Injection Molding Basic & Systematic Mold Proving ④

5. Preparation for Molding Work and Mechanical Operation

Different from the factors that influence the process, various other factors should be considered in order to secure the zero defect production process. The items to be considered are briefly described below.

1) Mold

If this was not performed as part of the pre-inspection routine, the following should be checked before production.

Visual Inspection of Molds

• Has the repair work required for the mold been completed?

• Are there items that are suitable for the machine such as locate ring, sprue bush(nozzle diameter), and ejector coupling of the mold?

• Has an insulation plate been installed?

• Have you checked if any damage exists on the visible side or the parting side?

• Is a clean banding supplied?

• Has the date stamp been set properly?

• Has grease been injected into moving components?

Functional Inspection of Mold

• Have the mold protection pressure and distance been optimally set?

• Is the ejector easy to operate?

• Is the slide in the correct position?

• Was the functionality of the limit switch checked?

• Was the tightness of the thermostat or hydraulic pipe in the mold verified?

• Was the transformation process verified?

• Do you have a temperature profile with regard to a hot runner or holding temperature while being heated?

• Are all coolants connected properly?

• Is the output of a thermostat sufficient?

• Was the initial product thoroughly inspected?(comparison with the final product)

Mold Management after Production Completion

• Conduct a rust-proofing and grease it after cleaning the mold.

• Inspect if there was any damage to the mold.

• Request mold repair if necessary.

• Drain a medium so that the thermostat can be sealed and seal the channel.

• Attach the final product to the mold.

2) Materials

Injection molding machine, material preparation and insufficient cleanliness around the facility can be a cause of contamination in raw materials and molded products.

• Clean dryer, filter and hopper when exchanging materials.

• Place a cover on the hopper.

• Put a magnet into the hopper.

• Protect against contamination by sealing the bags of the opened materials.

• Do not expose the materials that absorb a lot of moisture after the drying process to humid places for a long time.

• Dry the materials based on accurate factors including drying time.

• In case of a low injection volume, adjust the amount of resin in the hopper to prevent water absorption.

3) Machines

Periodic maintenance of injection molding machines, molds and peripheral devices reduce unnecessary interruptions that can occur during the production process.

• All monitoring devices related to safety and function are regularly inspected. (For instance, safe door, cover, limit switch, and location sensors, etc.)

• Check the temperature, level, and condition of the operating oil (cleanness, kinetic viscosity, metallic content, etc.).

• Check the lubrication status of the central lubricating oil supply device or the machine.

• Check the temperature of the resin supply section in the cylinder (barrel).

• Check the function and the correct installation location of the temperature sensor.

• Check the proper installation and fixation of the band heater.

• Check the function of the non-return valve (screw tip).

• Check the wear and tear of the plasticization cylinder (barrel).

• Check the leaking status of the machine.

• Check if the maximum clamping force is sufficient.

4) Peripherals

• Was the correct operating temperature set into the thermostat?

• Is the throughput sufficient?

• Is the capacity of the thermostat used sufficient?

• Have you checked the material shipment?

5) Process Transformation

The items below can be the causes of the changes in cycle time or quality.

• Is there any change in the amount of cushion remained?

– Check for wear and tear on the non-return valve (screw tip) and heating cylinder

– Accurate suck back setting

– Measurement condition check

– Increase in the initial injection rate (To increase the closing behavior characteristics of the non-return valve(screw tip))

• Set the correct back pressure.

• Isn"t the amount of cushion too small or too big within the optimal range?

• Is there any change in the measurement time?

• Is the measurement time within the cooling time?

• Very short measurement time can result in heterogeneity of thermo-mechanical materials.(Checking the measurement capacity of a machine)

• Is the injection volume suitable for screw diameter?

• Is there any significant change in injection pressure?

• Is there any excess or fall short of the switchover point?

• Does the screw slide back as soon as it reaches the switchover point?

• Inspect the temperature of the resin supply section.

• Is the supply of materials from the resin supply section smooth??

• Does the pressure reach the injection pressure limit?

• Is the measurement value of melting temperature within the recommended process temperature range?

• It should be injected according to the injection profile configured by a melting.

• Measure the temperature with a needle thermometer (remove the materials ejected from the frame of the machine).

• Is there any change in mold temperature during production?

Screw Speed Curve

Maximum Circumference Speed (m/s)

6. Data of Plastic Resin

Uncrystalline Thermoplastic Resin

Semi-crystalline Thermoplastic Resin

* Source: www.lsinjection.com