Ultrasonic machining and reconfiguration of braking surfaces
The novel methods, apparatus and reworked rotary braking surface product, for example those exhibited on interior cylindrical braking surfaces of a cast iron brake drum, serve to replace manufacturing defects exhibiting residual tensile stresses and outwardly directed tool marks with smooth compressed braking surfaces in a final manufacturing stage. The plastically deformed surface shape with reduced roughness and surface irregularities furthermore presents improved braking strength above the yield point and approaching the ultimate material strength of the base drum material. An ultrasonic transducer drives individual freely moving impact elements of a set at frequencies up to 55 kHz into the braking surface to effect plastic deformation at surface and sub-surface layers. Physically, the small sized ultrasonic transducer is inserted into a drum cylinder and driven by a lathe producing relative motion between the braking surface and the ultrasonically vibrating impact elements scanning only the braking surface in a readily controlled ultrasonic impact machining cycle for attaining specified braking surface performance.
1. A reworked metallic braking rotor or drum having a braking surface adapted to engage a brake pad or brake shoe, respectively, in dry sliding contact and frictional loading characterized in an initial manufacturing process by presence of residual tensile stresses and tooling mark indentations in said braking surface comprising:
an ultrasonically impacted reworked braking rotor or drum presenting a smoothed, plastically deformed braking surface with a compressed sub-surface layer, thereby introducing increased braking surface contact area.
2. The braking rotor or drum of claim 1 further comprising a depth of said compressed sub-surface layer exceeding the limits of braking wear depth.
3. A reworked metallic braking rotor or drum having a braking surface adapted to engage a brake pad or brake shoe, respectively, in dry sliding contact and frictional loading characterized in an initial manufacturing process by presence of residual tensile stresses and tooling mark indentations in said braking surface comprising:
an ultrasonically reworked braking rotor or drum presenting a smoothed, plastically deformed braking surface with a compressed sub-surface layer introducing increased braking surface contact area, wherein said reworked rotor or drum surface further comprises a machined surface established by ultrasonic impact machining with a set of individual randomly impacting indenter elements wherein random movement of the indenter elements is accompanied by ultrasonic oscillations of the elements upon contact with the drum or the rotor surface and wherein frequency of the random movement is equal to frequency of contact.
4. The braking rotor or drum of claim 1 wherein the smoothed plastically deformed braking surface has a roughness not exceeding 200 micro-inches.
5. A reworked metallic braking rotor or drum having a plastically deformed, smoothed ultrasonically impacted braking surface with a compressed sub-surface layer, wherein said braking surface has a surface roughness of less than 200 micro-inches and presents a uniform surface and sub-surface stress distribution over and to the braking surface to a depth of 12 mm, thereby ensuring uniform deformation eliminating stress concentration at the surface and reducing possibility of crack development.
6. The reworked braking rotor or drum of claim 5 wherein the braking surface is cast iron with a strength exceeding the yield point of the cast iron prior to reworking.
7. The reworked braking rotor or drum of claim 5 wherein the braking surface has a surface of higher contact area for abutment with the brake lining.
8. The reworked braking rotor or drum of claim 5 wherein the braking surface has a smoother surface finish with increased contact surface area with the applied brake lining during operation resulting in less heat build up during brake application providing more efficient braking and a safer application of the brake.