Performance of Beryllium Copper

(2) Bending Formability

The temper of age hardenable material ranges from "O", suitable for deep drawing, to "H", cold rolled to obtain high strength with moderate formability. However, as the cold reduction rate increases, material tends to exhibit some anisotropy. It is one of the key factors to choose the highest temper that can be formed in order to optimize the performance and efficiency of a spring part. This also improves dimensional stability during heat treatment.Although mill-hardened material is not fully aged, it did pass through an aging process. Therefore, it is necessary to consider formability when you choose the temper. For critical bending, mill-hardened Type-B or Type-S are suitable.

The ratio of the inside bend radius "R" to the thickness "t" is relative formability (See Fig.3). In 90° bending, the test specimen is placed upon the V-block with 90° concave angle and force is applied with a tool so that the specimen will have a right angle bend. The minimum inside radius where no micro crack or intensive orange peel is generated on the outside of the bending point represents "R," and "t" is the material thickness. Table 1 to 3 show the relative formability of NGK beryllium copper strip. Relative formability slightly changes depending on the thickness, i.e. thinner strip tends to have smaller R/t value. These table show the typical value in thickness 0.15mm.

Fig. 3 Relative Formability R/t

Table1 Relative Formability of High Strength Material(90° bending)

Alloy	Type	Temper	R/t		Typical R/t in thickness 0.15mm
			Long.	Trans.	Long.	Trans.
25	AH	O	0.0	0.0	0.0	0.0
		1/4H	1.0	2.0	0.0	0.0
		1/2H	3.0	4.5	0.0	0.0
		H	-	-	0.0	1.7
	MH	OM	0.8	2.0	0.0	0.6
		1/4HM	1.0	3.0	0.3	1.0
		1/2HM	2.0	4.0	0.6	2.7
		HM	3.0	6.0	1.0	4.0
		XHM	4.0	-	3.0	-
		XHMS	6.0	-	4.0	-
	MH TypeB	OMB	0.8	0.8	0.0	0.0
		1/4HMB	1.0	1.0	0.0	0.0
		1/2HMB	1.3	1.3	0.0	0.0
		HMB	2.5	2.5	0.6	0.6
		XHMB	3.4	3.8	1.7	1.7
		XHMSB	4.1	6.0	3.5	6.0
	MH TypeS	HM-TypeS	1.5	1.5	0.0	0.0
		XHM-TypeS	2.5	2.5	1.0	1.0

Table2 Relative Formability of High conductive Material(90° bending)

Alloy	Temper	R/t		Typical R/t in thickness 0.15mm
		Long	Trans	Long	Trans
8	HT	1.0	1.0	0.0	0.0
11	HT	2.0	2.0	0.0	0.0

Table3 Relative Formability of Midrange Material(90° bending)

Alloy	Temper	R/t		Typical R/t in thickness 0.15mm
		Long	Trans	Long	Trans
7	1/2HT	0.0	0.0	0.0	0.0
	HT	1.5	1.5	0.0	0.0
	EHT	2.0	1.5	0.3	0.0