How to check crimp terminals on wires?

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A good crimping of a terminal on a cable increases the usable life time of the connection and avoids micro cuts when using the cable in a car or an aircraft.

When do you check wire terminal crimps ?
During the manufacturing cycle and at each change of processing settings, including :
- Checking the first batch manufactured
- Check for each new setup of machines or crimping pliers (tool exchange)
- Check each coil change (if terminals are supplied in a coil)
- Interim checks (every 1000 crimps for example)
- Check the final crimp

There are 2 types of control: visual inspection and a tensile test.

A / Visual control: This is to visually check that the terminal is properly positioned on the wire. The lug rings must be tightly wrapped around the cable, no strand shall be out of the crimping. The cable end must appear at the end of the terminal and should not be folded or bent.

Wiretest 2
testeur
Wiretest T1
B / Tensile test: This very simple test is used to verify the correct crimp pull out force. Tensile tests are performed on a motorized test machine called a 'crimpt tester ' or' terminal pull tester' that performs this tensile test. These tests are destructive. They are performed either on pieces issued from the manufacturing process and prepared for these trials, or on samples made with wire of the same section (in the case of very long harnesses that canot been inserted on the machine.

The testing machine is equipped with a special receptacle for maintaining the terminal or utilizing a self closing grip. The cable is held by a special tool designed for not injuring the jacket. It can be a bit eccentric or self closing. Self closing grips can also be used in the case of high capacity, forces higher than 200 lbs (1000N).
The testing machine generally provides tension at a constant speed of 2 inch per min until failure of the crimp or the cable. It is also possible to use manual testers for small wires. The test sample is passed if the value found is above a reference value.


To define the reference value, there are general standards such as CEI760, or standards specific to certain industries (rail, aerospace, automotive).
The main values used are given, for guidance, in the following table :
 
 
Minimum pull strength
Wire size (AWG)
Wire size (mm²)
MIL-T-7928
UL 486
MIL-DTL-22520G
AWG
mm² (1 wire)
Lb
N
Lb
N
Lb
N
26
0,128
7
31
 
 
5
22
24
0,205
10
45
 
 
8
36
22
0,324
15
67
8
36
12
53
20
0,519
19
85
13
58
20
89
18
0,75
38
169
20
89
 
 
16
1,31
50
223
30
134
50
223
14
2,08
70
312
50
223
70
312
12
3,31
110
490
70
312
110
490
10
5,26
150
668
80
356
150
668
8
8,37
225
1001
90
401
220
979
6
13,3
300
1335
100
445
300
1335
4
21,15
400
1780
140
623
400
1780
2
33,62
550
2448
180
801
550
2448
1
42,41
650
2893
200
890
650
2893
0
53,49
700
3115
250
1113
700
3115
00
67,43
750
3338
300
1335
750
3338
000
85,01
825
3671
350
1558
 
 
00000
107,22
875
3894
450
2003
875
3894


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