U.S. patent application number 11/853391 was filed with the patent office on 2009-03-12 for die cooling apparatus and method thereof.
This patent application is currently assigned to HONDA MOTOR CO., LTD.. Invention is credited to James Paul Lewis, Philip Vais.
Application Number | 20090065170 11/853391 |
Document ID | / |
Family ID | 40430590 |
Filed Date | 2009-03-12 |
United States Patent
Application |
20090065170 |
Kind Code |
A1 |
Vais; Philip ; et
al. |
March 12, 2009 |
DIE COOLING APPARATUS AND METHOD THEREOF
Abstract
A die cooling system for cooling a cast wheel for an automotive
vehicle is provided that includes a die, multiple thermocouples
embedded in the die, which measure the actual cast metal
temperature, adjustable cooling valves, and a control system. The
control system receives actual casting metal temperature data from
each thermocouple to control the operation of the adjustable
cooling valves.
Inventors: |
Vais; Philip; (Powell,
OH) ; Lewis; James Paul; (Bellefontaine, OH) |
Correspondence
Address: |
RANKIN, HILL & CLARK LLP
38210 GLENN AVENUE
WILLOUGHBY
OH
44094-7808
US
|
Assignee: |
HONDA MOTOR CO., LTD.
Tokyo
JP
|
Family ID: |
40430590 |
Appl. No.: |
11/853391 |
Filed: |
September 11, 2007 |
Current U.S.
Class: |
164/458 ;
164/154.6 |
Current CPC
Class: |
B22D 17/32 20130101;
B22D 46/00 20130101; B22D 17/2218 20130101; B22D 15/005
20130101 |
Class at
Publication: |
164/458 ;
164/154.6 |
International
Class: |
B22D 46/00 20060101
B22D046/00 |
Claims
1. A die cooling system for cooling cast metal comprising: a die; a
plurality of thermocouples embedded in the die, such that each
thermocouple contacts the casting metal; a plurality of cooling
zones arranged such that cooling air is supplied to the cooling
zones to cool the die; and a feedback control system, wherein each
thermocouple measures the temperature of the cast metal, and
wherein the control system continuously receives temperature data
from each thermocouple and controls the supply of cooling air to
the cooling zones based on the temperature data.
2. The die cooling system of claim 1, wherein a tip of each
thermocouple is flush with an inside surface of the die.
3. The die cooling system of claim 2 further comprising a plurality
of adjustable cooling valves to supply cooling air to the cooling
zones, wherein the control system calculates a critical
solidification rate of the cast metal and activates and deactivates
the adjustable cooling valves to supply cooling air to
corresponding cooling zones in such a manner that the die is
gradually cooled at the critical solidification rate from an outer
most portion of the die toward an inner most portion of the
die.
4. The die cooling system of claim 3, wherein during activation of
the adjustable cooling valve the control system varies the cooling
air flow rate of the adjustable cooling valve to maintain the
critical solidification rate of the cast metal.
5. The die cooling system of claim 1, wherein a tip of each
thermocouple is embedded in the casting metal.
6. The die cooling system of claim 5 further comprising a plurality
of adjustable cooling valves to supply cooling air to the cooling
zones, wherein the control system calculates a critical
solidification rate of the cast metal and activates and deactivates
the adjustable cooling valves to supply cooling air to
corresponding cooling zones in such a manner that the die is
gradually cooled at the critical solidification rate from an outer
most portion of the die toward an inner most portion of the
die.
7. The die cooling system of claim 6, wherein during activation of
the adjustable cooling valve the control system varies the cooling
air flow rate of the adjustable cooling valve to maintain the
critical solidification rate of the cast metal.
8. A die cooling system for cooling a cast wheel for an automotive
vehicle comprising: a die; a plurality of thermocouples embedded in
the die such that each thermocouple contacts the cast wheel; a
plurality adjustable cooling valves to supply cooling air to
various portions of the die; and a feedback control system, wherein
each thermocouple measures the actual temperature of the cast
wheel, and wherein the control system continuously receives
temperature data from each thermocouple and controls the operation
of the adjustable cooling valves based on the temperature data.
9. The die cooling system of claim 8, wherein a tip of each
thermocouple is flush with an inside surface of the die.
10. The die cooling system of claim 9, wherein the control system
calculates a critical solidification rate of the cast wheel,
wherein the control system includes a computer and a programmable
controller, wherein the computer receives temperature data from
each thermocouple and transmits the temperature data to the
programmable controller, and wherein the programmable controller
activates and deactivates the adjustable cooling valves to supply
cooling air to corresponding cooling zones in such a manner that
the die is gradually cooled at the critical solidification rate
from an outer most portion of the die toward an inner most portion
of the die.
11. The die cooling system of claim 10, wherein during activation
of the adjustable cooling valve the control system varies the
cooling air flow rate of the adjustable cooling valve to maintain
the critical solidification rate of the cast wheel.
12. The die cooling system of claim 8, wherein a tip of each
thermocouple is embedded in the cast wheel.
13. The die cooling system of claim 12, wherein the control system
calculates a critical solidification rate of the cast wheel,
wherein the control system includes a computer and a programmable
controller, wherein the computer receives temperature data from
each thermocouple and transmits the temperature data to the
programmable controller, and wherein the programmable controller
activates and deactivates the adjustable cooling valves to supply
cooling air to corresponding cooling zones in such a manner that
the die is gradually cooled at the critical solidification rate
from an outer most portion of the die toward an inner most portion
of the die.
14. The die cooling system of claim 13, wherein during activation
of the adjustable cooling valve the control system varies the
cooling air flow rate of the adjustable cooling valve to maintain
the critical solidification rate of the cast wheel.
15. A method of cooling a cast wheel for an automotive vehicle
comprising the steps of: providing a die having a plurality of
thermocouples embedded in the die such that each thermocouple
contacts the cast wheel, a plurality of adjustable cooling valves
to supply cooling air to the die, and a control system; calculating
a critical solidification rate of the cast wheel based on
parameters of the wheel; filling a cavity of the die with molten
metal; measuring the cast wheel temperature continuously at each
thermocouple location; and controlling the supply of cooling air
from the adjustable cooling valves to achieve the critical
solidification rate during a solidification period.
16. The method of claim 15 further comprising the steps of:
activating and deactivating the adjustable cooling valves to supply
cooling air to each cooling zone to gradually cool the die from an
outer most portion of the die toward an inner most portion of the
die; and varying the cooling air flow rate of an activated
adjustable cooling valve to maintain the critical solidification
rate.
17. The method of claim 16 further comprising the steps of:
transforming the molten metal from a liquid to a solid; and cooling
the entire die rapidly to a temperature such that the cast wheel
can be extracted from the die.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an apparatus and method for
cooling a die casting product and more specifically to an apparatus
and method for measuring the actual temperature of the die cast
product and controlling the solidification rate of the die cast
product based on the actual temperature of the die cast
product.
[0003] 2. Description of Related Art
[0004] Low pressure die casting methods and procedures to produce
cast products are well known in the industry. Basically, the low
pressure die casting method comprises a metal die mounted above a
sealed furnace that contains molten metal. A refractory lined tube,
called a stalk tube, extends from the bottom of the die into the
molten metal. Air or a gas under low pressure is introduced into
the furnace. The air or gas forces the molten metal up the tube and
into the die cavity. When the metal inside the die has solidified
the pressure in the furnace is released and the molten metal in the
tube returns to the furnace. After an additional cooling time the
die is opened and the casting is extracted.
[0005] Specific methods and procedures during this process can
significantly alter the resulting end product. For example, the
cooling rate and hence the solidification rate at which the molten
metal solidifies can affect the microstructure of the finished
product. More specifically, a fast solidification rate produces a
fine microstructure, which leads to good elongation properties. If
the solidification rate is too fast, however, shrinkage-porosity
may develop in the end product. On the other hand, a slow
solidification rate results in unacceptable mechanical properties.
More specifically, a slow solidification rate creates a coarse
microstructure in the material, which in turn creates poor
elongation properties.
[0006] Conventional methods to control the cooling rate and
ultimately the solidification rate of the cast product include
using thermocouples to measure the temperature of the die, referred
to as an in-die thermocouple system, and using this information to
control on/off type cooling valves, which blow cooling air directly
onto the die. One disadvantage to the in-die thermocouple system is
that the in-die thermocouple system can be affected by variations
in atmosphere temperature, die coating thickness, die coating
thermal diffusion, die cooling air temperature and humidity, and
metal temperature fluctuations. The present invention can adjust to
these variations, which results in more uniform properties
throughout the entire cast product than in the in-die thermocouple
system. This in turn reduces the amount of scrap, which is yet
another advantage of the present invention over conventional
methods.
[0007] In today's the automotive industry, however, the trend is to
manufacture larger diameter wheels for aggressive styling. In 2001
the typical wheel diameter on North America automotive vehicles
ranged from 14 inches to 17 inches. As of 2005, while the majority
of the wheel diameters still ranged between 15 inches to 17 inches,
nearly 10% of the wheel diameters were greater than or equal to 18
inches. An increase in the wheel diameter, however, introduced
problems in the casting process. More specifically, conventional
methods. Like those mentioned above, to control the cooling rate
are no longer efficient enough to achieve the proper mechanical
properties in all areas of the wheel and more specifically in the
spoke portions of the wheel. Thus, what is required is a die
cooling apparatus and method to more uniformly cool a cast
automotive wheel.
SUMMARY OF THE INVENTION
[0008] In accordance with one aspect, the present invention
overcomes the above mentioned disadvantages by providing a die
cooling system for cooling cast metal comprising a die, multiple
thermocouples embedded in the die, adjustable cooling valves, and a
feedback control system. The thermocouples are embedded in the die
and contact the cast metal and measure the actual casting metal
temperature. The control system receives measured temperature
signals from each thermocouple to thereby control the operation of
each adjustable cooling valve to maintain the proper solidification
rate of the casting metal.
[0009] Additional benefits and advantages of the present invention
will become apparent to those skilled in the art to which it
pertains upon a reading and understanding of the following detailed
specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The invention may take physical form in certain parts and
arrangement of parts, a preferred embodiment of which will be
described in detail in this specification and illustrated in the
accompanying drawings that form a part of the specification.
[0011] FIG. 1 shows a die cooling system in accordance with the
present invention.
[0012] FIG. 2 is a view of a spoke portion of the die.
[0013] FIG. 3 is a view taken along line 3-3 of FIG. 2.
[0014] FIG. 4 is a graph showing a die cooling graph.
DETAILED DESCRIPTION OF THE INVENTION
[0015] Referring now to the drawings, FIG. 1 shows a die cooling
system 10 for cooling a low-pressure die for forming large die cast
wheels. The die cooling system 10 includes a die 12, adjustable
cooling valves 14, multiple thermocouples (TC1 . . . TCN), and a
feedback control system 16. The die cooling system 10 overcomes the
above mentioned disadvantages by systematically controlling the
operation of the adjustable cooling valves 14 to maintain a
solidification rate of the casting metal during the cooling process
to produce optimum mechanical properties. It should be noted that
although the die cooling system disclosed herein is designed to
improve the casting process for wheels with a diameter greater than
or equal 18'', the die cooling system 10 can be implemented for
casting wheels having a diameter less than 18''.
[0016] For simplicity and illustrative purposes only, the present
invention will be described with reference to one spoke portion of
the die 12, as shown in FIGS. 2 and 3. It should be noted, however,
that each spoke portion of the die 21 has the same cooling
arrangement as will be subsequently described.
[0017] Referring to FIGS. 2 and 3, the die 12 is a conventional die
of the type commonly known in the art that includes a top core 18,
an inner-side core 20, an outer-side core 22 and a bottom core 24.
The die 12 further includes a conventional cooling air delivery
structure (not shown) of the type commonly known in the art and
will not be described herein. Thus, the adjustable cooling valves
14, shown schematically in FIG. 3, deliver cooling air to the die
12 via the delivery structure. It should be noted that the number
of adjustable cooling valves 14 shown in FIG. 3 is for illustrative
purposes only and is not intended to limit the scope of the
invention. Thus, the number of adjustable cooling valves 14 may
vary depending on the size of the die 12 the material of the cast
product, etc.
[0018] Referring to FIG. 4, the thermocouples TC are embedded into
the die 12 such that a tip 26 of each thermocouple TC is either
flush with an inside surface 28 of the die 12 or slightly embedded
into the casting metal. Thus, each thermocouple TC contacts the
casting metal and, therefore, measures the actual casting metal
temperature and not the die temperature. Because the thermocouples
TC measure the actual casting metal temperature, the die cooling
system 10 ensures that casting metal solidifies at the
solidification rate, as explained further below. It should be noted
that the number of thermocouples TC may vary depending on the
diameter of the wheel being cast. For example, a wheel having a
diameter of 18'' may require fewer thermocouples than a wheel
having a diameter of 20''. In addition, because the casting metal
will solidify at the same rate from either side of the die 12, it
is contemplated that thermocouples TC may be required on only one
side of the die.
[0019] A release agent may be applied to the inside surface 28 of
the die 12 to facilitate the removal of the cast product when
completed. Prior to applying the release agent the thermocouples TC
are masked off so the release agent does not hinder the performance
of the thermocouples TC.
[0020] Referring to FIG. 1, the feedback control system 16 includes
a computer 30 and a programmable controller 32. The computer 30 is
electronically linked to each thermocouple TC and continuously
receives signals indicative of the actual casting metal temperature
(temperature data) from each thermocouple TC. The computer 30
transmits the temperature data to the programmable controller 32.
In order to achieve and maintain the solidification rate, the
programmable controller 32 processes the temperature data to
control the operation of the adjustable cooling valves 14. In
addition, the programmable controller 32 communicates the status of
each adjustable cooling valve 14 back to the computer 30.
[0021] FIG. 4 illustrates an example embodiment of a die cooling
graph comprising a combination bar graph and line graph. The bar
graph represents a cooling zone diagram and illustrates how the die
12 is cooled. The line graph, referred to as metal cooling curves,
represents the temperature of the casting metal collected by each
thermocouple TC. As an option, the cooling zone diagram and the
metal cooling curves can be displayed on a monitor (not shown)
connected to the computer 14. It should be noted that the cooling
zone diagram and the metal cooling curves shown in FIG. 4 is just
one example of a cooling a die and is for illustrative purposes
only and is not intended to limit the scope of the invention.
[0022] Referring to the cooling zone diagram (bar graph) of FIG. 4,
a cooling zone CZ is defined as a location within the die cooling
system 10 where cooling air is applied to the die 12. The cooling
zones CZ are schematically represented by the adjustable cooling
valves 14, as shown in FIG. 3. Thus, the cooling air applied to the
die 12 at the cooling zones CZ is supplied by the adjustable
cooling valves 14 via cooling air delivery structure and is
regulated by the programmable controller 32. As explained below,
cooling air is supplied to the cooling zones CZ in a manner such
that the die 12 is systematically cooled from the outer most
portion of the die 12 toward the inner most portion of the die 12.
It should be noted that the operation of the adjustable cooling
valves 14, and hence, the cooling zones CZ operate independently of
each other. For example, the time at which the cooling zone
adjustable cooling valve 14 is activated, the duration of its
activation and it subsequent deactivation depends on the casting
parameters of the wheel being cast explained further below and the
temperature of the casting metal and not necessarily on the status
of the previous cooling zone CZ. In addition, activation of
adjustable cooling valves 14 for adjacent cooling zones CZ may or
may not overlap. Still further, the amount of overlap may vary.
[0023] Referring to the line graph of FIG. 4, as mentioned above,
the metal cooling curves represent the actual casting metal
temperature. For example, the metal cooling curve denoted as TC1 is
the actual casting metal temperature as measured by thermocouple
TC1, the metal cooling curve denoted as TC2 is the actual casting
metal temperature as measured by thermocouple TC2, etc. As
illustrated by the metal cooling curves the casting metal is a
liquid above a first temperature and becomes a solid below a second
temperature. As the casting metal cools from the first temperature
down to the second temperature the casting metal is in a semi-solid
state and undergoes a transformation from a liquid to a solid. This
applies to any metal that has a transformation temperature, such
as, for example but not limited to aluminum. This transformation
occurs over a time period referred to as a solidification period.
The rate at which the casting metal transforms from a liquid to a
solid is the solidification rate mentioned above. Maintaining the
proper solidification rate, referred to as a critical
solidification rate, during the solidification period is critical
in order to achieve optimum mechanical properties of the casting
metal.
[0024] For example, if the casting is not cooled at the critical
solidification rate then either macro-shrinkage porosity or
micro-shrinkage porosity may occur within the casting. More
specifically, if a portion of the casting is cooled too early or
too aggressive then the molten metal feed from the gate will be cut
off. This in turn causes macro-shrinkage porosity between portions
of the casting, such as for example, between the spoke and the
flange. Micro-shrinkage porosity can occur in a more localized area
if the solidification rate falls below the critical solidification
rate. More specifically, if the solidification rate falls below the
critical solidification rate then the dendrite arms become too
long. This leads to micro-shrinkage porosity between the dendrite
arms.
[0025] Prior to operation of the die cooling system 10 the feedback
control system 16 calculates the critical solidification rate of
the casting metal at each thermocouple TC location. The critical
solidification rate is calculated by taking into account certain
casting parameters for a particular cast wheel, such as the
temperature of the casting metal during the casting process, the
diameter, width, thickness, design, material, etc. of the wheel,
etc. The casting parameters are entered into the feedback control
system 16 whereby the feedback control system 16 calculates the
critical solidification rate for the cast wheel. It should be noted
that the critical solidification rate of the casting metal may vary
for each thermocouple TC location due to characteristics of the
wheel, such as thickness.
[0026] During operation of the die cooling system 10, molten metal
is introduced into the die 12 using the low-pressure die casting
method described above. The computer 30 continuously processes
temperature data from each thermocouple TC and transmits this
information to the programmable controller 32. The programmable
controller 32 uses the temperature data to control the operation of
the adjustable cooling valves 14 for each cooling zone CZ
accordingly. In addition, the programmable controller 32 uses the
temperature data from a given thermocouple TC to control the
operation of a downstream adjustable cooling valve 14. For example,
the programmable controller 32 can control the operation of the
adjustable cooling valves 14 downstream from thermocouple TC1 based
on the temperature data received from thermocouple TC1. Thus, based
on the temperature data the programmable controller 32 activates,
deactivates and adjusts the flow rate of the adjustable cooling
valves 14 such that cooling air is systematically supplied to the
cooling zones CZ from the outer most portion of the die 12 toward
the inner most portion of the die 12 to thereby maintain the
critical solidification rate. As shown in the bar graph of FIG. 4,
the presence of a bar indicates that an adjustable cooling valve 14
is activated and is, thus, supplying cooling air to the
corresponding cooling zone CZ. It should be noted that when an
adjustable cooling valve 14 is activated the programmable
controller 32 may also regulate the amount of air flow from each
adjustable cooling valve 14. For example, the adjustable cooling
valves 14 may be variably opened between 0% and 100%. Thus, based
on the temperature data from the thermocouples TC the programmable
controller 32 can regulate the on/off operation of the adjustable
cooling valves 14 or vary the flow rate of the adjustable cooling
valves 14.
[0027] As an example, referring to the embodiment shown in FIG. 4,
as the cooling process begins the casting metal begins to cool
gradually as shown by the metal cooling curve represented by
thermocouple TC1. The programmable controller 32 activates the
adjustable cooling valve 14 for cooling zone CZ1 and the casting
metal represented by metal cooling curve TC1 begins to cool more
rapidly. As the casting metal enters and proceeds through the
transformation phase described above, the programmable controller
32 may also adjust the flow rate of the adjustable cooling valve 14
to thereby more precisely maintain the critical solidification
rate. When the feedback control system 16 determines that the
transformation has successfully occurred or will successfully occur
at cooling zone CZ1 the programmable controller 32 will either
deactivate the adjustable cooling valve 14 for cooling CZ1 or
adjust the flow rate of the adjustable cooling valve 14. This
process continues through each cooling zone CZ such that the
casting metal systematically solidifies from the outer most portion
of the die 12 (the wheel flange 34) toward the inner most portion
of the die 12 closest to the stalk tube. Once the entire casting
metal is transformed from a liquid to a solid the die 12 is quickly
cooled to a temperature such that the cast wheel can be extracted
from the die 12.
[0028] The die cooling system 10 embodiment described above is
capable of cooling casting metal at a critical solidification rate
calculated from casting parameters to thereby ensure that the
casting metal solidifies with optimum mechanical properties. This
example embodiment employs a combination time-temperature based
method to control the operation of the adjustable cooling valves
14. Thus, the feedback control system 16 controls the operation of
the adjustable cooling valves 14 based on the temperature data from
the thermocouples TC and on the solidification rate of the cast
metal.
[0029] It is contemplated, however, that a time based method may be
employed to control the operation of the adjustable cooling valves
14. For example, the adjustable cooling valves 14 can be activated,
deactivated, or varied based on the based on the critical
solidification rate of the cast metal.
[0030] It is further contemplated that a temperature based method
may be employed to control the operation the adjustable cooling
valves 14. For example, the adjustable cooling valves 14 can be
activated, deactivated, or varied based on the temperature data
received by the feedback control system 16 from the thermocouples
TC. Thus, the cooling air flow from the adjustable cooling valves
14 at each cooling zone CZ can be regulated based on the
temperature of the casting metal.
[0031] It is still further contemplated that the adjustable cooling
valves 14 for each cooling zone CZ may be all activated once the
cooling process begins and that the programmable controller 32
varies the flow rate of each adjustable cooling valve 14
accordingly to achieve and maintain the critical solidification
rate.
[0032] While specific embodiments of the invention have been
described and illustrated, it is to be understood that these
embodiments are provided by way of example only and that the
invention is not to be construed as being limited but only by
proper scope of the following claims.
* * * * *