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Home » Plastic molding » Plastic molding basic design of sample P2

Plastic molding basic design of sample P2

September 21, 2018 by mechanicaleng blog Leave a Comment

To continue P1, today i will update plastic molding basic design: draft angle  of sample, boss of sample,….

Post contents

  • 1.Plastic molding: How to make draft angle of product.
    • 1.1. Box, top form
    • 1.2. Boss
    • 1.3. Rib
  • 2. Plastic molding: how to make boss of product.

1.Plastic molding: How to make draft angle of product.

If the draft angle is not enough, resist when releasing the mold will be big and the molded product might deform by the ejector pin, so the draft angle should be taken as big as possible.

Plastic molding draft angle in mold
draft angle in mold

The picture below will show for you how to choose draft angle of product.

Plastic molding draft angle of product
draft angle of product

1.1. Box, top form

: Make the draft angle of the outside (cavity side) big to make it easy to take out. Make the inside bit small to take balance of the cavity left and the core (outside 1 to 2°, inside 0.5 to 1°). When placing the inverse warpage as a countermeasure against the warpage, taking the draft angle bigger is good.

1.2. Boss

: Boss is relatively difficult to take out, so the draft angle need to be big (0.5 to 1°). The base area will be big if the boss height is high, so making a hollow is one way to prevent the sink marks.

Plastic molding draft angle of boss
draft angle of boss

1.3. Rib

: In the case of longitudinal rib, draft angle of more than 0.25°, in the case of bottom rib, draft angle of more than 0.5°is referred. Also, from workability point of view, more than 1mm thickness for the tip of a rib is preferred.

Plastic molding draft angle of rib
draft angle of rib

2. Plastic molding: how to make boss of product.

Boss functions as an assemblage of the molded product, and is used in a self-tapping screw mounting press fit. If boss is too thick or the root radius is too round, it will be the cause of sink marks and air bubbles, which will end up with poor appearance and strength reduction.

Plastic molding boss of product
boss of product

+ If we need to increase durability of boss, we can add rib for its. The picture below will show how to make ribs for boss.

Plastic molding add rib for boss
add rib for boss
design rib for boss
design rib for boss
rib of boss
rib of boss

+ If boss for self-tapping screw is too big, there will be sink marks on the surface of the molded product, and if it is too small, when screwing the self-tapping screw, it might cause crack. General design example of boss for self-tapping screw is shown in picture below.

Design of boss for self tapping screw
Design of boss for self tapping screw (m-ep.co.jp)

Related posts:

rib for increasr stiffnessplastic molding basic design of sample P1 plastic injection molding ring gate designplastic injection molding gate design overview design side gate have chamferdesign side gate in injection molding plastics injection molding sink marksinjection molding troubleshooting sink mark defect

Filed Under: Plastic molding Tagged With: molding design

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