{"id":1574,"date":"2010-04-02T14:09:41","date_gmt":"2010-04-02T19:09:41","guid":{"rendered":"https:\/\/www.ulprospector.com\/knowledge\/?p=1574"},"modified":"2018-02-09T14:06:05","modified_gmt":"2018-02-09T20:06:05","slug":"rapid-injection-molding-design","status":"publish","type":"post","link":"https:\/\/ulprospector.ul.com\/1574\/rapid-injection-molding-design\/","title":{"rendered":"4 Rules for Successful Rapid Injection Molding Design"},"content":{"rendered":"

By Protomold<\/a> – Nobody’s Faster In The Short Run.\u00ae<\/p>\n

The fundamental rapid injection molding design rules for this decade are the same as those for the last decade (and several before that). But we wanted to reiterate them to help keep your projects on track as we stride confidently into the two-thousand-tweens.<\/p>\n

When Proto Labs Customer Service Engineer Dave Nyseth proposed the following list of rules, we asked him to put them in order of importance. “They\u2019re all Number One,” he replied. “Ignore any one of them and it can stop you in your tracks.” For that reason, we present Four #1 Rules for Successful Rapid Injection Molding: <\/strong><\/p>\n

1a) Maintain uniform wall thickness
\n1b) Maintain appropriate draft
\n1c) Understand the resins you plan to use
\n1d) Understand the Protomold manufacturing process<\/p>\n

Uniform wall thickness<\/strong>
\nUneven wall thickness<\/a> is an open invitation to a multitude of problems. Depending on gate placement, it can lead to incomplete mold filling if resin has to pass through a thin area to reach a thick one. And because resin shrinks as it cools, thick areas may shrink more than thin ones, which can lead to warp in the finished part.<\/p>\n

So, if walls are to be identical (or at least similar) in thickness, what should that thickness be? If it is too thin, parts won\u2019t be structurally sound, but if they are too thick they may shrink enough to cause unsightly, potentially risky surface sink. Also, because dissolved gases are released as resin cools, thick walls can develop bubbles at or below the surface, weakening the part. The ideal thickness of a wall will depend on its function and on the resin used. Our ProtoQuote\u00ae design analysis can make some guesses about wall thickness issues, but since we don\u2019t require you to select a resin type until you\u2019re ready to order, you need to factor in resin-specific properties when designing your part.<\/p>\n

If a feature needs to extend above or below the rest of the part surface, it need not be thicker than the adjacent areas. Instead, it can be designed as a cored-out feature rather than a solid one.<\/p>\n

Appropriate draft<\/strong>
\nIt may be January, but for a moment, let\u2019s think spring and baseball. Picture a base-runner sliding into second base just under the fielder\u2019s throw. Now imagine the condition of his uniform (and maybe his hip as well) as a result of that slide. That\u2019s what can happen to undrafted surfaces when a mold opens and the part is ejected. Proper draft ensures that the part surface and mold surface will draw apart instead of being dragged across one another during ejection. The required degree of draft needed to avoid damage depends on a variety of factors including height, location, and surface texture of the feature.<\/p>\n

Draft is almost always required for surfaces that are parallel to the direction of mold opening. In parts with cam-driven side actions, draft is also required for surfaces parallel to the direction of cam action. And shutoffs\u2014surfaces where mold faces meet\u2014that are parallel to the direction of mold or cam opening require draft as well.<\/p>\n\n\n\n
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\"Undrafted-Drafted\"<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Resin characteristics<\/strong>
\nThe characteristics of various resins differ across too many dimensions to discuss in detail here, but we want to remind you of the issues that can affect the molding of your part:<\/p>\n