Mold fitter marking
Mold marking is the process of marking machining boundaries, positioning references, and inspection lines on the surface of a blank or semi-finished part using a marking tool according to the mold drawing requirements. It is a crucial preparatory step before mold processing. Marking clarifies the machining range and dimensions of the part, providing a basis for subsequent processing (such as filing, milling, and grinding). It also verifies the shape and dimensions of the blank, allowing defects to be identified and remedial measures implemented promptly, thus avoiding wasted processing time. Mold marking requires high precision, typically within a range of 0.1-0.05mm. For precision mold parts, the marking accuracy can even reach 0.02mm, requiring skilled techniques and meticulous execution.
Marking tools are essential for ensuring marking accuracy and primarily include four categories: datum tools, measuring tools, marking tools, and clamping tools. Datum tools are used to establish the reference plane for marking, such as marking plates (flatness ≤ 0.03mm/1000mm), square boxes (perpendicularity ≤ 0.01mm/100mm), and V-shaped irons (used for positioning cylindrical workpieces). The marking plate is the core datum and requires regular accuracy verification to avoid marking errors caused by plate deformation. Measuring tools include steel rulers (accuracy 1mm), vernier calipers (accuracy 0.02mm), micrometers (accuracy 0.001mm), universal angle rulers (accuracy 2′), and gauge blocks (accuracy 0.0005mm), used to measure dimensions and angles. Marking tools include styluses (tip diameter ≤ 0.5mm), rule gauges (for marking circles and arcs), marking discs (for marking parallel lines), height vernier calipers (0.02mm accuracy, for precision marking), and sample punches (for punching holes at the marking point, with a diameter of 1-5mm). Clamping tools include vises, pressure plates, and magnetic chucks to secure the workpiece and prevent it from moving during marking.
The basic steps for mold marking by a mold fitter include preparation, determining the datum, marking the outline, and punching the holes, and each step requires strict execution. Preparation includes cleaning the workpiece surface (removing oil, rust, and burrs), applying a marking paint to the marked area (such as gentian violet mixed with alcohol, or white lime water, to make the marking clearly visible), and checking whether the size and shape of the blank meet the drawing requirements. Determining the datum is key to marking. The appropriate datum plane (usually the machined surface or center of symmetry) must be selected based on the part drawing. For parts with multiple datums, the primary and secondary datums must be clearly defined to ensure the accuracy of the marked dimension chain. For example, the marking of the mold cavity is based on the bottom and one side surface. First, the cross centerline is marked, and then the position lines of each cavity are marked using the centerline as the reference.
When marking contour lines, begin with the baseline, then horizontal lines, vertical lines, diagonal lines, and finally curves and arcs to ensure clear and accurate lines. When marking straight lines, move the marking disc close to the workpiece surface, with the stylus at a 45-60° angle to the workpiece surface. Apply even pressure to avoid excessively thick lines (line width ≤ 0.1mm). When marking circles and arcs, the toe of the marking compass should be sharp. After locating the center of the circle, gently rotate the compass to ensure a smooth and continuous arc. For circles with larger diameters, add auxiliary points before connecting them to form the circle. When marking angles, use a universal protractor to locate the angles, or determine the position of the angle lines by calculating the side lengths of a right triangle. For example, to mark a 60° angle, determine the two points using the right-angled side (30mm) and the opposite side (51.96mm) (tan60° = 1.732). Connect these points to create a 60° angle.
Punching holes is the final step in marking, used to mark the line locations and prevent blurring or erasure. Punching holes should be made at intersections, turning points, and arc centers, with a depth of 0.1-0.5mm (depending on the workpiece thickness). For finish-machined surfaces, the holes should be shallow and small to avoid affecting surface quality. When punching holes, the punch should be placed vertically and tapped gently to confirm its position. Adjust the verticality and then tap firmly to ensure the holes are accurately positioned on the line. After marking, check the dimensions and position of each line against the drawing to ensure accuracy before proceeding with further processing. For complex mold parts (such as multi-cavity dies), a marking template can be used to assist with marking to improve efficiency and accuracy. The template should be made of 0.5-1mm thick steel plate and have a precision level 1-2 higher than that of the part.
Marking special mold parts requires specialized techniques. Large parts (such as templates for automotive panel molds) must be marked on a large marking platform, using a gantry marking machine to ensure full coverage of the entire part. Special-shaped parts (such as cores with irregular curves) require positioning with auxiliary fixtures or using a coordinate measuring machine to determine the coordinates of key points before marking. Precision parts (such as the mating surfaces of guide pins and guide sleeves) require precise marking with a height vernier caliper, with dimensional errors controlled within 0.02mm. Safety precautions must be taken during marking, and the tip of the marking tool must be properly stored to avoid injury. The workpiece must be securely clamped to prevent tipping, and the marking platform must be kept clean to prevent iron filings from affecting the datum accuracy. Through accurate marking, mold fitters can provide reliable dimensional data for subsequent processing, reduce machining errors, and improve the yield rate of mold parts.
