When the forge, the CNC cell, the thread roller, and the heat-treat furnace all report to the same production manager, quality happens at the handoffs, not despite them.
Each process stage is gated by in-process inspection. A part does not advance until the previous gate is signed off. Below is how we build a superalloy bolt.
Superalloy billets are heated to 1,050-1,200°C and forged under 2,500 tons of closed-die force. This breaks down the as-cast dendritic structure from VIM+ESR/VAR melting, producing a uniform, fine-grained wrought microstructure. Forging ratio is controlled to a minimum 4:1 reduction to meet ASTM B564 / AMS 5662 grain-size requirements. Every billet is thermocouple-monitored with a 5-second logging interval, and under-forged parts are scrapped before they reach machining.
For production volumes above 5,000 pieces, cold heading displaces material at room temperature to form the bolt head and shank geometry in a single stroke. This preserves the wrought grain flow from forging: the grain lines follow the bolt contour without interruption, unlike machined heads where grain flow is cut. Our multi-station cold headers support M6-M24 diameters at rates up to 180 pieces per minute, with in-die load monitoring that rejects any stroke outside the control band.
For larger diameters (M30-M100), complex geometries, or low-volume orders where cold-heading tooling is uneconomical, we use 5-axis CNC turning centers with live tooling. All critical dimensions (thread pitch diameter, under-head radius, shank diameter, and bearing surface flatness) are machined to ±0.01 mm. In-process probing on every 10th part verifies conformance; a tool-wear compensation algorithm adjusts offsets automatically. Programming is CAM-driven from customer STEP files with full revision control.
Threads are cold-rolled after heat treatment (for roll-after-HT grades) or before (for cut-thread grades). Rolling compresses the thread root, introducing a residual compressive stress layer that improves fatigue life by 30-50% over cut threads. Root radii are 100% optically inspected against ASME B1.1 Class 2A/3A or ISO 965/6g-6H standards. Thread profile is verified on a Zeiss CONTURA G2 CMM with a 0.5-micron scanning probe, and every thread form parameter (pitch diameter, major dia, minor dia, root radius, flank angle) is reported.
Every heat-treatment cycle is furnace-mapped with at least three load thermocouples and logged to the heat number. Solution annealing (typically 980-1,150°C followed by rapid quench), aging (720-760°C for precipitation-hardening grades), and stress relief are performed in computer-controlled pit furnaces and vacuum furnaces. Furnace uniformity surveys to AMS 2750F Class 2 (±6°C) are conducted quarterly. Post-HT hardness testing (Rockwell and Brinell) on every lot ensures the specified mechanical properties are met before the parts move to final inspection.
A bolt that changes hands four times between forging and final inspection accumulates four sets of paperwork, four shipping delays, and four opportunities for a heat number to get mixed up. When the forging crew and the CNC operator share the same shift meeting, a surface defect spotted during machining is traced back to forging parameters before lunch. That speed of feedback, from finished dimension back to raw process parameter, is what vertical integration buys. It cannot be outsourced.
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