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Treatment methods for mold weld marks/shrinkage marks and fractures

2025-08-09

Treatment methods for mold weld marks/shrinkage marks and fractures

Mold weld marks/shrinkage marks

Phenomenon: During the production process of the electrical knife dispensing table, obvious weld marks/shrinkage marks appeared at the middle bone position.

Analysis: Due to the two-point injection of the mold design, the exhaust at the end of the material flow fusion is not smooth, resulting in obvious weld marks and shrinkage marks.

（1）Characteristics of injection molding machines

Grade: HT80T, clamping force: 80t, plasticizing capacity: 130g.

(2) Mold characteristics

Mold ejection number: 1×2, glue injection method: point gate, ejection method: Ejection by ejector pin, mold temperature: 85°C (constant temperature machine)

(3) Product characteristics

Material: ABS PA757, Color: White, Product weight (single piece) :7.5g, Spout weight: 8.5g.

(4) Analysis of causes of defects

The mold design adopts two-point injection of glue and uses the material flow speed of blocks for glue filling. Due to the influence of the product structure, the exhaust at the middle bone position of the material flow end is not smooth, resulting in obvious weld marks and shrinkage marks.

(5) Countermeasures

1. Use multi-stage injection with slow speed and low mold temperature for filling injection.

2. In light of the glue flow status of the product structure, the three-stage injection is adjusted. The mold temperature should not be too high. A low injection speed is used to allow the material to flow slowly for glue filling, thereby changing the position of the weld line and improving the obvious weld line and shrinkage defects of the product.

Injection molding process table

Injection molding machine: HT80T, injection capacity 130g			Product Name: Knife Dispenser
Raw material: ABS PA757	Colour: White	Drying temperature: 85°C	Drying method: Dehumidifying dryer	Drying time: 4 hours	Recycled material usage: 0
Finished product weight: 7.5g×2=15g		Nozzle weight: 8.5g	Mold output: 1×2	Gate injection method: Point gate

Barrel temperature					Mold temperature	Use machines	"Settings	"Actual
1	2	3	4	5	before	Oil temperature control machine	85°C	85°C
230°C	220°C	205°C	190°C	/	before	Oil temperature control machine	85°C	85°C
△	△	△	△	△	after	Oil temperature control machine	85°C	85°C
△	△	△	△	△	after	Oil temperature control machine	85°C	85°C

	/	45	50	Holding pressure	Pressure-holding position	85	110	95	Injection pressure
	/	0.5	1.3	Holding pressure time	11	14	19	28	Injection pressure position
Residual amount of injection glue			/		/	16	28	15	Injection velocity
7.5			/	/	/

Middle position	Injection time	Cooling time	The entire duration	Back pressure	Rotational speed	Retraction speed	Material quantity position	Retraction position
5	3.1	12	32	5	10 15 10	10	32	3

Mold closing protection time	Injection time	Clamping force	Ejection length	Ejection times	Rotation position	Blowing delay	Blowing time
1	10	65	32	1	15 32 35	/	/

Auto Mould_Taizhou Jiefeng Mould Co.,Ltd. (jfmoulds.com)

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Mold fracture

Phenomenon: The scraper cover of the electrical product breaks in the middle during the production process.

Analysis: As the fracture site is the position of the weld line; The product is affected by stress.

（1）Characteristics of injection molding machines

Grade: HT80T, clamping force: 80t, plasticizing capacity: 130g

(2) Mold characteristics

Mold ejection number: 1×2, glue injection method: point gate, ejection method: Ejection by ejector pin, mold temperature: 110°C (constant temperature machine)

(3) Product characteristics

Material: POM M270, Color: Grey, Product weight (single piece) : 1.9g, nozzle weight: 3.6g.

(4) Analysis of causes of defects

The mold design adopts a single-point injection of glue. Due to the influence of the product structure, the exhaust is not smooth at the middle fusion point at the end of the material flow, and the welding mark is obvious. Excessive injection pressure and too fast injection speed can cause product stress and lead to product breakage.

(5) Countermeasures

1. Add venting to the mold

2. Use multi-stage injection with low pressure speed and high mold temperature for filling injection.

3. Adjust to reduce the residual amount of injection glue.

Injection molding process table

Injection molding machine: HT80T, injection capacity 130g			Product Name: Scraper Cap
Raw material: POM M270	Colour: White	Drying temperature: 85°C	Drying method: Dehumidifying dryer	Drying time: 2 hours	Recycled material usage: 0
Finished product weight: 1.9g×2=3.8g		Nozzle weight: 3.6g	Mold output: 1×2	Gate injection method: Point gate

Barrel temperature					Mold temperature	Use machines	"Settings	"Actual
1	2	3	4	5	before	Oil temperature control machine	110°C	110°C
210°C	200°C	195°C	165°C	/	before	Oil temperature control machine	110°C	110°C
△	△	△	△	△	after	Oil temperature control machine	110°C	110°C
△	△	△	△	△	after	Oil temperature control machine	110°C	110°C

	/	35	Holding pressure	Pressure-holding position	50	75	65	Injection pressure
	/	0.5	Holding pressure time	7	9	14	18	Injection pressure position
Residual amount of injection glue		/		/	10	18	12	Injection velocity
4.2		/	/	/

Middle position	Injection time	Cooling time	The entire duration	Back pressure	Rotational speed	Retraction speed	Material quantity position	Retraction position
5	1.6	6	20	5	10 15 10	10	22	2