17 Design Consideration In Sheet Metal  Machine Design
Following are some basic sheet metal design, Thump rules for Sheet metal Design
1. Bends
 For the ease of manufacturing,
multiple bends on the same plane should
occur in the same direction.  Avoid large sheet metal parts with
small bent flanges.  In low carbon steel sheet metal,
the minimum radius of a bend should be
one half the material thickness or
0.80 mm (0.03 inch), whichever is
larger.  Bends specified as angles may
be tolerance at plus or minus
onehalf degree at a location adjacent
to the bends.
Edge Flange Design Consideration 
2. Curls
 The minimum radius is two times
the material thickness with an
opening to a minimum of one material
thickness.  The minimum distance between a curl
and the edge of a hole is the radius
of the curl plus the material
thickness.  The minimum distance a curl should
be from an internal bend is six times
the material thickness plus the
radius of the curl.  The minimum distance a curl should
be from an external bend is nine
times the material thickness plus the
radius of the curl.
Sheet metal designcurls 
3. Dimples
 The maximum diameter should be six times the
material thickness, and a maximum depth of onehalf
the inside diameter.  The minimum distance that a dimple should
be from a hole is three times the material
thickness plus the radius of the dimple.  The minimum distance that a dimple should
be from the edge is four times the material
thickness plus the inside radius of the
dimple.  The minimum distance that a dimple should be
from a bend is two times the material thickness
plus the inside radius of the dimple plus the
radius of the bend.  The minimum distance between one dimple and
another is four times the material thickness plus
the inside radius of each dimple.
Dimple Sheet metal Design 
4. Embossments
 The maximum depth is
proportional to the internal radius or material
thickness.  The maximum depth for a
flat embossment is equal to the internal radius
plus the external radius.  The maximum depth for a V
embossment is equal to three times the material
thickness.
Embossments 
 The minimum distance between two
extruded holes is six times the material
thickness.  The minimum distance from an extruded
hole to an edge is three times the material
thickness.  The minimum distance from an extruded
hole to a bend is three times the material
thickness plus the bend radius.
Extrude Cut,Holes 
6. Flanges gap

The minimum height of a bent flange
isdirectly related to the
material thickness, bendradius, and length of bend.

The minimum width of a bend relief is
onematerial thickness or 1.50 mm
(0.06 inch),
Flange Gap 
7. Gussets

The width and
depth,recommended
at an
angle of
45degrees,
is
directly
proportional
tothe
radius
and
meterial
thickness. 
The minimum
distance that agusset
should be
from the
edge
ofa hole
in a
parallel
plane is
eighttimes the
material
thickness
plusthe
radius of
the
gusset.
Gussets 
8. Hems

The minimum diameter
of a teardrop hem is
equal to the material
thickness, with a
return flange height
equal to or greater
than four times the
material thickness,
and a minimum opening
of 1/4 of the
material thickness. 
The minimum diameter
of an open hem is
equal to the material
thickness with a
return flange height
equal to or greater
than four times the
material thickness. 
The minimum return
flange height of a
closed hem is equal
to or greater than
four times the
material thickness
(the diameter is
zero).
NOTE:
Closed hems tend to
fracture at the bend
and cause entrapment
of solutions during
the finishing
process. 
The minimum distance
from a hole to a hem
is two times the
material thickness
plus the radius of
the hem. 
The minimum distance
a hem should be from
an internal bend is
five times the
material thickness. 
The minimum distance
a hem should be from
an external bend is
eight times the
material thickness.
Hem Design 
9. Holes

The minimum
diameter of a
hole should
be equal to
the materials
thickness or
1.00 mm (0.04
inch),
whichever is
greater. 
The minimum
distance
between holes
is directly
proportional
to the size
and shape fo
the hole
feature and
the material
thickness 
The minimum
distance the
edge of a
hole should
be from a
form is three
times the
material
thickness
plus the form
radius. 
The minimum
distance the
edge of a
hole should
be from a
bend is two
times the
material
thickness
plus the bend
radius. 
The minimum
distance
between a
hole and the
edge of the
material is
directly
proportional
to the size
and shap of
the hole and
the material
thickness. 
The minimum
distance
between the
leading edge
of a hole
through a
bend should
be equal to
the thickness
of material
plus the bend
radius or two
times the
material
thickness,
whichever is
greater.

The
minimum
width of
an open
lance is
two times
the
material
thickness
or 3.00
mm (0.125
inch),
whichever
is
greater,
with a
maximum
length of
five
times the
width. 
The
minimum
width of
a closed
lance is
two times
the
material
thickness
or 1.60
mm (0.06
inch),
whichever
is
greater,
and a
maximum
height of
five
times the
material
thickness
at a
45degree
angle. 
The
minimum
distance
from a
lance to
a bend in
a
parallel
plane is
eight
times the
material
thickness
plus the
radius of
the bend.

The
minimum
width
is
equal
to
the
material
thickness or
1.00
mm
(0.04
inch),
whichever
is
greater. 
The
maximum
length
for a
straight/radius
end
notch
is
equal
to
five
times
the
width. 
The
maximum
length
for a
V
notch
is
equal
to
two
times
the
width. 
The
minimum
distance
between
a
hole
and
the
edge
of a
notch
is
directly
proportional
to
the
size/shape
of
the
hole
and
the
material
thickness. 
The
minimum
distance
from
a
notch
to a
bend
in a
parallel
plane
is
eight
times
the
material
thickness
plus
the
radius
of
the
bend. 
The
minimum
distance
from
a
notch
to a
bend
in a
perpendicular
plane
is
three
times
the
material
thickness
plus
the
radius
of
the
bend. 
The
minimum
distance
beyond
the
bend
on
the
side
edge
is
equal
to
the
thickness
of
the
material
plus
the
bend
radius,
or
two
times
the
material
thickness,
whichever
is
greater.
Notches and Relief Cut 

The
maximum
inside
radius
is
equal
to
three
times
the
material
thickness,
with
a
maximum
depth
of
the
inside
radius. 
The
minimum
distance
from
a
center
line
of
a
rib
to
the
edge
of
a
hole
is
three
times
the
material
thickness
plus
the
radius
of
the
rib. 
The
minimum
distance
a
rib
should
be
from
an
edge
in
a
perpendicular
plane
is
four
times
the
material
thickness
plus
the
radius
of
the
rib. 
The
minimum
distance
a
rib
should
be
from
an
edge
in
a
parallel
plane
is
eight
times
the
material
thickness
plus
the
radius
of
the
rib. 
The
minimum
distance
a
rib
should
be
from
a
bend
perpendicular
to
the
rib
is
two
times
the
material
thickness,
plus
the
radius
of
the
rib,
plus
the
radius
of
the
bend.
 The minimum distance
from a semipierced hole
and a form is three times
the material thickness
plust the form radius.  The minimum distance
from a semipierced hole
and a bend is two times
the material thickness
plus the bend radius.  The minimum distance
between semipierced
holes is eight times the
material
thickness.
14.
Slots
 The minimum width of
a slot is equal to the
material thickness or
1.00 mm (0.04 inch),
whichever is greater.  The minimum distance
from the inside surface
of a bend to the edge of
a slot is directly
proportional to the
length of the slot,
material thickness, and
radius of the bend.  When using slots and
tabs the maximum width of
the slot must be greater
than the thickness of the
tab and the tab length
should equal the material
thickness.
15.
Tabs
 The minimum width is
equal to two times the
material thickness or
3.200 mm, whichever is
greater, while the
maximum length is five
times the width.  The minimum distance
between tabs is equal to
the material thickness or
1.00 mm (0.04 inch),
whichever is greater.
16.
Counterbores
 The minimum distance
between two counterbores
is eight times the
material thickness.  The minimum distance
from a counterbore to an
edge is four times the
material thickness.  The minimum distance
from a counterbore to a
bend is four times the
material thickness plus
the bend radius.
17.Countersinks
 The maximum
depth is 3.5 times the
material thickness at an
angle of the hardware.  A minimum of 50%
contact between the
hardware and the
countersink is required.  The minimum distance
between two countersinks
is eight times the
material thickness.  The minimum distance
from one countersink and
an edge is four times the
material thickness.  The minimum distance
from a countersink and a
bend is four times the
material thickness plus
the bend radius.
18.Welding
 Spot welding should
be restricted to joining
coplanar surfaces.  The minimum distance
between welds is 10 times
the material thickness.
Using 20 times the
material thickness is
ideal.  The minimum distance
between a weld and the
edge is two times the
diameter of the spot
weld.  The minimum distance
from a weld to a form is
the spot diameter plus
the bend radius.  Use PEMs instead of
threaded inserts.
19.
Plating
 Outside sharp corners
receive twice as much
plating as flat surfaces.  Allow for pitch
diameters for screw
threads, which can
increase four times the
plating thickness.  Tapped holes may need
to be retapped after
plating to ensure
accuracy.  Projections
accumulate more plating
than other areas.  Recessed areas may be
difficult to plate,
resulting in little or no
coverage.  Lapwelded joints
trap plating solutions.
One solution is to raise
welds on embossed areas
by 0.015 in. (0.3 mm) to
allow for flushing and
blow drying between the
surfaces.  Maskings of stampings
and fabrications to
anodize certain areas is
not recommended.  Design drain
holes/vent holes for
plating solutions and
rinsing.  Design tabs/holes for
attachment to part racks.