Precision tool manufacturers face growing challenges, including small batch sizes, rapidly changing tool geometries, and tight grinding tolerances. These demands are compounded by rising energy costs and a global shortage of skilled labour. At ANCA, we have adopted EDM dressing—a wire-erosive process for dressing and profiling grinding wheels—to address these challenges. This innovative approach simplifies work preparation, boosts productivity, and enhances quality, particularly in flute grinding, cylindrical grinding, and profile grinding applications.
Importance of grinding wheels and dressing methods in efficient grinding
The choice of grinding wheel is based on a combination of cutting performance, dimensional stability and the surface quality to be produced on the workpiece. A grinding wheel with a metal bond is ideal for deep grinding with the aim of maximising material removal. The same grinding wheel bond is usually also selected for a 14E1 pointed grinding wheel for profiling so that the point radius retains its shape for a long time and thus ensures long-lasting material removal. A metal-hybrid bond with an admixture of synthetic resin is ideal for creating surfaces during finishing.
One of the advantages of both grinding wheel variants is that they can be wire-erosively dressed and profiled using the EDM dressing process. Wire-erosive dressing does not destroy the cutting material (grain), diamond or CBN, but burns out the bond that binds the grain. The positive side effect is that the amount of bond removed can be defined via the EDM process parameters. Tests at the KSF Institute for Advanced Manufacturing at Furtwangen University have shown that a grain protrusion of 50% is advantageous for the cutting performance of the grinding wheel and for a stable EDM process. This means that if the grain protrudes 50% from the bond, the bond force is still sufficient to counteract the load during the grinding process and, on the other hand, so-called pockets are formed between the grains, which “take along” the coolant lubricant (KSS) from the coolant nozzle and transport it to the cutting point.
During the sanding process, the sanding disc is subjected to two main types of stress. The grain is subjected to mechanical stress and thus wears down. In addition, the “pockets” that were previously eroded are clogged with grinding chips, which leads to a lower cutting effect and higher friction during the grinding process. The spindle power increases as the grinding wheel experiences more resistance. The grinding process becomes unstable, which can lead to chatter marks on the surface.
Applications of EDM Dressing at ANCA provide advantages in quality, grinding times and tool life
Conditioning the grinding wheels with EDM Dress technology is mainly used at ANCA in the three grinding applications of flute grinding, cylindrical grinding and part-roll grinding.
The flute grinding and pre-grinding of solid hobbing wheels in carbide requires a deep grinding of several millimetres. The effects of the EDM dress on the grinding spindle load and the dimensional stability of the corner radius of the grinding wheel are analysed. For flute grinding, this refers to the corner radius and for profile grinding with a point profile (14E1) to the centre radius. When cylindrical grinding using the pinch/peel method, the corner radius of the rough grinding wheel is stressed and must have the highest possible dimensional stability so that the finishing wheel does not have to remove a lot of material in an uncontrolled manner. In part peel grinding, the profile accuracy after profiling is crucial for the tight tolerances of a shaping or hobbing wheel for gear cutting. In order to achieve AA or AAA (80% of AA) quality, it may be necessary to profile the grinding wheel profile to a tolerance of +-0.003 mm.
A 1A1 grinding wheel with a metal bond is used for flute grinding. The workpiece is a carbide blank into which four grooves are ground. This is a typical work step that takes up the majority of the grinding time. Ten blanks were ground using EDM dressing and a further 10 blanks were ground using conventional dressing with a SiC disc. The grinding was carried out with an automated feed control. The maximum feed rate should be 180 mm/min with a maximum permissible spindle load of 13%. The grinding time required while maintaining the spindle load is analysed.
With the conventionally dressed grinding wheel, the spindle load already exceeds the set limit on initial contact and the feed rate is reduced. The EDM dressed grinding wheel increases slowly and reaches the set limit without significant load peaks. The EDM dress wheel requires a shorter grinding time for the four grooves than the conventionally dressed wheel.
After ten workpieces, the sanding time with the conventionally dressed disc has already increased by 25%.
Cylindrical grinding of blanks
Cylindrical grinding on the ANCA CPX machine benefits from an easy-cutting grinding wheel that can concentrate the spindle power and machine rigidity on material removal. With standard grinding wheels, we reach the limits of material removal in terms of grinding times in tests using the combination of a D91 and D15 for the pinch/peel grinding process. With an EDM Dress grinding wheel, the material removal can be increased in (mm³/s), as shown in a test with a carbide blank Ø16mm, which is ground down to several steps.
The grinding length for the grinding disc is 150mm per workpiece (70+50+30mm) and 10 workpieces are ground. The removal volume is set to 10mm³/s, which is a stable empirical value from production. With the EDM dress process, the corner radius of the very hard metal bond could be profiled to R0.15mm and the wiper flat to 0.36mm. After a grinding length of 1500mm, the diameter of the grinding wheel has decreased by 0.023mm. The radius has increased to 0.22mm. Significant advantages could be demonstrated here with the grinding wheel combination D91 (Vc 80m/s) metal-bonded and D15 (Vc 55m/s) resin-bonded. Transferred to production, this means that the grinding wheel keeps the defined corner radius in shape for longer, which means that the finishing wheel can also guarantee constant material removal for longer with a consistently good surface finish.
Profiled disc – Skiving disc
The EDM Dress process offers the greatest advantage when profiling grinding wheels. Here, a hard metallic or hybrid bond is cut independently of the operator and to tolerances of +-0.004 mm or less.
In addition to standard grinding wheel packages, ANCA often uses the available Mitsubishi MP1200 wire EDM machine to profile grinding wheels for grinding hobbing gears, either from the solid or from a centre profile. Depending on which module is to be ground, the new profile is fitted into an existing grinding wheel, set up and eroded. On the one hand, this process is based on the fact that the grinding wheel is very easy to cut after the EDM dress and is therefore ideally suited to consistently removing the large amount of material that can occur with a larger number of teeth and module. On the other hand, the profile tolerance of +-0.003 mm or less can be maintained with the EDM dress for the tight tolerances for skiving wheels.
At ANCA, EDM dressing has proven to be a transformative technology, enhancing productivity, precision, and tool life in diverse grinding applications. By integrating this process, manufacturers can overcome industry challenges, reduce costs, and achieve consistent, high-quality results.
Whether you’re optimising flute grinding, cylindrical grinding, or skiving applications, EDM dressing provides a cutting-edge solution for modern tool manufacturing. Reach out to ANCA for more insights and tailored solutions.
COMMENTS