Molding Machine Operation

ME 3221 Design and Manufacturing I: Lab

Molding Machine Operation

Cincinnati - Millacron Injection Molding Press

Machine Setup

The operation of the injection molding press involves:

Mold Installation
Machine Startup
Temperature Specification
Mold Setup
Specifying Injection Conditions
Ejector Setup
Building a Shot
Producing Parts
Machine Shutdown

The most important requirement is to operate the machine safely. If you have any questions or doubts about machine operation, do not proceed with using the machine. Seek help and answers to your questions.

The Cincinnati - Milacron injection molding press is a multi-user machine. It is used in several courses. All users and TA's are expected to shut down the press using the REQUIRED SHUT DOWN PROCEDURE detailed here. The next user will then find the press in proper working condition and will be able to bring it on-stream with minimum difficulty and annoyance. You must leave the press in its SHUT DOWN MODE. If you find the press in other than shutdown mode contact Prof. Ramalingam or Prof. Klamecki who will identify the last user.

Molding Press State in SHUT DOWN MODE

Hopper Empty and valve shut pellet control slider fully in
Barrel Empty Completely devoid of polymer melt and resin
Sled Completely retracted Sled/screw assembly at extreme right
Screw Completely retracted Screw at extreme right in the barrel
Hydraulic pump Off Handle rotated counter-clockwise to shut power off
Machine power Off Button 29 on Operator Station Assembly pushed in
Water Off Yellow handle on valve for blue hose on rear wall
Main power Off Electrical box on rear wall

Shut Down Procedure

To leave the press with the barrel empty, and the sled and screw in the fully retracted condition, the first thing to do is to PURGE the barrel. Purge the barrel by carrying out the following steps.

Purging the Press

At the end of making parts:

  1. Close off the hopper by pushing the pellet flow control slider fully in. This prevents flow of polymer pellets from the hopper into the barrel during purging.
  2. Select Mode Button 13 on the Operator Station Assembly (OSA) Panel - MANUAL mode button - punch the button; verify that CYCLE = MANUAL is displayed on the LCD screen. (Button 16 toggles MANUAL/MLDSET)
  3. Select Mode Button 10 on the OSA Panel - SLED button - punch the button; verify that CYCLE = MANUAL and FUNCTION = SLeD is displayed on the LCD screen.
  4. Close the door.
  5. Select Mode Button 5 on the OSA panel - RIGHT ARROW BUTTON - and push and hold the RIGHT ARROW button until the sled moves all the way back to its extreme right position. The end point of motion can be recognized by the change in pitch of the hydraulic motor.
  6. Select Mode Button 11 on the OSA panel - INJection button - and punch the button; verify that CYCLE = MANUAL and FUNCTION = INJ is displayed on the screen.
  7. Select Mode Button 4 on the OSA panel - LEFT ARROW button - and push and hold the LEFT ARROW button until the INJection screw moves all the way forward, i.e., extreme left position. the end point of motion can be recognized by the change in pitch of the hydraulic motor.

Purged polymer melt is hot and sticky -- do not touch or handle the purged material until it is completely cool. Be safe.

Moving the INJection screw forward in the barrel pushes out the melt in front of the screw. At this position, the melt between the flights of the screw is still inside the barrel. To purge this residual melt, the screw has to be rotated to extrude out the residual melt.

Note: EXTrude will not function unless the screw is at the extreme left position of its travel.

To extrude the melt

  1. Select Mode Button 12 on the OSA panel - EXTruder button - and punch the button; verify that CYCLE = MANUAL and FUNCTION = INJ is displayed. Note that FUNCTION = INJ will change to FUNCTION = EXT only as long as Button 12 is held in.
  2. Push and hold the EXTruder button 12 until the barrel is completely purged. The end point of purging can be recognized from the pressure reading displayed on the LCD, menu 11, screen. The pressure will decrease to about 100 psi and will stay close to it when the barrel is completely purged.
  3. Operating the EXTruder will tend to move the INJection screw to the right leaving some melt in front of the screw. To eject the small amount of melt remaining in front of the screw Select Mode Button 11 on the OSA panel - INJection button - and push the button; verify that CYCLE = MANUAL and FUNCTION = INJ is displayed on the screen.
  4. Select Mode Button 4 on the OSA panel - LEFT ARROW button - and push and hold the LEFT ARROW button until the injection screw moves forward and completely empties the barrel.
  5. This one extrude-injection cycle may leave a small amount of material in the barrel, so cycle through it once more.
  6. After the barrel is empty select Button 11 and Mode Button 5 - RIGHT ARROW button - and push and hold the RIGHT ARROW button until the injection screw moves all the way back to its extreme right position, i.e., the fully retracted position inside the barrel. The end point of motion can be recognized by a change in pitch of the hydraulic motor.

Machine Shut Down

  1. Once the barrel is empty, turn the hydraulic pump OFF by pushing Button 29 (Push in the red button) on the OSA panel.
  2. Turn the electrical power to the machine OFF by throwing the MACHINE POWER Handle on the electrical panel which is on the lower right front of the machine.
  3. Turn the main electrical power to the press OFF at the Electrical box on the wall behind the machine.
  4. Approximately 10 minutes later, turn the water to the press OFF. The water supply valve is on the wall behind the machine, the press is supplied with water through the blue hose.
  5. Empty the Hopper and dispose of the resin pellets.

    DO NOT place pettets in open, unlabeled bags or containers. If you have made arrangements to leave material in the hopper, LABEL the resin (Vendor and Vendor product number) and leave a copy of the Material Safety Data Sheet attached to the hopper.


Press Start-Up

  1. Verify that the machine is in the SHUT DOWN MODE. The press state should be:
    Hopper Empty and valve shut pellet control slider fully in
    Barrel Empty Completely devoid of polymer melt and resin
    Sled Completely retracted Sled/screw assembly at extreme right
    Screw Completely retracted Screw at extreme right in the barrel
    Machine power Off Handle rotated clockwise to shut power off
    Hydraulic pump Off Button 29 on Operator Station Assembly pushed in
    Water Off Yellow handle on valve for blue hose on rear wall
    Main power Off Electrical box on rear wall

  2. Turn the water to the press ON - the water supply is the blue marked water line mounted on the wall behind the press.
  3. Turn the main electrical power to the press ON at the main electrical supply box on the wall behind the press.
  4. Turn the electrical power to the machine ON by throwing the switch located on the lower right front of the machine.
  5. The LCD screen of the Operator Station Assembly (OSA) panel will POWER UP; Diagnostics will be run, the microprocessor will initialize and run to verify that all systems are working. When all electronic tests have been passed, MENU 1 will appear on the OSA screen.
    The menu number is displayed in the upper left corner of the screen.

Press Setup

A very useful feature of the machine is the FAULTS menu, Menu 43. Calling menus and reading them is explained below. The point here is that if during machine operation problems are encountered, (particularly no response to commands), looking at the FAULTS menu is often useful for identification of the problem.

The major concerns here are the MACHINE SETUP SECTION (Menu 10 and associated Menus) and the PROCESS INFORMATION (Menu 30 and associated menus).

Entering Machine and Process Parameter Values

Machine and process parameters have to be specified before the press can be used to produce parts. Many of the parameters are related to the machine itself, e.g., die height which is explained below. Other parameters are for the specific process to be run, e.g., melt temperature and injection velocity. The process parameter values have to be determined from process models and material properties.

The facilities for setting up and operating the press are presented in a number of Menus. When the press is powered up and after the diagnostic tests are successfully completed, Menu 1 is displayed on the OSA screen. This menu lists general facilities which can be used to control the machine and gather information. The Menu number is shown at the top left corner of the screen. The Machine Mode is shown on the second line of the menu and on startup it is

Note the soft keys/buttons (those which assume different functions) which are the first row of buttons on the OSA immediately below the display screen. This row of buttons is referred to as "row 2" on the OSA Figure. These buttons lead directly to often-used setup facilities and the alarm status screen. The first of these soft buttons, which is blank on startup, will change during machine use. The important change of function of this soft button is when it functions as SWTCH and is used to switch or toggle between choices when the machine is being setup and used.

Their are four kinds of machine and process parameters displayed in menus.

1. Current values are shown on the screen as light numbers or letters on a dark background, i.e., they are read only
2. Black alphanumerics on a white background show the set points specified for the parameter value.These are values that can be changed or set
3. When the cursor is moved to a 'setable' parameter the displayed value will blink and the value can be changed.
If only two states are available (e.g. heater ON or OFF) toggle the value by pushing the SWTCH soft key. The switch button, Button 2.1 comes up as SWTCH when this is the relevant choice.
If a numerical value is needed for the parameter, it is entered using the numeric keypad and then pushing the ENTER key, Button 27 at the lower right corner of the keypad.
4. Some parameter values cannot be specified. The value is displayed and moving the cursor to it will not cause the display to blink.

To change menus, either enter the Menu number using the numeric keypad on the OSA and then push the ENTER key, Button 27, or, step through the menus by pushing the NEXT MENU key, Button 17. The second procedure (stepping through the menus) is recommended since there is no chance of altering the machine parameters. That is, when entering menu numbers it is possible to push the wrong keys and instead of changing menus a machine parameter may be changed.

Machine Setup

Menu 10 is a list of menus which are useful for machine setup; enter 10 using the numeric keypad on the OSA and press ENTER, Button 27.
Notice that

- the first soft key (Button 2.1, the first button in the first row of keys or the '2 row') is MAIN which when pushed will return the system to Menu 1
- this soft key will change to switch, SWTCH, in instances of setting the machine when toggling between values is required.
- some of the commonly used menus are available by pushing the soft keys in the '2 row', e.g., pushing the TeMPerature button will bring up Menu 15 which is the temperature setup menu. Alternately, page through the menus using the NEXT MENU key, Button 17.
Bring up Menu 11.

This page displays some of the important machine and process parameters. The top section of the display shows temperature values. The barrel and nozzle temperatures are a logical choice for starting the machine setup procedure since other parameters can be set while the temperatures are coming up to the specified levels. Remember that readings are shown by light numbers on a dark background.

Set Barrel and Nozzle Temperatures - Menu 15

  1. Select SOFT BUTTON 2.6 (in the top row of buttons immediately below the screen it is the 6th of 7 counting from the left) which is labeled TMP for temperature and push it. The display will show the TeMPerature setup screen which is Menu 15.
  2. Use the UP ARROW, Button 25, or the DOWN ARROW, Button 26, to select the right, middle, left barrel heat zones and set the desired temperature in each zone. The Blinking quantity can be set. To change a value move the cursor to it, use the numeric keys to set the value and ENTER the value by pushing Button 27. The approriate temperatures should be available from a quantitative process design effort.

    Typically the middle zone temperature is set 10 - 20 degrees F below the temperatures set for the right and left zones.

  3. Set the nozzle temperature using the same set of buttons and procedure. Typically the nozzle temperature should be set at 10 - 20F below the temperature for the left heater zone.

  4. The Alarm Band adjustment range is 1% - 20%.

  5. Hydraulic oil and feed throat temperature are shown but these are not controllable. This and other menus show some machine conditions.

Go to Menu 27 to see machine status and to make sure the heaters are ON. Again, notice that if the cursor is moved to a parameter with two states, say the Barrel Heats parameter which can be OFF or ON, the soft key which was MAIN changes to SWTCH and is used to toggle the selected parameter.

It will take 20 - 30 minutes for the barrel and nozzle temperatures to reach the set temperatures.

Material Supply

Now a shot must be built. The barrel, though hot is empty, and the press is set for mold filling.
The machine and mold setup procedure requires that the screw position be close to the position needed for the specified shot size, so make certain that the shot size is realistic for the part to be made and that the following procedure is followed.

  1. Turn on the Hydraulic Power if it is not already on.
  2. To build a shot, fill the hopper with about 2 kg of dry resin pellets (about 2 liters). Open the slider at the bottom of the hopper so that the resin can flow into the extruder barrel.
  3. Set the shot size. This is a linear distance of screw motion during mold filling. The shot volume is related to this distance and the screw diameter. It is best to start with short shots and to build toward the final shot size. (The shot size for the tensile test dog bone mold is about .6 in., for the spiral flow mold the shot size will vary depending on the test to be run)
  4. Move the screw to its fully forward position by choosing Button 11 for screw linear motion and then using the left arrow button, Button 4, to move the screw.
  5. Rotate the screw to move resin down the barrel, Button 12. Melt should be extruded out of the nozzle. Typically the initial material extruded will have visible bubbles and these will become smaller and the melt will look smoother as more material is extruded.
  6. Move the screw back past the shot size and run a cycle of the machine. Since the extrude run part of the cycle is not implimented yet, this initial shot will be a short shot. The barrel should be fully packed after this first shot. The next cycle of the machine will give a full shot which may still be a shot shot if the shot size set is less than that necessary to fill the mold.
  7. To minimize wasted material, when shot building is complete, the barrel should be full with the screw at a position slightly behind the shot size that is to be used.

Mold Set-Up - Die Height and Clamp Tonnage - Menu 12

Mold height must be set and at the same time safe machine (clamping force) tonnage is also set.

The setting of these quantities and the operation of the machine require hydraulic pressure. Hydraulic fluid temperature is shown on the TeMPerature screen which can be displayed by pushing the SOFT BUTTON 2.6 which is label TMP on the OSA panel or by bring up Menu 15. Recommended operating temperature for the hydraulic fluid is between 90F and 130F. It oil temperature rises to above 130F during machine use, the press will shut itself down.

The Cincinnati - Milacron injection molding press is a microprocessor-controlled unit capable of automated mold setup and real-time monitoring of the molding process. Part of the real-time monitoring includes continuously tracking the position of the moving platen with respect to the stationary platen using a linear position transducer. Move to Menu 12 and the display in the lower right corner of the screen shows the transducer reading. The position of the moving platen can be reset periodically (every N machine cycles, N about 25) to compensate for tie rod expansion, machine/mold compliance, etc.

Every time the press is turned off, the linear position transducer MUST be reset to establish an origin for the machine movements specified.

Therefore, Mold and Clamp setup is a MANDATORY requirement every time the press is turned on.

The press uses a toggle linkage to hold the mold halves together during melt injection. The toggle position and the hydraulic pressure clamping the mold closed are also set during mold setup. This is referred to as adjusting the "press tonnage". Automated mold setup includes this step of the machine setup procedure.

Again, the OPEN MOLD GRAPHIC that is displayed at the lower right corner of some menu screens indicates platten position - but is not a direct measure of platten position. The numerical value displayed is the position of the piston in the hydraulic cylinder which drives the moving platten. Since the platten is driven through a toggle mechanism, there is a relation between the piston position and the platten position but the piston position displayed is not the platten position.

NOTE: We've had only one recurring problem in setting up the mold. The toggle mechanism must be in a correct range of position for the tonnage to automatically set itself. If it is not, in the part of the following procedure where the machine should cycle a few times and set the tonnage the machine will continue to cycle. This problem seems to occur when molds and the MUD set (Master Unit Die which the mold halves are mounted to) are changed and the die/mold height changes greatly. The toggle is then out of its effective working range. The fix is to move the left end of the toggle mechanism to a useful position - find someone who knows how to do this.

Mold Setup Procedure:

  1. Set up the mold and ejector system,
  2. Install and bolt the mold set in place; slide the safety door shut,
  3. If it is not on, turn the hydraulic power ON with Button 28 (green) on the OSA panel.
  4. Display Menu 12 by entering 12 using the number key pad and the Enter Button, button 27.
    The first page of menu 12 will display the title 'Clamp Set Up', machine state and numerical values close to the following:
    Mold closing speed parameters Mold protection parameters
    Open Limit 6.00 Mold Touch 0.32

    The Mold Touch value (0.32 in this example) is set by the machine after the auto tonnage setting.

    Mold retraction (mold operating speed parameters)
    and the current position of the moving platen (about 6.00) is indicated in an OPEN MOLD GRAPHIC at the lower right corner of the screen.
  5. Use Button 13, the OPEN PALM, to set the machine in MANUAL mode. On the screen the display will show
  6. Toggle to MoLDSET cycle by using Button 16. On the screen the display will show
  7. Select FUNCTION Die Height (DIH) with Button 6. The screen display will show
  8. Use the LEFT ARROW, Button 4, and retract the moving platen (move it to the left) about 1/4 to 1/2 inch.

    If the mold set has not been changed since last press use, retract about 1/8 inch.

    If a new mold set has been bolted in to the press, retract to the extreme left position. See the Note above about a problem which may occur below in setting tonnage.

    Observe the OPEN MOLD GRAPHIC at the lower right corner of the screen. It should show the position measure (numeric value) of approximately 6.00.

    If the ejection cycle was not completed in the last operating cycle of the previous run, the next operations cannot be executed - the press will not respond. There is a Note below that describes where in the setup procedure this problem may be seen.

  9. Select FUNCTION CLamP by pushing Button 7. The display will show
  10. Use the RIGHT ARROW, Button 5, and bring the moving platen to the right until it just touches the stationary platen - to do this push and hold the RIGHT ARROW button.

    Platen touching and contact are recognized by change in pitch of the hydraulic motor.

    NOTE: If the ejection cycle was not completed in the last operating cycle of the previous run, the following steps cannot be executed - the press will not respond.

    If the moving platen stops within about 1/8 inch from the stationary platen, automated mold setting will correct for this during mold setup. There is no absolute need to force the mold halves to touch. However, if the mold halves are brought to contact the automated mold setting is easier and quicker since the machine has to make fewer adjustments.

    Observe the OPEN MOLD GRAPHIC at the lower right corner of the screen. The linear position transducer will reset and indicate a position measure of about zero.

    During automated mold setting, this number will be corrected to a value dependent on the tonnage (in this example, to close to 0.31) as the origin of the linear position transducer is set.

    If this condition is encountered, select FUNCTION EJecT with Button 9, push the LEFT ARROW button, Button 4, and retract the EJecTion cylinder. Some machine conditions may stop operation of the press, e.g., the purge cover may be up. Menus 43 and 44, the FAULTS and ALARMS, often show what is the problem.

  11. Once the mold halves are in contact, or very close to it, stay in FUNCTION mode CLamP with the screen showing
    Push and hold the LEFT ARROW, Button 4, to retract the moving platen to its normal (left) position.

  12. Go to page 2 of the current menu (Menu 12) by pushing the PAGE DOWN button, Button 19. Switch ADJUST TONNAGE to ON by moving the cursor to OFF, pushing the soft key SWTCH, which is what Button 2.1 is now, and then moving the cursor back to the top of the menu.

  13. Set the value for the required tonnage by moving the cursor, using the number pad and then the ENTER button, Button 27.

  14. Return to the first page of Menu 12 (page up is Button 18) and set the press in cycle MANUAL by toggling Button 16. The screen display will be
    NOTE: Other that setting tonnage, the only other recurrant problem we've had in machine operation is in the next few steps. The machine needs close to a full shot or it will not run, and so the screw position must be close to the shot size. This characteristic of the press is not documented. If the screw is not retracted far enough from the mold section, it may not be possible to enter the MANUAL mode below. If the machine will not repond to this command below, AND ALL OTHER POSSIBILITIES HAVE BEEN CHECKED, try moving the screw back slightly, linear motion not rotation. The situation can be checked - shot size is shown and set in Menu 17 and screw position shown in Menu 11.

    Again, this kind of action should not be necessary and resorted to only as a last alternative. Check shot size, check screw position when screw is fully retracted, go to Manual Mode, move screw back so that shot size and screw position are roughly equal, go back to Single Cycle Mode

  15. Open the sliding door past the safety limit switch.

  16. Set the press in cycle SINGLE with Button 14. The screen display will show
  17. Close the sliding door completely.

    The moving platen will advance toward the stationary platen, the red light on top of the press will turn ON. The moving platen will approach/contact the stationary platen and the automatic mold setting process will begin.

    Observe the OPEN MOLD GRAPHIC at the lower right corner of the screen. The position value will decrease to zero and increase to approximately 6.00 when the moving platen retracts and stops.

  18. Once the forward-return cycle is complete,
    The sliding door should remain shut - there is no need to cycle the door.
    set the press in CYCLE mode CONTinuous by pressing Button 15. The screen display should show
  19. The microprocessor will now take over. The press will automatically cycle several times (3 to 10 cycles) while completing the mold height/tonnage setup.

    When it is completed, the red light on top of the machine will go OFF. The display should show
    The OPEN MOLD GRAPHIC should show a position value of about 0.31 when the moving platen touches the stationary platen.

Mold height and tonnage setting is now complete.

Mold Platen Motion - Menu 12

The motion of the moving platen during the molding cycle is set using Menu 12.

The top part of the Menu 12 display shows the specified mold closing motions.

- CLS SPEED 1 is how fast the moving platen approaches the fixed platen
- SLOWDOWN indicates the distance from the minimum mold height at which the moving platen slows down to the mold closing speed which is set at the factory
- MOLD PROTECT pressure is used to close the mold in the Slowdown region. It is set so that if there is an obstruction between the platens, the machine will stop platen motion and hold its position for the amount of time specified and then will drop out of the automatic cycle mode.
The lower part of the display shows
- the position of the moving platen at which the mold halves first touch, MOLD TOUCH
- the maximum distance that the clamp can open, OPEN LIMIT. This is not the actual clamp openin g but a measure of the clamping mechanism position.
- the speeds during various parts of the mold opening motion
BREAKAWAY - moving platen speed at start of clamp opening sequence
OPEN FAST - distance at which speed changes from Breakaway to speed for main part of mold opening until SLOWDOWN position is reached where the factory set slowdown speed is imposed
The Clamp Position is displayed in the OPEN MOLD GRAPHIC at the lower right corner of the display.

There is a second page to Menu 12 which provides the possibility of the machine automatically checking die height to provide the set clamp tonnage. It can be reached by pushing the PAGE DOWN button, Button 19.
In general

- the Initial Tonnage will be set
- the Adjust Tonnage switch will be OFF since if it is on, the machine will adjuct tonnage on the very next cycle which is not normally useful since the mold height has just been set during machine setup
- Auto Check of mold height is useful and sets the number of cycles between adjustments of clamp tonnage during operation
- Tonnage Auto Check ON

Ejector Mechanism Setup - Menu 13

ForWarD SPEED, ForWarD LIMIT and DWELL are the ejector mechanism forward speed, maximum distance of motion and how long the ejector mechanism remains at the forward position before retracting.

RETract LIMIT and RETract SPEED specify the ejector mechanism speed and home position after the foward motion.

Some machines have both hydraulic and pneumatic ejectors. If the Hydraulic Eject switch is ON in Menu 27, (which it will be for this machine which does not have the pneumatic ejector option) the ejector must be fully backed out to the RET LIMIT position before the clamp will close for the next cycle. The EJECT STOP RET SINGLE on Menu 27 can be used to control the ejectors.

PULSE(S) sets the number of complete forward/reverse strokes of the ejection mechanism in each press cycle.
PULSE RETRACT is the the distance the ejector mechanism retracts between pulses.

CLAMP and EJECTOR positions are shown on the OPEN MOLD GRAPHIC.

There are no general rules for ejector motions since successful ejection depends critically on the specific part shape and the part mechanical properties and temperature.

Process Timers - Menu 16

The allowable times (maximum times in some instances) for various parts of the molding cycle are set in the PROCESS TIMERS menu.

CYCLE ALARM LIMIT is the maximum time for one cycle and if exceeded an alarm will be generated.

CURRENT CYCLE TIME is the elapsed time since the current cycle started.

INJECT HIGH is the maximum length of time that the machine can stay in the Inject High state. The Inject High state is the part of the injection stroke under specified velocity control. The part of the injection stroke under pressure control is called the Injection Pack state.

PACK is the amount of time (absolute value of time, not a fraction of the cycle) allowed for the Injection Pack state.

HOLD is the (absolute) time alloted to the Injection Hold machine state.

COOLING specifies how long (absolute time value) the part is allowed to cool before the clamp opens.

EXTRUDER DELAY is the length of time between the end of Injection Hold and the start of the Extruder Run, a zero value is appropriate. Extruder Run is the part of the molding cycle in which the shot is made for the next injection.

OPEN DWELL is the time the clamp is open between opening at the end of one cycle and closing for the start of the next cycle. This Open Dwell time is used in both Single Cycle and Continuous Cycle operation.

In SINGLE CYCLE operation the machine door must be opened and closed before a new cycle will begin.

Injection Velocity Profile - Menu 17

The top part of this menu is used for setting the cushion.

CUSHION is the amount of material left in front of the screw in the barrel at the end of the injection stroke. As is Shot Size, this process parameter is a distance corresponding to a particular volume of material.

ADAPTIVE SHOT SIZE is a facility which automatically adjusts Shot Size and Transfer Position to maintain the Cushion setpoint. The Trasfer (XFER) position is where injection screw forward speed control (the Injection High mode) changes to pressure control, the PACK mode. The Adaptive Shot Size feature is only useful if only good parts are being produced, i..e, truly steady state operation has been achieved.

% ERROR CORRECTION is the % of the error (error = measured screw position - cushion setpoint) which is corrected during each cycle if ADAPTIVE SHOT SIZE is ON.

The bottom part of the menu is used to set parameters for the Injection High stroke. Injection High mode is the part of the injection stroke when the screw moves forward at specified velocities - velocities in 1 to 5 segments of the stroke can be specified.

SHOT SIZE is the distace (corresponding to material volume) the screw backs up during the Extruder Run part of the molding cycle. It is the distance away from the screw's fully extended position and so includes the cushion as well as the part volume and is set in Menu 19.

The number of the segments in the injection stroke is shown in the squares under SHOT SIZE. The number of segments is set in Menu 61, as NUMBER OF SEGMENTS TO PROFILE. The display shows the length of each segment of the Injection High stroke as the %age of the stroke remaining. For example, if segment 1 is 20% of the stoke length, a display of 80% is used to show the segment length as 80% of the stroke remaining.

Segment 1 is the setpoint for screw translation speed during segment 1 of the Injection High stroke. The screw moves forward at this speed until it reaches the position for the start of segemnt 2.

The other Segment setpoints (2 - 5 possible) specify the screw translation speed for other segments of the Injection High stroke.

XFER POS is the Transfer Position and specifies the location in the screw advance at which the injection sequence changes from velocity mode (Injection High state) to pressure mode (Injection Pack state). This position can be set based on one of

- screw position which is set in Menu 17
- hydraulic pressure in the last segment of the Injection High stroke and this is set at HYDraul ic XFER pressure in Menu 18
- time
- cavity pressure which is not an option on the press. With this option Transfer of mode is based on an in-mold measurement of pressure

The actual values of Cushion, Transfer Position, Fill Time, Screw Position and Injection Pressure are shown along the bottom of the display screen.

Injection Pressure Profile - Menu 18

FILL PRS HI LIMIT sets the maximum injection pressure allowable during the Injection High stroke.

HYD XFER sets the hydraulic pressure at which the velocity to pressure (PACK) control change takes place, if Hydraulis Transfer is ON in Menu 27.

PACK sets the total length of time of the Injection Pack state which can be composed of 1 - 5 segments. If Injection Pack is composed of more than one segment, each is set to the same length of time equal to the time set divided by the number of segments.

psi is used to set the pressure in each of the packing segments.

HOLD is the total length of time of the Injection Hold state. Total time is set and if more than one segment is specified, each segment length is set to an equal portion of the total time specified, as in PACK.

psi is used to set the pressure for each segment of Injection hold.

The actual and setpoint hydraulic pressures are also show on the display.

Extruder RPM & Back Pressure - Menu 19

After an injection stroke another shot has to be built for the next press cycle. This is done during the
Extruder Run machine state or mode during which

- before Extruder Run starts the injection screw can be pulled backward, away from the mold, by a distance set in DECompress BEFORE, a zero value is adequate.
- the motor is rotated at a preset speed set in the rpm box
- the screw rotates in the barrel
- screw rotation causes feed material to move down the barrel
- melted material is augered down the barrel
- the build up of material at the front of the barrel forces the screw backward
Back Pressure, specified in the psi box, is maintained in the injection cylinder resisting screw backward motion
- the screw continues to rotate and move backward until the SHOT SIZE setpoint is reached
- the screw stops rotating
- the screw is moved backward a small distance to the Decompress After setpoint to remove press ure on material in the barrel

One to five segments of the Extruder Run can be specified.

Especially note that in specifying the segments of Extrude Run motions, the length of the segment completed is specified as a % - this is in contrast to the Injection stroke segments being specified as % of the stroke still to be completed.

The actual rotation speed, position and pressure are shown at the bottom of the screen.

Machine Operation

Operate the machine only in the single cycle mode.

Problems That Have Occurred

Most of the problems that have occurred are related to not shutting the machine down fully or shutting it down incorrectly. Problems having to do with operating the machine do not occur very often if the operation of the machine - the nature and sequence of the machine actions - is understood.

As pointed out above, the starting place to look for solving problems is Menu 43, the faults menu.

The cover above the nozzle is eazy to overlook, and if it is not down a safely interlock will not let the machine run.

Continuous cycling during tonnage setting usually indicates that the toggler mechanism is not in a useful position and the left, support location has to be reset.

Sometimes mold height setup and tonnage setting procedures cannot be done. The machine refuses to go into the MANUAL mode. Moving the screw back slightly seems to cure this problem. This is described in the Mold Set-Up procedure above. In general, the machine should be close to actual operating conditions during setup.

If there are air spaces in the machine barrel, not only will short shots result but the extrude run phase of machine operation in which the next shot is made, will not operate correctly. The symtom is that the screw (position shown on Menu 17) will not retract to past the shot size. Progressively shorter and shorter shots will be made. The cure for this problem is to re-make the shot ensuring that the first shot is made correctly.

On rare occasions running the machine in single cycle mode to make the first shot has given trouble. This has happened with very small parts or intentionally very short initial shots and/or materials and processing conditions resulting in very low melt viscosity. It seems that not enough back pressure is developed to enable the screw to return to the shot size distance during the extrude run part of the cycle. The fix is to make the first shot by running through the molding cycle step-by-step in manual mode making sure that enough material is injected into the mold to build enough pressure for the screw to work against in the screw rotation phase of making the next shot.

Instances of insufficient pellet flow into the barrel have been traced to buildup of solid material in the hopper-barrel throat area. This is due to inadequate purging of the machine on shutdown.

© 1999 by B. E. Klamecki and S. Ramalingam. All rights reserved.