# Heat Treat Distortion and Scrap in Gear Manufacturing: How to Reduce It > Source: https://netray.co/resources/heat-treat-distortion-gear-scrap-how-to-reduce > Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems. > Section: Knowledge Base ## Short answer Reduce heat treat distortion and scrap on carburized gears: steel, quench, fixturing, grind stock and the data gear makers should track by lot and furnace load. ## Category ai-automation ## Content **Intro:** Heat treat distortion in gears is the change in lead, profile, pitch and roundness that happens when a part is carburized and quenched, and it is a major source of scrap and rework at US gear shops. You reduce it by controlling the inputs: steel chemistry and hardenability, prior machining stress, load pattern and fixturing, quench method, and the stock you leave for finishing. Shops that record furnace load, quench, and before-and-after measurements by part number can predict movement and cut scrap instead of discovering it at the grinder. **Sections:** #### What Actually Moves in a Carburized Gear **Body:** Carburizing adds carbon to the surface, and quenching transforms it, causing volume change and thermal stress. The result is predictable in kind and variable in amount: lead (helix) error changes, involute profile shifts, tooth thickness grows, bores go out of round, and thin-webbed or large-diameter gears can dish or cone. Ring gears and long shafts tend to bow. The amount depends on geometry, steel batch hardenability (8620, 4320, 9310, 16MnCr5), residual stress from machining or forging, and how the part sat in the load. Because it varies, the right goal is a stable process with known movement, not zero movement. #### Controls That Reduce Distortion **Body:** Start upstream. Normalize or stress relieve forgings and heavy rough cuts so machining stress is not released in the furnace. Keep hardenability bands tight with the mill cert and a Jominy requirement where it matters. Choose load pattern and fixturing consistently, and use press quenching, plug or ring dies on parts that need roundness. Select quench oil temperature and agitation, or high-pressure gas quench with low-pressure vacuum carburizing, based on the part. Then lock the parameters by part number. **Bullets:** - Stress relieve and rough-to-finish machining sequence - Tight steel hardenability and chemistry limits on the PO - Consistent loading, fixture or press quench by part family - Quench oil temperature, agitation and cycle recorded per load #### Set Grind Stock From Data, Not Habit **Body:** Many shops leave a standard amount of grind stock and hope. Better practice is to measure a sample of each lot before and after heat treat (lead, profile, tooth thickness, bore size and runout), record the movement against the furnace load and quench, and set stock allowances per part number from those averages and ranges. Too little stock leaves unclean teeth; too much extends the grind cycle and raises grinding burn risk. Where parts are heat treated outside, require the shop to report load and cycle data and case depth results, and keep them with the lot in your system. #### Track Scrap by Cause, Not Just by Count **Body:** A scrap number of 6 percent tells you little. A reason-coded record tells you what to fix: out-of-round bores from quench, lead error above grind capability, case depth short, soft spots, cracks, or grinding burn. Record the heat treat vendor or furnace, the load, steel heat number and the operation where the defect was found. In ERP terms this means NCR or scrap transactions with reason codes that are enforced at the shop floor, linked to lot and routing. Without that, every investigation starts as a manual search through travelers and spreadsheets. #### Using AI to Find Patterns in Distortion and Scrap **Body:** A private AI layer over ERP, quality records and heat treat certs can answer questions an engineer would otherwise dig for: which part families show lead error after a given furnace, how scrap changed after a quench oil change, which steel heats correlate with out-of-round bores. It can also read scanned heat treat reports and tie case depth and hardness to the lot. It will not fix a process, and it is not worth building if you only heat treat a few part numbers or do not capture reason codes. The value is turning records you already keep into answers in minutes. **Cta:** Talk to Netray about connecting heat treat certs, NCRs and inspection data so scrap by cause and furnace load can be asked in plain English, privately. **Faq:** #### Why do carburized gears go out of round? **Answer:** Quenching transforms the case unevenly and releases residual stress, so rings and bores change shape. Large thin sections, uneven wall thickness, machining stress, and the way the part sits in the load all contribute. Press or plug quenching and consistent fixturing help, and so does stress relief before heat treat. #### How much of gear scrap comes from heat treat? **Answer:** It varies by shop and part family, so measure it. Reason-coded scrap records by operation show whether defects are found after heat treat, at grinding or at final inspection. Without reason codes, shops often blame heat treat when machining stress or grinding practice is the cause. #### Can we predict distortion before heat treat? **Answer:** Partly. Simulation software exists for heat treat, but most shops get reliable results from their own before-and-after measurements by part number, steel and load. Recording that movement and using it to set grind stock and fixturing gives a practical prediction without special software. ## Related Slugs - heat-treatment-and-testing-costs-in-forging-quotes - nadcap-heat-treat-audit-preparation-small-shop - spc-integration-erp-quality - how-to-estimate-cost-of-a-custom-gear ## Search terms heat treat distortion gears, carburizing distortion gear scrap, reduce gear heat treat scrap, gear lead error after heat treat, gear grind stock after carburizing, press quench gears --- Talk to an engineer: https://netray.co/contact?intent=erp_ai | Machine catalog: https://netray.co/agent/catalog.json