The production of the fully automatic double-end terminal crimping machine is occasionally defective, so we need to know these things. 

First of all, it is helpful to understand that there are three main parts of the terminal, that is, the plug zone, the transition zone, and the crimping zone（shown in Figure A）.

As the name implies, the plug area is the part, designed by the connector designer, where the terminal is to engage with the docking terminal and work in some way. If the joint is deformed during crimping, the performance of the connector will be reduced.

The transition zone is also designed to be unaffected during crimping. If the position of the elastomer or terminal is changed, it will also affect the performance of the connector.

The crimping area is the only part whose design is affected by the crimping process. And it shall be firmly connected to the cable.

Ideally, all work of crimping terminals on the insulation and conductors of the cable will only be done in the crimping zone. The conductor crimping zone is trumpet-shaped at both ends, while the transition zone and bonding zone remain unchanged before and after the crimping process.

An example of crimping performed correctly is shown in Figure B.

The insulation layer at the insulation crimping zone shall not be pierced. The distance of the wire core (or wire strands) protruding from the front of the crimping area of the conductor roughly equals the diameter of the cable conductor. For example, the AWG18 cable should protrude at least 0.04mm. The insulation layer and conductor can be seen in the part between the insulation and the conductor crimping zone. The conductor crimping zone is trumpet-shaped at the introduction end and tail end, while the transition zone and plugging zone remain unchanged before and after the crimping process.

If your crimping terminal looks different from the one in figure B, it may be due to an error in the crimping process. Here are the 13 most common problems that may arise in the crimping process and how to avoid them.

1. Crimping height is too small 

Crimping height is the cross-sectional height of the body crimping area after crimping, and it is the most important feature of good crimping.

The connector manufacturer provides the crimping height for each cable size designed for the terminal.

The correct crimping height range or tolerance for a given cable may be as small as 0.002mm. Under such strict specifications, it is very important to verify that the crimping machine is set correctly for good crimping.

Too small (Figure 1) or too large (Figure 2) crimping height does not provide the required crimping strength (holding force on cable terminals), which will reduce the cable drawing force and rated current, and generally cause performance degradation of crimping joints under abnormal working conditions.

Too small crimping height will also break the wire core or break the metal in the crimping zone of the conductor.

2. Crimping height is too small

Too high crimping height can not compress the wire core correctly, resulting in a too-large invalid gap in the crimping area, because there is not enough metal-to-metal contact between the wire core and the terminal metal.

The solution to the problem # 1 & # 2 is simple: adjust the crimping height of the conductor on the crimping machine.

When using the crimping machine for the first time, use the Vernier caliper or micrometer shown in Figure B to verify that the crimping height is within the specified range, and should be re-checked according to the required frequency during the working process to maintain the correct crimping height.

3 & 4. The insulation crimping area is too small or too large (Figure 3 and Figure 4)

Due to the diversity of insulation types and thickness, connector manufacturers generally do not provide the crimping height of the insulation.

Insulation crimping provides stress release for the crimping area of the conductor so that the core will not be broken when the cable is bent.

Too small an insulation crimping zone will make the metal stress in the insulation crimping zone too large and weaken its stress release function.

Most types of crimping tools can adjust the insulation crimping height independently of the conductor crimping height.

The correct adjustment allows the terminal to clamp the insulation layer at least 180 degrees without piercing the insulation layer.

When the outer diameter of the insulation crimping part of the terminal is nearly the same as that of the cable insulation, the best method is IDT technology.

5. Some wire strands are excluded in the crimped conductor

Loose wire strands (Figure 5) are another common cause of crimping problems.

If all the cores are not completely enclosed in the crimping area of the conductor, the strength and current load capacity of the crimped parts will be greatly reduced.

To achieve good crimping, you must meet the crimping height specified by the connector manufacturer.

If not all wire cores play a role in crimping height and crimping strength, then the performance of crimping parts will not meet the specified requirements.

In general, the problem of loose cores can be easily solved by rewinding the cable into a bundle and then inserting it into the crimped terminal.

If stripping the insulation from the cable is a separate operation, the core may be accidentally separated during processing or clustering.

Remove the insulation layer so that the insulation sleeve is not completely removed from the cable until it is ready to be crimped to the cable with a terminal, which helps to minimize the problem of loose core.

6. Stripping length is too short 

If the stripping length is too short, or if the cable is not fully inserted into the conductor crimping area, the termination may not reach the required drawing force because the metal contact between the cable and the terminal is reduced.

As shown in Figure 6, the stripping length of the cable is too short (note that the insulation is in the correct position), and the distance extending from the front of the conductor crimping area cannot obtain the required conductor diameter of the cable.

The solution is simple: increase the stripping length of the stripping equipment to the specified value of the terminal.

7. Cable inserting too much

Another crimping problem associated with too short stripping length occurs when the cable insertion crimping area is too deep.

As shown in Figure 7, the insulation layer is inserted too deep into the insulation crimping zone, and the conductor extends to the transition zone.

In practical application, this may lead to three failure modes.

Two of them are due to the reduction of metal-to-metal contact in the conductor crimping zone, resulting in the reduction of rated current and cable drawing force.

The contact between metal and plastic is not as firm as metal contact, and it does not conduct electricity.

The third failure mode may occur when the connector is engaged.

If the cable extends too deep into the transition zone, the tip of the pin terminal collides with the cable, which may prevent the connector from being fully seated or may cause the pin or Jack terminal to bend.

In extreme cases, even if the terminal is fully seated in the housing, it will be pushed out of the back of the housing.

To solve this problem, make sure that no excessive force is used to insert the cable into the crimping machine to cross the cable stop of the crimping machine, or adjust the position of the cable stop to correctly position the stripped cable in the axial direction.

8. “Banana” (over-bent) terminal

One of the most vivid crimping problems is called “banana” crimping (Figure 8) because the crimping terminal is in the shape of a banana.

This makes it difficult for the terminal to insert into the housing and may cause the terminal to collide.

This problem can be easily solved by adjusting the position of the limiting pin on the crimping machine.

The pin is located in the crimping machine and touches the plugging area of the terminal when the crimping area is crimped on the cable.

In the crimping process, a large amount of metal at one end of the terminal (in the crimping zone) moves.

Such a large force tends to force the front of the terminal to tilt up unless it is limited by an appropriate “limiting pin”.

9. Crimping is too close to the transition zone

One of the obvious crimping problems is that the transition zone is partially damaged, as shown in Figure 9.

In the terminal shown, the vertical protruding part is a design feature called “terminal stop”.

Its function is to prevent the terminal from being inserted too deep into the housing.

If the stop is completely damaged, the actual terminal will be pushed all the way through the housing.

The cause of this problem is that the terminals and metal bars (the metal bars connected when you receive the goods from the manufacturer) are not in the correct position relative to the crimping machine.

The problem can be solved simply by loosening the substrate of the interchangeable tool and then realigning the crimping machine.

10. Trumpet mouth is too small 

The correct size of the trumpet mouth (Figure 10) is near twice the thickness of the terminal material.

For example, if the terminal is made of a material with a thickness of 0.08mm, the horn should be about 0.16mm.

Although a deviation of a few thousandths of an inch does not essentially affect the performance of the terminal, there is a risk of cutting the wire core if the horn is missing or is less than the thickness of the terminal material.

The reduction of retained cores reduces the termination strength.

To correct the problem, make sure the punching blades and anvil on the crimping device are aligned correctly.

11. Trumpet mouth is too small

Problems can also occur if the trumpet mouth is too large (Figure 11), as this reduces the total area of the terminal crimping area in contact with the cable.

The smaller the contact surface between the cable and the terminal, the smaller the cable drawing force.

If the crimping height is correct, then the problem may be caused by tool wear and should be replaced.

12. Terminal tail is too long

In the crimping process, the terminal tails are cut from the terminal.

Problems can occur if the retained tails are too long (Figure 12).

When the terminal is inserted into the housing, the excessively long metal tail extends to the back of the connector, causing an arc between the adjacent contacts of the connector when a higher voltage is applied.

If the tail material at the front of the terminal is too long, it will interfere with the engagement of the connector and cause “terminal collision”.

The solution is relatively simple.

Adjust the substrate on the crimping machine so that the terminal is centered correctly in the crimping machine.

Another sign that the terminal is not centered correctly is that the trumpet mouth is not shaped correctly.

This occurs because there is a space between crimping blades for the trumpet mouth and the substrate.

13. Barb openings are changed

Although barb opening changed is not necessarily the result of an incorrect crimping process, the connector will fail.

The barb (Figure 13) may open excessively inward or outward, which affects the ability of the terminal to fully lock into the plastic housing.

The damage of the barb may be due to the over-tightening of the friction wheel on the hinge retainer of the crimping machine when the terminal is unfolded from the disc, or it may be caused by the handling after the terminal is crimped on the cable.

Usually terminated cables are bundled, stored, or transported to another location in the factory.

Barbs may also change during bundling, or when each terminated cable is removed from the harness.

If the damage occurs on the crimping machine, then the tightness of the friction wheel needs to be adjusted, as long as the terminal disc will not unfold because of its self-weight.

If the problem is in the bundling process, a smaller wire harness or improved handling procedures are required.

Conclusion,

Although 13 problems can arise during crimping, there are only four simple guidelines to help ensure a successful connector application:

A. Choose the correct connector for your application requirements.

B. Use the correct crimping tool to crimping qualified products.

C. Correctly adjust and maintain the crimping tool to make it in good working condition.

D. Replace metal replacement parts regularly (such as conductor and insulator punching blades, anvil, and terminal cutters).

Here is one of our terminal crimping machines for your kind review.