What Should Overseas Buyers Prepare for a Factory Audit? Prepare These Four Documents Before Scheduling a Visit

The documents buyers are most often asked to provide before a factory audit are purchase specifications, material certificates, and 2D/3D drawings, which form the basis for subsequent quoting and process evaluation. The purchase specification should state tolerance grades, surface roughness, and key dimension callouts, such as specific values like ±0.02 mm or Ra 0.8, to prevent suppliers from glossing over details with vague references to the drawing. The material certificate should specify the grade of aluminum alloy, stainless steel, carbon steel, or brass/copper, such as 6061, 304, AISI 1045, or C3604, and indicate heat treatment and surface treatment requirements. For 2D/3D drawings, it is recommended to provide them in STEP or IGES format, along with tolerance datums and geometric dimensioning and tolerancing (GD&T) annotations. If the drawings involve five-axis machining or slender part features for Swiss-type lathes, tool interference zones and minimum internal diameter limits should be clearly marked, as this information directly affects whether the supplier can assess feasibility during the trial production stage. Once the documents are ready, buyers can email them to the supplier's engineers for pre-review before the visit, shortening the agenda on the day.

The purpose of verifying the CNC equipment list is to determine whether the supplier can complete all processes from trial production to mass production in-house, avoiding outsourcing of critical processes. In the precision machining cluster in Tanzih, Taichung, factories typically have brand equipment such as BROTHER milling machines, Star Swiss-type lathes, and TAKISAWA turning-milling combined machines. During the audit, buyers can request a machine-by-machine check of model, year of manufacture, and controller specifications. Swiss-type lathes are particularly suitable for slender shaft parts with a length-to-diameter ratio greater than 10:1, such as sensor probes or medical device guide rods. If the factory does not have such equipment, slender part machining would have to be outsourced, increasing quality risks. Turning-milling combined machines can complete turning and milling in a single clamping, reducing cumulative tolerances from secondary setups for valve or fitting parts requiring multi-face machining. Buyers should obtain the equipment list and note each machine's maximum travel and repeat positioning accuracy as a basis for subsequent quoting and delivery commitments.

On the day of the factory audit, buyers should visit the incoming materials area, machining area, measurement area, and shipping/packaging area in sequence, as each area has corresponding key checkpoints. In the incoming materials area, confirm that raw materials are stored and segregated by material type, with labels indicating grade and batch number, to avoid mixing different aluminum alloys or steels. In the machining area, observe the actual operating status of CNC turning-milling combined machines and Swiss-type lathes, including cutting fluid concentration, chip removal, and whether operators set parameters according to engineering drawings. The measurement area is the core of the audit; buyers should verify that measuring equipment such as CMMs, projectors, and surface roughness testers are within their valid calibration period, and review calibration records and traceability sources. In the shipping/packaging area, check whether rust prevention treatment, individual packaging, and shipping inspection records are complete, especially for parts exported to European and American buyers, where the choice of rust-preventive oil and packaging method directly affects the quality of goods upon arrival. It is recommended that buyers reserve 3 to 4 hours to walk through the entire production line to avoid rushing and missing key areas.

After the factory audit, buyers should evaluate whether a supplier is worth long-term cooperation by comprehensively assessing three aspects: process completeness, communication efficiency, and delivery record. Process completeness refers to whether CNC turning-milling combined, Swiss-type lathe, and three-stage inspection processes are completed in-house; if key processes are outsourced, the risk of long-term cooperation is higher. Communication efficiency can be judged by the response speed and depth of technical answers on the day of the audit, such as whether explanations of 5-axis machining tool paths or deformation control for slender parts are specific. Delivery record requires reviewing the supplier's past on-time delivery rate, especially the delivery history for OEM parts and Tier-1 suppliers; such customers have strict cycle time requirements, and factories that can supply stably usually have mature scheduling systems. Buyers can ask the supplier to provide shipment achievement rates for the past 6 to 12 months, and cross-reference customer types and batch sizes, as a reference for long-term cooperation decisions.