Thermoforming

An ideal 100 × 100 mm tray with 25 mm vertical walls has 20,000 mm² formed area. If exactly 10,000 mm² of 2.00 mm sheet supplies it without loss or draw-in, volume balance gives 1.00 mm average wall. Verify corner and local minimum thickness on the actual formed tray.

Spartech's August 2022 manual covers vacuum, plug-assist, pressure, twin-sheet and matched-mold routes. Specify the tooling and controlled surface before applying process data. Spartech, process manual

Choose the route and controlled surface

RIDAT describes the vacuum and pressure routes; Spartech describes matched-mold forming, for which vacuum is not mandatory. These mechanisms are not interchangeable process qualifications. RIDAT, process guidance, undated, Spartech, matched-mold section

In single-sided forming, identify the tool-contact face and the opposite face on the drawing. RIDAT emphasizes that the tool side is the controlled surface. Thickness variation means an accurately located tool-contact surface does not automatically establish the opposite surface's position. Tool choice should therefore follow the functional and cosmetic surfaces, not merely the easiest direction in which to draw the model. RIDAT

Specify sheet grade and preparation

Provide the exact resin/sheet grade, thickness range, color, texture, coating or laminate, protective masking and extrusion direction where relevant. “Plastic sheet” is not a complete process input. Do not transfer heating or drying instructions between grades simply because both are transparent or carry the same broad polymer abbreviation.

A bounded example is TUFFAK polycarbonate. Plaskolite's fabrication guide, marked FAB015_TUF_EN, May 2024, requires pre-drying before thermoforming to prevent absorbed moisture from producing bubbles or voids at processing temperature. It also advises prompt processing after drying, with environmental humidity affecting the available interval. These are instructions for the named product, not a universal drying schedule for every thermoplastic. Obtain the current grade-specific instructions for the actual sheet and masking. Plaskolite, TUFFAK guide, printed p. 33 and back cover

Heating must penetrate the sheet, not merely raise an oven display to a nominal setting. Plaskolite's VIVAK PETG guide lists 280–320°F as a typical sheet-temperature range for vacuum forming and separately lists mold-temperature guidance. Its discussion relates sag to sheet size and thickness and describes screening to control hot spots. These are product-specific examples: neither the indicated temperature nor an observed sag transfers automatically to another sheet, heater layout or geometry. No separately verified issue date is assigned here to that guide. Plaskolite, VIVAK guide, printed p. 9

Material distribution, plugs and release

Formech's August 31, 2022 plug-assist newsletter identifies reduced thinning in deep or multiple cavities and reduced webbing between tall or closely spaced tools as uses of a plug. It distinguishes single-speed pneumatic assistance from programmable servo motion and relates plug shape to where thickness is needed. A plug is therefore a material-distribution device, not proof of uniform walls. Qualify its geometry, contact and motion with the sheet and tool. Formech, plug-assist guidance

Draft, radii, spacing and texture affect release and local material flow. RIDAT explains that cooling sheet shrinks onto a male tool and away from a female tool; textured tooling may require more taper to avoid scraping on ejection. Its numerical draft suggestions are supplier guidance, not universal minimum angles. Confirm the actual release route, including any removable tooling needed for undercuts, before accepting a shape from CAD alone. RIDAT, design guidance

Keep webbing, incomplete detail and excessive local thinning as separate trial outcomes. Increasing starting thickness does not by itself establish that every corner fills or releases properly. Define the locations where remaining thickness or appearance is functionally important and examine those regions after the complete forming and cooling sequence.

Original area-and-thickness example

Assume an ideal open square tray with a 100 × 100 mm base and 25 mm vertical walls, excluding radii, draft, flanges and trim. Its formed area is:

base + walls = 100 × 100 + 4 × 100 × 25 = 20,000 mm²

Assume exactly 10,000 mm² of 2.00 mm-thick sheet supplies that area, with no material entering from outside the assumed footprint, no loss and unchanged density. Volume conservation gives:

average thickness = 10,000 × 2.00 / 20,000 = 1.00 mm

The defined area ratio is 2:1. It is not a depth-to-width ratio, nor does it establish a 1.00 mm local minimum. Real material distribution can leave corners thinner while other regions remain thicker. Tool contact, plug assistance, sheet-temperature distribution and draw-in are excluded. This is an original bookkeeping model, not evidence that the tray can be formed from the assumed blank or that a 2:1 ratio is an allowable design limit.

Cooling, trimming and final geometry

Separate forming-tool requirements from trim-fixture requirements. Associated Thermoforming describes temperature-controlled forming molds and a trim fixture that holds parts under vacuum during CNC trimming. That named supplier route illustrates why the final edge and hole locations are not fully defined by the forming mold alone. Confirm how the part is located during trimming and measured after release. Associated Thermoforming, manufacturing FAQs, undated

Specify whether holes, slots and edges are formed or cut afterward, along with burrs, chips, cosmetic witnesses and the delivered cleaning state. A part held flat by a trimming fixture may move when released; define permitted measurement restraint rather than silently comparing different states. Keep nominal sheet thickness, minimum formed wall and assembled fit as distinct requirements.

Manufacturing handoff and acceptance

Provide four groups of information:

1. Sheet: exact grade, condition, thickness envelope, orientation, surface/masking and traceable lot.
2. Part definition: model/drawing revision, tool-contact face, functional thickness locations, datums, trim and cosmetic requirements.
3. Route: forming method, tool/plug and release strategy, preparation, heating/cooling and downstream operations.
4. Acceptance: measurement stage and support, thickness coverage, dimensional and surface criteria, and required application tests.

Agree the trial using the proposed material, tooling and finished condition. Neither a supplier's generic capability nor a successful visual sample establishes all dimensions, local wall thickness or service performance. The original calculation is deliberately bounded; the drawing, contract and qualified inspection procedure set actual acceptance limits.