What is Spark Erosion? 

Spark Erosion is a type of machining used to cut a variety of shapes, or through hardened metals where conventional drilling/machining is not an option. Electrical conductivity is required in the base material for the process to work. 

Spark Erosion, sometimes referred to as metal disintegration, is a process of removing material from metals using electrical discharges. Sparks are created between an electrode held in a vibrating head, making a quick connection with the workpiece (a broken stud, bolt, tap etc) and creates an arc – each contact/break, removes part of the workpiece in the form of a spark.  

How it works

While the electrode is vibrating with the cutting current turned on, there is a constant supply of coolant passing through the centre of the electrode, cooling the sparks, and flushing them away in the form of small particles, The coolant keeps the workpiece and surrounding area cool with no heat transfer. The coolant also flushes the particles away to prevent choking of the electrode.  Spark Erosion on Steam Turbine

     How do we use Spark Erosion?  

Using our in house developed site portable machinery, we can offer spark erosion services to: 

  • Remove broken studs in large marine/power generation engines, Cylinder head studs, for example, can be removed without the requirement to remove the cylinder head using our bespoke spark erosion and extraction tooling. 
  • Removing extremely hard, seized studs or bolts in flanges or casings of turbines where heat has caused them to pick up.  
  • Remove broken taps and drills. 
  • Many other onsite issues – with over 20 years’ experience in spark erosion we are always happy to adapt to unique requirements! 

Foretract Engineering’s engineers calculate and design the correct size electrode for the workpiece in question:  

For seized broken studs, these will be a square electrode, enabling us to cut a precision square hole directly down the centre, we will then be able to collapse the stud and extract.  

On studs that are not seized but have restricted access, then we can use the square hole that is now in the centre as a drive socket to unscrew it from the hole.  

We can spark erode bolts from M3 – M100 

What is required for Spark Erosion to take place? 

  • 3 Phase 415v power supply (32A minimum) 
  • A water supply 

How long does it take?  

The time depends on the size of workpiece; however, an example would be for a M40 stud, with a depth of 50mm it would take 25-30minutes, cutting at a rate of 2mm a minute. The cutting rate will drop to 1mm per minute for bigger pieces.  

In summary, Spark Erosion offers an extremely effective method of stud, bolt, tap removal with plenty of adaptability and flexibility for various industrial needs.


Take a look at a recent job completed on a snapped tap here

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