0 Introduction
The pressure sensor consists of a sintered housing assembly, a pressure-sensitive chip, a diaphragm, a welding ring, and other main components. The pressure is sensed and transmitted to the chip through the diaphragm, and then converted into a voltage signal output through a Wheatstone bridge [1]. The diaphragm welding process is an important process in the manufacturing of pressure sensors and has attracted much attention. Once welding defects occur, the sealing performance and performance of the product will gradually deteriorate, and may even affect safe operation. Therefore, it is particularly necessary to optimize the diaphragm welding process of pressure sensors, which is also a key process to improve the quality and performance of pressure sensors.
At present, many sensor manufacturers at home and abroad use laser welding technology. Laser welding is an efficient and precise welding method that uses a high-energy-density laser beam as a heat source [2]. Laser welding is one of the important aspects of laser material processing technology. It has the advantages of high input energy density, small heat-affected zone of workpiece, easy to realize automated control, and no tool wear and replacement. Laser welding has advantages that traditional welding cannot match. It can effectively reduce defects and has been successfully applied to the precision welding of micro and small parts [3]. However, many sensor manufacturers still use argon arc welding. This is based on years of accumulated experience. Argon arc welding has high operational flexibility and is easy to realize the welding of complex products. However, the heat during the welding process is high, which can easily produce welding defects and requires high skills from operators.
This paper optimizes the welding process by comparing laser welding and argon arc welding experiments; optimizes the welding material by comparing the welding materials of 4J29 and 316L for the pressure sensor base metal; and optimizes suitable welding parameters by comparing the welding effects of different welding parameters. Ultimately, this achieves the goal of optimizing the pressure sensor diaphragm welding process, thereby improving diaphragm welding quality, increasing the yield rate of pressure sensors, meeting increasingly stringent technical requirements from users, and opening up wider and more application areas.
1. Research on Laser Welding Technology
1.1 Laser Welding Principle
Laser welding utilizes the principle of atomic radiation to excite the working material and generate a beam of light with high monochromaticity, strong directionality and high brightness. After focusing, the beam can be focused to the focal point to obtain extremely high energy density. It interacts with the workpiece to cause the metal to evaporate, melt, crystallize and solidify to form a weld [2-5].
1.2 Advantages of laser welding
1) High density and fast speed. The depth-to-width ratio of laser welding process can reach up to 10:1[5]. During the welding process, the energy density is high and small holes will appear on the material. The laser is transmitted to the workpiece welding direction through the small holes, while the transverse transmission is less. Therefore, the speed is faster and the energy is more concentrated during the laser welding process.
2) Low heat input. Due to the high power density and fast welding speed of laser welding, a good weld can be achieved with very little heat input. The low heat input in laser welding results in minimal product deformation, a small range of metallographic changes in the heat-affected zone, and minimal deformation due to heat conduction.
3) Good mechanical properties of the weld. After the laser beam is focused, a very small spot can be obtained and it can be precisely positioned. By adjusting the spot and the moving speed, the weld has good mechanical properties and high strength after welding. The weld is narrow and has a good surface condition, eliminating the need for post-weld cleaning.
2. Research on Argon Arc Welding Process
2.1 Principle of Argon Arc Welding
Argon arc welding is a welding process that uses a non-consumable electrode (tungsten electrode) under the protection of rare gas to melt the base metal by utilizing the arc heat generated between the electrode and the base metal [6].
2.2 Advantages of Argon Arc Welding
1) The shielding gas is a rare gas that does not react chemically with the metal or melt into it, making the metallurgical reaction during the welding process simple and easy to control.
2) Tungsten induction arc can automatically remove the oxide film on the surface of the workpiece, and can successfully weld metals that are easily oxidized, nitrided, and chemically reactive.
3) Good welding process performance, open arc, and the ability to observe the electric arc and molten pool.
4) Tungsten inert gas arc is stable and can burn stably even at very small welding currents (less than 10 A), and is often used to weld thin workpieces[7].
2.3 Disadvantages of Argon Arc Welding
1) Argon arc welding is slower and has a much higher heat input than laser welding, making the product more prone to deformation.
2) Tungsten electrodes have limited current carrying capacity. Excessive welding current can cause the tungsten electrode to melt and evaporate, requiring regular repair or replacement, resulting in low production efficiency.
3. Diaphragm Welding Process Experiment
Under the condition that other external variables are the same, comparative experiments were conducted on different welding processes, welding materials, and welding parameters to study the diaphragm welding process, thereby optimizing the diaphragm welding process, welding component materials, and welding parameters. Based on the principle of improving the welding quality of pressure sensor diaphragms, this aims to increase the yield rate of pressure sensors and enhance their market competitiveness. The specific experimental research content is as follows:
3.1 Preparation of Experimental Parts
Prepare 120 components for the pressure sensor test piece (sintered seat, weld ring, diaphragm). The sintered seat is made of 4J29, the weld ring is made of 4J29 and 316L, and the diaphragm is made of 316L.
3.2 Welding using argon arc welding process
Using 4J29 and 316L welding ring materials, welding experiments were conducted using the maximum and minimum current specified in the process specifications. Ten pressure sensors were welded for each parameter variable, for a total of 40 pressure sensors.
3.3 Welding using laser welding technology
Using 4J29 and 316L welding ring materials, welding was performed at experimental voltages of 7, 6, 5, and 4V respectively, with 10 welding rings for each parameter variable, for a total of 80 pressure sensors.
4. Experimental Results
After the pressure sensor welding is completed, the weld appearance of the experimental piece is first visually inspected to observe the impact of different welding processes on the pressure sensor. The severity of oxidation on the experimental piece is used to determine the heat concentration, and the integrity of the weld fusion is assessed when different welding materials are used. Secondly, the experimental piece is cross-sectionally inspected. The size of the heat-affected zone of the sintered seat is visually observed after cross-section to determine whether excessive heat was generated during the diaphragm welding process, thus affecting the pressure sensor's pass rate. The depth of penetration during cross-section is used to determine whether the strength and sealing requirements are met. Specific experimental results are as follows.
4.1 Visual inspection of weld appearance on test specimens
4.1.1 Argon arc welding process is adopted.
The weld surface shows severe oxidation, and there is a significant heat-affected zone around the pressure sensor weld, requiring subsequent grinding and polishing processes. As shown in Figure 1, when the weld ring material is 4J29, the weld surface fusion is good, but a small amount of oxide scale is produced; when the weld ring material is 316L, the weld surface fusion is poor.
4.1.2 Laser welding process is adopted.
As shown in Figure 2, when both the sintering base material and the weld ring material are 4J29, the weld formation is aesthetically pleasing, the fusion degree is good, and the weld exhibits its metallic color. When both the sintering base material and the weld ring material are 4J29 and 316L, the weld is thin and has a rough surface, with poor fusion degree. Experiments under different welding parameters showed that when the welding voltage was 7 V, the weld ring exhibited slight oxidation and a yellowish surface. When the welding voltages were 6, 5, and 4 V, the weld ring surface showed no oxidation and retained its metallic color.
4.2 Sectional Inspection of Test Specimens
4.2.1 Visual inspection of the experimental specimen after sectioning.
As shown in Figure 3, in the experimental specimen using argon arc welding, the thin-walled area of the sintering seat was completely oxidized and turned black after being cut open, indicating a very severe oxidation phenomenon. In the experimental specimen using laser welding, the oxidation of the thin-walled area of the sintering seat was more obvious when the voltage was 7 V; when the voltage was 6 V and 5 V, the oxidation range of the thin-walled area of the sintering seat was significantly reduced, but oxidation still existed; when the voltage was 4 V, the oxidation range of the thin-walled area of the sintering seat only covered a very small area near the membrane.
4.2.2 Inspection of weld penetration after sectioning the test piece
Test specimens with minimal weld appearance and post-section oxidation were selected for comparative penetration depth experiments. Laser welding was employed, with welding voltages of 6, 5, and 4 V used for penetration depth experiments. The sintering base material was 4J29, and the weld ring materials were 4J29 and 316L, respectively, to compare the differences in penetration depth. Figure 4 shows that when both the sintering base and weld ring materials were 4J29, the weld coverage width was larger, and the welding tolerance was higher; conversely, when both materials were 4J29 and 316L, the weld was narrower, and the welding tolerance was lower.
5. Experiment Summary
Based on the above experimental results, laser welding is the preferred welding process for the pressure sensor diaphragm. The preferred materials for the diaphragm welding assembly are sintered base 4J29 and welding ring 4J29. After welding, the weld seam exhibits a metallic appearance, is continuous and smooth, and shows no oxidation on the surface. The welding quality meets standard requirements and requires no secondary processing such as grinding or polishing. The preferred laser welding parameters are a voltage of 5 V, a weld penetration depth of 0.2~0.5 mm, which meets sealing and strength requirements, and a weld width greater than 0.5 mm, indicating high welding tolerance.
6. Conclusion
The market demand for pressure sensors is growing, and their industrial applications are becoming increasingly widespread [8]. This paper studies the optimization and application of diaphragm welding technology, which fully demonstrates the importance of diaphragm welding technology and proves the feasibility and effectiveness of laser welding technology in pressure sensors. Through experimental comparison of pressure sensor welding technology, welding materials and welding parameters, this paper achieves the goal of optimizing diaphragm welding technology, improves the welding quality and welding capability of pressure sensor diaphragms, and increases the pass rate of pressure sensors, thereby meeting higher user requirements and helping to improve the market competitiveness of pressure sensors.
