Differences in different process routes and selection references for adhesive coating of humanoid robots

As the core precision rubber process in human-computer interaction scenarios, the encapsulation of humanoid robots directly determines the safety and operational stability of robot joints, feet, and interactive contact surfaces, and is a key link in the current flexible upgrade of industrial robots. This article systematically breaks down the technical differences between different process routes from four dimensions: material adaptation, manufacturing technology, quality control, and iterative implementation. It provides practical selection references for engineers and procurement decision-makers to avoid common problems such as adhesive detachment, insufficient wear resistance, and unsatisfactory tactile sensation. 1、 Material adaptation characteristics 1. Safety and compliance requirements The material compliance of the adhesive coating for humanoid robots needs to cover the mandatory standards for human-machine contact in all scenarios. The adhesive components that directly contact the human body must meet the requirements of GB/T 16886 biocompatibility, EU REACH Appendix 17 restricted substances, and RoHS 2.0 hazardous substance control to avoid skin irritation or harmful substance precipitation caused by long-term contact. Products aimed at exporting to the European and American markets require additional FDA or LFGB food contact certification for the adhesive materials used in the hand and facial interaction areas, which are suitable for the harsh use scenarios of medical companionship and household service humanoid robots.

There are significant differences in the compliance priority of adhesive materials for humanoid robots in different application areas. The biocompatibility requirements can be appropriately relaxed for the adhesive of joint transmission parts, but it must meet the flame retardant standard of UL94 V-0 insulation level to avoid the risk of material thermal decomposition caused by circuit faults. During the material selection stage, it is necessary to request a full compliance report issued by a third-party testing agency in advance to avoid batch scrap issues caused by certification discrepancies in the later mass production stage.

2. Use performance matching The material properties of the adhesive coating for humanoid robots need to be accurately matched according to the functions of the components. The hardness, tensile strength, and wear resistance parameters in different areas can vary by more than three times. The key points for matching core performance are as follows: (1) Foot walking contact surface: using Shore A 55-70 degree wear-resistant silicone, Akron wear ≤ 0.15cm ³/1.61km, suitable for continuous walking ground friction conditions (2) Hand interaction contact surface: High rebound liquid silicone with a tensile strength of ≥ 8MPa is selected from Shore A 20-40 degrees, ensuring cushioning performance when grasping fragile items (3) Joint transmission damping layer: Shore A 70-90 degree butyl rubber is selected, with a compression permanent deformation rate of ≤ 15%, and stable damping torque is maintained during long-term operation Conventional rubber materials cannot directly adapt to the multi scenario requirements of humanoid robots, and the material formula needs to be adjusted according to specific working conditions. For example, the packaging of outdoor humanoid robots requires the addition of UV resistant additives to ensure that there are no cracking or sticking problems in the environmental temperature range of -30 ℃ to 80 ℃, and to extend the service life of the components. 2、 Core manufacturing process 1. Mold accuracy control The precision of the mold for humanoid robot encapsulation directly determines the contour tolerance and interface stability of the encapsulation layer. The mold cavity tolerance of mainstream liquid silicone rubber encapsulation should be controlled within ± 0.02mm, and the coaxiality deviation of metal embedded positioning should be ≤ 0.01mm to avoid stress cracking caused by uneven thickness of the encapsulation layer. Mold processing requires the use of five axis CNC to complete the precision machining of the cavity surface, followed by mirror discharge treatment to reduce the surface roughness of the cavity to Ra 0.8 μ m or less, ensuring a smooth and ripple free surface feel after encapsulation molding. There are significant differences in mold costs and precision adaptation scenarios for different process routes. The following table compares the mold parameters of three mainstream humanoid robot encapsulation processes: Solid rubber molding has the lowest precision for encapsulation (cavity tolerance ± 0.05mm, software positioning ± 0.03mm), using P20 mold steel, suitable for small batch production of 1000-10000 pieces; The precision of liquid silicone injection molding encapsulation is centered (± 0.02mm/± 0.01mm), using S136 steel, suitable for medium batches of 10000-100000 pieces; The dual material integrated injection molding has the highest precision for encapsulation (± 0.015mm/± 0.008mm), using STAVAX steel, and is designed for large-scale production of over 100000 pieces. The overall rule is that the higher the precision requirements and the larger the batch size, the higher the required grade of mold steel and the complexity of the process. During the mold design phase, it is necessary to reserve a reasonable layout of exhaust slots and flow channels to avoid the problem of trapped air and material shortage during the complex molding process of curved bread adhesive. Especially for the thin-walled adhesive structure of the finger part of the humanoid robot, needle point dispensing is required to ensure that the adhesive material quickly fills the complete mold cavity.

2. Molding parameter setting The molding parameters of humanoid robot encapsulation need to be accurately adjusted according to the material type and insert material. The typical molding process parameters of liquid silicone encapsulation can be set according to the following steps: (1) Pre treatment of embedded parts: Use isopropanol to wipe the surface of metal or plastic embedded parts, apply matching primer, and let it stand for 15-20 minutes (2) Mold temperature setting: Raise the mold temperature to 120-150 ℃, preheat for 5-10 minutes to ensure uniform temperature in the mold cavity (3) Injection parameters: The injection pressure should be controlled at 80-120 bar, and the injection speed should be 30-50mm/s to avoid high-pressure impact on the embedded parts (4) Sulfurization and insulation: The vulcanization time is 30-90 seconds, adjusted according to the thickness of the coating layer. For every 1mm increase in thickness, the vulcanization time is extended by 20 seconds (5) Post treatment: After molding, place it in a 180 ℃ oven for secondary vulcanization for 2 hours to remove residual small molecule volatiles inside the material The mold temperature fluctuation range shall be strictly controlled during the molding process, and the temperature difference of the same mold cavity shall not exceed ± 5 ℃, otherwise the uneven hardness of the rubber coating caused by partial incomplete vulcanization will occur, which will directly affect the consistency of the use performance of the rubber coating parts of the humanoid robot. For the encapsulation scenario of engineering plastic inserts, it is necessary to verify the thermal deformation temperature of the plastic in advance to avoid warping and deformation of the inserts during high-temperature vulcanization. 3、 Key points of quality control 1. Interface bonding strength detection The interface bonding strength of the adhesive layer of the humanoid robot is the core indicator to avoid the detachment of the adhesive layer during use. The industry standard tensile strength requirement is ≥ 3MPa, and the shear strength requirement is ≥ 2.5MPa. During testing, a universal tensile machine is used to apply force to the adhesive layer at a constant speed of 50mm/min, and the maximum tensile force value during interface separation is recorded. For curved and irregular adhesive structures, customized fixtures can be used to complete non planar tensile testing, ensuring that the testing data conforms to the actual operating conditions. In addition to static mechanical testing, it is also necessary to carry out bonding strength verification after cold and hot cycles. The encapsulated components should be placed in an environmental box at -40 ° C to 120 ° C for 50 cycles of testing, and then the interface bonding strength should be tested again. The retention rate should reach more than 80% of the initial value to avoid coating delamination failure of the robot in cross regional use scenarios with large temperature differences. All testing data must be retained with traceable records, corresponding to the production process parameters of each batch. 2. Service life verification The service life verification of the rubber components of humanoid robots requires simulating real operating conditions. The foot rubber components need to complete a wear resistance test of 1 million walks, with a load corresponding to 1.2 times the weight of the robot. After the test, the wear of the rubber layer should not exceed 10% of the initial thickness. The hand wrap adhesive needs to complete 500000 grasping cycles to simulate the contact pressure of grasping different materials. After the test, the adhesive layer should not have problems such as cracking, delamination, or obvious permanent deformation. An additional 1 million cycles of reciprocating fatigue testing are required for the damping rubber of the joint area. During the testing process, the fluctuation range of the damping torque should be recorded, and the fluctuation value should not exceed 15% of the initial value to ensure the smoothness of the robot joint operation. After all life verification tests are completed, it is necessary to disassemble and observe the interface state between the encapsulation and the embedded parts to confirm that there are no potential failure risks such as hidden microcracks before entering the mass production process. 4、 Prospects for Implementation Applications 1. Optimization of working condition adaptation The subsequent technological iteration of adhesive coating for humanoid robots will revolve around customized adaptation for segmented scenarios. For heavy-duty humanoid robots in industrial collaboration scenarios, a high load tear resistant adhesive coating formula will be developed to further enhance interface bonding strength and impact resistance. For humanoid robots in home service scenarios, the tactile characteristics of the encapsulation material will be optimized to simulate the warm texture of human skin and enhance the friendliness of human-machine interaction. At the same time, with the continuous expansion of the application scenarios of humanoid robots, encapsulation materials for special extreme working conditions such as firefighting and exploration will gradually be implemented, achieving special properties such as high temperature resistance above 200 ℃ and strong acid and alkali corrosion resistance, expanding the operating boundaries of humanoid robots. In the future, flexible pressure sensing units can be integrated into the encapsulation material to enable the encapsulation layer to have contact force detection function, further enhancing the environmental perception ability of robots. 2. Batch production iteration The mass production process of humanoid robot encapsulation will gradually upgrade towards automation and intelligence. By integrating automation units such as automatic feeding of embedded parts, plasma surface pretreatment, and online visual inspection, the proportion of manual intervention will be significantly reduced, and the production cycle of single components will be compressed to less than 1 minute. At the same time, the batch yield will be increased to over 98%. The molding parameters of each the first mock examination are collected in real time through the MES system, and the injection pressure, mold temperature and other parameters are dynamically adjusted with the AI algorithm to achieve adaptive optimization of the process. With the large-scale expansion of the humanoid robot industry, the unit production cost of humanoid robot encapsulation will gradually decrease, further promoting the popularization and application of flexible encapsulation technology on more humanoid robot components. The subsequent industrial chain will gradually establish unified standards and testing specifications for humanoid robot encapsulation technology, promote the collaborative improvement of the entire industry's process level, and provide reliable process support for the large-scale commercialization of humanoid robots.