SOLUTION BULLETIN KNOCKOUTS 101 DEFINITION

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Kevin Thornton
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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 successful knockout is dependent upon a favorable combination of material properties, tab sizes, and tab location. FEATURES Knockouts are common in sheet metal fabrication.

A very important feature of a knockout is the tabs, which keep the knockout attached to the sheet.

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.

1 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.

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

2 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.

ABOUT TONNAGE: Contact your Mate Application Specialist for information about your needs, but there are some general guidelines for press capacity that you can use.

14 x Diameter x Material Thickness X Metal Factor = Tonnage Metal factors, English(Metric): Mild Steel 25(22,5); Aluminum 14(12,6); Stainless 50(45) Example (English): 0.

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: 1 st hit = single knockout down 2 nd hit = single

3 ABOUT TONNAGE: Contact your Mate Application Specialist for 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 used to punch knockouts. Following is an equation for tonnage calculated from knockout size and material: 3.14 x Diameter x Material Thickness X Metal Factor = Tonnage Metal factors, English(Metric): Mild Steel 25(22,5); Aluminum 14(12,6); Stainless 50(45) Example (English): knockout in.060 Mild steel = 3.14 x.875 x.060 x 25 = 4.12 English tons Example (Metric): 20 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: 1 st hit = single knockout down 2 nd hit = single knockout up with relief Triples, if tonnage is over capacity: 1 st hit = single knockout up 2 nd hit = double knockout up with relief Quads, if tonnage is over capacity: 1 st hit = double knockout up 2 nd 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: Mate Sheetmarker to etch brief instructions,

4 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 (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: fabrication-solutions/special-applications-gallery/lance-form/

5 INDUSTRY TAB LOCATIONS INDUSTRY TAB LOCATIONS WILL BE FURNISHED UNLESS OTHERWISE SPECIFIED Actual Diameter * (0-6.3) ( ) ( ) KNOCKOUT Single KO Double KO Lower Upper Lower Upper SPLITTING PUNCHING FORCE WITH TWO HITS DOUBLES 1.1 X MATERIAL THICKNESS If punching force is over capacity, make first hit single K.O. down, second hit single K.O. up with relief. > (34.9) * Tab needed on lower K.O. if material is thicker than.063(1.6). PUNCHING FORCE CHART SINGLE KNOCKOUT, MILD STEEL REF Conduit Size in inches 3/8 1/2 3/4 1 Actual Diameter.375 (9.5).500 (12.7).687 (17.5).750 (19.0).875 (22.2) (25.4) (28.6) (31.8) (34.9) (38.1) (41.3) 20 Ga..035(0.9) 1.0 tons 8.9 kn 1.4 tons 12.3 kn 1.9 tons 16.8 kn 2.1 tons 18.3 kn 2.4 tons 21.4 kn 2.7 tons 24.5 kn 3.1 tons 27.5 kn 3.4 tons 30.6 kn 3.8 tons 33.6 kn 4.5 tons 39.7 kn 18 Ga...047(1.2) 1.4 tons 12.3 kn 1.8 tons 16.4 kn 2.5 tons 22.6 kn 2.8 tons 24.6 kn 3.2 tons 28.7 kn 3.7 tons 32.8 kn 4.2 tons 36.9 kn 4.6 tons 41.0 kn 5.1 tons 45.2 kn 5.5 tons 49.3 kn 6.0 tons 53.4 kn 16 Ga..060(1.5) 1.8 tons 15.7 kn 2.4 tons 21.0 kn 3.2 tons 28.8 kn 3.5 tons 31.4 kn 4.7 tons 41.9 kn 5.3 tons 47.2 kn 5.9 tons 52.4 kn 6.5 tons 57.6 kn 7.1 tons 62.9 kn 7.7 tons 68.1 kn INDUSTRY TAB DIMENSIONS MATERIAL THICKNESS.14 Ga..075(1.9) 2.2 tons 19.7 kn 2.9 tons 26.2 kn 4.0 tons 36.0 kn 4.4 tons 39.3 kn 5.2 tons 45.9 kn 5.9 tons 52.4 kn 6.6 tons 59.0 kn 7.4 tons 65.5 kn 8.1 tons 72.1 kn 8.8 tons 78.6 kn 9.6 tons 85.2 kn 12 Ga..105(2.7) 3.1 tons 27.5 kn 5.7 tons 50.4 kn 6.2 tons 55.0 kn 7.2 tons 64.2 kn 8.2 tons 73.4 kn 9.3 tons 82.5 kn 10.3 tons 91.7 kn 11.3 tons kn 12.4 tons kn 13.4 tons kn 11 Ga..120(3.0) 3.5 tons 3I.4 kn 4.7 tons 41.9 kn 6.5 tons 57.6 kn 7.1 tons 62.9 kn 8.2 tons 73.4 kn 9.4 tons 83.8 kn 10.6 tons 94.3 kn 11.8 tons kn 13.0 tons kn kn 15.3 tons kn TRIPLES Make first hit single K.O. up, second hit double K.O. up with relief. QUADS Make first hit double K.O. up, second hit double K.O. up with relief. 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. 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. 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. SHEDDER SPRING SHEDDER INSERT UPPER INSERT RETAINING RING(S) STRIPPER MATERIAL THICKNESS C D LOWER INSERT ( ).060(1.52).030(0.76) ( ) ( ).090(2.29).120(3.05).050(1.27).060(1.52) STRIPPER SPRINGS ( ) ( ).180(4.57).250(6.35).090(2.29).125(3.18) Dimensions in inches (millimeters) DIE BODY 1 1/4 B STATION 2 C STATION 3 1/2 D STATION 4 1/2 E STATION

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