Wire EDM (WEDM) - cutting speed versus conventional milling (titanium)

[dculp1]

I'm trying to find any information on comparative machining rates for wire EDM versus conventional milling. This is for machining through-slots in ultrasonic horns - examples in

http://krell-engineering.com/fea/industr/industrial_resonators.htm.

The supporting web page is

http://ultrasonic-resonators.org/machining/edm/edm.html.

The slots are typically 10 mm wide. The slot length varies but 100 mm can be used as an example. The slot depth may range between 40 mm and 200 mm. I'm particularly interested in machining Ti-6Al-4V annealed. My assumption is that slots can be milled much faster than EDM'd, especially if reasonable EDM'd surface finish must be maintained.

One source gives a wire EDM feed rate of 1.75 mm/min for a part that is 10-15 mm thick. For this thickness, the above slot with a perimeter of 220 mm would take about 2 hours. I assume that the feed rate would decrease (at least somewhat) for thicker parts. However, what is the relationship (or a reasonable estimate)?

For milling I assume a 10 mm diameter tool (the slot width isn't terribly critical). I also assume that multiple passes would be necessary. For instance, perhaps 10 mm deep per pass might be reasonable? (Please correct this based on your machining experience with Ti-6Al-4V annealed or similar material.) Then the 200 mm thick horn would require 20 passes. However, since the slots are completely through, the horn could be flipped to take 10 passes from the first side and 10 passes from the opposite side. Assuming CNC and best tooling, speeds, feeds, coolant, etc., what is a reasonable time estimate to mill a slot through 40 mm or 200 mm? Also, what slot width tolerance could reasonably be held?

Thanks,
Don C.

 

[3DDave]

I would think using waterjet and leaving some stock to cleanup via milling would be faster. This should speed up the removal of material that would otherwise get chewed to chips, though 200 mm is pretty aggressive either way.

 

[dculp1]

I hadn't considered waterjet but it might be reasonable. It would eliminate EDM's two major fatigue problems -- surface pitting and recast surfaces.

However, I'm still hoping for info on comparative machining rates for conventional versus wire EDM machining.

 

[3DDave]

They really aren't comparable. Wire edm is in square inches per hour and milling is in cubic inches per hour but also, for each internal cut, time to drill an access hole.

Milling time will depend on the horsepower available and the cutters - it may be for some slots that turning it all to chips is faster while for others, using a core drill will save time.

Waterjet cannot by itself replace wire edm - the kerf is not uniform through the thickness of the part, unless taper is acceptable.

 

[dculp1]

For core drills, were you referring to diamond-impregnated drills such as are used on hard materials like ceramic or drills like

https://www.hougen.com/cutters/cutters_index.html

? If the latter, I have only been able to find these in 7/16" (11 mm) diameters and larger, with lengths up to 100 mm. My slots are 10 mm x 200 mm (max).

Using the core drill on the thicker parts, could it drill half way through and then finish drilling from the opposite side (after flipping the part)?

Are you aware of any smaller diameter core drills that would be suitable?

I assume with the core drills that there would be a series of adjacent holes that would have to be finished (connected) with an end mill. A gun drill (

https://www.mscdirect.com/product/details/53733457)

could use a similar process. How would the performance of a gun drill compare with a core drill? Gun drills have the required through-lengths and multiple close diameters are available - 9.00 mm, 9.48 mm, 9.95 mm, 10.00 mm (

https://www.mscdirect.com/browse/tn...ts/Gun-Drill-Bits?navid=12109052+4287019186).

Because of their simplicity I would think that gun drills would cost less initially and also be cheaper to resharpen. Also, the time between resharpenings might be longer. Thoughts?