A hot-bending order for curved cover glass rarely fails at the furnace. It fails at handover, when nobody can prove the machine actually holds the shape, the yield and the atmosphere it was sold on. An acceptance plan written before the purchase order removes that argument. It converts the supplier's datasheet into a set of checks both factories can sign off on the same day, and it tells your quality team which records to keep once the line is running.
On a machine such as the 3D curved glass hot bending forming machine listed by Shenzhen PowerDe Automation Precision Equipment, the published specification already reads like a partial acceptance sheet: cycle time under 180 seconds per piece, applicable size 14 inch and within, failure rate at or below 2%, product pass rate at or above 80%, cavity oxygen content at or below 50 ppm, 30 moulds in normal cycle, dual high-frequency heating, and a forming range of 600–850 °C. The first job of your plan is to turn each of those lines into a measured test with a defined sample size, rather than a claim you hope to see again at FAT.
1. Scope, part definition and the drawings that govern it
Start with the part, not the equipment. Attach the curved cover glass drawing that will run on the machine: the bend radii, the free-form contour tolerance, total thickness, flat-region dimensions and the optical class required. State whether the acceptance parts are supplied by you, by the machine builder, or by both, because glass that arrives out of spec will be blamed on the forming tooling during a live trial. A short list of reference parts, one per geometry family, is enough — but those parts have to be the ones actually loaded during the test, not the samples the supplier keeps on their shelf.
Then write down the machine envelope. If your portfolio stays within the 14-inch class the supplier advertises, say so and accept against that class. If you expect to run larger or deeper parts later, that is a different machine and it belongs in a different purchase order, not in an acceptance clause you will renegotiate at FAT.
2. Forming accuracy: contour, not just a visual match
Curved glass is accepted by geometry. Define the metrology before the trial: a profilometer scan, a 3D scan or a contour gauge, plus the fixture that holds the part in the same datum the drawing uses. Agree in writing which measurement instrument is authoritative when the two factories disagree, and record the sampling plan — how many pieces per cavity, how many cavities, how many repeats. A pass rate quoted as 80% means nothing unless you also fix the number of pieces behind it; a run of thirty parts is a very different statement from a run of three hundred.
Ask for the deviation to be reported as a distribution rather than a single "best piece" photograph. Surface waviness, sag on the flat region and springback after unloading are the three places curved glass commonly drifts, and each behaves differently with tooling wear. Repeating the measurement after a defined number of cycles, with the thirty moulds in normal cycle all in place, shows whether the accuracy you saw on day one survives into week three.
3. Thermal process control and recipe repeatability
Hot bending is a temperature story. Forming temperature for this class of equipment is commonly specified in the 600–850 °C band with dual high-frequency heating, and the acceptance question is not "does it reach 800 °C" but "does the profile repeat, part after part, with the same recipe loaded". Confirm that heating temperature and heating time can be set and displayed on the touch screen — the product page for the PowerDe machine states this — and then test it: save a named recipe per part family, run a block of pieces, restart the machine from cold, reload the recipe and compare the first pieces after restart against the block.
Write the recipe-management rules into the plan as well. Who is allowed to edit a recipe, whether parameters are locked behind an operator level, and whether the machine keeps a log of parameter changes. When yield drops two months after commissioning, the change log is usually the fastest way to find out why, and it is far cheaper to require at contract stage than to request later.
4. Atmosphere control and glass surface quality
Nitrogen is there to keep the hot glass from oxidising and to protect the tooling. The specification on the PowerDe machine requires cavity oxygen content at or below 50 ppm, with circulating oxygen detection on four nitrogen-filled chambers and a controller holding the oxygen value. Your plan should state how that figure is verified: which port is measured, how long the chamber must purge before the reading counts, what the alarm threshold is, and what happens to the pieces already inside when an alarm trips. Ask the supplier to demonstrate an intentional low-nitrogen condition and show the interlock response; a sensor that only proves itself on a good run is not proof at all.
Judge the surface with the same rigour as the shape. Define the acceptable level of scratches, tool marks, haze and particle picks, and inspect under agreed lighting at an agreed distance. Decide now whether defects are counted per part or per area, and photograph a reference set of acceptable and rejectable examples with both parties' signatures. Half of all acceptance disputes over decorative glass are arguments about what counts as visible.
5. Tooling, mould condition and changeover
Tooling is a consumable, and an acceptance plan that ignores it will not survive the first year. Record the mould material, the initial contour measurement of every new mould, and the wear limits that trigger replacement. The equipment specification for the PowerDe machine includes detection and monitoring of mould thickness before discharging; ask what the system does when thickness falls outside the window, what the recorded thresholds are, and whether an out-of-window mould blocks discharge or only flags it.
Time the changeover. With thirty moulds in normal cycle, a mould set swap is a routine operation, so measure it under the conditions you will actually run: one shift crew, standard tools, no supplier engineer holding the parts. Set a target time in the plan and require the supplier to provide the changeover procedure and a training session covering it.
6. Throughput, availability and the definition of a cycle
Cycle time of under 180 seconds per piece and a failure rate at or below 2% are the two lines most often quoted and most often argued about afterwards. Fix the measurement basis. Is the cycle counted per piece or per chamber load? Does it include load and unload, the purge, and the recipe stabilisation after a stop? Is the failure rate a count of machine faults per run, or downtime as a share of scheduled time? Put the formula in the plan, together with the length of the continuous run — a two-hour demonstration and a three-day production run regularly produce different numbers.
Then specify what is running during that test. Consumables, glass supply, nitrogen purity and flow, upstream and downstream handling, and the utilities available on the shop floor all belong in the description of the trial. If the machine is tested with the supplier's glass, nitrogen generator and support staff, that should be written down and your own conditions noted separately.
7. Documentation, spares and the after-sales terms
Equipment acceptance is a paperwork event as much as a technical one. The plan should list the deliverables: wiring and pneumatic diagrams, the parameter manual, the spare-parts list with order codes, the software version, a backup of the recipes, the calibration certificates for the oxygen and temperature measurement, and the factory test report with raw data rather than a summary page. Ask for the consumables schedule and expected mould life in the same document.
Cover the support terms with numbers: response time, whether a resident engineer is available for the ramp-up, the warranty period for the heating elements and the chamber, and the lead time on the parts most likely to fail first. For a customised line, the engineering side of the supplier matters as much as the machine — automated production line solutions and non-standard automation equipment work is where integration scope, cycle-time responsibility and site acceptance get defined, and it is worth settling in the contract.
8. Safety and installation requirements
A furnace running at 600–850 °C needs guarding, interlocks, surface-temperature limits on reachable panels, emergency stop placement, and clear procedures for a hot chamber during a power loss. Nitrogen handling needs oxygen-deficiency monitoring in the room, not only inside the chambers, plus ventilation and signage. Write these into the plan as acceptance items with the standard you require, and confirm your local rules before the machine ships — an installation change discovered after delivery is one of the most expensive findings in the whole process.
Confirm utilities with the same care: electrical supply and protection, nitrogen purity and flow, compressed air, floor loading and clearance, and the space required for mould changeover. Send the supplier your floor data and get their installation drawing back in writing.
9. How to run the FAT and the SAT without surprises
Two events, two documents. The factory acceptance test happens at the supplier: run your own glass, your own measurement instruments, your own quality engineer on site, against the tests listed above, with a signed report before the machine is released for shipment. The site acceptance test happens after installation on your utilities and your crew, and it should repeat the short version of the same checks over a longer production run. Define what blocks shipment, what blocks final payment, and what is accepted as a punch-list item to be closed inside an agreed window.
Keep a single table of test items across both stages: item, method, sample size, required value, measured value, pass or fail, signature. Every number in that table came from the specification you agreed at the start, which is exactly why the specification has to be written with numbers before the order is placed.
10. Documentation of the accepted state, and the path to production
Close the acceptance by recording the baseline: the recipe set that produced a passing run, the mould serials in use, the instrument readings from the winning run, and the software version. That baseline becomes the reference for every future deviation investigation. From there the plan should hand over to production with a first-article procedure, a patrol-inspection frequency, and an agreed escalation path when the pass rate drops below the accepted figure.
Checklist: what to bring to the supplier meeting
- Part drawing with contour tolerances, and the reference parts you will actually run
- Authoritative metrology method, instrument, and sampling plan per cavity
- Recipe names, edit permissions, and the parameter change log requirement
- Oxygen measurement port, purge time, alarm threshold, and interlock demonstration
- Signed defect reference photos for surface quality
- Mould material, wear limits, thickness-monitoring behaviour, and changeover time target
- Written cycle-time and failure-rate formulas, plus the length of the continuous run
- Documentation, spares, consumables schedule, response time and warranty terms
- Safety standards, nitrogen room monitoring, and your floor and utility data
- FAT and SAT criteria: what blocks shipment, what blocks payment, what is a punch-list item
If you want the specification reviewed against a specific part geometry before the order, send the drawing and your target volume to the PowerDe engineering team; a quotation that already carries your acceptance numbers is far easier to hold to than one that does not.
