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Explanation Of Sheet Metal Drawing Operations

In MechanicalBase.com, there are lots of kinds of articles about sheet metal technology and sheet metaş production techniques. You can find out various kinds of informative and deep information about the sheet metal industry here. 

In this article, we will talk about sheet metal drawing operations. As you know that, sheet metal cutting and sheet metal bending operations are the other two major categories of sheet metal operations. As a third one, you will be informed about the sheet metal drawing operations. 

What Is The Sheet Metal Drawing?

Fundamentals of Modern Manufacturing: Materials, Processes and Systems, Seventh Edition

If you are interested in the guidebook that is used for this article, click on the given link above or the ‘Shop Now’ button to check it from Amazon!

In sheet metal drawing operations, generally cup-shaped, box-shaped sheet metal structures are obtained. These structures are generally complex, concave-shaped structures that can be produced with sheet metal drawing operations easily. 

To do it, a workpiece is placed upon a blank hole and it is attached with blank holders. Upon the hole and the workpiece, a punch makes the reciprocating motion to make the workpiece take the shape of the blank hole. 

With this very basic mechanism, beverage cans, cooking appliances, ammunition shells, etc. are produced. 

Basic Principles Of Sheet Metal Drawing Operations

Image Source: Mikell P. Groover; Fundamentals Of Modern Manufacturing, 4th edition, pg. 455.

If we take a look at the basic principles of sheet metal drawing operations, we can introduce the basic parameters like below. 

‘Dp’ is the diameter of the punch which makes reciprocating motion in the sheet metal drawing mechanism. 

‘Rp’ is the corner radius of the punch and the ‘Rd’ is the corner radius of the die. These radius values are very important to obtain successful drawing operations. Without these radius values, hole-punching will be obtained which is an expected technique from sheet metal cutting operations. 

The blank holders are applying ‘Fh’ force to the workpiece. ‘Db’ is the diameter of the workpiece sheet metal. 

A specific amount of clearance ‘c’ must be designed between the punch and die. This clearance value is generally 10% greater than the diameter of the thickness of the workpiece. 

As you understand from the mechanism that there will be a gradual bending occurring at the beginning of the operation. When the punch moves and starts to deform the sheet metal workpiece, bending occurs at the edges of the dies. While the punch moves to the bottom of the die, straightening of the cup-shaped part’s wall occurs. 

Because of the force application of the blank holders, friction takes place between the workpiece and the die. This friction must be designed correctly to obtain a successful sheet metal drawing operation. 

Severity Of The Sheet Metal Drawing Operations

There are some basic calculations related to the severity of sheet metal drawing operations. One of these calculations is the drawing ratio, DR. Drawing ratio is calculated as the ratio of blank diameter to punch diameter. In general, the upper limit of the drawing ratio is defined as 2.00. The greater the ratio means a severe drawing operation. 

Eliminating Wrinkling

Wrinkling is one of the most encountered defects in sheet metal drawing operations. But, it can be eliminated with a very simple calculation. The thickness to diameter ratio must be calculated to overcome this problem. The thickness to diameter(t/Db) ratio is expressed as a percentage and it must be over 1%. With the increasing thickness to diameter ratio, the tendency to wrinkle decreases. 

Conclusion

This article is a good summary of sheet metal drawing operations. 

Do not forget to leave your comments and questions below about the sheet metal drawing operations!

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