1.How to control raw materials?
Thickness Tolerance (Thickness Accuracy): Full-length monitoring is performed using a high-precision thickness gauge (such as X-ray or laser thickness gauge). Thickness fluctuations directly lead to variations in forming dimensions, opening dimensions, and cross-sectional shape distortion.
Mechanical Property Uniformity: Ensure that the material's yield strength, tensile strength, and hardness remain consistent within and between rolls. Inconsistent properties result in inconsistent springback, affecting the final shape and dimensions.
Sheet Shape (Flatness): Good sheet shape is a prerequisite for stable feeding. Severe waviness, edge waviness, or camber can cause feeding jams, deviations, hole position errors, edge wrinkling, or distortion.
Surface Quality: Free from oil, oxide layers, and hard particles. Surface condition affects the coefficient of friction, thus impacting feeding stability and surface appearance.
2.What is the precision of the forming machine (rolling line) itself?
Frame Rigidity and Alignment: Each frame must have sufficient rigidity to resist forming forces and prevent deformation. The centers of all frames must be aligned (alignment), typically requiring an accuracy within ±0.05mm.
Spindle Accuracy and Axial/Radial Runout: The spindle is the foundation for mounting the rollers, and its runout must be extremely small (typically <0.01mm).
Transmission System Stability: The servo motor or mechanical transmission system must be smooth to avoid speed fluctuations that cause "stripping" (periodic dimensional fluctuations).
3.How to maintain and ensure the precision of the mold (forming roller)?
Design and Machining Precision: The dimensions, surface finish, and heat treatment hardness of the roller cavity are crucial. Modern high-precision rollers are generally machined using CNC wire EDM and precision grinding.
Gap Adjustment: The gap between the upper and lower rollers or the horizontal rollers must be precisely set, typically 90%-105% of the material thickness (depending on the material). A precision eccentric shaft or wedge adjustment mechanism is required.
Roller Installation and Locking: Ensure the rollers are installed correctly, without gaps, and with uniform locking force to prevent movement during operation.
Cooling and Lubrication: Stable cooling (oil or water cooling) prevents dimensional drift caused by thermal expansion. Appropriate process lubrication (oil or emulsion) reduces wear, scratches, and forming forces.
4.How is the process controlled?
Feeding and Guiding
Feeding Accuracy: Servo feeding is the mainstream method, requiring optimization of the feeding curve to reduce start-stop impact. Ensure stable feeding length.
Guiding Device: Vertical rollers and side guide plates are installed at the inlet to ensure the strip always enters the first pass along the centerline. This is fundamental to ensuring the accuracy of the symmetrical cross-section.
Molding Process
Pass Allocation and Deformation Rate: Scientifically allocate the deformation amount for each pass to avoid excessive local deformation that could lead to material instability, wrinkling, or tearing.
Springback Compensation: This is the most challenging aspect of roll forming precision control. Precise pre-compensation must be performed during the roller design phase using empirical formulas and CAE simulations (such as COPRA RF software). During production, fine-tuning of key pass rollers is performed based on the first piece measurement results.
Tension Control: For continuously formed long parts or those with finishing processes at the end, appropriate tension needs to be established before and after the production line to help stabilize the shape, reduce springback, and improve flatness.
Cutting and Length Control
Length Accuracy: The accuracy of servo flying shears or inline cutting saws directly affects product length tolerances. Length measurement systems (such as encoders) need to be calibrated periodically.
Cut-off Deformation: Optimize cutting dies or sawing parameters to prevent cut deformation (such as crushing or burrs), which can affect final assembly.
5.How are measurement and quality controlled?
First Article Inspection: A high-precision coordinate measuring machine (CMM) or dedicated contour projector is used to perform a comprehensive scan of the first article and compare it with the design drawings.
In-Process Sampling Inspection: Strict sampling frequencies are established, and critical dimensions are rapidly measured using calipers, micrometers, angle gauges, feeler gauges, etc.
Statistical Process Control (SPC): Critical dimensional data is collected, X-R control charts are generated, process stability is monitored, and timely warnings and adjustments are made before any trend deviations occur.
Full Inspection and Sorting: For products with extremely high requirements, an online vision inspection system can be used for full inspection and automatic sorting.