The question requires a clarification:

1. Which composite exactly is under consideration?

2. Which type of forging was applied: open-die or close die? The illustration figure is unclear.

3. Which temperatures the workpiece had achieved?

Anyway, undesired dimensional distortion of the product may be caused by:

- differences in thermal expansion of different materials composing the workpiece;

- improper die design;

- improper operating load or/and stress rate;

- improper overall strain per one forging stage; 

- etc.

dear Abdul Basit, as Alexander pointout, it would be good to know the type of composite you are talking about. It seems you talk about a composite with metal as base or filler material, but what kind of additional materials are in this composite and how are they distributed (orientation, density, ...). If your software allows for an element distortion or deformation analysis (it would be helpful to include such a figure as well).

However the reason the rectangular structure in the squared block is most likely due to your inner material flow. Since you start from a cylindrical shape early stage compression will be also a cylindrical but flatend one as well. When the perimeter surface starts to touch the die faces, friction starts to constrict the material flow in this local area and the material to fill the corners of squared die is not distributed equally anymore from that point of time onwards. Staring from the cylinder the diagonals provide the longest flow distance for the material (the shortest are the center lines parallel to the side faces). The diagonals are longer by the factor of 1.41 (sqrt 2). The exact shape of the star-like or rectangular shape depends on local temperature and friction mostly as well as on further (composite) material properties.

It this helps, vote up / recomment this answer. Thank you!

Just let us know more about your materials and processes. Now Looks like folded surfac ( too fast cool) or underfilling.

Alexander Katz-Demyanetz Rüdiger Rentsch Xu Wang Thanks alot for your kind reply. The material is Al 6061(90 %) + B4C (10 %). forging is open die hot forging with hydraulic forging press. the ingot is heated in furnace at 550 degree during 6 hours. the die is also heated at 350 to 400 degree. the effective ingot temperature during forging is around 300 degree as when we move ingot outside furnace toward forging press some temp loss. the forging is done step wise.

Alexander Katz-Demyanetz can you please elaborate how to set overall strain per one forging stage & operating load or/and stress rate? also i want to know does direction of forging effects the final properties of billet? i mean if we forge the ingot in axial or radial direction or by combination of both direction does it effect the final properties of material. Rüdiger Rentsch Xu Wang Alexander Katz-Demyanetz

Dear Abdul Basit,

Thank you for the information about your material and process. I would perform a set of preliminary experiments to answer great questions you asked. I would take a “standard” prism of pure Al as well of your composite material, would plot on them a “lattice” and then would subject them to various strains. Then I would measure local distortions (using a plotted lattice) and would check microstructure. Actually, you need a set of such prisms to try a set of various strains. Analyzing the results to be obtained, I would exactly define your forging process’s parameters. Anyway, I suppose, that a forging at different directions will result in different properties. So, on my opinion, you have very interesting brief applicative research.

If you will have any questions, I would be happy to help.

Alexander Katz-Demyanetz thanks for taking interest in my research.yes i would very much appreciate your help. how would you plot the lattice i mean to say which software you use for this purpose? i would like to know about the software for this purpose if this is easily available. what do you think if we have an isotropic ingot before forging then also forging direction will result in different properties? and in which direction will get better properties in longitudinal or radial? i also agree with the point of Rüdiger Rentsch that friction will also effect as during process we are not using proper lubrication of die .

Xu Wang too fast cool means after forging we have to furnace cooled the billet? currently we cooled in open environment? but this impression comes during forging also .

Dear Abdul Basit,

Speaking about plotting a “lattice”, I meant just a physical plotting of a set of parallel/perpendicular lines onto the workpiece by a temperature-resistant pen. I did that manually and then measured distances between the lines at various places of the workpiece after forging. When you will do that, you will see that how and where you process is uniform, and then you will be able to “play” with the process parameters (stain, strain rate, lubricant, temperature, amount of ceramic reinforcement, etc,) and see how each of them affects process uniformity. Most possible, that you will reveal that indeed, the friction is responsible for the uniformity. But, probably, amount of a ceramic particulate affects it too (I did not remember any non-uniformity problem with pure Al6061).

Additionally, I recommend to perform finite element (FE) analysis of stresses/strains in your process. Since I am not an expert in FEA, I cannot help you in this task (please, check experts/companies doing that in you area), but it will be interesting to compare strain FEA prognosis with those you will obtain experimentally.

Dear Abdul Basit from what you have been writing, I think you deal with fundamental principles in forming / forging which are simply material flow and friction in general. you wrote the effective ingot temperature during forging is around 300 degree which refers to the squared die of the final shape right? unless you make intermediate forging steps to alter your material flow you will only reduce the effect of different flow length into the corners by influencíng the friction using lubricants. The pattern may look more symmetric with less pronounced flow into the diagonal corners, but it must look similar unless you change the material flow by intermediate steps. FEM can help to design than material flow, also surface grid using a temp resistant pen a. It depends on how much effort you like to put into.

Rüdiger Rentsch sir your guess is true i am attaching the actual picture of forged sample. the pattern as per your guess is almost same having less pronounced flow in the diagonal corners and also symmetric. by intermediate steps you want to say that during steps direction of forging along with the strain can effect the metal flow. it means by lubrication this impression will be same unless we have to change the intermediate steps.? also i want to know that with in impression metal flow is good as compare to edges am i right? what would be the effect of mechanical properties within impression and out side impression specially tensile ,yield strength and also hardness.

Rüdiger Rentsch also we are performing open die forging to make this shape not closed die forging. we perform forging in different directions longitudinal axial and radial to get this final shape.