Spring End Grinding Machine

Overview

A spring end grinding machine grinds the two ends of a coil spring flat and square to the spring axis. A compression spring is wound from round wire, so straight off the coiler its ends are sloped and the last coil is open. A spring with sloped ends will not sit upright under load: it leans, it buckles, and it pushes off-centre. Grinding the ends to a plane that is square to the axis is what lets a compression spring seat flat against a flange and carry load down its centreline. This machine does that grinding in volume, taking springs from a coiler and turning out ground springs at 600 to 3,000 pieces an hour depending on their size.

The common form is the double-disc grinder. Two large grinding wheels face each other, one above and one below, with a gap between them set to the finished spring length. Between the wheels turns the Rotary Carrier Disc, a thick plate full of vertical pockets. Each pocket holds one spring standing on end. As the disc indexes slowly round, it carries the springs through the gap, and the Upper Grinding Spindle grinds the top end while the Lower Grinding Spindle grinds the bottom at the same time. One pass through the gap grinds both ends of every spring on the disc.

How it works

Springs are dropped into the disc pockets at the Load/Unload Station, either by hand or from a feeder fed by the coiler. Each pocket has a hardened Spring Pocket Bush sized to the spring outside diameter, so the spring is held upright and square to the two wheel faces rather than leaning. The Disc Index Drive, a Servo Motor through a reduction Gearbox Housing, turns the Carrier Plate at a slow steady speed. The speed sets the dwell, meaning how long each spring spends under the wheels, and that dwell controls how much is ground off. A spring entering the gap is taller than the wheel spacing, so the wheels grind it down until its ends match the gap, then it indexes out the far side at the finished length and a fresh blank takes its place.

Because both wheels run at once and the disc holds many springs, grinding is continuous. While one spring is being finished, the springs behind it in the Carrier Plate are partway through and the ones ahead are done and dropping out. There is no load-grind-unload stop for each part, which is where the throughput comes from.

Grinding spindles and wheels

Each spindle is a heavy job because a grinding wheel 350 to 610 mm across throws a large side load when it bites into hardened spring wire. The Spindle Shaft runs in a preloaded pair of Ball Bearing inside the Spindle Housing, sealed by Oil Seal against coolant. The wheel is clamped between two Wheel Flange and driven by a Spindle Motor of 7.5 to 22 kW through a Drive Belt. The two Grinding Wheel are usually segmented vitrified or resin-bond abrasive, picked for the spring wire grade.

The wheels wear and glaze as they grind, so the machine trues them. The Infeed & Dressing carries each spindle on a slide driven by a Ball Screw and a Servo Motor along a Linear Guide Rail. As the wheel wears and stock comes off, the Infeed Slide feeds the spindle in to hold the gap. The Wheel Dresser sweeps a diamond across the wheel face to true it flat and reopen the grit when it stops cutting. A Length Gauge checks finished free length and tells the infeed when to close in, so the springs stay on length as the wheels shrink.

Carrier and coolant

The grind generates heat, and heat draws the temper out of a spring and burns the ground end. Flood coolant holds that down. The Coolant System system runs a Coolant Pump that pushes filtered coolant through four Coolant Nozzle aimed straight at the wheel-spring contact. Used coolant drains through the Coolant Tray back to the Coolant Tank, where a Coolant Filter strips out the grinding fines before it recirculates. A Pressure Sensor watches delivery pressure so the machine stops if coolant fails, because grinding dry would scorch every spring on the disc.

Grinding also throws a fine abrasive dust and a coolant mist. The Dust Extraction system pulls that off through a Extraction Hood over the grinding zone, drawn by a Extraction Blower through a Extraction Filter. Keeping the zone under slight negative pressure stops the dust coating the machine and the operator. The whole grinding area sits inside Guarding & Interlocks with interlocked doors that drop spindle power if opened while the wheels turn.

Materials, variants and use

The spindle shafts, flanges and disc bushes are hardened steel because they take load and abrasion every cycle. The carrier disc is thick steel, drilled and bushed for one spring size; a different spring diameter or length usually means a change of disc or bushes and a new wheel gap. Smaller machines grind one spring size at a time by hand loading, while production lines run the grinder inline behind a coiler with automatic feed and a Motion Controller holding length to a recipe set at the Touchscreen HMI. End grinders are used by spring makers, automotive suspension and valve-spring suppliers, and anyone making compression springs that have to seat square, which is most of them.