Page 478 - Subyek Computer Aided Design - [David Planchard] Engineering Design with SOLIDWORKS

Swept, Lofted and Additional Features Engineering Design with SOLIDWORKS® 2018

Investigate surface finishes that support the customer's advertising requirement. You

have two fundamental choices:

• Adhesive label

• Silk-screen

There are time, quantity and cost design constraints. For the prototype, use an adhesive

label. In the final product, create a silk screen.

Investigate the options on 0-Ring material. Common 0-Ring materials for this

application are Buna-N (Nitrile®) and Viton®. Be cognizant of compatibility issues

between 0-RING materials and lubricants.

The LENSCAP encloses the LENS. The HOUSING protects the BATTERY. How do

you design the LENSCAP and HOUSING to ease the transition from development to

manufacturing? Answer: Review the fundamental design rules behind the plastic

injection manufacturing process:

• Maintain a constant wall thickness. Inconsistent wall thickness creates stress.

• Create a radius on all comers. No sharp edges. Sharp edges create vacuum issues

when removing the mold. Filleting inside comers on plastic parts will strengthen the

part and improve plastic flow characteristics around comers in the mold.

• Understand the Draft feature. The Draft feature is commonly referred to as plus draft

or minus draft. Plus draft adds material. Minus draft removes material.

• Allow a minimum draft angle of 1 °. Draft sides and internal ribs. Draft angles assist in

removing the part from the mold.

• Ribs are often added to improve strength. Ribs must also be added to improve plastic

flow to entirely fill the cavity and to avoid a short shot not enough material to fill

the mold.

• Generally use a 2:3 ratio for rib thickness compared to overall part thickness.

• Shrinkage of the cooling plastic requires that the cavity is larger than the finished

part. Shrinkage around the core will cause the part to bind onto the core. The Draft

feature helps eject the part from the mold. Shrinkage on the cavity side will cause the

part to pull from the mold. Less draft is needed on the cavity faces than on the core

faces.

• Sink marks occur where there is an area with thicker material than the rest of the part

wall thickness. A problem may occur where a tall rib with draft meets a face of the

part.

• Mold cavities should be vented to allow trapped gases to escape through the channels.

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