Direct connection of wires and enameled wires with cable lugs by resistance welding

hot crimping – reliable connections of WIRES AND ENAMELED WIRES without prior stripping

STRUNK has introduced a new technology that enables enamelled wires to be connected without prior stripping. This process is based on the general resistance welding process from STRUNK, which has been a proven process in the automotive, medical and solar industries since 1984.

The welding heads or welding tongs of the resistance welding devices from STRUNK Connect have a special mechanical structure so that a reliable and high-quality welded connection is created in accordance with customer specifications. Each individually designed construction is calculated and designed specifically for the customer’s application using FEM software in order to generate the required welding pressure and transfer the high welding current within a very short welding time. Due to these properties and in combination with the intelligent power sources and the precise monitoring by the PC-based welding controls from STRUNK, our process evaporates the insulation of each individual enamelled wire without affecting the copper. The insulation vapors are extracted by an extraction system.

What is hot crimping and which wires is it suitable for?

Hot crimping is a proper welding process that is based on STRUNK’s resistance welding process for non-ferrous metals, e.g. B. copper based. It is suitable for enamelled wires (motor, stator, generator production, medical applications), insulated HF strands (e.g. for transformers, chargers …) or conventional copper wires (highly flexible, regularly stranded or braided strands, e.g. . for electric or hybrid vehicles).

STRUNK can process all wire types as single strands from a cross-section of 0.05 mm2 or as stranded or braided bundles up to 400mm2. The thickness of the individual wires does not matter. This means that HF lines are also possible. In addition, all conventional wires with different coatings (silver, tin, nickel …) can be processed. This means that this process is also suitable for high-temperature applications. Plugs and sleeves can be made of bare copper, tinned, nickel-plated or silver-plated.

What applications is hot crimping suitable for?

Connections between enamelled wires or between enamelled wires and cable lugs have been extremely time-consuming and expensive in the past. The reason for this was the manual effort involved in removing the lacquer layer from each individual wire. If a wire bundle had to be contacted, stripping this bundle in one step was almost impossible. An employee had to heat the wires with a flame and connect the wire bundle manually by feeding in a hard gate (in the form of a rod). This process takes time and was not reliable. Today, STRUNK can weld these wires to a terminal or sleeve without prior stripping. Resistance welding evaporates the insulation and connects each individual wire to the others. This procedure has the following advantages:

  • In all of the test methods used in the automotive and medical industries, no aging of the welded joints could be determined during the entire service life.
  • No more crimp connections that can loosen or relax over the course of their service life.
  • Completely safe process due to the monitoring of all necessary parameters.
  • Particularly high conductivity without voltage drop due to the low contact resistance.
  • Due to the high tensile strength (high tensile forces) of the individual wires, there is no slip effect when pulling.
  • The connection is vibration-proof and temperature-resistant.
  • The connection is insensitive to environmental influences.
  • The process can be fully automated.

How is hot crimping different from traditional crimping?

With conventional crimping, a mechanical connection is established that can loosen again during the service life of the product due to aging (relaxation of materials). In contrast to this, during hot crimping, the materials are fused together by resistance welding without stressing the copper and a connection is created between the joining partners that has virtually no contact resistance and does NOT AGE during its service life. Due to the perfect resistance and intermetallic connection, there will be no oxidation later, which would increase the resistance during the use of the product. Even in heavy current applications with large cross-sections, this technology achieves safe and reliable connections that function without failures even after the required power supply cycles. In addition, the mechanical tensile forces are particularly high and stable because the sleeve and wires are connected to one another. STRUNK’s PC welding controls allow process parameters to be monitored, including data tracking in a database or product identification for full traceability as required in the automotive, medical and solar industries.

How does hot crimping work?

Resistance welding creates a welded connection between the individual wires. Specially designed welding heads generate the necessary welding force on the cable lug or sleeve and transfer the welding current to the joint partners within a very short time without stressing the copper. Optionally, this process can be monitored and regulated with the intelligent power sources and PC-based controls from STRUNK. In specially programmed pulses, the welding current generates the temperature required to evaporate the insulation and weld the wires together. This creates an alloy between the wires and the sleeve or cable lug, which ensures a perfect electrical connection between the individual wires. The required mechanical tensile forces for each wire in the bundle are also achieved without slip effects.

What are the essential parameters for the hot crimping process?

Only three essential parameters are important for creating a welded joint: welding current, welding time and welding pressure. So that the operator does not have to deal with these parameters first, the PC systems from STRUNK can specify standard parameters that only require fine adjustment by the operator. These standard values are recommendations from STRUNK, which were set by STRUNK taking into account the corresponding application. Alternatively, the operator can also use freely programmable profiles.

What equipment is required for hot crimping?

In order to cover the entire spectrum of customer requirements, STRUNK Connect produces and supplies turnkey systems from table-top units to fully automatic production systems. These devices process the products in sequence to enable different crimp sizes or product combinations. The welding device (hot crimping device) itself can be designed as a module or with welding head or pliers, depending on the space available at the customer’s premises. For a detailed offer on suitable equipment, customers are welcome to send samples to STRUNK Connect.


(Individual customer solution as an example)

Fully automatic gun welding system 150KVA with transfer tape for hot crimping of phase connections and star points of geared motors

The system is designed for standing stators on tool carrier systems. It has a STRUNK servo rotary / lifting unit, as well as a portal system …

Fully automatic welding system for hot crimping with a rotary lifting table mechanism

The welding cell has an S-MMD2 or S-MMD3 module for hot crimp connections of sleeves and ring or tubular cable lugs for geared motors in the BEV or HEV …

Semi-automatic welding cell for hot crimping of stators incl. Interchangeable tool carriers for different sizes and designs

The system is designed as a 150 KVA AC tong welding system with STRUNK X / Y / Z servo portal, with the transformer and secondary being firmly connected so that the secondary paths are extremely brief …

S-MMD1 for hot crimping of stators

The S-MMD1 system can be prepared as a manual workstation or a module for assembly. Welding module with drawer system guard …

S-MMD3 for hot crimping applications

The S-MMD3 system can be designed as a single module or table structure. The welding module with a left-aligned table structure …

Strip welding system for processing in the hot crimping process

Manual STRUNK gun welding system as a strip welding system with servo feed of a Cu punched strip to a bending unit …

Manual welding system for high cross-sectional areas

The system is designed as a manual gun welding system 200 KVA AC as a flat bed machine, with the transformer and secondary being firmly connected …

Semi-automatic welding system for hot crimping with a rotary lifting table mechanism

The system is designed as a tong welding system 150 KVA AC with STRUNK X / Y / Z – servo portal, with the transformer and secondary being firmly connected …

Portal welding system for hot crimping of stators

Thanks to the free tool access, the portal system enables the processing of very short cable / tap lengths …