| Recast Layer AFM |
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The thing about the Recast-Layer ...
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An incredible, disastrous thunderstorm. Hundreds of thousands of electrical discharges per second. An overwhelming succession of flashes as thin as a hair. Each one leaves a trace where it strikes and the temperature rises to an extreme level. Even the hardest steel melts like butter and evaporates to a whirl of gas, metal pieces, ions and electrodes. What are left are craters on the surface and unprecedented devastation in miniature. |
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The high temperature on the work piece surface cause thermal damage in the edge zones which has, as a rule a negative influence on the components life the condition produced is termed “The Recast Layer”
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This surface condition or "Recast Layer" is the result of dissipated energy in both the roughing an finishing phases of the EDM. The energy discharge changes the structure of the original material in the near Surface Layer. This results in a brittle combination of martensite and cementite with cavities and multiple micro cracks. Using electro microscopy three distinct layers can be detected. |
![[click to enlarge]](img/en_s23/img_4_1.jpg)
(Click to enlarge!)
Removal of the Recast Layer is one of the most important Jobs what has to be done to achieve the required results with eroded tooling.
MicroStream® helps you to reach ultimate perfection.
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I. Marginal area or white layer. It is often very irregularly formed and may be interrupted in places. Its width of 0,02 mm on an average depends on the surface contour.
II. Transformation area. Due to the high thermal stress in EDM operations there may be cracks on the grain boundaries.
III. Area of internal stress. The area of internal stress, the transformation can as a rule not be distinguished from the original basic structure. Nevertheless, under certain circumstances internal stress may penetrate into the basic structure.
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Die manufacturer have the need to remove the white layer after wire erosion completely. The energy discharge changes the structure of the original material in the near Surface Layer. This results in a brittle combination of martensite and cementite with cavities and multiple micro cracks – the so called Recast Layer. |
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A component such as a die is mounted in a fixture and hydraulically clamped between the upper and lower media cylinders.
The die is hydraulically clamped between the two pistons in the working area located in a fixture
Made to suit the die or workpiece. During the manufacturing process the lower piston first moves with a defined pressure from the lower to the upper arrest point. During this phase, there is no back pressure on the upper piston.
When the process is started the lower media piston rises and forces the Streamer through the part and
into the upper media cylinder. The process then reverses until all the media returns to the lower cylinder. This is designated as one cycle.
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Manufacturers of components and or dies which are produced in this way must eliminate this Recast Layer in order to achieve longer service life and surface finish, higher precision and shape definition and most importantly less process time.
MicroStream® - Abrasive Flow Machining (AFM) Technology, which had been developed and sold by Micro Technica Technologies GmbH Kornwestheim (Germany) is the answer.
MicroStream® uses a grit laden polymer based media called the Streamer© which is used to remove the Recast Layer and or polish the component. The streamer can be formulated to suit the application IE. De-burring, edge contouring or polishing. Once the media selection has been made it is loaded into the machine and flowed through or over the surfaces that require processing. Using the machine parameters a controllable result of surface finish or metal removal can be achieved. The following diagram shows the procedure.
The Streamer© (media) consists of a polymer plastic material, (the base) in which abrasive grit such as silicon carbide is incorporated. This provides the cutting tool needed to remove the recast layer and or edge contour and polish the appropriate features.
This result is achieved by passing the streamer in a laminar flow condition backwards and forwards across and through the die or workpiece |
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The removal of the brittle Recast Layer using MicroStream® ensures that the possibility of surface breakdown is removed. Which means that the quality and service life of the dies increases and proportionately the throughput of the extruded profiles increases, with the added bonus of superior surface finish.
It is for this reason the MicroStream® technology is used worldwide by the leading die suppliers to all kind of extrusion industries especially aluminium and plastic. |
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More information about our additional services for this product/ method you can get here:
- subcontracting/ contract services (job polishing)
- services
Look also for our additional product for Aluminium-Extrusion:
- Save and parallel opening of Aluminium Extrusion Dies
If you have questions about Recast Layer please use our
 Web Request or call us by phone. |