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How Do You Choose a Molding Method for Your Production? A Primer

Molding machine

How Do You Choose a Molding Method for Your Production?  A Primer


Congratulations!  You have a new product design blessed by engineering, marketing and all other stakeholders in your group to commission a new production run of a revolutionary molded product.  Assuming you have not designed around an existing in-house molding process, a choice must be made among the optional processes on which direction to go.


Capability Factors

What kinds of capability factors do you need to consider when selecting a process?  Recent discussions with local molders revealed just some of those considerations.  The discussion was not couched in one process being ‘better’ than another, but rather, a comparison of those processes to aid in decision-making.


Things to Consider….
Tooling Cost (example)

  •  Blow Molding:  $30,000+  Requires cooling lines, in-mold punches, etc.
  •  Rotational Molding:  $10,000  Fabricated tooling from sheet materials


Tooling Lead Time

  •  Blow Molding:  12-16 weeks
  •  Rotational Molding:  6 weeks

Radius Tolerances

  •  Blow Molding:  Corners based on wall thickness
  •  Rotational Molding:  90° corners, more robust corners


Wall Thickness

  •  Blow Molding:  Usually 0.100” – 0.150”, though may range from 0.100” -  0.750” and difficult to control over part
  •  Rotational Molding:  0.0312” to 1.0”+

Typical Unit Demand (annual)

  •  Blow Molding:  50,000+/year
  •  Rotational Molding:  1,000/year

Production Considerations                                                                                                                           

  •  Blow Molding:  Purges required for color/tool changes; secondary operation inserts; ‘Kiss-offs’ for wall panels
  •  Rotational Molding:  Batch feed/no purges; heavy mold-in bosses possible; Mold-in inserts; Kiss-offs or double wall molding                                                                                                       


Piece weights

  •  Blow Molding:  Less mass due to wall thickness;  Lower material usage per part
  •  Rotational Molding:  Higher mass due to wall thickness;  Higher material usage per part

Bottom Line Considerations

Specific part applications and quantities required will ultimately have a hand in determining process.  For example, a tank designed to retain 30-70 gallons of fluid will require a heavier wall thickness for support than would a biomedical ‘sharps container’.  Time to market determined by tooling, production cycles and secondary finishing will also contribute to the decision making process.


Next Steps

Utilizing the expertise and services of a seasoned counselor, like a manufacturers’ representative, will help you down the proper path.  That direction will also take some of the project management headaches away as you move forward!