A purchase request for a 3D curved glass hot bending machine usually arrives as one sentence: “we need a hot-bending line for curved cover glass.” The quotation that comes back is only as good as what the buyer wrote underneath that sentence. Two buyers asking for the same machine can end up with different mould sets, different furnace atmospheres and different acceptance tests, because the geometry, the glass and the volume were documented to different levels of detail.
The purpose of a requirements document is not to describe the supplier's machine. It is to state, in numbers and in drawings, the result your factory has to produce and the conditions your factory can offer. This article walks through the sections an engineering team should fill in before the first technical meeting, using the published data of our semiconductor process equipment range as a reference for the kind of parameters a machine specification is normally built around.
1. Part geometry and the drawing revision
Hot bending copies a mould, so the mould defines the part. Attach the 2D drawing and the 3D model of the finished cover glass, not a photograph of a sample, and state the drawing revision and date on both. A document that says “curved glass, as per sample” gives the machine builder nothing to size a mould against.
For each part, record:
- The bend area and the flat area, and which one carries the functional tolerances.
- Corner radius and edge radius, written as a nominal value with a tolerance band rather than as a single number.
- Total thickness after forming, plus the thickness of the incoming flat glass, because thickness change is part of the process, not an accident.
- Printed or coated surfaces, if any, and which side faces the mould. A coating that is already on the glass changes the temperature profile the part can tolerate.
- Whether the part is symmetric. A single asymmetric curvature is often the reason a bending programme needs an extra trial run.
2. Glass type, thickness and the incoming condition
Name the glass family and the supplier grade. Chemical-strengthened, aluminosilicate and soda-lime glass soften at different temperatures and respond differently to a long soak, so the same recipe on two glass types produces two different shapes. Give thickness with its tolerance, and state whether the glass arrives as pre-cut pieces, on a carrier, or in sheets that have to be cut before forming.
Also state the maximum dimension of the piece. The published specification of our 3D curved glass hot bending forming machine lists an applicable size of 14 inch and within, which is a practical limit that both sides should confirm early instead of discovering at the design review. If your parts are larger, the machine must be dimensioned differently and the mould handling changes with it.
3. Cycle time, mould quantity and monthly volume
Separate three numbers that are often written as one:
- Target cycle time per piece. The equipment capacity shown for our 3D curved glass hot bending forming machine is under 180 seconds per piece. Write your own target and say whether it includes loading, unloading and mould change, or only the heating and forming step.
- Moulds running per machine. The same machine lists 30 pieces of mould in a normal cycle. That number, multiplied by your cycle time, is what tells you whether one machine or two is needed.
- Monthly volume and its range. Give a normal month and a peak month. A line sized on the peak month runs idle most of the year; a line sized on the normal month cannot be judged on the peak.
4. Forming temperature and atmosphere
Forming temperature is a machine envelope, not a recipe. The machine we list supports a forming temperature range of 600–850 °C with dual high-frequency heating; your glass and your coating determine where inside that range the process actually sits. Ask for the temperature uniformity across the working area, the temperature rise time from a cold start, and how the controller holds the set point during a continuous cycle.
State the atmosphere requirement in the same section. Our machine detects and circulates the oxygen content of four nitrogen-filled chambers, and the specification records a cavity oxygen content of 50 ppm or below with controller monitoring. If your process requires a different oxygen level, write the target and the maximum deviation you will accept. If your factory cannot supply nitrogen, say so in the utilities section and let the supplier design around that constraint instead of assuming the line will run in air.
5. Dimensional tolerances and pass-rate criteria
Write the acceptance criteria your quality department will actually measure. A typical set covers contour deviation against the 3D model, thickness distribution across the bend, edge chipping and crack criteria, surface defects such as mould marks and scratches, and residual stress where the part will later be strengthened or laminated.
Then state the yield you expect, and the yield that triggers a joint investigation. Our machine's specification records a product pass rate of 80% or above and an equipment failure rate of 2% or below. Those figures come from the machine's own configuration, not from your glass, so treat them as the starting line of the discussion: agree which rate is measured on which sample size, on which glass, and with which mould condition.
Add the inspection equipment available on your side. If your factory owns a contour measuring instrument and a polariscope and nothing else, the supplier knows which criteria can be closed out on site and which have to be verified at the supplier's workshop.
6. Mould supply, monitoring and spare parts
Moulds are consumables in a hot-bending line, and they are frequently the item nobody specified. State who supplies the moulds, how many sets you want at handover, and what the expected service life is per set. Record the mould material and the surface finish you require, because both show up on the glass surface.
Ask for mould condition monitoring in the machine itself. Our machine performs thickness detection and monitoring of the mould before discharging, which turns mould wear from a surprise into a scheduled replacement. In the document, state the wear limit at which a mould must be taken out of production, and the spare-part lead time you can tolerate before the line is considered down.
7. Utilities, floor space and operator input
Every machine specification eventually meets your building. Document the available power supply and total connected load you are allowed to draw, the compressed-air and cooling arrangements on site, the nitrogen supply if the process needs one, and the floor area with the door width the machine has to pass through. Include the ceiling height, because mould handling equipment is often taller than the machine itself.
Describe the crew. The number of operators per shift, their training level, and the language of the touch-screen interface decide how much process control has to be built into the software. Our machine's heating temperature and heating time can be set and displayed on the touch screen; if your operators are not process engineers, the document should ask for recipe management with locked limits, so that a recipe cannot be changed by accident during a night shift.
8. Process trials and the parameter record
A bending recipe is found, not guessed. Plan the trials in the document: how many sample pieces you will send, how many trial iterations you expect, and who pays for the glass consumed in them. Agree what a trial report contains — the temperature curve, the dwell time, the resulting contour measurement, and the defect classification of each piece — so that the third trial is comparable with the first.
Ask for the parameter record to be exportable. A line that has been running for six months is worth more when the recipe that produced yesterday's good batch can be retrieved, compared with the batch that failed, and handed to the next shift.
9. Acceptance test, documentation and after-sales
Write the acceptance test into the contract before the order is placed. It should define the sample size, the glass lot, the run duration, the pass rate to be reached, and what happens to the schedule if the rate is not met. State who measures, where, and which instrument is authoritative when two measurements disagree.
Then list the documents you expect in your language: the spare-parts list with part numbers, the electrical and pneumatic diagrams, the software and recipe backup, the commissioning report, and the operator and maintenance manuals. Close with the support terms — remote response, on-site attendance, and what a supplier is expected to supply during the warranty period.
A short checklist for the review meeting
- Drawing revision attached, with tolerance bands on the bend, the corner radius and the thickness.
- Glass family, grade, incoming thickness and maximum piece dimension confirmed against the machine's applicable size.
- Cycle time target written with its scope, mould quantity per machine, and monthly volume with its peak.
- Forming temperature range, uniformity, oxygen target and nitrogen availability all stated.
- Pass-rate and failure-rate criteria written with the sample size and the measuring instrument.
- Mould supplier, quantity, wear limit and spare-part lead time fixed.
- Utilities, floor space, door width and operator profile documented.
- Trial plan, parameter record format and acceptance test agreed in writing.
- Documentation list and support terms confirmed, including the engineering services and contact arrangement for the project.
If you send that set of numbers with your enquiry, the technical reply you receive will already be a machine proposal rather than a list of questions. Send your drawing and target volume through our contact page, and our engineering team will review the geometry against the machine configuration before quoting.
