Precision Laser Welding Equipment - Introduction of ML-2052A-

FME Co., Ltd.
? ? Shinichi Nakayama

1. Introduction
Laser welding has broadly been utilized to joint such as electronic parts because it reduces heat effect to the surrounding of parts. Miniaturization and tendency to micro-parts seen in such as watches, cellular phones have been advanced; recently, laser welding has come to be well received for welding of micro-electronic parts. This technological tendency inevitably requires new laser welding equipment suited for welding those micro-parts. Conventional pulsed laser welding equipment is rated at 5J to 100J/pulse of output energy, and its pulse width ranges 0.5ms to 20ms. It laser spot welds stainless steel, presenting nugget of several hundred micrometers (400μm to 800μm) diameter and also several hundred micrometer penetration depth.
To assure weld quality of the micro-parts, penetration depth of no less than 200 μm, and smaller nugget diameter (100μm or less) are required. We are introducing our newly developed precision laser welding equipment ML-2052A, responding to the weld quality requirement.

Photo 1. Precision laser welding equipment

Laser equipment: ML-2052A
Optical fiber: Type SI fiber, 100μm core diameter
Output unit: L-shaped output unit (Image formation ratio: 0.5 times) with CCD camera

2. Fine laser welding system
2.1 Fine laser welding equipment ML-2052A
Table 1 shows the specification of our newly developed ML-2052A.
Basically, it is designed to project laser beam to a fine type SI fiber of small diameter (100μm core diameter) to obtain a fine spot size. Also, fine resolution of oscillation pulse waveform is fitted to shorten the pulse width. Maximum repetition rate is 30 pps.

Table 1. ML-2052A Specifications

Power supply	Single-phase 200, 220, 240VAC +10% -15%
Maximum rated output	250 mW (0.5 ms)
Maximum rated energy	250 mJ/P (0.5 ms)
Pulse width setting	60 to 500μs (20μs increment)
Repetition rate	1 to 30 pps
Oscillation wave length	1064 nm
Number of schedule settings	32 schedules
Optical fiber specification	Type SI fiber of φ0.1mm core dia., Type SI fiber of φ0.2mm core dia.
Cooling	Forced fan air-cooled
External communication	RS-485
Outline	310(W) x 665(D) x 700(H) mm
Mass	70 kg

2.2 Output optics
To achieve weld nugget of not more than 100μm diameter, image formation ratio of approximately 0.5 times is required. In addition, since geometric optics aberration must be taken into account, makeup of lens was optimized using optical calculation software. Figure 1 is an example calculation which shows the condensed diameter of 40μm or less. Photo 2 shows optics with CCD camera of fine laser welding system employed in this experiment.

2.3 Fine laser welding system
Is composed of fine laser welding equipment ML-2052A; optics, with CCD camera, having an image formation ratio of 0.5 times; and Type SI fiber of 100μm core diameter. Figure 2 shows the characteristics of processing energy on the workpiece. The condensed spot diameter (weld nugget diameter) was measured with respect to work distance while welding was carried out on stainless steel. Consequently, we confirmed that condensed spot diameter was about 40μm minimum.

2.4 Experimental welding
Photos in Figure 3 show the welding nugget and depth of penetration obtained by the fine laser welding system. Metal used for the experimental welding were stainless steel. Photo 4 is an example welding conducted by our conventional equipment ML-2050A using optics of 1:1 image formation ratio and fiber of 400μm core diameter. The conventional system presented that the diameter of nugget and the depth of penetration were similar in dimension which is so called "conduction welding". Therefore, the conventional system is unlikely to be used for fine welding because the smaller nugget diameter is, the shallower penetration is. On the contrary, this fine laser welding system presented that the ratio of nugget diameter to penetration was approximately 1:3, i.e., like keyhole welding. In other words, welding nugget having sufficient penetration to maintain weld strength and minimizing thermal effect to its surroundings was obtained. Photo 5 shows an example application of welding: 1mm diameter cathode of electronic gun.

Photo 4. Nugget diameter and depth of penetration
by conventional laser welding system

Laser equipment: ML-2050A (1J/pulse)
Optical fiber: Type SI fiber of φ400μm core dia.
Output optics: Image formation ratio = 1:1

Photo 5. Example welding by fine laser welding system

3. Conclusions
Our newly developed laser ML-2052A revealed a possibility of fine laser welding for micro parts that the conventional system cannot perform. Achievements of this new laser system are as follows:
(1) Condensed beam spot diameter of φ40μm was obtained.
(2) Nugget diameter of φ80μm and penetration depth of 250μm for stainless steel were achieved.
(3) Nugget diameter of φ100μm for a commercial electronic gun was realized.

It is important to increase example applications; so, we intend to conduct high repetition-rated seam welding for hermetic sealing.