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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
# p' j, L4 ~% E' A+ @& ]manufacturing process discusses to a certain extent the tool geometry, the body of ! ^6 M( `( O* A6 @3 K) V, R
knowledge on the subject is scattered and confusing. Moreover, there is no clear
$ {8 V4 K2 ^( Sobjective(s) set in the selection of the tool geometry parameters so that an answer
8 Z0 b$ R: C. P2 @& l: _to a simple question about optimal tool geometry cannot be found in the literature
7 Z* w. ^; D3 X) H' }* j4 oon the subject. This is because a criterion (criteria) of optimization is not clear, on 0 u F' a0 L9 z5 r$ G
one hand, and because the role of cutting tool geometry in machining process * i% e/ a, K. k5 O( k8 ~
optimization has never been studied systematically, on the other. As a result, many
, n6 y4 ^& e, Kpractical tool/process designers are forced to use extremely vague ranges of tool - j! m1 g) R% l' q
geometry parameters provided by handbooks. Being at least 20+ years outdated, 8 p3 K1 L/ T7 R5 v. N
these data do not account for any particularities of a machining operation including 8 h, n' h; x) N/ B7 Z1 i
a particular grade of tool material, the condition of the machine used, the cutting
0 H P) ~4 G( a" G+ afluid, properties and metallurgical condition of the work material, requirements to
" z, F3 c3 J0 N2 d s" _the integrity of the machined surface, etc.
/ d+ Y. v% \. [ b0 _5 J7 C: \Unfortunately, while today's professionals, practitioners, and students are
/ C w( h& m% N$ R3 W- Jinterested in cutting tool geometry, they are doomed to struggle with the confusing 8 U& C+ a- n( U# g% m4 L1 o
terminology. When one does not know what the words (terms) mean, it is easy to + l( P9 c, l; ~/ x: k+ j/ |
slip into thinking that the matter is difficult, when actually the ideas are simple, 8 _$ n8 X2 R1 {+ {0 }5 H+ C
easy to grasp, and fun to consider. It is the terms that get in the way, that stand as a
" ` R. Z" R7 d" K6 G; V# t3 Awall between many practitioners and science. This books attempts to turn those
% ]% J5 @0 I& G) uwalls into windows, so that readers can peer in and join in the fun of proper tool 2 B% A0 J) n; w' {, k- A
design.
W4 U A: i( S1 H D0 ]So, why am I writing this book? There are a few reasons, but first and foremost, , l3 K3 p0 q3 U7 C( f, F2 L# m1 N1 Q
because I am a true believer in what we call technical literacy. I believe that
' \! c2 `5 H# _5 d) L# ?everyone involved in the metal cutting business should understand the essence and $ t5 h5 p5 G% O4 T0 S; `( E3 _
importance of cutting tool geometry. In my opinion, this understanding is key to
9 U+ P5 S# z9 v, p! himproving efficiency of practically all machining operations. For the first time, this
% n- _ x2 L5 |& Xbook presents and explains the direct correlations between tool geometry and tool 6 L x! Y. Q; I9 Y/ J" x
performance. The second reason is that I felt that there is no comprehensive book
& K) F" `, ^. ~! k4 J/ h0 Don the subject so professionals, practitioners, and students do not have a text from
/ M2 c2 n6 ?4 A5 \9 V& \which to learn more on the subject and thus appreciate the real value of tool ' }- l! c4 y3 p3 p. e- `% P6 e/ S
geometry. Finally, I wanted to share the key elements of tool geometry that I felt + X6 V R0 e& Q0 e/ r* w
were not broadly understood and thus used in the tool design practice and in
8 V7 w# d- e$ g7 K$ n: _optimization of machining operations in industry. Moreover, being directly 6 ~9 J1 ~; u- b. p
involved in the launch of many modern manufacturing facilities equipped with ) y$ m8 }# G- A+ ^) h
state-of-the-art high-precision machines, I found that the cutting tool industry is not " E# c; S0 s. \/ f% J$ {8 b
ready to meet the challenge of modern metal cutting applications. One of the key
6 f2 I8 i4 G; \issues is the definite lack of understanding of the basics of tool geometry of
/ v9 N) R4 q! ^ M& g% i: B$ _standard and application-specific tools. ! c" p& [* w7 m* W+ h% v) U
The lack of information on cutting tool geometry and its influence on the : ^2 X4 c; P: `8 H& C" B$ t
outcome of machining operations can be explained as follows. Many great findings : g' t v N: ~& [7 \# e* [: g
on tool geometry were published a long time ago when neither CNC grinding ' P4 u4 {7 R& F' V3 O+ _8 v
machines capable of reproducing any kind of tool geometry were available nor ' B& l% e/ z' u4 p& y: W
were computers to calculate parameters of such geometry (using numerical 5 h3 [0 Q0 h7 O Z8 o, a( n
methods) common. Manual grinding using standard 2- and 3-axis simple grinding : }' V# u& n4 h/ z
features was common so the major requirement for tool geometry was the simpler
: i8 t" ?1 i$ G; W1 O. }5 |0 I8 C" ]the better. Moreover, old, insufficiently rigid machines, aged tool holders and part ' N: W I' ]" b2 B( L \6 Y
fixtures, and poor metal working fluid (MWF) selection and maintenance levered
M/ f) K6 J% P* j$ X8 M: r( i" Q/ Gany advancement in tool geometry as its influence could not be distinguished under # A W# C( }9 r
these conditions. Besides, a great scatter in the properties of tool materials in the * r) g3 M* P9 n% m- y
past did not allow distinguishing of the true influence of tool geometry. As a result,
! U1 U9 j- Z7 B- Ustudies on tool geometry were reduced to theoretical considerations of features of 7 q$ |; ^. ?4 [2 ]( g" i
twist drills and some gear manufacturing tools such as hobs, shaving cutters,
" S6 t$ J5 A1 D6 @8 |9 O' [shapers, etc. 5 Q5 X* o" J+ Y1 `0 ^* z. Y- z% y$ m
Gradually, once mighty chapters on tool geometry in metal cutting and tool 9 I1 q* U, P0 D9 o4 L6 Q. z/ e. d
design books were reduced to sections of few pages where no correlation between 5 Z, G# }/ L ?5 t/ ~ m# O
tool geometry and tool performance is normally considered. What is left is a
% @0 i* N& S& l4 F' Qgeneral perception that the so-called “positive geometry” is somehow better than
- n; v+ l" l5 z5 c' D) i“negative geometry.” As such, there is no quantitative translation of the word ) @' ]7 v5 b5 _* i0 [% O
“better” into the language of technical data although a great number of articles ; T. P% V$ Q2 y, h/ l( r
written in many professional magazines discuss the qualitative advantages of - a" b) B( p8 V/ D4 N3 R
“positive geometry.” For example, one popular manufacturing magazine article * G. r. L$ P6 a( z& h
read “Negative rake tools have a much stronger leading edge and tend to push
: {5 j: C" n$ }* x8 ]against the workpiece in the direction of the cutter feed. This geometry is less free
; m$ u, C. k" _4 j- w+ Y+ g0 Wcutting than positive rakes and so consumes more horsepower to cut.” Reading
0 d. X- a1 c# Q* V9 T* t7 Ythese articles one may wonder why cutting tool manufacturers did not switch their
) A2 i) B! R) x8 X' [6 v; |tool designs completely to this mysterious “positive geometry” or why some of
# g5 O; J, y8 Cthem still investigate and promote negative geometry.
- c! P: I9 @$ dDuring recent decades, the metalworking industry underwent several important
' ~- b" ^6 B! ]7 A; P8 L8 `changes that should bring cutting tool geometry into the forefront of tool design 0 o' P/ ]6 a6 O$ j n6 U
and implementation: |
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