Baby Folding Bath Tub Injection Mold

I. Main Product Structure & Molding Process

 

1: PP+TPE dual-color / two-shot overmolding (mainstream baby and maternity product on the market)

Hard frame: PP (upper edge of the bucket, bottom support ring, ensuring rigidity)

Folded pleated soft wall: TPE/TPR (repeated bending, resistant to hydrolysis, safe for mother and baby)

Manufacturing method:

· ① Integrated molding with two-color injection machine,

· ② First injection PP hard skeleton → Place in secondary mold → Cover TPE flexible folded wall (two sets of molds + vertical rubber coating mold)

Advantages: Seamless integration, no leakage, high folding lifespan; Challenges: Interface bonding of the two materials, demolding of the pleated cavity, and exhaust control.

 

2: Integrated single-layer foldable modified PP (simple and economical type)

The barrel body is made of a single material and achieves folding through a ring-shaped crease and thin-wall structure. There is no rubber coating. Materials: High-toughness copolymer PP. The wall thickness of the crease area is controlled at 0.8 - 1.2mm; the frame is thickened by 2.2 - 3.0mm.

The cost is lower, and only one injection mold is needed; drawback: Repeated folding is prone to discoloration and cracking.

 

 

II. Key Design Points of the Mold (Deep cavity, thin walls + Folded Structure Focus)

 

1.Classification scheme

The bathtub has a deep cavity shell structure and should be divided externally. The folded annular area should avoid having the dividing line crossing the crease to prevent burrs from affecting the folding process; large R-shaped rounded corners should be made at the four corners to reduce stress concentration.

 

2.Molding gate system

Large bathtub (dimensions 800-900mm): The hot runner system uses multiple injection points, with the preferred design being a fan-shaped gate at the top of the basin rim / edge gate;

It is not recommended to use a single large gate, as this can lead to insufficient glue at the far end and melting marks at the wrinkled area;

·Rubber-coated version: The gate is independently arranged using TPE, to prevent the PP base material from being dispersed.

 

3. Cooling system (the most crucial part)

The wall of the barrel has a significant height difference and obvious thickness variation. A circumferential layered waterway is adopted:

• Core (inner mold): The waterway is arranged along the folded contour to conform to the shape;
• Mold cavity (outer mold): The thick-walled area around the rim is densely equipped with waterways; This ensures uniform mold temperature and prevents the uneven contraction of PP from causing the barrel to twist or the crease position to warp.

 

4. Exhaust design

Folded grooves are highly prone to trapping air!

• A venting groove of 0.02 to 0.04mm is set around the entire parting surface;
• At the end of each fold, a separate insert for venting is made; otherwise, there will be air patterns, burning, decreased strength at the fold area, and the folding will be prone to breaking.

 

5. Push-out system

• Deep cavity products are produced by a combination of top plate, top pipe and flat top for ejection; for the wrinkled ribs, flat top is used; direct top pressing with fine pins is prohibited to avoid thinning the wall and causing ejection failure or discoloration; simultaneous ejection is adopted to ensure the product smoothly detaches from the core without pulling the flexible TPE wall.

 

6.draft

• PP rigid frame: 1° to 1.5°;
• TPE flexible folded area: ≥1.5°, the soft rubber is prone to sticking to the mold, insufficient slope is likely to cause scratches and wrinkling; all corner transitions of the creases are R-shaped, and sharp corners are prohibited.

 

 

III. Reference for Mold Steel Configuration

 

Mold cavity core (polished version, surface): S136 / 2316, corrosion-resistant, suitable for high-gloss / textured surfaces of baby products;

· Ordinary mass production economy type: 718H;

· Mold base: S50C;

For baby products, it is recommended that the molds have the ability of mirror polishing, without sanding, without burrs, to avoid sharp edges of the products.

 

 

IV. Common Defects in Molded Products and Countermeasures for the Mold

 

The creases repeatedly fold and crack.

✅ Product: The crease position is properly set and the wall thickness is moderate, avoiding sudden changes in thickness; Mold: The corners are enlarged with a larger R value, and the exhaust is sufficient to reduce internal stress.

The PP and TPE encapsulation layers have separated and disintegrated.

✅ PP frame with grooves / through holes for mechanical locking adhesive; controls the temperature of two material molds; the gate flow direction promotes the full immersion of the soft rubber in the substrate.

The bucket body is deformed and the water level is tilted.

✅ The waterway provides balanced cooling; the pressure holding curve is optimized; the rim reinforcement ring is appropriately increased.

Folded groove mold and demolding abrasion

✅ Increase the ejection angle; polish the inserts; optimize the ejection layout.

 

 

V. Reference for Mold Basic Parameters (Conventional Large-Size Foldable Baby Bath Tub)

 

• Dimensions: Approximately 860×460×220mm
• Product weight: 1800 - 2500g
• Mold specifications: Compatible with 450T - 650T injection machines
• Mold cavity: Mostly single-cavity molds (due to the large size of the product, double-cavity molds are rarely used)
• Cycle time: 45 - 70 seconds (depending on cooling and whether it is covered with a coating)

 

Hot Tags: baby folding bath tub injection mold, China baby folding bath tub injection mold manufacturers, factory