Factory Acceptance Testing (FAT): What to Test Before CNC Shipment, Test Pieces, and Who Attends

What Decision This Actually Supports

Factory Acceptance Testing (FAT) is often framed as a "pre-shipment inspection" for custom or capital equipment like CNC machines. But the real decision it enables is far more consequential: will this machine perform reliably enough to meet your production requirements for its intended use case, without requiring costly, unplanned rework or modifications after delivery?

This question is critical because CNC machines are high-investment assets (often $50,000 to $500,000+) that are integrated into production lines, supply chains, and quality systems. A machine that fails FAT is returned or repaired before it leaves the manufacturer’s facility, avoiding the far higher costs of troubleshooting, disassembling, and shipping a defective machine across borders. FAT also serves as a formal handoff point: it is the last opportunity for both buyer and seller to agree that the machine meets all contractual specifications before ownership or risk transfers.

How It Works in Practice

FAT is a structured, pre-agreed test sequence conducted at the machine builder’s factory (e.g., Gree CNC’s production facility) before shipment. It is not a random inspection; every test is tied to a pre-defined requirement in the purchase contract. Below is a breakdown of its mechanics, typical timelines, and roles:

Core Test Categories

FAT for CNC machines covers three broad areas, with tests tailored to the machine’s model and the buyer’s production needs:

1. Specification Verification: Confirming the machine’s built-in parameters match the contract. This includes:

   • Travel ranges (e.g., the GA-DV750 vertical machining center’s X/Y/Z travel of 700/500/300 mm)
   • Spindle performance (max speed, power, torque; e.g., the GA-MV856’s 12,000 rpm max spindle speed and 95.5 Nm peak torque)
   • Tool system metrics (tool capacity, tool change time; e.g., the GA-VT540 drill/tap center’s 1.2 s tool change time)
   • Accuracy and repeatability (positioning accuracy: the ability to move to a specified coordinate; repeatability: the ability to return to the same coordinate consistently; e.g., the GA-UHD500 5-axis machining center’s 0.006 mm positioning accuracy)
   • Control system functionality (PLC logic, safety interlocks, HMI operation)

2. Functional Testing: Validating that all systems operate as intended. This includes:

   • Power-up and shutdown sequences
   • Axis movement and rapid traverse (e.g., the GA-GF2755 gantry machining center’s 80 m/min X-axis rapid traverse)
   • Spindle start/stop, speed control, and load testing
   • Tool changer operation (full cycle testing of all tools in the magazine)
   • Coolant, chip management, and lubrication system performance
   • Safety systems (emergency stop, door interlocks, overload protection)

3. Performance Testing with Test Pieces: The most critical part of FAT for production-focused buyers. Test pieces are custom-machined parts designed to replicate the buyer’s actual production requirements. They are used to validate that the machine can produce parts to the required tolerance, surface finish, and cycle time.

Typical FAT Timeline

FAT timelines vary by machine complexity:

• Small machines (e.g., GA-VT540 drill/tap center): 1–2 days
• Mid-sized machines (e.g., GA-MV856 vertical machining center): 2–3 days
• Large/complex machines (e.g., GA-FMB3020D 5-axis gantry machining center, GA-MVD2560 dual-spindle vertical machining center): 3–5 days

Who Attends FAT

FAT requires cross-functional representation from both the buyer and seller to ensure alignment and accountability:

Where the Money or Risk Is

FAT is designed to mitigate two major cost drivers: post-shipment rework and production downtime. Below is a breakdown of the financial impact of skipping or failing FAT:

Cost of FAT vs. Cost of Failure

Key Risk Drivers

1. Inaccurate Test Pieces: If test pieces do not replicate the buyer’s actual production requirements, FAT results are meaningless. For example, a test piece for a GA-DV750 vertical machining center that does not include the 300 mm Z-axis travel required for the buyer’s parts will not reveal if the machine can handle the full depth of cut needed.
2. Unclear Acceptance Criteria: If the purchase contract does not specify exact test parameters (e.g., "the GA-MV856 must produce the test piece within ±0.01 mm tolerance"), disputes can arise over whether the machine passes.
3. Delayed FAT: Postponing FAT to speed up shipment increases the risk of shipping a defective machine, as issues are not identified before the machine leaves the factory.

Common Mistakes

Even experienced manufacturers make costly errors during FAT. Below are the most frequent and their impacts:

1. Skipping Test Piece Performance Testing Many buyers prioritize specification verification over test piece testing, assuming that if the machine’s specs match the contract, it will produce good parts. This is a mistake: machine performance is the result of the interaction between the machine, tooling, material, and part design. For example, a GA-VT540 drill/tap center with a 0.006 mm positioning accuracy may still produce out-of-tolerance holes if the test piece does not replicate the material hardness or hole depth of the buyer’s production parts.

2. Using Generic Test Pieces Generic test pieces (e.g., a standard cube or cylinder) do not replicate the specific challenges of the buyer’s parts, such as tight tolerances on complex features, deep cuts, or high surface finish requirements. For example, a generic test piece for a GA-FA500 5-axis machining center will not reveal if the machine can maintain tolerance on a 5-axis contoured part.

3. Not Validating Cycle Time Buyers often focus on part quality and ignore cycle time during FAT. If the machine’s cycle time is 20% longer than required, it will not meet production volume targets. For example, a GA-MVD2560 dual-spindle vertical machining center that is designed to double output may have a longer tool change time for one spindle, resulting in a 15% longer cycle time than expected.

4. Failing to Document All Tests Verbal sign-off on FAT results is risky. If a machine fails after shipment, undocumented test results make it difficult to prove that the issue existed before delivery. For example, if a GA-GF2517 gantry machining center’s spindle fails 3 months after delivery, the buyer may be responsible for repair costs if there is no documented proof that the spindle failed during FAT.

5. Sending Unqualified Personnel to FAT Sending personnel who are not familiar with the machine or the buyer’s production requirements (e.g., a project manager who has no CNC experience) can result in missed issues. For example, an unqualified inspector may not notice that a GA-UHD500’s 5-axis positioning accuracy is out of spec, leading to production problems after delivery.

Honest Limitations

FAT is a powerful tool, but it has important limitations that buyers must understand:

1. FAT Does Not Test Long-Term Reliability FAT is a short-term test (1–5 days) that does not simulate months or years of production. It cannot predict issues that arise from wear and tear, such as spindle bearing failure, tool changer wear, or axis backlash over time. For example, a GA-HT6065 CNC lathe may pass FAT with no issues, but its spindle may fail after 6 months of heavy use due to a manufacturing defect that was not detectable in a short test.

2. FAT Results Are Dependent on Test Conditions FAT is conducted at the manufacturer’s factory, which has controlled environmental conditions (temperature, humidity) and consistent power supply. These conditions may not match the buyer’s facility. For example, a GA-DV750 that passes FAT with a 0.003 mm positioning accuracy may have reduced accuracy in a buyer’s facility with temperature fluctuations of 5°C or more.

3. FAT Cannot Fix Design Flaws FAT can identify manufacturing defects (e.g., a misaligned axis, a faulty tool changer), but it cannot fix design flaws in the machine. For example, if a GA-VT445 drill/tap center’s spindle is not powerful enough to drill the buyer’s required holes, FAT will reveal this issue, but the machine cannot be modified to increase spindle power without a major redesign.

4. FAT Requires Pre-Agreed Test Plans FAT is only effective if the test plan is agreed upon before the machine is built. If the buyer changes their production requirements after the machine is built, the FAT test plan may not be relevant. For example, if a buyer initially orders a GA-MV856 to machine aluminum parts and then changes to machining steel, the original FAT test plan (which used aluminum test pieces) will not validate the machine’s performance for steel.

When FAT is not sufficient, buyers should engage independent third-party testing services for long-term reliability testing, environmental testing, or design validation.

Worked Comparison Table: FAT Test Requirements by Machine Type

The table below outlines FAT test requirements for three common Gree CNC machine types, based on their intended use cases:

Practical Checklist Before Committing

Before agreeing to FAT, ensure the following steps are completed:

1. Finalize the test plan: Include all test categories, test parameters, acceptance criteria, and test piece requirements.
2. Approve the test piece design: Verify that the test piece replicates all critical features, materials, and tolerances of your production parts.
3. Assign qualified personnel: Ensure your FAT team has the technical expertise to validate test results.
4. Review the purchase contract: Confirm that FAT is a required condition for shipment and that all test requirements are documented.
5. Schedule FAT in advance: Allow enough time for testing and any required rework before the desired shipment date.

FAQ

1. Can I skip FAT if I am buying a standard machine? No. Even standard machines can have manufacturing defects. FAT is the only way to confirm that the machine meets your production requirements before shipment.

2. Who pays for FAT? FAT costs are typically included in the machine price, but travel and accommodation for the buyer’s personnel are usually the buyer’s responsibility.

3. What happens if the machine fails FAT? The manufacturer is responsible for repairing or modifying the machine to meet the acceptance criteria before shipment. The buyer can also negotiate a discount or terminate the contract if the machine cannot be fixed.

4. How long is FAT valid? FAT results are valid for a limited period (usually 30–90 days) after testing. If the machine is not shipped within this period, a re-test may be required to confirm that the machine is still in working order.

5. Can I modify the FAT test plan after the machine is built? Modifying the test plan after the machine is built can lead to delays and additional costs. It is best to finalize the test plan before the machine is built to avoid these issues.

← Back to home