# Detailed explanation of the connector terminal stamping process: quality control points for the entire process of materials, molds, and electroplating
Terminals are the core functional components of connectors and play a key role in electrical conduction and mechanical connections. The quality of the terminals directly determines the contact reliability, current carrying capacity and service life of the connector. The manufacture of terminals mainly relies on precision stamping processes. From raw materials to finished terminals, precision machining and strict quality control in multiple processes are required. This article will deeply analyze the stamping manufacturing process of connector terminals and its quality control points from the perspective of material selection, mold design, stamping process, electroplating processing and other aspects of the whole process.
# # First, the terminal material: the basis and source of performance
The choice of terminal material is the first step in terminal manufacturing and the basis for determining terminal performance. Different application scenarios have different performance requirements for terminal materials, including electrical conductivity, elasticity, strength, corrosion resistance, heat resistance, solderability, etc.
# # # Common terminal materials and their characteristics
* * Brass * *: Copper-zinc alloy, one of the most commonly used terminal materials. Brass has good electrical conductivity and processability at a relatively low cost. However, its elasticity is general, its stress relaxation resistance is poor, and it is not suitable for contact shrapnel with high elasticity requirements. Brass terminals are often used for pins, pins, and other structural parts that do not require high elasticity, or contact parts for cost-sensitive products. Common grades are C2680 (brass 65), C2600 (brass 70), etc.
* * Phosphor Bronze * *: Copper-tin alloy with a small amount of phosphorus added to improve performance. Phosphor bronze has better elasticity and strength than brass, good fatigue resistance and good electrical conductivity, and is the mainstream material for terminal contacts. Widely used in elastic contacts such as springs and sockets of various connectors. Common grades are C5191, C5210, etc. The higher the tin content, the better the strength and elasticity, but the conductivity decreases slightly.
* * Beryllium Copper * *: Copper-beryllium alloy, one of the best performing elastic copper alloys. Beryllium copper has extremely high strength, elasticity and fatigue resistance, while maintaining good electrical conductivity and corrosion resistance. After aging heat treatment, its elasticity and strength can reach a very high level. Beryllium copper is mainly used for connectors with high reliability requirements, such as automotive connectors, military connectors, high-speed connectors, etc. However, beryllium copper is expensive, and beryllium elements are toxic and require special protection during processing. Common grades are C17200, C17410, etc.
* * Titanium Copper * *: Copper-titanium alloy is a high-performance elastic copper alloy. The elasticity and stress relaxation performance of titanium copper are close to that of beryllium copper, and it does not contain beryllium elements, making it more environmentally friendly and safe. The elastic retention capacity of titanium copper is superior to that of phosphor bronze at high temperatures. In recent years, with the increasing demand for beryllium copper substitution, titanium copper has become more and more widely used. Common grades are C1990, C1995, etc.
* * Nickel silver/copper nickel zinc alloy * *: has good corrosion resistance and elasticity, silvery appearance, in some cases can save the surface nickel plating process. However, the conductivity is relatively poor, mainly for specific application scenarios.
# # # Material Selection Considerations
The following factors need to be considered when selecting a model:
1. * * Conductivity * *: Materials with high conductivity are preferred for applications with high current-carrying requirements.
2. * * Elasticity and stress relaxation * *: For elastic parts that need to maintain contact with positive pressure for a long time, materials with good elasticity and stress relaxation resistance should be selected, such as beryllium copper, titanium copper or high tin phosphor bronze.
3. * * Operating temperature * *: The elasticity of the material will decay under high temperature environment, so it is necessary to choose an alloy with good high temperature performance.
4. * * Corrosion resistance * *: It is necessary to choose a material with good corrosion resistance under corrosive environment, or with an appropriate surface coating.
5. * * Cost * *: Under the premise of meeting performance requirements, lower-cost materials are preferred.
6. * * Processing performance * *: The stamping and electroplating properties of different materials are different and need to be matched with the manufacturing process.
# # II. Stamping die: Process core of precision terminals
Terminal stamping is the process of machining a metal strip into terminals of a specific shape by a die. The design and manufacturing level of the mold directly determines the accuracy, quality and production efficiency of the terminals. The dimensional accuracy of precision connector terminals is usually required to be ± 0.01 mm or more, and the requirements for molds are extremely stringent.
# # # Continuous die and stamping process
Almost all connector terminals are produced by continuous die (progressive die). The continuous die sequentially arranges a plurality of stamping processes in a pair of dies. The metal strip is fed from one end, and after gradual processing at each station, the finished product terminal is finally obtained at the discharging end. This production method is efficient, consistent and suitable for mass production.
A typical terminal stamping continuous die consists of the following main processes:
* * 1. Punching/punching * *: Punching process positioning holes and preliminary contours on the strip. The positioning hole is the benchmark for the precise positioning of the subsequent stations, and its accuracy directly affects the dimensional accuracy of the entire terminal.
* * 2. Outline punching * *: Gradually punch out the outline of the terminal, including the terminal head, tail, spring arm and other structures. Complex terminal shapes often require multi-step punching to avoid deformation or excessive burrs caused by a single punch.
* * 3. Bending forming * *: Bending the blank after punching into the desired three-dimensional shape, such as elastic arm bending, pin bending, etc. Bending is one of the most critical processes in terminal stamping, and the control of bending angle and springback directly affects the assembly and use performance of terminals.
* * 4. Shaping * *: Finish the bent terminals, correct the springback, and ensure that the dimensional accuracy meets the requirements.
* * 5. Cutting/blanking * *: Separate the molded terminals from the belt. Some terminals remain on the belt (connecting terminals) for subsequent plating and assembly; others fall directly into a single terminal.
# # # Key Control Points for Mold Design and Manufacturing
* * 1. Punch clearance * *: The clearance between the male and female dies is one of the most important parameters of the punching process. If the gap is too small, the burr will increase and the mold will wear faster; if the gap is too large, the section quality will be poor and the collapse angle will be large. The blanking clearance of precision terminals is usually controlled between 3% and 8% of the material thickness, and the specific value is determined according to the material and thickness.
* * 2. Positioning accuracy * *: The step accuracy and positioning accuracy of the continuous die directly affect the size consistency of the terminals. Commonly used positioning methods include guide pin positioning, guide plate positioning, etc. The precision mold adopts high-precision guide pin, and the positioning accuracy can reach ± 0.005mm.
* * 3. Bending springback control * *: Elastic springback occurs after the metal material is bent, resulting in a deviation of the bending angle and size from the design value. When designing the mold, it is necessary to consider the springback amount in advance, and compensate for the springback by bending and shaping. The springback characteristics of different materials are different, and the specific compensation needs to be determined through experiments and simulations.
* * 4. Die materials and heat treatment * *: The working parts of precision stamping die are usually made of high-performance materials such as high-speed steel, powder metallurgy steel or cemented carbide, and undergo strict heat treatment to ensure the hardness, wear resistance and service life of the die. Mold life is an important factor affecting the production cost of terminals.
* * 5. Guide accuracy * *: The continuous mold usually adopts a high-precision guide mechanism such as a ball guide column guide sleeve to ensure the mating accuracy of the upper and lower molds. The guiding accuracy directly affects the uniformity of the blanking gap and the dimensional accuracy of the terminals.
# # III. Stamping process: Process control determines product quality
With good materials and good molds, precision stamping process control is also required to produce high-quality terminals. Process parameter control and quality monitoring in the stamping process are key links to ensure product quality.
# # # Selection of stamping equipment
Precision terminal stamping requires the use of a high-precision punching machine. There are two common types of high-speed precision punching machines and servo punching machines:
* * High-speed precision punching machine * *: high number of trips (up to hundreds or even thousands per minute), good rigidity, stable accuracy, suitable for the production of large quantities of standardized products.
* * Servo punching machine * *: driven by a servo motor, the motion curve of the slider can be precisely controlled, the stamping speed and stroke are adjustable, suitable for stamping of complex shapes and difficult to form materials. Although the speed is not as fast as the high-speed punch, the molding quality is better and the process is more adaptable.
The accuracy of the punching machine mainly includes: parallelism, perpendicularity, total clearance, lower dead center repeatability, etc. Precision terminal hedge machine under dead center repeat accuracy requirements are usually within ± 0.005mm.
# # # Control of key process parameters
* * Feeding accuracy * *: The accuracy of the feeding step directly affects the positioning accuracy of the continuous mold. Precision stamping usually uses roll feeders or clamp feeders with feeding accuracy up to ± 0.01 mm. The tension control of the belt is also important, and tension fluctuations can affect the feeding accuracy.
* * Stamping speed * *: Different materials and processes have different optimal stamping speeds. Too fast may cause the material to fracture before it can deform, or the mold will heat up; too slow may lead to low production efficiency. It is necessary to select the appropriate stamping speed according to the characteristics of the product and the characteristics of the material.
* * Material status * *: Before stamping, it is necessary to check whether the thickness tolerance, hardness, surface quality, etc. of the raw material meets the requirements. The hardness uniformity and directionality of the material have an important impact on the stamping quality.
* * Lubrication * *: Suitable stamping lubricants can reduce friction, reduce mold wear, improve stamping section quality and bending formability. However, the type and amount of lubricating oil need to be controlled, and excessive oil pollution will affect the quality of subsequent plating.
# # # Process Quality Monitoring
Continuous quality monitoring is required during stamping production to ensure stable product quality:
* * 1. First-piece inspection * *: After each startup, mold change, and machine adjustment, the first-piece inspection is required to comprehensively inspect the dimensions and appearance of the terminals, and mass production can only be carried out after confirmation.
* * 2. Process sampling inspection * *: During the production process, key dimensions are sampled according to a certain frequency to detect process drift in a timely manner. Precision stamping usually adopts SPC (statistical process control) method for quality control.
* * 3. Online monitoring * *: The high-end stamping production line is equipped with an online visual inspection system, which can detect the appearance defects and dimensional deviations of the terminals in real time and find that the non-conforming products are automatically eliminated. This is especially important for high-speed, high-volume production.
* * 4. Burr control * *: Burr punching is one of the most common quality issues in terminals. Too large burrs may cause short circuits, poor plastic shell filling and other problems. It is necessary to regularly check the height of the burr, and repair the mold in time when it is out of error.
# # IV. Electroplating process: final guarantee of surface performance
Stamped terminals also need to be surface plated to improve conductivity, corrosion resistance, solderability and wear resistance. Electroplating is an indispensable part of the terminal manufacturing process.
# # # Common Plating Types and Characteristics
* * Tin Plating * *: The most commonly used coating with low cost, good solderability, and certain corrosion resistance. Widely used in general industrial connectors and consumer electronics connectors. However, the tin plating layer is soft, the wear resistance is poor, and the plugging life is limited; it is easy to oxidize and discolor under long-term storage or high temperature, and the contact resistance is increased.
* * Gold Plating * *: Gold plating has excellent conductivity, corrosion resistance and chemical stability, with low and stable contact resistance. It is the preferred coating for high-reliability connectors and is widely used in automotive, communications, military and other fields. But gold is expensive and plating is expensive. In practical applications, the process of “nickel plating bottoming + local gold plating” is often used to plate a thin layer of gold in the contact area, and tin plating or maintaining a nickel base in other areas to reduce costs while ensuring performance.
* * Nickel Plating * *: Often used as a priming coating, it improves the corrosion resistance and surface hardness of the substrate, providing a good substrate for subsequent plating. Pure nickel plating has poor weldability and contact properties and is generally not used as a final contact coating.
* * Silver Plating * *: Silver is the most conductive metal with excellent conductivity and is often used for high current and high frequency connectors. However, silver is easily oxidized and vulcanized, and the contact resistance is unstable, so it needs to be used with protective measures.
# # # Electroplating process quality control points
* * 1. Coating thickness * *: The coating thickness is the most basic quality index for electroplating. Insufficient thickness will lead to poor protective performance and poor contact; excessive thickness will increase costs and may also lead to out-of-dimension. Different applications have different requirements for the thickness of the coating. Generally, industrial tin plating is 3 ~ 5μm, and the gold plating contact area is usually 0.1~0.8μm.
* * 2. Coating adhesion * *: There must be a good adhesion between the coating and the substrate, otherwise the coating may fall off and blister during use. The bonding force is usually tested by tests such as bending, thermal shock, etc.
* * 3. Uniformity of the coating * *: The thickness distribution of the coating should be uniform to avoid local over-thinning or over-thickness. The hanger design, current distribution, additives, etc. of the electroplating process will affect the uniformity of the coating.
* * 4. Weldability * *: For terminals that need to be welded, the weldability of the coating is a key indicator. Solderability is generally assessed by wetting equilibrium or tin-impregnation tests.
* * 5. Porosity * *: The porosity of the coating directly affects the corrosion resistance. Excessive porosity can lead to substrate corrosion and reduce product life.
* * 6. Local plating control * *: Many connector terminals use a local plating process, gold plating only in the contact area and tin plating in other areas. Position accuracy and boundary clarity of local plating are important quality control points.
# # V. Whole Process Quality Assurance System
The production of high-quality terminals is inseparable from a sound quality assurance system:
* * Incoming Inspection (IQC) * *: Strict incoming inspection of raw materials (copper strips, electroplating chemicals, etc.) to ensure that the quality of raw materials meets the requirements.
* * Process inspection (IPQC) * *: Patrol inspection and sampling inspection during stamping and plating production to detect and correct process deviations in a timely manner.
* * Finished product inspection (FQC/OQC) * *: Comprehensive quality inspection before the finished product leaves the factory, including dimensions such as size, appearance, electrical properties, mechanical properties, etc.
* * Reliability verification * *: Regularly conduct product reliability tests, such as salt spray test, plugging life test, temperature rise test, contact resistance test, etc., to ensure long-term reliability of the product.
Conclusion
The manufacture of connector terminals is a systems project, from material selection to mold design, from stamping process to plating treatment, every step is vital. The material is the basis of performance, the mold is the core of the process, the stamping process control determines the dimensional accuracy and consistency, and the electroplating determines the surface performance and long-term reliability. Only when the whole process is strictly controlled can high quality and high reliability connector terminals be produced.
Ruixin Shengye has established a complete terminal stamping and electroplating quality control system, from raw materials to finished product layers to ensure that each terminal meets high quality standards. For more information on the terminal manufacturing process and connector products, please refer to the Rui Xin Sheng Ye product line, which provides customers with reliable connection solutions with precision manufacturing and strict quality control.
