Material, wall thickness, demoulding angle, reinforcing ribs, pillars/screws, stoppers, buckles, and others

 

Uses: toys, daily necessities, packaging plastic bags, bottles
Features: elastic, strong toughness, large extensibility, but cannot be coated with glue, working temperature -30℃~140℃
Application: Mostly used in places where parts need to be disassembled for drop tests.

 

-Use: soft pipes, hard pipes, soft boards, hard boards, wires, toys
-Features: soft, tough and elastic, working temperature -25C~75℃; 200℃ easily decomposes to produce corrosive and irritating gases.
-PVC wires and cables will produce a large amount of dioxins, hydrochloric acid, lead and other harmful substances during manufacturing, use and disposal.
Design application: mostly used in toys, or some places that need shock absorption or shock absorption.

Uses: Insulating transparent parts, decorative parts, chemical instruments, optical instruments; foamed PS (styrofoam), building sound insulation, heat insulation layer, refrigerator insulation layer, disposable lunch box, helmet buffer layer;
-Characteristics: good insulation, hard and brittle, colorless and transparent, dyeable, heat-resistant. Foamed PS cannot be recycled;

 

Uses: vehicle front and rear lights, dashboards, refrigerator drawer mixers, network cable crystal plugs, disposable medical devices;
Features: colorless and transparent, non-toxic, dyeable, impact-resistant, wear-resistant, corrosion-resistant, antibacterial, flame-retardant, high and low temperature resistant (-60~120℃)
Application: Mostly used in transparent parts, replacing glass

 

Use: Mechanical parts, gears, home appliance housing
Features: Wear-resistant, hard but fragile, easy to have sharp edges when damaged.
Application: Mostly used in rubber gears, pulleys, some places that need transmission and withstand large torque or stress.

 

-Use: gears, pulleys, textiles
-Features: tough, water-absorbent, wear-resistant, shock-absorbing, heat-resistant, but becomes fragile when water evaporates completely.
-Application: Because accuracy is difficult to control, it is mostly used for some gears with larger modules

 

-Applications: motor pads, hand tool handles
-Features: soft, elastic, high toughness, strong elongation.
-Design applications: mostly used as motor pads to absorb motor vibration and reduce noise.

 

 

Generally, it should not be less than 0.6~0.9mm, and 2~4mm is often selected.
ABS: Generally, material is selected first, and wall thickness is usually 1, 1.2, 1.5, 2, 2.5, 3mm, depending on size and function of product.
PP: Because it is relatively soft and based on shrinkage problem, it cannot be too thick, generally 1, 1.2, 1.5mm. Wall thickness of thin-walled parts is 0.6mm.
PVC: Because it is mostly used due to its appearance, it is mostly solid, so there is no big restriction.
PS: 1.5~5.0mm.
PC: 1.0~4.0mm.
POM: Generally 1, 1.2, 1.5, 2, 2.5, 3mm, depending on size of product.
Basic design principles
Generally, thickness of plastic parts is 2~3mm, such as wall thickness of our range hood panel is 2~3mm, and maximum design wall thickness of thermoplastics is 4mm.
Size of wall thickness depends on:
a External force that product needs to withstand;
b Whether it is used as a support for other parts:
c Number of supporting columns;
d Number of reinforcing ribs
e Selected plastic material
From an economic point of view, if product is too thick, it will not only increase material cost, extend cooling time of production cycle, and increase production cost. From perspective of product design, it increases possibility of causing cavitation and pores, weakening rigidity and strength of product every day, and increasing shrinkage of product.
Plane principle
The most ideal wall thickness distribution is undoubtedly a uniform thickness at any place on cut surface, but it is always inevitable to change wall thickness to meet functional requirements. Thick wall area cools slower than thin wall area next to it, and shrinkage marks appear on the surface of connecting area after gate solidifies. Worse still, it leads to shrinkage marks, thermal internal stress, distortion of flexure part, different colors or different transparency. If it is inevitable that thick wall area gradually becomes thin wall, it should be designed as much as possible so that plastic flows from thick wall area to thin wall area, and transition between different planes should change gradually, and ratio of wall thickness should not be less than 3:1. Following figure is for reference.

 

Corner Guidelines
Key to uniform wall thickness is also required at corners to avoid inconsistent cooling time. Areas with long cooling time will shrink, causing deformation and deflection of parts. In addition, sharp fillets usually lead to defects and stress concentration in parts. Sharp corners often cause unwanted material accumulation after electroplating process. Places with concentrated stress will break when loaded or impacted. Larger fillets provide a solution to this shortcoming, not only reducing factors of stress concentration, but also making flow of plastic smoother and easier to demold finished product. There is a certain ratio between arc position and wall thickness. Generally between 0.2 and 0.6, and ideal value is around 0.5. Following figure can be used for reference.

 

Wall thickness design

 

 

Basic design principles
In design of plastic products, it is usually necessary to set an inclined mold release angle on inner and outer sides of edge in order to easily release product from mold. Otherwise, if product is perpendicular to outer wall and in same direction as mold opening, mold will require a lot of mold opening force to open after plastic is formed. Moreover, after mold is opened, process of product being released from mold is also believed to be very difficult. In addition, if mold is forced to be released, it will leave a pull mark on product. If mold release angle has been reserved during design process of product and all mold parts that contact product have been highly polished during processing process, demolding becomes a piece of cake.
Since injection molded parts often attach to punch after cooling and shrinking, in order to make product wall thickness uniform and prevent product from attaching to hotter die after mold opening, draft angle corresponding to die and punch should be equal. However, in special cases, if product is required to attach to die after mold opening, draft angle of connecting die can be minimized, or an appropriate amount of undercut can be deliberately added to die.
There is no fixed standard for size of draft angle, which is usually determined by depth of product.
General draft angle is 0.5°-1.0.
For products with deep or textured textures, draft angle requirement increases accordingly depending on depth of texture, generally 2°-3°.
Required draft angle is clearly listed on general texture plate for reference.

 

Ribs are an indispensable functional part of plastic parts. They can increase rigidity and strength of products without significantly increasing cross-sectional area of products. The most effective shape of ribs is an "I" iron, which is particularly suitable for some plastic products that are often subjected to pressure, torsion, and bending. However, "I" iron shape has undercuts and is difficult to demold. It is generally designed in a "┴" shape. In addition, ribs can also serve as internal flow channels to help fill mold cavity, which plays a great role in helping plastic flow into branch parts of components.
· Rib placement
Ribs are generally placed on non-contact surface of plastic products. Their extension direction should follow direction of maximum stress and maximum offset of product. Location of ribs is also subject to some production considerations, such as direction of plastic flow, shrinkage and demoulding.
· Rib shape
Length of rib can be consistent with length of product, with both ends connected to outer wall of product, or only occupy part of length of product to locally increase rigidity of a certain part of product. If reinforcement is not connected to outer wall of product, end part should not end suddenly, but should gradually reduce height until it ends, so as to reduce problems of trapped air, incomplete filling and burn marks, which often occur in insufficient exhaust or closed positions.

 

1. To prevent shrinkage defects and ensure strength of reinforcing ribs, width of reinforcing ribs is generally 1/2~2/3 of wall thickness;
2. Reinforcing ribs should have a demoulding slope. If allowed, the greater slope, the better;
3. To ensure that plastic parts are basically flat, end face of reinforcing ribs should not be flush with supporting surface of plastic parts, and should be at least 0.5mm lower than supporting surface.

 

 

Height of pillars should generally not exceed two and a half times diameter of pillars

 

 

Draft angle of pillar is usually based on plane at the top of pillar as neutral plane, and angle is usually 0.5°~1.0°. If height of pillar exceeds 15.0mm, in order to strengthen strength of pillar, some reinforcing ribs can be connected to pillar for structural reinforcement.
Pillar sleeve
According to general safety standards, screw head must be stored in a position that cannot be touched, so height must be 2.5mm or more. Since there will be sharp edges after adding pillar sleeve, a fillet of R1.0 or more must be added to each place where pillar sleeve is placed to receive screw.

 

 

True stopper
Purpose: Used for comparison during production and assembly, and can also be used for applying glue.

 

False stopper
Purpose: It can be used to cover up appearance of blemish.

 

Semi-false stop
If average material thickness is 2.0mm or more, because groove is too deep, it is necessary to add an extra layer of material at stop position to maintain the appearance of finished product.

 

Double stopper
Application: Mostly used in finished products that need waterproofing. In addition, ultrasonic welding will be used for assembly to enhance effectiveness.

 

Case 01

 

Design summary
1. Material selection;
2. Appearance design: Use copy geometry and release geometry to split shell;
3. Wall thickness: Set according to material and part size;
4. Draft angle: After designing each feature, pay attention to checking angle
5. Stop: Use offset tools, pay attention to virtual position matching; inactive virtual position (0.1), active virtual position (0.3)
6. Pillar: Use stretching tools, pay attention to stretching order, and check size table;
7. Rib: Use EDM, no draft angle is required on both sides.
8. Interference check