General Principles of forging

Die forging.Image by sino industry.

Forging is the process in which the material is shaped accordingly by compression by use of pair of dies.
The conventional definition can be simplified if you see the operation of smith .
A smith uses his hammer on hot metal.
And we know engineering simplifies these works in efficient way.
How do we do that?

Power source and dies.

Grain structure by tpub.com

These dies simply have the condition that their strength should be more than that of work piece.

In material science,the study of material is not only to the level of atomic arrangements but it goes upto a new level which is macroscopic in nature.
The fascinating Grain structure arrives!
What are they?That's pretty important to know.
When a the material solidifies from molten state then the solidification starts from different points.It is just like ice cube solidification in refrigerator in trays.They solidify from free surface( which is cooler) to bottom.In that way,at different points solidification starts.Each point has its own direction of solidification.At end there are different solidified points which are separated by boundaries.These solidified points are grains and all together form grain structures.
These grains define different mechanical properties.

Let's come back to our concerned point,forging!
When the force is applied on material here then the direction of force  can be controlled thus,the flow of grains can also be controlled and desired mechanical properties can be achieved .

Original               Modified with draft

But then also a proper design of forging should always be considered before the actual operation.
So some basic principles of forging design are as follows:

1.Draft should be provided.
 Because when the work piece which is hot cools down in die then it shrinks,For easy removal proper draft angle should also be provided.
With that one important point is also needs to be considered that if the work piece is hollow then the outer surface will shrink and detach with die but inner surface after shrinking will tighten to the die projections.
So draft angle should be larger in inner surface for easy removal so that it con loose its grip.

2.Forging Plane and Parting plane.
A die is just like two cups.But they can align in different ways according to their shapes.
A parting plane is the line formed along the periphery when dies meet.
A forging plane is the imaginary plane perpendicular to die motion.They both can coincide but not in all cases.But the cases where both don't coincide there unbalanced forces can occur.It is better that both coincide and the dies are symmetric in nature.

Dotted line- parting plane and Red line- forging plane

Forging press.Image by machineryforsale.com

3.Fillet radius and corner radius
It shouldn't be too large or too small.
Small radius causes high forging forces,improper filling of die and can cause poor die life.
Large radius is not desirable for the parts which have to be machined further as strain fields break.

4.Thin sections should be avoided as removal from die is not easy.
 Thin sections cool faster and can effect die life.
How?
Die design can be challenged if the material is too hot.Faster rate of cooling is also not favorable.

5.Fiber lines and load.
 The design of component should be in such a way that fibers of material should be parallel to axial load.The biggest advantage of forging is these fiber lines can be directed during the process and thus they can counter their loads during their work life.

image by nps.gov showing fiber lines