Profile Grinding Machine

Overview

A profile grinding machine reproduces a complex two-dimensional form on hardened tooling: the lands of a Profile Grinding Wheel are dressed to a master shape and then ground into dies, punches, form tools and gauges. The shapes carried are too intricate or too hard for milling, and the tolerances are too tight for spark erosion alone, so the work is finished by abrasion to single-micron form accuracy. This machine is a CNC contour grinder: the part sits on the C-Axis Rotary Table or the work table, a small high-speed wheel runs in the Z Wheelhead & Spindle, and the controlled axes trace the programmed outline while the wheel skims a few microns per pass.

Everything stands on the Granite Machine Base. A hand-lapped granite slab carries the axes because granite expands far less with temperature than cast iron and damps vibration well, and on a machine measuring to fractions of a micron a half-degree thermal drift is a real error. The granite sits on a cast iron sub-frame and elastomer isolation pads that keep floor vibration out of the cutting zone.

How it works

The operator loads a hardened blank onto the C-Axis Rotary Table or a fixture on the work table, then references the part to the wheel using the Optical / Vision Station station. The CNC then runs the part program. The X Cross Slide carries the work across the wheel, the Y In-Feed Slide feeds it toward the wheel to set depth of cut, and the Z Wheelhead & Spindle sets height on the Z axis. For forms that wrap around a centre, the C-Axis Rotary Table turns the part under the wheel as a C axis so a single dressed wheel edge can grind a full radial contour.

Position on every axis is read directly by the Glass-Scale Feedback, not inferred from the ball-screw. A Glass Linear Scale etched with a fine grating runs alongside each slide, and a Scale Read Head tracks it to 0.05 µm. Feeding back the true slide position cancels ball-screw pitch error, backlash and thermal growth, which is how the machine holds form accuracy of about one micron over the whole profile.

The grinding is done by the High-Speed Spindle, a small spindle running at tens of thousands of rpm. A Spindle Cartridge carries the wheel arbor on hybrid ceramic Ball Bearing sets, and a Wheel Balancer trims residual unbalance because at high speed a few grams off-centre would chatter into the finish. The wheel itself is dressed by the CNC Wheel Dresser, a CNC station that runs a Rotary Diamond Disc across the wheel to cut the required form into its face and to re-expose sharp abrasive as the wheel wears.

Wheel and dressing

Profile grinding lives and dies on wheel form. The Profile Grinding Wheel is either a fine vitrified aluminium-oxide wheel or an electroplated CBN wheel for the hardest tool steels. Whatever shape the part needs, the CNC Wheel Dresser grinds the inverse of it into the wheel edge under CNC control. The Dressing Spindle spins the diamond disc while the Dresser Feed Drive feeds the Dresser Slide along the programmed path. Dressing runs in-process: the control re-trues the wheel at set intervals so the form does not drift as abrasive wears away over a long cut.

Measurement and inspection

The Optical / Vision Station station lets the operator check the ground form without removing the part. An Optical Projector casts a magnified silhouette of the part edge onto a Comparator Screen for comparison against an overlay chart, while a Vision Camera feeds the Vision Processor Board for automatic edge measurement against the nominal profile. A collimated Backlight LED Panel backlight gives the crisp edge a measurement needs. Found errors are corrected by re-running the relevant program segment with an offset.

Coolant and thermal control

The Coolant & Filtration system floods the contact zone with chilled fluid. Grinding pumps heat into both wheel and work, and on a precision form heat means distortion, so a Coolant Chiller holds the coolant within about a degree of the machine temperature. A Paper-Band Filter removes the fine swarf that would otherwise glaze the wheel, and the Coolant Pump feeds the Coolant Nozzle outlets aimed at the wheel-work line.

Control and variants

The CNC Control coordinates the four axes, the dressing cycle and the grind sequence from a single part program, with a Servo Amplifier amplifier per axis closing the loop on the glass-scale feedback. The Electrical Cabinet holds the Power Supply units, distribution and protection for the whole machine. Simpler optical profile grinders drop the CNC and the rotary axis: the operator hand-feeds the slides while watching the part outline against a chart on the projector screen. At the top end, machines add a second wheel spindle, automatic wheel changing and on-machine probing so dies and form tools run unattended through a full grind and inspect cycle.