What should be paid attention to in the processing of metal shrapnel stamping parts in the field of mobile phones?

Metal shrapnel stamping parts in the field of mobile phones (such as button shrapnel, battery contact shrapnel, connector shrapnel, etc.) have the characteristics of small size, high precision, strict elasticity requirements, harsh appearance quality, etc., and their processing process needs to take into account dimensional accuracy, mechanical properties, assembly adaptability and mass production stability. The following are the core matters that need to be paid attention to in the processing process, which is carried out according to the whole process of "pre-preparation-stamping process-quality control-post-processing-production management".

First, preliminary preparation: accurate adaptation of design and material selection

Product design and mold development

Based on the assembly requirements of the whole mobile phone, the elastic parameters (such as resilience and fatigue life), dimensional tolerance (usually ±0.01~±0.03mm) and assembly interface size of the elastic sheet should be defined to avoid the conflict between design and actual assembly.

Die design should consider the forming process of elastic sheet (such as blanking, bending, stretching and flanging), and adopt "one-time forming" or "multi-station continuous die" design to reduce the positioning error between processes; The die gap should be strictly matched with the material thickness (usually 5%~10% of the material thickness) to avoid excessive blanking burr or deformation of the elastic sheet.

High-strength wear-resistant steels such as SKD11 and DC53 are preferred as the mold materials, and the key molding parts need heat treatment (hardness HRC58~62) to ensure the service life of the mold (it needs more than 1 million times in batch production).

Selection and pretreatment of raw materials

Shrapnel materials should have high elasticity, high toughness and good stamping formability. Commonly used materials include SUS301 stainless steel (excellent elasticity, suitable for high-frequency key shrapnel), phosphor bronze (good conductivity, suitable for contact shrapnel) and beryllium copper (high elastic modulus, suitable for high-precision shrapnel), and the thickness of the material is usually 0.05 ~ 0.3 mm..

Raw materials should meet RoHS, REACH and other environmental protection standards to avoid excessive heavy metals; When purchasing, check the mechanical performance report of materials (such as tensile strength, yield strength and elongation) to ensure that the elastic requirements of shrapnel are met.

Pretreatment of raw materials: Kaiping and leveling are needed to eliminate the internal stress of the material (to avoid warping of the spring sheet after stamping); The surface should be clean and free of oil stain and oxide layer, and if necessary, it should be pickled and passivated to ensure the fluidity of materials in the stamping process and the service life of the die.

Second, stamping process: dual control of precision and stability

Selection and debugging of stamping equipment

Choose a high-precision high-speed punch (punching times ≥600 times/minute), and the equipment should have stable slider movement accuracy (verticality ≤0.01mm) and positioning accuracy (repeated positioning error ≤±0.005mm) to avoid the size fluctuation of the shrapnel caused by equipment vibration.

When debugging, it is necessary to calibrate the concentricity between the die and the punch, and adjust the punching speed, stroke height and feeding accuracy to ensure the smooth feeding of materials, and there is no material jam or deviation. For the multi-station continuous die, it is necessary to ensure that the positioning pins of each station are accurately aligned and the error is controlled within 0.005 mm.

Control of key process parameters

Blanking process: control the blanking speed (usually 300~800 times/minute according to the material thickness) to avoid material tearing or excessive burr caused by too fast speed; The edge burr of the punched spring sheet should be ≤0.005mm, otherwise the assembly fit and appearance will be affected.

Bending process: the bending radius should match the material characteristics (for example, the minimum bending radius of SUS301 stainless steel is ≥0.1mm) to avoid cracks or excessive rebound at the bending part; The springback compensation (usually 1 ~ 3 according to the elastic modulus of the material) should be reserved for the bending angle to ensure that the angular tolerance after molding meets the requirements.

Stretching/flanging process: For the shrapnel with bulge or flanging (such as battery contact shrapnel), the stretching coefficient should be controlled (usually ≥0.6) to avoid wrinkling and cracking during stretching; The flanging height should be uniform, and the flanging mouth should be free of burr and deformation.

Feeding and positioning accuracy control

Adopt automatic feeding mechanism (such as roller feeding and servo feeding), and the feeding accuracy should be ≤±0.01mm to ensure the accurate positioning of materials in the stamping process; For narrow or thin materials, it is necessary to install a material pressing device to prevent the material from deviating or warping when feeding.

Precise positioning pins and guide plates should be set in the die, the fit clearance between the positioning pins and the material holes should be ≤0.003mm, and the unilateral clearance between the guide plate and the material should be ≤0.01mm, so as to avoid the material from moving in the stamping process.

Third, quality control: whole process inspection and defect prevention

Tolerance detection of size and shape and position

High-precision inspection equipment (such as two-dimensional imager, three-coordinate measuring instrument and laser caliper) shall be used to conduct 100% full inspection or sampling inspection on key dimensions of shrapnel (such as length, width, thickness, bending angle and aperture) (sampling ratio ≥5% in mass production) to ensure that the dimensional tolerance meets the design requirements.

Focus on the detection of form and position tolerances, such as flatness (≤0.01mm), verticality (≤0.008mm) and coaxiality (≤0.005mm), so as to avoid problems such as failure to fit and poor contact of shrapnel after assembly due to form and position errors.

Mechanical property testing

Elasticity test: the resilience of the elastic sheet (usually 50~500g) is detected by an elasticity tester, so as to ensure that the elasticity is stable within the specified journey, and after more than 100,000 fatigue tests, the elasticity attenuation is less than or equal to 10% (to avoid the "collapse" and "failure" of mobile phone keys).

Strength test: detect the tensile strength and yield strength of the elastic sheet to avoid deformation or fracture during use due to insufficient strength; For contact shrapnel, it is necessary to test its conductivity (such as contact resistance ≤50mΩ).

Appearance quality control

The surface of the shrapnel shall be free of scratches, pits, oxidation spots, corrosion and other defects, and the surface roughness Ra shall be ≤ 0.8μ m; For shrapnel exposed outside the mobile phone (such as button shrapnel), the appearance should meet the standard of "no visible defects".

To avoid the phenomenon of "die sticking" in stamping process (surface strain caused by adhesion between material and die), it can be prevented by coating release agent on the surface of die and optimizing the polishing process of die (the roughness of die forming surface Ra≤0.02μm).

Fourth, post-treatment: surface treatment and assembly adaptation

Selection of surface treatment process

Mobile phone shrapnel should be corrosion-resistant, conductive and wear-resistant. Common surface treatment methods include electroplating (gold plating, nickel plating and tin plating, the thickness of gold plating layer is usually 0.1~0.3μm to improve conductivity and corrosion resistance), passivation (stainless steel shrapnel to enhance rust resistance) and oil spraying (insulating shrapnel to improve insulation performance).

The surface treatment should meet the environmental protection standards, the coating should be uniform, bubble-free and peeling-off, and the salt spray test should last for more than 48 hours (to avoid the rusty shrapnel of the mobile phone in wet environment); The tolerance of coating thickness (0.05 μ m) should be controlled for gold-plated spring plate to avoid the decrease of electrical conductivity caused by coating thickness that affects assembly or coating thickness that is too thin.

Deburring and cleaning treatment

The edge of the stamped spring sheet needs to be deburred. Chemical deburring, electrolytic deburring or ultrasonic deburring (suitable for tiny spring sheets) can be used to ensure that the burr is ≤0.005mm, so as to avoid scratching other parts or affecting the contact effect during assembly.

After surface treatment, it needs to be cleaned to remove residual impurities such as oil stain and electroplating solution. Ultrasonic cleaning+pure water rinsing+drying process can be adopted to ensure the surface cleanliness of the elastic sheet (no visible impurities) and avoid affecting the assembly fit and electrical conductivity.

Assembly suitability verification

Before mass production, it is necessary to carry out sample assembly test, and adapt the elastic sheet to the mobile phone shell, keys, circuit board and other parts to verify whether the installation method of the elastic sheet (such as snap-in and welding) is reliable, and whether there are problems such as looseness, jamming or poor contact after assembly.

For the elastic sheet of the key, it is necessary to test its fit with the key to ensure that the elastic force is uniform and rebound quickly when pressed, and there is no "key stuck" or "empty key" phenomenon; For the battery contact elastic sheet, it is necessary to test its contact pressure with the battery to ensure stable conduction.

V. Production Management: Batch Stability and Cost Control

Production environment control

The stamping workshop should be kept clean and dry, and the ambient temperature should be controlled at 20~25℃ and the humidity should be ≤60% (to avoid material rusting or mold corrosion caused by humidity); The workshop should be equipped with dust-proof facilities to prevent dust from adhering to the surface of shrapnel and affecting its appearance and performance.

Mold maintenance and maintenance

Regularly clean, lubricate and inspect the mold, remove iron filings and oil stains on the mold surface, and apply special lubricating oil (such as high-temperature grease) on the molding parts to avoid mold wear; Regularly check the key parts of the mould, such as locating pin, guide post and cutting edge, and repair or replace them in time if they are worn or deformed to ensure the accuracy of the mould.

Batch production process monitoring

The quality control mode of "first article inspection-patrol inspection-last article inspection" is adopted, and the first article can be mass-produced only after it has passed the full-scale inspection of the three-coordinate measuring instrument; The frequency of inspection shall be ≥ once per hour, and the size, appearance and elasticity shall be mainly detected. If any abnormality is found, it shall be stopped immediately for adjustment.

Establish a production data traceability system to record raw material batches, mold numbers, stamping parameters, test results and other information, so as to quickly trace the root causes when quality problems occur.

Cost and efficiency control

Optimize stamping process, adopt multi-station continuous die instead of single-process die, reduce transfer time between processes, and improve production efficiency (the daily output of a single set of dies can reach more than 100,000 pieces in batch production).

Control the loss of raw materials, reasonable typesetting (such as nested typesetting), reduce material waste; For unqualified products, it is necessary to analyze the causes and take corrective measures (such as adjusting the mold and optimizing the process) to reduce the defective rate (the target defective rate is ≤0.3%).

summary

The processing core of mobile phone hardware shrapnel stamping parts is "precision is king, elasticity reaches the standard, appearance is flawless, and batch stability", which needs to be finely controlled from the whole process of design, material selection, technology, testing and management. In particular, we should pay attention to the machining accuracy of micro-size, the consistency of elastic parameters and the reliability of surface treatment, and at the same time give consideration to the efficiency and cost of mass production. In addition, it is necessary to strictly follow the environmental protection standards and quality systems of the mobile phone industry (such as ISO9001 and IATF16949) to ensure that the products meet customer requirements and avoid assembly failure of the whole machine due to quality problems.