Ten Tips for Effective Design-for-Manufacturing Analysis

MoldMaking Technology editorial advisory board member Andrew Garstkiewicz of GE Appliances, a Haier Co., offers sage advice on DFM analysis.
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MMT editorial advisory board member Andrew Garstkiewicz of GE Appliances, a Haier Co., offers sage advice on design-for-manufacturing (DFM) analysis.

Laser scanning, 3D printing, holographic representations—these new technologies have pushed the envelope on plastic part design and the manufacturing of molds that produce the parts. One key aspect of plastic part manufacturing is that of a proper DFM analysis, starting as early in the design process as possible.

A good DFM analysis should be made by someone who has some knowledge of the part function and of the material that has been selected. The following steps are the responsibility of the designer. With the following information in hand, the DFM analyst should be able to dissect the CAD model and the part design intent to provide good feedback to the designer about the feasibility of the design and subsequent mold that will produce the parts for the intended tool life:

  1. Maintain a uniform wall thickness for the main form of the part, except for supporting structures such as ribs, bosses, etc.
  2. Be aware that thickness variances that are greater than 10 percent of the nominal thickness of the main form can cause issues with cosmetics as well as the final shape.
  3. Spread thickness transitions from across the form of the part over three times the thickness difference in the variation.
  4. Utilize ribs and gussets instead of adding thickness to add structure to the form.
  5. Ensure that the maximum thickness of the rib is no more than 60 percent of the thickness for non-cosmetic thermoplastics to strengthen part form (with ribs, gussets, etc.) or to integrate other features into the form. This must include radii and true intersection thickness against the main-form wall stock.
  6. Ensure that the thickness of the rib is less than 40 percent of the nominal thickness for cosmetic surfaces that comprise the form. This must include radii, too. (This, of course, can vary somewhat because of proximity to the gate and because amorphous resins shrink relatively less than semi-crystalline resins.)
  7. Add radii to intersections of form to structure as well as structure to structure. A small radius goes a long way to reduce stress concentrations.
  8. Prepare for and apply adequate draft on the form and structure of the part. Ejection forces on the part from the mold should be low to prevent deformation, and proper draft will directly affect these forces.
  9. Understand and prepare for gate location or locations with respect to manufacturability, strength of form and structure, cosmetics and the final part cost.
  10. Consult with colleagues and industry professionals that have depth of knowledge in all the above considerations every time. Speak with them early in the design phase to maximize benefits and realize lower costs.

All the above will go a long way to obtaining a useful, valuable DFM analysis that should lead to smoother tool builds and trials and optimized production life.