Machining time in electrical-discharge machining vs. drilling Calculate the machining time for producing the hole in Example 9.5 by EDM, and compare the time with that for drilling and for ECM. Assume that the titanium alloy has a melting point of 1873.15 K(see Table 3.3) and that the current is

Question

Machining time in electrical-discharge machining vs. drilling

Calculate the machining time for producing the hole in Example 9.5 by EDM, and compare the time with that for drilling and for ECM. Assume that the titanium alloy has a melting point of 1873.15 K (see Table 3.3)

Table 3.3

Physical Properties of Various Materials at Room Temperature
	Density	Melting point	Specific heat	Thermal conductivity	Coefficient of thermal expansion
	(kg/[latex]m^3[/latex])	(K)	(J/kg K)	(W/m K)	[latex](1×10^{–6}/ K)[/latex]
METAL
Aluminum	2700	933	900	222	23.6
Aluminum alloys	2630–2820	749–927	880–920	121–239	23.0–23.6
Beryllium	1854	1551	1884	146	8.5
Copper	8970	1355	385	393	16.5
Copper alloys	7470–8940	1158–1533	337–435	29–234	16.5–20
Gold	19,300	1366	129	317	19.3
Iron	7860	1810	460	74	11.5
Steels	6920–9130	1644–1805	448–502	15–52	11.7–17.3
Lead	11,350	600	130	35	29.4
Lead alloys	8850–11,350	455–599	126–188	24–46	27.1–31.1
Magnesium	1745	923	1025	154	26
Magnesium alloys	1770–1780	883–894	1046	75–138	26
Molybdenum alloys	10,210	2883	276	142	5.1
Nickel	8910	1726	440	92	13.3
Nickel alloys	7750–8850	1383–1727	381–544	12–63	12.7–18.4
Niobium (Columbium)	8580	2741	272	52	7.1
Silicon	2330	1696	712	148	7.63
Silver	10,500	1234	235	429	19.3
Tantalum alloys	16,600	3269	142	54	6.5
Titanium	4510	1941	519	17	8.35
Titanium alloys	4430–4700	1822–1922	502–544	8–12	8.1–9.5
Tungsten	19,290	3683	138	166	4.5
NONMETALLIC
Ceramics	2300–5500	—	750–950	10–17	5.5–13.5
Glasses	2400–2700	853–1813	500–850	0.6–1.7	4.6–70
Graphite	1900–2200	—	840	5–10	7.86
Plastics	900–2000	383–603	1000–2000	0.1–0.4	72–200
Wood	400–700	—	2400–2800	0.1–0.4	2–60

and that the current is 100A. Calculate the wear rate of the electrode, assuming that the melting point of the electrode is 1373.15 K.

Accepted Answer

1. Using Eq. (9.18),

[latex]MRR= 4 imes 10^4 IT_{w}^{-1.23},[/latex] (9.18)

[latex]MRR= (4 imes 10^4) (100)(1873 .15-273 .15)^{-1.23},[/latex]

[latex]=458 \ mm^{3}/min.[/latex]

The volume of the hole is

V = [latex]\pi \left[\frac{(12.5)^{2}}{4} ight](20)= 2452 \ mm^{3} [/latex]

Hence, the machining time for EDM is 2454/458 = 5.4 min; this time is 2.35 times that for ECM and 11.3 times that for drilling. Note, however, that if the current is increased to 300 A, the machining time for EDM will be only 1.8 minutes, which is less than the time for ECM.

2. The wear rate of the electrode is calculated using Eq. (9.19).

[latex]W_{t}=(1.1 imes 10^{11}) IT_{t}^{-2.38} [/latex] (9.19)

Thus,

[latex] W_{t}=(11 imes 10^3)(100)(1373.15 - 273.15)^{-2.38}= 0.064 \ mm^{3}/min.[/latex]

Question 9.6: Machining time in electrical-discharge machining vs. drillin...

This Question has been Answered.

Already have an account?

Login

Related Answered Questions