焊 接 (Welding)

目的 :1.結合兩個或數個工件成一體。2.期望經焊接後之組件能夠符合實際 應用上之要求 :

(1) 強度、韌性、延性， (2) 耐腐蝕， (3) 耐高溫

3. 應用 : 機械結構件、航空零件、船體、 儲油槽、天然氣槽

焊接相關專業領域

1. Fusion Zone: T ＞ TM

(Melting & Solidification) – 凝固理論2. Heat Affected Zone: T ＞ TC

TC ： A critical temperature above which mechanical and/or physical properties of the welding alloys will change – 熱處理原理 ( 但程序或溫度變化較激烈 )

3. Base Metal: T ＜ TC

(No changes in both metallurgical and mechanical properties)

Fig26-12

26-12

Fusion Weld Zone

Figure 29.1 Characteristics of a typical fusion weld zone in oxyfuel gas and arc welding. See also Figs. 27.16 and 28.14.

Fig26-1026-10

• 溫度及熱傳分析• 顯微組織分析• 焊接參數• 焊料• joint 設計• 應力分析

4.

Welding Engineering / Metallurgy

1. Thermal analysis 瞭解焊件上任何一點 (A) 在焊接過程中之溫度變化曲

線 – Thermal cycle2. Effects of welding parameters on the thermal cycle of HAZ

Welding voltage, E Welding current, I Travel speed, S Preheat temperature Alloy composition Section thickness of the workpiece

Hi (Heat input ) = (E x I) / S

3. Factors affecting the microstructures and

properties of fusion zone

• Composition of the filler rod

(selection of the filler material)

• % dilution

• Solidification cooling rate

4. Welding Design

• Joint design

• Weld type

• Stress analysis

5. Welding Methods

6. Inspection & Testing (destructive and non-destructive)

Destructive: 拉伸試驗、衝擊試驗、疲勞試驗…。 Non-destructive: 超音波探傷、 X 光探傷、磁粉探 傷…。

26.4 Types of Fusion Welds and Types of Joints

Fig. 26-6

26-6

Multiple Pass Deep Weld

Figure 27.6 A deep weld showing the buildup sequence of individual weld beads.

Distortion After Welding

Figure 29.10 Distortion of parts after welding: (a) butt joints; (b) fillet welds. Distortion is caused by differential thermal expansion and contraction of different parts of the welded assembly.

Incomplete Fusion

Figure 29.6 Low-quality weld beads, the result of incomplete fusion. Source: American Welding Society.

Discontinuities in Fusion Welds

Figure 29.7 Schematic illustration of various discontinuities in fusion welds. Source: American Welding Society.

Welding Methods

1. Electrical: Resistance welding Induction welding Electroslag welding Electron beam welding Arc welding Shielded metal arc welding (SMAW) Gas metal arc weldind (GMAW) Gas tungsten arc welding (GTAW) Plasma arc welding (PAW) Submerged arc welding (SAW))

Welding Methods

2. Mechanical: Friction, Ultrasonic, etc.

3. Chemical: Oxy – Acetylene welding,

Thermit reaction

4. Optical: Laser beam welding

5. Solid State: Diffusion bonding

1. Resistance Welding Processes

• Resistance spot welding

• Resistance seam welding

• Projection welding

Mass production

一、 Electrical

Fig28-1

Fig28-2

Fig28-4

28-4

Resistance welding

R (resistance): areas to be controlled1. Contact resistance between electrode and

workpiece.

2. The resistance of workpiece itself.

3. Contact resistance between workpieces

( 希望電阻集中在此處 ).

4. The resistance of electrode itself.

workpiece

electrode

Resistance Spot WeldingFigure 28.5 (a) Sequence in resistance spot welding. (b) Cross-section of a spot weld, showing the weld nugget and the indentation of the electrode on the sheet surfaces. This is one of the most commonly used process in sheet-metal fabrication and in automotive-body assembly.

Fig28-5

Fig28-3

Resistance Seam Welding

Figure 28.9 (a) Seam-welding process in which rotating rolls act as electrodes. (b) Overlapping spots in a seam weld. (c) Roll spot welds. (d) Resistance-welded gasoline tank.

Fig28-9

Fig28-8

28-8

Resistance Projection Welding

Figure 28.11 (a) Schematic illustration of resistance projection welding. (b) A welded bracket. (c) and (d) Projection welding of nuts or threaded bosses and studs. Source: American Welding Society. (e) Resistance-projection-welded grills.

Fig28-11

Spot Welding Example

Figure 28.8 Robots equipped with spot-welding guns and operated by computer controls, in a mass-production line for automotive bodies. Source: Courtesy of Cincinnati Milacron, Inc.

1.2 High frequency resistance welding

( 高週波電阻焊接 )`

Frequency ： 200KHz ~ 450KHz

Skin effect ：電流集中在表面之程度 Freq.

Fig28-10

High-Frequency Butt Welding

Figure 28.10 Two methods of high-frequency butt welding of tubes.

2. Electroslag welding ( 電熱熔渣焊接 )

原理 :

Electrode is fed into a molten slag pool.

An arc is drawn initially but is then snuffed

out by the molten slag, and the heat of

fusion is provided by resistance heating in

the molten slag.

Suitable for thick section welding

Electrogas Welding

Figure 27.11 Schematic illustration of the electrogas welding process. Source: American Welding Society.

Fig28-2128-21

Equipment for Electroslag Welding

Figure 27.12 Equipment used for electroslag welding operations. Source: American Welding Society.

3. Electron beam welding ( 電子束焊接 )

• Heat Source

A focused beam of high-velocity electrons

which impinge on the workpieces.

動能 (kinetic energy) → 熱能 (heat)

• Equipment

An electron gun ( 電子槍 ) → Generate electrons

→ Focus them into a beam ( 聚焦成一電子束 ) →

Accelerate them to a very high speed ( 加速 )

• Some data:

1. Accelerating voltage: 30 ~ 175 kV

2. Speed: 0.1 ~ 0.7 光速3. Beam current: 50 ~ 100 mA

4. Beam spot size: 0.25 ~ 0.75 mm

• Degree of Vacuum (in operation)

High Vacuum --- 10-3 ~ 10-6 torr

Medium Vacuum --- 10-3 ~ 25 torr

Non-Vacuum --- Atmosphere (760 torr)

(1 torr = 1 mmHg)

Fig28-2228-22

Advantages:

1. Max. weld penetration (H/D: 25/1)

2. Minimum weld width (HAZ)

3. Minimum weld shrinkage in HAZ

and workpieces

4. Maximum weld purity

Disadvantages:

1. Equipment costs are high

2. Chamber size limits the size

of workpieces

3. Production rate is low

Fig28-2328-23

Tab28-4

TABLE 28-4

1. Friction Welding

Figure 28.3 (a) Sequence of operations in the friction welding process: (1) Left-hand component is rotated at high speed. (2) Right-hand component is brought into contact under an axial force. (3) Axial force is increased; flash begins to form. (4) Left-hand component stops rotating; weld is completed. The flash can subsequently be removed by machining or grinding. (b) Shape of fusion zone in friction welding, as a function of the force applied and the rotational speed.

(a)

(b)

Fig28-15

28-15

28-16

28-17

2. Ultrasonic welding ( 超音波焊接 )

• Transducer ( 變能器 )

10 KHz ~ 75 KHz (High frequency vibration)

• Welding mechanism:

–Static normal stress + Oscillating shearing stress

–(Plastic deformation + Solid state bonding)

二、 Mechanical

Fig28-19

28-19

Ultrasonic Welding

(a) (b)

Figure 28.2 (a) Components of an ultrasonic welding machine for lap welds. The lateral vibrations of the tool tip cause plastic deformation and bonding at the interface of the workpieces. (b) Ultrasonic seam welding using a roller. (c) An ultrasonically welded part.

28-18

Laser beam welding ( 雷射束焊接 ) (Light Amplification by Stimulated

Emission of Radiation)

ElectricalChemicalThermalOpticalNuclear

CoherentElectromagneticradication

heat

energy

absorbed

light

Lasing material:

固體： Cr, Ruby, 鈾

氣體： He, N2, CO2

Excitation of a specific energy level

三、 Optical

Fig28-25

28-25

Fig28-26

28-26

Tab28-5

TABLE 28-5

Diffusion bonding

焊接參數：1. 溫度 ~ 約 0.5Tm (oK)

2. 壓力 (clamping force)

3. 時間4. 二接觸表面之清靜度

應用：1. 不同種類之金屬材料2. 難焊接之材料3. 複合材料 e.g. Ti alloys,

superalloys, etc.

Diffusion: movements of atoms across the interface between two workpieces to be welded — produces chemical bonds

Diffusion Bonding/Superplastic Forming

Figure 28.17 The sequence of operations in the fabrication of various structures by diffusion bonding and then superplastic forming of (originally) flat sheets. Sources: (a) After D. Stephen and S.J. Swadling. (b) and (c) Rockwell International Corp.

Arc Welding

• Shielded Metal Arc Welding (SMAW)

• Gas Metal Arc Welding (GMAW)

• Gas Tungsten Arc Welding (GTAW)

• Plasma Arc Welding (PAW)

• Submerged Arc Welding (SAW)

Power supply

AC: Alternating current DC: Direct current

Eo ： transformer output voltage

EL ： reactance voltage drop

ER ： load （ welding ） voltage drop

A simple R - L circuit

ω ： angular freq. of the sine function for 60 cycle AC line supply = 376.8 rad./sec

θ ： phase angle, θ =

2 2 2

Eo( ) sin ( )

Ri t t

L

R

L1tan

Reactance (L):

(1) produce a phase shift (θ)

(2) control V-C characteristics

(1) constantant voltage(2) constant current

Half-wave rectifier circuit

Full-wave rectifier circuit

filter

(a) E(t)→D2→L→R→D3→E(t)(b) E(t)→D4→L→R→D1→E(t)

Choke: a variable inductor (the inductance retards the rate of current rise when the arc is being started)

27.1 Arc Welding

• An arc between two electrodes was a

concentrated heat souse that could

approach 4000°C.

• Current 1 to 4000 A (large)

Voltage 20 to 50 V (low)

Shielded Metal-Arc Welding

Figure 27.4 Schematic illustration of the shielded metal-arc welding process. About 50% of all large-scale industrial welding operations use this process.

Figure 27.5 Schematic illustration of the shielded metal-arc welding operations (also known as stick welding, because the electrode is in the shape of a stick).

Fig27-1

Fig27-4

Fig27-5

TABLE 27-1

Flux-Cored Arc-Welding

Figure 27.10 Schematic illustration of the flux-cored arc-welding process. This operation is similar to gas metal-arc welding, showing in Fig. 27.8.

27-6

TABLE 27-2

Gas Metal-Arc Welding

Figure 27.8 Schematic illustration of the gas metal-arc welding process, formerly known as MIG (for metal inert gas) welding.

Fig27-7

In order to maintain a constant arc gapwire melt-off rate = wire feed speed (dynamic

equilibrium)

． gap arc voltage

． wire melt-off rate arc current

g a p d e c r e a s i n g g a p c o n s t g a p i n c r e a s i n g

V

I

C o n st vo lta g e

I 1 I 0 I 3

V1

V2V0

V

I

C o n st c u rre n t

I 1 I 0 I 3

V1

V2V0

微小的 V 變化產生很大的 I 變化

很大的 V 變化產生微小的 I 變化

TABLE 27-3

Gas Tungsten-Arc Welding

Figure 27.13 The gas tungsten-arc welding process, formerly known as TIG (for tungsten inert gas) welding.

Figure 27.14 Equipment for gas tungsten-arc welding operations. Source: American Welding Society.

27-12

Comparison of Laser-Beam and Tungsten-Arc Welding

Figure 27.16 Comparison of the size of weld beads in (a) electron-beam or laser-beam welding to that in (b) conventional (tungsten-arc) welding. Source: American Welding Society, Welding Handbook (8th ed.), 1991.

TABLE 27-5

Plasma-Arc Welding

Figure 27.15 Two types of plasma-arc welding processes: (a) transferred, (b) nontransferred. Deep and narrow welds can be made by this process at high welding speeds.

TABLE 27-6

Submerged-Arc Welding

Figure 27.7 Schematic illustration of the submerged-arc welding process and equipment. The unfused flux is recovered and reused. Source: American Welding Society.

Fig27-8

27-8

TABLE 27-4

28.8 Welding-Related Processes

• Surfacing process of depositing a layer of weld metal on the surface or edge of a base material of different composition

• Thermal spray coating or metallizing offer a means of applying a coating of high-performance material (metals, alloys, ceramics, intermetallics, ceramets, carbides, or even plastics)

Fig28-30

28-30

Fig28-31

TABLE 28-6