What matters should be paid attention to in injection molding of plastic parts of sweeper?
As the core component of the whole machine, the plastic parts of the sweeper cover a variety of structures, such as the fuselage shell, the roller brush bracket, the dust cup assembly, the traveling wheel, etc. The quality of its injection molding directly affects the appearance accuracy, assembly adaptability, durability and running stability of the sweeper. The following key points should be paid attention to in the processing process:
Accurate selection of materials to match the needs of use scenarios.
The functional differences of different plastic parts determine the direction of material selection, which needs to be comprehensively considered in combination with the stress situation of the parts, environmental adaptability and cost control. The fuselage shell should give consideration to both rigidity and impact resistance, and ABS+PC alloy material is preferred, which has good formability and scratch resistance, and can avoid deformation or scratches caused by daily bumps; Moving parts such as roller brush bracket and driving wheel should be wear-resistant and fatigue-resistant. POM (polyoxymethylene) or PA66+glass fiber can be used to improve the wear-resistant coefficient and bearing capacity of the parts. The dust cup assembly should have the characteristics of stain resistance and easy cleaning, and it is recommended to use highly transparent PP (polypropylene) or PET, and ensure that the material meets the food contact level standard (if the dust cup is involved in the detachable cleaning scene); For sealing parts, such as sealing rings and shock absorbing pads, TPE/TPR elastomer materials should be selected to ensure their sealing performance and anti-aging ability. In addition, all materials must meet the environmental protection standards such as RoHS and REACH, and meet the compliance requirements of the sweeper export market.
Optimize mold design to ensure molding accuracy and demoulding efficiency.
Mold is the core factor that determines the quality of injection molded parts, and it needs to be customized according to the structural characteristics of plastic parts of sweeper. First of all, it is necessary to set the parting surface and gate position reasonably, and the exterior parts such as fuselage shell should adopt hidden gate or point gate to avoid the influence of gate trace on the appearance; For deep cavity parts such as dust cup, it is necessary to increase the exhaust slot of the mold to prevent bubbles, shrinkage marks and other defects during injection molding. Secondly, an accurate cooling waterway system should be equipped to optimize the waterway layout for parts with uneven wall thickness (such as the ribs of the shell) to ensure uniform cooling of plastic parts and reduce warping deformation caused by temperature difference; At the same time, the mold needs to be provided with a reliable demoulding mechanism. For parts with inverted buttons and complicated buckles (such as battery compartment buckles), inclined top or slider structure can be adopted to avoid pulling plastic parts during demoulding. In addition, wear-resistant steel (e.g. S136) should be selected for the die, and nitriding treatment should be carried out to prolong the service life of the die and ensure the dimensional stability in mass production.
Strictly control injection molding process parameters to improve the molding quality of plastic parts
Accurate control of injection molding process parameters is the key to avoid defects, which needs to be adjusted in real time according to material characteristics and plastic structure. First, control the temperature parameters, including the barrel temperature and the mold temperature. For example, when processing ABS+PC materials, the barrel temperature should be set at 230-260℃ and the mold temperature should be kept at 60-80℃ to ensure the full plasticization and stable fluidity of the materials; When processing POM materials, it is necessary to strictly control the barrel temperature to prevent material decomposition. Secondly, the injection parameters should be optimized, and the injection speed should be controlled by stages of "slow-fast-slow" to avoid problems such as flash and obvious weld marks caused by high-speed injection; Holding pressure and holding time should match the wall thickness of plastic parts, and the holding time of thick-walled parts should be extended to prevent shrinkage cavity and depression; For thin-walled parts, it is necessary to increase the injection pressure to ensure that the melt fills the cavity quickly. The third is to control the cooling time. Insufficient cooling will lead to the deformation of plastic parts, while excessive cooling will reduce the production efficiency. It is necessary to determine the optimal cooling time according to the wall thickness and material characteristics of plastic parts, such as ABS plastic parts with a wall thickness of 2mm, and the cooling time can be set at 15-20 seconds.
Strengthen process quality control and ensure quality through whole process inspection.
It is necessary to establish a three-level inspection system of "incoming materials-process-finished products" to ensure that each batch of plastic parts meets the quality standards. In the incoming stage, the melting index, color difference and impurity content of raw materials are detected to avoid molding defects caused by unqualified materials; In the process stage, the first part needs to be tested in full size, and the key dimensions of the plastic parts (such as the aperture of the assembly hole, the hole spacing and the flatness of the shell) are detected by using a two-dimensional measuring instrument to ensure that it matches the assembly size of the whole machine; At the same time, visually inspect the appearance defects of plastic parts, such as lack of materials, flash, weld marks, color difference, scratches, etc. For appearance parts, strict appearance judgment standards need to be formulated. In the finished product stage, sampling performance tests should be carried out, including drop test (simulating the impact resistance of the fuselage shell), wear test (for the walking wheel and roller brush bracket) and sealing test (for the dust cup assembly) to ensure that the plastic parts meet the durability requirements of the sweeper.
Pay attention to the production environment and process details and avoid hidden problems.
The plastic parts of the sweeper are precision structural parts, which have high requirements for the production environment. The workshop needs to maintain constant temperature and humidity (temperature 20-25℃, humidity 50%-60%) to avoid moisture absorption of materials or dimensional changes of plastic parts due to environmental temperature and humidity fluctuations. At the same time, the workshop should take anti-static measures to prevent electrostatic adsorption of dust, which will affect the appearance and assembly accuracy of plastic parts. In addition, attention should be paid to process details, for example, when processing transparent parts, the cylinder should be thoroughly cleaned to avoid noise pollution; For plastic parts that need secondary processing (such as screen printing and ultrasonic welding), the process position should be reserved during injection to ensure the accuracy of secondary processing; In mass production, it is necessary to maintain the mold regularly, clean up the carbon deposit in the exhaust groove and check the wear of the mold to ensure the stable molding accuracy of the mold.
