Constrained Ironing

Abstract

Constrained ironing as a new ironing method is proposed for producing thin-walled cans and components with uniform thickness and based on compressive stresses could reach a higher ironing limit ratio or thickness reduction ratio (TRR) without interruption for additional processing such as multi-stage ironing and annealing between different stages. The punch pushes the constrained material to reduce the thickness from the outer surface of the cup. The state of the stresses is fully compressive in this new process while it is tensile in the conventional ironing method.

1 - A new method of constrained ironing process comprising the steps of:
 a) Deep-drawn cup is placed on a punch;   b) Then said cup and punch are placed inside a special die;   c) Applying force to said punch via any type of hydraulic, water or electric press;   d) Said cup is forced and driven into said ironing die, wherein during this process walls of said cup are deformed and reduced in thickness.   
     
     
         2 - The method of  claim 1 , wherein said punch is cylindrical and directly receives required force for said constrained ironing process from a press machine. 
     
     
         3 - The method of  claim 2 , wherein an edge of said cylindrical punch imposes force into said deep-drawn cup and according to an internal geometry of said die, said thickness of said deep-drawn cup is at least 80% in just one step of stress to said deep-drawn cup, without a need of an ironing ring. 
     
     
         4 - The method of  claim 3 , wherein said die includes a knob with a specified angle (ironing angle) and said die comprises a step pattern and therefore an edge of said punch fits and sits on an edge of said cup. 
     
     
         5 - The method of  claim 4 , wherein in addition to ironing ductile parts, said process is capable of ironing crisp pieces and parts. 
     
     
         6 - The method of  claim 5 , wherein after constrained ironing process, tensile strength and hardness increased to 204 MPa and 85 HV respectively from an initial value of 71 MPa and 25 HV. 
     
     
         7 - The method of  claim 6 , wherein a TRR (Thickness reduction ratio) is calculated using formula: TRR=(t i −t f )/t i  wherein t i  and t f  define an original and final thickness of said cup respectively. 
     
     
         8 - The method of  claim 7 , wherein in said process there is no need for annealing parts between each step of ironing process to improve ductility and removing hardening. 
     
     
         9 - The method of  claim 8 , wherein said final drawn cup comprises a very high strength-to-weight ratio and can be utilized in various industries, comprising but not limited to food packaging industry, automotive and defense industry. 
     
     
         10 - The method of  claim 9 , wherein hardness and strength of said drawn cup increases significantly in comparison to basic raw piece (at least double).