Challenge

Week 8 - Challenge 2 - Base Bracket Design

CChiranth Radhakrishnan28 Dec 2021

Aim

Create the tooling axis for the given Base Bracket model meeting the requirements of the draft angle and perform the Draft analysis on the model.

Introduction

Having easier ejection from the mold may seem like a minor concern, but draft is crucial to manufacturing parts that meet your quality standard. Without draft, major problems can arise in the injection molding process that increase the time and cost of production.

When no draft is designed into the part, problems can come from friction and vacuums. These issues can damage both your part and even your mold in extreme cases. These problems are a direct result of having insufficient draft. Because plastic shrinks as it cools, portions of the part may pull away from the mold while others grip the core. If there is no draft angle that allows a simple push from the ejector pins to pop the part out of the mold, the part’s surfaces will often drag along the mold as it is being ejected. This friction between the two surfaces can cause scratches or gouges in your part and affect the appearance. This is particularly troublesome if your part is being molded with a surface finish or texture. The friction will scrape away texture and leave you with many rejected parts.

Recommended draft angle

3 degree is the nominal draft

0.5 is the nominal draft

Above 5 degree for textured face

Procedure followed for draft analysis

1)check for any gap between the surfaces and make sure there is no gap by visually or by checking with boundary feature

2)Creating the best possible dummy Axis(Makeing sure there are no undercuts)

3)Creating axis in y direction

(Note) X direction tooling axis can be neglected as there are no surface almost parallel to the tooling axis ) hence Y direction tooling axis is considered as the tooling axis

Analysis of the Class A surface

Before starting of with the designing the Class B and C surface it is necessary to check if there is any undercut and also if proper draft is given to the given class A surface

Creation of class B surface

considering the thickness of the component 2.5 mm we offset the Class A surface to 2.5 mm neglecting the fillets as fillets causes problems during thickening and also do not form a smooth surface

Class B Rib

Class B base

After the Final trim and fillets of Class B surface

The fillet provided on the class B surface has certain calculation in order to maintain uniform thickness of the product.

example say The class A surface fillert radius is 3 mm the corresponding fillet at class B should be 3±(the offset value)

Defects of non uniform thickness

Flow lines in plastic parts appear when molten plastic flows through variable thickness section with low injection speed . which results in the solidification of plastic at different speed.

Creation of Class C surface

To have the parting line on the Class B surface we give the draft angle outwards as shown in the image below