Plastic parts structure design knowledge

First, in the process of designing plastic parts, we will consider following items:

1. Selection of plastic parts

2. Design of?wall thickness of plastic parts

3. Design of surface, bottom case, screw column, buckle, etc.

4. Design of plastic parts?stop?and?art line!

5. Design of plastic ribs

Second, consideration of choice of materials

Any industrial product in the early stages of design must involve consideration of choice of forming materials. Because materials have an interactive relationship during production, assembly, and completion time. In addition, quality verification level, market sales and price determination are also considered. So it is not possible to use a comprehensive consideration to determine a systematic approach to determining materials and production processes that are optimal.

Third, characteristics of different materials

ABS

Uses: Toys, cabinets, daily necessities

Features: Hard, non-fragile, glueable, but may be beneficial when damaged.

Design applications: Most are applied to toy housings or parts that are not subjected to force.

PP

Uses: Toys, daily necessities, packaging plastic bags, bottles

Features: Elastic, tough, and extensible, but not glued.

Design applications: Most are used in some places where you need to accept drop test.

PVC

Uses: Soft hose, hard hose, soft board, hard board, wire, toy

Features: Soft, tough and elastic.

Design applications: Most are used for toy figures, or some places that require shock absorption.

POM

Uses: Mechanical parts, gears, masts, appliance housing

Features: Wear-resistant, hard but fragile, easy to appear when damaged

Design applications: Most are used for rubber gears, pulleys, some places that require transmission and are subject to high torque or stress.

PA nylon

Uses: gears, pulleys

Features: Tough, absorbent, but becomes brittle when water is completely volatilized.

Design application: Because accuracy is more difficult to control, it is mostly used for some gears with large modulus.

Kraton

Uses: MOP

Features: Soft, elastic, high toughness and strong extensibility.

Design application: Most of them are used as mats to absorb friction and reduce noise.

Fourth, commonly used wall thickness

Thickness of wall depends on external force of product, whether it is supported by other parts, number of columns, number of extensions and choice of plastic materials. Wall thickness design of general thermoplastics should be limited to 4mm. From an economic point of view, excessive product design not only increases material costs, extends production cycles (cooling time), and increases production costs. From a product design?point of view, an excessively thick product increases likelihood of creating voids (pores), greatly reducing rigidity and strength of product.

The most reasonable wall thickness distribution is undoubtedly uniform thickness of cut surface in any place, but it is inevitable that wall thickness will change in order to meet functional requirements. In this case, transition from thick material?to thin material?should be as smooth as possible. Too sudden wall thickness transitions can result in dimensional instability and surface problems due to different cooling rates and turbulence.

Fifth, common wall thickness of different materials

ABS

Generally, material selected firstly has a wall thickness of 1, 1.2, 1.5, 2, 2.2, 2.5, 3 mm, depending on the size and function of product.

PP

Because it is softer and based on shrinkage, it can't be too thick, generally 1, 1.2, 1.5mm.

PVC

Because it is mostly used on figure and is mostly solid, so restriction is not big.

POM

Generally 1, 1.2, 1.5, 2, 2.5, 3mm depends on the size of product.

PA

Because shrinkage rate is relatively high, average material thickness and proportion of bones can be relatively small. Nylon shrinks very little after strengthening.

Kraton

Because most of them are used as mats or non-exposed parts, restrictions are not significant.

Sixth, reinforcing bars are an indispensable part of plastic parts.

Ribs effectively increase rigidity and strength of product without significantly increasing cut surface area of product, but there is no shape problem that is difficult to form,?and it is especially suitable for some plastic products?that are often subjected to pressure, torque and bending. In addition, ribs act as internal flow passages, which help to fill cavity and play a large role in helping plastics flow into branches of part.

Ribs are generally placed on non-contact surface of plastic products. Direction of extension should follow direction of maximum stress and offset of product. Position of ribs is also subject to some production considerations, such as cavity filling,?shrinkage?and demoulding. Length of ribs may be same as length of product, ends of ribs may be connected to outer wall of product, or only occupy length of product portion, to locally increase rigidity of a part of product. If ribs are not attached to outer wall of product, end portion should not be abruptly terminated. Height should be gradually reduced until end is completed, thereby reducing problems such as gas trapping, filling dissatisfaction and burnt marks. These problems often occur in locations where exhaust is insufficient or closed. Moreover, because of problem of shrinkage, thickness of bones cannot be greater than thickness of average wall thickness. General design method: less than 0.7 times uniform wall thickness.

Seventh, design of art line is usually 0.30, 0.60, 1.00, depending on the size of product.