Difference Between Bulk Deformation and Sheet Metal Forming

The key difference between bulk deformation and sheet metal forming is that in bulk deformation, the work parts have a low area to volume ratio whereas, in sheet metal forming, the area to volume ratio is high.

Deformation processes are important in transforming one shape of a solid material into another shape. Usually, the initial shape is a simple one. We can deform it using tools to obtain the desired shape. Moreover, this process is important to increase the tolerance of a solid material.

CONTENTS

1. Overview and Key Difference
2. What is Bulk Deformation 
3. What is Sheet Metal Forming
4. Side by Side Comparison – Bulk Deformation vs Sheet Metal Forming in Tabular Form
5. Summary

What is Bulk Deformation?

Bulk deformation is the metal forming operation where a significant change in shape occurs via plastic deformation in metallic parts. Usually, the initial shapes of the material can be cylindrical bars, billets, rectangular billets, slabs, etc. In this process, we plastically deform these structures in cold or warm/hot conditions to get the desired shape. The bulk deformation process is important in manufacturing complicated shapes having good mechanical properties. Furthermore, in this process, we can observe a considerable increase in the surface-to-volume ratio. We can list the characteristic of bulk deformation as follows:

• The plastic deformation of the workpiece is large, making a considerable change in shape and cross-section
• Generally, the permanent elastic deformation is larger than the elastic deformation of the workpiece.

The operational steps of bulk deformation are as follows:

1. Forging – squeezing and shaping the initial structure between two dies
2. Rolling – squeezing a slab r plate-like initial structure between two rotating rolls to reduce the height
3. Extrusion – squeezing the initial shape through a shaped die so that the shape of the workpiece changes into the shape of the die
4. Wire and bar drawing – changing the shape of wire-like and bar-like structures

What is Sheet Metal Forming?

Sheet metal forming is a metal forming operation in which the geometry of a piece of sheet undergoes modification upon the addition of a force. Here, no removal of the material is done. Furthermore, the applied force has to be larger than the yield strength of the metal. It causes the metal to undergo plastic deformation. Using this method, we can either bend or stretch a metal sheet into the desired shape.

Moreover, this process includes plastically deforming a sheet metal into a complex 3D configuration. Generally, this method does not make any significant change in thickness and surface characteristics of the sheet. The characteristics of this method are as follows:

• Workpiece – a sheet or a part fabricated from a sheet
• Changes the shape but not the cross-section
• Sometimes, the permanent plastic deformation and elastic deformation are comparable. Thus, elastic recovery is significant

What is the Difference Between Bulk Deformation and Sheet Metal Forming?

Bulk deformation is the metal forming operation where a significant change in shape occurs via plastic deformation in metallic parts, while sheet metal forming is a metal forming operation in which the geometry of a piece of sheet undergoes modification upon the addition of a force. The key difference between bulk deformation and sheet metal forming is that in bulk deformation, work parts have a low area to volume ratio whereas, in sheet metal forming, the area to volume ratio is high.

Moreover, the initial shape of the workpiece can be billet, rod, slab, etc. in bulk deforming process while, in sheet metal forming process, the initial shape is a sheet.

The below infographic provides more description of the difference between bulk deformation and sheet metal forming.

Summary – Bulk Deformation vs Sheet Metal Forming

Bulk deformation and sheet metal forming are important deformation process for metal workpieces. The key difference between bulk deformation and sheet metal forming is that in bulk deformation, the work parts have a low area to volume ratio whereas, in sheet metal forming, the area to volume ratio is high.

Reference:

1. “Read ‘Unit Manufacturing Processes: Issues and Opportunities in Research’ at NAP.edu.” National Academies Press: OpenBook, Available here.
2. “Mechanical Engineering – Design For Manufacturing.” NPTEL, IIT Bombay, Available here.

Image Courtesy:

1. “Huge drop hammers work day and night forming sheet metal parts for United Nations bombers and fighters at the North American Aviation plant, Inglewood, Calif” By Alfred T. Palmer –  from the United States Library of Congress’s Prints and Photographs division (Public Domain) via Commons Wikimedia