Copper Machining and Fabrication in Burlington, NC: C101, C110, and Tellurium Copper

C101 (oxygen-free high conductivity, OFHC) copper is specified when electrical conductivity must be maximized and resistance to hydrogen embrittlement is required. At 99.99 percent minimum copper purity, C101 achieves conductivity of 101 percent IACS and is the standard for high-quality wire, bus bar, waveguides, and any application where hydrogen atmosphere processing (annealing, brazing) could cause embrittlement in standard C110 material. Burlington shops machining C101 for electrical assembly components manage its gummy cutting behavior with sharp tooling and cutting lubricants rather than flood coolant, since water-based coolants on pure copper can cause contamination concerns in high-conductivity applications. C110 (electrolytic tough pitch, ETP) copper is the most widely available and widely used copper grade. At 99.9 percent minimum copper, its conductivity is 100 percent IACS — effectively identical to C101 for most practical applications. C110 is the default for bus bars, electrical terminals, heat exchangers, and general electrical contacts. It machines similarly to C101: sticky chips that prefer sharp high-speed steel or uncoated carbide tooling with positive rake angles and light cutting fluid. Burlington screw machine shops with Swiss-style turning centers produce high volumes of C110 connector pins, standoffs, and contact bodies with short cycle times. Tellurium copper (C145) is the machinist's preference within the copper family. The addition of 0.4 to 0.7 percent tellurium transforms copper's machining behavior dramatically: chips become short and break cleanly rather than forming long stringy ropes, and surface finish on turned parts improves significantly. Electrical conductivity drops slightly to about 90 to 93 percent IACS, which is acceptable for most connector and switch contact applications. Burlington precision CNC shops producing close-tolerance copper components in meaningful quantities frequently negotiate with customers to allow C145 as an alternate to C110 because the productivity gain is substantial — reduced cycle time, better surface finish, and longer tool life more than offset the modest material cost premium.

Pure copper and near-pure copper alloys present a specific set of machining challenges that distinguish them from copper-zinc brasses and copper-tin bronzes. The primary issue is that copper's high ductility and relatively low shear strength cause material to smear onto the cutting tool face, building up a deposited edge that changes the effective cutting geometry and causes tearing rather than clean shearing. This built-up edge problem produces rough surfaces, tight tolerance drift, and rapid edge degradation. Burlington shops mitigate built-up edge on copper through several mechanisms. Sharp edges are essential: worn or honed carbide inserts that work well on steel perform poorly on copper. Positive-rake uncoated carbide or high-speed steel tooling with polished chip faces reduces the tendency for material adhesion. Cutting speed selection matters — too slow allows more time for material to weld onto the tool face, while moderate to high surface speeds (300 to 600 SFM for turning C110 with HSS tooling) create enough heat at the interface to prevent cold-welding. Sulfurized cutting oils and light mineral oils work better than water-soluble coolants for copper surface finish because they provide lubrication at the chip-tool interface without the contamination risk that water-based fluids can introduce for electrical-grade parts. For tight-tolerance bores in copper connector bodies, Burlington shops use multi-flute reamers with sharp, polished flutes to achieve consistent diameter and roundness. Broached square and hex features in copper must be cut in a single pass to avoid the work-hardening that accumulates with multiple light passes, so broach sizing is critical to get right before cutting starts.

Beyond machining, Burlington-area fabrication shops work copper in several other forms. Sheet copper C110 bends readily on press brakes to Ra 90-degree and tighter angles without cracking when bend radii respect the minimum bend radius tables for the temper. Bus bars and heat-spreader plates are cut from plate or sheet on CNC plasma or waterjet cutting equipment, then formed and drilled to drawing. The thermal conductivity of copper (about 226 BTU/hr-ft-F for C110) makes it the material of choice for heat spreaders and thermal interface components in power electronics and heavy switching gear, applications that are growing as Burlington's regional industrial customer base adds electrification content to vehicles and equipment. Brazing is the preferred joining method for copper assemblies requiring a permanent, thermally and electrically conductive joint. Silver-alloy brazing filler metals (such as AWS BAg-7 or BAg-28) wet copper surfaces readily and flow at temperatures between 1145 and 1400 degrees Fahrenheit, well below copper's 1981 degree Fahrenheit melting point. Burlington shops with induction brazing or torch brazing capabilities can produce copper heat exchanger cores, fluid manifolds, and bus bar assemblies with consistent, leak-tested joints. Surface treatment of copper parts depends on the end application. Electroplated tin or nickel over copper is standard for solderability-critical electrical contacts, providing a solderable surface that resists oxidation. Silver plating over copper (common base layer of nickel strike first) is used for high-frequency RF contacts and bus bars where even lower surface resistance matters. Bare copper parts destined for atmospheric exposure should be specified with a protective coating or bagged in VCI packaging to prevent the oxide layer that forms within days in humid industrial environments.