0 1. What is resistance welding?
After the weldments are joined, pressure is applied by the electrodes, and a stable and firm joint is obtained between the two separated surfaces by using a large amount of plastic deformation energy generated by resistance heat and current passing through the contact surface and the adjacent area of the joint. This method of metal connection is called resistance welding.
Resistance welding can be divided into resistance spot welding, resistance seam welding and resistance butt welding according to joint types and process methods.
02. What is precision resistance spot welding?
Two weldments are placed between two opposite electrodes, and pressure is applied to the electrodes, and then the loop (electrode ①-workpiece ①-workpiece ②-electrode ②) is electrified, so that a connection solder joint is formed between the two weldments whose electrodes are pressed. This welding method is called resistance spot welding. Resistance spot welding of precision micro parts is called precision resistance spot welding.
Precision resistance spot welding machine is most suitable for small electronic parts with high performance requirements and small parts assembly in precision machinery industry.
03. What is the principle of resistance spot welding?
The principle of resistance spot welding is to apply pressure on the workpiece between two opposite electrodes to conduct a large current, and then the total resistance R(R 1+R2+R3+R4+R5) between the two electrodes generates heat, especially at the contact part of the workpiece, and a nugget is formed at the contact part of the workpiece. After power failure and pressure maintenance, the nugget solidifies to form a solder joint, and finally the two workpieces are connected. As shown in the figure below.
R: total resistance between two electrodes
R 1: contact resistance between electrode ① and workpiece ①.
R2: resistance of the workpiece ① itself
R3: Contact resistance between workpieces ① and ②.
R4: resistance of the workpiece ② itself
R5: Contact resistance between electrodes ② of workpiece ②.
04. What are the key elements of resistance spot welding?
There are five key factors that determine the quality of resistance spot welding: ① welding current, ② welding time, ③ welding pressure, ④ electrode material type, ⑤ electrode tip shape and surface state.
05. What is contact resistance and its function?
Total contact resistance in resistance spot welding = contact resistance between electrode ① and workpiece ①+contact resistance between workpiece ① and workpiece ②+contact resistance between electrode ② and workpiece ②.
The heat contacted by the workpiece is directly proportional to the contact resistance. That is to say, if the contact resistance is doubled, the heat at the contact part of the workpiece will be doubled. This is the internal condition of heat in the contact part of the workpiece.
06. What is the role of current in resistance spot welding?
The heat in the contact part of the workpiece is proportional to the square of the current. When the current is doubled, the heat in the contact part of the workpiece will increase by four times.
07. What is the role of the electrifying time in resistance spot welding?
The heat in the contact part of the workpiece is directly proportional to the power-on time. When the power-on time is doubled, the heat at the contact part of the workpiece will also be doubled.
08. What is the function of applying pressure in resistance spot welding?
The pressure exerted by welding is mainly related to the contact resistance and the formation of solder joints by solidification of nuggets. Increasing welding pressure leads to the decrease of contact resistance, and then the heat in the contact part decreases, which is not conducive to the formation of nuggets; Increasing the welding pressure can solidify the nugget with a certain size, and form a solder joint with fewer defects and better quality. On the contrary, the conclusion is the opposite.
09. What role does the electrode material type play in resistance spot welding?
With the different material types of the workpiece to be welded, it is necessary to choose the appropriate electrode material type to match when welding.
Optimum welding quality.
Selection principle: Generally speaking, the lower the resistivity of the material to be welded, the better its electrical conductivity and thermal conductivity, so the material with higher resistivity should be selected as the electrode. On the contrary, the conclusion is the opposite.
10. What are the commonly used electrode materials and their applicable scope?
Commonly used electrode materials are: pure copper metal, pure tungsten metal, pure molybdenum metal, aluminum-copper alloy, chromium-copper alloy, beryllium bronze, tungsten-copper alloy, molybdenum-copper alloy and so on.
Applicable examples: low-carbon steel workpiece-selective electrode (chromium-copper alloy), stainless steel workpiece-selective electrode (chromium-copper alloy), pure copper workpiece-selective electrode (pure tungsten metal, pure molybdenum metal, tungsten-copper alloy, molybdenum-copper alloy), brass workpiece-selective electrode (chromium-copper alloy), pure silver workpiece-selective electrode (tungsten-copper alloy) and pure nickel workpiece-
1 1. What role does the electrode play in resistance spot welding?
The electrode has four basic functions: ① conducting welding current to the workpiece, ② applying welding pressure to the workpiece, ③ ensuring the heat dissipation and cooling of the welding point, and ④ ensuring the current density of the welding point.
12. What are the common electrode shapes and their applicable scopes?
The shape of the end face of the electrode has a great relationship with the current density of the welding point of the workpiece, so it should be kept hard, non-deformed and wear-resistant as far as possible. In addition, the shape of electrode end face also affects the generation and cooling of heat during welding, and then affects the formation of weld nugget.
Commonly used electrode shapes are: ① cylindrical, ② frustum, ③ hemispherical, ④ cuboid and ⑤ frustum.
13. What are embedded electrodes and their characteristics?
When welding some materials with high electrical conductivity and thermal conductivity (pure copper, pure silver, etc.). ), using embedded electrodes, that is, most of tungsten or molybdenum is embedded in chromium copper, and only a few welding heads are exposed. With the help of copper, the stable output of loop current is improved, the heat dissipation effect is improved and the cost is reduced.
14. What is the self-leveling electrode and its characteristics?
When multi-point projection welding or large-size convex ring welding is carried out, one of the electrodes has a spherical hinge, and the planes of the two electrodes can be automatically parallel when pressurized, so that the workpiece pressure is balanced and the welding uniformity is good. The electrode with this structure is called self-leveling electrode.
15. What is a soft electrode and its characteristics?
When welding the workpiece with fragile structure, one of the electrodes is made of thin conductive copper tape wrapped with soft pad, so that the soft electrode can press the workpiece with fragile structure without damaging the workpiece under the condition of obtaining sufficient welding pressure, and at the same time, the conductivity uniformity is good. The electrode with this structure is called soft electrode.
16. what is the basic composition of precision resistance spot welding machine?
Usually, modern precision resistance spot welding machines are modular in design, and their basic modules include: ① mechanical modules (mainly indenter, frame, electrode, etc.). (2) Power supply and electrical module (mainly welding power supply, welding transformer, timing action controller, etc.). ), and ③ auxiliary components (mainly workbench, pedal start switch, connecting cable, positioning fixture, etc.). ).
17. What are the basic types of power supply for precision resistance spot welding machines?
There are generally four kinds of power sources for modern precision resistance spot welding machines: ① precision AC power sources (such as AP5K and AC5K). ), ② precision capacitor energy storage power supply (such as SP 125, DP250, etc. ), ③ precision inverter DC power supply (such as HF25KA and HF50KA). ) and ④ precision transistor DC power supply.
18. What is a precision AC spot welder and its characteristics?
The welding transformer is controlled by power frequency AC mains through thyristor as a switch, and the conduction angle can be accurately adjusted, and low voltage and large current are output to the workpiece in a given number of cycles, thus realizing spot welding under a certain welding pressure. The spot welding machine working according to this principle is a kind of precision AC spot welding machine. As shown in the figure below.
Characteristics of precision AC spot welding machine: ① simple principle and high reliability; (2) popularization and convenient use; ③ low price; (4) the instantaneous input power is large and the power grid load is heavy; ⑤ Suitable for ordinary materials with low welding requirements (low carbon steel, stainless steel, brass, phosphor copper, etc.). ).
19. What is a precision capacitor energy storage spot welder and its characteristics?
The rectifier of power frequency AC power supply is accurately and quantitatively stored in the capacitor, and the electric energy in the capacitor is released to the primary of the welding transformer through the thyristor as a switch, and then the secondary of the welding transformer outputs the fixed energy stored in the capacitor to the workpiece in the form of low voltage and high current, thus realizing spot welding under a certain welding pressure. The spot welding machine which works by this principle is a precision capacitor energy storage spot welding machine. As shown in the figure below.
The characteristics of precision capacitor energy storage spot welding machine are as follows: ① The principle is complex; ② Accurate output energy, saving electricity; ③ Moderate price; (4) need a larger welding pressure, otherwise easy to splash; ⑤ Especially suitable for welding high conductivity materials (copper, silver, aluminum, gold, etc.). ), of course, it is also suitable for welding ordinary materials (low carbon steel, stainless steel, brass, phosphor copper, etc.). ).
20. What is a precision inverter DC spot welder and its characteristics?
The power frequency alternating current commercial power is converted into direct current through the rectifier circuit, and this direct current is converted into high frequency alternating current by the inverter bridge controlled by the circuit with current or voltage feedback control function and released to the primary of the welding transformer, and then the secondary of the welding transformer is rectified by the rectifier and output to the workpiece in the form of direct current, and spot welding is realized at a certain welding pressure. The spot welding machine working on this principle is a precision inverter DC spot welding machine. As shown in the figure below.
Characteristics of precision inverter DC spot welding machine: ① complex principle, ② closed-loop (current, voltage and power) feedback control, accurate output energy, ③ high price, ④ low welding pressure, not easy to splash, ⑤ excellent weldability, suitable for welding various materials (low carbon steel, stainless steel, brass, phosphor copper, silver, aluminum, gold, etc. ).
2 1. What is a precision transistor DC spot welder and its characteristics?
Power frequency AC mains power is changed from input transformer to low voltage AC power supply, and then it is changed into DC power supply through rectifier circuit with smoothing capacitor. The DC power supply is controlled by a circuit with current or voltage feedback control function, and outputs transistor groups to the workpiece in a DC low-voltage and high-current mode, thus realizing spot welding under a certain welding pressure. The spot welder working according to this principle is a precision transistor DC spot welder. As shown in the figure below.
The characteristics of precision transistor DC spot welding machine are as follows: ① The principle is complicated and it is not suitable for making too much power; ② Closed-loop (current, voltage, power) feedback control to accurately output energy; 3 expensive; (4) welding pressure is small, not easy to splash; ⑤ Excellent weldability, suitable for welding tiny workpieces of various materials (low carbon steel, stainless steel, brass, phosphor copper, copper, silver, aluminum, gold, etc.). ).
22. What is the rated output power of the spot welder?
Generally, spot welding machines output power intermittently during spot welding. Under the cooling conditions specified in the manual, the maximum output power of the spot welder at rated duty ratio is the rated output power of the spot welder.
23. What is the maximum output power of the spot welder?
The maximum output power of the spot welder working in the output test loop of the standard spot welder is the maximum output power of the spot welder.
24. What is the no-load voltage of spot welder?
When the output circuit of the spot welder is open, the maximum output voltage of the welder is the no-load voltage of the spot welder.
25. What is the duty cycle of spot welder?
The ratio of the sum of the actual power-on welding time periods of the spot welder to the total working time period is the duty cycle of the spot welder.
26. What is the short-circuit current of spot welder?
The maximum output current of a standard spot welder working in the short-circuit state of its output test loop is the short-circuit current of the spot welder.
27. What is the actual welding current of spot welder?
The actual welding current of spot welder is the measured value of current when welding workpiece.
28. What is multi-section welding current and its function?
Some multi-function spot welding machines can output multi-segment current in a spot welding cycle program. Generally, the first current is called preheating current (when it is mainly used for welding coated metal, part of the coating can be removed to make the contact conductivity consistent), the second current is called main welding current (mainly used for welding the workpiece itself), and the third current is called post-heating current or tempering current (mainly used for avoiding brittleness when welding hardened metal).
29. There are several basic types of precision resistance spot welding machine head?
The head of precision resistance spot welding machine is divided into: ① manual pedal power head, ② cylinder drive head, ③ electric servo drive head and ④ manual chuck. As shown in the figure below.
The head structure of precision resistance spot welding machine is divided into: ① fixed single-point head, ② fixed double-point head, ③ combined modular single-point head and ④ combined modular double-point head.
In addition, some spot welding machine heads are also equipped with auxiliary stroke module or auxiliary pressure module.
30. What is the welding stroke of precision resistance spot welder?
The moving distance of the movable electrode of the main module in the head of precision resistance spot welding machine is the welding stroke of precision resistance spot welding machine. Generally, the distance from the movable electrode to the workpiece is less than the maximum welding stroke of the precision resistance spot welder.
3 1. What is the auxiliary stroke of precision resistance spot welding machine?
The moving distance of the movable slide table of the auxiliary stroke module in the head of precision resistance spot welding machine (the main module is installed on this slide table) is the auxiliary stroke of precision resistance spot welding machine. The auxiliary stroke of precision resistance spot welding machine is generally mainly to avoid obstacles.
32. What is the throat depth of precision resistance spot welding machine?
The distance between the movable electrode of the main module in the head of precision resistance spot welding machine and the head bracket is the throat depth of precision resistance spot welding machine. Generally, the throat depth of the welder has a limit on the maximum distance from the welding spot on the workpiece to the edge of the workpiece.
33. What is the actual precision resistance spot welding pressure?
The actual test value of welding pressure applied by electrode when welding workpiece by spot welder is precision resistance spot welding pressure.
34. What is pressure following and its function?
When a spot welder welds a workpiece, the welding is dynamic during the heating process of the workpiece, and the electrode will follow this dynamic process to ensure the stability of the welding pressure applied by the electrode, which is the pressure follow-up of precision resistance spot welding.
If the pressure of precision resistance spot welding follows well, it is not easy to splash and the core is well formed.
35. What is the spot welding cycle program and its meaning?
The standard spot welding cycle program is generally a description of the first spot welding sequence process of spot welder, which consists of four continuous time processes: ① electrode preloading time, ② electrifying welding time, ③ cooling and pressure maintaining time and ④ electrode rest time.
Electrode preloading time is the time from moving covered electrode to clamping workpiece before power welding.
Power-on welding time is the time required to power-on and heat the workpiece.
The cooling and holding time is the time from the end of energizing the workpiece to releasing the electrode and releasing the workpiece.
The electrode rest time is the time from the electrode release to the next time.
36. What is the function of current monitor?
Because the welding current is a very large current (about 100A-50KA) that flows in a very short time (1ms-500ms) and its current waveform is different, it can't be measured by ordinary pointer or digital ammeter at all. Therefore, a professional high current monitor (WBT- 1 12A) is needed to measure, which can judge and alarm the current exceeding the limit, and at the same time, it can automatically record the current data of each solder joint, which is convenient for quality management.
37. What is the function of the pressure detector?
The electrode pressure of resistance spot welding machine can be adjusted, but most of the pressure values are not displayed, so it needs to be measured by a professional wide-range pressure detector (Smart Indicator 9000) to accurately adjust the electrode pressure.
38. What is the concept of precision resistance spot welding specification?
The welding specification of resistance spot welding is the concept of formulating the combination strategy of welding parameters (welding current, welding time and welding pressure) according to the welding process requirements of the workpiece.
Strong welding specification: the combination of high welding pressure, high welding current and short welding time.
Medium welding specification: the combination of medium welding pressure, medium welding current and medium welding time.
Weak welding specification: the combination of low welding pressure, low welding current and long welding time.
39. What are the quality assurance methods for precision resistance spot welding?
Quality inspection methods of resistance spot welding: ① Visual inspection (manual visual inspection and metallographic inspection of core) ② Destructive inspection (manual simple tearing experience inspection and tensile strength inspection of core with tensile testing machine).
Quality assurance means: ① pressure detection (regularly check the welding pressure with a pressure detector to monitor the working condition of the welding head to ensure the stability of the welding pressure), ② current monitoring (monitor the welding current in real time to ensure that possible defects can be found immediately), ③ electrode polishing (regularly check the electrode shape and surface state, and repair or replace it in time if the deformation or wear exceeds the limit), ④ electrode overheating (regularly check the electrode cooling to prevent electrode overheating and shorten the service life), and ⑤ workpiece accuracy.
40. What is projection welding?
When the plates of two workpieces to be welded are thicker or different in thickness, a bump can be punched on one workpiece plate (usually a bump is punched on the thicker plate), so that the bump can contact with another workpiece and form a nugget on this bump. In this way, welding pressure and welding current are concentrated, which is convenient to improve welding quality. This resistance welding process is called resistance projection welding.
Sometimes some workpieces need to distribute multiple solder joints in a small range. At this time, in order to improve the efficiency and quality, bump drilling can also be used for one-time welding. However, some workpieces have sealing requirements for welding, and then they are welded once by stamping annular convex lines.
4 1. What is resistance seam welding?
Two workpieces are assembled in an overlapping manner and placed between the electrodes of two rollers. The roller is pressurized and rotated to supply power continuously or intermittently, thus forming a continuous weld on the rolling path of the roller. This method is called resistance seam welding.
Resistance seam welding is an important method of resistance welding, which is mainly used in: metal adhesive tape, sealed container joints and so on.
42. What are the transmission types of precision resistance spot welding?
There are two main ways of force transmission in precision resistance spot welding: ① Double-sided force transmission (two electrodes clamp the two sides of the workpiece relatively, generally welding one point at a time), ② Single-sided force transmission (two electrodes are parallel to one side of the workpiece, and the workpiece is pressed on a support table with good conductivity, generally welding two points at a time). Sometimes the electrode with a flat end only plays the role of power transmission, but actually only welds a little). As shown in the figure below.
43. Why is there shunt in precision resistance spot welding?
In precision resistance spot welding, a part of current does not flow through the welding core at the ongoing welding point, and this part of current cannot generate effective welding heat. We call this phenomenon shunt. Generally speaking, adjacent solder joints, some workpieces themselves or fixtures are the main factors that produce shunt.
44. What is the polarity effect?
When DC spot welder is used to weld two different materials (copper alloy and stainless steel) or some single-sided power transmission types (battery components), the welding strength of the welded object will be obviously different by changing the polarity of welding current. In addition, the change of current polarity also has a considerable influence on the adhesion between the electrode and the welded object. This welding phenomenon is called polarity effect.
When welding with AC spot welding machine, the heating value and loss of the two electrodes are the same due to the bidirectional flow of current, and there is no polarity effect.
45. Why should the workpiece positioning fixture be insulated?
When using precision resistance spot welding machine to weld workpieces, it is sometimes necessary to use fixtures to locate workpieces in order to achieve accurate welding. This fixture is best insulated from the workpiece to prevent unnecessary shunt.
46. What is the thermal balance of precision resistance spot welding?
When welding a workpiece with a precision resistance spot welder, there is a dynamic process of heating and radiating between the electrode and the workpiece. The thermal balance of precision resistance spot welding means that the workpiece is energized with equal heat, and the temperature of the solder joint (nugget) is the highest by adjusting the solder joint process design, electrode material or electrode shape and structure.
Common methods to obtain thermal balance: ① Use electrodes with poor conductivity for workpiece materials with good conductivity. The workpiece material with poor conductivity should use the electrode with good conductivity. (2) When the thickness of the workpiece varies greatly, an electrode with a small tip diameter can be used on the thick plate side, and an electrode with a large tip diameter can be used on the thin plate side to concentrate the heat on the welding core. (3) when welding thermal asymmetric workpiece, projection welding method is often used.
47. What is the spot welding of metal materials?
The spot welding weldability of metal materials is a measure of the difficulty of realizing high quality spot welding joints of metal materials under certain spot welding process conditions.
The main indexes for judging the weldability of metal materials in spot welding are: ① electrical conductivity and thermal conductivity of metal materials (the metal materials with high electrical conductivity and thermal conductivity are poor in weldability), ② high-temperature plasticity and plastic temperature range of metal materials (the metal materials with poor high-temperature plasticity and narrow plastic temperature range are poor in weldability), ③ sensitivity of metal materials to thermal cycle (the metal materials that are easy to be quenched and brittle in thermal cycle of spot welding are poor in weldability), and ④ melting point and hardness (the metal materials with high melting point and high hardness are poor in weldability)
48. How to resistance spot weld highly conductive (hot) materials?
In resistance spot welding, high conductivity materials such as copper, aluminum, gold and silver, tungsten, molybdenum, tungsten-copper alloy, molybdenum-copper alloy and copper-aluminum alloy are selected as electrodes (generally embedded electrodes are used). As for welding power supply, capacitor energy storage power supply or high-power inverter welding power supply is usually used to realize short-time high-current welding (fast heat storage and less heat dissipation). However, sometimes AC power supply is used for a long time with high current (slow heat storage and high heat dissipation) to realize welding.
49. How to resistance spot weld low conductive (hot) materials?
When resistance spot welding low conductivity materials such as low carbon steel, nickel and stainless steel, Cr-Cu alloy and Cu-Al alloy are selected as electrodes. Regarding welding power supply, AC power supply is generally used for welding joints with low requirements. Capacitive energy storage power supply is generally used for solder joints with high requirements. High-power inverter welding power supply is generally used for welding joints with high requirements.
50. How to resistance spot weld dissimilar materials?
When resistance spot welding different materials such as low carbon steel ≈ copper, nickel ≈ copper, nickel ≈ aluminum, stainless steel ≈ copper alloy and copper-aluminum alloy, low carbon steel, nickel and stainless steel are used as electrodes, while tungsten, molybdenum, tungsten-copper alloy, molybdenum-copper alloy and copper-aluminum alloy are used as electrodes of copper and aluminum. As for the welding power supply, the requirements for solder joints are not high, and the capacitor energy storage power supply is generally selected. High-power inverter welding power supply is generally used for welding joints with high requirements.