There are three types of switches named for the means they use to complete the circuit.  They are mechanical, magnetic and inductive.

Mechanical switches or “wand” style switches use a mechanical arm and a rotary cam to mechanically complete the circuit. These early switches dominated tools for many years and are still used today.

Magnetic “reed” switches were created in the 1930’s and became industrially popular in the 1940‘s. This switch combined a thin ferrous metal “reed” with the pull of an outside magnet to close the circuit. This combined a mechanical and magnetic approach that made very reliable sealed switches for many thousands of applications outside of resistance welding.  The strong pulsed magnetic field created by the resistance transformer also momentarily closed the mechanical reed and these switches soon gained an unfavorable reputation for false makes in resistance welding applications.

This reputation followed the magnetic “reed” switch through the change from mechanical reeds to solid state electronics in the 90’s because the resistance welding fields would still create unwanted momentary makes.  This stigma followed cylinder mounted switches until the introduction of weld field immune versions in 2015

Inductive sensors were invented in 1958 and became popular in automation in the late 60’s. Inductive Proximity switches create their own magnetic field and then sense interruptions in it by passing metal objects. The more magnetic the metal the longer the range of the switch.  Barrel prox and cylindicator configurations dominated the welding industry until the early 90’s. They are generally weld field immune and have proven reliability over time. Packaging of these large switches became cumbersome and expensive as the number of moving components in the cells increased and the component size shrank.

In the late 80’s a new small inductive sensor emerged and the “world clamp or chicklet switch” quickly became a preferred component.  It offered many advantages over cylindicators including 2 switches with one cord and reduced package size. The costs for the switch itself and the cylinder components were reduced.

The world switch also has some shortcomings that remain with it in its current form.  Most notably the connectors and switch wires are fragile. They require intricate machining to package into components negating the cylinder component savings. World switches require a switch dog to be mounted to one of the moving parts of the component and then a cover or holder to secure them. This cover must be removed when changing the switch, exposing the internal workings of the component to the welding environment.  Losing the cover or failing to replace it correctly leads to highly accelerated wear and premature failure. Employees feet and slag removal operations often break the plastic connector body of the ”world switch”.

In 2015 IFM Efector introduced the first weld field immune cylinder switch that matched the “world switch “in resistance weld field tests.  This switch works with standard magnets and fits the universal “T” style cylinder switch groove. This four year field-tested switch allows component designers to utilize the packaging, sealing and cost advantages of cylinder switches in resistance welding applications. The weld field immune cylinder switch is the E&E standard for pneumatic components.

Weld field immune cylinder switch advantages:

• Provides a sealed environment, no covers to remove or replace. No possibility of internal component exposure. This is especially important in laser cutting and welding where the contaminants are very fine.
• SEALED COMPONENTS = LONGER LIFE
• MTTR cylinder switch 5min vs world switch 60 min
• Minimizes component size and machining thereby lowering component price
• Switch is protected from maintenance and slag removal personnel by metal groove. It can be stepped on without damage.
• A third switch can be added for three position applications
• Cords are built for weld exposure unlike world switch cords that must be covered and short out if exposed.
• Flexible connector positioning = easier fixture wiring.
• E&E standard switches come with a 3 year E&E supported switch warranty. Other manufacturers do not support switch warranty leaving the customer to deal with the switch manufacturer.

APPLICATIONS

E&E believes in open sourcing of globally available components not private labeling or unique switch geometry. Switches are available from E&E or your local distributor. The following switches will fit in the universal “T” groove and are available in single or double configurations.

SUMMARY

Much has changed in the world of electronics since the late 80’s. I can remember our first office fax machine in 1985 that allowed confirmation of print changes without “runners” between companies. Now if I want to send a fax I do so from my computer or simply send the whole file with changes via email. Similarly the “world switch” was a great improvement in the 1980’s but retains all of its shortcomings of the era of development. Now that cylinder mounted switches have achieved the same functionality the advantages of compactness, cost, durability and protection can be confidently utilized by pneumatic component designers in all welding environments.  

Disclaimer: There are some applications in mid and low frequency DC resistance welding where neither the cylinder switch nor the world switch are immune to faults. In these cases, the switches of either type must be ignored during the welding cycle.