The Importance of DFM Analysis for Injection Molding

An ounce of prevention is worth a pound of cure. Or several pounds of scrapped parts. Of all the design requirements, meetings, specifications and documentation involved when it comes to injection molded plastic parts, one of the most critical elements of the design process is often skipped: a formal Design for Manufacturing (DFM) analysis.

When OEMs and contract manufactures skip this step, an opportunity is lost to combine engineering and manufacturing expertise to detect manufacturing issues and correct them before significant costs are incurred. Besides avoiding costly tooling modifications down the road, input receive from formal DFM analysis can also decrease part weight and cycle time, as well as improve the structural integrity of the part—all with slight modifications to the original design.

Formal DFM analyses are typically done during the initial phase of tool design, this allows costly mistakes to be avoided because no money has at this point been committed to creating the molds. This allows the OEM and contract manufacturer to precisely define the various tolerances, design rules and quality checks together, which prevents situations where the OEM’s requirements (such as dimensional tolerances) are unrealistic for the contract manufacturer to meet or are outright contradictory. The feedback received by the OEM can then be used to modify the original design, within the constraints of performance, cost, safety and dimensional requirements. In fact, here’s a partial list of items typically covered by a DFM analysis:

  • Draft
  • Wall and Rib Thickness
  • Warp Analysis
  • Weld Lines
  • Print Review
  • Surface Finish
  • Ejector Pin Marks
  • Gate Locations
  • Raw Materials Selection

By having both parties agree to a design which can actually be made as specified on the prints, the likelihood of getting the final design right the first time is greatly increased. This shortens the time to market and also prevents cascading delays further down the product launch schedule. Significant money is also saved by not having to modify or outright replace the tooling or scrapping parts which have already been delivered to the OEM.

With all these clear benefits, why are formal DFM analyses often skipped?

One reason is the fact that many contract manufactures who provide injection molding don’t have the in-house engineering talent or necessary tools (modeling/simulation/CAD software) required to do a thorough DFM analysis. This can be especially true if you’re using a smaller, local contract manufacturer who is spread thin over several other firms in your same area.

Another reason is that when the tools are first designed, the designers are often thinking only about the easiest way to make the tool. Attention to features like the runner, gate, cooling channels, air vents—with an eye toward smoother manufacturing—is then absent. The challenges and costs of making the tools are substantial, but the cost incurred by neglecting the actual use of the mold (to make high volumes of plastic parts dependably) is always much higher.

Other reasons have to do with OEM mindset. The OEM may claim to not have the time for what they think is an unnecessary step. Ironically, that same OEM who first claimed they didn’t have the time to do it right will later have the time to do it over, at much higher cost. Other times, the OEM really is pressed for time because some other step in the product launch process has finished behind schedule and steps like DFM’s are cut to make up for the lost time.

Formal DFM analyses may also be skipped because the OEM may be trying to operate too linearly, insisting that Engineering’s responsibility ends when the design is “tossed over the fence” to Production. To the contrary, a more iterative design approach actually ensures a smoother transition from Engineering prototype to production part.  The tool design and designing for manufacturing shouldn’t be two separate tasks. This means that the toolmakers and molders must both agree on the tooling design. It may take a little extra effort and time up front, but down the road it will save a lot of time and money.

Another common attitude, particularly prevalent in startups, is that an un-manufacturable or excessively expensive design is okay to move forward with because “we’ll fix that later”. That “later” recedes further into the distance as organizational inertia and other priorities push aside fixing those problems which could have been easily and cheaply fixed with a “get it right the first time” mindset . . .and of course a DFM analysis.

An unstated fear lurking behind all these excuses is that if the OEM actually tries to incorporate the findings of a formal DFM analysis, they’ll find that some other requirement will then become impossible to meet and the whole design will collapse like a house of cards.

There are experienced injection molding companies who are experts at meeting the performance, safety, cost, and dimensional requirements of their customers while at the same time ensuring that the part can be made quickly, reliably and in high volume. You may have to search outside your local area in order to find contract manufacturers with the production capabilities to meet your demand and the engineering expertise required for meeting your tolerances with zero defects and delays, but such a manufacturing partner is well worth that extra effort.

Whether you're making millions of disposable medical devices or hundreds of toy parts, a formal DFM can help you make better parts while at same time saving money, by knocking down the artificial wall between engineering and production.

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