1. Fundamental Principle of Profiling-Envelope Grinding
Brake linings are machined with inner arc positioning, taking the inner circular arc of the brake linings as the positioning datum and the outer circular arc as the machining target. The inner arc of the brake linings is fully fitted onto the outer cylindrical surface of a special hub fixture and clamped securely. A servo motor drives the hub together with the brake linings to perform rotary motion around the central axis of the hub. A high-speed rotating grinding wheel radially advances toward the workpiece, and the cutting edges of the grinding wheel contact the outer arc of the brake linings. Excess material of the friction lining is removed via relative motion to envelope and form an outer circular arc surface with qualified radius.
Geometric Logic
The center of the hub fixture serves as the theoretical center of the finished brake linings outer arc. As the brake linings rotates circumferentially with the fixture, once the grinding wheel completes radial feed positioning, one full rotation of the workpiece enables the grinding wheel to conduct one complete envelope cut over the entire outer arc. Multiple iterative rotations gradually remove machining allowance to yield an outer arc curved surface that meets drawing specifications in terms of curvature radius, arc length and roundness.
This principle is essentially form-envelope grinding, distinct from conventional cylindrical outer surface grinding. Machining quality heavily relies on two key factors:
① Zero-clearance fitting between the brake linings inner arc and the hub fixture;
② Stable rotary center and accurate feed positioning of the grinding wheel.
Any clearance between the workpiece and fixture during grinding will result in over-grinded edges and insufficient grinding at the middle section, causing uneven thickness distribution on the finished arc surface and scrapping of the brake linings.
For non-uniform-thickness Brake linings (with inconsistent thickness at both ends of the shoe), the equipment pre-detects the thickness orientation of the workpiece and matches the grinding feed logic via program. Variable allowance removal is realized on a single outer arc surface to ensure continuous and smooth finished outer arc profile, accommodating the production requirements of asymmetric commercial vehicle brake linings.
2. Complete Machining Process Flow
(1) Loading and Attitude Correction
Semi-finished brake linings are conveyed to the feeding station. Sensors detect workpiece attitude; non-uniform-thickness shoes undergo rotary correction to align thick and thin ends in accordance with machining program requirements. A pusher mechanism transfers the workpiece to the positioning hub station.
(2) Datum Positioning and Clamping
The brake linings inner arc is tightly attached to the outer surface of the hub fixture, and a pneumatic pressing block clamps the brake shoe to eliminate workpiece warpage and clearance, completing positioning and fixturing. A sensor signal verifies proper workpiece seating.
Rough Grinding Stage
A servo-driven grinding head rapidly advances the grinding wheel toward the workpiece for rough machining with a large grinding depth to remove most machining allowance quickly and correct major profile deviations of semi-finished parts. High-flow water cooling dissipates grinding heat.
(3) Finish Grinding Stage
Upon completion of rough grinding, the grinding wheel retracts and switches to a micro finish grinding feed rate with reduced cutting depth. The workpiece continues rotating for multiple revolutions to remove surface machining marks microscopically, calibrate roundness and profile tolerance, and achieve an outer arc radius dimension complying with drawing standards. Atomized cooling is adopted in finish grinding to mitigate water absorption and moisture risk of the friction lining.
(4) Dimension Compensation and Spark-out Finishing
The equipment automatically corrects the X-axis zero point based on grinding wheel wear compensation parameters to offset dimension drift induced by wheel abrasion. The workpiece rotates for several revolutions under spark-out grinding to reduce surface waviness.
(5) Clamp Release and Unloading
After grinding finishes, the grinding head retracts to the safe position; the clamping cylinder loosens. A stripping mechanism detaches the brake linings from the hub fixture, which is then conveyed to the discharge station via a turnover mechanism, concluding the single-piece machining cycle. The equipment proceeds to the machining cycle for the next workpiece.