Effective Reduction in Metal Adhesive Grinding Wheels in Grinding Machines

• 1
  What the metal adhesive grinding wheels bond does during reduction
• 2
  Reduction per pass with metal adhesive grinding wheels
• 3
  Dressing and trueing metal adhesive grinding wheels
• 4
  Coolant delivery that keeps reduction stable
• 5
  Where metal adhesive grinding wheels stop being the right choice
• 6
  Bond and dressing choices at a glance

A metal adhesive grinding wheel holds abrasive grit in a metallic matrix rather than in vitrified glass or resin. The matrix is tougher, so the grit stays put far longer. That is the whole reason these wheels survive hardened steel, cemented carbide and ceramic work that strips a vitrified wheel in minutes.

The trade is grain exposure. A hard matrix resists wear, and wear is what normally opens new cutting edges. When the matrix will not break down, the wheel face flattens. Pores fill with chips, the face glazes, and the wheel starts rubbing instead of cutting.

Rubbing is the failure mode that ruins reduction. Heat goes into the part, not into the chip. A 20 mm wide face on hardened 52100 can reach 600 °C at the contact zone within a few seconds of glazed cutting. By then the surface is tempered, the size is drifting, and the wheel needs a full dress before it will cut again.

Read the sparks and the sound. Sharp cutting gives short, bright, breakable sparks. Loading gives long orange streaks and a dull rumble. If the spindle load climbs while the table speed stays fixed, the face is dulling. Stop and dress before the part is scrap.

• 1
  Hard bondHolds grit, resists wear, keeps form on form-grinding work
• 2
  Closed faceLoads quickly when coolant cannot reach the contact zone
• 3
  Heat pathMost grinding heat leaves in the chip only if the grit stays sharp

On hardened steel above 55 HRC, a metal adhesive grinding wheel will take 0.01–0.03 mm radial depth per pass in roughing, then 0.002–0.005 mm in finishing. Below 0.005 mm per pass the grit tends to rub rather than bite, which is the opposite of what most operators expect. Too light a pass glazes the face faster than a heavy one.

Above 0.03 mm per pass the wheel can hold the cut, but the spindle load and the heat rise quickly. Watch the load meter. If it moves more than 15 percent above the stable roughing value, back off to 0.02 mm. On carbide and ceramic, keep roughing at 0.005–0.015 mm per pass and never let the face go dry.

Total stock matters more than pass count. For a 0.3 mm reduction on a hardened shaft, plan 15–20 roughing passes plus 3–5 finishing passes. Fewer, deeper passes work only when the wheel is freshly dressed and the coolant reaches the arc of contact.

Infeed rate on a cylindrical machine should stay between 0.5 and 2.0 mm/min for roughing on hardened steel. Crossing that band is the usual cause of chatter marks that no amount of spark-out will remove.

• 1
  Roughing0.01–0.03 mm radial on steel above 55 HRC
• 2
  Finishing0.002–0.005 mm radial, 2–3 spark-out passes
• 3
  Carbide and ceramic0.005–0.015 mm radial, wet only

A silicon carbide stick will not open a metal bond. It polishes the face and makes the loading worse. That is the most common mistake we see on a toolroom grinder. The bond is harder than the dressing abrasive, so the stick wears and the wheel does not.

Electro-erosion dressing, also called EDM dressing, is the method that works. A wire or a rotating electrode runs close to the wheel face, and short electrical pulses erode the metal matrix away from the grit. No mechanical contact, no force on the spindle, and the abrasive keeps its full exposure.

Typical settings are 0.05–0.1 mm of radial erosion per dressing cycle, with pulse durations in the microsecond range. The exact numbers come from the wheel maker, because grit size and matrix composition both shift the window. Run too long a pulse and you erode grit as well as bond.

For profile work, dress on the machine. Removing a metal-bond wheel to dress it on a separate unit costs you the setup and the concentricity. On-machine dressing holds runout under 0.005 mm, which is what a tight profile needs.

• 1
  Wrong waySilicon carbide stick or diamond stick polishing the face
• 2
  Right wayElectro-erosion or electrochemical dressing with no contact
• 3
  Profile workDress on the machine to keep runout under 0.005 mm

Heat is the limit on every pass. In grinding, most of the energy becomes heat at the contact zone, and the chip carries it away only when the grit is sharp. A glazed wheel leaves the heat in the workpiece, and the workpiece moves as it heats.

Deliver coolant at 1.5–3.0 MPa through nozzles aimed at the arc of contact, not at the top of the wheel. High-pressure through-spindle coolant works better on internal grinding, where the arc is hidden. Flow matters less than where the jet lands.

Keep the concentration at 6–10 percent for steel and check it weekly with a refractometer. A weak mix foams, rusts the table and stops carrying heat. Filtration to 10 μm keeps the chips from being re-cut, which is a quiet cause of surface scratches.

On carbide, oil-based coolant often holds size better than water-based. On hardened steel, water-based is fine and cheaper. Match the fluid to the material, then leave it alone for the whole batch.

• 1
  Pressure1.5–3.0 MPa aimed at the contact arc
• 2
  Concentration6–10 percent for steel, checked weekly
• 3
  Filtration10 μm keeps re-cut chips out of the contact zone

Soft aluminium and low-carbon steel are poor candidates. The chips smear across the face and fill the pores before the grit can cut. A vitrified wheel with a coarse grit and an open structure handles those materials with far less trouble.

Very large reductions are also a poor fit. If you need to remove 2 mm from a 100 mm steel plate, grind after milling, not instead of it. A metal bond is a finishing and form-holding tool, not a substitute for a roughing operation.

Thin-wall parts and long slender shafts are another boundary. The wheel cuts with force, and a 0.8 mm wall will deflect before the grit bites. Support the part, reduce the depth of cut to 0.005 mm, or switch to a softer bond.

Cost per wheel is higher, so the economics only work when the wheel lasts. On a short run of 20 soft steel parts, a vitrified wheel wins. On a 5,000 part run in hardened steel, the metal bond pays back in truing time alone.

• 1
  Poor fitAluminium, soft low-carbon steel, gummy alloys
• 2
  Poor fitRemoving millimetres of stock in one setup
• 3
  Good fitHardened steel, carbide, ceramic, long production runs