SOLUTION BULLETIN
KNOCKOUTS 101
DEFINITION
A knockout is a feature in sheet metal created by punching a slug free of but attached to the sheet with small un-cut areas called tabs. A
knockout allows for variation in a part by providing the opportunity to create a hole in the part at a later time by removing, or knocking out, the
retained slug. A successful knockout is dependent upon a favorable combination of material properties, tab sizes, and tab location.
FEATURES
Knockouts are common in sheet metal fabrication. Most frequently knockouts are used in electrical
enclosures as an access point to bring wires into the enclosure. A very important feature of a knockout is
the tabs, which keep the knockout attached to the sheet. The tab size, quantity, and location are critical to
determining the ease or difficulty of removing the knockout. The ease of knockout removal is subjective
and determined by the functional requirements of the product manufacturer or field installation personnel
who will be removing the knockout. There is a fine line between a “fall out” and a “beat out,” which is
determined by the tab specifications. Knockouts can be formed up or down with the direction determined
by the finished product requirements and manufacturing method.
PROCESS
Precise, consistent stroke control in the press is very important for producing high quality, consistent
knockouts. Variations in the stroke of the press and changes in the material being punched will result in
knockouts that are inconsistent in height and tab strength.
The single knockout punching process uses a single tool to create a slug and the tabs. It is common for the
slug to be displaced slightly more than one material thickness to ensure it has been cut free from the sheet.
The tabs are stretched and weakened when the slug is displaced. The ductility of the material (its ability to
be stretched) tab size, quantity, and location all can affect the success of the desired result. For example,
small tabs in thicker material may not be able to stretch enough to keep the slug attached to the sheet; the
tab fails and the knockout breaks free.
As with single knockouts, double round knockouts are used in electrical enclosures as access points, but
they bring the wires in through two different size openings on the same centerline location. The double
round knockout punching process uses a single tool to create a cut ring of material and the tabs. Multiple
rings and specifically placed tabs can be formed with customized tooling. For electrical enclosures, double,
triple, quad, and even quint knockouts are common, which allow different opening sizes to be selected,
depending on the application.
It is common for knockouts to be pressed back into the sheet (planished) to create a closed feature.
Although this flattening process will not press a knockout completely flat back into the sheet it does prevent
dust intrusion into the enclosure. Planishing knockouts introduces stresses into the sheet that may result in
a slight bowing of the knockout and/or the surrounding sheet.
[Dimensions in Inches(mm)]
Mate Precision Tooling, Inc. | 1295 Lund Boulevard, Anoka, Minnesota 55303 USA. Phone: 763.421.0230 Fax: 763.421.0285 | mate.com
Toll Free: Tel 800.328.4492 Fax 800.541.0285
© 2015 The Mate logo is a registered trademark of Mate Precision Tooling Inc. Ultra XT is a trademark of Mate Precision Tooling.
LIT01173
SOLUTION BULLETIN
SUCCESSFUL KNOCKOUTS
Successful knockouts result from a favorable combination of material properties and tab features. The force required to produce a knockout
is essentially the same as that required for punching a hole. If problems are experienced with a knockout, such as sticking, burrs, tabs failing,
difficult removal or damaged forms, improved results will be achieved by:
•
•
•
•
•
•
•
•
•
Confirming the form height is correct (1 to 1.1 times the material thickness). Ensure full initial shear.
Closing the KO (planishing if necessary – see Additional Helpful Information below)l
Using forming lubricant on the sheet
Confirming the tool was designed for the material thickness being formed
Sharpening or replacing the cutting components when they become dull
Reviewing tab sizes, locations, and quantities
Improving machine alignment – alignment of upper and lower critical
Replacing ejector springs/urethane as they wear
Forming up whenever possible
HOW TO FORM KNOCKOUTS THAT EXCEED STATION RANGE OR PRESS TONNAGE CAPACITY
Many knockouts fit within the ranges of the punch press station sizes. Sometimes knockouts are
required that are larger than possible to make within available stations or the tonnage required
is too high for the machine. Following are some ways to accomplish making these over range or
over tonnage knockouts.
Segmented or multiple knockouts are probably the best way to handle these situations. While
they won’t be as “pretty” as one formed by a standalone knockout tool, they get the job
done. The photo at right shows a large 4.00”(102,00mm) knockout that was made using the
segmented method. The tool design places the tabs at specific locations to facilitate removal.
A variation of the segmented knockout is an arch bridge
lance and form. With this tool, each edge of the arch is
chamfered to help overlap the hits and minimize distortion.
See photo at left.
An additional advantage of segmented or multiple knockouts is that they reduce the tonnage required, so it is
easier on your machine. A tip and technique to consider is down forming. When you form down, you can get a
larger footprint without the increased tonnage. This is because up forming uses a spring stripper that requires
additional force.
Even if you think a knockout may be too large, let your Mate Applications Specialist take a look at it; they may
be able to develop other options for you.
[Dimensions in Inches(mm)]
Mate Precision Tooling, Inc. | 1295 Lund Boulevard, Anoka, Minnesota 55303 USA. Phone: 763.421.0230 Fax: 763.421.0285 | mate.com
Toll Free: Tel 800.328.4492 Fax 800.541.0285
© 2015 The Mate logo is a registered trademark of Mate Precision Tooling Inc. Ultra XT is a trademark of Mate Precision Tooling.
LIT01173
SOLUTION BULLETIN
SOLUTION
BULLETIN
ABOUT TONNAGE:
Contact your Mate Application Specialist for information about your needs, but there are some general guidelines for press capacity that you
canABOUT
use. Up to TONNAGE:
three-fourths of press capacity may be safely used to punch knockouts. Following is an equation for tonnage calculated from
knockout
size and
material:
Contact
your
Mate Applications Specialist for specific information about your needs, but there are some
general guidelines for press capacity that you can use. Up to three-fourths of press capacity may be safely
3.14 x Diameter
x Material
Thickness
Metal Factor
= Tonnage from knockout size and material:
used to punch knockouts. Following
is an
equation
for Xtonnage
calculated
Metal factors, English(Metric): Mild Steel 25(22,5); Aluminum 14(12,6); Stainless 50(45)
3.14 x Diameter x Material Thickness X Metal Factor = Tonnage
Example (English): 0.875” knockout in .060 Mild steel = 3.14 x .875 x .060 x 25 = 4.12 English tons
Metal infactors,
English(Metric):
Mild
Aluminum
14(12,6); Stainless 50(45)
Example (Metric): 20 mm knockout
2 mm Mild
Steel = (3.14 x 20
x 2 Steel
x 22,5)25(22,5);
/ 25,42 = 4,38
metric tons
Example (English): 0.875” knockout in .060 Mild steel = 3.14 x .875 x .060 x 25 = 4.12 English tons
SPLITTING
HITS:
ExampleTONNAGE
(Metric):WITH
20 TWO
mm knockout
in 2 mm Mild Steel = (3.14 x 20 x 2 x 22,5) / 25,42 = 4,38 metric tons
SPLITTING TONNAGE WITH TWO HITS:
Doubles, if tonnage is over capacity:
• 1st hit = single knockout down
• 2nd hit = single knockout up with relief
Triples, if tonnage is over capacity:
• 1st hit = single knockout up
• 2nd hit = double knockout up with relief
Quads, if tonnage is over capacity:
• 1st hit = double knockout up
• 2nd hit = double knockout up with relief
AVAILABLE TOOLING STYLES AND STATION SIZES
• All
MATERIAL AND OTHER RESTRICTIONS:
• Contact your Mate Applications Specialist
OTHER MATE PRODUCTS TO CONSIDER:
[Dimensions
in Inches(mm)]
• Mate Sheetmarker™ to etch brief instructions, entry/exit points, ground
symbol
or logos
• Mate
EasyBend™
for
easy
bending
of
parts
by
hand
(e.g.,
electrical
boxes)
Mate Precision Tooling, Inc. | 1295 Lund Boulevard, Anoka, Minnesota 55303 USA. Phone: 763.421.0230 Fax: 763.421.0285 | mate.com
Toll Free: Tel 800.328.4492 Fax 800.541.0285
• Mate EasySnap™
forlogoeasy
removal
parts
from
sheet.
© 2015 The Mate
is a registered
trademark of
of Mate
Precision
Toolingthe
Inc. Ultra
XT is a trademark of Mate Precision Tooling.
LIT01173
SOLUTION BULLETIN
AVAILABLE TOOLING STYLES AND STATION SIZES
• All
MATERIAL AND OTHER RESTRICTIONS:
• Contact your Mate Applications Specialist
OTHER MATE PRODUCTS TO CONSIDER:
• Mate Sheetmarker™ to etch brief instructions, entry/exit points, ground symbol or logos
• Mate EasyBend™ for easy bending of parts by hand (e.g., electrical boxes)
• Mate EasySnap™ for easy removal of parts from the sheet.
• V-line stencils to mark ground symbol locations, positioning, logos
Additional Helpful Information
• The material thickness range for knockouts is .023 (.6mm) to .118 (3.0mm).
• The tool can be used with other material thickness within a range of + .016 (0.4mm) from design thickness.
• Maintain .236 (6.0mm) difference between diameters used for knockout.
• Planishing tools can be used to flatten the form back into the sheet if the customer desires. The planishing punch pushes the knockout
back to 75% material thickness, leaving 25% still raised. Planishing the knockout further makes it difficult to remove the knockout while
distorting the sheet. Satisfactory knockouts can be produced without planishing.
• Note to Thick Turret Customers: For machines without upforming capability, forming tools should not be placed next to each other in the
turret. Brush dies can be used around form tools to help “ramp” the material up the angled surface of the stripper plate.
• Tool ejector considerations:
○○ Ejectors are used to eject the sheared section of the Knockout from the tool
○○ Selection of ejector type varies by design and is subject to many factors. Mate optimizes the ejector application per the
application and tooling style.
○○ As a general rule, urethane is preferable due to its uniform load distribution, thus providing the most favorable results in the
sheet metal
○○ In some cases, restricted application space (e.g. close-spacing of a knock out pattern) requires using metal ejectors. In other
cases, the tool design envelope may not be practical/possible to include metal ejectors which results in urethane ejectors by
default
○○ If a customer has a specific desire to deviate from Mate’s standard, Mate will evaluate each request
• Custom Knockouts: Custom knockouts are available to suit your application; rectangular knockouts for circuit boxes, oval knockouts for
locking cylinders, 9-pin connections for computer chassis, small knockouts for screw holes or slots, etc. Be sure to reference Mate’s
Solution Gallery on the web to see what is possible for knockouts and other special forming applications: http://www.mate.com/en/
fabrication-solutions/special-applications-gallery/lance-form/
[Dimensions in Inches(mm)]
Mate Precision Tooling, Inc. | 1295 Lund Boulevard, Anoka, Minnesota 55303 USA. Phone: 763.421.0230 Fax: 763.421.0285 | mate.com
Toll Free: Tel 800.328.4492 Fax 800.541.0285
© 2015 The Mate logo is a registered trademark of Mate Precision Tooling Inc. Ultra XT is a trademark of Mate Precision Tooling.
LIT01173
SOLUTION BULLETIN
KNOCKOUT
SPLITTING PUNCHING FORCE WITH
TWO HITS …
INDUSTRY TAB LOCATIONS
INDUSTRY TAB LOCATIONS WILL BE FURNISHED UNLESS OTHERWISE SPECIFIED
Actual
Diameter
Single KO
Lower
Upper
Double KO
Lower
Upper
1.1 X MATERIAL
THICKNESS
1st Hit
*0 -.249
(0 - 6.3)
2nd Hit
.250 -.313
(6.4 - 8.0)
DOUBLES …
I f punching force is over capacity, make first
.314 -1.374
(8.0 - 34.9)
hit single K.O. down, second hit single K.O.
up with relief.
> 1.375
(34.9)
2nd Hit
1st Hit
* Tab needed on lower K.O. if material is thicker than .063(1.6).
2nd Hit
TRIPLES …
PUNCHING FORCE CHART –
Make first hit single K.O. up, second hit double
K.O. up with relief.
SINGLE KNOCKOUT, MILD STEEL
MATERIAL THICKNESS
REF
Conduit
Size in
inches
3/8
1/2
3/4
1
Actual
Diameter
20 Ga.
.035(0.9)
18 Ga..
.047(1.2)
16 Ga.
.060(1.5)
.14 Ga.
.075(1.9)
12 Ga.
.105(2.7)
11 Ga.
.120(3.0)
2nd Hit
.375
(9.5)
1.0 tons
8.9 kN
1.4 tons
12.3 kN
1.8 tons
15.7 kN
2.2 tons
19.7 kN
3.1 tons
27.5 kN
3.5 tons
3I.4 kN
1st Hit
.500
(12.7)
1.4 tons
12.3 kN
1.8 tons
16.4 kN
2.4 tons
21.0 kN
2.9 tons
26.2 kN
4.1 tons
36.7 kN
4.7 tons
41.9 kN
QUADS …
Make first hit double K.O. up, second hit double
K.O. up with relief.
.687
(17.5)
1.9 tons
16.8 kN
2.5 tons
22.6 kN
3.2 tons
28.8 kN
4.0 tons
36.0 kN
5.7 tons
50.4 kN
6.5 tons
57.6 kN
.750
(19.0)
2.1 tons
18.3 kN
2.8 tons
24.6 kN
3.5 tons
31.4 kN
4.4 tons
39.3 kN
6.2 tons
55.0 kN
7.1 tons
62.9 kN
.875
(22.2)
2.4 tons
21.4 kN
3.2 tons
28.7 kN
4.1 tons
36.7 kN
5.2 tons
45.9 kN
7.2 tons
64.2 kN
8.2 tons
73.4 kN
1.000
(25.4)
2.7 tons
24.5 kN
3.7 tons
32.8 kN
4.7 tons
41.9 kN
5.9 tons
52.4 kN
8.2 tons
73.4 kN
9.4 tons
83.8 kN
1.125
(28.6)
3.1 tons
27.5 kN
4.2 tons
36.9 kN
5.3 tons
47.2 kN
6.6 tons
59.0 kN
9.3 tons
82.5 kN
10.6 tons
94.3 kN
1.250
(31.8)
3.4 tons
30.6 kN
4.6 tons
41.0 kN
5.9 tons
52.4 kN
7.4 tons
65.5 kN
10.3 tons
91.7 kN
11.8 tons
104.8 kN
1.375
(34.9)
3.8 tons
33.6 kN
5.1 tons
45.2 kN
6.5 tons
57.6 kN
8.1 tons
72.1 kN
11.3 tons
100.9 kN
13.0 tons
115.3 kN
1.500
(38.1)
4.1 tons
36.7 kN
5.5 tons
49.3 kN
7.1 tons
62.9 kN
8.8 tons
78.6 kN
12.4 tons
110.0 kN
14.1 tons
125.8 kN
1.625
(41.3)
4.5 tons
39.7 kN
6.0 tons
53.4 kN
7.7 tons
68.1 kN
9.6 tons
85.2 kN
13.4 tons
119.2 kN
15.3 tons
136.2 kN
2nd Hit
SHEDDER SPRING
Thickness Variation …
A knockout tool assembly accommodates a
± .016(0.4) range in material thickness. Beyond
± .016(0.4), penetration is affected and knockout
performance deteriorates.
SHEDDER INSERT
Planishing …
The planishing punch pushes knockout back
to 75% material thickness, leaving 25% still
raised. Planishing the knockout further makes
it difficult to remove and distorts the sheet.
Satisfactory knockouts can be produced without
planishing.
UPPER INSERT
Custom Knockouts …
Custom knockouts are available to suit your
application; rectangular knockouts for circuit
boxes, oval knockouts for locking cylinders,
small knockouts for screw holes or slots, etc.
RETAINING RING(S)
STRIPPER
INDUSTRY TAB DIMENSIONS
MATERIAL THICKNESS
“C”
LOWER INSERT
“D”
.020 - .045(0.51 - 1.14)
.060(1.52)
.030(0.76)
.046 - .070(1.16 - 1.78)
.090(2.29)
.050(1.27)
.071 - .097(1.80 - 2.46)
.120(3.05)
.060(1.52)
.098 - .127(2.49 - 3.23)
.180(4.57)
.090(2.29)
.128 - .179(3.25 - 4.55)
.250(6.35)
.125(3.18)
STRIPPER SPRINGS
DIE BODY
Dimensions in inches (millimeters)
Mate Precision Tooling, Inc. | 1295 Lund Boulevard, Anoka, Minnesota 55303 USA. Phone: 763.421.0230 Fax: 763.421.0285 | mate.com
Toll Free: Tel 800.328.4492 Fax 800.541.0285
© 2015 The Mate logo is a registered trademark of Mate Precision Tooling Inc. Ultra XT is a trademark of Mate Precision Tooling.
4 1/2” E STATION
3 1/2” D STATION
2” C STATION
1 1/4” B STATION
[Dimensions in Inches(mm)]
Dimensions
LIT01173