Extrusion dies are one of the most important tools in the extrusion equipment. Dies are used to form extruded profiles that of virtually limitless array of sizes and shapes. With regard to the extrusion process that is of aluminium, rubber or plastics there can be various types of dies that are used. The following image shows typical dies that are used in aluminium extrusion process. Take a careful look at the opening of the dies, actually they correspond to the cross section of the profiles.

Dies irrespective of the extrusion process must have a good design for a successful operation. These design criteria of dies are described here.

Design Criteria of Dies
For designing dies with certain cross sections, there is need to take the following points into consideration.

• Avoiding Knife edges
• Smooth transitions
• Keeping the wall thickness uniform
• Symmetry
• Strong die for improved performance
• Avoiding thin details at the end of Flange

Challenges in the Extrusion Design
For most of the companies that are engaged in extrusion, every one would agree that obtain the final shape of the extruded profile is the most time consuming and challenging task. Often it is seen that a dozen or so trials are required before finally the correct die cut is obtained that will result in the correct shape. Some of these challenges are with regard to:

• Die swell
  In case of plastic extrusion, as the melt leaves the die there is a tendency of large deformation throughout the free jet. This is known as die swell and may result in actual contraction of the flow section especially near the die region.
  
• Die imbalance
  An unbalanced die can result in the extrudate leaving the die at varying speeds this can lead to deformation.
  
  
• Coextrusion
  The main challenge in the co extrusion process is to ensure a perfect interface between the two materials.
  
  
• Die Deformation
  Die deformation takes place due to high internal pressure: this is true while extruding wide and thin films.
  
  

Types of Extrusion Dies
Broadly extrusion dies can be classified into three categories:

• Aluminium Extrusion Dies
• Rubber Extrusion Dies
• Plastic Extrusion Dies