What are the processing technologies of plastic parts of sweeper during injection molding?

Injection molding of plastic parts of sweeper should combine its structural diversity (such as shell, gear and dust cup) and functional requirements (such as wear resistance, sealing and light weight). The core technology covers basic injection molding, special molding and post-treatment, so as to ensure the product accuracy and service performance meet the standards.

1. Injection molding process of core foundation: to meet the molding requirements of different structural parts.

The basic technology is the core of plastic parts processing of sweeper, so it is necessary to choose the adaptation mode according to the component structure (thin-walled/thick-walled, complex/simple) to ensure molding efficiency and quality.

Ordinary injection molding: suitable for most conventional parts.

Application scenario: parts with relatively simple structure and uniform wall thickness (1-3mm) such as body shell, dust cup body and water tank of sweeper.

Key points: using single cavity or multi-cavity mold, injecting molten plastics (such as ABS and PP) into the mold cavity by injection molding machine at high pressure, maintaining pressure and cooling, and demoulding. It is necessary to control the barrel temperature (ABS 200-240℃, PP 180-220℃) and mold temperature (ABS 50-80℃) to avoid shrinkage marks and flash of the shell, ensure the smooth surface (Ra≤0.8μm) and meet the appearance requirements.

Precision injection molding: suitable for high-precision fitting parts.

Application scenario: components that need to be accurately matched with metal parts or other plastic parts, such as walking wheels, driving gears and sensor mounting seats of sweepers (matching clearance ≤±0.05mm).

Key points of the process: use high-precision mold (machining tolerance ≤±0.02mm), adopt closed-loop control injection molding machine, and accurately control the injection pressure (80-120MPa), speed (controlled by sections to avoid the melt scouring the cavity) and holding time (5-10 seconds). The modified plastics with good dimensional stability (such as PA66+glass fiber and POM) are preferred as materials to reduce the shrinkage deformation after molding (the shrinkage rate is controlled at 0.5%-1.5%).

Thin-walled injection molding: suitable for lightweight and small parts.

Application scenario: Thin-walled (0.5-1mm in wall thickness) and small-sized components such as filter screen frame and internal terminal seat of sweeper should give consideration to both lightweight and structural strength.

Key points of the process: select high-fluidity materials (such as high-fluidity PP, PC/ABS alloy, melt index ≥20g/10min) and adopt high-speed injection (injection speed ≥100mm/s) to shorten the melt filling time and avoid material shortage or bubbles; The mold needs to be provided with an efficient exhaust slot (0.01-0.02mm in depth) to prevent scorching caused by trapped air, and at the same time, the cooling system should be strengthened (such as adopting conformal cooling water channel) to ensure the rapid solidification and setting of thin-walled parts.

Second, the special molding process: to meet the needs of functional parts

Aiming at some special functional parts of the sweeper (such as sealed, wear-resistant and complex appearance parts), it is necessary to realize the performance and structural requirements through special processes.

Two-color/multi-color injection molding: improving the integration of appearance and function

Application scenario: the operation panel of the sweeper (such as soft keys and hard panel integrated) and the decorative strip of the fuselage (spliced with different colors or materials) should take into account the hand feel and appearance recognition.

Key points of the process: using a two-color injection molding machine and a rotating mold, the first material (such as hard ABS) is injected first, and then the second material (such as soft TPE) is injected after the mold rotates. The two materials need to have good compatibility (for example, TPE and ABS can be firmly bonded through formula adjustment). It is necessary to accurately control the temperature and pressure matching of the two injections to avoid flash or separation at the joint of the two materials.

Insert injection molding: realize the combination of plastic and metal/other materials.

Application scenario: motor mounting seat of sweeper (metal threaded sleeve needs to be embedded to facilitate later assembly of motor) and charging interface seat (metal terminal needs to be embedded to ensure conductivity and structural strength).

Key points of the process: firstly, accurately put the pretreated insert (the metal parts need to be degreased and roughened to enhance the bonding force with plastic) into the mold cavity, and then inject the plastic to wrap the insert. It is necessary to control the injection pressure (to avoid the displacement of the insert caused by excessive pressure) and the cooling time (to ensure that the plastic and the insert are closely combined without gap) to prevent the insert from loosening or entering water in the later use.

Gas-assisted injection molding: optimizing the structure of thick-walled parts and reducing defects

Application scenario: Heavy-walled parts (wall thickness ≥3mm) such as sweeper handle and large fuselage frame need to avoid shrinkage marks and reduce weight (10%-20%).

Key points: When the injection molding machine injects the melt to 70%-90% of the cavity, high-pressure nitrogen (pressure 10-30MPa) is injected into the melt to push the melt to fill the cavity and form a hollow structure; In the pressure maintaining stage, the melt shrinkage is compensated by nitrogen pressure to eliminate surface shrinkage marks. It is necessary to design a reasonable airway (2-5mm in diameter) to ensure the uniform diffusion of nitrogen and avoid the formation of bubbles or uneven hollowness.

Third, the key post-processing technology: to ensure the quality of finished products and assembly adaptability.

Post-treatment after injection molding is an indispensable part of plastic parts of sweeper, which mainly solves molding defects, improves performance and adapts assembly.

Deburring and trimming: eliminating molding defects

Applicable parts: all plastic parts of the sweeper, especially the assembly interface (such as buckles and screw holes) and the edge of the appearance surface, need to remove the gate and flash (thickness ≤0.1mm).

Technology: simple parts are trimmed manually (with art knife and sandpaper); Automatic equipment (such as vibration grinder and laser deburring machine) is used for batch parts to ensure smooth edges and no sharp points, to avoid scratching hands or other parts during assembly, and to ensure smooth snap fit (insertion force ≤50N, pull-out force ≥100N).

Surface treatment: improve appearance and functional characteristics

Exterior parts treatment: Exterior parts such as fuselage shell and operation panel can be sprayed (such as matte paint, wear-resistant paint to improve scratch resistance, pencil hardness ≥HB), screen printed/pad printed (printing key LOGO, brand logo, pattern adhesion needs to pass the 100-grid test without falling off) and vacuum coated (such as metal texture coating to improve aesthetics).

Functional parts treatment: wear-resistant parts such as walking wheels and roller brush brackets can be treated with surface texture (such as knurling and sandblasting to increase friction and avoid slipping); Seals (such as the installation groove of dust cup sealing ring) can be polished (Ra≤0.4μm) to ensure that the sealing ring fits tightly and prevent dust leakage.

Testing and screening: excluding unqualified products.

Appearance inspection: Eliminate defects such as lack of materials, cracks and color difference (ΔE≤1.5) through manual visual inspection or machine visual inspection.

Dimension detection: use caliper, micrometer or coordinate measuring instrument to detect key dimensions (such as the diameter of mounting hole and the height of buckle) to ensure that the design tolerance (usually within ±0.1mm) is met.

Performance sampling inspection: the mechanical properties of components (such as shell impact strength and gear wear resistance) are regularly sampled to ensure that the long-term use requirements of the sweeper are met (such as shell dropping test with 1.2m height without damage).