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Vollmer has developed machines to remove polycrystalline diamond (PCD) by combining traditional grinding with electrical discharge grinding (EDG).

Cutting edge geometries and final dimensions of cutting tools are typically produced on CNC tool and cutter grinders.

However, tooling with PCD cutting edges, as used in the processing of aerospace-grade materials and carbon-fibre components, pose a problem.

Grinding PCD puts the hardest known substance to man (diamond) against an equally hard grinding wheel – a situation that consumes time and grinding wheels.

A Vollmer UK technical engineer said: ‘What you are effectively doing is taking two substances of equal hardness and expecting one to remove the other.

‘This results in an almost one-to-one wear ratio that is very expensive,’ the engineer added.

To limit the expense, manufacturers can remove the PCD via electrical erosion with either EDG with a copper tungsten disc or wire EDM.

The cobalt binder in PCD acts as a conductor for the electrical energy.

The Vollmer engineer said: ‘This method uses a non-contact electrical charge to remove material as opposed to wearing down an expensive diamond wheel.

‘With optimised erosion techniques used, in a lot of applications we are duplicating a ground finish with a surface finish of 0.2microns Ra possible,’ the engineer added.

Despite the finishes, post-erosion grinding is necessary to further extend tool life.

‘The decision to follow erosion with grinding to improve the surface finish is driven by economics with two primary questions: first, how much time should the manufacturer take for grinding; and second, by how much will the tool life be improved,’ the Vollmer engineer said.

Vollmer UK conducted tests to compare the tool life of an eroded tool with that with a ground finish on an aluminium part with high silicone content.

The tool life difference was 15 per cent, with the ground tool outperforming the non-ground tool.

The question for the end user or cutting tool manufacturer is whether the cost of the grinding wheel and machining time are outweighed by the tool life benefits.

Tools that are eroded and not ground can be very effective on materials such as high-silicone aluminium, titanium and composites.

However, some tools significantly benefit from finely ground finishes while other tools with PCD cutting edges also require grinding on their carbide shanks.

To this end, machine tool manufacturers such as Vollmer have developed machines to remove PCD by combining traditional grinding with EDG.

Such machines combine conventional grinding with rotary EDG and also multi-axis wire EDM for shaping the PCD tooling.

The Vollmer engineer said: ‘Wire EDM can offer an advantage compared with rotary erosion as it can create small internal radii and additional complex tool forms that a rotary disc cannot.

‘Alternately, the rotary electrode is a stiff and thick tungsten copper component that does not deflect like wire.

‘This provides faster removal rates up to 0.3 to 0.4mm; excess PCD stock above this should be removed with wire EDM,’ the engineer added.

The six-axis Vollmer QXD series includes the QXD 200, a universal machine for eroding, grinding and polishing various PCD-tipped tools up to 250mm in diameter and 200mm in length.

With the simultaneously controlled path interpolation of six CNC axes, the QXD can combine measuring, eroding, grinding, and polishing.

The specially developed machine and generator for the machining of PCD and PCBN tipped tooling has an integrated six-slot tool exchanger, direct drives and full integration of all peripheral devices.

The integrated tool changer accommodates up to six different eroding, grinding and polishing wheels to guarantee the perfect machining variation for an array of work pieces.

Loading and unloading of the workpiece magazines can be done parallel to the automatic machining mode.

This capability has been effectively put into practice.

The Vollmer UK engineer said: ‘We have one customer using the QXD 200 to manufacture aerospace tooling.

‘One example was a 14mm-diameter carbide rod tipped with 3.8mm of diamond.

‘The diamond was attached to the rod via a high-temperature and high-pressure process, so there was no brazed joint between tip and shaft.

‘To machine this, the customer used disc erosion to flute the diamond tip and then switch to conventional grinding for the carbide flutes.

‘The finishing process was to go back to eroding, to finish the end of the tool.

‘This multi-step process is fully automated and conducted in one single tool clamping to maintain impeccable accuracy, quality and batch consistency,’ the engineer added.

The Vollmer Group specialises in the processing of tools in respect of both production and services. Its product range embraces the latest sharpening and eroding machines for saw blades and tools used in the metal and wood processing industries.

The Group's headquarters in Biberach, Germany, is the design and development centre for its products. Other production sites are located in Mörlenbach, Germany, and Taicang, China.

With 700 employees in nine branches and 30-plus agencies, the company works closely with customers at local level, thus ensuring the same high standard of consulting and customer care worldwide.

Product Range

  • Machines for precision sharpening of circular saws
  • Tooling industry: high-precision and performance wire EDM and grinding centres for manufacturing cutting tools 
  • Sawmill industry: tensioning, straightening and grinding of bandsaw blades

Company history

  • 1909 — Heinrich Vollmer develops the first patentable saw blade setting and filing machines
  • 1952 — Vollmer develops first machines for carbide-tipped circular saw blades
  • 1979 — subsidiaries open in France, Brazil, UK, Italy, US and Japan
  • 1988 — Vollmer develops erosion machine for diamond-tipped saw-blade machining
  • 1998 — wire erosion machine introduced for the metalworking industry
  • 2006 — Vollmer purchases Loroch GmbH to complete product range for processing of saw blades

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