3.1.2
Friction
3.1.2
磨擦
Whenever
there
is
a
relative
motion
between
two
touching
surfaces,
there
is
a
resistance
to
this
motion
called
friction.
当两个接触的表面之间存在
相对运动
时，对这一运动就有一种称为磨擦的阻力。The
mechanics
of
friction
are
complex.
摩擦的机理很复杂。Although
the
fundamentals
of
the
phenomenon
have
been
given
much
study,
very
little
that
is
known
would
facilitate
formulation
of
the
exact
functional
relationship
between
friction
and
the
other
process
variables
.
虽然这一现象的基本原理已由很多研究所提供，但已知很少有助于在磨擦和其他工艺变量之间形成准确的
函数关系
。The
most
common
simplifying
assumptions
made
with
regard
to
friction
stress
(J)
between
the
workpiece
and
the
tool
are
the
following
:
关于工件和工具之间的磨擦应力（J）所做的最常用的简化假设如下：
1.
Coulomb
Friction.
It
is
assumed
that
the
shear
stress
J
is
proportional
to
the
pressure
p
between
the
workpiece
and
the
die.
Then
J
=
μp,
where
the
proportionality
factor
μ
is
called
the
Coulomb
coefficient
of
friction.
1.
库伦
磨擦。它假设
剪切应力
J与工件和模具之间的压力p成正比。于是J＝μp，式中的
比例因子
μ被称为库伦磨擦系数
2.
Constant
friction.
It
is
assumed
that
the
shear
stress
is
proportional
to
the
strength
of
the
workpiece
material.
Then
τ
=
m/√3,
where
the
proportionality
factor
m
is
called
the
shear
factor,
with
0
<
m
<
1.
The
factors
μ
and
m
are
assumed
constant
for
a
given
die,
workpiece
and
lubricant.
2.
恒定的磨擦。它假设剪切应力正比于工件材料的强度。于是，T＝m/√3，式中的比例因子m被称为剪切因子，0
<
m
<
1。因子μ和m对于给定的模具、工件和润滑剂而言都被假设为常数。
3.
Hydrodynamic,
Hydrostatic,
and
Thick
Film
Lubrication.
When
a
lubricant
film
separates
the
workpiece
from
contact
with
the
die,
then
hydrodynamic
or
hydrostatic
film
lubrication
prevails
together
with
its
special
laws
of
shear
within
the
lubricant
medium.
Sometimes
high-
viscosity
lubricants
adhere
to
the
workpiece
to
form
similarly
thick
film
separation
of
the
workpiece
from
the
tool.
Film
lubrication
may
separate
the
workpiece
from
the
die
on
the
entry
side
to
a
smaller
or
larger
extent.
At
the
extreme
(Sec.
7),
the
entire
workpiece
is
separated
from
the
die
by
this
film
of
the
lubricant.
3.
流体动力润滑、静压润滑和厚油膜润滑。当一层润滑剂膜将工件与接触的模具隔离时，那么流体动力的或静压的油膜润滑，以及其在润滑剂介质中特殊的剪切定律就会占上风。有时，高粘度润滑剂黏结到工件上，形成工件与工具类似厚油膜的隔离。油膜润滑可以在入口侧将工件与模具以较小或较大的程度隔离。在极端情况下（第7节），整个工件就被此润滑剂膜与模具隔离开来。