U.S. patent application number 11/393248 was filed with the patent office on 2006-08-03 for dry machining of aluminum castings.
Invention is credited to Carolina C. Ang, Yang T. Cheng, Jean M. Dasch, Robert F. Paluch, Bob R. JR. Powell, Vadim Rezhets.
Application Number | 20060168806 11/393248 |
Document ID | / |
Family ID | 35668780 |
Filed Date | 2006-08-03 |
United States Patent
Application |
20060168806 |
Kind Code |
A1 |
Ang; Carolina C. ; et
al. |
August 3, 2006 |
Dry machining of aluminum castings
Abstract
Additions of small but effective amounts of one or more of
bismuth, indium, lead and/or tin to an aluminum casting alloy
markedly improved the dry machinability of a casting made from the
modified alloy. The added elements, which are softer and lower
melting than the matrix alloy form as small globules dispersed in
the microstructure of the aluminum casting. These globules do not
adversely affect the strength or hardness of the casting but enable
the casting to be machined without the use of a cooling and
lubricating machining fluid.
Inventors: |
Ang; Carolina C.;
(Bloomfield, MI) ; Dasch; Jean M.; (Bloomfield
Township, MI) ; Cheng; Yang T.; (Troy, MI) ;
Rezhets; Vadim; (Cape Coral, FL) ; Powell; Bob R.
JR.; (Birmingham, MI) ; Paluch; Robert F.;
(Allenton, MI) |
Correspondence
Address: |
KATHRYN A. MARRA;General Motors Corporation
Legal Staff, Mail Code 482-C23-B21
P.O. Box 300
Detroit
MI
48265-3000
US
|
Family ID: |
35668780 |
Appl. No.: |
11/393248 |
Filed: |
March 30, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10900648 |
Jul 28, 2004 |
|
|
|
11393248 |
Mar 30, 2006 |
|
|
|
Current U.S.
Class: |
29/888.01 |
Current CPC
Class: |
C22C 21/003 20130101;
Y10T 29/49231 20150115; Y10T 29/49989 20150115; C22C 21/02
20130101 |
Class at
Publication: |
029/888.01 |
International
Class: |
B21K 3/00 20060101
B21K003/00 |
Claims
1. A method of making an aluminum alloy article comprising: making
a casting of the article from an aluminum alloy comprising, by
weight, 5% to 18% silicon, a small amount up to about 2% by weight
of one or more machining lubricity imparting elements selected from
the group consisting of bismuth, indium, lead and tin, and
aluminum; the casting containing a dispersed phase containing the
lubricity imparting element; and machining a surface of the casting
with a cutting tool to remove cast material without the use of a
machining fluid.
2. A method of making an aluminum alloy article as recited in claim
1 comprising machining a surface of the casting with a tungsten
carbide cutting tool.
3. A method of making an aluminum alloy article comprising: making
a casting of the article from an aluminum alloy comprising, by
weight, 5% to 18% silicon, 1.3% max iron, 0.2% max copper or 2% to
5% copper, 1.3% max magnesium, 0.6% max manganese, about 0.1% to
about 2% of one or more machining lubricity imparting elements
selected from the group consisting of bismuth, indium, lead and
tin, and aluminum; the casting containing a dispersed phase
containing the lubricity imparting element; and machining a surface
of the casting with a cutting tool to remove cast material without
the use of a machining fluid.
4. The method of making an aluminum alloy article as recited in
claim 3 comprising making a casting of the article from an aluminum
alloy comprising, by weight, 5% to 13% silicon, 1.3% max iron, 0.2%
max copper, 1.3% max magnesium, 0.6% max manganese, about 0.1% to
about 2% of one or more machining lubricity imparting elements
selected from the group consisting of bismuth, indium, lead and
tin, and aluminum.
5. The method of making an aluminum alloy article as recited in
claim 3 comprising making a casting of the article from an aluminum
alloy comprising, by weight, 5% to 13% silicon, 1.3% max iron, 2%
to 5% copper, 1.3% max magnesium, 0.6% max manganese, about 0.1% to
about 2% of one or more machining lubricity imparting elements
selected from the group consisting of bismuth, indium, lead and
tin, and aluminum.
6. The method of making an aluminum alloy article as recited in
claim 3 comprising making a casting of the article from an aluminum
alloy comprising, by weight, 16% to 18% silicon, 1.3% max iron, 4%
to 5% copper, 0.4% to 0.65% magnesium, 0.1% max manganese, about
0.1% to about 2% of one or more machining lubricity imparting
elements selected from the group consisting of bismuth, indium,
lead and tin, and aluminum.
7. The method of making an aluminum alloy article as recited in
claim 3 comprising making a casting of the article from an aluminum
alloy comprising, by weight, 5% to 7.5% silicon, 1% max iron, 2% to
5% copper, 0.5% max magnesium, 0.6% max manganese, about 0.1% to
about 2% of one or more machining lubricity imparting elements
selected from the group consisting of bismuth, indium, lead and
tin, and aluminum.
8. The method of making an aluminum alloy article as recited in
claim 3 in which the lubricity imparting element is selected from
the group consisting of bismuth and tin.
9. The method of making an aluminum alloy article as recited in
claim 4 in which the lubricity imparting element is selected from
the group consisting of bismuth and tin.
10. The method of making an aluminum alloy article as recited in
claim 5 in which the lubricity imparting element is selected from
the group consisting of bismuth and tin.
11. The method of making an aluminum alloy article as recited in
claim 6 in which the lubricity imparting element is selected from
the group consisting of bismuth and tin.
12. The method of making an aluminum alloy article as recited in
claim 7 in which the lubricity imparting element is selected from
the group consisting of bismuth and tin.
13. The method of making an aluminum alloy article as recited in
claim 1 in which the lubricity imparting element is selected from
the group consisting of bismuth and tin.
Description
[0001] This application is a continuation-in-part of co-pending
application Ser. No. 10/900648, filed Jul. 28, 2004.
TECHNICAL FIELD
[0002] This invention pertains to the machining of aluminum alloy
castings. More specifically, this invention pertains to the
machining of aluminum castings without the use of a metalworking
fluid for lubrication and/or cooling.
BACKGROUND OF THE INVENTION
[0003] Aluminum alloy castings are used in making many articles of
manufacture. In the automobile industry, for example, many engine
and transmission parts, chassis parts, body parts and interior
parts are made of silicon-containing aluminum alloy castings. Many
of these parts such as engine blocks, cylinder heads, crank cases,
transmission cases and the like are initially formed as castings
using sand molding, permanent mold, high pressure die casting and
lost foam processes. These casting processes are capable of forming
complex shapes to reasonably close tolerances. But after the
castings have been trimmed, ground and cleaned by sand blasting (or
various other blast-cleaning processes), many surfaces of the parts
still have to be machined to specified dimensions within very close
tolerances.
[0004] Engine and transmission castings, for example, may require
precision machining processes such as milling, honing, and/or
drilling and reaming. In these machining processes the casting is
carefully positioned in a fixture and a cutting tool, carried and
powered by an operator or computer controlled machine tool, cuts a
cast surface to remove chips of cast metal to bring the surface to
a specified finish and dimension. During the metal removal
operation the machined surface is flooded with a machining fluid
for the purposes of cooling and lubricating the region impacted by
the cutting tool. The lubrication promotes cutting by minimizing
adherence of tool and work. Ultimately, the machining fluid is
drained from the machining area for recovery and re-use, or for
disposal.
[0005] It is an object of this invention to provide a method for
making aluminum alloy castings that can be machined without the use
of a machining fluid. In accordance with this invention such a
practice is termed "dry machining." It is a more specific object of
this invention to provide an aluminum alloy casting that can be dry
machined.
SUMMARY OF THE INVENTION
[0006] The relatively high silicon content of aluminum casting
alloys increases the difficulty with which they are machined and
has required the use of a machining fluid, typically a liquid based
fluid. The purpose and goal of this invention is to accomplish dry
machining of certain compositionally modified aluminum alloy
castings without damage of the part and with tool life that is
comparable to fluid lubricated and cooled machining.
[0007] In accordance with the invention suitable
silicon-containing, aluminum casting alloys are modified to contain
relatively small amounts of certain finely dispersed elements that
are softer and lower melting than the aluminum casting alloy matrix
material, and which significantly increase the machinability of
surfaces of a casting into which they are incorporated. These
elements include bismuth, indium, lead and tin and one or more of
them may be added to the casting alloy. These lubricity-imparting
additives are not very soluble in the solidified aluminum-rich
matrix phase of the castings although they may combine with
alloying constituents such as magnesium. Thus, they are dispersed
as very small, globular bodies in the cast metallurgical
microstructure. And in this form, the dispersed phase of low
melting elements surprisingly enables drilling and other metal
removal machining of surfaces of the casting without the use of
machining fluids. Sufficiently low amounts of one or more of soft
elements are added to the casting alloy so that the dispersed,
relatively low melting, soft phase (either as a pure additive phase
or mixed with another constituent of the alloy in a low melting
phase) is present in the solid casting more or less uniformly
through the casting, and surfaces of choice can be machined
regardless of the position of the machined surface.
[0008] Aluminum casting alloys typically contain a significant
amount of silicon to increase the fluidity of the molten phase for
castablity and mold filling. Silicon is also added to reduce the
thermal expansion of the casting, as well as to increase its
corrosion and wear resistance. The silicon content of aluminum
alloys for casting may range from about four percent to about
eighteen percent by weight of the cast alloy. Aluminum casting
alloys for automotive and other applications such as aerospace also
contain suitable amounts of one or more of copper, iron, manganese
and/or magnesium for solid solution strengthening and for formation
of strengthening phases. Other alloying constituents or impurities
such as nickel, zinc, titanium, chromium and rare earth elements
may also be present in the casting alloy to enhance the physical
properties of a cast product.
[0009] But in accordance with this invention, small additions of
one or more of bismuth, indium, lead and/or tin are made to these
casting alloys for internal lubricity and dry machining of the
castings. Typically a total of at least about 0.1% by weight of low
melting elements, alone or in combination, is added to the melt
before casting. The minimum amount of the additive depends on the
casting composition, its microstructure, and on the selected
additive(s). The minimum amount of additive may also depend on the
amount and severity of required machining operations. Preferably
the total addition of one or more of these soft, lubricity
imparting elements does not exceed about two percent by weight of
the casting so that the other properties of the casting are not
significantly altered. Bismuth and/or tin are preferred
additives.
[0010] Cemented tungsten carbide cutting tools are particularly
suitable for use in dry machining operations of this invention.
They provide a good combination of durability and cost.
[0011] These and other objects and advantages of the invention will
become more apparent from a detailed description of preferred
embodiments which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is an oblique view of a cast cylinder block for a V8
internal combustion engine for an automobile, and
[0013] FIG. 2 is a photomicrograph (at 1000.times.) of the
microstructure of Aluminum Alloy B319 casting alloy showing
globules of bismuth as the soft, low melting additive for dry
machining.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0014] This invention is applicable, for example, in making cast
parts in large volume for automotive applications. Vehicle engine
and transmission parts are examples of such parts. Most automotive
castings require some machining to produce surfaces to a shape
and/or dimensional specification. The machining requires the uses
of high quality and expensive precision cutting tools such as
drills, reamers and milling and honing tools. Heretofore the
machining has also required the use of machining fluids for part
and tool protection and for machine chip removal. The machining
practices have required close management to produce high quality
cast parts with good tool life and related management of machining
costs.
[0015] This invention is applicable to the making of cast aluminum
parts and enables dry machining of surfaces of the casting without
uneconomical reduction of cutting tool life. Cast aluminum parts
are made from many known casting alloys. Among those commonly used
for automobile parts are, for example, Aluminum Alloys 319.0,
B319.0, 333.0, 336.0, A356.0, 356.0, A360.0, A380.0, 381.0, 383.0,
390.0, and 396.0. The principal alloying components of these
commercial alloys in nominal parts by weight are as follows:
319-Si6Cu3, B319-Si6Cu4Mg, A356-Si7Mg, 333-Si9Cu3, 336-Si12Cu,
356-Si7Mg (Fe), A356-Si7Mg, A360-Si10Mg, A380-Si8Cu3Fe,
381-Si10Cu4Fe, 383-Si10Cu2Fe1, 390-Si17Cu4Fe1, and
396-Si11Cu2.25Fe0.45. In accordance with this invention, however,
small additions of one or more of bismuth, indium, lead, and or tin
are made to aluminum alloys such as these alloys for dry
machinability. For many dry machining applications the addition of
one, or a combination, of these lubricity-imparting elements is
suitably in the range of about 0.1% to about 2% by weight of the
casting.
[0016] In general, it is suitable to use tungsten carbide cutting
tools in the practice of this invention.
[0017] FIG. 1 is an oblique, outline view of a cast aluminum engine
cylinder block 10 for a V8 engine. Such an engine component is
often cast from an aluminum casting alloy such as a 319 alloy, a
356 alloy, a 390 alloy, or a 396 alloy. Such castings, especially
if they are of a complex part such as cylinder block 10, require a
substantial amount of machining in their manufacture to finished
parts. For example, each of the eight cylinder bores 12 (four are
visible in FIG. 1) is honed to a close dimensional tolerance and
degree of roundness. At the top of cylinder bores 12, cylinder
block casting 10 has a deck portion 14 that is machined very flat
to seal with a cylinder head casting, not shown. Several bolt holes
16 are bored or drilled from deck surface 14 for secure attachment
of a cylinder head on each V-portion of cylinder block 10. As is
known and illustrated in FIG. 1, an engine block casting has many
bolt holes, coolant passages, oil passages and the like that are
drilled, or drilled and reamed, or otherwise machined in the
manufacture of such a cast product. And there is a long succession
of such castings in an engine production line so that machining
operations and the cost of machining tools is very important in
such a manufacturing operation. It is now found that in many
applications of the machining of aluminum castings, the addition of
a suitable quantity of soft, low melting point element permits the
dry machining of the thus self-lubricated cast alloy surface.
[0018] Aluminum alloy B319 is a casting alloy used in cylinder
block, cylinder head, and inlet manifold applications. The
specified composition of B319 is, by weight, 5.0% to 7.5% silicon,
3.0% to 5.0% copper, 1.0% max iron, 0.1% to 0.6% manganese, 0.1% to
0.5% magnesium. 0.3% max nickel, 2.0% max zinc, 0.3% max lead, 0.1%
max tin, 0.15% max titanium, a total of 0.15% other elements and
the balance aluminum. A specific B319 alloy that was free of lead
and tin was used as a starting material in the following examples
and tests.
[0019] Drilling tests without any machining fluid were conducted on
a cast plate of B319 alloy to obtain baseline dry machining data.
The macro-hardness of the surface of the plate was determined to be
74 to 80 Brinell and its microhardness was 90 Knoop units. In the
machining tests, commercial one-quarter inch diameter, tungsten
carbide drills were used to drill closed end holes to a depth of
three-quarters of an inch. The drilling of such closed end holes is
considered a particularly challenging operation for successful dry
machining. Only twelve holes could be drilled in the unlubricated
B319 plate before the drill had to be discarded. The drilling of
the twelve holes required an average power of 2.8 Kw and torque
values reaching 2.6 Nm. It is to be understood that there are
variations between identical or like castings and between like
cutting tools. Accordingly, there will be variations in cutting
data obtained from testing using like tools and castings. But with
repeated tests; a difference in the machinability of different
castings becomes apparent.
B319 Alloys Modified with Bismuth
[0020] Samples of the B319 aluminum alloy were then modified by the
addition of bismuth. The bismuth-containing B319 material was
prepared as follows.
[0021] Bismuth needles (1/2-in length by 1/8-in wide at
mid-section) were added in the desired amount (0.2%, 0.5% and 1% by
weight in these examples) to melted aluminum B319 alloy at
1360.degree. F. using a perforated spoon/ladle. The needles were
gently stirred and dispersed into the melt with the spoon moving
the melt in a circular pattern with the needles held at a level of
about two inches below the melt surface. This was continued for
about two minutes and then the melt was held at temperature for 30
minutes. The alloy melt was then stirred for one minute and
degassed with nitrogen gas using a rotary degasser at 650-700 rpm
for about 15 minutes (for a normal melt of 30 lbs). The alloy melt
was then gently skimmed and the temperature stabilized at
1310.degree. F. for about 5 minutes before the crucible was pulled
out of the furnace. The alloy, having cooled to 1260.degree. F.,
was poured into Zircon sand molds. Following shakeout and cleaning,
the cast plates were heat treated using a conventional T-5 aluminum
alloy heat treatment schedule to minimize bismuth segregation.
[0022] B319 aluminum casting alloys were prepared respectively
containing, by weight, 0.2% bismuth, 0.5% bismuth and 1.0% bismuth.
FIG. 2 is a photomicrograph at 1000-fold magnification showing a
portion of a bismuth-containing B319 casting. The photomicrograph
shows a matrix material of Al--Si eutectic material 200 and
globular bismuth 202 adhered to needles of AlFeSi intermetallic
phases 204. While the eutectic acicular silicon needles make a
casting more difficult to machine, the small amount of soft bismuth
globules markedly increase its machinability.
[0023] Hardness Testing of the Bi Modified B319 Material:
TABLE-US-00001 Microhardness Macrohardness Substrate (Knoop)
(Brinell) Conventional B319 90 74 to 80 B319 + 0.5% bismuth 90
74
[0024] It is seen that the addition of 0.5% by weight of bismuth
did not appreciably reduce the surface hardness of the cast plates.
But, as will be seen, the bismuth additions did change the
machinability of the plates. Microstructure analysis of
conventional B319 and Bi-containing B319 showed no difference among
the two alloys except that small globules of elemental bismuth are
clearly visible in the B319 alloy with 0.5% bismuth added as seen
in FIG. 2. These small globules are believed to be responsible for
the lubricious characteristics of the alloys containing bismuth
and/or tin, indium and lead.
[0025] Dry machining tests where rows of one-quarter inch closed
holes were drilled to a depth of three-quarters inch using the
separate self-lubricating bismuth-containing B319 alloy plates
showed lower horsepower and torque, good hole integrity, small chip
size, and at least two orders of magnitude improvement in tool life
compared to dry machining of the conventional B319 alloy plate.
TABLE-US-00002 Tool Life Substrate (no. of holes) Power (Kw) Torque
(Nm) Conventional Al B319 12 2.8 2.6 Al B319 + 0.2% Bi 667 2.8 2.0
Al B319 + 0.5% Bi >5000 1.9 1.5 Al B319 + 1.0% Bi >5000 1.8
1.2
[0026] The benefits to dry machining of Bi-containing B319 aluminum
alloy are thus demonstrated. The tool life and power consumption
values are comparable to those obtained when machining bismuth-free
B319 alloy castings using machining fluids. And the costs of
handling and disposing of the fluids is avoided. Benefits of dry
machining are still appreciable even if it is not practical to use
dry machining in all operations on a casting or family of
castings.
B319 Alloys Modified with Tin
[0027] Samples of the B319 aluminum alloy were then modified by the
addition of tin. Tin was selected for testing because of its benign
health and safety effects. Preliminary microstructure tests also
showed that, unlike bismuth, tin does not seem to form the higher
melting intermetallics with the magnesium in the alloy. The
tin-containing B319 material was prepared as follows.
[0028] Tin chunks were added in the desired amount (0.1% to 0.5% by
weight in these examples) to melted aluminum B319 alloy at
1360.degree. F. using a perforated spoon/ladle. The chunks were
gently stirred and dispersed into the melt with the spoon moving
the melt in a circular pattern with the needles held at a level of
about two inches below the melt surface. This was continued for
about two minutes and then the melt was held at temperature for 30
minutes. The alloy melt was then stirred for one minute and
degassed with nitrogen gas using a rotary degasser at 650-700 rpm
for about 15 minutes (for a normal melt of 30 lbs). The alloy melt
was then gently skimmed and the temperature stabilized at
1310.degree. F. for about 5 minutes before the crucible was pulled
out of the furnace. The alloy, having cooled to 1260.degree. F.,
was poured into Zircon sand molds. Following shakeout and cleaning,
the cast plates were heat treated using conventional T-6 aluminum
alloy heat treatment schedule to minimize tin segregation. T-6 heat
treatment produced a harder substrate (96-100 Brinell hardness)
compared to T-5 (74-80 Brinell hardness).
[0029] Bismuth, indium, and/or lead may be added with tin,
depending on the choice of master alloy for the alloy to be
modified for dry machinability. Certain combinations of the above
as master alloys may enable more effective dissolution and
dispersal of the dry machining agents into the melt. As an example,
binary master alloys generally have lower melting points than the
individual alloys. The majority of aluminum alloys are heat treated
to enhance the properties above those achievable in the as-cast (F)
state. In the example given, B319 was subjected to T-6 aging,
although this alloy is also used with T-4, T-5, or T-7, etc., heat
treatments depending on the final requirements for the casting. It
is recognized that these heat treatments may affect the benefit of
the dry machining agent, positively or negatively, depending on the
diffusion behavior and relative stabilities of intermetallics in
the alloy, which in turn affect the degree of dispersion and
coarseness of the dry machining agents in the final
microstructure.
Hardness Testing of the Tin-Modified B319 Material:
B319 Alloys Modified with Indium or Lead
[0030] Separate samples of B319 aluminum alloy were then modified
by the separate additions of small quantities of indium or lead.
Molten indium-containing aluminum alloys and molten lead-containing
aluminum alloys were prepared in the same manner as the above
described bismuth-containing and tin-containing B319 alloys. Cast
plates were formed from the respective molten alloys. Again, it was
found that the hardness of the B319 castings was not affected by
small additions (no more than about two percent by weight) of
indium or lead. Small globules of indium or lead were uniformly
dispersed throughout the respective cast plates.
[0031] Dry machining tests were conducted on indium containing B319
alloy castings with the following results: TABLE-US-00003 Tool Life
Substrate (no. of holes) Power (Kw) Torque (Nm) Conventional Al
B319 5 7.2 6.6 Al B319 + 0.25% In >1800 4.4 3.6 Al B319 + 0.5%
In >2600 3.2 2.7
[0032] The benefits to dry machining of In-containing B319 aluminum
alloy are thus demonstrated. The tool life and power consumption
values are comparable to those obtained when machining indium-free
B319 alloy castings using machining fluids.
[0033] Dry machining tests were conducted on lead-containing B319
alloy castings with the following results: TABLE-US-00004 T-5 T-6
Substrate (Brinell) (Brinell) Conventional B319 74-80 96-100 B319 +
0.5% tin 74-80 96-100
It is seen that the addition of up to 0.5% by weight of tin did not
appreciably reduce the surface hardness of the cast plates. But, as
will be seen, small tin additions did change the machinability of
the plates.
[0034] Dry machining tests where rows of either one-quarter inch
closed holes or 6.8 mm thru-holes were drilled to a depth of either
three-quarters inch (closed holes) or one inch (thru-holes) using
the self-lubricating tin-containing B319 alloy plates showed lower
horsepower and torque, good hole integrity, small chip size, and at
least two orders of magnitude improvement in tool life compared to
dry machining of the conventional B319 alloy plate. TABLE-US-00005
Tool Life Substrate (no. of holes) Power (Kw) Torque (Nm)
Conventional Al B319 5 to 12 7.3 6.4 Al B319 + 0.10% tin >5000
5.9 4.3 Al B319 + 0.15% tin >5000 3.1 3.0 Al B319 + 0.25% tin
>5000 3.7 3.0 Al B319 + 0.50% tin >5000 2.7 2.5
[0035] The benefits to dry machining of Sn-containing B319 aluminum
alloy are thus demonstrated. The tool life and power consumption
values are comparable to those obtained when machining tin-free
B319 alloy castings using machining fluids. Benefits of dry
machining are still appreciable even if it is not practical to use
dry machining in all operations on a casting or family of castings.
TABLE-US-00006 Tool Life Substrate (no. of holes) Power (Kw) Torque
(Nm) Conventional Al B319 11 3.8 2.0 Al B319 + 0.09% Pb 160 2.8 2.0
Al B319 + 0.15% Pb >396 1.9 1.3
[0036] Again, the benefits to dry machining of Pb-containing B319
aluminum alloy are thus demonstrated. The tool life and power
consumption values are comparable to those obtained when machining
lead-free B319 alloy castings using machining fluids.
[0037] The practice of the invention has been illustrated by
additions of single elements to a specific aluminum casting alloy
in a series of drilling tests. However, these lubricity adding
elements may be beneficially used either individually or in
combination in other casting alloys and in other machining
operations. And the benefits of dry machining are still important
even if it is not practical to use dry machining in all operations
on a casting or family of castings. The scope of the invention is
limited only by the following claims.
* * * * *