ME-542 Manufacturing with Non-metallic Materials

Operating Instruction Manual for the Boy Model 15/5 Injection Molding Machine

By: Don Abbe, Steve Bodmer, and Chris Grainger

12/11/95

 

Table of Contents

Page

1. Purpose 3

2. Overview of injection molding machine operations 3

3. Injection molding processes 5

A. Polymer intake and metering 5

B. Mold and mold movement 7

C. Nozzle movement 8

D. Polymer injection 9

E. Ejection of finished part 10

4. Operating procedure for the Boy Model 15/5 injection molding machine 11

A. Manual operations 11

B. Semi-automatic operations 14

C. Automatic operations 16

5. Boy Injection Molding Machine Shut Down Procedures 18

6. Troubleshooting Checklist 20

7. Injection Molding Terminology 21

8. Boy 15/5 Injection Molding Machine settings for sample part made. 22

9. Appendix 1: "Operating Instructions, Injection Moulding Machine 23

Boy 15/5" ,serial no. 5800, Dr. Boy KG, W. Germany.

10. Appendix 2: "Supplement to the Operating Instruction Manual for the

Boy Model 15/5 Injection Molding Machine", R. Short, Spring 1989.

 

1. Purpose

The intent of this manual is to provide a general knowledge of the injection molding process and specifically, the operation of the Boy 15/5 machine. A step by step procedure for shop floor operation of this machine is also included.

In the creation of this manual, the procedures were validated by making sample parts from polystyrene (see Figure 1). The control settings used for the sample parts are shown in section 8.

2. Overview of Injection Molding Machine Operations

In the injection molding process, molten polymer is forced under high pressure into a closed mold cavity. The injected polymer is then cooled inside the cavity before opening the mold and ejecting the finished part.

The basic injection molding machine consists of a screw which feeds raw polymer pellets into a heated extruder barrel. A hydraulic ram creates the high pressure required to inject the polymer into the mold. These machines can be either single-screw, or multi-screw types. The machine discussed in this manual is the Boy 15/5, which is a horizontal single-screw injection molding machine (see Figure 2).

Polymer in a granular form is fed into the machine through an intake hopper (see Figure 3). The rotating screw feeds the polymer into the extruder barrel until a sufficient amount of material has been ingested to completely fill the mold cavity. As the material is moved forward toward the nozzle it is heated to a soft plastisized state. This action, called "metering" of the polymer, also mixes the polymer if colors are being used. The nozzle, located at the forward end of the barrel, remains closed during this time which allows the desired volume to be built up within the barrel.

During injection, the nozzle is opened while the screw is pushed forward. This action forces the molten polymer to enter into the mold cavity. The polymer solidifies when it comes into contact with the cold mold surface. During injection, the mold is held closed by a hydraulically operated clamping system. After a few seconds, the machine opens the mold and ejects the finished part from the cavity via ejector pins. The part falls through a collection chute, and the process is repeated for additional parts.

For the Boy 15/5 machine, this cycle can be accomplished manually (step by step), semi-automatic (automatic for one cycle only), or fully automatic (continuous cycles).

3. Injection Molding Process

The basic steps for one complete cycle of injection molding using the Boy 15/5 injection mold machine (single horizontal screw type) has been broken down into the following processes:

A. Polymer intake and metering

B. Mold and Mold movement

C. Nozzle movement

D. Polymer injection

E. Ejection of finished part

3A. Polymer intake and metering

Polymer, in a granular form, is fed into the machine via an intake hopper. The polymer materials used for the injection process can be polystyrene, polyethylene, nylon, etc. However, each material possesses different properties which will affect the set up and operation of the machine. In order for the machine to operate properly, the materials used may require different melting temperatures, injection pressures, injection times, cooling times, etc. Sample parts have been successfully made using polystyrene.

During metering, the polymer is drawn into the extruder barrel and forced forward toward the closed nozzle by the rotation of the screw. The metering process begins by actuation of the "metering" push-button (b5) on the main control panel. This starts the screw motor which rotates the screw within the barrel and draws the polymer in from the hopper. Once in the barrel, the polymer is melted by heaters surrounding the barrel. There are two heaters within the barrel (Heater Zone 1 and Heater Zone 2), and a heater in the nozzle as well (see Figure 4). Prior to the metering operation, the barrel and nozzle zones must be heated to the required operating temperatures.

The temperatures of each zone is set from the side panel dials (see Figure 5). Next to each dial is a signal lamp. The lamps are illuminated during heating, and will switch off when the zone temperatures have been reached. The temperature settings of the machine will depend on the type of polymer(s) used and the size and shape of the mold and feed ducts.

While being melted, the polymer is forced toward the forward end of the barrel by the extrusion action of the screw. The nozzle valve at the end of the barrel is closed during this time, which allows the molten polymer to collect within the barrel end. The screw is pushed backwards by this build-up of material.

The amount of polymer intake (injection volume) is manually controlled by the setting of the micro-switch stop (b14). This switch then shuts off the screw motor, which in turn stops the screw rotation. The amount of injection volume required to completely fill the mold cavity is determined by trial and error. If not enough polymer is injected, the part will not be fully formed. If too much material is injected, the excess polymer will come out of the mold at the mold parting lines (flashing) or around the nozzle at the mold entrance. The excess polymer at the sprue could then become too long, resulting in the part not ejecting properly. Once the barrel has been filled with the correct injection volume, and the mold and nozzle are in the proper positions, the molten polymer is ready to be injected into the mold cavity.

 

3B. Mold and mold movement

The mold consists of two halves, in which an internal cavity and core are machined out to conform to the dimensions of the part being formed (see Figure 6). A "runner" is also machined out of the mold which channels the molten polymer into the cavity. A tapered sprue bushing directs the polymer from the nozzle to the mold runner. The molds are fitted into a steel mold base in which one half of the mold base is bolted onto the machine, while the other half moves during opening and closing. The two halves are aligned using precision dowel "leader" pins. These guide pins should be lubricated with grease. The ejection plate and ejector pins are attached to the moving half of the mold base. After the mold has been filled and the polymer has hardened, the ejector pins push the part from the cavity when the mold opens and the mold halves separate. The taper in the sprue bushing allows the polymer in the sprue to be extracted along with the part.

The mold base is constructed from thick steel due to the high injection pressures and high temperatures of the molten polymer. The thick steel allows the mold to remain relatively cool as compared to the incoming polymer. This allows the part to consolidate quickly as the polymer cools once in contact with the mold walls. Water cooling can also be used if the mold contains water passages (see Figure 7). Water cooling of the mold would be required to keep the mold cool during high volume production runs. At the time of this writing, the water cooling system was not connected and was not known to be operational.

The mold is opened and closed using push-buttons, b2 and b3, respectively. The "mold closed" micro-switch must remain depressed during the injection process in order for the hydraulic pressure to be maintained. The shroud that encloses the mold must be pulled shut in order for the mold to operate. Two redundant safety switches located on the cage rail prevent the mold closure while the cage is open. The mold must be closed in order for the nozzle to move forward and for polymer injection to take place. The mold automatically locks when it is closed.

The rate of mold movement is controlled by the mold speed adjustment knob located on the side of the machine. Turning the knob clockwise decreases the speed. Adjustment, if necessary, should be made when the mold is open. Caution must be taken not to close the mold faster than the ejector can retract because the ejector pins may become damaged. Ejector rate can also be controlled.

3C. Nozzle movement

Prior to the injection process, the nozzle must be moved up against the sprue bushing of the mold. During manual operation, this is accomplished by turning the nozzle switch (located on the main control panel, b6) to the forward position. The nozzle switch must be left in the forward position during polymer injection in order to maintain contact between the nozzle and mold during the injection process. During semi-automatic and fully automatic operations, the nozzle switch is left in the forward position as well.

The nozzle may be retracted manually by turning the nozzle switch to the reverse position if access to the sprue intake is required or injection of polymer outside of the mold is desired (i.e. evacuate barrel, change polymer color, etc.). During semi-automatic or fully automatic operations, the amount of retraction may be set by the nozzle retract switch. A small amount of retraction may be required to break the polymer from the sprue. This retraction distance is typically 1 to 5 mm. The amount of nozzle forward movement can also be adjusted. The nozzle retract and nozzle forward micro-switches are located along side of the barrel (opposite side of the metering micro-switch). The travel is set by loosening the knurled knob and sliding the stop to the desired position and re-tightening the knob. When the nozzle is in the forward position, the mold is ready for injection.

 

3D. Polymer injection

Once the proper amount of polymer has been metered into the heated barrel and becomes molten, the mold may be filled. Upon actuation of the injection button (b4), the nozzle valve is opened and the screw is forced toward the mold under hydraulic pressure. The plastic is forced through the mold sprue and into the mold cavity. The plastic in the mold is then allowed to cool and harden.

The correct volume of polymer needed to fill the mold is determined by trial and error. A small amount of material is first injected into the mold. Once the part is produced, it should be checked to determine if more volume is required. If more polymer is necessary, increase the travel of the micro-switch until the mold cavity is completely filled. If the volume is too great, the excess material will show up as flashing at the mold parting line or at the contact point between the nozzle and the mold.

The pressure developed by the hydraulic ram and its forward velocity during injection can be adjusted to match the flow requirements of the mold and material being used. The pressure is adjusted via a flow valve. Turning the valve counter-clockwise increases the pressure. 3E. Ejection of finished part

Upon completion of the injection process, the finished part must be allowed to cool in the mold. As the polymer consolidates within the mold, the part geometry is maintained. If the mold is opened too soon, part warping will occur. The cooling time of an injected part will depend upon its size, shape and polymer .

After an appropriate amount of time, open the mold. Pressing the mold open button (b2) reverses the hydraulic clamping pressure which forces the mold open. A synchronized hydraulic ejector system is activated when the mold is opened (see Figure 7). This pushes the ejector plate and attached ejector pins through the mold cavity, thus ejecting the part.

After ejection, the part falls through a collection chute. During semi-automatic and automatic operations, a parts counter is indexed by a micro-switch attached to the collection chute door.

 

4. Operating procedures for the Boy Model 15/5 injection molding machine.

4A. Manual Operation

1. Power up the machine at the breakers.

 Flip the 220 volt wall breaker switch to the "ON" position.

 Plug the 110 volt power cord (which powers the ejector system) into the wall socket. Unplug the socket to break the circuit.

2. Power up the machine at the control panel.

 Turn the "RED" power switch to the "ON" position. This will energize the 220 volt power circuit.

 The 110 volt power circuit has no "ON/OFF" switch.

3. Set the machine for MANUAL operation.

 Turn the "BLACK" three-way switch to "MANUAL" operations (middle setting).

4. Bring the heaters up to operating temperature.

 Set the nozzle heater to 70% of scale (total).

 Set barrel "Heater Zone 1" and "Heater Zone 2" thermostats to 150 degrees centigrade.

 When the indicator lights on the dials go off, the heaters are up to temperature and the machine is ready for production.

5. Load the raw polymer granules into the hopper.

 Pour polymer pellets into the feed hopper.

6. Close the mold shroud (safety shield).

 Slide the mold shroud closed by hand.

7. Close the mold to maintain hydraulic pressure.

 Press the "MOLD CLOSE" button located on the main panel.

8. Move the injection nozzle forward to contact mold.

 Turn the nozzle movement switch to the "FORWARD" position. Leave in forward position.

9. Meter the injection shot.

 Actuate the meter control button. This will fill the barrel with plastic.

 Adjust the micro-switch stop to change the shot volume.

10. Fill the mold.

 Press the "INJECTION" button to activate the ram.

 The ram pressure and speed can be set independently.

11. Let the part cool.

 Leave the part in the mold for 5 to 10 seconds.

12. Eject the part from the mold.

 Press the "MOLD OPEN" button located on the main panel.

13. Close the mold.

Press the "MOLD CLOSE" button.

14. Make more parts.

 Repeat steps 9-13.

4B. Semi-Automatic Operations

1. Power up the machine at the breakers.

Flip the 220 volt wall breaker switch to the "ON" position.

Plug the 110 volt power cord (for the ejector system) into the wall socket. Unplug the socket to break the circuit.

2. Power up the machine at the control panel.

Turn the "RED" power switch to the "ON" position.

This will energize the 220 volt power circuit.

The 110 volt power circuit has no "ON/OFF" switch.

3. Bring the heaters up to operating temperatures.

Set nozzle heater to 70% of scale.

Set barrel "Heater Zone 1" and "Heater Zone 2" thermostats to 150 degrees centigrade.

When the indicator lights on the dials go off, the heaters are up to temperature and the machine is ready for production.

4. Set the mold-open delay timer.

Adjust the timer to allow the injected part to cool in mold for at least 5 seconds.

5. Load the raw polymer granules into the hopper.

Pour polymer pellets into the feed hopper.

6. Close the mold shroud (safety shield).

Slide the mold shroud closed by hand.

7. Close the mold to maintain hydraulic pressure.

Press "MOLD CLOSE" button located on the main panel.

8. Move the injection nozzle forward to contact mold.

Turn the nozzle movement switch to the "FORWARD" position. Leave in forward position.

9. Open the mold before starting cycle.

Press the "MOLD OPEN" button.

10. Set the machine for Semi-Automatic operation.

Turn the "BLACK" three-way switch to "SEMI-AUTOMATIC" operating.

11. Close the mold to start the Semi-Automatic cycle.

Press the "MOLD CLOSE" button to start each cycle.

12. End the cyclic operations.

Turn the "BLACK" three-way switch to "MANUAL" operations.

 

4C. Automatic Operations

1. Power up the machine at the breakers.

Flip the 220 volt wall breaker switch to the "ON" position.

Plug the 110 volt power cord (for the ejector system) into the wall socket. Unplug the socket to break the circuit.

2. Power up the machine at the control panel.

Turn the "RED" power switch to the "ON" position. This will energize the 220 volt power circuit.

The 110 volt power circuit has no "ON/OFF" switch.

3. Bring the heaters up to operating temperatures.

Set nozzle heater to 70% of scale.

Set barrel "Heater Zone 1" and "Heater Zone 2" thermostats to 150 degrees centigrade.

When the indicator lights on the dials go off, the heaters are up to temperature and the machine is ready for production.

4. Set the mold-open delay timer.

Adjust the timer to allow the injected part to cool in mold for at least 5 seconds.

5. Load the raw polymer granules into the hopper.

Pour polymer pellets into the feed hopper.

6. Close the mold shroud (safety shield).

Slide the mold shroud closed by hand.

7. Close the mold to maintain hydraulic pressure.

Press "MOLD CLOSE" button located on the main panel.

8. Move the injection nozzle forward to contact mold.

Turn the nozzle movement switch to the "FORWARD" position. Leave in forward position.

9. Open the mold before starting cycle.

Press the "MOLD OPEN" button.

10. Select the AUTOMATIC operations mode.

Turn the "BLACK" three-way switch to "AUTOMATIC" operating.

11. Close the mold to start Automatic cycle.

Press the "MOLD CLOSE" button to start the continuous cycle.

12. End the cyclic operations.

Turn the "BLACK" three-way switch to "MANUAL" operations.

5. Boy Injection Molding Machine Shut Down Procedures

1. Set the machine to "MANUAL" mode.

 Turn the "BLACK" three-way switch to "MANUAL" operation.

2. Close the mold.

 Press the "MOLD CLOSE" button.

3. Move the nozzle back to reverse position.

 Turn the nozzle switch to "REVERSE" position.

4. Clear the polymer from the barrel.

 Alternately activate the meter and inject buttons until the extruder barrel is clear of polymer.

5. Open the mold.

 Press the "MOLD OPEN" button.

6. Open the mold shroud.

 Slide the mold shroud open by hand.

7. Power down the control panel.

 Turn the "RED" power switch to the "OFF" position.

8. Turn off the breakers.

 Unplug the 110 volt power cord.

 Turn the 220 volt breaker to the "OFF" position.

 

6. Boy Injection Molding Machine Troubleshooting Checklist

1. Hydraulic pump is not running when the mold is closed.

 Make sure the mold shroud is closed.

 Check the "MOLD CLOSED " micro-switch contact.

1. No charge is being metered into the barrel.

 Check for a broken shear pin between the screw motor and shaft.

1. Broken shear pin.

 Check that both barrel heaters are up to temperature.

1. Shot is not injected.

 Be sure that the nozzle heater is up to temperature.

1. Plugged feed sprue in the mold.

 Nozzle valve should be closing completely.

 Check the nozzle temperature.

 Make sure the sprue duct is smooth.

1. Part will not eject from the mold.

 Apply mold release to the mold.

 Make sure the mold surface is smooth.

 Be sure the 110 volt power cord is plugged in.

 Ejector pins are too long.

1. Mold is underfilled.

 Check the length of the micro-switch stop.

 Check polymer pellet feed hopper.

1. Excess flashing on the parts.

 Shot volume too large.

 Mold is damaged at the parting line.

 

7.0 Injection Molding Terminology

Feed Screw: Screw used as an axial compressor during metering and a plunger during injection.

Flashing: Excess polymer that seeps between the mold halves (at the parting lines) during injection.

Hopper: A large funnel through which the raw polymer is added through the barrel.

Mold Base: A large steel fixture that holds the mold.

Metering: Collecting the proper amount of polymer in the extruder barrel.

Plasticizing: To soften the polymer.

Shroud: A protective cage surrounding the mold.

Sprue: A runner or passage into the mold cavity from the injection nozzle.

Thermoplastic: A polymer which can be softened by heating and will retain a given shape after molding and cooling.

8.0 Boy 15/5 Injection Molding Machine

settings for sample part made:

Material: Polystyrene Granules (High and Low impact)

Shot size (b14) 68 mm

Heat Zone 1 and 2 150 deg C

Nozzle heat 70% of full scale

Injection time 0.3 sec

Cool time 5 sec

Mold Speed 5 3/4 turns open

Inject Pressure 750 psi

 

Appendix 1: "Operating Instructions, Injection Moulding Machine Boy 15/5" ,serial no. 5800, Dr. Boy KG, W. Germany.

Appendix 2: "Supplement to the Operating Instruction Manual for the Boy Model 15/5 Injection Molding Machine", R. Short, Spring 1989.