What are the requirements for the mold design of household appliances injection molding parts?

The design core of the processing mould for household appliances injection molding follows the principle of * * "product adaptation, high efficiency in mass production, stable precision, smooth demoulding and controllable cost", which needs to match the characteristics of high appearance requirement, diverse structure, accurate size and large batch of household appliances injection molding, take into account the differentiated needs of different household appliances parts (shells/structural parts/functional parts), and adapt to the efficient pace of household appliances production and the convenience of mold maintenance in the later stage. The following are the full-dimensional mold design requirements * * that fit the actual injection molding production of household appliances, covering the core links such as appearance, structure, precision, mass production, demoulding, etc., and are suitable for various injection molding parts of household appliances such as refrigerators, washing machines, air conditioners and small household appliances:

1. Design requirements: match the face value and surface texture of household appliances without defects.

Injection-molded parts of household appliances (especially shells, panels and fuselage parts) are the core of product value. Mold design should avoid appearance defects such as shrinkage marks, weld marks and flash from the source to meet the surface texture requirements of household appliances:

Adaptation of surface texture and gloss: according to the design requirements of household appliances, the mold cavity should be treated with dermatoglyphics/sunburns/highlights (such as fine dermatoglyphics commonly used in household appliances and mirror cavities for high-gloss panels), the texture should be uniform without broken lines, and the high-gloss surface should be polished to Ra≤0.02μm, and the cavity surface should be free of knife marks and scratches;

Avoid appearance defects

Gate optimization and wall thickness transition (wall thickness difference ≤20%) should be made for thick-walled parts of household appliances (such as shell ribs and buckle roots) to prevent shrinkage marks and depressions;

Arrange the gate and runner reasonably, reduce the number of weld marks, design the weld marks in the invisible area/non-stressed area, and ensure the weld strength by increasing the material temperature and pressure at the weld marks;

The matching gap between the cavity and the core is accurate (0.02~0.05mm), and the parting surface is closely attached to prevent flash and burr (visible flash is not allowed in the exterior parts of household appliances, and trimming is required);

Appearance consistency: Multi-cavity mold should ensure that the cavity size, texture and gate position are completely consistent, ensure that there is no difference in the appearance of mass-produced injection parts, and adapt to the assembly consistency of household appliances;

Anti-scratch and demoulding protection: the surface of cavity and core is treated with hard coating (such as nitriding and PVD coating) to improve wear resistance and prevent scratching the surface of injection molded parts during demoulding; At the same time, an anti-scratch ejector pin/supporting plate is designed at the demoulding part to avoid scratching the appearance surface during ejection.

Second, the structural design requirements: adapt to the function and assembly of household appliances, and the structure is stable.

The injection-molded parts of household appliances are divided into appearance parts, structural load-bearing parts and precise functional parts (such as buckles, slots and rotating shaft seats). The mold design needs to accurately match the structural functions of the parts, so as to ensure that the structural dimensions of the injection-molded parts are compliant, the assembly is smooth, and there are no problems of jamming and looseness;

Accurate design of buckle/slot: the buckle and slot for household appliances assembly are the core structures, and the mold cavity needs to be accurately engraved, and the fit gap should be designed as 0.03 ~ 0.08 mm. The root of the buckle should make an R-angle transition (to prevent demolding fracture), and at the same time, a reasonable demolding slope (1 ~ 3) should be designed to avoid demolding deformation of the buckle.

Adaptation of reinforcing ribs and supporting structures: The reinforcing ribs of household appliance shells/structural parts should be designed according to the aspect ratio ≤3:1 and the spacing ≥2 times the height of the ribs, and the root of the ribs should be at an angle of R (R≥0.5mm) to prevent stress concentration cracking of injection molded parts; Load-bearing parts (such as washing machine inner cylinder bracket and air conditioning base) need to strengthen the rigidity of mold cavity to ensure the structural strength of injection molded parts;

Accurate hole position and shaft seat: the tolerance of the installation hole, screw hole and shaft seat of household appliances should be ≤0.05mm, the mold should adopt insert core/cavity (convenient for later mold repair and size adjustment), and the screw hole should be designed with a burr-free structure to ensure smooth hole wall and no burr;

Structural adaptation of inserts: For household appliances with metal inserts (such as air-conditioning terminals and metal rotating shafts of small household appliances), insert positioning mechanisms (such as positioning pins and clamping grooves) should be designed for the mold to ensure accurate positioning of the inserts without deviation or inclination, and meanwhile, an anti-overflow structure should be designed to prevent plastic from wrapping the mounting surface of the inserts;

Shapes of parts adapted to demoulding structure: Special-shaped household appliances (such as air-conditioning guide vanes and refrigerator door handles) need to be designed with a combined ejection mechanism (ejector pin+supporting plate+inclined top) to ensure uniform stress during demoulding without deformation and warping; Deep cavity parts (such as rice cooker liner and washing machine material box) need to be designed with core-pulling mechanism (inclined guide post/hydraulic core-pulling), and 10% margin should be reserved for core-pulling stroke to prevent demoulding interference.

Third, the precision design requirements: match the mass production and assembly of household appliances, and the size is stable.

The production of household appliances is a batch assembly line, and the dimensional accuracy of injection-molded parts directly affects the assembly efficiency. Mold design should ensure dimensional stability and high precision of repeated positioning, and the dimensional deviation of injection-molded parts in batch production is within the allowable range, with no accumulated error:

Accurate tolerance of core dimensions: the mold is designed according to the tolerance of IT8~IT10 for the installation fit size, hole position and buckle clearance of household appliances, and the precision functional parts (such as thermostat bracket of small household appliances) are designed according to IT7; Mold cavity and core are processed by high-precision processing equipment (CNC carving, wire cut), and the shape and position tolerance is ≤ 0.005 mm;

Mould rigidity and anti-deformation design: household appliance moulds are mostly multi-cavity and large-size moulds (such as refrigerator shell moulds). The mould base should be made of high-strength steel (such as 45# steel and P20 steel), and the cavity core should be made of pre-hardened steel (HRC28~35). For large-size moulds, it is necessary to add mould base ribs and support columns to prevent the mould from being deformed by compression during injection, which will lead to the dimensional deviation of injection parts.

Uniform temperature control system: the mold should be designed with a uniform water cooling system (the cooling hole is 15~20mm away from the cavity surface and the aperture is 8~12mm) to ensure the uniform temperature of the cavity and core (the temperature difference is ≤ 2℃), so as to avoid the dimensional deviation and warpage of injection molded parts caused by uneven cooling; High gloss parts/precision parts need to design a mold temperature machine interface to accurately control the mold temperature (1℃);

Multi-cavity simultaneous filling: Multi-cavity mold should adopt balanced runner design (such as fan runner and spiral runner) to ensure that all cavities are filled with plastic melt synchronously, and the size deviation of injection parts in each cavity is ≤0.03mm to avoid size inconsistency in batch production.

Fourth, mass production efficiency requirements: adapt to the household appliance assembly line, with high beat and low loss.

The injection molding production of household appliances requires high production capacity and low rejection rate (rejection rate ≤1%). Mold design should be optimized around mass production, improve the injection rhythm, reduce the time of mold changing and mold repairing, and adapt to the efficient production of household appliances assembly line;

Optimization of injection time: the runner and gate of the mold are designed according to rapid filling and rapid cooling, the runner adopts hot runner system (the first choice for mass production of household appliances, to reduce the waste of material heads and improve the filling speed), and the gate adopts pin-point gate/submerged gate (cutting without residue and trimming-free) to shorten the injection cycle (the injection cycle of conventional household appliances is controlled at 10 ~ 30s);

High wear-resistant design: Wear-resistant steel (such as SKD61 and H13) is used in the easily worn parts of the mold cavity, core and thimble, and nitriding treatment (surface hardness ≥HV800) is carried out to ensure that the mold is mass-produced ≥ 500,000 times without obvious wear and frequent mold repair;

Design of quick die change and die repair: the die adopts standardized insert structure, and the vulnerable/easy-to-adjust parts such as cavity, core and sprue sleeve are independent inserts, so it is not necessary to disassemble the whole die when changing/repairing the die, and the die change time is controlled within 1~2 hours; At the same time, the repair modulus (0.1~0.3mm) is reserved, which is convenient for fine-tuning according to the actual size of injection molded parts in the later stage;

Automatic adaptation design: the mold needs to be adapted to the parts taken by the injection manipulator, and the automatic cutting structure of the positioning groove and nozzle of the manipulator is designed to avoid manual operation and improve the mass production efficiency; At the same time, anti-sticking mechanism (such as air top device) is designed to prevent injection molding from sticking and reduce downtime.

Five, demoulding design requirements: to ensure that the injection molded parts are in good condition, and the demoulding is smooth without damage.

Injection molded parts of household appliances are mostly special-shaped, thin-walled and precise parts, and demoulding is the key link in mold design. It is necessary to ensure that the demoulding is evenly stressed, without deformation, fracture and scratch, and it is suitable for automatic picking;

Reasonable demoulding inclination: the demoulding inclination of cavity and core is designed according to * * appearance surface 1 ~ 2 and non-appearance surface 2 ~ 5 * *, and the inclination of deep cavity/high-precision parts is appropriately reduced (0.5 ~ 1), and the demoulding resistance is reduced by polishing the cavity;

Uniform arrangement of ejector mechanism: ejector pins are arranged according to the principle of uniform stress, avoiding the appearance surface and weak stress parts, and the matching gap between ejector pins and ejector pin holes is ≤0.01mm to prevent material leakage; Thin-walled parts (such as air conditioning guide vanes and home appliance panels) are pushed out by supporting plates as a whole to avoid local ejection deformation;

Core-pulling and inclined ejector mechanism are reliable: for household appliances with side holes/side recesses, the core-pulling mechanism adopts inclined guide pillar+slider (conventional) or hydraulic core-pulling (long stroke and high precision), the fit clearance between slider and guide chute is ≤0.02mm, and locking mechanism (such as wedging block) is designed to prevent the slider from deviating during injection molding; Wear-resistant guide blocks are used for the inclined roof to ensure smooth movement and no jamming;

Anti-sticking mold and anti-dropping design: the mold cavity is polished to reduce mold sticking, and an air cap/vacuum adsorption device is designed to assist demoulding; For small household appliances (such as small household appliances buttons and card slots), the linkage demoulding structure between the nozzle and the product is designed to prevent the product from falling off when taking the parts.

6. Material and process requirements: match the characteristics of household appliances, and the mold is durable.

The selection and processing technology of mold steel directly determine the life of mold and the quality of injection-molded parts. It is necessary to accurately select the mold according to the material (PP/ABS/PC/PMMA), batch number and accuracy requirements of household appliances, and ensure the processing technology compliance:

Accurate selection of die steel

Exterior parts of common household appliances (PP/ABS material, mass production ≤ 500,000 modules): P20 pre-hardened steel is used for the cavity/core, and 45# steel is used for the mold base;

High-precision/high-mass-produced household appliances (PC/PMMA high-gloss parts, mass production ≥ 1 million modules): SKD61 and H13 steel are used for the cavity/core, and nitriding+PVD coating is used to improve the wear resistance and mirror effect;

Corrosive plastic parts (such as PPS/PA66+glass fiber for temperature-resistant parts of household appliances): stainless steel for molds (S136) to prevent the glass fiber from wearing and corroding the cavity;

Compliance of processing technology: wire cut cutting, CNC carving and mirror polishing are adopted for mold cavity and core, and there are no knife lines and steps; Interference fit (H7/k6) is adopted for the fit between the insert and the die frame to ensure firm connection and no looseness; The welding parts are welded by argon arc welding, and polished after welding without welding marks;

The heat treatment process is up to standard: the easily worn parts of the mold (ejector pin, slider and core) need to be quenched (HRC45~55), and the thickness of nitriding layer is ≥0.1mm to ensure hardness and wear resistance; The die frame shall be stress-relieved and annealed to prevent the deformation of the die in use.

Vii. design requirements of auxiliary system: ensure the stable operation of molds and adapt to production.

The auxiliary systems such as cooling, exhaust and runner of mold are the key to ensure the quality and production stability of injection molded parts, which need to be designed accurately according to the material and structure of household appliances to avoid injection defects caused by the defects of auxiliary systems:

The cooling system is uniform and efficient: the water channel is designed according to the synchronous cooling of the cavity and the core, the cooling hole is close to the cavity (15~20mm), and the straight-through/spiral water channel is adopted, without cooling dead angle; Thick-walled household appliances (such as refrigerator door liner, washing machine base) are designed with watertight waterway to improve cooling efficiency and shorten injection cycle;

Sufficient exhaust system: the mold is designed with exhaust grooves at the end of the cavity, at the weld mark and at the dead angle of the deep cavity. The depth of the exhaust groove is designed according to the plastic material (PP/ABS≤0.03mm, PC/PMMA≤0.02mm), and the width is 5~10mm, so as to ensure that air is exhausted when the plastic melt is filled, and avoid bubbles, lack of materials and loose weld marks of injection molded parts;

Optimization of runner and gate: adopt hot runner system (the first choice for mass production of household appliances), the runner diameter is designed according to the weight of injection molded parts (1~5mm), the gate position is selected at the non-appearance surface and stressed part, the pin-point gate diameter is 0.8~2mm, and the latent gate is designed at the side of injection molded parts, and there is no residue after cutting;

Hydraulic/pneumatic system adaptation: the hydraulic system is adopted for core-pulling and ejection of large-size molds, with stable pressure (10~16MPa) and accurate stroke; Small precision mould adopts pneumatic ejection, which has fast response and is suitable for high-beat production.

Eight, environmental protection and adaptation requirements: conform to the production specifications of household appliances, taking into account the later maintenance.

Environmental protection requirements: no harmful substances are separated from the parts where the mold is in contact with the plastic, and the steel and processing accessories meet RoHS standards, meeting the environmental protection production requirements of household appliances;

Convenient maintenance: the mould design is standardized for vulnerable parts (thimble, sprue sleeve, sealing ring), which is easy to purchase and replace; Set mold maintenance rings and positioning pins to facilitate mold disassembly, installation and maintenance; Mark the mold model, the number of cavities and the parameters of the injection molding machine on the side of the mold to facilitate on-site operation;

Adaptation of injection molding machine: The installation size, mold opening stroke and clamping force of the mold should match the parameters of the injection molding machine used for household appliances production, and the mold base should adopt standardized specifications (such as Longji mold base) to avoid production failures caused by improper adaptation of the injection molding machine.

Nine, different household appliances parts mold design special requirements

High-gloss panel of household appliances (such as TV and air-conditioning panel): mirror polishing of cavity (Ra≤0.02μm), hot runner+pin gate, accurate temperature control of mold temperature machine (60~90℃), miniature exhaust slot (≤0.02mm) to prevent surface pitting;

Thin-walled shell of household appliances (such as small household appliance shell and mobile phone accessories): short and thick runner, large and many gates, efficient cooling system, properly reduced demoulding slope, and uniform shell wall thickness (deviation ≤ 0.1 mm);

Precision functional parts of household appliances (such as buckles and rotating shaft seats): adopt insert structure, the cavity accuracy is IT7, the ejection mechanism is accurate, there is no demoulding deformation, and the matching gap is stable;

Large-scale structural parts of household appliances (such as refrigerator shell and washing machine outer cylinder): high-strength mold base, multi-cavity balanced flow channel, integral supporting plate ejection, and full coverage of cooling system to prevent warpage and dimensional deviation of injection molded parts.

Summary of core design principles

The core of the mold design of household appliances injection parts is * * "taking products as the core, giving consideration to appearance, function and mass production" * *: the appearance meets the requirements of home appliances' texture and defect-free, the structure adapts to the assembly and function of home appliances, and the size of mass production is stable in accuracy, and the mass production adapts to the high beat and low loss of household appliances assembly line, while taking into account the durability of the mold and the convenience of post-maintenance, so as to finally realize the high-quality and efficient production of household appliances injection parts.