6 Design For Manufacture Rules

Attention to the following main design-for-manufacture rules, will aid to reduce cost and time:


1.  Wall thickness:  The most important design requirement for getting good moulded parts is maintaining constant wall thickness.  A consistant wall thickness minimises the potential for warped or distorted parts.  Wall thickness needs to also be considered when creating screw bosses.  Thick sections can cause sink and voids in your part.


2.  Core Parts:  Core out parts, eliminates thick walls.  If wall sections are thick it can throw off part dimensions, reduce strength and require post machining, adding to higher costs.


3.  Sink Marks – Ribs/Bosses:  To prevent sink marks in the part, ribs or bosses should be no more than 60% of the wall’s thickness.


4.  Warping:  Eliminate details that may cause moulded stress, such as sharp transitions, or areas that dont support themselves.  Adding ribs or curved angles will prevent this.


5.  Texture:  CAD must be adjusted to accommodate for surface variance.  If texture is on a surface that is angled away from the mould opening then no draft changes are necessary.  If the texture is parallel, then increased draft is required.  Rule of thumb, 1.5 degrees of draft for each 0.03mm of texture.


6.  Drafting:  Creating sloped walls and curved angles makes it easier to eject parts without causing cosmetic defects.  Use 1 degree of draft or more.  A rough rule of thumb is 1 degree of draft for each of the first 50mm of depth.  And approx. 3 degrees of draft for 50mm to 100mm of depth.

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