Overcoming Core Deflection and Part Sticking in Micro-Bore Medical Plastic Injection Molding

In high-volume medical device manufacturing, producing long-thin functional geometries requires extreme engineering precision. As an ISO-certified leader in precision plastic injection molding china, we recently designed and manufactured a 1* 2 cavity china medical mould for a medical infusion tube component (12 *8 *151 mm, featuring a deep varnothing φ2 mm* 150mm blind hole) with a flawless high-gloss finish and a strict parting line mismatch specification of under $0.05 mm component (12 * 8* 151 mm， featuring a deep varnothing φ2mm *150 mm blind hole) with a flawless high-gloss finish and a strict parting line mismatch specification of under 0.05 mm

The Challenge: Core Pin Displacement and Demolding Friction

The primary failure mode in manufacturing micro-bore components is the extreme aspect ratio of the internal core pin. Under high-velocity filling pressures, standard tools encounter:

  1. Core Deflection: Asymmetric melt-front velocity bends the slender core pin, yielding uneven wall thickness and structural rejection.
  2. Vacuum Adhesive Sticking: The closed blind hole creates a severe internal vacuum during core pulling. The molded PP part often tracks the moving slider, causing physical elongation and micro-tears.

The Engineering Solution: Rheological Balancing and Active Mechanical Interlocks

To bypass these critical defects, our engineering team introduced a robust stabilization protocol, proving our competitive edge as a high precision mold provider in Asia.

We conducted non-linear fluid dynamics simulations via molding simulation analysis to balance the 1* 2 feed gates. By calibrating the sub-gate land lengths to a micro-tolerance, the melt-front wraps the φ 2 mm core pin simultaneously from exact opposing vectors. This layout neutralizes lateral kinetic forces, preventing core deflection and securing a flush parting line alignment within 0.05 mm.

To solve part-deformation caused by vacuum adhesion, we engineered a proprietary active retaining mechanism within the front cavity plates. The moment the side hydraulic slider initiates its retraction stroke to extract the core pin, this mechanical interlock exercises an equal-and-opposite holding force, securing the molded tube in its strict ejector orientation. This active system completely eliminates friction marking, fulfilling stringent medical regulatory compliance.

The Result

The validation process concluded with a flawless T1 trial run. CMM concentricity reports confirmed perfect dimensional metrics with zero flash or cosmetic defects, allowing the client to instantly initiate mass production runs.