What is the processing technology of stamping terminal products?

The stamping process of terminal products is a precise, continuous and automatic production process. The core is to punch, bend, form and rivet metal coils (such as copper, brass and phosphor copper) through dies to make terminal parts (such as wiring terminals, automobile terminals and connector terminals) with conductive and connecting functions. The following are the detailed processing flow and technical points:

First, the preparatory stage

1. Selection and pretreatment of raw materials

(1) Material selection

Terminal products require high conductivity, elasticity and corrosion resistance, and commonly used materials are:

Brass (H62/H65): cost-effective, suitable for ordinary terminals;

Phosphor copper (C5191/C5210): Good elasticity and fatigue resistance, suitable for terminals that need to be plugged and unplugged repeatedly (such as automobile connectors);

Red copper (T2): the best conductivity, suitable for high current terminals;

Stainless steel: strong corrosion resistance, suitable for outdoor or harsh environment terminals.

(2) material pretreatment

Coil leveling: the purchased coiled metal strip (usually 0.1~1.5mm in thickness) is leveled by kaiping machine to ensure flatness ≤ 0.05 mm/m;

Surface cleaning: remove the oil stain and oxide layer on the surface of the material (ultrasonic cleaning or pickling passivation can be used) to avoid the oil stain from affecting the life of the mold and the surface quality of the product;

Coating protection: high-precision terminals need to be coated with PE protective film on the surface of the material to prevent scratching the surface during stamping.

2. Mold design and manufacturing

Terminal stamping dies are mostly continuous dies (progressive dies), which can complete multiple processes on one set of dies, and are the core of terminal mass production.

(1) Mold structure design

Process decomposition: according to the shape of the terminal, it is divided into feeding → blanking (trimming/blanking) → bending → forming → riveting → cutting and other processes, which are arranged at different stations of the die;

Example: The process flow of plug-in terminal: feeding the coil → punching the locating hole → cutting the shape → pre-bending → final bending → riveting the crimping lug → cutting off the finished product.

Key component design:

Punch/die: hard alloy (such as YG15) or high speed steel (SKH-51) is selected, the heat treatment hardness is HRC58~62, and the edge roughness Ra is ≤ 0.4μ m;

Discharging plate/pressing plate: wear-resistant materials are used to ensure smooth discharging and prevent product deformation;

Guide parts: use ball guide post guide sleeve to ensure that the mold coaxiality is ≤ 0.005 mm.

(2) Die test and debugging

The material for die test shall be coiled material consistent with mass production, and the feeding accuracy shall be adjusted (step error ≤ 0.01 mm);

Check the size of the first piece (such as terminal pin spacing and bending angle) to ensure that it meets the requirements of the drawings. If it is unqualified, it can be corrected by grinding the punch or adjusting the discharging force.

Second, the core stamping stage

Terminal stamping takes high-speed precision punching machine as the core equipment and cooperates with automatic feeding system to realize continuous automatic production. The typical process is as follows:

automatic feed

The coil is sent to the mold through servo feeder, and the feeding step is determined by the terminal expansion size, and the repeated positioning accuracy is ≤ 0.005 mm;

The locating pin on the mold is inserted into the locating hole of the coil, which further ensures the accuracy of each feeding and prevents the product from being scrapped due to deviation.

Multi-station continuous stamping coil passes through each station of the die in turn to complete a series of processing:

Blanking process: the excess waste of the terminal is cut off to form the outline, and the blanking gap (8%~12% of the material thickness) needs to be controlled. If the gap is too small, the die will be stuck, and if it is too large, the product burr will exceed the standard (the height of the terminal burr should be ≤ 0.03 mm);

Bending process: the material is plastically deformed in the female die by pressing down the male die to form the required angle (such as 90 bending angle), and the bending rebound should be controlled (usually 0.5 ~ 3 rebound compensation is reserved);

Forming process: for terminals with complex structures (such as terminals with inverted buttons and convex hulls), stretching, flanging and other processes should be adopted to ensure uniform material flow and avoid wrinkling or cracking;

Riveting process: if the terminal needs to integrate the wire pressing cylinder and positioning column, rivet different parts by riveting die to ensure riveting strength (drawing force ≥ 50n);

Cutting process: cut and separate the finished terminal from the coil, and the cutting surface should be smooth and burr-free.

waste treatment

The waste generated by blanking passes through the waste discharge channel of the die and is collected by the conveyor belt or directly falls into the waste box;

The carrier of the continuous die (the material belt connecting the terminal) needs to be cut off and recycled synchronously to avoid winding the die.

Third, the post-processing and detection stage

1. Post-treatment process

(1) deburring

Precision terminals need to be deburred by roller grinding (adding grinding stone and grinding liquid) or electrochemical deburring, so as to remove tiny burrs generated by stamping and ensure smooth plugging and unplugging;

Some terminals need to be chamfered to prevent sharp edges from scratching wires or connectors.

(2) Surface treatment

According to the usage scene of the terminal, carry out targeted surface treatment to improve the conductivity and corrosion resistance;

Electroplating: the most common processes, such as tin plating (anti-oxidation), gold plating (high conductivity, wear resistance) and nickel plating (anti-rust), need to control the thickness of the coating at 3 ~ 10μ m;

Passivation: stainless steel terminals can be passivated to form a protective film to improve corrosion resistance;

Cleaning and drying: after surface treatment, it needs to be cleaned with pure water to remove the residual electroplating solution, and then dried in a drying furnace (temperature 80~120℃).

2. Quality inspection

Terminal products require extremely high precision, and the detection needs to cover all dimensions of size, performance and appearance:

(1) Size detection

Routine inspection: use caliper, micrometer and angle ruler to inspect key dimensions such as pin spacing, bending angle and thickness;

Precision detection: complex dimensions (such as convex hull height and hole position) are detected by two-dimensional image measuring instrument and coordinate measuring machine, and the accuracy can reach 0.001 mm.

(2) Performance testing

Plugging force test: the plugging force between terminals and wires shall be tested by a plugging force tester, which shall conform to industry standards (for example, the plugging force is 10 ~ 50N);

Pull-out force test: test the connection strength between the terminal and the wire. If the pull-out force is not up to standard, the terminal will fall off;

Conductivity test: Use a micro-resistance tester to test the contact resistance of the terminal, which usually requires ≤ 5mω.

(3) Appearance inspection

Visually or through CCD visual inspection equipment, check whether there are any defects such as scratches, deformation and coating shedding on the surface of the product, and automatically reject the unqualified products.

Fourth, packaging and storage

Packaging of finished products: use braided tape packaging (automatic patch terminal) or blister box packaging (manual assembly terminal) to prevent the terminal from being deformed and scratched during transportation;

Storage requirements: Store in a dry warehouse at constant temperature (20 5℃) to avoid oxidation of the coating. The shelf life is usually 6~12 months.

V. Key process control points

Die accuracy: the error of the station spacing of the continuous die is ≤0.005mm, and the cutting edge wear exceeds 0.01mm, so it needs to be repaired in time;

Punch parameters: the speed of the punch needs to match the die and material (usually 100~500 times/minute), too fast speed will easily lead to die wear and product deformation;

Material thickness tolerance: the thickness tolerance of raw materials should be ≤±0.005mm, otherwise the stamping accuracy and product consistency will be affected;

Surface treatment quality: the electroplated layer should be uniform, without missing plating and peeling, and the salt spray test should be 48~72 hours without corrosion.