Re-evaluating the EDM Process for Aerospace Components

Source: Ken Baeszler
Added 03.14.2009

New methods to reduce cost and improve performance

 

Aerospace manufacturing is also changing…

Excerpts from the Bureau of Labor Statistics –

The way in which commercial and military aircraft are designed, developed, and produced continues to undergo significant change in response to the need to cut costs and deliver products faster...

 

...Increasingly, firms bring together teams composed of customers, engineers, and production workers to pool ideas and make decisions concerning the aircraft at every phase of product development...

 

Source: Bureau of Labor Statistics, U.S. Department of Labor, Career Guide to Industries, 2008-09 Edition, Aerospace Product and Parts Manufacturing, on the Internet at http://www.bls.gov/oco/cg/cgs006.htm (visited July 15, 2008).

 

The aerospace improvement imperative:

Reduce cost:

  • Capital cost
  • Operating cost
  • Material cost
  • Floor space requirements

Reduce time to market:

  • Reduce secondary operations
  • No harm to quality and consistency

 

EDM and Aerospace: Current perspective / Breaking Barriers

What we know about EDM:

  • EDM can remove material that is otherwise difficult to machine.
  • EDM does not face the same machining challenges of today’s ultra-tough alloys.
  • Component material only needs to be electrically conductive.

 

What we also know about EDM:

  • Material is removed by heat, thus causing the potential for a recast layer on the parent material.

 

We are breaking barriers:

  • We have improved the process to significantly reduce and/or eliminate the recast layer.

 

Process Review: EDM

Events before electrical discharge

  1. The workpiece and tool are placed in the work position so that they do not touch.
  2. A gap remains, filled by the "dielectric".
  3. The workpiece and tool are connected to a power source via a cable.
  4. A switch is inserted in the connection.
  5. When closed, an electrical voltage is set up between the workpiece and tool.

 

The electrical discharge.

  1. At first no current flows because the dielectric acts as an insulator.
  2. When the gap is decreased to a given distance (very small), an electrical discharge with spark is struck.
  3. During the discharge, the voltage is decreased and the current causes considerable increase in temperature at the spark point.
  4. This causes small quantities of metal to melt and evaporate.

 

The formation of the surface

  1. When the switch is opened, the molten material is dispersed just like an explosion.
  2. The discharge channel is deionized and a small crater remains.

 

 

 

Summary of the EDM Process:

ELECTRICAL DISCHARGE MACHINING (EDM)

  • A controlled spark is struck between conductive materials.
  • The sparks cause a series of small craters, with consequent material removal.

 

The EDM improvement imperative:

 

The 21st century wire EDM generator:

  • Improved surface integrity
  • Improved speed
  • Improved energy efficiency

 

History of Generator/Servo technology in the 20th century

The early years: wire EDM

 

History of Generator/Servo technology in the 21st century

Improving Performance

 

Electronics Efficiency = Spark Efficiency

Innovations:

  • Process control as close to the spark as possible
  • High, process-dedicated computer performance (40 MIPS)
  • Complete digital data aquisition
  • FPGA technology


Results:

  • Fast, precise servo
  • Optimal and fast process control
  • Constant EDM results

 

 

New Generator results:

 

Material: Inconel

 

Material: Titanium

 

Titanium Surface Oxidation: Then and Now

Surface oxidation caused when machining titanium. 
On the right side is the old generator; on the left side is the new generator.

 

 

Wire EDM erosion speed in the 21st century

Improving Erosion Speed

 

 

The 21st century Die-SInk EDM generator:

  • Improved surface integrity
  • Improved speed
  • Improved energy efficiency

 

 

History of Generator/Servo technology in the 20th century

The early years: Die-sink EDM

 

 

History of Generator/Servo technology in the 21st century

The early years: Improving Performance

 

 

Wire EDM Spark vs. Die-sink EDM Spark

Improving Performance

 

 

Intelligent Pulse Generators


Innovations:

  • Process control as close to the spark as possible
  • High, process-dedicated computer performance (40 MIPS)
  • Complete digital data aquisition
  • FPGA technology

 

Results:

  • Fast, precise servo
  • Optimal and fast process control
  • Constant EDM results

 

 

Programmed discharge during asymptotic state

Patented process

 

 

Results of intelligent spark discharge

Patented process

 

 

Waiting for the right moment...

Patented process

 

 

Almost...but not yet!

Patented process

 

 

We're getting close!

Patented process

 

 

Discharge at the “end phase” of the pulse

Patented process

 

 

Intelligent spark discharge: why it works

  1. Asymptotic behavior determines that the discharge voltage is in balance with the instantaneously flowing discharge current.
  2. Current amplitude is increased just before the end of the pulse
  3. The high energy at the “end phase” of the pulse prevents re-solidification of the fused phase.
  4. The thermally damaged layer therefore becomes smaller.
  5. Subsequent cuts need less time to remove this layer.

 

 

The results of intelligent spark discharge

Legacy Generator Results:

  • Larger area of thermal damage
  • Deeper crater
  • Rough, inconsistent finish
  • Inefficient stock removal rate

Intelligent Generator Results:

  • Smaller area of thermal damage
  • Shallow crater
  • Fine, consistent finish
  • Efficient stock removal rate

Intelligent Power Generation

 

 

Surface improvement with intelligent spark control

  • True Ra 0.05 um surface quality
  • No white layer

 

 

Additional benefit with die-sink EDM: decreased electrode wear

 

EDMing of one Cavity with one Trident Shape Electrode.

Workpiece Material: Steel 1.2343
Electrode Material: Graphite (EDM3)

Cavity Info:
Undersize0.40mm
Erosion depth - 34 mm
Roughness Ra 1.68µm

Result: with iQ Technology:
Erosion time: 3 h 27 min.
Wear = 5 µm

With Standard technology:
Total Time: 3 h 15 min.
Wear = 468 µm

 

 

Incorporate EDM as part of the improvement imperative!

 

 

Opening doors: economical use of materials

Wire EDM:

  • Off cut can be used for smaller components
  • Single setup potential
  • High scrap value

Conventional machining:

  • No off cut, only chips
  • Multiple setups
  • Low Scrap value

 

 

Opening doors: efficient use of energy

The energy savings could amount to over $4,000.00 per year!
Calculator Source: http://www.csgnetwork.com/energycostcalc.html

 

 

something else to consider...

chart caption: On average, wire prices have increased 50% over 3 years

 

 

Opening doors: reducing consumable needs

Combines high generator efficiency and lower power requirements with:

Less wire consumption

  • Rough with large wire, finish with small wire.

OR

  • Utilize .006” wire for cuts that once demanded .010” wire.

Less filter and resin consumption -

  • Smaller wire means 40 percent less filter and resin consumption.
  • Reduces environmental hazards.

 

 

Wire EDM and the improvement imperative:
How intelligent generators reduce cost

  1. By consistent spark generation:
      • Reduce or eliminate recast layer.
      • Repeatable results, time after time
  2. By improving cycle times:
      • Faster generators
      • Less trim cuts
  3. By cutting operating costs:
      • Wire consumption
      • Power consumption

 

 

Die-Sink EDM and the improvement imperative:
How intelligent generators reduce cost

  1. By consistent spark generation:
      • Reduce or eliminate recast layer.
      • Repeatable results, time after time.
  2. By improving cycle times:
      • Faster generators
      • Improved process control
  3. By cutting operating costs:
      • Zero-wear technology
      • Utilizing economical electrode material

 

 

The improvement imperative: Our shared goals

  1. Replace troublesome manufacturing processes.
  2. Reduce Material Costs.
  3. Reduce Capitol Costs.

 

 

Time to investigate!

Aerospace manufacturing needs to change with the times.

  • We must lower cost and improve performance.

 

We must break the mindset that the EDM process is still the same.

  • Results are clear about intelligent generator performance.

 

We must work together to bring about change we can believe in!

  • Joint projects to benchmark old processes and test new ones. 

 

Applications

  • Aeronautic
  • Aerospace
  • Defense
  • Education
  • Electronics
  • General Machining
  • Household
  • Leisure
  • Luxury
  • Mecatronics
  • Medical Appliances
  • Medical Instruments
  • Molds
  • Automotive
  • Motorsport
  • Power Generation
  • Research
  • Sports