Injection molding design: The 10 keys to success (2)

7. Draft angle orientation
When we begin detailing a concept and transforming it into a production injection molded part, draft angles must be added to all surfaces in line of draw. In most cases the draft orientation is obvious. However, there are instances where the draft can be oriented toward the core or cavity. These decisions affect parting lines, tool design, fits between parts and cost. There are instances where the location of the parting line could unnecessarily complicate the mold and increase tooling cost. Reviewing these details with a molder during the development process will ensure that the design has been optimized for minimal cost and optimal performance when it is transferred to the molder for production.

8. Texturing and draft
Experienced designers and engineers familiar with plastic injection molding are well aware of the effect surface finish has on draft angles. High gloss smooth surfaces can be ejected from a mold much easier than a rough or textured surface. There are numerous instances during the detailing of production parts where designers must minimize draft angles or specify textures on exterior surfaces. For example, core pins and bosses may require a ½° draft or less to eliminate potential sink marks. Core pins with minimal draft should be polished for easy part ejection. The same is true for ribs or other features that are typically internal to a part.
On external surfaces, specific textures usually are etched into the steel to a certain depth. Deep textures are sometimes specified for a desired effect. Generally, exterior surfaces should include 1°draft for each mil of textured depth in addition to a starting draft angle of 1°. Although this basic rule appears straightforward, there are instances where the texture may have to bleed off on surfaces where the draft cannot comply with these requirements. It is advisable to discuss these requirements with a molder to ensure that the parts comply with the aesthetic and functional requirements of the design.

(source:https://www.hthc-tech.com/injection-molding-design-the-10-keys-to-success-2/)