Views: 212
1. Design multifunctional parts
Injection molds are usually expensive and designing multi-functional plastic parts can share the cost of the mold, thus reducing part development costs; at the same time, because plastic parts can have complex shapes and internal structures, one plastic part can often replace two or even more parts processed by traditional process methods, and multiple plastic parts can in some cases be combined into one plastic part to save costs.
For example, in electronic and electrical products, reasonable cable routing and fixing are critical to product heat dissipation and electromagnetic interference, etc.
Cable wire fixing is generally accomplished byspecial cable ties or clips, while cable wire fixing can be achieved by adding some simple features to the plastic parts, as shown in Figure 1, thus reducing the use of cable ties or clips.
2. Reduce the material cost of parts
Plastic materials are one of the products of the oil industry. As the oil reserves continue to decrease, the price of plastic materials is also increasing. In previous years, when the price of oil rose, the price of plastic materials rose, and even caused home appliance companies to raise the price of home appliances.
Therefore, parts should be designed to use as little material as possible while maintaining product function and other requirements. Fewer materials can reduce the cost of the part while avoiding increased injection time when the part is injected, which can increase injection costs. When reducing the use of part materials, care needs to be taken to.
1. The strength of the part is improved by adding reinforcement rather than increasing the wall thickness.
2. The thicker part of the part removes material.
3.Simplify part design and reduce mold cost
The simpler the design of plastic parts is also the better. Complex plastic parts shape and structure will not only increase the complexity of the mold structure and increase the cost of the mold, but also affect the quality and performance of the parts.
Plastic parts should be designed as multifunctional parts as possible, but multifunctional parts do not mean complex parts. If the design of plastic parts multi-functional instead caused the overall cost of the product to rise, this is precisely against the purpose of plastic parts multi-functional, because one of the purposes of plastic parts multi-functional is to reduce the cost of the product.
4. Avoid tight tolerances on parts
The factors affecting the dimensional tolerance of plastic parts are shown in Table 1.
Plastic properties | Product Design | Mold Design | Injection molding process |
Shrinkage (isotropic and anisotropic) | Product Structure | Mold accuracy | Injection molding machine performance |
Dimensional stability | Wall thickness | Number of mold cavities | Injection pressure/speed |
Viscosity | Demolding slope | Runner system | Holding pressure/speed |
Whether to add reinforcing fiber | Symmetry | Ejector system | Melting temperature and mold temperature |
Surface treatment | Cooling System | Clamping force | |
Size | Mold design/layout | Repeated production capacity |
The dimensional tolerance accuracy of injection processing can be divided into three grades: general grade injection, technical grade injection and high precision grade injection. Table 2 lists the cost indices of the three grades and their requirements for injection processing.
| Dimensional tolerance grade for injection molding process | General grade injection | Technical grade injection | High precision grade injection | |
Cost Index | 100 | 170 | 300 | |
Injection molding processing requirements | Mold precision requirements | General mold processing technology | Requires high precision in mold processing dimensions | High precision mold processing technology |
Mold cavity requirement | Multiple cavities in one mold | Some cases can be multiple points in one mold | A model of a cave | |
Injection Molding Process Parameter requirements | Injection Molding Process Parameter requirements are not strict | Injection Molding Process Strict parameter requirements | Injection Molding Process Parameters need to be closely monitored | |
Waste material use | Waste material can be reused | The waste material can be reused within a certain range | No waste material can be used | |
Inspection | Occasional testing | Statistical quality control | Statistical process control | |
The tighter the dimensional tolerances of plastic parts, the higher the requirements for mold accuracy, mold cavities, injection molding process, inspection, etc., and the higher the cost of plastic parts. Product design engineers should be aware of the huge impact of strict plastic part dimensional tolerances on the cost of plastic parts and mold costs. Therefore, in the design of the product, to ensure the function of the part and other premises, through the optimization of product design, try to avoid the use of strict plastic parts dimensional tolerances. For plastic parts, some additional measures include.
1. Designing a reasonable clearance.
2. Simplify product assembly relationships.
3. Use positioning features.
4. Use points or lines to match the plane
5. In applications requiring high dimensional accuracy, choose plastics with low shrinkage.
6. Additional alignment errors exist at the fit of the mold cavity to inserts, bevel pins and slides, etc. Avoid tight tolerance requirements in this area.
7. Predict the warpage deformation area of plastic parts and avoid tight tolerance requirements in that area; usually warpage deformation can be reduced by adding reinforcement, etc.
5. Parts design to avoid backward buckling
A chamfer is a feature where the part cannot be released properly, such as an opening on the upper side of the mold opening direction and a tab on the side. In the mold, the inverted buckle is realized by the lateral parting and core extraction mechanism, which is one of the more complicated structures in the mold and an important factor to increase the mold cost. The commonly used lateral parting and core extraction mechanism includes tilt pins and sliders.
To reduce tooling costs, part design to avoid backlash is an important tool.
(1) Some external buckling can be avoided by redesigning the parting surface
As shown in Figure 2, redesigning the parting surface can avoid the part from being backed up on the outside and not being released smoothly.
(2) Redesign of part features to avoid part backlash
Many parts inverted features can be removed by feature optimization design, thus avoiding the use of lateral core extraction mechanism and reducing the part tooling cost, as shown in Figure 3.
As shown in Figure 4, in the original design, the part had an inverted buckle that required a lateral core extraction structure such as a tilt pin or slider to release the mold; by redesigning the part features, the use of a lateral core extraction mechanism can be avoided, and four methods are provided in the improved design, see Figure 4b, c, d and e.
6. Reduce the cost of mold modification
When a pair of plastic parts injection molds are manufactured, it is very costly to make further mold modifications. Incorrect plastic part design often increases the number of mold modifications and raises the cost of the mold, thus increasing the cost of the part and the product. Therefore, the design of plastic parts needs to minimize or even avoid mold modifications.
(1) Design for injectability of parts
Plastic parts design should be fully considered when the injectability of the parts. Good injectability of the parts, high quality of the parts after injection molding, the number of mold modifications will be less, mold modification costs are low. If the plastic parts design does not consider the injectability of the parts, parts injectability is poor, the parts after injection molding quality is low, the number of mold modifications, mold modification costs are high.
(2) Reduce the number of product design revisions
Of course, mold modifications may also be due to the plastic parts in the entire product can not achieve its proper function, so before mold development, product design engineers need to improve and optimize the design of the parts through CAE analysis and motion simulation, sample production and other means to ensure that the parts design is foolproof, and then the design and development of the mold, so as to reduce product design modifications after the completion of mold manufacturing.
(3) Avoid adding material for mold modification
It is easier to remove material from the mold and the modification cost is low; it is more complicated to add material to the mold and the modification cost is high. Therefore, the design modification of plastic parts is best to make the mold remove material rather than add material, then the design modification of plastic parts should be to add material rather than remove material. In the design of the part, if the design of the part is not sure, then you can keep a certain margin for the size of the part, and then verify the design of the part by removing the material.
7. Use clips instead of screws and other fixed structures
The fixing methods of plastic parts include snap, screw, hot melt and ultrasonic welding, etc. Snap can be quickly assembled and quickly disassembled, while snap has the lowest cost, and the use of snap can reduce the cost of parts under the premise of meeting the product assembly as well as function.
8.Reasonable selection of mold cavities and runner system
The number of cavities in the mold affects the processing efficiency of the plastic parts. The higher the number of cavities, the more complex the mold, but the higher the processing efficiency of the plastic part, the lower the processing cost, and the lower the share of runner material for a single part. The number of cavities can be reasonably selected by calculating the cost of the plastic part (material cost, mold cost sharing and processing cost) under the expected plastic part capacity requirement.
In addition, proper selection of runner system also helps to reduce the cost of plastic parts. The traditional cold runner system has the disadvantage of runner material depletion, especially for expensive plastic materials. In contrast, hot runner system basically does not have runner material loss, and because there is no runner system, the cooling time of the plastic parts and mold opening stroke can be shortened, which can shorten the molding cycle, in addition, no need to trim the gate and recycling process sprue and other processes, conducive to production automation; but the disadvantage is that the price is more expensive than the traditional cold runner mold.
9.Other
1. Parts appearance decorative features and parts on the text and symbols should be convex outward, mold processing for the concave, easy processing.
2. Design parts and molds so that gates can be automatically removed or hidden inside the product to avoid secondary processing of gates. Hide the parting face inside the product to avoid secondary removal of the parting face.
