Why is the MCB Automatic Rivet Insertion Machine only suitable for 1P and 2P products?

I. Rivet Geometry and Mechanical Stability

For 1P and 2P MCBs, the rivets are relatively short, resulting in a low length-to-diameter ratio and sufficient rigidity.
During automatic feeding and insertion, the rivet remains stable and is not prone to bending or deflection.

For 3P and 4P MCBs, the rivet length increases significantly. The rivet behaves like a slender rod with reduced stiffness.
During automatic feeding, positioning, and pushing, even a small lateral force may cause:

* Rivet deflection
* Rivet bending
* Rivet head tilting

Once deflection occurs, it is very difficult for the automatic insertion process to self-correct, leading to insertion failure or damage to the housing.

II. Accumulated Hole Tolerance in Multi-Pole Housings

In 3P and 4P MCBs, the rivet does not pass through a single hole, but through multiple holes distributed across several poles of the housing.
Each pole is manufactured with its own molding tolerance.

Although the tolerance of each individual hole may be acceptable, the axial misalignment caused by tolerance accumulation across multiple poles becomes significant.

As a result:

* Hole axes are no longer perfectly coaxial
* Insertion resistance increases along the rivet length
* The risk of jamming or scratching the plastic housing rises sharply

For 1P and 2P MCBs, the accumulated tolerance remains within a controllable range for automatic equipment.
For 3P and 4P MCBs, this accumulated deviation exceeds the stable compensation capability of automatic insertion systems.

III. Coaxiality Requirements of Automatic Rivet Insertion

Automatic rivet insertion is not a simple pressing action; it is a high-coaxiality process.
To achieve stable insertion, the following three axes must be precisely aligned:

* Rivet axis
* Housing hole axis
* Pushing mechanism axis

In 3P and 4P MCBs:

* The housing length is longer and more susceptible to slight deformation
* A single guiding structure cannot effectively maintain full-length coaxiality
* High-speed automatic insertion further amplifies misalignment risks

Maintaining reliable coaxial alignment over a long rivet length is therefore extremely difficult under mass-production conditions.

IV. Equipment Complexity versus Manufacturing Return

In theory, stable automatic rivet insertion for 3P and 4P MCBs could be achieved by adding:

* Multi-stage guiding mechanisms
* Intermediate support or floating alignment structures
* Hole alignment detection or correction systems

However, this would lead to:

* Significantly increased equipment complexity and cost
* Reduced production speed
* Marginal improvement in yield rate

Given that 3P and 4P MCBs typically account for a smaller proportion of total production volume, the return on investment does not justify such a high level of automation.

As a result, most manufacturers adopt manual rivet insertion for 3P and 4P MCBs, followed by automatic riveting, to balance quality, stability, and cost.