When I first started my forging shop 12 years ago, I thought quality control was just “checking the parts before they leave the loading dock.” I quickly learned that was only a tiny piece of the puzzle. Forging is a process where we heat metal (usually steel, aluminum, or brass) above its recrystallization temperature and use a hammer or press to shape it, locking in strength that cast parts can’t match. But that strength only matters if every step—from selecting raw material to shipping the finished part—stays tight. Today, my team runs 12 specific quality control checks, no shortcuts, because our customers rely on us for parts that hold up in construction, aerospace, and farm equipment. Let me walk you through what we actually do, not some textbook fluff. Forging
First, we start with the raw material. I’ve seen too forges skip this step and end up with parts that crack mid-process because the bar stock had hidden defects. When a steel supplier drops off a delivery, our quality lead, Maria, pulls a random bar every time, no exceptions. She uses a portable spectrometer to test the chemical composition on the spot—we need precise carbon, manganese, and chromium levels per customer specs. Last year, we caught a batch where the supplier had mixed in low-grade steel with 0.12% less carbon than we ordered. That’s a small number, but it would have made the finished part 20% weaker, dangerous for a customer building bridge supports. If the spec doesn’t match, the entire load goes back immediately—no arguments, even if the supplier offers a discount. We also do a visual check for surface cracks or dents on the raw bar, because those small marks can expand during forging and ruin the whole part.
Next, once the metal is heated and in the die, we track every move. Forging requires consistent temperature—if it’s too cold, the metal won’t flow properly and will have internal voids; too hot, and it becomes brittle. We use infrared thermometers at three points: when the metal enters the furnace, when it’s transferred to the press, and right before we apply force. A few months back, our furnace’s sensor glitched, and a batch of steel came out 50 degrees too cool. We caught it mid-shift because the thermometer reading was off, pulled the parts before we finished forging them, and reheated the metal correctly. If we’d forged them as-is, those parts would have failed a bend test later, costing the customer thousands in downtime. We also use die temperature gauges—dies expand as they heat up, so we adjust the press gap to maintain consistent shape, which stops parts from being undersized or having uneven walls.
Then comes the in-process dimensional checks, done right after forging and before trimming excess metal (called flash). We don’t wait until everything is done to measure—we check every part’s key dimensions as it comes out of the die. My team uses digital calipers for small parts and coordinate measuring machines (CMMs) for large ones, like 10-foot-long crane hooks. Last quarter, a new operator set the die gap wrong for a run of hydraulic fittings. We caught the first 5 parts were 0.2mm too narrow, fixed the gap, and only had to rework 5 parts instead of 500. That mistake taught me: in-process checks aren’t about policing—they’re about catching small errors before they turn into big ones. We also use dye penetrant testing on every forged part at this stage. It’s simple: spray a red dye on the part, wipe it off, and apply a developer. Any tiny surface cracks (so small you can’t see with the naked eye) will pull the dye up into a line on the developer. We discard those parts—even if the crack is 0.1mm long, it’s a failure.
After trimming, we move to heat treatment, another make-or-break step. Forging hardens metal, but we need to adjust its hardness to match what the part is designed for. We use quenching (cooling rapidly in oil or water) and tempering (heating again to reduce brittleness) under strict time and temperature controls. We track each batch’s heat treatment log—sensor readings from the oven, time in quenching oil, tempering temperature—every single number. We also test a “test coupon” that’s forged from the same raw material, same batch, same heat as the production parts. We cut the coupon in half, polish it, and do a Rockwell hardness test. If the hardness is off, we re-treat the whole batch. A few years ago, a customer requested a gear shaft for a wind turbine that needed HRC 35 hardness. Our coupon came out at HRC 30, so we adjusted the tempering time and got it exactly right. That gear shaft is now spinning in a turbine in Iowa, and they’ve never had an issue.
Once heat treatment is done, we do non-destructive testing (NDT) to find internal flaws that aren’t on the surface. Ultrasonic testing is our go-to here: we run a sound wave over the part, and a machine picks up any internal voids, inclusions, or cracks. These flaws are invisible but can make a part break under stress. Last year, we tested a run of agricultural plow shares and found 8% of them had small internal voids near the center. We pulled them all, re-forged those parts from the same batch (we hadn’t finished trimming them yet), and avoided sending bad parts to a farmer who depends on those plows for planting season. We also do magnetic particle testing for ferromagnetic metals like steel: magnetize the part, spray iron particles, and particles will line up over any internal or surface cracks. It’s faster than dye penetrant for steel, and we run every part for aerospace or construction through this test.
Next is final dimensional inspection, when the parts are cleaned and ready for finishing. We use CMMs for complex parts, like aerospace turbine blades, which have curved surfaces and tight tolerances (sometimes within 0.05mm, thinner than a human hair). For simple parts, like bolts, we use go/no-go gauges—if the bolt fits the go gauge and won’t fit the no-go gauge, it passes. We also check surface finish with a profilometer, which measures how smooth the part is. A part with a rough surface will wear out faster, so we keep our Ra value (roughness average) under 1.6 microns for almost all parts. Last month, a customer ordered valve stems for a car engine and required a Ra under 0.8 microns. Our profilometer showed the first batch was at 0.9, so we sent them through a secondary grinding step to get it right, instead of letting them use a part that would wear out too quickly.
We also do destructive testing for a small percentage of parts, usually the first run of a new customer or a new part design. We take a test part from a batch and cut it apart, examining the grain structure under a microscope. A good forged part has a grain structure that flows with the part’s shape, not against it—this is what gives it strength. If the grain is straight or cracked, that means the forging press didn’t apply enough force, and we adjust the press pressure for the next run. We also do tensile testing: pull a test part until it breaks, measuring how much force it takes, its yield strength, and elongation. For example, our farm equipment parts need to have a tensile strength of at least 600 MPa. Last year, a test part broke at 550 MPa, so we increased the forging force by 10% for that batch, and the tensile strength hit 620 MPa, which was perfect.
Packaging and shipping are the final checks, and they matter too. A good part damaged in shipping is as bad as a bad part. We wrap small parts in anti-rust paper and put them in cardboard boxes with foam inserts. For large parts, like crane hooks, we use steel crates lined with foam and add moisture-absorbing packets. We also label every box with the part number, batch number, and inspection results, so if a customer has a problem, we can trace it all the way back to the raw material. A customer once called us saying they had a broken gear shaft, and we pulled our batch records: the raw material was from mill X, forged on shift 3, tested with a hardness of HRC 35, and the grain structure was perfect. Turns out the customer had installed it incorrectly, not that the part was bad. That traceability is worth its weight in gold.
I know some forges cut corners on quality control to save money, but that’s not how we do business. Our customers come back because they know every part we ship has been checked 10 times, not once. If you’re a manufacturer needing forged parts that you can trust, let’s talk. We can work with your design, run tests on the first prototype, and make sure every batch meets your exact specs. No surprises, no shortcuts.
Metal Parts References
- John, C. (2018). Forging Technology: Principles and Quality Control. Industrial Press.
- ASM International. (2020). Non-Destructive Testing Handbook, 5th Edition. Materials Park, OH.
- Davis, J. R. (2005). Metallurgy of Forging and Quality Assurance. ASM International.
- International Organization for Standardization. (2019). ISO 10243: Forgings – Quality Control Systems. Geneva, Switzerland.
Taiwan Hardware Corp.
Taiwan Hardware Corp. is one of the most experienced forging manufacturers and suppliers in Taiwan, featured by quality products and good service. Please feel free to buy ISO certified forging from our factory. For customized service and OEM service, contact us now.
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