cornering北美压铸压铸件公差标准(NADCA Standard, Brief)

2021年1月19日发(作者：打电话的英文翻译)
NADCA Standard

Linear Dimensions: Standard Tolerances



Linear Dimensions: Precision Tolerances


Parting Line: Standard Tolerances
Parting Line Tolerance is the maximum amount of die separation allowed for the end product to meet
specified
requirements
of
form,
fit
and
function.
This
is
not
to
be
confused
with
Parting
Line
Shift
Tolerance which is the maximum amount die halves shift from side to side in relation to one another.

Parting Line Tolerance is a function of the surface area of the die from which material can flow from
one die half to the other. This is also known as Projected Area.

Projected
Area
is
always
a
plus
tolerance
since
a
completely
closed
die
has
0
separation.
Excess
material
and
pressure
will
force
the
die
to
open
along
the
parting
line
plane
creating
an
oversize
condition. The excess material will cause the part to be thicker than the ideal specification and that is
why Projected Area only has plus tolerance. It is important to understand that Table S-4A-2 (Projected
Area
Tolerance)
does
not
provide
Parting
Line
Tolerance
by
itself.
Part
thickness
or
depth
must
be
factored in to give a true idea of Parting Line Tolerance. Parting Line Tolerance is a function of part
thickness perpendicular to the Projected Area plus the Projected Area Tolerance.

Example: An aluminum die casting has 75 in
2
(483.9 cm
2
) of Projected Area on the parting die plane.
From table S-4A-2, Projected Area Tolerance is +0.012. This is combined with the total part thickness
tolerance from table S-4A-1 to obtain the Parting Line Tolerance.

The
total
part
thickness
including
both
die
halves
is
5.00
in.
(127
mm)
which
is
measured
per-
pendicular to the parting die plane (dimension “E2 E1”). From table S
-4A-1, the Linear Tolerance is
±
0.010 for the first inch and
±
0.001 for each of the four additional inches. The Linear Tolerance of
±
0.014 inches is combined with the Projected Area Tolerance of +0.012 to yield a Standard Parting Line
Tolerance of +0.026/-0.014 in. or in metric terms
±
0.35 mm from Linear Tolerance table S-4A-1 plus
+0.30 mm from Projected Area Tolerance table S-4A-2 = +0.65/-0.35 mm.



Parting Line Shift: Standard Tolerance
Example: Parting Line Shift Tolerance
The cavity area at the parting line is 75 inches squared. From Table S-4A-6, the Projected Area Parting
Line
Shift
Tolerance
is
±

0.006
(
±
0,152
mm).
This
is
added
to
the
Linear
Tolerance
from
table
S/P-4A-1.



Draft Requirements: Standard Tolerances
In the case of an inside surface for an aluminum cast part, for which the constant
“C” is 30 (6 mm), the
recommended Standard Draft at three depths is:






Cored Holes for Cut Threads: Standard Tolerances
Cored
holes
for
cut
threads
are
cast
holes
that
require
threads
to
be
cut
(tapped)
into
the metal. The table below provides the dimensional tolerances for
diameter, depth and
draft
for each specified
thread type
(Unified and
Metric Series). When required,
cored
holes
in
Al,
Mg,
Zn
and
ZA
may
be
tapped
without
removing
draft.
This
Standard
Tolerance
recommendation is based on allowing 85% of full thread depth at the bottom D2 (small
end)
of
the
cored
hole
and
55%
at
the
top
D1
(large
end)
of
the
cored
hole.
A
countersink
or radius is also recommended at the top of the cored hole. This provides relief for
any displaced material and can also serve to strengthen the core.
Threads extend through the cored hole as by Y
. X shows the actual hole depth. As with the countersink
at the top of the hole, the extra hole length provides relief for displaced material and allows for full
thread engagement. Tolerances below apply to all alloys.


Table S-4A-9: Cored Holes for Cut Threads (Standard Tolerances)
–
Unified Series and Metric Series



Additional Considerations for Large Castings
1 Fillet Radii:

1.1: Definition:
Wall
thickness
is
the
distance
between
two
parallel
or
nearly parallel
surfaces. Wall thickness may vary depending on the application of draft. Wall
thickness should be maintained as uniform as possible. A general guideline would
be
to
keep
the
range
of
thickness
within
2X
of
the
thinnest
wall.
A
second
guideline
is
to
keep
the
wall
as
thin
as
possible
to
meet
the
castings
functional
requirements.
1.2: General:
0.14
”

(3.5mm
(+/-
0.5mm)
1.2.1 Deviations:
from
the
nominal
condition
are
based upon product function and manufacturing process requirements.
2 Radii:

2.1 Fillet Radii: 2.1.1 General:
0.14
”
(+0.08/-0.04
”
) [3.5mm (+2.0mm/-1.0mm)]
2.1.1.1 Deviations:
from the nominal condition are based upon product
function and manufacturing process requirements.
2.1.2 Minimum:
0.060
”
(1.5mm)