Aluminum Bronze C95400: Bearing and Bushing Tooling

Aluminum Bronze C95400: Bearing and Bushing Tooling Guide

Aluminum Bronze C95400 (CDA 954, also known as CuAl10Fe3 or BS 1400 AB2) is the most widely specified aluminum bronze for bearing, bushing, and wear plate applications. Its combination of high load capacity (690 MPa compressive yield), excellent wear resistance, and corrosion resistance in seawater and industrial atmospheres makes it indispensable in heavy machinery, marine propulsion, and oilfield equipment. While aluminum bronze is softer and more ductile than steel, C95400 presents specific machining challenges related to built-up edge, chip control, and surface finish that require dedicated tooling approaches.

Material Properties

• Composition: 82% Cu, 10.5% Al, 3.5% Fe, 1% Ni, 1% Mn
• Hardness: 170-210 HB (as cast), 200-240 HB (heat treated)
• UTS: 580-690 MPa, yield: 290-380 MPa, elongation: 12-18%
• Thermal conductivity: 59 W/m-K (significantly higher than steel, aiding heat dissipation)
• Machinability rating: 55-70% of B1112

C95400 machines more easily than steel in terms of cutting forces but presents unique challenges: severe built-up edge on uncoated carbide, long stringy chips, and a tendency for the iron-rich kappa phase to cause localized abrasive wear on insert coatings.

Key Machining Challenges

1. Built-up edge (BUE): The high copper content creates strong chemical adhesion between the workpiece and uncoated or polished carbide inserts. Material builds up on the rake face, eventually tearing away and degrading surface finish. Coated inserts with low-friction surfaces are essential.
2. Chip control: C95400 produces long, continuous, stringy chips that wrap around the workpiece. These chips are hot, sharp, and difficult to break without dedicated chipbreaker geometries.
3. Kappa phase abrasion: The iron-rich kappa phase precipitates (Fe3Al) embedded in the copper matrix are harder than the surrounding alpha phase and cause localized flank wear, particularly at higher cutting speeds.
4. Surface tearing: Worn inserts or incorrect geometry can tear the soft alpha phase around hard kappa particles, creating pits and roughness on machined surfaces. This is unacceptable for bearing ID surfaces that must maintain oil film contact.

Insert Grade Selection

ISO Application Group: N (Non-Ferrous) or M (Stainless/Superalloy for tougher grades)

Roughing:

• Sandvik H13A (uncoated carbide, fine-grain) or Sandvik GC1025 (PVD TiB2-coated for non-ferrous). CNMG 120412 with polished rake face and sharp edge (0.01mm hone). TiB2 coating provides extremely low friction and excellent BUE resistance on copper alloys.
• Kennametal K68 (uncoated fine-grain carbide, N10 equivalent). Proven performer on aluminum bronze.
• Mitsubishi NX2525 (PVD TiAlN on tough substrate) for interrupted cuts or cast surfaces with scale.

Finishing:

• Sandvik H10F (uncoated mirror-polish carbide) or CVD diamond (PCD) inserts for bearing bore finishing. PCD delivers Ra below 0.4 micrometers with virtually unlimited tool life in continuous cutting.
• Kennametal KD1400 (PCD-tipped insert) for high-volume finishing operations.
• Sumitomo DA1000 (CVD single-crystal diamond) for mirror finish requirements on thrust face surfaces.

Key principle: Use polished or TiB2-coated inserts for roughing to prevent BUE. Reserve PCD for finishing operations where surface finish and dimensional accuracy are critical. Avoid standard TiN, TiAlN, or Al2O3 coatings as they can react chemically with copper at cutting temperatures.

Cutting Parameters

Turning – C95400 (As Cast):

• Vc: 120-250 m/min (uncoated/polished carbide), 300-600 m/min (PCD finishing)
• fn: 0.20-0.40 mm/rev roughing, 0.08-0.20 mm/rev finishing
• ap: 2.0-5.0 mm roughing, 0.3-1.0 mm finishing
• Coolant: Flood emulsion at 6-8% concentration, 30-50 bar. Water-soluble coolant preferred to avoid oil staining on bearing surfaces.
• Tool life: 60-120 minutes per edge (polished carbide at 180 m/min), 500+ minutes (PCD finishing)

Turning – C95400 (Heat Treated, 220 HB):

• Reduce speeds by 15-20%: Vc 100-200 m/min (carbide), 250-500 m/min (PCD)
• Same feed rates and depths as as-cast condition
• Expect 20-30% shorter tool life due to harder kappa phase distribution

Milling

• 4-5 flute solid carbide end mills, uncoated polished or TiB2 coated, 12-25mm diameter
• Vc: 100-200 m/min
• fz: 0.06-0.12 mm/tooth
• Radial engagement: 50-70% diameter (peripheral), 8-12% (trochoidal slotting)
• Axial depth: 0.8-1.5 x diameter
• Flood coolant directed at the cut zone to prevent chip rewelding

Indexable face milling: SEKN 1203 or APKT 1604 inserts in Sandvik H13A or Kennametal K68 grade. Vc: 120-220 m/min, fz: 0.15-0.30 mm/tooth. Positive-rake cutter bodies improve surface finish on bearing faces.

Boring – Bearing ID Surfaces

The internal bore of a bushing or bearing is the most critical surface. It must maintain a precise diameter (tolerance H7 or H8) and surface finish (Ra 0.4-1.0 micrometers) for proper hydrodynamic oil film formation:

1. Use PCD-tipped boring inserts for finishing. Kennametal KD1400 or Sandvik CD10 provide the surface finish and dimensional accuracy required.
2. Vc: 300-500 m/min (PCD), fn: 0.06-0.15 mm/rev, ap: 0.1-0.5mm
3. Use rigid boring bars with minimum overhang. Anti-vibration bars for L/D exceeding 4:1.
4. Target Ra 0.4-0.8 micrometers with a uniform lay pattern parallel to the bore axis.
5. Measure bore diameter with air gauging or bore micrometers. C95400’s high thermal conductivity means the bore may contract as it cools after machining. Allow thermal stabilization time before final measurement.

Drilling and Tapping

Drilling:

• HSS-E or solid carbide drills, 118-135 deg point, polished flutes
• Vc: 40-80 m/min, fn: 0.08-0.18 mm/rev (8-15mm drills)
• Peck depth: 3-5 x diameter (C95400 chips are less problematic in drilling than turning)
• Flood coolant through tool preferred

Tapping:

• Spiral-flute HSS taps with TiN or polished flute surface
• Speed: 10-20 m/min
• Form tapping is highly effective in C95400. The ductile alpha matrix forms threads with excellent strength and no chip evacuation issues.
• Use TiCN-coated form taps for extended tool life in production tapping.

Bearing and Bushing Production Workflow

Typical production sequence for C95400 bearings and bushings:

1. Centrifugal casting: Near-net-shape cylindrical blanks with 2-4mm machining allowance per surface.
2. Rough turning (OD and faces): Polish carbide inserts at Vc 150-200 m/min. Remove casting skin and achieve concentricity.
3. Rough boring (ID): Open the bore to within 0.5mm of final diameter. Use polished carbide at Vc 120-180 m/min.
4. Grooving: Cut oil grooves (spiral or axial) using N-style grooving inserts with polished rake. Groove width typically 2-4mm.
5. Finish boring (ID): PCD insert at Vc 350-500 m/min. Achieve H7/H8 tolerance and Ra 0.4-0.8 micrometers.
6. Deburring: Remove all sharp edges. Chamfer both bore ends 0.5-1.0mm x 45 deg to facilitate assembly.
7. Inspection: Bore diameter, OD, length, surface finish, and visual inspection for kappa phase pull-out or surface tears.

Cost Optimization

C95400 machining is generally cost-effective compared to steel and superalloy programs. Key optimization factors:

• PCD finishing inserts pay for themselves within 5-10 parts due to virtually unlimited tool life and eliminated insert change downtime.
• Dry machining is feasible for roughing if dust extraction is available, eliminating coolant costs.
• C95400 turnings (chips) have high scrap value ($4-8/kg) and should be collected separately from ferrous chips for recycling.
• Centrifugal casting produces near-net shapes that minimize roughing time. Work with foundries to reduce machining allowances where possible.