires a water-cooled
copper coil (primary transformer) that follows the shape of the
workpiece (secondary transformer) and accommodates the variables of
the process (frequency, voltage, and others), coil, and workpiece.
This process is illustrated in FIG. 1 which depicts a water-cooled
induction coil 100 for heat treating a tubular workpiece 102. The
voltage level depends on the number of electrical turns in the
primary transformer. Heating of the workpiece is accomplished by
the induced current (arrows I) causing a Joule heating effect.
Heating efficiency and uniformity is achieved through coil design
and contouring relative to the workpiece 102 design/shape. Overall,
induction annealing is an efficient and effective process for
annealing discrete portions of a workpiece 102.
[0020] Therefore, induction annealing was considered as a potential
method for recovery heat treatment to alleviate occurrence of
splits during workpiece pre-forming, bending, hydroforming, etc.
However, induction annealing was found to be unsuitable for certain
workpieces due to their size and/or conformation and/or location of
target areas to be annealed. For example, for pre-formed and/or
bent tubing used to form vehicle boxed frame rails and other such
components, it was found that cycle time and temperature
requirements rendered induction annealing inconvenient and
unfeasible for incorporation into the manufacturing process.
[0021] In more detail, in considering tube hydroforming/annealing
processes for aluminum or other metal or alloy tubing intended for
fabrication into vehicle boxed frame rails and other such
components it was found that no suitable level of energy/heat flux
induced by an induction coil could achieve a desired average target
temperature of 140.+-.10.degree. C. within a desired 21 second
cycle time. Higher levels of flux were able to achieve this average
target temperature within the 21 second cycle time, but produced
unacceptable temperature gradients in excess of 300.degree. C. On
the other hand, using lower levels of flux to achieve the desired
average target temperature of 140.+-.10.degree. C. required cycle
times of at least 90 seconds, which significantly exceeded the
desired 21 second production cycle time target.
[0022] Therefore, alternative recovery heat treatment methods were
considered. At a high level, the present disclosure describes a
recovery heat treatment method for raising a workpiece or workpiece
portion to a desired target annealing temperature. The described
recovery heat treatment method may also be provided as a first step
in a multiple-step annealing process wherein a workpiece is heated
to a desired intermediate temperature using the presently described
recovery heat treatment process, and then in a subsequent second
step is heated to a final target temperature using a second heating
process. In embodiments, the second heating step may comprise the
induction annealing process described in U.S. Published Patent
Appl. No. 2015/0315666 to Harrison et al. published on Nov. 5, 2015
and entitled "Induction Annealing as a Method for Expanded
Hydroformed Tube Formability," the entirety of the disclosure of
which is incorporated herein by reference. However, use of other
known annealing processes for the second heating step is
contemplated.
[0023] The presently described processes may be incorporated as a
portion of a process of hydroforming the workpiece 102, for example
the hydroforming processes described in U.S. Published Patent Appl.
No. 2015/0315666, comprising various steps performed in varying
order of bending, annealing, pre-forming, hydroforming, trimming,
and aging the workpiece. This representative hydroforming process
200 for a rail is illustrated in FIG. 2A. The process illustrated
in FIG. 2A comprises steps of bending a workpiece (not shown) into
a first preliminary shape (see step 202). This is followed by
recovery heat treatment process applied to the workpiece (see step
204). The recovery heat treatment process 204 locally heats the
workpiece in order to alleviate excessive strain hardening within
the workpiece thereby allowing for increased formability during
later stages of the hydroforming method.
[0024] This is then followed by pre-forming the workpiece into a
second preliminary shape (step 206). Next, the workpiece is
hydroformed to a desired final shape (note step 208). Subsequent to
hydroforming, the workpiece may optionally be trimmed to a desired
length (step 210. Next, the workpiece may be subjected to a heat
treatment in order to impart desired strength properties to the
workpiece (note step 212). In one exemplary embodiment the heat
treatment can be a T6 treatment at 180.degree. C. for six hours in
order to induce or impart average yield strength of typically 290
MPa to the workpiece. In alternative embodiments the heat treatment
may be completed at temperatures between 160-200.degree. C. for 4
to 10 hours. In still other alternatives, natural aging without
heat treatment may be implemented to allow the workpiece to harden
to the desired average yield strength.
[0025] Of course, alternative step orders are contemplated as
described in U.S. Published Patent Appl. No. 2015/0315666. For
example, the steps of bending and pre-forming may precede the step
of recovery heat treatment. Alternatively, each step of bending and
pre-forming may be followed by a separate step of recovery heat
treatment. All such alternative step orders are contemplated
herein.
[0026] A similar process 214 for forming a planar workpiece such as
sheet metal is illustrated in FIG. 2B, showing steps of blanking
(step 216), primary forming (step 218), recovery heat treatment
according to the present disclosure (step 204), secondary forming
(step 220), and optionally trimming (step 222). Again, alternative
step orders are contemplated.
[0027] For purposes of illustration, processes 204 of recovery heat
treatment/annealing a vehicle boxed front frame rail formed of a
bent and/or preformed extruded aluminum alloy are described herein.
In the described embodiments, the aluminum alloy is a 6xxx aluminum
alloy or a 5xxx aluminum alloy including without intending any
limitation an AA6082 aluminum alloy, an AA6061 aluminum alloy, an
AA6063 aluminum alloy, an AA6111 aluminum alloy, an AA6022 aluminum
alloy, an AA6016 aluminum alloy, an AA5754 aluminum alloy, or an
AA5182 aluminum alloy. However, the skilled artisan will appreciate
that the described processes equally apply to other workpieces and
other workpiece compositions, for example sheet metal, steel and
other alloys, etc., and so the descriptions should not be taken as
limiting.
[0028] As summarized above, in an embodiment the step 204 of
recovery heat treatment of the workpiece according to the present
disclosure comprises contacting at least a portion of the workpiece
with a fluid heated to a temperature sufficient to heat the at
least a portion of the workpiece to a predetermined temperature
range in a predetermined time period providing a desired annealing
effect in a time frame conducive to conventional manufacturing
processes. As will be appreciated by the skilled artisan, the term
"fluid" describes substances that continually deform (flow) under
an applied shear stress, and encompasses various phases of matter
including liquids, gases, plasmas, and to a degree plastic solids.
In an alternative embodiment, the step 204 of recovery heat
treatment of the workpiece comprises contacting at least a portion
of the workpiece with a fluid comprising a solid, all heated to a
temperature sufficient to heat the at least a portion of the
workpiece to the predetermined annealing temperature range in the
predetermined time period.
[0029] This step 204 includes contacting at least a portion of the
workpiece with an annealing substance heated to a suitable
annealing temperature range, i.e. heated to a temperature
sufficient to heat the at least a portion of the workpiece to a
suitable annealing temperature. As will be appreciated, specific
annealing temperature ranges will vary in accordance with physical,
mechanical, and chemical properties of the workpiece, of the
annealing substance, and with target annealing cycle times for a
particular production setting. For example the specific annealing
temperatures required to anneal a particular aluminum alloy will
vary in accordance with the alloy properties. As will be
appreciated, the skilled artisan is readily able to ascertain
specific annealing temperature ranges for particular metals and
metal alloys. For purposes of example only, particular combinations
of annealing temperature and alloy are set forth in U.S. Published
Patent Appl. No 2008/0105023 to Golovashchenko et al., published on
May 8, 2008 and incorporated herein by reference.
[0030] In an embodiment, this step 204 includes contacting the
workpiece with a fluid heated to a temperature sufficient to heat
the at least a portion of the workpiece to a temperature of from
about 130.degree. C. to about 150.degree. C. in 20 to 30 seconds.
Some or all of the workpiece may be contacted with the fluid. For
example, as shown in FIG. 3 only a bent portion of the workpiece,
being the portion with a high amount of accumulated plastic
deformation and, thereby, most susceptible to defect related
splits, may be contacted by the fluid.
[0031] In embodiments, the fluid may be a liquid or a gas. In
embodiments comprising contacting the workpiece with a liquid, the
liquid may be selected from the group consisting of an oil, a
lubrication oil, a quenching oil, a heating oil, a synthetic oil, a
semi-synthetic oil, a mineral oil, water, a water-oil emulsion, a
polymer water, oil based solutions and emulsions, a molten salt
such as sodium and potassium nitrates, nitrites, and chlorides,
alkali salts, and combinations.
[0032] In other embodiments, the annealing step may be accomplished
by contacting at least a portion of the workpiece with a solid,
such as in a fluidized bed device including a fluid comprising dry,
finely divided solid particles. Such devices are known in the art,
being devices wherein fluid/solid mixtures are held under
conditions causing the mixtures to behave as a fluid.
[0033] It will be appreciated that the particular recovery heat
treatment substance (fluid, liquid, gas, liquid/solid mixture) will
be selected according to the physical, chemical, mechanical, and
other properties of the workpiece and the target annealing
temperatures and/or cycle times to be implemented. Specifically,
the substance will be selected whereby the target annealing
temperature to be reached will be above the substance melting
temperature but below the substance flashpoint temperature. In
turn, the evaporation rate at the target annealing temperature
should be considered, as well as compatibility with down-stream
processing equipment/processes. In general, water-based substances
are suitable for lower target annealing temperature ranges,
oil-based substances are suitable for intermediate target annealing
temperature ranges, and molten salt-based substances are suitable
for higher target annealing temperature ranges, although the ranges
may overlap. Selection of a particular annealing substance is well
within the abilities of the skilled artisan.
[0034] As shown in FIG. 3, some or all of the workpiece 102 may be
contacted with a liquid 300, for example by immersing at least a
portion of the workpiece in a container 302 holding the liquid. In
the depicted embodiment, a "two-sided" exposure, i.e. contact of
the heated liquid 300 with both inner and outer surfaces of the
portion of the workpiece subjected to recovery heat treatment, is
provided. However, it will be appreciated that partial submersion
resulting in contact of only one of an outer surface or an inner
surface of the bent portion 304 of the workpiece with the liquid
300, i.e. a "one-sided" exposure, is also contemplated.
[0035] Advantageously, the process illustrated in FIG. 3 allows
annealing or recovery heat treatment of component that are
particularly large and/or that define a complex exterior geometry
at a higher heating rate/shorter cycle time than would be possible
using other annealing processes. For example, the presently
described process allows providing uniform heating of workpieces
102 having a much larger size and more complex geometries than is
possible by induction annealing, due to limitations imposed by the
configuration of the induction coil apparatus 100 (see FIG. 1). In
turn, the simplicity of the illustrated process results in
significant cost savings during the recovery heat treatment and
subsequent hydroforming processes.
[0036] In another embodiment, consideration was given to situations
where a desired target temperature range required for annealing a
workpiece 102 or workpiece portion might exceed a boiling point of
a desired liquid 300, or situations when for safety reasons a
maximum liquid 300 temperature cap would be required that was lower
than the desired target temperature range for annealing a workpiece
102. In such situations, a two-stage annealing process was
contemplated.
[0037] With reference to FIG. 4, a two-stage recovery heat
treatment process for a rail workpiece is illustrated as a portion
of a hydroforming process 400. While not specifically depicted, it
will be readily appreciated that the described two-stage recovery
heat treatment process is easily incorporated into processes for
forming a planar workpiece such as sheet metal as is illustrated in
FIG. 2B. Substantially as shown in FIG. 2, the process 400 includes
steps of bending (step 402), recovery heat treatment (step 404),
pre-forming (step 406), hydroforming (step 408), optionally
trimming (step 410), and optionally aging (step 412). Again,
alternative step orders are contemplated. For example, the steps of
bending and pre-forming may precede the step of recovery heat
treatment. Alternatively, each step of bending and pre-forming may
be followed by a separate step of recovery heat treatment. All such
alternative step orders are contemplated herein.
[0038] The two-stage recovery heat treatment process includes a
first step 404a of heating at least a portion of the workpiece (not
shown) to a first, intermediate temperature by immersing some or
all of the workpiece 102 in a suitably heated fluid or solid,
substantially as described above and as shown in FIG. 3. The
specific intermediate temperature range and time period may be
fixed, or may vary according to physical, chemical, and mechanical
properties of the workpiece 102 as described above.
[0039] Alternatively, the workpiece 102 may be preheated to bring
the workpiece to the desired intermediate temperature range using
alternative heat sources. In one embodiment the heat source is a
suitable heating element. As shown in FIG. 5, in one possible
embodiment a conveyer 500 passes one or more workpieces 102 past
one or more heating elements 502. The workpieces 102 may be
arranged such that a specific portion of the workpieces (bend 504)
is closest to the heating elements 502, which in the depicted
embodiment are installed substantially above where the workpieces
will pass, and so will receive the most heating.
[0040] In the depicted embodiment, heating elements 502 are
infrared heaters (also referred to as heat lamps), which as is
known transfer heat by radiation (emitting energy in the infrared
wavelengths). However, alternative heating element types are
contemplated, including without intending any limitation heat guns,
pressurized blowers for delivering a heated gas over a surface, or
exposure of the workpieces 102 to a low temperature convection or
radiation oven. This could occur by placing the workpieces 102 in
the described oven, or alternatively by passing a conveyer such as
is shown in FIG. 5 through such ovens.
[0041] Once the workpiece or desired portion of the workpiece has
been heated to the first, intermediate temperature range, the
workpiece may then be heated to a second, annealing temperature
range (step 404b) to complete the two-stage recovery heat treatment
process 404. In an embodiment, the workpiece may be heated to the
second, annealing temperature range by an induction annealing
process substantially as summarized above (see FIG. 1) and more
fully described in U.S. Published Patent Appl. No. 2015/0315666.
However, other suitable annealing processes are also
contemplated.
[0042] In turn, the skilled artisan will appreciate that particular
temperatures needed to heat all or a portion of a workpiece to a
predetermined annealing temperature or temperature range (FIGS. 2A,
2B, 3), or to a predetermined intermediate temperature (FIG. 4)
within a predetermined time frame according to the processes set
forth above can readily be calculated in accordance with the known
physical properties of the heating fluid/heating elements being
used and of the workpiece. In an embodiment, the fluid or solid
used to heat the workpiece or workpiece portion is heated to the
predetermined annealing temperature or temperature range, or to the
predetermined intermediate temperature or temperature range.
[0043] In summary, numerous benefits result from the described
methods of recovery heat treatment 204, 404 of a workpiece 102 as
disclosed herein. The methods support high volume automotive
manufacturing. Any contemplated process of metal forming benefits
from the method, including forming of both structural and seamless
tubes. In fact, structural tubes may now be readily used in the
production of difficult-to-form boxed frame rails, A-pillar roof
rails, and others. Thus, the method allows for the use of a higher
tolerance and more manufacturing efficient material for
hydroforming roof rails.
[0044] Advantageously, the described methods are simple, efficient,
and economical, and can be performed in a manner restricted to a
specific region of interest to be annealed in a workpiece 102, for
example a bend in a boxed frame rail, where plastic strain
capability has been reduced by bending and/or pre-forming steps or
stages during the production process. Heating of the workpiece 102
can be easily localized to the to-be-annealed region, and therefore
there is no specialized equipment required for material handling of
the workpiece in the unheated regions.
[0045] The foregoing has been presented for purposes of
illustration and description. It is not intended to be exhaustive
or to limit the embodiments to the precise form disclosed. Obvious
modifications and variations are possible in light of the above
teachings. All such modifications and variations are within the
scope of the appended claims when interpreted in accordance with
the breadth to which they are fairly, legally and equitably
entitled.
* * * * *