Plastic extrusion, we usually think of it only used in the construction industry, as doors and windows. But in fact, plastic extrusion can also be used in many industries, such as lamps, electrical appliances, transportation and medical treatment. Product structure design also requires learning and mastering plastic extrusion. In some cases, extrusion may be a powerful tool for cost reduction.
Extrusion molding process
1.1 Process introduction
Extrusion molding is a plastic material processing field with many changes, high productivity, strong adaptability, and wide range of uses. The molding processing method that accounts for the largest proportion.
Extrusion molding is to continuously shape polymer melt or viscous fluid through a die of a certain shape under the extrusion of the screw or plunger of the extruder. The resulting parts are Continuous profile with constant cross-sectional shape.
The extrusion molding of rubber is usually called extrusion. Rubber extrusion molding was used earlier, and the equipment and technology are relatively mature. Extrusion is a process in which rubber materials are continuously made into semi-finished products of various shapes through an extruder. It is widely used in the manufacture of tire treads, inner tubes, rubber hoses and Various semi-finished products with complex cross-section shapes or hollow or solid products can also be used for rubber lagging operations, which is an important process in the rubber industry production.
1.2 Process advantages and disadvantages
Advantages of extrusion molding:
Simple operation, easy process control, continuous, industrialized, automated production, and high production efficiency , stable quality.
It has a wide range of applications and is widely used in the molding and processing of plastics, rubber, and composite materials. It is also commonly used in the coloring, mixing, plasticizing, granulation, and mixing modification of plastics.
The extrusion die is easy to process and easy to replace.
The equipment is simple, the investment is small, and the results are quick.
The production environment is hygienic and the labor intensity is low.
The parts cost is low and suitable for mass production.
Disadvantages of extrusion molding:
Only linear parts can be produced with simple geometric shapes.
The section (or section) of the part cannot be changed.
Compared with injection molding, the precision of parts is lower.
1.3 Application
Extrusion molding is suitable for plastic films, nets, coated products, pipes, plates, rods, sheets with a certain cross-section and continuous length, Films, monofilaments, cable wrapping layers, various special-shaped materials, etc. can also be used for powder granulation, dyeing, resin blending, etc.; they are also widely used in the production of various reinforced plastic pipes, rods, special-shaped cross-section profiles, etc.
DFM Design Guide for Extruded Parts
2.1 Material Selection
Not all thermoplastics can be processed by extrusion molding.
Common basic materials include hard materials and elastic materials.
Hard materials: PVC, PC, PETG, ABS, PP, HIPS, PMMA, LDPE, HDPE, POM, ASA, PA, AS, EVA, PC ABS, etc.
Elastic Materials: PVC, TPU, TPE, POE, TPR, TPV, TPEE, etc.
2.2 Uniform wall thickness
Same design as injection molded parts, aluminum extruded parts, etc., uniform wall thickness Crucial.
If the wall thickness of the plastic extrusion is uneven, thick in some places and thin in others, this will cause the plastic to flow at an uneven speed when it is extruded in the mold, resulting in different cooling rates and ultimately causing the parts to deform.
If deformation needs to be controlled, additional cooling processes need to be added, which will reduce the efficiency of the production line and increase production costs.
2.2 Avoid complex hollow structures
(1) Avoid complex hollow structures
Since plastic extrusion is a continuous process, the extruded parts just The strength is low during extrusion and requires support such as air pressure and mandrels to maintain shape and avoid deformation. However, the hollow part cannot provide support. Complex hollow structures can only be realized by opening the cross-section.
(2) Avoid hollows in hollows
Hollows in hollows will inevitably deform because they cannot provide support before cooling and solidification.
(3) Provide openings for internal features
If the extrusion design has an opening or groove, buckles or other features can be designed internally.
2.3 Design of rounded corners
The sharp corners on the extruded parts will become a weak point of the extruded parts due to stress concentration, which is prone to cracking or Failure will also reduce the impact resistance of the extruded parts.
In extruded parts, sharp corners should be avoided as much as possible, and fillets should be added to the sharp corners. The radius of the fillet is equal to the wall thickness of the product, which helps the material flow more smoothly during the extrusion process. flow, and reduce stress at the corners of the profile.
2.4 Design to avoid shrinkage
At the intersection of multiple walls, there will usually be a thicker wall area, so shrinkage will easily occur on the outer surface of the extruded part. Poor appearance, very similar to injection molding.
If the extruded part is an appearance part, the shrinkage can be avoided or the shrinkage defect can be covered up through the optimized design as shown in the figure below.
2.5 Avoid setting strict tolerances in the length direction
Where possible, try to avoid setting strict tolerances in the length direction. Thermoplastics shrink and expand with temperature, and cutting plastic extrusions to very critical lengths can unnecessarily increase costs.
Generally speaking, the tolerance on a 1000 mm long extrusion is /-5 mm. Of course, the tolerance accuracy is related to the length. The shorter the length, the higher the accuracy that can be achieved.
2.6 ***Extrusion
*** extrusion refers to extruding two or more materials at the same time between the cooling of the extrusion parts and combining them in the same extrusion On the pressing piece.
It is possible to combine two different colors in the same extrusion, or to produce a two-color extrusion with primary and secondary color stripes.
It is also possible to compose a hard material and a flexible material in the same extrusion, which allows a rigid extrusion to have a flexible lip or tab, or allows two rigid extrusions to pass through a flexible Hinge connection.