A large number of products are made of austenitic stainless steel, especially for the highly competitive industrial market such as beverage machinery, meat, filling machines, pumps, valves, impellers, storage tank equipment gas, tube and plate heat exchangers, medical implants, in particular, this research focuses on kitchen equipment, tableware, and utensils used in the food industry, etc. Therefore, the manufacturers of the above-mentioned products must find ways to respond to consumers in order to cope with the competition. First of all, when using the material for its manufacture, it must have good resistance to corrosion and heat resistance, in particular, the plate assembly of the product structure must be solid and durable. Furthermore, fixing product components by welding shall make such welds strong, resistant to external forces, prevent internal corrosion within the weld, and absorb shock. Again, competitive products must include affordable features that are convenient to use, provided that a team of manufacturing engineers manufactures them to ensure quality meets the requirements. As for the sheet used as the critical component of the product, the sheet is made of welded 316L stainless steel with good weldability, corrosion resistance, and high strength, which is very important for use in this competitive manufacturing industry.
Strength and durability after welded to various product components made of steel plates, primarily used for kitchen equipment, tableware, and food industry appliances, provided they are very well resistant to corrosion. One of the essential methods is to modify the composition of the steel sheet so that it can be used for the intended purpose or by choosing 316L stainless steel material. Due to the many characteristics of composition modification, in order to obtain what is known as well stainless steel, the proportion of elements must be set accordingly. Usually, it is produced in industrial production by divided into several grades. Therefore, the desired quality must be selected to be suitable for the production of competitive products for the product market. Type 316L stainless steel is, therefore, an appropriate variable for the manufacturing sector of the product that this time needs to be able to withstand corrosion failures and, importantly, to have strengths for long-term use [1–4]. Therefore, the essential microstructures of such materials used in industrial production, which can be considered in detail, are also presented (Fig. 1).
1.1 Determination of suitability for electrical applications on resistance spot-welded joints
Characteristics of bonding several thin sheets together, a suitable method is spot welding to provide electrical resistance at the pressure point of the heated sheet. The pressure between the two electrodes can make the workpiece we want to bond together very well (Fig. 2). Nowadays, workpieces can be welded by manual spot resistance welding machines or by robots for speed. However, productivity requirements must be based on consideration of the material properties for welding and the desired weld point characteristics. Therefore, many variables such as welding current, electrode pressure, and time of welding must be automatically controlled. In addition, the low voltage and high current required must also be considered. The welding system is supplied by a transformer and is powered by hydraulic, mechanical, and pneumatic equipment (Fig. 3) [5–7].
Previous knowledge said that the resistance of the work material to be spot welded, the opposition to the flow of electric current through the material generates a lot of heat for such welding processes. During welding, which consists of relatively high wind by the short current path with a welding time limitation, therefore necessary heat developed is generated. At least three thermal development factors are recent duration, conductor resistance, and amperage. Thus, the heat generated for the spot welding process can be considered to be derived from all three factors, which can be integrated into the Q = I2 Rt formula. Therefore, it can be clarified clearly that Q is the amount of heat generated during welding is measured in J, I is the current flowing through the welding point, this is measured in A (ampere), and R is the resistance of the sheet to be welded measured in Ω (ohm). Finally, t is the duration of the established current, measured in s (second).
In order to determine in part the overall characteristics of a series of resistances, it is important to consider the point welder associated with the secondary circuit first, and then the nature of the sheet to be welded. The nature of the fact that the total resistance of the current path affects the magnitude of those currents on the temperature distribution of the spot welding. It can be considered that those resistances are in series with up to seven, given as R according to the appearance (Fig. 2). However, if considering the value of the overall resistance, it will look like R = R1 + R2 + R3 + R4 + R5 + R6 + R7 = Ri. Based on the overall values of the above resistances, it can also be considered to be divided into two categories, namely the contact side while welding between the sheet and the contact point of the electrode, which means R1 and R5. Another category is the contact side while spot welding according to the sheet material resistance characteristics when considering especially R2, R4, R6, and R7. The physical properties of the sheet to be welded will produce resistance, depending on the material itself, in this research it can be defined as R2 and R4. It also determines the required resistance such as an indication of the physical properties of the electrode, which are defined as R6 and R7. Once the total resistance from the sheet and the electrode is determined, it is indeed a constant to a certain extent, then the variation that has been generated must be considered, that is, the conditional contact resistance of the electrode toes. Part of the consideration is R3, which is the resistivity characteristic required for spot weld formation. However, the welding work that we want must be very good, depending on the welding ability mentioned above. If there is a high, there will be good results. It is important to consider the voltage of the electrode, the surface condition of the base metal, the welding current, and the welding interval established, all of which affect the magnitude of the overall resistance. As mentioned above, this generates heat towards the melting basin of the resistive weld. It is noteworthy that the surface of the base metal is insufficiently heated to sustain the melt which occurs during the passage of current flow. Due to the relevance of the electrodes used in the current flow circuit, the electrode material has a very good thermal conductivity to provide resistance which leads to a large amount of the desired heat, but because the amount of heat is lower than the fact that it must be cooled by water.
If we analyze in detail the resistance welding process to cause high heat at the contact point, it can be seen that the influence caused by the welding pressure from the electrode rod strikes through the contact point of the impending resistance of the sheet at point R1, R3, and R5 (Fig. 2) [8–10]. Therefore, we are considering the contact points of resistance R1 and R5, which will cause heat to the end of melting, and become the sheet's welding point, resulting in the required strength. However, the reality of the high-melting heat we need is not always the case because the contact point of such resistance, which is the part that transmits the contact force from the electrode tip to the sheet to be welded, is cooled by water. In addition, there are also several other thermal degradation problems such as poor thermal conductivity of the electrode material, excessive rust, or the presence of oil stains on the resistance contacts. Such issues can be prevented from occurring, however, there must be an appropriate analysis of the work for each problem to be solved [11].
1.2 Consider the details of welding current interesting
The relationship of the welding current (I) to the heat generation at the resistance welding point is so meaningful that they are consistent when considering the Joule law parameters, Q = I2Rt. Therefore, if analyzing the possibility of the secondary voltage (U) will be I = [U (√ (R2 + ω2 L2))], however, when considering L which represents the value of the total induction (R), that value (Ω) should be the value of the resistance of the real ohm related to the secondary circuit relative to ω, and finally the frequency of the course (1/f).
The nature of the increased resistance along with the constant induction in the secondary voltage leads to a decrease in the welding current. When considering the magnetic material and the lever spacing in the secondary circuit, there is a difference in the magnitude of induction. Finally, the capacity which will affect the integrity of the weld must be obtained from the parameters of the welding current which should be constant, in addition to the continuous induction and resistance. If analyzing the requirements tensile-shear strength of the resistance weld, which must not be reduced, should be considered based on heat energy, and welding current. In particular, void formations cause cracks and molten metal during spurt welding out as a result of excessive welding current [12].