In the design process of plastic products, there are some basic considerations that cannot be ignored. Raw material manufacturers can be said to be important promoters of plastic product design. This paper introduces the basic skills and principles of plastic product design from the aspects of material selection, processing selection, strength consideration, mold design, etc.
Design checklist
The goal of new product development or product improvement is to make products have excellent performance while obtaining low production cost. Design tasks mainly include the selection of raw materials, processing methods, strength calculation and mold design.
Only by considering these factors and following up systematically can we produce high quality and commercial mould. It must be emphasized that the practicability and cost efficiency of plastics are not inevitable, and designers must pay great attention to the correct solution of raw material selection and processing process.
Raw material comparison
Compared with other traditional raw materials, special attention should be paid to the design of plastic raw material parts.
The properties of plastics can vary in a wide range. By adding fillers, reinforcing materials and modifiers, their properties will be greatly transformed.
Sometimes under the same operating conditions, plastic will show completely different performance from metal. Therefore, the economical and effective functional design of casting metal, if applied to plastics in a hurry, will easily fail.
When the temperature of the material is close to its melting point, the temperature and time will directly affect the deformation behavior of the raw material.
The properties of plastics are not just the properties of pure raw materials. If the raw materials are processed in an unsuitable range, the best design will fail. In the same way, products cannot be processed to solve design weaknesses. Therefore, the quality of plastic parts can be guaranteed only when all factors are considered.
Cost saving design
Designers are mostly responsible for the final cost of plastic parts. His decision predetermines the cost of production, mold making and assembly. Later revisions and optimizations are often expensive and infeasible.
To give full play to the advantages of plastic raw materials can save costs in many aspects. Multifunctional integrated design, low-cost assembly technology (such as buckle, welding device, fixed device, double material injection molding technology, etc.), self-lubricating characteristics, free surface treatment procedures, etc. Pay attention to wall thickness, mold, tolerance, raw materials, etc. to further save costs.
Gate location
Designers should not only calculate the design of plastic products, but also pay special attention to the gate design of the mold. They must choose the correct gate system and the number and location of the points. Different gate types and locations will have a great impact on the quality of products.
The choice of gate location will determine the following properties of plastic products:
Filling behavior
Final dimension (tolerance) of product
Contraction behavior, warping
Mechanical performance level
Surface quality (appearance)
If the designer chooses the wrong gate, it is almost impossible to correct the consequences from optimizing the processing parameters.
Basic design principles:
Do not place the gate in a high pressure area;
Avoid or reduce the fusion line as much as possible;
Keep the fusion line as far away from the high pressure area as possible;
For reinforced plastics, the gate position determines the warpage performance of the part;
Provide adequate vents to avoid air entrapment.
Basic assembly technology
Some simple assembly technologies recognized by all designers, such as buckle assembly, press assembly and thread assembly, can greatly save production costs by assembling components easily and quickly.
The biggest advantage of buckle assembly is that no additional assembly parts are needed. In the clasp design, the designer must ensure the geometric dimension of the fitting to avoid the loose of the assembly parts caused by the stress relaxation.
Press fitting can make plastic components assemble with high strength at the lowest cost.
Thread assembly is composed of the application of separate type, combined type screw or integral screw insert. In order to avoid the occurrence of unqualified components, it is a key step to ensure the correct shaft sleeve size. Many suggestions can be made by screw manufacturers in this regard.
Material selection
Generally speaking, there are no bad materials, only the wrong materials are used in specific fields.
Thermoplastic is the most commonly used in injection molding. It can be divided into amorphous plastic and semi crystalline plastic. Generally speaking, semi crystalline thermoplastic is mainly used for parts with high mechanical strength, while amorphous thermoplastic is often used for shell because it is not easy to bend.
There are unreinforced, fiberglass reinforced, mineral and glass filled thermoplastic products. Glass fiber is mainly used to increase the strength, firmness and application temperature; mineral and glass fiber have lower reinforcement effect, mainly used to reduce warpage.
A series of reinforcement materials, fillers and modifiers are added to some thermoplastics to change their properties.
Some thermoplastic materials, especially PA6 and PA66, have strong hygroscopicity. This may have a greater impact on their mechanical properties and dimensional stability. Special attention should be paid to this performance when proceeding.
