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Plastic Parts Design Guide

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Introduction to Plastic Part Design

plastic designPlastic part is the most common components for nearly every product, which is widely used iin automotive, medical, electronic, home appliance, and other industrial products. As plastic parts offers low cost, consistent repeatability, complex part structure, and thin of wall.

 

A plastic parts can be manufactured by injection molding, blow molding, extrusion molding, and silicone molding. However injection molding is the most popular process to manufacture plastic parts in large volume. So it is very important to understand some basic knowledge on its design and manufacturing.  

 

However it’s not easy to design a proper plastic parts with cost-effective, durable of use, and good appearance. Because a good plastic design requires the comprehensive background and experience on product functional, part structure, material selection, assembly efficiency, manufacturing cost, and injection molding manufacturing process. 

 

In theory, we must design parts with good aesthetics, enough strength, easy-for- manufacturing. Meanwhile, even thickness of wall, proper draft, ribs, radius, and chamfer are most common design fundamentals for parts structure. On the other hand, a correct material choose is also very important to plastic part design.

 

Here below we would like to share some useful experience about plastic injection molding parts design, which would be helpful for product designer, project manager, or other related people.

Plastic Parts Design Skills

Plastic injection molded parts play an very important role when we design a new product. Nowadays, nearly every product requires to use plastic components.

A good plastic part design can offer excellent product appearance, durable mechanical strength, and easy manufacturing-ability by injection molding manufacturing process. On opposite, a bad plastic parts design could result in assembly interference, cost increasing, and hard for injection moulding.

In order to help our clients understand some basic rule of designing plastic parts, we would like to share our experience on how a plastic parts should be designed as below.

1. Make part thickness as even as possible

Design Purpose:

  • In order to enable plastic resin flows smoothly and evenly while injection molding, we must design the thickness of wall evenly, and try to avoid too thick or too thin wall when we design a plastic part structure.
  • To avoid shrinkage issue to happen, we must avoid too thick or too think wall when we design a plastic part structure.

 

Design tips:

  • Design part thickness ranging from 1.2mm~2.5mm
  • Make the overall thickness evenly

Incorrect

Uneven thickness of wall

Uneven Thickness of Wall

Correct

Uneven thickness of wall-1

Uneven Thickness of Wall

2. Try to make ribs to enhance part strength

Design Purpose:

  • In order to eliminate internal stress and improve mechanical strength of features, like pillars, screw boss, rotating shaft, side edge, etc, we should make those features with ribs enhanced
  • The thickness of ribs should be 0.5~0.85 of overall thickness of parts.(this is to avoid shrinkage issue when injection molding production)

 

Design tips:

  • A 2-ribs or 4-ribs should be designed for a supporting pillars
  • A 4-ribs should be designed for a screw boss
  • A 4~8 ribs should b designed for a thin of wall(edge)

Incorrect

image of rib-1

Without Rib Enhancement

Correct

image of rib-2

Ribs Design

3. Make radius when there is a strength requirement

Design Purpose:

  • In order to eliminate internal stress and improve mechanical strength of part, we should make those connected corners with radius feature

 

Design Tips:

  • Design corners with radius of 0.2~2.0mm, and we need to choose a proper size of roundness according to part size, edge length, and part material.
  • A 0.5~1.5mm of radius should be designed for a hole.
  • A 0.3mm~2.5mm of radius should be designed for a pillar

Incorrect

image of radius-1

Straight Corner

Correct

part radius-2

Radius Corner

4. Make proper chamfer to facilitate assembly process

Design Purpose:

  • In order to make assembly process more efficient, we normally design chamfer on hole or slot while a plastic part design.

 

Design Tips:

  • Around 0.5×0.5mm chamfer should be designed for a screw hole
  • Around 1.0×1.0mm chamfer should be designed for a clipper feature
  • Around 5×0.5mm chamfer should be designed for an assembly shaft

Incorrect

image of chamfer-2

No Chamfer on the Boss

Correct

image of chamfer-1

Chamfer Design

5. Proper draft is needed for mold release

Design Purpose:

  • In order to enable plastic parts release easily from mold tool, a certain degree of draft must be designed when design a plastic injection molding parts.
  • Depends on parts length and size, a 0.5~5.0 degree of draft should be designed.

 

Design Tips:

  • Make a small to medium size feature(50~150mm in depth) as 0.5~2.0 degree of draft
  • Make a self-screw hole as 1.0~3.0 degree of draft
  • Make a deep feature(150~500mm) with as big draft as possible(2.5~5.0degree)

Incorrect

draft-2

No Draft

Correct

draft -1

Drafted

6. Less part weight, & avoid mold slider, & use normal resin

Design Purpose:

  • In order to save injection molding manufacturing cost, we strongly recommend to design the part with as lighter weight and normal raw material as possible.
  • To save the mold tool cost, try to avoid mold sliders and lifters while designing a part structure.

 

Design Tips:

  • Design the part thickness as thin as possible
  • Avoid unnecessary part structure so as to save part weight
  • Design the part structure that can be molded without sliders and lifter

Incorrect

image of light weight

Heavy Weight

Correct

part weight - 1

Light Weight

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How to Choose Right Plastic Material?

There are numerous of plastic resin that can be used to manufacture plastic parts. It seems so confused to choose a proper plastic material when we design a plastic product. In fact, it’s not true! As we can narrow our choice by considering the part function, intended application of the part, using condition of part, and your budget of the project. Then choose the most suitable material easily.

Part Function

Definition:

For different function of plastic component, we can divide plastic part into outer case, interior housing, connecting hub, rotating parts(agitator, gear, wiper,etc)

 

Material Application:

  • Cover, Housing: ABS, PC, ABS+PC, PS, PP, TPU,etc
  • Rotating parts(agitator, gear, wiper,etc): POM, POM+GF, PA6, PA66, PA+GF, HIPS, etc
  • Normal Parts: PP, PE, PS, ABS, etc

Using Condition

Definition:  

There could be many different condition while a plastic part used in a product. When choose a plastic material, we should consider the impact resistance, dimension stable-ability, electronic conductivity, anti-fire ability, high-temperature condition, etc.  

 

Material Application:

  • High Impact Resistance Material: ABS, PC, ABS+PC, HIPS, POM, PA, PSF, etc
  • High Abrasion Resistance Material: POM, PA6, PA66,PPO
  • High Temperature Resistance Material: ,PPI,LCP,PEI,PPA, etc
  • Anti-fire Material: PBT,PVC,POM, PA
  • Stable Dimension(Less Shrinkage Rate): PC, ABS, ABS+PC, PF(phenol-formaldehyde)
  • High Transparent Material: PMMA, PC, PP
  • Light Weight of Part(Cheap at Cost): PP,PE,PS, PVC

Cost

Definition:  

Since there are different level of plastic rein which perform totally different result, of course, those material has different price. When we choose a plastic material, we try to sort out the cheapest and practical material to use.

 

Material Application:

  • Cheap Plastic Material: PP,PE,PS, PVC,PET, PU
  • Medium Cost of Plastic Material: ABS, POM, PA, PP, PMMA, PET, TPE
  • High Cost of Plastic Material: PC, PPO, PPSU,

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