Introduction
Low-voltage contact riveting assemblies are key parts in electrical appliances. They are usually suitable for small and medium current application conditions and play a vital role in the performance of electrical appliances. For a long time, both electrical appliance manufacturers and contact material manufacturers have paid great attention to the quality of contact assemblies. The main indicators for measuring the quality of contact assemblies include dimensional tolerance, riveting strength, surface quality, etc. Among them, surface quality includes surface morphology characteristics and control of surface impurities in addition to conventional appearance quality, because this directly affects the contact resistance of electrical appliances, and thus affects the service life of electrical appliances.
The shape of the contact bridge of the contact riveted assembly is often relatively complex. The contact bridge of the In-die Riveting Silver Contacts is thin and small, and is prone to deformation. In the past, due to the limitations of mold technology and the level of corresponding automation equipment, the manufacturing of riveted assemblies was usually mainly manual production. After the contact bridge and contact (rivet) were processed separately, they were manually riveted on a small press. In order to avoid the influence of subsequent processing on the shape of the product or the introduction of other substances to affect the surface quality of the product, the manual riveting process is usually strictly controlled to avoid the introduction of other substances, so that the surface of the product is kept clean, thereby avoiding the introduction of the cleaning process, that is, the product after manual riveting usually becomes a finished product directly and is installed in the electrical appliance for use. The surface quality of the rivet is mainly controlled by the rivet cleaning process and the cleanliness of the riveting process. In fact, during the riveting process, the mold will cause inevitable processing marks on the rivet surface, which will change the original surface quality of the rivet; and it is impossible to achieve very good cleaning control during the riveting process, so the stability of the contact assembly quality is not good.
With the development of automation technology, mold technology, and the increase in the labor cost of manual riveting, various companies have gradually developed in-mold riveting and turntable automatic riveting technology, especially the application of in-mold riveting technology, which has greatly reduced production costs and improved production efficiency. But at the same time, it also poses a challenge to the cleaning process. How to improve the surface quality of In-die Riveting Electrical Silver Contacts by cleaning while ensuring that the riveted components are not deformed is an inevitable demand for the development of industry technology.
The traditional cleaning process mainly adopts the rolling method for bright cleaning, and the equipment used is usually an inclined rolling machine or a centrifugal grinder. During cleaning, the product is placed in a rolling barrel, an appropriate amount of abrasive is added, and a specially configured brightener is added to perform mechanical polishing on the product. Due to the development of in-mold riveting technology, the degreasing and cleaning steps of riveted components have been introduced into the manufacturing process. Degreasing and cleaning are combined with brightening treatment to solve the surface quality problem of riveted components after riveting. This study uses different cleaning processes to clean riveted components, and combines the use of different degreasing agents to clean riveted components. The effects of each process on the surface morphology of the product and the distribution of surface impurity elements are analyzed, providing a reference for finding a cleaning process solution suitable for riveted components.
1 Research plan
The In-Die Riveting with Silver Plating for Switch Part selected for the study has a widely used AgNi(10)/Cu rivet. After riveting, the contact surface is processed into a serrated shape (as shown in Figure 1), and the contact bridge material is copper-plated steel.
Table 1 shows the comparison schemes selected for the study. The cleaning process used for the AgNi(10)/Cu rivets is a conventional cleaning process, that is, the rivets are degreased and then mechanically polished. In order to study the quality of the riveted components after cleaning, the effects of different degreasing cleaning agents on the surface quality and the effects of the cleaning process combining degreasing cleaning and polishing on the surface quality of the riveted components were compared.
Optical microscope and scanning electron microscope (SED, BED) were used to compare the contact surface morphology after cleaning by different processes; X-ray fluorescence analyzer and energy spectrum analyzer were used to analyze the contact surface elements.
2 Research results and analysis
2.1 Effect of cleaning process on surface morphology
Figure 2 shows the surface morphology of the original rivet observed by different methods, and Figures 3 to 6 show the surface morphology after cleaning by different processes. The original surface morphology of the rivet (Figure 2) and the surface morphology of the assembly after polishing (Figure 4, Figure 6) both show that after polishing, obvious polishing marks will be left on the contact surface, showing a relatively rough surface morphology; the contact surface of the unpolished Contact Terminals with Silver Electroplating is relatively smooth.
The morphology of the contact surface directly affects the contact resistance in electrical appliances. The contact resistance of the contact is a basic and important technical parameter for measuring the performance of electrical contacts and directly affects the reliability of the electrical contact system. A large contact resistance will generate more heat during electrical contact, resulting in higher temperature rise and greater power consumption, which may cause early welding or bonding, and in severe cases will lead to electrical contact failure. There are many factors that affect the contact resistance of electrical contacts. In addition to contact pressure, contact form, and the resistance, shape, and hardness of the contact itself, there are also surface roughness, surface foreign matter, and surface film of the contact . The products selected for the study have a serrated surface, the main purpose of which is to improve the contact reliability of the contact and reduce the contact resistance. After polishing, the surface roughness increases, which is bound to affect the electrical contact reliability of the appliance.
2.2 Effect of cleaning process on surface impurities
Table 2 shows the results of X-ray fluorescence detection of the contact surface. As shown in Table 2, the impurity elements on the contact surface are mainly Cu and Fe, and the Cu and Fe contents of the polished components are significantly higher than those of the unpolished components. This is because during polishing, the grinding effect on the product surface causes part of the material on the product surface to fall off and form debris. During the collision between the abrasive and the product, some debris is pressed into the contact surface again. Some debris cannot be completely washed away during flushing, and thus adheres to the contact surface again.
Table 3 shows the results of the energy spectrum detection and analysis of the contact surface. The data shows that Cu is still the main impurity element on the contact surface. Affected by the characteristics of energy spectrum detection, the surface C and O content is relatively high. Comparing the two processes of organic solvent cleaning, namely samples No. 2 and No. 3, their surface element composition is similar to that of the original rivets, and the impurity element content is lower than that of samples No. 4 and No. 5 cleaned with aqueous solvents; however, the C and O element content increases on the surface of the product after polishing, which is mainly due to the introduction of new organic substances during the polishing process, which increases the probability of C and O elements adhering to the surface.
The results of the two processes (No. 4 and No. 5) of aqueous solvent cleaning show that the distribution of elements on the contact surface is more complex, especially in the element composition of the unpolished surface, the C content is significantly higher. On the one hand, it shows that the residual C element is relatively high after the aqueous solvent is degreased, and on the other hand, it also shows that the degreasing effect of the aqueous solvent is not as good as that of the organic solvent. In the surface element composition after aqueous solvent cleaning and polishing, although the C content is reduced, the copper content is significantly increased, which shows that its comprehensive cleaning effect is not ideal.
Some studies have shown that foreign matter on the surface of the electrical contact is extremely harmful to the electrical contact element. In the case of light, the contact resistance increases, and in the case of severe contact failure. In the process of evaluating the performance of the electrical contact, the electrical contact often causes the contact resistance to be too large and the temperature to rise due to foreign matter on the surface, and some even cause the electrical contact to fail early. Copper chips are the main foreign matter on the contact surface. Under the action of the arc, they are oxidized to form copper oxide or cuprous oxide, or copper oxide and copper salt at the appropriate time, which will lead to an increase in contact resistance and affect the contact reliability of the electrical appliance. It can be seen that under the premise of ensuring the cleaning quality of In-Die Riveting with Pure Silver Plate, the polishing process should be avoided in the cleaning process.
3 Conclusions
(1) The polishing process will lead to the deterioration of the surface roughness of the contact of the riveted components produced by in-mold riveting, which may have an adverse effect on the contact resistance;
(2) After cleaning with organic solvents, the content of impurity elements on the surface of the product is lower than that after cleaning with aqueous solvents, which is more conducive to improving the contact reliability of the riveted components;
(3) The impurity elements on the surface of In-Die Staking with Pure Silver Plate for Switch are mainly copper. The presence of copper will lead to reduced contact reliability. Therefore, in the cleaning process of riveted components, the polishing process should be avoided while ensuring the cleaning quality of riveted components;
(4) In this study, the surface of the riveted components cleaned and dried with organic solvents is relatively smooth and the content of impurity elements on the surface is lower. Therefore, the organic solvent cleaning and drying process is more suitable for the treatment of riveted components.
Our Products
This In-die Riveting Silver Contact is made of high-quality pure silver and is carefully crafted through advanced in-mold riveting technology. The pure silver material ensures excellent conductivity and can achieve efficient and stable signal transmission, and can perform excellent performance in both complex electronic devices and high-performance systems. At the same time, the in-mold riveting process gives the product strong mechanical strength, which can withstand various mechanical stresses and vibrations and can operate stably in harsh environments. It also has good flexibility and is easy to integrate into different designs and applications. In addition, the product has excellent durability, corrosion resistance, wear resistance, and a long service life.
