During the riveting process of round head rivets, ensuring tight contact between the rivet head and the workpiece surface is a key requirement for enhancing joint strength and sealing. Achieving this goal requires comprehensive measures across multiple aspects, including process control, mold matching, material coordination, and standardized operating procedures. The essence of riveting is the plastic deformation of the round head rivet rod through external force, forming a full rivet head that fills the workpiece pores. Improper control of any of these steps can easily lead to gaps or localized stress concentrations on the mating surfaces, compromising joint reliability.
Control of the riveting equipment's pressure and stroke are primary influencing factors. Insufficient pressure prevents the round head rivet rod from fully deforming and filling the workpiece hole, resulting in microscopic gaps between the rivet head and the workpiece surface, reducing sealing. Excessive pressure can cause excessive deformation of the rivet head and even crack the workpiece surface, damaging the joint structure. In practice, the equipment pressure should be adjusted based on the round head rivet material (such as aluminum, steel, and copper) and the workpiece characteristics. For example, aluminum alloy rivets, due to their greater plasticity, can require lower pressure to avoid excessive deformation, while steel rivets require higher pressure to ensure sufficient deformation. At the same time, stroke control must precisely match the rivet length to the overall workpiece thickness to avoid incomplete rivet head formation due to a too-short stroke, or excessive protrusion of the rivet head due to a too-long stroke, which would affect the fit.
Mold design directly impacts the molding quality of round-head rivets. The cavity dimensions of the rivet head mold must be highly consistent with the designed rivet head shape. Excessive deviation will result in an incomplete rivet head contour and a poor fit to the workpiece surface. The mold material should be a high-hardness, wear-resistant alloy steel to prevent dimensional changes caused by cavity wear over time, which would affect the rivet head's molding accuracy. Furthermore, the mold surface must be smooth to prevent scratches on the rivet head or workpiece caused by rough surfaces, which could create microscopic leak channels. For irregularly shaped workpieces (such as curved or inclined surfaces), specialized molds are required to ensure a perfect fit between the rivet head and the workpiece surface, avoiding partial overhang due to angular deviations.
Material compatibility is a key factor influencing the fit. A significant difference in the thermal expansion coefficient between round-head rivets and the workpiece material can cause gaps during temperature fluctuations. For example, when using steel rivets on aluminum alloy workpieces, a high-temperature-resistant sealant must be applied to compensate for thermal deformation. Material hardness differences are also important to consider. If the rivet hardness is significantly higher than the workpiece, the workpiece surface may be damaged during riveting; conversely, insufficient rivet deformation may result in a poor fit. In practice, rivet hardness is typically slightly lower than the workpiece to ensure the rivet shank can fully deform and fill the hole during riveting, while also avoiding damage to the workpiece.
The accuracy of workpiece hole machining directly impacts the quality of the fit. An overly large hole diameter will result in a large gap between the rivet shank and the hole wall, preventing adequate material filling during riveting, resulting in voids. An undersized hole diameter may prevent the rivet shank from being inserted or cause cracking in the workpiece during riveting. Therefore, strict dimensional accuracy must be maintained during workpiece hole machining to ensure that the hole diameter matches the rivet shank diameter. The hole wall must be smooth to avoid surface irregularities that could cause local gaps in the rivet head after forming. In addition, hole edges must be deburred and chamfered to prevent burrs from embedding in the rivet head during riveting, potentially compromising sealing.
Operational standards are the last line of defense for ensuring a good fit. Before riveting, clean the workpiece surface and rivet to remove impurities such as oil, oxide layers, and other impurities to prevent impurities from embedding and causing poor sealing at the mating surfaces. During riveting, the rivet and workpiece hole axes must be aligned. Excessive deviation can cause the rivet head to deflect, resulting in only partial contact with the workpiece surface. For multi-rivet joints, rivets should be placed sequentially in diagonal order to avoid localized stress concentration that can cause workpiece deformation and compromise the fit of subsequent rivets.
Quality inspection should combine visual inspection with functional verification. Visual inspection can identify obvious poor fit, such as visible gaps between the rivet head and the workpiece surface or rivet head deflection. Functional verification uses simulations of actual use scenarios to check for leaks or looseness at the joint. Destructive testing should also be performed on critical joints to verify riveting strength and ensure the fit meets design requirements. Through strict control of the above links, the round head rivets can be effectively and tightly fitted to the workpiece surface, thus improving connection reliability.
