Stamped terminals and connectors

What a stamped terminal has to do

A terminal does three jobs at once. It grips a conductor, it carries current into a contact interface, and it stays in its housing under vibration. A design that satisfies one of those jobs can still fail the other two, which is why terminal problems so often appear late in a programme.

The stamped route suits terminals because the part is a folded strip. A progressive die cuts the outline, forms the barrel, bends the contact and separates the part in one cycle. The same part machined from solid would need several operations and would still not produce a thin spring contact as cleanly.

The design work is therefore mostly about section, bend and spring. The tool can hold a shape; it cannot add material where the current path is thin, and it cannot rescue a spring that has been over-formed.

The four zones of a stamped terminal

Most stamped terminals share the same anatomy, whether the part is a ring terminal, a receptacle or a header pin. Reading a drawing zone by zone makes the critical calls obvious.

1. 01

   Wire barrel

   The barrel is formed into a U or a closed cylinder and crimped onto the conductor. Its length, inner diameter and wall thickness set the crimp height and the pull strength.

2. 02

   Transition

   The transition carries the current from the crimp to the contact and absorbs the forming strain. A sharp step here becomes a stress riser and a hot spot.

3. 03

   Contact and spring

   The contact area is usually a folded box, a blade or a pair of fingers. The spring rate and the deflection range decide the normal force on the mating part.

4. 04

   Retention

   A locking lance, a shoulder or a clip holds the terminal in the housing. The lance must flex during insertion and then resist pull-out without yielding.

Material and temper: the compromise

Copper carries current well but is soft. Brass is stronger and cheaper but conducts less. Phosphor bronze and beryllium copper give better spring properties at a higher cost. The choice is rarely about conductivity alone, because the contact spring has to hold force for the life of the part.

Temper is as important as alloy. A hard temper raises yield strength and improves retention, but it also reduces elongation, which makes a tight bend more likely to crack. A soft temper forms easily but takes a set under load and loses normal force.

For a contact spring, the design usually wants a temper that keeps stress below roughly half the yield strength at maximum deflection. That is a starting point, not a guarantee, because temperature and stress relaxation move the number. If the terminal runs warm, ask for stress relaxation data at the working temperature rather than room-temperature data alone.

• Pure copper: best conductivity, lowest strength, rarely used for a spring contact.
• Brass: good formability and cost, moderate conductivity, common for general terminals.
• Phosphor bronze: good spring and fatigue, lower conductivity than copper, common for receptacles.
• Beryllium copper: high strength and good conductivity, higher cost, used where force and current both matter.
• Copper nickel silicon: a lead-free alternative with good strength and moderate conductivity.

Plating: what each finish buys

The plating protects the base metal and controls the contact interface. It is not a cosmetic layer. A terminal with the right alloy and the wrong plating will fail either at the crimp, at the contact or in the corrosion test.

Crimp performance starts at the drawing

A crimp is a cold weld. The barrel is compressed until the strands deform against each other and against the barrel wall, and the joint holds by mechanical interference and by clean metal contact. The crimp height, the crimp width and the barrel geometry decide whether that happens.

The drawing should give the wire range, the conductor class, the barrel inner diameter and the crimp height with a tolerance. It should also say whether the terminal is for a stranded or a solid conductor. A barrel designed for a flexible conductor with many fine strands will not crimp correctly onto a coarse stranded cable, even if the nominal area matches.

Insulation support is a separate decision. A terminal with an insulation crimp relieves strain on the conductor and improves vibration resistance, but it adds height and requires the insulation diameter to be controlled. A terminal without it is smaller and cheaper but relies on the housing for strain relief.

Validation is a pull test to a stated force plus a cross-section of the crimp. The cross-section shows strand deformation, voids and barrel cracks, which a pull test alone can miss. For a high-reliability joint, add a resistance measurement across the crimp and a thermal cycle before the final pull test.

Tolerances that matter on a stamped terminal

The overall length is rarely the critical dimension. The calls that decide function are the contact gap, the spring deflection, the barrel inner diameter, the lance height and the position of the contact relative to the locking feature.

A progressive die can hold a tight tolerance on a feature formed in one station. It struggles when a tolerance crosses several bends, because each bend adds springback variation. The drawing should use a datum that reflects how the terminal locates in the housing, and it should avoid stacking tolerances across the contact and the lance.

Springback also changes with material lot and temper. If the contact gap is critical, the drawing should allow a functional gauging check rather than a pure dimensional one. A go and no-go gauge on the contact gap tests the function directly and is faster than a CMM routine on a high-volume part.

• Contact gap and normal force at stated deflection
• Barrel inner diameter and crimp height
• Lance height and insertion force
• Contact position relative to the housing datum
• Plating thickness on the contact and crimp areas
• Burr direction on the mating face

Inspection and the first article

A first article for a stamped terminal should include the dimensional report, the material certificate, the plating thickness and a crimp cross-section with a pull test result. If the part is supplied on reel, the report should state the reel orientation and the carrier pitch, because a reel that runs the wrong way stops the customer line.

In production, the crimp height is the usual in-process check because it correlates with pull strength and is quick to measure. The contact gap and the lance height are checked on a sample basis. Plating thickness is checked per lot or per certificate, depending on the agreed control plan.

Defects to watch are cracks at the barrel bend, an open seam on a rolled barrel, a lance that has been over-formed, and plating that has cracked at a bend. A crack that is visible at the first article will grow in service, especially where the part flexes during mating.

What to send with a terminal RFQ

Send the drawing, the wire range and conductor class, the mating part, the housing, the plating, the annual volume and the test requirements. Add the crimp tool if one is already fixed, because the terminal and the tool interact.

If the terminal is new, include the mating interface and the insertion and withdrawal forces the housing can accept. A terminal that needs 30 N to insert may be fine in a large housing and impossible in a small one. That number belongs in the RFQ, not in a late design review.