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發(fā)表于 2011-6-24 22:02:25
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Although almost any book and/or text on metal cutting, cutting tool design, and 4 n3 z |; j6 o
manufacturing process discusses to a certain extent the tool geometry, the body of 4 b6 s0 s+ }/ V* Z2 b0 F, Y
knowledge on the subject is scattered and confusing. Moreover, there is no clear
$ F$ v. d. O9 w! f u" qobjective(s) set in the selection of the tool geometry parameters so that an answer ' ?' ?4 a- l, {2 f9 _
to a simple question about optimal tool geometry cannot be found in the literature
* M% ]5 i) Z5 V8 u% ^- q. t% M& m2 ~on the subject. This is because a criterion (criteria) of optimization is not clear, on $ I2 w3 Z9 x3 _: e# a
one hand, and because the role of cutting tool geometry in machining process
( K; |9 a5 l/ P# Noptimization has never been studied systematically, on the other. As a result, many
8 ]" B2 a x4 Q6 Gpractical tool/process designers are forced to use extremely vague ranges of tool
* p$ l( y7 G; }$ K4 s) b2 {6 g* ]2 Ggeometry parameters provided by handbooks. Being at least 20+ years outdated, 7 K9 l2 k" Z" ?8 m
these data do not account for any particularities of a machining operation including
& W- m% r2 a3 Z. }( @" la particular grade of tool material, the condition of the machine used, the cutting
1 R3 z. Q. G- B, m+ m4 nfluid, properties and metallurgical condition of the work material, requirements to
- A1 p, O* i8 [# L8 \the integrity of the machined surface, etc. ! B4 ]3 w( P& F1 T# {" ^) g) n: T
Unfortunately, while today's professionals, practitioners, and students are
( p/ ^; u2 x R0 }& S0 T9 jinterested in cutting tool geometry, they are doomed to struggle with the confusing 3 U# J# x" M* i) N& m
terminology. When one does not know what the words (terms) mean, it is easy to & S6 t5 E/ R, d% g+ {: G
slip into thinking that the matter is difficult, when actually the ideas are simple, ) G; O' u6 C: N) V
easy to grasp, and fun to consider. It is the terms that get in the way, that stand as a 1 J2 D" L6 o- H+ n" L
wall between many practitioners and science. This books attempts to turn those
* C4 q, V* V( e. ]* b i$ iwalls into windows, so that readers can peer in and join in the fun of proper tool
8 T" W- y. B0 ?5 m6 kdesign. 7 \4 ~, U& z% }' _ P8 w* }
So, why am I writing this book? There are a few reasons, but first and foremost, 8 `& o- n+ |4 I. o
because I am a true believer in what we call technical literacy. I believe that
?9 o' Q6 y/ J* J' W. q3 feveryone involved in the metal cutting business should understand the essence and
) u1 s% M$ L" U& m$ W' L: Himportance of cutting tool geometry. In my opinion, this understanding is key to ( `: }& q4 u1 y' X7 U
improving efficiency of practically all machining operations. For the first time, this
, c* ^, X$ H" l4 y. Abook presents and explains the direct correlations between tool geometry and tool
: ?! [& y, f, ^0 W; a) K! F6 _performance. The second reason is that I felt that there is no comprehensive book
% d4 \3 k/ i! c( n! Fon the subject so professionals, practitioners, and students do not have a text from ! V# `0 o( [6 y* v# G) P- N) L2 B
which to learn more on the subject and thus appreciate the real value of tool
# z4 W& H6 v1 _! w! s# i6 g Bgeometry. Finally, I wanted to share the key elements of tool geometry that I felt 0 p7 y* j+ S% F" S
were not broadly understood and thus used in the tool design practice and in
9 [( `6 _' \2 E( woptimization of machining operations in industry. Moreover, being directly % Y5 N m& g: m7 X" C
involved in the launch of many modern manufacturing facilities equipped with 5 J5 f' A6 a+ |, f9 [
state-of-the-art high-precision machines, I found that the cutting tool industry is not
6 P' ^' Y. N' y" y3 zready to meet the challenge of modern metal cutting applications. One of the key
2 N* S- ?$ q$ Z1 lissues is the definite lack of understanding of the basics of tool geometry of ' Z0 Z/ s1 e h3 _2 O0 a/ ]& W
standard and application-specific tools.
8 T6 X8 I1 k8 H% I2 e- ]The lack of information on cutting tool geometry and its influence on the ) E: M7 o1 F* W8 i9 @
outcome of machining operations can be explained as follows. Many great findings
/ `: S. O/ `4 v' T" ^/ N3 N& J! F! uon tool geometry were published a long time ago when neither CNC grinding ' `! c& m* r' Z% {5 g
machines capable of reproducing any kind of tool geometry were available nor . A4 {1 ^+ h9 n# l2 Q# Y- B
were computers to calculate parameters of such geometry (using numerical 9 m n. x# t* q9 F! \
methods) common. Manual grinding using standard 2- and 3-axis simple grinding 2 X: A p( _ p: I4 ^3 h6 K: C
features was common so the major requirement for tool geometry was the simpler
8 S: \: h3 u$ Mthe better. Moreover, old, insufficiently rigid machines, aged tool holders and part
0 P4 k( t, x* z1 ?fixtures, and poor metal working fluid (MWF) selection and maintenance levered 9 _& N. I: M1 E* n* C8 Z
any advancement in tool geometry as its influence could not be distinguished under
1 [% H# o' g6 Y. ?5 Y9 k5 Vthese conditions. Besides, a great scatter in the properties of tool materials in the
3 |% O% G4 |" [ @' s$ Qpast did not allow distinguishing of the true influence of tool geometry. As a result, 7 x5 ]- c5 P- h$ l) e" f7 U3 K A
studies on tool geometry were reduced to theoretical considerations of features of
) \3 n" s9 ]! k% |; [9 o" Xtwist drills and some gear manufacturing tools such as hobs, shaving cutters, ' e$ x0 n% J( P- a4 }1 n% \
shapers, etc. 5 ?- O2 ?( u# c
Gradually, once mighty chapters on tool geometry in metal cutting and tool 4 S" l0 L/ l6 s8 K
design books were reduced to sections of few pages where no correlation between
5 _* P$ o/ U$ |( q! Mtool geometry and tool performance is normally considered. What is left is a
, Y) F2 v: x1 p4 I- y' K1 [general perception that the so-called “positive geometry” is somehow better than
8 Q) Y! u3 ^9 X3 ?“negative geometry.” As such, there is no quantitative translation of the word 3 b1 E* a" G' V/ g; M2 z
“better” into the language of technical data although a great number of articles 7 b* S+ ?; H4 s
written in many professional magazines discuss the qualitative advantages of 5 @$ z e7 e f
“positive geometry.” For example, one popular manufacturing magazine article
, M5 F. q) @$ N* C6 N2 Z1 Zread “Negative rake tools have a much stronger leading edge and tend to push ( I1 ?$ z. U' ~, y
against the workpiece in the direction of the cutter feed. This geometry is less free
/ M+ c% u& X; `5 m1 {cutting than positive rakes and so consumes more horsepower to cut.” Reading
8 w' F, }+ m" ]$ f2 }- v+ a6 Othese articles one may wonder why cutting tool manufacturers did not switch their 7 L; a2 I6 G" o+ M
tool designs completely to this mysterious “positive geometry” or why some of % F, [) d. Q2 H& j% B
them still investigate and promote negative geometry. 9 l( j W& g. z2 R' D
During recent decades, the metalworking industry underwent several important
0 g. R! |/ P6 @changes that should bring cutting tool geometry into the forefront of tool design 6 w* j' F" ^' n# h; V4 S3 c a6 O! }
and implementation: |
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