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Sheetpress Process Overview

Plastic Sheet Press – Operator Manual

Section titled “Plastic Sheet Press – Operator Manual”

Scope
This manual covers three production methods for forming flat plastic sheets on a hydraulic hot press.
It is intended for trained operators familiar with general workshop safety.

General Introduction

Section titled “General Introduction”
  • Shrinkage & Warping
    When the plastic cools it shrinks 5 – 10 % in length/width (~10mm for 10mm sheets) and 5 – 10 % in thickness (~1mm for 10mm sheets).
    Uneven shrinkage can lift the sheet away from the press faces, leading to warping. Always keep the mould engaged (or under light clamping pressure) until the core temperature drops below the material’s glass-transition temperature.

Moulds

Section titled “Moulds”
  • Mould Guidance & Alignment
    Each mould can be fitted with roller bearings that ride on tracks machined into the press platens. A locating recess (“snap-in sink”) ensures that the mould sits in the exact same XY position every cycle. Mis-alignment of even a few millimetres can twist the frame when the press reaches full load (≈ 20 t) – check seating before every cycle. Mould finish: mirror-polished and scratch-free.

Material

Section titled “Material”

Material cleanliness: remove dust/film; dry the flakes or pellets thoroughly (desiccant dehumidifier recommended) to avoid bubbles and surface haze. Surface & Material Cleanliness

  • Ultra-clean feedstock is critical. Remove dust, shavings, labels, and contamination before charging the mould.
  • Pre-dry the plastic to prevent bubbles and haze. Aim for ≤ 0.02 % moisture by:
    • Using a desiccant dehumidifier dryer (typ. 10 h @ ~80 °C).
    • Storing dried material in sealed containers until use.

Firmware & Signal-Plot Editor

Section titled “Firmware & Signal-Plot Editor”

The control software lets you program:

  • Set-point temperatures over time
  • Ram position or pressure over time
  • Stack-light output (“traffic-light” LED tower): The three lamps (Green, Orange, and Red) indicate the machine’s state. Refer to Appendix C – Stack-Light States for a detailed breakdown. In general:
    • Solid Orange: Cycle is running.
    • Blinking Orange: Cycle is paused.
    • Solid Green and Orange: Cycle is finished, ready for operator action.
    • Blinking Red: System error. Configure light changes in the profile so the operator flow is fool-proof.

Method 1 – Standard Flat-Sheet Press (≤ 20 mm sheet)

Section titled “Method 1 – Standard Flat-Sheet Press (≤ 20 mm sheet)”
StageActionTypical Values¹
1Pre-dry material2 h @ 80 °C
2Pre-heat platens145 °C
3Load mould & chargeAlign with bearings, close until sheet just contacts both faces
4Heat-soak & pressHold 155 °C, ramp pressure to full load over 3 min
6DemouldEngage orange → green stack-light, remove sheet

¹ Adjust time/temperature per resin data sheet.

Notes

Section titled “Notes”
  • Keep compression gradual
  • plastic should flow without flashing.

Important Warnings

Section titled “Important Warnings”
  • Wear heat-resistant gloves and face shield when handling hot moulds.

Method 2 – Die-Assisted Forming (≤ 20 mm sheet, complex surface texture)

Section titled “Method 2 – Die-Assisted Forming (≤ 20 mm sheet, complex surface texture)”

Steps

Section titled “Steps”
  1. Perform Method 1 steps 1-3.
  2. Insert the form die between mould halves; secure with guide pins.
  3. Profile:
    • 0 – 3 min  → ramp platen temperature from 145 °C to 150 °C while applying light contact.
    • 3 – 6 min  → advance ram until die is 90 % seated.
    • 6 – 9 min  → hold pressure to allow material to fill cavities.
  4. Cooling and demoulding as in Method 1.

Notes

Section titled “Notes”
  • A hand-held IR pyrometer or embedded thermocouples ensure die face hits target temperature.
  • Program the stack-light to flash orange at 6 min to remind the operator to inspect vent holes for melt bleed-through.

Important Warnings

Section titled “Important Warnings”
  • Keep hands clear of die faces; use the long-reach extraction hooks supplied.
  • Verify die bolts are torqued to spec before every shift.

Method 3 – Thick-Sheet Reheat & Compression (≥ 20 mm / 2 – 3 cm sheet)

Section titled “Method 3 – Thick-Sheet Reheat & Compression (≥ 20 mm / 2 – 3 cm sheet)”

Thicker panels need a second heating phase to drive out trapped air.

Steps

Section titled “Steps”
  1. Follow Method 2 through the initial die engagement.
  2. Reheat phase:
    • Raise platen temperature to 155 °C.
    • Maintain light pressure for ~5 min to re-soften the core.
  3. Slow final compression:
    • Over the next ≥ 10 min gradually bring the ram to full tonnage.
    • Watch pressure graph; aim for a smooth rise, no spikes.
  4. Cool and demould as usual.

Notes

Section titled “Notes”
  • Slow compression permits internal air to migrate to vent grooves.
  • For sheets > 30 mm consider drilling pilot vents through the blank before pressing.

Important Warnings

Section titled “Important Warnings”
  • Do not force the ram quickly; sudden loads can fracture the die inserts.
  • Confirm thick-sheet recipes in firmware have extended soak/press times – rushing this step is the main cause of voids.

Appendix A – Quick-Reference Stack-Light Logic

Section titled “Appendix A – Quick-Reference Stack-Light Logic”
Cycle EventLamp State
RunningOrange
PausedBlinking Orange
Finished / ReadyGreen + Orange
ErrorBlinking Red

Program these points in the signal-plot editor for every product profile.

Appendix B – Daily Checklist

Section titled “Appendix B – Daily Checklist”
  • Mould roller bearings clean, rotate freely
  • Platens level (±0.05 mm)
  • Stack-light tower functional
  • Emergency-stop test passed
  • Check each heat partition for failed heaters (9x for a 65x65cm press plate)

Appendix C – Stack-Light States

Section titled “Appendix C – Stack-Light States”

The machine status is indicated by a 3-color stack light (Green, Orange, Red). The lights can be on, off, or blinking depending on the machine’s operational mode. These modes are controlled automatically by the firmware but can be overridden via Modbus for manual control or diagnostics.

ModeGreen LightOrange LightRed LightTypical Meaning
STARTUPONONONSystem is starting up or performing a self-test.
STANDBYONONOFFCycle is complete and machine is ready for the next operation (e.g., unload/load).
RUNNINGOFFONOFFA process cycle is active.
WARNINGOFFBLINKINGOFFThe cycle is paused and requires operator attention to resume.
ERROROFFOFFBLINKINGA system error has occurred and the machine is stopped.
MANUALOFFOFFOFFThe stack light is in manual control mode (via Modbus) or off.

Appendix D – Available Signal Plot Events

Section titled “Appendix D – Available Signal Plot Events”

The Signal Plot editor allows you to trigger specific actions at precise times during a cycle. This is useful for automating tasks like activating valves, showing operator messages, or pausing the process. Below are the types of events you can program.

Action (Editor Label)Technical TypeDescription & Use Case
Display MessageDISPLAY_MESSAGEShows a custom message (e.g., “Check material”) on the user interface.
Pause ProfilePAUSEPauses the cycle until manually resumed, allowing for inspection.
Set Digital (Coil)MB_WRITE_COILSends an On/Off command (Modbus Coil) to a device like a valve or fan.
Set Value (Register)MB_WRITE_HOLDING_REGISTERSends a number (Modbus Register) to a device, e.g., to set a temperature.
Set Hardware PinGPIO_WRITEDirectly controls a physical I/O pin on the controller for lights or relays.
Call System MethodCALL_METHODExecutes a complex, pre-programmed function within the firmware.