1.What is the core control concept?
By moving the control points forward, preventing problems at the source (materials), stabilizing them during the process (technology), and creating a closed loop through detection and feedback.
2.How to control materials?
Thickness Tolerance:
Control: Require suppliers to provide stricter thickness tolerances (e.g., ±0.03mm instead of ±0.05mm). First-piece inspection must include multiple thickness measurements, especially at the beginning, middle, and end of the coil.
Impact: Thickness variations directly affect material flow, drawing depth, and springback, leading to dimensional fluctuations.
Mechanical Property Consistency:
Control: Verify material quality certificates, focusing on yield strength, tensile strength, elongation, and n-value (hardening index) and r-value (plastic strain ratio). Performance differences between different batches, and even within the same coil, are one of the root causes of dimensional fluctuations.
Action: Require suppliers to provide materials with more stable performance, and implement same coil/batch production for critical components.
Surface Condition and Coating:
Ensure surface cleanliness and freedom from oil contamination and unevenness. The coating thickness and coefficient of friction of coated materials such as galvanized sheet affect material flow.
3.How to control it from the mold?
Mold Design and Manufacturing Precision:
Design Phase: Utilize CAE simulation (such as AutoForm) to accurately predict springback, material thinning, and forming forces, and perform springback compensation. This is an essential step in modern mold design.
Manufacturing Precision: Ensure the machining accuracy of mold surfaces, clearances, and guide components reaches the micron level.
Mold Maintenance and Care:
Regular Inspection: Inspect cutting edge wear, surface scratches, guide component wear, and spring/nitrogen spring force decay.
Cleaning and Lubrication: Keep the mold cavity clean, ensure proper lubrication, and prevent material debris from affecting pressing.
Mold Temperature Stability:
Continuous high-speed stamping can cause mold temperature to rise, leading to thermal expansion and affecting dimensions. For precision parts, a mold cooling system should be considered, or the mold should be preheated to a stable state at the beginning of production.
4.How to adjust the stamping equipment and process parameters?
Equipment Stability:
Tonnage and Rigidity: Ensure the press has sufficient tonnage and high machine rigidity, resulting in minimal deformation under load.
Slide Parallelism and Repeat Positioning Accuracy: Regular calibration is necessary. Servo presses offer advantages over traditional mechanical presses in stroke control.
Process Parameter Standardization and Optimization:
Blank Binding Force: This is crucial for controlling material flow. Excessive force leads to cracking, while insufficient force results in wrinkling and dimensional insufficiency. A closed-loop blank binding force control system should be used.
Drawbead Setting: The resistance of virtual or actual drawbeads is an important means of controlling material flow.
Lubrication: The type, application amount, and uniformity of lubricant must be standardized. Inconsistent lubrication alters the coefficient of friction, leading to dimensional fluctuations.
Production Rhythm: Maintain a stable production speed to avoid excessive mold temperature fluctuations.
5.How is the process control and testing feedback handled?
First Article Inspection and Patrol Inspection System:
First Article Full-Dimensional Inspection: A coordinate measuring machine (CMM) is used to measure the full dimensions of the first article. The measurements are compared with CAD data, and mass production only begins after the first article has passed inspection.
Regular Patrol Inspection: During production, key dimensions are randomly selected at fixed frequencies (e.g., every 50 pieces) for rapid measurement (using calipers, height gauges, or online vision inspection).
Statistical Process Control (SPC):
Key dimensional data (e.g., aperture, positional accuracy, overall dimensions) are collected in real time and X-R control charts are generated. By observing the trends in the charts, abnormal fluctuations in the process (e.g., mold wear, material property drift) can be detected before dimensional deviations occur, enabling preventative control.
Positioning Datum Consistency:
Ensure the feeding accuracy and repeatability of the feeding system (whether it's a coil leveling line or robotic feeding). Check and standardize processing datum points.