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Why turned loose piece terminals?

Loose piece crimping technology
Why turned loose piece terminals?

There are two basic types of terminals – banded terminals and loose piece terminals. Even though both types are crimped to connect them to the conductor of a stripped wire by deforming the terminal, there are significant differences for automating the crimping and quality process.

Martin Furer, Director of Engineering, Schleuniger Solutions AG

Whereas banded terminals are connected to a carrier strip for simple and fast positioning in the crimp applicator, loose piece terminals come in single pieces that need to be positioned individually. They come in various shapes and sizes and are used in almost all industries. Turned, closed barrel terminals are predominantly used whenever quality requirements of the connection are high and die-cut, open barrel terminals can not be used. Very often they can be found in the military industry, aerospace, control- and signalling cables, as well as in electronics manufacturing for different D-sub applications.
Advantages of turned loose piece terminals
Because of their round shape, turned terminals have a much lower electrical transfer resistance than die-cut terminals. With identical wire cross sections and electrical currents, the heat generated in the terminal is substantially less, while voltage drops between conductor and terminal are also lower. This implies that when using conventional open barrel terminals, the dimensions of the connector must be significantly larger – requiring more space.
Roundness makes a perfect fit
Another advantage is the roundness of the turned loose piece terminal. Male and female connectors fit perfectly to each other and guarantee a very reliable, gas-tight and spark-free connection. Additionally, vibration tolerances are comparably high due to the high quality terminal design. Standard pull-force tests often lead to test results where the cable breaks before strands are pulled out of the crimped connection. A commonly used definition of the quality requirements for such a 4-indent crimp can be found in the SAE standard (a.k.a “MIL-spec”) – which is mainly used in the military and aerospace industry.
Loose piece terminals are more difficult to handle
Loose piece terminals are significantly more difficult to handle compared to banded terminals. Accurate and reliable positioning of the terminal requires automatic sorting and positioning prior to crimping, whereas banded terminals are simply pulled from a terminal reel and positioned using the transport pitch of the carrier strip. On top of positioning each terminal individually, the process of inserting a stripped wire end into the closed crimp barrel of the terminal is also more complex. The wire can’t be inserted into the crimp zone from above – requiring an additional drive for insertion (= horizontal movement) in bench top strip & crimp machines.
Both fully automatic and semi-automatic systems require a number of automated process steps for reliable crimping of loose piece terminals:
  • Sorting of terminals
  • Feeding and positioning of single terminals in the crimp applicator
  • Guiding and positioning of stripped wire ends inside the terminals (which are already positioned inside the crimp applicator of the machine)
  • Crimping of the terminals (4-indent crimp) including quality assurance
  • Extracting the terminal after crimping without damaging the terminal.
Bench top machines combine all processes
Each step requires a technical solution, which differs greatly from those used in crimping standard, open barrel terminals. High-precision bench top machines such as the Schleuniger StripCrimp LPC combine all processes including quality assurance in one single machine. The loose piece stripper-crimper sorts and feeds terminals using a combined drum / track system. An integrated stripping unit with trigger sensor strips the inserted wire end – if required also with a zero cut.
Short cycle times combined with precision mechanics allow for efficient and precise processing – making the StripCrimp LPC the preferred choice for demanding customers in the aircraft industry. Depending on production requirements, Schleuniger also offers its loose piece crimping technology in automatic stations for fully automatic production with CrimpCenter machines or transfer systems.
During sorting, loose piece terminals are brought into a defined position for further processing. A proven process is to use a rotating drum, which „dumps“ terminals on a vibrating feed track.
The track is specifically designed for the shape of a terminal, so that they can only “fall” into the track in a defined way and are automatically lined up for further processing. A gripper then positions each terminal into the crimp applicator.
The terminal type determines how linear feeding and positioning is executed. Depending on the terminal’s center of gravity and shape, there are 3 basic terminal types (see picture 5). Feeding is either done vertically (crimp zone up or down) or horizontally.
With years of experience in loose piece crimping, Schleuniger has proven technologies and in-house knowhow in order to process a great variety of terminal types and shapes. Quick-change systems reduce change-over times to a minimum – for high productivity even when frequently changing applications.
The three most important terminal types are:
  • Type 1: Vertical feeding with crimp zone up This terminal type has a „collar“ (or shoulder) between connection area and crimp zone. Its center of gravity is below the “collar” in the connection area
  • Type 2: Horizontal feeding Type 2 terminals have no „collar“ and their center of gravity is not clearly defined. Therefore suspended feeding is not possible and the terminal must be fed horizontally.
  • Type 3: Vertical feeding with crimp zone down This terminal type also has a „collar“, but its center of gravity requires „upside-down“ feeding, with the crimp zone down.
Feeding and positioning
Lined up terminals are moved inside the vibrating feed track towards the positioning unit. Depending on the terminal type, this unit consists of a combined tilting- / turning-module with gripper (see picture 6). Each terminal is positioned inside the crimping head, so that the stripped wire can be inserted and crimped.
Handling type 2 terminals is the most complex feeding method, because the crimp zone can be on the leading or the trailing end. The machine must therefore be able to accurately detect the position of the crimp zone and turn it into the correct position for further processing.
Once the terminal is positioned inside the crimp applicator, it can be crimped onto the stripped wire. Precise wire positioning ensures that insertion depth is correct and all conductor strands are located inside the closed barrel – hence, no strands are bent during centering. With high-quality machines such as the StripCrimp LPC, the operator inserts the wire into a gripper. A sensor trigger automatically closes the gripper jaws and holds the wire in position during the entire processing cycle.
Crimping and quality assurance
To ensure the quality of every crimp, modern stripper-crimpers like the StripCrimp LPC have an integrated crimp force monitoring system. Although the force curve of an indent crimp looks different than conventional crimp force curves, the system also compares curve and area of a reference crimp and allows for individual tolerance settings. The trapezoid shape of the curve is caused by the pins of the crimp applicator that simultaneously create 4 indentations from all sides into the loose piece terminal. The crimping head is very simple to adjust and calibrate, as only the crimp depth needs to be adjusted.
Additional quality assurance methods and test procedures known from “conventional” crimping, such as pull-force testing or visual analysis using cross sectional views also apply to indent crimps. Quality criteria of a gas-tight crimp include correct strip length, insertion depth and pull-force.
Turned loose piece terminals are predominantly used in applications where high-quality connections are needed and very limited space is available. They are difficult to handle in automated processes. Modern machines like the Schleuniger StripCrimp LPC ensure reliable quality production with precision results. Furthermore, automating the entire process significantly reduces cycle times, increases output and thereby reduces costs per cable.
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zusammenfassung
Das Handling von losen Teilen in der Kabelkonfektionierung stellt hohe Anforderungen an die Verarbeitungsmaschinen. Spezialist Schleuniger bietet hier entsprechendes Know-how und dazugehörige Maschinenkonzepte an.
La manipulation de pièces détachées pour la fabrication de câbles exige la plus grande précision des machines de traitement. Le spécialiste suisse Schleuniger fournit le savoir-faire et les concepts de machine correspondants.
Current Issue
Titelbild EPP EUROPE Electronics Production and Test 11
Issue
11.2023
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