1. Course: Micro Electrical Discharge Machining
Reporter：徐鉅威 MA21V204
Instructor：Prof.戴子堯
Course: Micro Electrical Discharge Machining
06/08/2015

2. Outline Introduction Experiment Work Results and Discussion
Equipment and work piece materials
Test procedures and operating parameters
Results and Discussion
Conclusions

3. Introduction
Source: Industry & technology Intelligence Service

4. In terms of generator design
enabled full control of electrical pulse shape
trapezoidal current pulses of more than Imax = 1000 A
slopes of up to 600 A/μs
require low line and machining zone inductance of 0.5 μH
Roughing and finishing (multiple trim cut) strategies were employed on two high specification machines with pulse generators designed to provide minimum work piece integrity damage.
Determine work piece surface integrity when employing current WEDM technology

5. Experiment Work
Source: Industry & technology Intelligence Service

6. Equipment and work piece materials
Testing equipment
involved two current commercial state-of-the-art WEDM systems
Twin wire machine
primarily intended for micro-EDM
accommodate wires 20–200 μm diameter
200 μm, zinc coated brass wire was used
located at Birmingham
“Clean Cut” generator technology incorporating facilities
without causing surface oxidation/coloring
uncoated brass wire 250 mm diameter was employed
located in Geneva

7. Equipment and work piece materials
Analysis equipment
Measurements were replicated twice at 25 different locations up to 1 mm
Nicolet Technologies Sigma 60-4 digital oscilloscope
appropriate voltage and current probes
Taylor Hobson Form Talysurf 120 L
Work piece surface roughness and integrity
cut-off length of 0.8 mm and evaluation length of 4 mm
Mitutoyo HM-124 unit with a Knoop diamond indenter
Micro hardness depth profiles
load of 25 g for 15 s
Three dimensional topographic maps were taken over ~1 mm2 using 6.13 μm spacing

8. Equipment and work piece materials
Working piece materials
α+ β titanium alloy (Ti–6Al–4V)
annealed to provide a bulk hardness of ~330 HK0.025
Inconel 718 nickel based superalloy
solution treated and aged condition with a hardness of ~450 HK0.025

9. Test procedures and operating parameters
Nicolet Technologies Sigma 60-4 digital oscilloscope
Target work piece surface roughness values for all cuts (main/roughing cut ~1.5–0.2 μm Ra for trim pass 4)
Machine A：reduce the incidence of wire breakage and provide stable machining
Machine B：minor adjustments
The trends were similar with kHz frequencies for roughing
Trims 1 2 and exceptionally high frequencies utilized at the Trims 3 and 4 levels ( 1 MHz)

10. Test procedures and operating parameters
Both machines employed deionized water dielectric which was subject to close monitoring and control of both particulate content and deionization level.

11. Results and Discussion
Source: Industry & technology Intelligence Service

12. Results and Discussion
Taylor Hobson Form Talysurf 120 L
work piece surfaces sparked on Machine B with the main cut ‘M’

13. Results and Discussion
Target Ra of 1.5 μm
Machine A：database technology was developed for steel materials

14. Results and Discussion

15. Results and Discussion
scanning electron microscopy (SEM)
Average recast thickness was <11 μm
several trim passes showing no apparent recast or damage

16. Results and Discussion
Mitutoyo HM-124 unit with a Knoop diamond indenter
No significant change in work piece micro hardness variation was observed with cracking confined to the recast layer

17. Future Work Conclusion
The extremely low level of work piece damage using current WEDM technology employing ultra high frequency/short duration pulses
Process productivity is a factor where multiple trim passes are utilized.
suited to unmanned/24 h operation.
Recast material was evident.
The data presented demonstrates the potential of WEDM for aerospace applications.
fatigue testing.