WEB – This is the “minimum” width requirement of material on the circumference of your blank to assure proper trim to prevent rolling edges and burrs. To arrive at the minimum required WEB you use your known Nominal Material Gauge (.119) and ADD to this ½ of the known gauge (.060). However, you will NEVER use “less” than .187 at any time for the Web in calculations. Examples as follows:

Known Material Gauge (.119) + ½ of the known gauge (.060). In this case .119 +.060 = .179 which is less than the firm rule of a minimum of .187 so we would want to use a .187 in any of our calculations. If we had started with a known gauge of .300, we would have to add .150 (1/2) and we would have a WEB at .450 for all calculations. Never less than .187!!

PROGRESSION or PITCH – This is the distance that you will have to move the material forward with each feed in order to assure a burr free blank.

PROGRESSION is arrived at by using your known Circle Blank Diameter (18.00”) and adding to it the previously established WEB (.187) as follows:

18.00” + .187” = 18.187” PROGRESSION

REQUIRED COIL WIDTH – This is the “minimum” required Coil Width that you will use when applying your material to the Press and Die to arrive at a Burr Free Blank. First thing you need to determine is how many blanks per stroke of the press (Parts per Hit) do you plan on producing? Many factors come into play when making this determination a few of which are die build cost, annual piece volume and not least of all equipment capabilities. Once known you can establish your REQUIRED COIL WIDTH by using the following Formula:

If Producing on a Single Cavity Die you will use – Circle Diameter + 2 Webs.

Example:

18.00 +.375 = Required Minimum Coil Width of 18.375”

If Producing on a Multiple Cavity Die (2 or more) you will use the following:

Circle Diameter + 1 Web x .86603 x number of blanks per hit (less 1 Blank Diameter) + 1 Blank Diameter +2 WEB’s.

Example to Calculate Width requirement for a 3-Out Die:

18.00 + .187 x .86603 x 2 + 18.00 +.375 = Required Minimum Coil Width of 49.876”

BLANK GROSS WEIGHT – Required weight of raw material expected to be used when producing (1) each Circle Blank. This is calculated by using your previously established Gauge, Coil Width, Progression and the following formula:

Nominal Gauge x Required Coil Width x Progression x Per Inch Density of Low Carbon Steel Divided by Number of Die Cavities (blanks per hit). It is standard to then add 2% to this to cover for Coil Head & Tails Scrap as well as expected Production loss due to unforeseen issues.

Example Using a 1-Out Single Cavity Die:

.119 x 18.375 x 18.187 x .2833 = 11.267 lbs. Per Blank x 1.02 = 11.49 lbs. Per Blank

Example Using a 3-Out Multiple Cavity Die:

.119 x 49.876 x 18.187 x .2833 Divided by 3 = 10.194 Lbs. Per Blank x 1.02 =10.40 lbs. Per blank

(Note that in above examples the 10% Material Reduction per Blank being generated by using a 3 Cavity Die Production method vs. the 1 Cavity Method)

BLANK NET WEIGHT – This is the “final free-standing” weight of each Circle Blank minus all scrap. This weight is calculated as follows:
Circle Blank Diameter Squared (Circle Blank Diameter x Circle Blank Diameter) x .7854 x Nominal Gauge x Per Inch Density of Low Carbon Steel.

Example:
18.00 x 18.00 x .7854 x .119 x .2833 = 8.58 lbs. Per Circle Blank

SCRAP/OFFAL – These are the Industry Standard Terms used to describe any of the material that is left over after production, being the difference between the Gross Weight and Net Weight. This is shown as follows using both our previous Die Layouts:

Example Using a 1-Out Single Cavity Die: Gross Weight of 11.49 lbs. – Net Weight of 8.58 lbs. = Scrap Each of 2.91 lbs. or 25%

Example Using a 3-Out Multiple Cavity Die: Gross Weight of 10.40 lbs. – Net Weight of 8.58 lbs. = Scrap Each of 1.82 lbs. or 17.5%

(Note again the difference between a 1-Cavity Scrap % vs. a 3-Cavity Scrap % is significant)

NESTING – The act of producing a layout that gives you multiple blanks per hit thereby reducing scrap content/material cost per piece by using the previous calculations provided under “Required Coil Width”.   

PRESS TONNAGE REQUIREMENT – As mentioned earlier Press Tonnage Required to Produce is one of the major factors in determining how many “Cavities” or Number of Blanks per hit you can accommodate. The following is not exact however a good “rule of thumb formula” handed down to me years ago by a wise old tooling engineer and was used to determine the “tons per cavity” required to produce any given blank. There are other factors that can reduce or increase this Tonnage such as “staggering” and” timing” of your die and also material Tensile and Grades that should be taken into account and adjusted to accordingly. Again, this is an approximate calculation assuming utilizing “Low Carbon Steel” only!

Blank Diameter x Gauge x 80 (Approximate Tons required per Lineal Inch to Cut Low Carbon Material) = Tons Required per Cavity x Number of Cavities = Total Press Tonnage Requirement.

Example Approximate Tonnage Requirement to Run a 1-Cavity Blank Die:

18.00 x .119 x 80 = 171 Tons

Example Approximate Tonnage Requirement to Run a 3-Cavity Blank Die:

18.00 x .119 x 80 x 3 = 514 Tons

Final Considerations – Any time that you can accommodate utilizing a full Master Width Mill Coil you want to do so. All Mills have their “minimum” limits for width production and begin to charge accordingly once you drop beneath them (most want a minimum of 48.00” before adding extras). This will also provide you savings by reducing your scrap cost (Gross vs. Net Weights) additionally eliminating the Charges for Slitting the Coils down to a Narrower width for your use and the associated 2% additional scrap for doing so. At all times always try to utilize Multiple Cavity Tooling and Master Mill Coil Widths and eliminate “scrap” which is money in your pocket!