Selecting suitable plastic particles or plastic raw materials is a complex but important process that requires consideration of multiple factors.

If it is used to manufacture high-strength parts, it is necessary to select plastic raw materials with high tensile strength and hardness, such as ABS or PC. If good chemical resistance is required, PTFE or PEEK may be selected.

Some plastic raw materials are easier to process, such as PP and PE, which have good fluidity and moldability and are suitable for large-scale production. However, some engineering plastics may be difficult to process and require special processing equipment and processes.
In addition, cost factors should be considered. Different plastic raw materials vary greatly and need to be selected according to specific budgets. It is necessary to meet performance requirements while trying to control costs and avoid excessive waste.
In addition, environmental factors need to be considered. If plastic products need to be used outdoors or exposed to specific environments, such as high temperature, low temperature, humidity, etc., it is necessary to select corresponding plastic raw materials with good environmental resistance.
At the same time, refer to relevant standards and regulations. Different application areas may have specific standards and requirements for plastic raw materials. Make sure that selected plastic meets relevant regulations to ensure quality and safety of product.
Top observation effect

 

Bottom observation effect

 

1) Buckle and screw hole: positioning, connection function (structural use function)
2) Reinforcement ribs: improve strength of part (structural function) and rough positioning (use function).
3) Stretching gap: heat dissipation and ventilation
4) Stretching incision: line channel
5) Stretching concave platform: make plane processing process simple
In summary: basic breakout part is a protective cover for an electrical component. It needs to have good heat dissipation, heat resistance, insulation, strength, corrosion resistance, oxidation resistance, stress cracking resistance, etc.
Among many plastic materials such as polyvinyl chloride (PVC), polyethylene (PE), polystyrene (PS), organic glass (PMMA), polyethylene-acrylonitrile copolymer (AS), styrene-butadiene-acrylonitrile copolymer (ABS), polyamide (PA), polyoxymethylene (POM), polycarbonate (PC), polyphenylene ether (PPO), etc., according to characteristics of each plastic and functional requirements of the parts, final priority is: polyethylene series: polyethylene (PE) + ABS(PVC has poor thermal stability, PS is brittle, PE is prone to stress cracking, POM has poor stability, is easy to burn, and will age under exposure, PC has a tendency to stress cracking, and PPO has slightly poor heat resistance.)
Its characteristics: high melting point, rigidity, hardness and strength, good stress cracking resistance, low water absorption, outstanding insulation, radiation resistance, and corrosion resistance.(I personally think that material selection for parts is not unique, because there are additives that can change strength, corrosion resistance, flame retardancy, etc. of plastics)

(I) Basic properties of polyethylene (PE)
It has excellent corrosion resistance and electrical insulation (especially high-frequency insulation). It can be chlorinated and irradiated and can be reinforced with glass fiber.
PE has good thermal stability. Generally, there is no obvious decomposition phenomenon below 300 degrees, which has little effect on quality.
PE has good molecular chain flexibility, small inter-bond force, low melt viscosity and excellent fluidity. Therefore, it does not require too high pressure to form products during molding. General injection pressure is 50~100MPa.

 

PE has a wide shrinkage range, large shrinkage value, and obvious directionality. Therefore, it is easy to deform and warp. Mold cooling conditions have a great influence on shrinkage, so mold temperature should be controlled to keep cooling uniform and stable.
PE has a high crystallization ability, and temperature of mold has a great influence on crystallization condition of plastic part. High mold temperature and slow melt cooling will result in high crystallinity and strength of plastic part.
PE has a low melting point, but a large specific heat capacity, so it still needs to consume a lot of heat during plasticization, so plasticizing device is required to have a large heating power to improve production efficiency.

 

(II) Characteristics of ABS plastic
From a morphological point of view, ABS is a non-crystalline material. This determines low temperature resistance, impact resistance, appearance characteristics, low creep, excellent dimensional stability and easy processing of ABS materials. Surface hardness is high and chemical resistance is good. At the same time, by changing ratio of above three components, various properties of ABS can be changed, so ABS engineering plastics have a wide range of uses.
Injection temperature: 180~270℃ (for injection plug machine, furnace temperature is maintained at 180~230; for screw machine, furnace temperature is maintained at 160~220).
Injection pressure of ABS is 70~90 MPa.

 

ABS has high impact strength and surface hardness in a relatively wide temperature range, its heat deformation temperature is higher than that of PA and PVC, with good dimensional stability, and shrinkage rate is in the range of 0.4%~0.8%. If it is reinforced with glass fiber, it can be reduced to 0.2%~0.4%, and there is very little post-plastic shrinkage.
Fluidity of ABS melt is better than that of PVC and PC, but worse than that of PE, PA and PS. Flow characteristics of ABS belong to non-Newtonian fluids. Its melt viscosity is related to both processing temperature and shear rate, but is more sensitive to shear rate.

 

PE has a wide range of shrinkage, (1.5-3.6%) large shrinkage value, and obvious directionality. Therefore, it is easy to deform and warp. Mold cooling conditions have a great influence on shrinkage, so mold temperature should be controlled to keep cooling uniform and stable.
PE has a small softening temperature range and melt is easy to oxidize. Therefore, melt should be avoided as much as possible during molding process to avoid contact with oxygen to avoid reducing quality of plastic parts.
1. Preparation and drying of ABS raw materials. During feeding process, attention must be paid to sealing to ensure that raw materials are clean. In particular, if raw materials contain moisture, surface defects such as silver streaks will occur during injection molding, so materials must be fully dried before injection molding, and a drying hopper must be used during injection molding.
2. During injection molding, flame retardants may decompose and produce corrosive gases, causing corrosion and wear of mold. Therefore, set an appropriate molding temperature during processing and avoid storing material in barrel for a long time. At the same time, after using flame-retardant plastics, injection molding machine must be cleaned with general resin.

 

Selected materials are: polyethylene (PE) + ABS. Drying is required during injection molding.
Plastic parts with a wall thickness of less than 6mm should use a higher mold temperature. (Thickness of this part is 2mm) Melting: The best temperature is 220-260 degrees Celsius. Temperature of mold is 50-95 degrees Celsius.
· For small heat dissipation gaps and bayonet sizes, it is necessary to pay attention to sufficient cooling during water cooling
Concave part in the middle of part and layered boss strengthen strength of part. Although more materials will be used, focus is on finding flat point between the two, reducing costs, and achieving maximum economic benefits.
Surface area of part is relatively large (47203.8mm2), and demoulding force it is subjected to should also be large. Therefore, it is necessary to ensure that ejector rod is evenly distributed with force and can withstand demoulding force during ejection process so as not to damage part.

 

(I) Preliminary selection of injection molding machine
1. Calculation of volume of plastic parts
Use UG software to perform solid modeling and directly analyze through software. Volume of plastic part is:
VPart=48.21601cm3
2. Preliminary selection of injection molding machine
According to manual, injection pressure of ABS and PE is in the range of 60~120 MPa. Plastic parts are relatively simple, so P=70Mpa
(1) Calculation of projected area of plastic part A=10132.4mm2
(2) Calculation of cavity pressure Pcavity=2/3xP=46.7Mpa
(3) Calculation of clamping force F=APcavity=470x103N
Based on calculation, check table (2-33)[1] to preliminarily select screw injection molding machine: XS-Z-60.
(II) Verification and final selection of injection molding machine parameters
1. Verification of mold closing height
Height of installed mold should meet: Hmin<H<Hmax
Designed as a two-plate mold, estimated mold height is Htotal=190mm (10+25+25+30+40+30+30 from top to bottom)
Since minimum mold thickness allowed by XS-ZY-60 injection molding machine is Hmin70mm and maximum thickness is Hmax200mm, mold closing height meets installation requirements.

 

2. Verification of mold opening stroke
Mold opening stroke should meet: Sm<Sz. Among them: Sz is maximum mold opening stroke. Check injection molding machine XS-ZY-60 model Sz=200mm, Sm is mold opening stroke of mold; Sm=height of plastic part+height of pouring system+ejection height of ejector+(5-10) =25+30+20+7 =82mm. It can be seen that Sm<Sz, and XS-ZY-60 meets its mold opening stroke.

 

3. Parameter verification of injection molding machine

 

V type=48.21601cm3
① Verification calculation of maximum injection volume
Verification formula: (0.8~0.85)V male ≥ V type. Among them: V type= 48.21601cm3
(0.8~0.85)V male=0.85x60=51cm3. It can be seen that verification formula is met, that is, injection volume of designed mold meets maximum injection volume requirement of XS-ZY-60.
2. Verification of injection molding machine pressure
Pmachine ≥ Pplastic
Pmachine--maximum injection pressure of injection molding machine, MPa
Pplastic--injection pressure required for molding plastic parts, MPa
Generally, ABS+PE takes 60-120MPa, and maximum injection pressure of XS-ZY-60 injection molding machine is Pmachine = 154Mpa. It can be seen that XS-ZY-60 injection molding machine meets requirements of ABS+PE injection pressure.
3. Verification of clamping force
Clamping force required for part is 470x103N, and clamping force of the XS-ZY-60 injection molding machine is 500KN to meet requirements.
Comprehensive verification shows that XS-ZY-60 injection molding machine can fully meet injection requirements of this part.