In AMTS we develop the following forming processes:

• Deep drawing
• Super plastic forming
• Closed die forging

Deep drawing:
In deep drawing process the indirect effect is typical.
The required process load moves from the bottom of the shape through the walls to the flange (sheet metal in the die shoulder area) while the deformation exists under radial tensile stresses and tangential compression stresses.
The typical drawing processes lean on two different sub-processes: deep drawing and stretch forming.

When drawing a cup, until the final and complete shape is achieved, the part is shaped mainly by tensile stresses in cylindrical symmetry (conditions of stretch forming). In this stage the deformation is defined by the reduction of the sheet thickness. Then the real deep drawing process starts and is defined by transfer of the flange material into the cup walls. If the tangential compression stresses in the flange overcome the buckling resistance, wrinkles occur. As the result of the flange holding, normal forces are operated in order to abolish wrinkles occurrence.
The drawing ratio (Dblank/dpunch) characterizes the deep drawing capability at a required geometry.

In the deep drawing process one should refer to:

Maximum material investigation data including the integration of hot forming lubricants.

1. Forming simulation process according to a 3D model given by the customer.

The next step is to design a steel die, fixtures and heating tools. At this point the use of FE software to verify desirable heat transfer is much necessary.

During the process we keep the following parameters:

• Lubricants dispersion: on the blank sheet as well as on the die surface.
• Pre-heating schedule.
• Die segments temperature: the non-homogeneity of the temperature throughout the formed sheet should be a key parameter.
• Blankholder pressure.
• Drawing speed function. 

Full computerized control system of a triple action 1000 ton hydraulic press, together with on-line thermal and true stress indication of internal die-set, provide us to run a quite sensitive process of deep drawing.

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	Sketch of deep drawing process

Super Plastic Forming:
AMTS has acquired significant experience in Super Plastic Forming of magnesium sheets.

Exteremly complex geometry out of sheet metal requires the use of super plastic forming technology. This method is carried out at high temperatures, sometimes, and using inert gas or fluid pressure.
The materials that are most often used in SPF for aircraft structures are 5083 and 2004 aluminum alloys.
Before the SPF process is done, the sheet must undergo a fine mechanical polishing.

Superplasticity is the ability of some materials to develop very large tensile elongations (up to hundreds and thousands percents) without necking. There are several requirements for a material to be able to exhibit superplasticity: 

• Fine and equiaxed microstructure (grain size generally < 10 µm).
• Grains stable under high temperature: Temperature higher than 0.4 Tm (absolute melting point).
• Strain rate sensitivity exponent )M).

Basic HCP structure of magnesium alloys with addition of refined microstructure (which might occur due to preliminary plastic processes followed by full annealing procedures) enable very good results in the production of thin wall magnesium complex parts.

SPF development process pays special attention to the following parameters:

• Gas pressure function (including manipulation of back pressure).
• Temperature regime within mold's segment.
• Deformation rate (obviously depends on the above two parameters).

The entire process is controlled by the main computer which controls the loads, the pressures and the temperatures.

Very large geometries can be produced by Palbam SPF system thanks to huge (hundreds tons) vertical pressing forces that can be applied upon the blankholder.

At the end of the SPF process examinations of thickness reduction in wall thickness within critical areas are performed. In addition mechanical tests of formed samples usually lead to farther conclusions.

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Closed Die Forging:
These are the stages of a forging process development:

1. Selection of the material that will best meet the mechanical requirements of the part to be forged.
2. Our experience in material investigation shows that the DC cast process is the key. A consequent extrusion or isothermic cross rolling process (for bar or thick plate configuration) shoulfd follow tight process procedure in order to refine the microstructure.
3. An elementary forging process is done in order to verify receiving of required mechanical (static and fatigue) properties.
4. Examination of the part geometry and design of die supported by simulation process.
5. When the theoretical process is approved we can produce the die, the tools and the heating and control systems.
6. During the forging process, the following parameters are examined:

• Force-displacement functional analysis.
• Influence of grain refining on strain rate.
• Influence of forging speed on cracking effect.
• Influence of pre-heating schedule.  
• Influence of microstructure on required forging temperature.
• Influence of forging temperature on mechanical properties and directionality.
• Influence of lubricants on material flow and mold filling.

The entire process has a computerized control, including a load cell placed on the forging tool (see lower picture).
Three synchronized press movements are controlled.
The strain rate, temperatures and heat remove (by water cooling rings) from clamping fixtures are also controlled.
The forging rate is limited due to cracking risk.
The advantage of using a hydraulic press is the ability to control forging rate, deformation scale and especially the option to hold back maximum press force at bottom dead center.

Cooling of the forged part in the apropriate schedule is done at the end of  the forging process in order to avoid grain growth.
Samples of the forged part undergo mechanical, metalographic and radiographic examination during the process iterations for online feedback.

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