Sheet Metal Process Flow-Sheet Metal Processing Flow
Sheet Metal Process Flow-Sheet Metal Processing Flow
What is Sheet Metal Processing Technology
Sheet metal processing is a comprehensive cold processing technology for sheet metal (usually less than 6 mm), including shearing, blanking, bending, welding, die forming and surface treatment. Its remarkable feature is that the thickness of the same part is the same.
Equipment for sheet metal processing
1. Cutting equipment: CNC shears, laser cutting machines, CNC punches
2. Forming equipment: ordinary punch, hydraulic press, CNC bending machine.
3. Welding equipment: argon arc welding machine, carbon dioxide shielded welding machine, spot welding machine, robot welding machine.
4. Surface treatment equipment: wire drawing machine, sandblasting machine, polishing machine, electroplating bath, oxidation tank, plastic spraying line.
5. Shaping equipment: leveller
Materials commonly used in sheet metal processing:
Cold rolled sheet (SPCC), galvanized sheet (SECC), copper sheet, aluminium sheet, stainless steel sheet, aluminium sheet and so on. Their functions are different. As for how to select, it is generally necessary to consider their use and cost.
1. Cold-rolled sheet, referred to as SPCC, is used for surface treatment by electroplating multicoloured zinc or spraying plastic parts.
2. Galvanized sheet, referred to as SECC, is used for surface treatment of spray-moulded parts. Without special requirements, SPCC is generally used to reduce costs.
3. Copper sheet. Usually used for nickel or chromium plating parts, sometimes not treated. Depending on customer requirements.
4. Aluminum sheet. Usually used for surface treatment is chromate or oxide parts.
5. Stainless steel plate. Split mirror stainless steel and fog stainless steel, it does not need any treatment.
6. Aluminum profiles. Usually used for surface treatment are chromate or oxide parts. They mainly support or connect and are widely used in various kinds of cartridges.
Sheet Metal Processing Flow
For any sheet metal part, it has a certain processing process, that is, the so-called process flow. With the different structure of sheet metal parts, the process flow may be different.
Consumption - 2 fetching - 3 punching - 4 bending - 5 welding - 6 grinding - 7 testing - 8 spraying - 9 semi-finished product testing - 10 storage.
1. Designing and drawing part drawings of sheet metal parts, also known as three views. Its function is to express the structure of sheet metal parts by drawing.
2. Draw an expansion diagram. That is to say, unfold a complex part into a flat piece.
There are many ways of cutting materials, mainly in the following ways:
A. Shearing machine blanking. It is to use the shear machine to cut out the width and length of the development drawing. If there is punching and cutting angle, then turn the punch machine to combine with punching and cutting angle forming of the die.
B. Punch blanking. It is to use the punch to punch the flat plate structure after the parts are unfolded in one or more steps. Its advantages are short time-consuming, high efficiency, low processing cost, and it is often used in mass production.
NC NC blanking. NC blanking should first compile NC processing program. That is to use programming software to compile the drawings into NC NC NC NC machine tool recognizable program. Let them follow these procedures step by step on a piece of iron plate, stamping out the structural shape of its plate.
D. Laser blanking. It uses laser cutting method to cut out the structural shape of its flat plate on an iron plate.
4. Flanging tapping. Flanging, also known as punching, is to draw a slightly larger hole on a smaller base hole and tap it on the punching hole. This can increase its strength and avoid slippery teeth. It is generally used for sheet metal processing with thinner thickness. When the plate thickness is larger, such as 2.0, 2.5 and so on, we can tap directly without flanging.
5. Punch processing. Generally, punch processing includes punching cutting angle, punching blanking, punching convex hull, punching tear, punching hole and so on, in order to achieve the processing purpose. Its processing needs corresponding die to complete the operation. Punch convex hull has punching hull die, punching tear has tearing forming die and so on.
6. Pressure riveting. Pressure riveting for our factory, often used riveting studs, riveting nuts, riveting screw, etc., its riveting method is generally through the punch or hydraulic riveting machine to complete the operation, riveting to sheet metal parts.
7. Bending. Bending is the process of turning a 2D flat part into a 3D part. Its processing needs a bending machine and corresponding bending die to complete the operation. It also has a certain bending sequence. Its principle is that the first bending without interference on the next knife will produce interference after bending.
8. Welding. Welding is to weld several parts together to achieve the purpose of processing or to weld the edge seam of a single part to increase its strength. Generally, there are several kinds of welding parties: CO2 gas shielded welding, argon arc welding, spot welding, robotic welding and so on. The selection of these welding methods depends on the actual requirements and materials. Generally speaking, CO2 gas shielded welding is used for iron plate welding; argon arc welding is used for iron plate welding. Aluminum plate welding; robotic welding is mainly used for larger parts and longer welds. For example, robotic welding can be used for cabinet welding, which can save a lot of tasks and improve work efficiency and welding quality.
9. Surface treatment. Surface treatment generally includes phosphating film, electroplating multicolor zinc, chromate, baking paint, oxidation, etc. Phosphating film is generally used for cold-rolled sheets and electrolytic sheets. Its main function is to coat the surface of the material with a protective film to prevent oxidation. Then it can enhance the adhesion of the baking paint. Electroplating multicolor zinc is generally used for surface treatment of cold-rolled sheets; Chromate and oxidation are generally used for aluminium sheets. And the surface treatment of aluminium profiles; the selection of specific surface treatment methods is based on the requirements of customers.
10. Assembly. The so-called assembly is to assemble multiple parts or components in a certain way to make them into a complete material. Among them, we should pay attention to the protection of materials, not scratch and bruise. Assembly is the last step to complete a material. If the material cannot be used due to scratch and bruise, rework and redo will waste a lot of processing time and increase the material.
Some problems are often encountered in sheet metal processing
Need you to optimize its process, make it a good product or achieve a specific purpose. Here is a brief introduction to some of the process problems we often pay attention to in sheet metal processing.
1. Door plate, generally using the processing method of long edge wrapping short edge, and then opening process holes in the corresponding corner, the size of process holes is generally determined by the thickness of the plate. When the thickness of the plate increases, the size of process holes should also be increased accordingly, otherwise the bending will produce edges and corners.
2. Welding parts are usually positioned by tools, holes or convex hulls. It can reduce the time wasted in positioning, ensure size, improve work efficiency and reduce costs. In some difficult-to-locate welding, convex hulls or holes are generally used for positioning.
3. For electroplating parts, because the electroplating solution has corrosive effect on the parts, process holes should be added in the corner of the electroplating parts to facilitate the timely discharge of the electroplating solution and ensure the quality.
4. For this large sheet metal part, when the material will be wasted, we should consider folding it into several sub-parts and processing them separately, and then welding them together, which ensures the quality, reduces the waste of materials and saves costs.
An Example of Sheet Metal Processing Technology
1.2 According to the basic processing methods of sheet metal parts, such as material, bending, stretching, forming and welding. This specification describes the process requirements that should be paid attention to in each processing mode.
1.3 Key words: sheet metal, blanking, bending, stretching, forming, layout, minimum bending radius, rough edge, springback, blanking, welding
According to the different processing methods, cutting can be divided into general punching, digital punching, cutting machine, laser cutting, plasma cutting. Because of the different processing methods, the processing technology of cutting is also different. The main cutting methods of sheet metal are punching and laser cutting.
2.1 digital punching is processed by numerical control punch. The thickness of sheet metal is less than 3.0 mm for cold and hot bonding plates, 4.0 mm for aluminium plates and 2.0 mm for stainless steel plates.
2.2 Minimum size of punching is required. Minimum size of punching is related to the shape of the hole, the mechanical properties of the material and the thickness of the material.
2.3 Hole Spacing and Hole Spacing of NC Punching
The minimum distance between the edge of the punch and the shape of the hole is limited by the shape of the part and the hole, as shown in Figure 2.3.1. When the punching edge is not parallel to the shape edge of the part, the minimum distance should not be less than material thickness t, and not less than 1.5T when parallel.
Figure 2.3.1 Diagram of Bore Margin and Hole Spacing of Blanking Parts
2.4 When punching the bending and drawing parts, the distance between the hole wall and the straight wall should be kept at a certain distance. When punching the bending or drawing parts, the distance between the hole wall and the straight wall of the workpiece should be kept at a certain distance (Figure 2.4.1).
Figure 2.4.1 Distance between the hole wall of bending and drawing parts and the straight wall of workpiece
2.5 The structural dimensions of screw, bolt through hole and countersunk seat screw, bolt through hole and countersunk seat are selected according to the table below. For countersunk head pedestal of countersunk head screw, if the sheet is too thin to guarantee both through hole D2 and through hole D, priority should be given to ensuring through hole d2.
2.6 Laser cutting is a flying cutting process with laser machine. The thickness of plate is less than or equal to 24.0 mm for cold and hot binding plate, and less than 12.0 mm for stainless steel. Its advantage is that the thickness of the plate is large, the shape of the cutting workpiece is fast, and the processing is flexible. The disadvantage is that it can not be processed and formed. The mesh parts should not be processed in this way, and the processing cost is high.
3.1 When the minimum bending radius of the bending part is bent, the outer layer is stretched and the inner layer is compressed. When the thickness of the material is constant, the smaller the inner r, the more serious the tension and compression of the material. When the tensile stress of the outer corner exceeds the ultimate strength of the material, cracks and breaks will occur. Therefore, in the structural design of bending parts, too small bending radius should be avoided.
The minimum bending radius of commonly used materials is shown in the table below (Table 5).
The bending radius is the inner radius of the bending part, and t is the wall thickness of the material.
Lt is wall thickness, M is annealed, Y is hard and Y2 is 1/2 hard.
3.2 Straight Edge Height of Bending Parts
3.2.1 In general, the minimum straight-edge height of bending parts should not be too small, and the minimum height should be H > 2T according to the requirement of (fig. 4.2.1).
Figure 3.2.1 Minimum Straight Side Height of Bending Parts
3.2.2 If the design requires the straight edge height of the bending part to be less than 2t, the bending edge height should be increased first and then processed to the required size after bending, or after shallow grooves are processed in the bending deformation area, bending can be done again (as shown in the figure below).
Figure 3.2.2 Requirements for Straight Side Height under Special Conditions
3.2.3 The height of the right side with an oblique angle at the side of the bend (Fig. 4.2.3). The minimum height of the side is h=(2-4)t>3mm when the bend with an oblique angle at the side of the bend (Fig. 4.2.3).
Figure 4.2.3 Right-sided heights with oblique angles on the side of the curved edge
3.3 The distance between the hole edge and the hole edge on the bending part: punching first and then bending, the hole position should be outside the bending deformation zone, so as to avoid the deformation of the hole when bending. The distance from the hole wall to the curved edge is shown in the table below.
3.4 Local Bending Process Cut
3.4.1 When the bending line of a bending part is locally bent at the edge of a certain section at the position of abrupt size change, in order to prevent stress concentration at the sharp corner from producing bending cracks, the bending line can be moved a certain distance away from the abrupt size change (fig. 3.4.1a), or the process groove (fig. 3.4.1b), or the punching process hole (fig. 3.4.1c). Attention should be paid to the size requirements in the drawing: S (> R); groove width K (> t);
Figure 3.4.1 Design and treatment of local bending
3.4.2 When the hole is located in the bending deformation zone, the notch form is adopted. When the hole is in the bending deformation zone, an example of the notch form is adopted (Figure 3.4.2).
3.5 Bending edge with oblique edge should avoid deformation zone
Figure 3.5.1 Bending edge with beveled edge should avoid deformation zone
3.6 The design requirement of the pressing edge is that the length of the pressing edge is related to the thickness of the material. As shown in the figure below, the minimum length of dead edge is generally L (> 3.5t+R). Among them, t is the thickness of material wall and R is the minimum inner bending radius of the front process (shown in the right of the following figure).
Figure 4.6.1 Minimum Length L of Dead Edge
3.7 In order to ensure the accurate positioning of the blank in the die and prevent the scrap caused by the offset of the blank during bending, the process positioning hole should be added in advance in the design, as shown in the following figure. Especially for parts formed by multiple bending, the process hole must be taken as the positioning datum to reduce the accumulated error and ensure the product quality.
Figure 3.7.1 Process positioning holes added during multiple bending
3.8 When marking the relevant dimensions of bending parts, the technological properties should be considered.
Figure 3.8.1 Example of Bending Marking
As shown in the figure above, a) Punching before bending, L dimension accuracy is easy to guarantee, and processing is convenient. B) and c) If the dimension L requires high accuracy, it needs to bend first and then process holes, which is troublesome.
3.9 The springback of bending parts is affected by many factors, including the mechanical properties of materials, wall thickness, bending radius and positive pressure during bending.
3.9.1 The bigger the ratio of the radius of the inner corner to the thickness of the plate, the bigger the springback.
3.9.2 The method of restraining springback in design for example, springback of bending parts is mainly avoided by manufacturers when designing dies. At the same time, some structures are improved to reduce the springback angle. As shown in the figure below, the stiffness of the workpiece can be improved and the springback can be restrained by pressing the stiffeners in the bending zone.
Figure 3.9.2 Design examples of resilience suppression methods
4.1 Requirements for the radius of the fillet between the bottom of the drawing part and the straight wall
As shown in the figure below, the radius of the corner between the bottom and the straight wall of the drawing piece should be larger than the thickness of the plate, that is, R1 (> t). In order to make the stretching process more smoothly, r1=(3~5)t is usually chosen, and the maximum radius of the fillet should be less than or equal to 8 times the thickness of the plate, that is, R1 < 8t.
4.2 The fillet radius between the flange and the wall of the drawing part should be two times larger than the thickness of the plate, that is, R2 (> 2t). In order to make the drawing process more smoothly, r2=(5~10) t is usually chosen, and the maximum radius of the flange should be less than or equal to 8 times the thickness of the plate, that is R2 (< 8t). (See Figure 5.1.1)
4.3 The diameter of the inner cavity of the circular drawing part should be D (> D + 10t), so that the pressing plate will not wrinkle during drawing. (See Figure 4.3.1)
4.4 The fillet radius between two adjacent walls of a rectangular stretching piece should be R 3 or more than 3 T. In order to reduce the number of stretches, R 3 or more H/5 should be taken as far as possible so that it can be pulled out at one time.
4.5 When a circular flange-free drawing part is formed at one time, the dimension relationship between its height and diameter is required. When a circular flange-free drawing part is formed at one time, the ratio of height H to diameter D should be less than or equal to 0.4, i.e. H/d is less than 0.4, as shown in the following figure.
Figure 4.5.1 Size relationship between height and diameter of circular flangeless drawing parts in one forming process
4.6 Notices for dimensioning on drawing design of stretching parts The thickness of stretching parts varies due to the different stress magnitude everywhere. Generally speaking, the center of the bottom keeps its original thickness, the material at the bottom corner becomes thinner, the material near the flange at the top becomes thicker, and the material around the corner of the rectangular stretching piece becomes thicker.
4.6.1 Standard method of product dimension for stretching parts When designing stretching products, the dimensions on the product drawing should be clearly indicated that the external or internal dimensions must be guaranteed, and the internal and external dimensions cannot be marked at the same time.
4.6.2 Marking method of dimension tolerance of drawing parts The inner radius of concave-convex arc of drawing parts and the height tolerance of cylindrical drawing parts formed at one time are two-sided symmetrical deviation, which is half of the absolute value of precision tolerance of grade 16 of national standard (GB), and is crowned with (+).
5.1 reinforcing tendons
Reinforcing bars on plate metal parts helps to increase structural rigidity. The structure and size of reinforcing bars are shown in the table below.
5.2 Limit Dimensions of Convex Spacing and Convex Edge Spacing
Limit dimensions of convex spacing and convex edge spacing are selected according to the table below.
Louvers are usually used for ventilation and heat dissipation on various shells or chassis. The method of forming louvers is to cut the material through one edge of the punch, while the rest of the punch deforms the material by stretching at the same time to form a undulating shape of one side opening. The typical structure of louvers is shown in Fig. 5.3.1.
Figure 5.3.1 Structure of louvers
Louver size requirements: a (> 4t); B (> 6t); h (< 5t); L (> 24t); R (> 0.5t). There are many types of flanging holes in 5.4 holes. This code only focuses on the flanging of inner holes to process threads, as shown in Fig. 5.3.2.
5.4. Size parameters of inner hole flanging with threaded holes
6.1 The classified welding methods include arc welding, electroslag welding, gas welding, plasma arc welding, melting welding, pressure welding and brazing. The welding of sheet metal products is mainly arc welding and gas welding.
6.2.1 arc welding is flexible, flexible, widely applicable, and can be used for all-position welding. It has the advantages of simple equipment, good durability and low maintenance cost. However, the labor intensity and quality are not stable, depending on the level of operators. Suitable for welding more than 3mm carbon steel, low alloy steel, stainless steel and non-ferrous alloys such as copper and aluminium
6.2.2 Angle between wire, torch and weldment.
When manual TIG welding is used, the correct relative position must be maintained between the torch, wire and welded parts, which is determined by the shape of the welded parts. The horizontal welding position of the manual tungsten argon arc welding torch, wire and welding angle are shown in the following figure.
Too small angle between torch and welding parts will reduce the protective effect of argon; too large angle makes it difficult to operate and fill welding wire. The angle of torch, wire and weldment in manual TIG welding is shown in the left figure below, and the angle of fillet weld is shown in the following figure.
6.2.3 starting arc
There are three kinds of arc initiation methods for manual TIG welding: contact short circuit arc initiation, frequency high voltage arc initiation and high voltage pulse arc initiation.
The contact short circuit method is to start the arc immediately after the end of tungsten pole is approximately vertical to the surface of the weldment (70 ~85). This method will produce large short-circuit current when short-circuit occurs, which will cause the tungsten extremity head to burn and shape to deteriorate. During the welding process, the arc will disperse or even drift, which will affect the stability of the welding process and even cause tungsten inclusion.
High-frequency and high-voltage arc ignition and high-voltage pulse arc ignition are equipped with high-frequency or high-voltage pulse devices in welding equipment. High-frequency or high-voltage pulses are automatically cut off after arc ignition. This method is simple to operate and can ensure the geometric shape of the tungsten pole end and the welding quality.
Arc extinguishing: If arc extinguishing is not properly operated, arc pits will be generated, which will cause cracks, burning through, blowhole and other defects. The following methods can be used to extinguish the arc during operation:
1. Adjust the attenuation current value on the welding machine, loosen the switch on the welding torch during arc extinguishing, make the welding current attenuate, gradually accelerate the welding speed and wire filling speed, and then extinguish the arc.
2. Reducing the angle between torch and welding parts, elongating arc makes arc heat mainly concentrated on welding wire, accelerating welding speed and increasing filling quantity, and quenching arc after filling arc pit.
3. When annular weld is extinguished, the arc should be slightly elongated and overlapped for 20-30 mm, without adding or adding a small amount of wire, and then extinguished.
The operation mode of welding torch: The torch of manual TIG welding only moves in a straight line, and the moving speed of welding torch can not be too fast, otherwise, the protection effect of argon will be affected.
Linear movement: There are three ways of linear movement: linear uniform movement, linear intermittent movement and linear reciprocating movement.
1. Linear uniform movement refers to the straight, smooth and uniform movement of the torch along the weld seam. It is suitable for the welding of stainless steel, heat-resistant steel and other thin plates. Its characteristics are that the welding process is stable and the protection effect is good. This can ensure the stability of welding quality.
2. Linear intermittent movement means that the torch needs to stay for a certain time in the welding process to ensure penetration, that is, the straight movement along the weld is a intermittent forward process. It is mainly used in the welding of medium and thick plates.
3. Linear reciprocating movement refers to the reciprocating linear movement of the torch along the weld seam, which is characterized by good heat control and weld formation, so as to prevent burning through. It is mainly used for welding thin plates of aluminium and its alloys.
Lateral swing: It is a small swing to meet the special requirements of welds and different joint forms. There are three common forms: zigzag swing of arcs, zigzag lateral swing of arcs and R-shaped swing.
When the zigzag shape of arc swings, the torch moves forward in a zigzag shape similar to that of arc, as shown in Fig. a below. This method is suitable for large T-joints, overlap joints of thick plates and butt joints of medium and heavy plates with grooves. During operation, the torch stays at both sides of the weld for a little longer, and the movement speed can be properly accelerated when passing through the center of the weld, so that the high quality weld can be obtained.
The zigzag lateral swing of arc is that the torch moves forward not only in arc, but also in oblique zigzag, as shown in Fig. B. This method is suitable for uneven corner joints. During operation, the torch deviates to the protruding part, and the torch moves sideways in a zigzag shape, so that the arc stays longer in the protruding part to melt the protruding part without or with less filling wire.
The R-shape swing is the movement of the welding torch which is similar to the R-shape lateral swing, as shown in Fig. C. This method is suitable for butt joints with unequal thickness plates. During operation, the torch not only makes R-shaped movement, but also the arc slightly deviates to the thick plate, which makes the arc stay on one side of the thick plate for a longer time, so as to control the melting speed of both sides and prevent the thin plate from burning through while the thick plate is not welded through.
Wire feeding method: The addition of filler wire has a great influence on the quality of weld. If wire feeding is too fast, the welding seam is easy to pile up high, and the oxide film is difficult to eliminate; if wire feeding is too slow, the welding seam is prone to undercut or concave. So wire feeding should be skilled. There are two commonly used wire feeding methods: finger continuation method and manual method.
1. finger continuation method: the welding wire is clamped between thumb and index finger, supported by middle finger and ring finger. When thumb moves the welding wire forward, the index finger moves backward, and then the thumb rubs the surface of the welding wire back to the index finger. The thumb moves the welding wire forward again and again, so the welding wire is continuously sent into the molten pool. This method is suitable for long welded joints.
2. Manual method: the welding wire is clamped between thumb, index finger and middle finger, and the finger is not moved. Instead, the welding wire is fed into the molten pool by moving the hand or arm around the weld and repeatedly moving the wrist up and down. This method is widely used. According to the way of wire feeding into molten pool, it can be divided into four kinds: pressing method, continuing method, point shifting method and dropping method.
As shown in Figure a below, press the wire down slightly by hand so that the end of the wire is close to the edge of the molten pool. This method is simple to operate, but it is difficult to feed because of the long wire in hand and the unstable end of the wire.
As shown in Fig. b, the end of the welding wire is inserted into the molten pool, and the hand moves forward, so that the welding wire is continuously added into the molten pool. This method is suitable for fine wire or joints with large gap, but it is not easy to guarantee the welding quality and seldom used.
As shown in Fig. C, the welding wire is gradually added into the molten pool by repeatedly moving the wrist up and down and slowly moving the hand backwards. When using this method, the oxide film on the surface of the molten pool can be removed sufficiently under the action of arc due to the repeated movement of the welding wire up and down, thus preventing slag inclusion. At the same time, the filling of the welding wire on the front edge of the molten pool is beneficial to reducing the porosity. Therefore, it is widely used.
As shown in Fig. d, the droplets melted by the welding wire are dripped into the molten pool repeatedly and actively. This method has the same advantages as the point shift method, so it is commonly used.
Left welding method and right welding method: As shown in the figure below, manual TIG welding can be divided into left welding method and right welding method according to the moving direction of welding torch and wire feeding position.
1. Left welding method: In the welding process, the welding heat source (welding torch) moves from the right end of the joint to the left end and points to the part to be welded. The operation method is called left welding method. The left welding wire is in front of the arc. This method is easy to observe the molten pool. Welding wire is often added by point-shift method and drop-by-drop method. The weld is well formed and easy to grasp. Therefore, it is widely used.
2. Right welding method: During the welding process, the welding heat source (welding torch) moves from the left end of the joint to the right end and points to the welded part, which is called right welding method. The right welding wire is located behind the arc. It is not easy to observe the molten pool and control the temperature of the molten pool during operation, but the penetration is deeper than the left welding method and the weld seam is wider. It is suitable for thick plate welding, but it is difficult to master.
Characteristics of Welding in Various Positions
Flat welding: Flat welding requires coordinated arc movement and wire feeding, which is suitable for all kinds of thickness and material welding. According to the thickness of welding parts, corresponding grooves are made, and the torch can move in zigzag or straight line. When welding unequal thickness weldments, the arc slightly deviates to one side of the thick plate, and the torch can move in a straight line or r-shape. If the root clearance is large, the angle between the torch and the weldment can be reduced, and the welding speed and wire feeding speed can be accelerated.
Vertical welding: In order to prevent molten pool metal and droplets from flowing downward, the temperature of the molten pool should be controlled, smaller welding current and finer filler wire should be selected, the arc should not be drawn too long, and the inclination angle of the torch should not be too small, otherwise various welding defects will be caused.
Horizontal welding: Horizontal welding is easy to master, but attention must be paid to the horizontal angle of the torch and the angle of wire feeding.
Upward welding: Upward welding is very difficult. In order to avoid metal and droplets from molten pool flowing down under gravity, the welding current should be small, the welding speed should be fast, and the gap between groove and root should be appropriately small.
6.3 The flame temperature and property of gas welding can be adjusted. The heat source of arc welding is wider than that of heat affected zone. The heat is less concentrated than that of arc welding, and the productivity is lower. It can be used for welding thin-walled structures and small parts, such as steel, cast iron, aluminium, copper and its alloys, cemented carbide, etc.
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