How Can We Tackle the Challenge of Shrinkage in Injection Molding?

Shrinkage in injection molding is a technical challenge that can significantly impact product quality. This pervasive issue prompts the question: How can precise control over the molding process reduce or eliminate shrinkage? Understanding the specific factors that contribute to this phenomenon is crucial, from mold design to process parameters. 

At the start of addressing shrinkage, one must consider the detailed aspects of mold construction and the role it plays in material flow and cooling. The technical nuances of water inlet size, venting efficiency, and cooling channel placement are just a few of the mold-related factors that can lead to shrinkage. Furthermore, process parameters such as holding pressure and time, melt volume, and mold temperature settings are pivotal in achieving dimensional stability in the final product. 

The following is based on our production experience, from the mold, design, process, machine and material five aspects of the main reasons for several shrinkage problems.

• Cause Analysis (Basis for Machine Adjustment: Reference Control Parameters)

1. Mold Causes:
   1. Water inlet too small, unable to maintain pressure
   2. Poor venting
   3. Inadequate mold cooling
   4. Mold misalignment
   5. Mold sticking causing depressions
   6. Broken needles, broken inserts
   7. Nozzle, gate channel too small
   8. Hot runner blocked
   9. Hot runner leaking

• Process Causes:
  1. Insufficient holding pressure
  2. Holding time too short
  3. Insufficient melt
  4. Mold temperature too high, leading to larger shrinkage
  5. Mold temperature too low, causing poor filling
  6. Mold clamping too tight, preventing venting
  7. Injection transfer position set unreasonably
  8. Injection pressure and speed set unreasonably
  9. Nozzle blocked
  10. Barrel temperature too high
  11. Leakage

• Design Causes:
  1. Improper gate location
  2. Uneven thickness
  3. Section too thick
  4. Incorrect shrinkage value
  5. Rib design too thick
  6. Improper cooling location, insufficient cooling channels

• Equipment Causes:
  1. Machine too small, insufficient pressure
  2. Wear and tear on the three small parts, the barrel is damaged, not sealing
  3. Injection cylinder oil seal leaking oil, unstable pressure
  4. Pump damaged, pressure unstable
  5. Barrel temperature abnormal (one does not rise, led by the side)
  6. Poor cooling effect of the barrel, resulting in material degradation
  7. Machine screw model not matching with the plastic material
  8. Inappropriate voltage output, unstable

• Material Causes:
  1. Material not properly dried
  2. Material, the sprue not mixed evenly
  3. Material particles too large, uneven distribution
  4. Material shrinkage rate too high

As we unpack the layers of complexity associated with shrinkage, we are reminded that in injection molding, precision and control are paramount. By dissecting the causes and implementing targeted solutions, we can fine-tune the injection molding process to produce consistently high-quality parts. With a focus on technical excellence and process optimization, the industry can advance toward eliminating shrinkage as a common defect, thereby enhancing the overall quality and reliability of injection-molded products.