U.S. patent application number 13/388530 was filed with the patent office on 2012-05-24 for tool grinding machine.
This patent application is currently assigned to GLEASON CUTTING TOOLS CORPORATION. Invention is credited to Roger L. Hackman, Wayne Martin, Mark A. Ritchie.
Application Number | 20120129434 13/388530 |
Document ID | / |
Family ID | 43513767 |
Filed Date | 2012-05-24 |
United States Patent
Application |
20120129434 |
Kind Code |
A1 |
Hackman; Roger L. ; et
al. |
May 24, 2012 |
TOOL GRINDING MACHINE
Abstract
A multi-axis computer controlled machine tool for relief
grinding of single and multiple start threaded hobs (46). The
machine comprises an angular oriented spindle (65) that can be
angularly (swivel) positioned thereby providing the flexibility to
utilize both cup-shaped grinding wheels (55) and pencil-shaped
grinding wheels (52) for grinding of hob and milling cutter
relieved tooth geometry without exchanging grinding spindles
assemblies or modifying the machine construction to accommodate two
types of grinding methods or utilizing an additional machine axis
for the spindle re-orientation.
Inventors: |
Hackman; Roger L.;
(Winnebago, IL) ; Martin; Wayne; (Roscoe, IL)
; Ritchie; Mark A.; (Machesney Park, IL) |
Assignee: |
GLEASON CUTTING TOOLS
CORPORATION
Loves Park
IL
|
Family ID: |
43513767 |
Appl. No.: |
13/388530 |
Filed: |
September 23, 2010 |
PCT Filed: |
September 23, 2010 |
PCT NO: |
PCT/US10/49963 |
371 Date: |
February 2, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61245309 |
Sep 24, 2009 |
|
|
|
Current U.S.
Class: |
451/48 ; 29/27R;
451/177; 451/179; 451/236 |
Current CPC
Class: |
Y10T 29/5109 20150115;
B24B 41/04 20130101; B24B 3/022 20130101; B24B 3/024 20130101 |
Class at
Publication: |
451/48 ; 451/177;
451/236; 451/179 |
International
Class: |
B24B 3/02 20060101
B24B003/02; B24B 41/04 20060101 B24B041/04 |
Claims
1. A machine for grinding rotary cutting tools, said machine
comprising: a table, a workpiece spindle for rotation of a
workpiece about a workpiece axis; a tool spindle for rotation of a
tool about a tool axis, a vertical assembly having a first side
facing said workpiece spindle; said tool spindle being located on
said first side and being movable vertically along said first side
of said vertical assembly, said tool spindle being capable of
swiveling about a swivel axis extending generally perpendicular to
said first side; said tool spindle being oriented slanted with
respect to said first slide at a predetermined slant angle.
2. The machine of claim 1 wherein said vertical assembly is located
on said table and is movable in at least one of a longitudinal
direction of said table and a width direction of said table.
3. The machine of claim 1 wherein said slant angle is 25
degrees.
4. The machine of claim 1 wherein said tool comprises a
pencil-shaped grinding wheel.
5. The machine of claim 1 wherein said tool comprises a cup-shaped
grinding wheel.
6. The machine of claim 1 wherein said tool spindle is located in a
swivel assembly with a probe being positioned on said swivel
assembly.
7. The machine of claim 1 further including an automatic tool
changing device comprising multiple tool storing stations.
8. The machine of claim 1 being operable to provide at least one of
a radial cam motion and an offset radial cam motion of said tool
relative to said workpiece.
9. The machine of claim 8 being further operable to additionally
impart an oscillating motion of said tool superimposed on said at
least one of a radial cam motion and an offset radial cam
motion.
10. The machine of claim 1 wherein said workpiece comprises a
single start hob, a multiple start hob or a milling cutter.
11. A method of grinding rotary cutting tools with a grinding wheel
on a grinding machine, said method comprising: providing for
rotation of said rotary cutting tool about a workpiece axis;
providing for rotation of said grinding wheel about a tool axis;
providing relative movement between said rotary cutting tool and
said grinding wheel in up to three mutually perpendicular
directions; providing for swiveling of said grinding wheel about a
swivel axis, said swivel axis being perpendicular to a vertically
oriented first side of a vertical assembly on said grinding
machine, said first side facing said rotary cutting tool, said
grinding wheel being oriented slanted with respect to said first
side at a predetermined slant angle; bringing said grinding wheel
and said rotary cutting tool into engagement with one another and
moving said grinding wheel and said rotary cutting tool relative to
one another to effect at least one of a radial cam motion and an
offset radial cam motion.
12. The method of claim 11 further comprising oscillating said
grinding wheel and superimposing the oscillating on said at least
one of a radial cam motion and an offset radial cam motion.
13. The method of claim 11 wherein said slant angle is 25
degrees.
14. The method of claim 11 wherein said grinding wheel comprises
one of a pencil-shaped grinding wheel or a cup-shaped grinding
wheel.
15. The method of claim 11 wherein said workpiece comprises a
single start hob, a multiple start hob or a milling cutter.
Description
FIELD OF THE INVENTION
[0001] The present invention is directed to machine tools, such as
tool grinding machines, and in particular to multi-axis, high
precision, computer controlled machine tools for grinding of
relieved tooth profiles of rotary cutting tools.
BACKGROUND OF THE INVENTION
[0002] In the grinding of tooth profiles of cutting tools, such as
gear hobs, worm gear hobs, constant pitch normal base hobs, and
milling cutters with module sizes greater that 8 module, a
multitude of grinding wheels are use to complete the entire tooth
profile on both flanks and tip features. As the module size
increases from 8 to approximately 16, different approaches to
grinding can be used depending on the desired finished tooth
re-sharpening life and the width of the tooth space at the root of
the profile. The tooth re-sharpening life or length of the cam
relieved tooth surface can be maximized using pencil-shaped tapered
cone grinding wheels having relatively small diameters in
comparison to length. The relieved length of the tooth surface is
dependent on the interference point of the grinding wheel with the
next adjacent tooth when radial cam grinding the relief along the
tooth helix of the hob thread or the index position in the case of
a milling cutter.
[0003] Dependent of geometry of the tooth space there is a
practical surface speed limit for grinding and bending/shear
strength weakness of the tip of the pencil-shaped wheel that must
be considered. When approaching the pencil-shaped wheel grinding
practical application limitations, a different process of grinding
utilizing cup-shaped grinding wheels with relatively larger
diameters compared to width can be employed. Surface speed of
grinding and strength of the portion of the wheel grinding the root
portion of the tooth are overcome. However, a disadvantage of
cup-shaped grinding wheels is that their larger diameters limit the
length of the cam relieved tooth surface to the interference point
as described previously. As the module size increase above 16
module and up to 50 module, the use of a cup-shaped wheel is
restricted because of the wheel to adjacent tooth interference
described. In most cases, a pencil-shaped tapered cone grinding
wheel must be used for module hob tooth sizes over 16 module in
order to provide an adequate tooth relieved length for
re-sharpening life.
[0004] Current tool manufacturing practices use the blending of
profiles produced from multiple grinding wheels and wheel shapes to
grind the tooth flanks, tooth tip radii, and tooth tip outside
diameter separately in multiple (e.g. up to five) setups. With CNC
machine motion technology and rotary truing/dressing devices it is
possible to contour the above mentioned pencil-shaped or cup-shaped
grinding wheels to incorporate multiple features, for example, the
tooth bottom radius/ramp, tooth pressure angle flank, tooth tip
radius, and tooth tip outside diameter. In the example mentioned,
the finish grinding process may be reduced to blending profiles of
just two pencil-shaped or cup-shaped grinding wheels. Probing of
profiles, utilizing probes such as the Renishaw 3-D with acoustical
touch sensing, assists in the relative positioning of the grinding
wheel to the left and right tooth reference points and blending of
profiles to achieve the required tooth profiles and tooth
thickness.
[0005] Given the above, many tool manufacturing facilities employ a
plurality of grinding machines dedicated to either pencil-shaped
wheels or cup-shaped wheels. A few incorporate a machine tool
design to allow the exchange of spindle assemblies and drive
mechanisms to accommodate the physical orientation for either
pencil-shaped wheels or cup-shaped wheels. Most require the use of
dedicated machines with physical orientation as capable for only
pencil-shaped wheel or only cup-shaped wheel grinding. In most if
not all cases, the cam relief motion on the machine tools use one
axis to provide the radial motion for the cam relief which limits
the machine's flexibility.
SUMMARY OF THE INVENTION
[0006] The present invention is directed to a machine tool with an
angular oriented spindle that can be angularly positioned (swivel)
thereby providing the flexibility to utilize both cup-shaped and
pencil-shaped grinding wheels for grinding of hob and milling
cutter relieved tooth geometry without exchanging grinding spindles
assemblies or modifying the machine construction to accommodate two
types of grinding methods or utilizing an additional machine axis
for the spindle re-orientation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIGS. 1(a), 1(b) and 1(c) illustrate the lead setting
angular relationships of a cup-shaped grinding wheel to a hob tooth
profile of universal module size.
[0008] FIGS. 2(a), 2(b) and 2(c) illustrate the lead setting
angular relationships of a pencil-shaped grinding wheel to a hob
tooth profile of universal module size.
[0009] FIG. 3 shows the design planes relative to the radial cam
relieving motion from the front to back profiles of the hob along
the involute helicoids.
[0010] FIG. 4 illustrates the change in pressure angle from front
to back of the constant base pitch hob tooth profile.
[0011] FIG. 5 illustrates the relationships and direction of cam
relief for the machine major components, hob workpiece and grinding
wheel spindle assembly orientated for using pencil-shaped grinding
wheels.
[0012] FIG. 6 illustrates the relationships and direction of cam
relief for the machine major components, hob workpiece and grinding
wheel spindle assembly orientated for using cup wheels
[0013] FIG. 7 is an enlarged view of the inventive grinding spindle
assembly in its operative position in a machine.
[0014] FIG. 8 is an enlarged view of an automatic wheel exchange
unit attached to the machine base for exchanging grinding wheel
packs and coolant manifolds between the grinding spindle mounting
interface and storage stations.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0015] Before any features and at least one construction of the
invention are explained in detail, it is to be understood that the
invention is not limited in its application to the details of
construction and the arrangements of the components set forth in
the following description or illustrated in the drawings. The
invention is capable of other constructions and of being practiced
or being carried out in various ways. Also, it is understood that
the phraseology and terminology used herein is for the purposes of
description and should not be regarded as limiting.
[0016] The use of "including", "having" and "comprising" and
variations thereof herein is meant to encompass the items listed
thereafter and equivalents thereof as well as additional items. The
use of letters to identify elements of a method or process is
simply for identification and is not meant to indicate that the
elements should be performed in a particular order.
[0017] Although references may be made below to directions such as
upper, lower, upward, downward, rearward, bottom, top, front, rear,
etc., in describing the drawings, there references are made
relative to the drawings (as normally viewed) for convenience.
These directions are not intended to be taken literally or limit
the present invention in any form. In addition, terms such as
"first", "second", "third", etc., are used to herein for purposes
of description and are not intended to indicate or imply importance
or significance.
[0018] FIGS. 1(a), 1(b) and 1(c) show the angular relationships of
a grinding wheel in a coordinate system for a cup-shaped grinding
wheel 1 in contact along a involute helicoid 2 of one of a
sequential series of hob teeth 3 along a thread path 4 with single
or multiple starts with a front profile 5 at the cutting face
defined by the intersection of the thread involute helicoid 2 and a
straight or helical flute 6 and with a relieved back profile 7 near
the end of the sharpening life of the tooth position that is
restricted in length by the interference point 8 of the grinding
wheel 1 with the adjacent hob tooth 9 along the involute helicoid
2. Relationships defined in FIGS. 1(a), 1(b) and 1(c) are the fixed
angle HA (angle 10) of the grinding spindle assembly, the grinding
wheel pressure angle PA (angle 11), and the axial pressure angle
APA (angle 12) of the hob tooth, the lead angles LAS.sub.1 and
LAS.sub.2 of the involute helicoids 13 as viewed from the front,
and the swivel setting angle setting 14 of the grinding head
assembly as viewed from the front, and the relieving direction 15
relative to the coordinate system.
[0019] FIGS. 2(a), 2(b) and 2(c) show the angular relationships of
the grinding wheel in a coordinate system for a pencil-shaped or
cone-shaped grinding wheel 16 in contact along a involute helicoid
17 of one of a sequential series of hob teeth 18 along a thread
path 19 with single or multiple starts with a front profile 20 at
the cutting face defined by the intersection of the thread involute
helicoid 17 and a straight or helical flute 21 and with a relieved
back profile 22 near the end of the sharpening life of the tooth
position that is restricted in length by the interference point 23
of the grinding wheel 16 with the adjacent hob tooth 24 along the
involute helicoid 17. Relationships defined in the FIGS. 2(a), 2(b)
and 2(c) are the fixed angle 25 of the grinding spindle assembly,
angle B (angle 26) which is difference between pressure angle PA
trued/dressed on the grinding wheel and the axial pressure angle
APA (angle 27) of the hob tooth, the lead angles LAS.sub.1 and
LAS.sub.2 of the involute helicoids 28 as viewed from the front,
and the swivel setting angle setting 29 of the grinding head
assembly as viewed from the front, and the relieving direction 30
relative to the coordinate system.
[0020] FIG. 3 defines the design planes used for optimizing the
grinding wheel geometry to reduce deviation from the theoretical
tooth profiles with or without involute modifications and the
inherent error of the hob tooth grinding wheel to tooth pressure
angle conjugant contact points. Design planes are defined at the
front 31, midpoint of cam relief 32 and back 33 sections. Also
shown are the related nominal hob outside radius 34, nominal hob
midpoint radius 35, and end of sharpening life nominal hob radius
36.
[0021] FIG. 4 shows the characteristic error for a hob tooth of an
involute profile produced by ordinary machine tool manufacturing
methods. Theoretically, a new and different hob is produced every
time the hob is sharpened from front to back. A sharpened hob will
cut a gear only to the approximate form as the new hob. In
addition, the more the hob is sharpened back, the worse the error
becomes. FIG. 4 shows two axial sections of the hob tooth involute
helicoid profile, without involute modifications for the
illustration, representing the theoretically correct front position
of a new hob 37 and the sharpened back position 38 near the end of
the sharpening life along the tooth involute helicoid. The inherent
error 39 (error A and error B) occurs when a grinding wheel or form
tool, which by nature has a fixed geometric profile, attempts to
contact this helicoid surface at both sections 37 and 38 when
driven in a fixed path by the machines relieving motions.
[0022] The recognition of the inherent error problem discussed
above and attempts to solve are known from "Buckingham, Earl, Spur
Gears, McGraw-Hill Book Co. Inc., NY, 1928", wherein it is
discussed relieving hob tooth surfaces utilizing special
characteristic of the involute helicoids. With the disclosed
method, contact between the relieved surface and the grinding wheel
will be the straight line generatrix of the involute helicoids and
the relieved surface itself will be an involute helicoid. However
this method makes no provision for modifications such as
semi-topping ramps, involute modifications, and protuberance. For
fine pitch hobs the inherent error is negligible and for coarse
pitch hobs of low quality the magnitude of the error is
unimportant. For accurate hobs the inherent error point of can be
identified with the following equation:
Q = ( Hob Outside Diameter ( mm ) ) ( Normal Module ( mm ) )
.times. ( Number of Hob Threads ) ( 1 ) ##EQU00001##
[0023] When the Q factor is greater than 20, it marks the
approximate region where hobs with a straight-line axial profile
will cut gears which, for all practical purposes, have true
involute profiles. As the Q factor decreases, the hob tooth axial
profile becomes more curved and the potential for inherent error
increases.
[0024] Computer analysis of the grinding wheel contact pattern with
modified tooth involute helicoid, setup angles and offset of the
grinding wheel can optimize the grinding process to reduce the
inherent error but can not eliminate it. Corrective machine motions
to change the pressure angle relations during the relieving process
can minimize the inherent error to acceptable level to provide a
more accurate, longer life, hobs. The grinding wheel head assembly
40 (FIG. 6) of this invention can provide the grinding wheel
oscillating motion synchronized with the relieving motion to
minimize the inherent error.
[0025] The CNC Controller (such as a Fanuc 160iB computer control)
of the inventive grinding machine is operable to provide the radial
or offset radial cam relieving motion either from a single axis
moving in a horizontal plane when the grinding head assembly is
positioned about a horizontal plane for using cup wheels for
grinding, or at a compound angle about the vertical plane using
multiple axes to provide the cam relieving motion when the grinding
head assembly is positioned about a vertical plane for using pencil
wheels for grinding. In addition, the grinding head assembly is
capable of imparting an oscillating motion to the grinding wheel
superimposed on the radial or offset radial cam relieving motion
which acts to change the swivel orientation of the grinding wheel
relative to the pressure angle of the hob tooth profile thereby
reducing the tooth pressure angle at the back of the hob tooth
relative to the front and midpoint of the relieved tooth profile.
This motion makes it possible to manufacture constant normal base
pitch hobs which could not be produced by hob grinding prior to the
present invention.
[0026] FIG. 5 illustrates the inventive machine having a table 41,
direct motor driven head stock 42, live center tailstock 43, steady
rests 44 to assist loading arbors assemblies, work holding arbor 45
(FIG. 6), hob work piece 46, linear motor driven drive longitudinal
axial slide assembly 47, linear motor driven vertical slide
assembly 48, linear motor driven horizontal radial in-feed slide
assembly 49, grinding spindle swivel assembly 50 orientated for
pencil wheel grinding, the slanted (preferably 25 degrees) grinding
spindle housing 51 with spindle 65, and pencil grinding wheel 52
with spindle mounted adapter 66. Vector 53 illustrates the relative
compound angle radial relieving motion (i.e. cam relieving motion).
Five axes synchronization is needed for the head stock 42 and the
longitudinal axial slide 47 to generate the hob thread lead, the
vertical slide assembly 48 and horizontal slide assembly 49
combined to generate the cam relieving motion 53, and the optional
oscillation of the grinding wheel swivel assembly 50 superimposed
on the cam reliving motion 53 to minimize the inherent pressure
angle profile errors.
[0027] FIG. 6 illustrates machine table 41, direct motor driven
head stock 42, live center tailstock 43, the steady rests 44 to
assist loading arbors assemblies, work holding arbor 45, hob work
piece 46, linear motor driven drive longitudinal axial slide
assembly 47, linear motor driven vertical slide assembly 48, linear
motor driven horizontal radial in-feed slide assembly 49, grinding
spindle swivel assembly 50 orientated for cup-shaped wheel
grinding, slanted grinding spindle housing 51 (preferably 25
degrees) with spindle 65, cup-shaped grinding wheel 55 with spindle
mounted adapter 66. Vector 56 illustrates the relative compound
angle radial relieving motion (i.e. cam relieving motion). Three
axes synchronization is needed to produce the cam thread relieving
positioning the head stock 42 and the longitudinal axial slide 47
to generate the hob thread lead, the horizontal slide assembly 49
to generate the cam relieving motion 56. The offset setting angle
of the grinding wheel swivel assembly 50 and vertical axes 48
height are held at a fixed position during the cam relieving
process during cup wheel grinding.
[0028] The grinding wheel head assembly 40 mounted for vertical
motion preferably comprises a variable speed high frequency
grinding spindle and capable of being automatically swung through a
vertical plane arc of at least plus or minus 120 degrees to a
desired setup compound angle dependent on the profile of grinding
wheel, thread lead of the cutter, and orientation of the grinding
spindle. The grinding spindle housing 51 is orientated from a
vertical swivel plane of the grinding wheel head 40 and in a fixed
angular position, preferably 25 degrees from the vertical plane,
with the grinding wheel position closer to the work piece and the
direct drive motor of the spindle 65 away from the work piece.
[0029] The preferred 25 degree orientation of the grinding spindle
65 provides additional clearance between the grinding spindle motor
housing 51 and the outside diameter of the work piece when using
cup shaped grinding wheels 55 (FIG. 6), with grinding wheel head 40
positioned approximately plus or minus 30 degrees from a horizontal
plane, and with relief grinding using a quick horizontal motion
combined with rotary and longitudinal motions. The preferred 25
degree orientated grinding spindle can also facilitate pencil
shaped grinding wheels 52 (FIG. 5) with the grinding wheel head 40
positioned approximately plus or minus 40 degrees or thereabout
from a vertical plane resulting in a relief grinding motion using
both quick vertical and horizontal motions combined with rotary and
longitudinal motions. In addition to the motions described, the
grinding wheel head assembly can be oscillated approximately plus
or minus 31/2 degrees from the setup angular position during the
relief motions to produce coarse module normal base pitch hobs
which will have corrected tooth profile pressure angle at the back
as well as at the front relieved hob tooth flank. While the fixed
25 degree orientated of the grinding spindle is preferred, the
present invention is not limited thereto. Other angular
orientations are contemplated and are within the scope of the
present disclosure.
[0030] FIG. 7 illustrates additional machine construction including
a grinding wheel exchanger cabinet 57, the grinding wheel swivel
assembly 50 that includes the slanted grinding spindle 51, a probe
58 (e.g. Renishaw 3D) for setup and inspection functions and a
table mounted rotary dresser (wheel truing) assembly 59. The
automatic grinding of hobs and blending of multiple wheel profile
preferably includes the in-cycle exchange of grinding wheel packs
mounted on spindle adapters, determination of the rough grinding
wheel locations relative to pitch points on respective tooth flanks
of a tooth space by use of the probe 58, use of acoustical touch
sensing to verify the contact position of the grinding wheel
profile to the hob existing tooth profile, contouring using the
machine axes with acoustical touch sensing for generating grinding
wheel profiles on a multitude of grinding wheel technologies
(including super abrasives like CBN) with the use of the table
mounted dresser 59, measuring of ground profile for blending and
error correction with the probing system 58, and the automatic
analysis and feedback for error correction of profiles.
[0031] FIG. 8 illustrates an example of an automatic wheel
exchanger 60 with multiple stations mounted on a rotary carousel 61
that stores wheel pack assembled to grinding spindle adapters
(collectively 62) and associated coolant manifolds 63. A
programmable slide assembly 64 facilitates the simultaneous
exchange of wheel packs 62 and coolant manifolds 63 between the
grinding spindle 51 and the multiple stations on the carousel 61.
The automatic wheel and coolant manifold exchange device 60
(located in cabinet 57) is attached to the machine tool to
facilitate complete automatic grinding of a hob or milling cutter.
The automatic wheel changer device can stage a multitude of
grinding wheels mounted on spindle adapters with associated coolant
manifolds and automatically exchange the grinding wheel pack with
coolant manifolds between the device and grinding spindle thus
automatically providing the multitude of wheels needed to complete
the entire hob or milling cutter tooth profile. The standard number
of stations in the wheel changer device is preferably 8 but
magazine storage devices can be interfaced to the wheel exchanger
to increase the number of available wheel packs with coolant
manifolds available or only limited by space restrictions. A
probing system (e.g. Renishaw 3D) is incorporated to provide the
tooth space setup positioning to multiple grinding wheels as well
as post-grinding inspection with automatic profile path
correctional feedback for truing/dressing. Measuring and reporting
of ground profile quality according to current AGMA and DIN
internationally accepted hob and milling cutter standards is also
contemplated.
[0032] The inventive machine is capable of grinding single and
multiple start hobs preferably greater than 200 mm outside diameter
and in the range of about 8 to about 50 module tooth sizes with
tooth cutting faces defined by multiple straight or helical flutes
(gashes). The machine can also relief grinding large milling
cutters preferably greater than 200 mm with axial indexing of teeth
and tooth cutting faces defined by multiple straight or helical
flutes. The machine preferably incorporates programmable quick
response direct and linear motor driven axes with precision glass
scale position feedback in a defined combination of rotational,
vertical, horizontal, longitudinal, and grinding head swivel
motions to relief grind each tooth profile of a hob or milling
cutter. Tapered or contoured outside diameter hobs and milling
cutters may also be ground. Multiple grinding wheels may be
required for grinding each tooth space to complete the left and
right flanks, tip radii, and tip diameter.
[0033] While the invention has been described with reference to
preferred embodiments it is to be understood that the invention is
not limited to the particulars thereof. The present invention is
intended to include modifications which would be apparent to those
skilled in the art to which the subject matter pertains without
deviating from the spirit and scope of the appended claims.
* * * * *