Injection Molding Troubleshooting

Injection Filling Stage Mode Description

Filling Mode		Application and Function
1		Common filling mode for thick transparent products. First stage fills the runner, second stage uses ultra-low speed through the gate; after stabilizing the skin layer, medium-low speed expands the skin layer, and finally a slightly slower speed fills the cavity. Mainly used to avoid flow marks on the surface and internal vacuum voids.
2		Avoids flow or jetting marks near the gate area; first stage fills the runner, second stage uses medium-low speed through the gate, third stage uses medium-high speed to complete injection. Very common and practical method; key is precise timing of stage switches. Allows uniform distribution of cold material without leaving marks.
3		A gradually appreciated high-speed molding method; uses high speed in first stage, then stepwise speed reduction from 80% to 99% of fill. Prevents thickening in thin products due to slow injection, and improves weld quality in thick products. Requires high injection pressure for speed stability. Allows large product molding with small clamping force machines. Gives air inside cavity sufficient time to escape, avoiding silver streaks and burns.
4		Uses medium-high speed through gate, then drops sharply to second speed to complete skin formation, then injects at high speed; suitable for thick products. Stabilizes overall melt flow and makes packing point easier to control. Prevents flash or burr formation.
5		Uses high speed to fill up to target location, then switches to low speed and high pressure to reduce weld lines. Reduces burrs by lowering injection speed during final high-pressure fill stage. Produces thicker products with more uniform density.
6		For parts with fewer runners; uses low speed through gate to avoid flow or jetting marks, followed by high-speed fill. Commonly used for precision parts to control weight and dimensional stability. Suitable for producing larger parts.
7		Fills over 90% at high speed, then drops to half speed to form pressure buffer zone, reducing burrs. Used for precision parts for stable weight and dimensions. Enables larger part production. Can be combined with method 6 for enhanced results.
8		Uses high-speed displacement tailored to varying wall thicknesses of product; switch positions depend on geometry. Ensures smooth flow into thicker areas, allowing faster fill. Improves quality of weld lines.
9		Speed reduction in the middle to reduce impact when product has many pillars or holes, avoiding weld lines. Reduction zone location varies by product. Avoids quality issues from using low speed throughout.
10		For thick products needing high density; starts with low-speed injection, then switches to high-speed, high-pressure forming. Requires large nozzle, runners, and gate dimensions. Low speed should be matched with high-pressure advancement for stability.

Note: The lines represent different injection speeds during the filling stage.

Filling Mode		Application and Function
1		After filling, reduce packing pressure to stabilize the skin, then increase injection pressure to finalize. Allows large parts to be molded with machines of low clamping force. Prevents flash. Eliminates potential stress.
2		After filling, increase packing pressure; suitable for thick products to avoid sink marks. Use with caution for crystalline plastics to avoid deformation. Makes surfaces of thick parts and electronic components smoother. Lower pressure during filling prevents flash.
3		After filling, maintain packing pressure to prevent sink marks and deformation, then reduce pressure to stable level without causing deformation. Eliminates stress and improves stability. Longer second packing stage can save energy and reduce wear on machinery.
4		After filling, reduce packing pressure; second stage packing pressure reduced again to prevent flash and increase stability. Commonly used for crystalline products to reduce deformation. Reduces potential stress; a commonly used mode.
5		After filling, packing pressure gradually decreases in a slope until dimensions stabilize. For situations requiring minimal stress. Improves density uniformity for crystalline plastics.

Note: The line represents various packing pressures during the holding stage; the curve on the right shows actual injection pressure variation during the filling stage.

Injection Molded Product Examples

1	Product Type	Issues
		Gate weld lines and jetting marks
	Injection Program Diagram	Principle Analysis
		Use slow speed near the gate to let the front cold material expand smoothly to form a skin layer, then switch to medium-fast injection.

2	Product Type	Issues
		Gate weld lines and jetting marks
	Injection Program Diagram	Principle Analysis
		For a longer runner, to avoid cold material not filling, push cold material into the cold well quickly, then slow down speed through the gate, followed by medium-fast injection.

3	Product Type	Issues
		Thin product shows waves near the gate or burrs on opposite edges.
	Injection Program Diagram	Principle Analysis
		Inject at high speed and high pressure, reduce speed at 90%, reduce pressure at about 98%, then apply holding pressure to eliminate the above issues.

4	Product Type	Issues
		Large medium-thickness product showing burrs or shrinkage.
	Injection Program Diagram	Principle Analysis
		Fast injection, reduce speed at about 80%, reduce again at 90%, lower pressure from high to low at 95%, stabilize edge skin, then set shape with medium pressure.

5	Product Type	Issues
		Long product showing warpage.
	Injection Program Diagram	Principle Analysis
		High pressure fast injection, slightly reduce speed at 70%, further reduce at 90%, holding pressure can be low at first stage and medium-high at second, or directly use medium-high holding pressure.

6	Product Type	Issue
		Long thin tube products tend to bend and are not straight; made of PP material.
	Injection Program Diagram	Principle Analysis
		The melt flow must be fast, injection speed should be full speed to the end; the secondary speed is set to 50% to avoid stress; injection pressure is high to support injection speed; packing pressure is slightly reduced to ensure stability of crystalline plastics.

7	Product Type	Issue
		Sheet-like product with weld lines on opposite sides of the circular hole.
	Injection Program Diagram	Principle Analysis
		Inject quickly to maintain melt temperature at the front end; reduce speed to 30% at the circular hole; increase pressure to fuse the melt flow; packing pressure is slightly reduced to avoid burrs.

8	Product Type	Issue
		Acrylic triangular prism with weld line bending and internal vacuum bubbles causing deformation.
	Injection Program Diagram	Principle Analysis
		Push cold melt quickly into the cold well; pass the gate at very low speed; reach about 30% length of product to stabilize the skin layer; then fill the product at medium-low speed; pressure during filling must be very high to stabilize the low speed; packing uses medium pressure to shape.

9	Product Type	Issue
		PC thin sheet with short shot and weld lines opposite the long hole; gate area shows haze.
	Injection Program Diagram	Principle Analysis
		Pass the gate at medium speed to eliminate haze, then inject at high speed to the end; packing uses medium speed; filling uses high pressure, packing maintains medium-high pressure.

10	Product Type	Issue
		Large computer accessories with ribs prone to short shots and burrs.
	Injection Program Diagram	Principle Analysis
		Fill at maximum speed up to 60%, then switch to half speed; apply high pressure to fuse and squeeze out air inside ribs; packing uses low pressure and low speed to avoid burrs.

Injection Product Case Descriptions

11	Product Type	Issues
		PP soup bowl, thickness 0.5mm, hot runner small point injection.
	Injection Program Diagram	Principle Analysis
		High-speed, high-pressure injection requires no holding pressure; injection time is within 0.4 seconds, holding pressure is not important.

12	Product Type	Issues
		PP speaker diaphragm 0.33mm thick, thin sheet injection requires uniform thickness.
	Injection Program Diagram	Principle Analysis
		High-speed, high-pressure injection with low holding pressure clears stress and maintains product quality.

13	Product Type	Issues
		Large plastic bucket made of PP plastic, no burr allowed.
	Injection Program Diagram	Principle Analysis
		High-pressure, high-speed injection; holding pressure is first reduced by 20% to form a skin, then pressure is increased to set shape.

14	Product Type	Issues
		PVC soft oxygen mask, no deformation, smooth surface.
	Injection Program Diagram	Principle Analysis
		Temperature must be sufficient, injection pressure extremely low, medium injection speed; main concern is no deformation.

15	Product Type	Issues
		Mobile phone battery cover, thickness 0.6–0.9mm, ABS+PC material, dimension accuracy required.
	Injection Program Diagram	Principle Analysis
		Thin molding requires high pressure and speed, but holding pressure is reduced to stabilize the skin, then medium pressure is applied for shaping to avoid stress and deformation.

16	Product Type	Issues
		Long computer terminal, no deformation or bending, stable dimensions.
	Injection Program Diagram	Principle Analysis
		First stage slow speed to eliminate flow marks, medium pressure with medium-high speed injection; holding pressure reduced to maintain dimensional stability.

17	Product Type	Issue
		Optical projection film, PMMA plastic, must have zero shrinkage to maintain projection pattern function.
	Injection Profile	Principle Analysis
		Injected at low to medium-low speed, with medium-high injection pressure and holding pressure. For this type of product, injection pressure is more important than injection speed.

18	Product Type	Issue
		0.25mm thin sheet, ABS plastic, no deformation, no material shortage.
	Injection Profile	Principle Analysis
		High pressure, high-speed injection; holding pressure is reduced only to stabilize dimensions.

19	Product Type	Issue
		12mm transparent round rod, PMMA plastic, no vacuum bubbles and smooth surface required.
	Injection Profile	Principle Analysis
		Low-speed injection; even lower speed when passing the gate to form a skin layer, then resume low-speed injection. Holding pressure uses low pressure to form a stable skin layer then increases pressure; the third stage slightly lowers pressure for molding.

20	Product Type	Issue
		CD case, PP material, low deformation required, no flash.
	Injection Profile	Principle Analysis
		High-speed injection, high pressure supports high injection speed. Holding pressure is two-stage: low first, then high, ensuring fast cycle time without flash.