Injection Molding Guideline

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1. Plastic Material

Assume the general purpose grade plastic materials to be used for our molding

In case of special grade materials, please list the material grade & brand on our tool plan

All the plastic materials for molding must be same as the materials during development stage.

In case of material shortage or cost issue, the new sourced material shall be tested and confirmed acceptable prior use.

2. Colorant

All the colorant must be conformed to heavy elements directives for both ASTM F963 & EN71.

Most of the dry pigments are hygroscopic; they must be properly sealed after use.

For the components with high color consistence, the masterbatches or pre-color plastic materials are required.

3. Regrind Material Ratio

For plastic material on structural components, no regrind is allowed

For general purpose material on non structural components, 20% maximum runner regrind can be blended with virgin material.

For those translucent or true white color components, no regrind is allowed.

For short glass filled materials, 15% maximum regrind can be blended with virgin material

For long glass filled materials, no regrind is allowed.

The maximum number of regrind passes for general purpose materials shall be 3.

Only 1 time of regrind pass is allowed for short glass reinforced materials

The regrind ratio shall be shown in our updated tool plan to follow.

The regrind ratio and no. of regrind passes has to be validated and confirmed during development stage. If not, no regrind will be allowed.

Burned or discolored sprues or parts must not be used as regrind.

Hot nozzle & hot runner is our preference to eliminate runner scrap.

4. Material Drying

Most plastic resins require thorough drying prior injection molding to assure maximum properties in the molded parts. Below table please find the recommended drying temperature & duration for reference:

For those hygroscopic materials, the dehumidifying hopper dryer with closed-loop air circulating system is required to ensure acceptable moisture content to be achieved during molding.

For those non-hygroscopic materials, the regrind have to be dried as 80oC for 2 hours to prevent surface blemishes due to volatiles, such as PE, PP, POM, HIPS.


Drying Temperature

Time required (Hour)

Dehumidifying Dryer required





Nylon 6 / PPO / PC+ABS




Nylon 66






twenty three




twenty three




twenty three


Regrind blench for PE / PP / HIPS / POM




5. Screw Design

For most of un-filled plastic, standard screw with L / D ratio 22:1 is recommended

For glass reinforced plastic, screw with lower L / D ratio 20:1 is recommended

Bi-metallic screw and barrel are required for glass reinforced plastic to have higher wear assistance

6. Molding Machine & Accessories Selection

The distance between two columns (Horizontal) shall be 10mm minimum longer than the mold width

For non engineering or unfilled plastic resin, up to 90% rated barrel capacity shall be utilized.

For engineering and all glass filled plastic resin, up to 70% rated barrel capacity shall be utilized.

For clamping tonnage consideration, the multiple of projectile area and fill pressure should be up to 90% of rated clamping tonnage of machine. However, the actual requirement will be depended upon the wall thickness, parts geometry and gate design. Below table please the fill pressure factor for common use plastic for reference.

Plastic Materials

Fill Pressure (Ton/Sq Inch)







Glass Filled Plastic

5 and Up

The minimum tonnage for mold size shall be put to Machine Size column on Tool Plan

For high precision parts & optical lens, electric molding machine is preferred.

Automatic parts / sprue removal system should be installed for 220 ton or above molding machines

Hopper loader should be installed for 220 tons or above machines

Proportional type hopper loader should be used for the molding with instant runner scrap recycling.

Hopper magnet shall be equipped for all material hoppers.

7. Mold Clamping

For machine capacity up to130 tons, all molds can be clamped onto machine platens by either clamping slots or mounting holes.

For machine capacity more than130 tons, all molds can only be clamped onto machine platens by clamping slots.

Always use appropriate clamping tonnage for clamping, 10% higher than the theoretical clamping tonnage as section 6d). Excessive clamping pressure will ruin the molds, especially on weak parting line areas.

Jiffy type plugs and connectors are preferred to speed up set-up time.

All Eyebolts must be removed before molding start in order not to interfere any mechanical movement

The Hoist Ring type is preferred to prevent accidents caused by traditional eyebolt failure

8. Mold Cooling

All cooling lines must be connected to water manifold of machines as per indication of mold drawing

The water temperature difference between inlet and outlet shall be less than 5º C.

Correct mold temperature shall be maintained for different materials to obtain good aesthetic and mechanical properties

Appropriate mold temperature should be depended upon the wall thickness, aesthetic requirement and flow length to thickness ratio (L/T). Below table please find recommended mold temperature for most common materials:

Plastic Materials

Mold Temperature


Chill water to 40ºC


20ºC to 50ºC

POM / Unfilled Nylon / Unfilled PET

40ºC to 70ºC


50ºC to 80ºC

Filled Nylon / Filled PET

60ºC to 100ºC

9. Molding Process Parameter

Set barrel heaters to ramp profile, lower at the feed throat and higher at front zone. Below table please find the recommended temperature range for reference:

lastic Materials

Cylinder Temperature ºC


190 – 220


180 – 220


190 – 240


170 – 210


260 – 300

Nylon 66

260 - 290

Set the injection to lower limit and add gradually to obtain good parts

Set the injection speed to high for crystalline material and medium for amorphous materials.

Set holding pressure and time to zero.

Start making short shots without any cushion, the incrementally increase shot volume until the part is approximately 95% full. This becomes the transfer point (time). Begin weighing parts.

Set the packing pressure 30% to 40% below first stage pressure and continue weighing parts (normally uses only 1 – 3 seconds pack time). Increase shot volume until a cushion is developed. Incrementally increase pack time until part weight does not increase. At this point, gate freeze-off has been reached.

Set the back pressure low but ensure to displace trapped air in the screw feed section and good melt homogeneity. For glass filled plastic, the recommended pack pressure should be 20 – 50 PSI to prevent glass breakage.

Set the cooling time to permit the parts to be ejected without the ejector pins marks or pushing into the parts.

The molding set-up sheet for every mold must be well documented and attached to molding machine for review during molding.

10. Cycle Time

Below table please find our expected quoting cycle time for different parts category and machine size:

Parts Description


Machine Size

Expected Cycle Time (S)

Small size parts with 1.5mm wall thickness or below

Button or POM components

70 ton or below


Medium size parts with 1.5mm wall thickness or below

Battery Door & 4 up Cartridge mold

70 to 120 ton


Small size Housing with 2.0mm wall thickness or below, or multi cavities components

LTLP Counting House & Fridge DJ Housing

Over 120 to 200 ton


Medium size Housing with 2.5mm wall thickness or below

LeapPad & MFLP Housing

Over 200 – 280 ton


Medium size Housing with 2.5mm wall thickness or below

Around the Block Housing

Over 280 ton – 350 ton


Large Housing with 3.0mm wall thickness or below

Baby DVD Base Housing

Over 350 – 450 ton


Extremely large Housing with 3.0mm wall thickness or below

Top & Bottom Housing for Learning Table

450 – 600 ton


The cycle time for all tooling will be finalized after verification by our tooling engineer during FEP stage.

The limited condition that keeps the molds from being run at a lower cycle time has to be specified in quotation and mold drawing approval stage, such as wall thickness, aesthetics, dimensional tolerance or components design.

11. Mold Releasing Agent

During first shot and EP stages, the mold releasing agent can be applied when parts’ sticking occurs.

During FEP and PP stages onwards, no mold releasing agent is allowed.

All mold releasing agent must be non-toxic and CFC - free aerosols

12. Second Operation

The fixture materials shall be made of Phenolic, Aluminum, coated steel or those materials with high resistance to worn-out and corrosiveness.

All the fixtures must be calibrated daily and once molding start.

No breakable knife or tools are allowed for degating and flashing trimming

13. Process Control

The signed shot sample and components’ specification shall be attached to machine for routine quality check by quality inspector or molding supervisor prior molding start.

The molded color, aesthetics and critical dimensions shall be inspected and confirmed acceptable by quality inspector prior molding start.

Bi-hourly process inspection shall be conducted to verify aesthetics and functional requirements

Critical dimensional check has to be performed for every 4 hours or first and last shot for every shift.

The shot sample should be stored in an air-conditioned environment for at least 1 hour before dimensional check.

Final inspection check shall be performed for every shift prior dispatch to further manufacturing process or storage.

Date code label shall be adhered to every outgoing lot for quality tracking.

14. Mold Maintenance

The mold surface and vents shall be routinely cleaned to eliminate the air trapped & worn-out problems, once for every shift molding. For the volatile materials, such as Polyacetal or PVC, the mold surface or vents shall be cleaned for every 4 hours molding.

The molds, which are in continuous molding, should be dismantled for preventive maintenance, proper cleaning and lubricating on ejector pins, slides, and bushings, etc., once for every week.

For those tailor made spare parts & hot runner consumable components, the safety inventory should be maintained to cover 2 times of lead-time for replenishing.

In case the actual number of shot exceeds our committed tool life as per our Tool Standard, LeapFrog will be responsible for expense for normal mold repair, except the carelessness from operator or poor molding practice. Moreover, the quotation must be approved prior mold repair start.

After any mold is repaired as section 14d, the tool life should be increased at least by 20% of committed tool life, 100K shots for injection mold and 60K shots for blow & die casting molds.

Appropriate mold repair machineries & facilities is required for daily repair & maintenance.

The Copper electrodes for all molds shall be identified and properly storage

15. Shutdown Procedures

When any molds becomes necessary to halt molding for a period of time, the barrel temperature shall be lower down or the cylinder should be purged at regular intervals to prevent material degradation, especially for Polyacetal, PVC, flame retardant or temperature sensitive materials.

And, the water shall also be turned off prior to last 30 shots such that the steel warms up to prevent condensation forming on mold inserts.

The completion of molding run, all traces of compound should be thoroughly purged from barrel with HDPE, PP, Acrylic, Polycarbonate, General Purpose Styrene or commercially available purging compounds.

And, the mold shall be thoroughly cleaned and then coated with rust preventive spray or grease.

16. Tool Plan Updating

The actual number of shots for all active items shall be updated on Tool Plan for every 3 months

The actual number of shots for all inactive items shall be updated on Tool Plan for every year

17. Injection Molding Trouble – Shooting





Wet Material

- Review drying procedure


- Reduce barrel / nozzle temperature


- Increase barrel / nozzle temperature

Weld Lines

- Increase injection pressure

- Increase melt temperature

Warped Parts

Part temperature differential

- Check mold cooling system

Excessive shrinkage

- Increase part packing

Orientation on material

- Change gate location

Ejection problem

- Increase cooling time

- Reduce mold temperature

- Increase ejector pin area


Inadequate Clamp Tonnage

- Use a larger machine

High Injection Pressure

- Reduce injection pressure

Excessive Vent Depth

- Review mold venting

Burn Marks

Air Trapped in Cavity

- Improve mold venting

Barrel or Nozzle Overheating

- Check heater control

Shear Heat

- Reduce injection speed


- Purge barrel

- Clean hopper dryer

Weak Weld-lines

Insufficient venting

- Improve cavity venting

Injection speed too low

- Increase injection rate

Mold temperature too low

- Increase mold temperature

Incorrect gate location

- Relocate gate or add overflow tab

Sticking in Mold

Over packing

- Reduce injection pressure

- Reduce injection speed

Mold design

- Check for undercuts

- Inspect ejector system

- Increase draft in tool

Surface Imperfections

Injection speed too slow

- Increase injection speed

Cold melt

- increase barrel temperature

Cold mold

- Increase mold temperature

Wet material

- Review drying procedure

Sinks or Voids

Holding pressure or time too low

- Increase holding pressure or time

Insufficient feed

- Increase shot size

Gate freezing off or located improperly

- Check gate dimension and location

Gate Blush

Cold material

- Add cold slug well in runner

- Increase melt temperature

Melt fracture

- Reduce injection speed

- Increase gate size

- Add radius to gate

Dimensional Inconsistency

Shot to shot variation

- Maintain adequate cushion

- Check for worn check ring

Melt temperature variation

- Check heater bands / controllers

Inadequate packing

- Increase hold time

- Enlarge gate to prevent premature freeze-off



Author: ConcepTEC.netEmail: This email address is being protected from spambots. You need JavaScript enabled to view it.
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