Fastening process between sheet metals
Preface
Sheet metal fastening: seemingly simple, cost and reliability determine the success or failure of a product
In industrial product design, sheet metal structures are ubiquitous, from cabinet shells, car bodies, home appliance shells, to industrial equipment panels, sheet metal is the fundamental component of product rigidity and form.
The fastening method between sheet metal may seem like the most basic detail, but it directly determines the reliability, assembly efficiency, and cost structure of the product.
The choice of fastening method by engineers during the design phase often not only affects the production cost of the product, but also affects subsequent assembly efficiency, maintenance costs, and product lifespan.
If we only rely on experience or follow conventions, and ignore process characteristics and cost analysis, it is easy to encounter problems in mass production or later maintenance.
The process of sheet metal fastening is rich and diverse, each with applicable scenarios, cost characteristics, and reliability indicators.
Reasonable selection can not only reduce manufacturing costs, but also improve product quality and customer satisfaction; Incorrect selection may lead to assembly rework, frequent repairs, and damage to brand reputation.
This article will comprehensively analyze the sheet metal fastening process and its cost logic from five categories: mechanical fastening, riveting, welding, bonding, and inserting.
1. Mechanical fasteners | Screws and buckles: flexible operation, but long-term cost cannot be ignored
1.1 Screw fastening
Screw fastening is the most commonly used mechanical fastening method, suitable for almost all sheet metal products, from cabinet shells, automotive chassis to industrial control equipment. Its advantages lie in flexible installation, disassembly, and no need for special process equipment, making it suitable for small batch production or products that require later disassembly and assembly.
But screw fastening relies on pre tightening force. If the pre tightening force decays under vibration, thermal cycling, or long-term load, it can easily lead to contact loosening, local deformation, and even fatigue cracks. Loose screws are a common root cause of malfunctions in car engine compartments, electrical equipment cabinets, and precision instruments.
Cost analysis: Screw materials have low costs, but manual installation, torque testing, and repair and maintenance costs may be high, especially in large-scale products where long-term maintenance costs may even exceed initial investment.
The buckle fastening relies on the elastic design of sheet metal to achieve quick assembly without tools, suitable for consumer electronics, home appliances, and small industrial equipment. The advantage is fast assembly speed and low manual skill requirements, making it very suitable for assembly line production.
The disadvantage is that long-term reliability relies on elastic material and design, and multiple disassembly and assembly may lead to buckle failure and decreased contact force, especially in vibration or thermal cycling environments.
Cost analysis: The initial unit cost is low and the assembly efficiency is high, but the repair and maintenance costs cannot be ignored, especially in industrial scenarios with long-term service.
1.3. Nut welding and self tapping screws
Nut welding (such as welding nuts or bolts) fixes threaded components to sheet metal through welding, ensuring that the sheet metal is not damaged during disassembly. Self tapping screws directly form threads on sheet metal, which is easy to operate, but has limited applicability to plate thickness.
Cost analysis: The equipment and process debugging costs for welding nuts are relatively high in the early stage, but they can improve long-term reliability; Self tapping screws have a low cost per piece, but they may become loose in long-term vibration environments, increasing the risk of repair.
2. Riveting type | Standardized and efficient, suitable for mass production
Riveting, which fixes two sheet metal parts together through plastic deformation without relying on threads or external components, is a very important type of fastening method in sheet metal assembly. The riveting process can be divided into: pulling riveting, pressing riveting, blind riveting, etc.
2.1. Blind Rivet
Riveting is suitable for single-sided assembly, which means it cannot be operated from the back. Stretch the rivet with a specialized riveting gun to expand the tail and fix the sheet metal.
Cost analysis: The cost of rivets is slightly higher than that of ordinary mechanical rivets, with moderate tool investment. However, in single-sided assembly or high-density assembly, it can significantly reduce labor costs.
2.2 Press fit Rivet
Riveting directly presses the rivet into the reserved hole through the mold, and uses the elastic fit between the rivet and the hole to fix the sheet metal. Suitable for large-scale automated assembly, such as automotive interior panels and electronic chassis.
Cost analysis: The investment in molds and automation equipment is relatively high in the early stage, but the production cost per piece is low, the assembly efficiency is high, and the overall lifecycle cost is lower than that of manual fastening methods.
2.3. Blind rivet nut
Installing blind rivet nuts on sheet metal can provide threaded fixing points on the sheet metal, suitable for small batch production and convenient maintenance needs.
Cost analysis: The cost of nuts is higher than that of ordinary rivets, with moderate tool investment, but it improves the feasibility of disassembly and long-term maintainability.
3. Welding class | High strength, high reliability, high initial cost
Welding fasteners fix sheet metal parts through melting or local plastic deformation between metals, suitable for products that require high strength and long-term reliability.
3.1. Spot Welding
Spot welding is the most common sheet metal welding method, which uses resistance heating to fuse local metal. Widely used in car bodies, home appliance casings, and industrial cabinets.
Cost analysis: Equipment investment is large, process debugging is complex, but single piece cost is low in mass production, and long-term maintenance requirements are small.
3.2. Resistance seam welding
Resistance seam welding is used for continuous welding of seams to ensure structural sealing and mechanical strength. Commonly used in water tanks, household appliance casings, etc.
Cost analysis: The initial equipment investment is higher, and the single piece production cost is slightly higher than spot welding, but it is suitable for scenarios with high sealing and mechanical strength requirements.
3.3. MIG/TIG arc welding
The arc welding method is suitable for medium thick plates or products that require high-strength welds, with high welding quality, but high equipment investment and labor costs.
Cost analysis: Suitable for small batch high-intensity demand, with high production cost per piece, but excellent long-term reliability.
3.4. Ultrasonic welding (mainly used for thin plates)
Ultrasonic welding utilizes high-frequency vibration to achieve local plastic bonding of sheet metal parts, suitable for lightweight metal or plastic composite materials.
Cost analysis: The equipment investment is high, but the welding speed is fast, suitable for automated assembly and high-precision requirements, and has good long-term reliability.
3.5. Laser beam welding
Laser welding is suitable for complex sheet metal structures, with small welds, low heat affected zones, and high welding accuracy. It is commonly used for automotive, precision instruments, and aviation parts.
Cost analysis: The initial equipment investment is huge, but it is suitable for high-value, high reliability products, and long-term use to reduce maintenance risks.
4. Adhesive and Composite Fasteners | Auxiliary and Special Scenarios
Adhesive and composite fasteners are mainly used in scenarios where welding is not possible, vibration reduction is required, or dissimilar materials are connected.
4.1. Structural adhesive
Use structural adhesives such as epoxy resin, acrylic or polyurethane to connect sheet metal to sheet metal or sheet metal to dissimilar materials. Suitable for automotive interiors, electronic chassis, and aerospace composite components.
Cost analysis: The material cost is moderate, and manual operation and curing time increase the initial cost, but reduce welding repair and vibration fatigue problems in the later stage, and the long-term total cost is controllable.
4.2. Crimping/pressing in combination
Tightening is achieved through convex platform, buckle design, and plastic or metal crimping. Suitable for lightweight design and fast assembly scenarios.
Cost analysis: Material and mold costs are low, assembly efficiency is high, but reliability depends on design accuracy and material elasticity, and long-term maintenance needs to be paid attention to.
4.3. Composite process
Multiple process combinations, such as screw+adhesive, riveting+adhesive, welding+anti-corrosion coating, are commonly used in high reliability or special functional requirements scenarios.
Cost analysis: The initial material, process, and design costs are high, but they can significantly improve long-term reliability and protective performance, and reduce maintenance costs.
5. Conclusion | Choosing the Right Tightening Process to Reduce Total Costs and Risks
The selection of sheet metal fastening technology is not only a product assembly issue, but also related to long-term cost, reliability, and customer experience. Mechanical fastening, riveting, welding, and bonding each have their own advantages and limitations: mechanical fastening is flexible and easy to operate, riveting is standardized and efficient, welding reliability is the highest, and bonding is suitable for special or composite scenarios.
From the perspective of engineering practice, selecting the appropriate process requires comprehensive consideration of product batch size, reliability requirements, assembly environment, long-term maintenance, and total cost, rather than just looking at the cost of a single BOM.
High reliability processes with high initial investment can often achieve the minimization of lifecycle costs by reducing repair and maintenance costs and improving product stability.
During the design phase, engineers must comprehensively evaluate the characteristics of various fastening processes, and make scientific decisions based on product application scenarios, material properties, and production capabilities.
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