Bull. Hiroshima Inst. Tech. Research Vol.49（2015）75-81

ArticleDifference of improving welder＇s skill through training progression
Nobuyoshi HASHIMOTO*（Received Oct. 31, 2014）

Abstract
Welding training has some disadvantages such as long time required and need for a considerable quantity of training material; in addition, it is dangerous for beginners. To overcome these limitations, effective
training methods are being explored. These researches target one of many welding methods. However, itis necessary to consider series training of several welding methods because almost all welders are required
to acquire multiple welding skills. This paper describes the influence of different training processes for
SMAW (shielded metal arc welding) and TIG (tungsten inert gas welding) on welding skill improvement. A
training experiment was conducted with 6 testees, who were students of the mechanical engineering department, and had never done welding before. The testees were divided into two groups-group A with 3testees, and group B with 3 testees-and were trained for SMAW and TIG over four days. The testees inGroup A were trained for SMAW during the first and second day, whereas the testees of Group B weretrained for TIG during the same time. On the third and fourth day-the testees of Group A were trained forTIG, whereas those in Group B were trained for SMAW. Each day after training, tip movement and welding bead shape were measured for skill evaluation. It was observed that welding time and welding beadshape on SMAW and TIG had improved after training for two days; however, the electrode tip movement
showed no improvement. Further, it was observed that skill improvement is influenced by welding methodtraining.

Key Words: training progression, effective training, SMAW, TIG

quires a considerable amount of material for training;in addition, it is dangerous for beginners. To overcome these limitations, effective training methods
are being explored. Asai produced an effective training system using the position sensor present on
6-Axis Robot and some cameras[1]. Asai＇s system
displays information for effective training, e.g., difference between the torch movement of the trainee
and an expert welder in the case of TIG (tungsteninert gas welding). Kadefors analyzed differences
between EMG (electromyography) signals from thearm muscle of an expert welder in some of the welding positions, such as overhead and vertical-down[2]. These aforementioned researches focus on training a trainee in one of many welding methods. How-

1. Introduction

Welding is a jointing technique by congelationof materials in which boundaries are melted by heat.
It is used to join together parts of many things fromatomic reactors, ships, bridges, to bicycles, and soon. Although in some mass production industries,
certain welding processes have been automated byusing robots, most welding processes are still performed by a human welder. Therefore, many welders are needed in industrial production processes,and thus, the welder training occupation is also ﬂourishing.
Welding training suffers from some time-related
and logistical problems: it is time-consuming and re＊＊＊Department of Intelligent Mechanical Engineering, Hiroshima Institute of Technology― 75 ―

Nobuyoshi HASHIMOTO

Fig. 1 Shield metal arc welding

Fig. 3 Workpiece clamper with cameras(a) Raw image(b) Binary image(c) Tip position

Fig. 2 Tungsten inert gas welding

Fig. 4 Welding arc image on screen

ever, it is necessary to consider effective training toacquire several welding methods, because most professional welders are required to obtain skills forseveral welding methods.
In general, a beginner learns the SMAW (shielded metal arc welding) method ﬁrst, and then the TIG
method later. Based on previous experience, welding trainers know that this training format is effective. SMAW is considered a basic skill required for
manual arc welding; however, this is subjective, andhas not been confirmed quantitatively. This paper
describes the inﬂuence of different training processes
for SMAW and TIG on welding skill.

above the weld line from the left to the right fromthe welder＇s perspective, and at a constant rate. During welding, the electrode is gradually shrinking because the tip melts.
Figure 2 shows TIG process [3]. In TIG, a welder uses a welding torch with the right hand and awelding rod with the left hand, and turns on theswitch present on the welding torch to generate anarc discharge at the tip of the tungsten electrode in
the torch. After that the arc discharge initiates, theangle between the tungsten electrode and the weld
line is kept between 60 and 70 degrees, and the tip ofthe electrode is moved 2-3 mm above the weld linefrom right to left as welder＇s perspective, and at aconstant rate. During welding, the tip of the welding
rod is subjected to the arc, because of which it melts
and the drops from the welding rod form the required
weld.

2. Objective weldingThis study examines the training processes for
SMAW and TIG, and their impact on welding skill
improvement.
Figure 1 depicts SMAW [3]. In SMAW, a welder uses a holder with an electrode shielded ﬂux withthe right hand, and hits or rubs the tip of the electrode on the workpiece to generate an arc discharge
at the tip of the electrode. After the arc discharge
initiates, the angle between the electrode and theweld line must be kept between 60 and 70 degrees,
and the tip of the electrode should be moved 2-3 mm

3. Evaluation of skill level

In this research, the welding skill level is evaluatedby studying the movement of the tip of the electrodeduring the welding task, and by the shape of welding
bead after the welding task is complete. The following subsections describe how these measurements
were recorded.
― 76 ―

Difference of improving welder＇s skill through training progression(a) X-Y axes

Fig. 6 Three-dimensional surface measuring instrument

Fig. 7 Example of welding beads shape(b) X-Z axes

Fig. 5 Example of electrode tip movement

3.1 Movement of the tip of the electrode(1)

Position of the tip of the electrode during welding is calculated using images of arc discharge light.
Figure 3 shows the workpiece clamper with cameras.
Cameras that capture images of arc discharge light
above the workpiece are fixed and do not obstruct
the welding process; in addition, they are covered by
the stainless steel boxes to protect them from spattersthat occur in welding. In order to prevent camera
halation by the intense light of the discharge arc,
shutter time is ﬁxed at 1/10000 of a second, and there
are optical ﬁlters, ND1.0，ND3.0，BPM53 (FujiﬁlmCo.), that are inserted in front of the lenses.
Figure 4 shows an example of an arc image andhow it is processed. The electrode cannot be observed in the raw image (a). This binary image (b) iscreated by evaluating all the pixels from the raw image (a) and transposing only those pixels that havean intensity rating 95% or higher. The position of
the tip is determined from the horizontal center andupper end of arc in the image as shown in (c). The
coordinate of the tip (x, y, z) is calculated by eq. (1)[4].

where, (u, v) is the coordinate of tip as observed
from one camera, (u＇, v＇) is the coordinate of the tip
observed from another camera, and M, M＇, are thematrices of extrinsic parameters of each camera, respectively. Accordingly, the three-dimensional coordinate of the tip, or the movement of the tip, is measured.
Figure 5 shows an example of movement of theelectrode tip. Based on such data, skill evaluation
indices Ya, Ys, Za, and Zs are calculated by follow
equations.

― 77 ―

Nobuyoshi HASHIMOTO

Fig. 9 Workpiece for evaluation
Table 1 Appropriate value of welding

Welding time
Fig. 8 Experiment ﬂow

Width of welding bead
Height of welding beadwhere, n is the number of calculated coordinates, andZo is the ideal z-coordinate of the electrode.
3.2 Shape of the welding bead

SMAW

TIG

30 s

80 s

9±1 mm

7±1 mm

1.5±0.5 mm

Y coordinate of electrode tip

0±1 mmZ coordinate of electrode tip

1.5±0.5 mm

4. Improving welder's skill through training

Figure 6 shows the device used for measuring
the shape of the welding bead. The laser displacement sensor measures the height of workpiece surface on the X-Y table by moving the table using thestepping motors.
Figure 7 shows an example of the shape of awelding bead. In our experiments, the welding beadis more than 0.5 mm higher than the surface of theworkpiece. Figure 3.5 shows the projection of thebead shape. Based on this data, skill evaluation indices Wa, Ws, Ha, and Hs are calculated using the following equations [5].

progression

4.1 Method for experiment

We conducted a training experiment with 6 testees, who were students from the mechanical engineering department at a university and had neverdone welding earlier. Figure 8 shows the ﬂow of thisexperiment. The testees are divided into two groups,and were trained for SMAW and TIG over 4 days.
The three testees that were part of Group A weretrained for SMAW during ﬁrst and second day, andthen TIG during third and fourth day, whereas thethree testees in Group B were trained for TIG during
first and second day, and then SMAW during thirdand fourth day. Before the training each day, the testees trained in the art of welding and learnt about theappropriate shape of welding bead as shown in table
1. After the training, they were evaluated on theirskill. During the training and evaluation, the testees
undertook the bead-on-plate welding operation,
which involves depositing the welding bead on thepainted white line on the workpiece surface, as
shown in fig. 9. The workpieces are made of steel(SS400 JISG3101), and have dimensions of 100 mm
×100 mm×4.5 mm. In the training stages, the test-where, ny is the divided number of the welding beadon x-axis, Wo is the ideal welding bead width, andHo is the ideal welding bead height― 78 ―

Difference of improving welder＇s skill through training progression(a) SMAWFig. 10 Welding time

ees were trained by repeatedly preforming the beadon-plate operation for a 15-min period during arc
discharge. During the evaluation stages, the tip
movement and welding bead shape were measured
when testees operated the SMAW and TIG equipment. Testees＇ skills were evaluated in their welding
area as shown in ﬁg. 9.

(b) TIG

could concentrate only on accurate rate of the electrode tip in welding. Probably, if testees take training
for an extra 1 or 2 days, the characteristic tendency
would appear.
Figure 12 shows the variation of the welding
bead shape. Similar result trends as those in welding
time is found in the cases of Wa, Ws, Ha, and Hs.
5. Conclusion

4.2 Result and discussion

Figure 10 shows the variation of welding time.
Both groups showed an improvement in the welding
time in both the cases-SMAW and TIG-because #5
data is closer from ideal time than #1 data. The testees in Group A showed an improvement in the welding time for SMAW, but not in TIG until the third
evaluation of SMAW training on the ﬁrst and secondday, after which, their TIG welding time improved
because of TIG training on the third and fourth day.
Similarly, the testees of Group B showed an improved welding time for TIG, but did not show any
improvement in that of SMAW until the third evaluation of TIG training on the ﬁrst and second day, after which, their SMAW welding time improved because of SMAW training on third and fourth day.
This indicates that the electrode tip rate remained
ideal because of training. In the ﬁfth evaluation, theSMAW welding time of group A was closer to theideal time than that of group B, whereas the TIG
welding time of group B was closer to the ideal timethan that of group A. This shows that skill improvement is inﬂuenced by performing the welding method training.
Figure 11 shows the variation of electrode
movement in welding. Although there is improvement in a few indices such as Ya of SMAW by group
A, no characteristic tendency was found. Testees

We evaluated the difference in welding time improvements, welding bead shape, and electrode tipmovement through training progression of SMAW
and TIG by examining bead-on-plate operations performed by 6 testees, who were trained for 4 days.
We observed that the welding time and welding beadshape on SMAW and TIG improved after training in
SMAW and TIG for two days; however, the electrode tip movement showed no improvement. Therefore, we conclude that skill improvement is influenced by undergoing welding method training.

References1)

ASAI Satoru, SAKUMA Masatake, Digitization ofwelder＇s skill and development of welding support
system, quarterly journal of the Japan Welding
Society, 2002, 20, 185-190 (in Japanese).

2)

R. Kadefors, I. Peterson and P. Herberts, Muscular
reaction to welding work: An electromyographic
investigation, Ergonomics, 19, 5, 543-558, 1976.

3)

Klas Weman, Welding Processes Handbook, CRC
Press LLC, 2003.

4)

Jun SATO, Computer Vision, CORONA publishingco., 2003 (in Japanese).

5)

Welding Technique Editorial Members, Establishmentof ＂Guideline for Evaluation by Visual Inspection＂,
Welding Technique, 1998, 46, 4, 109-112(in Japanese).

― 79 ―

Nobuyoshi HASHIMOTO(a) Ya (SMAW)(b) Ya (TIG)(c) Ys (SMAW)(d) Ys (TIG)(e) Za (SMAW)(f) Za (TIG)(g) Zs (SMAW)

Fig. 11 Electrode movement― 80 ―(h) Zs (TIG)Difference of improving welder＇s skill through training progression(a) Wa (SMAW)(b) Wa (TIG)(c) Ws (SMAW)(d) Ws (TIG)(e) Ha (SMAW)(f) Ha (TIG)(g) Hs (SMAW)

Fig. 12 Welding bead shape― 81 ―(h) Hs (TIG)