What matters need to be paid attention to in the process of high-precision engraving machine cutting die?

The core of high-precision engraving machine in cutting die processing is to achieve high flatness, edge sharpness and dimensional consistency of cutting die (cutting edge die used for die cutting and stamping, which is common in packaging, electronics and other industries) through precise control. The details need to be controlled around the four dimensions of "equipment stability, process adaptation, quality control and safety specification". The specific precautions are as follows:

First, before processing: basic adaptation of equipment and materials

Equipment state calibration

Regularly check the accuracy of the core components of the engraving machine, including the straightness of the guide rail (which can be detected by a laser interferometer with an error of ≤0.01mm/m), the radial runout of the main shaft (≤0.005mm to avoid "vibration marks" when the cutting edge is cut), and the levelness of the workbench (calibrated with a level, with a four-corner error of ≤0.02mm to prevent the plate from being deformed due to uneven stress).

Clean up the key transmission parts: the lead screw and guide rail should be coated with special grease regularly (to avoid the formation of "sludge" caused by dust mixed grease, which will affect the movement accuracy), and at the same time, check the back clearance of the lead screw to eliminate the clearance error through parameter compensation (especially for the dimensional deviation during reciprocating cutting).

The base material of the cutter die is adapted to the fixture.

Pretreatment of base material: The common materials of knife die are SKD11 (alloy tool steel) and Cr12MoV (cold-working die steel). Before machining, the flatness of base material (measured by dial indicator, flatness ≤0.03mm/100mm) should be confirmed to avoid the difference of cutting edge height after machining due to deformation of base material; If the substrate has oxide scale, the surface should be removed by milling for 2-3mm to expose the smooth metal surface.

Fixture Selection and Fixation: Select the suitable fixture (such as vacuum chuck, pressure plate fixture) according to the size of the die, so as to ensure uniform clamping force and no damage to the substrate. For thin die (thickness < 5 mm), it is suggested to use "multi-point pressure plate" or "magnetic sucker" to avoid the warping of the plate caused by single-point clamping; After clamping, it is necessary to retest the flatness of the substrate with a dial indicator and confirm that there is no displacement before starting processing.

Specification for tool selection and installation

Tool matching processing requirements: Tool die processing involves three stages: "roughing (removing the allowance), semi-precision carving (trimming the shape) and precision carving (forming the cutting edge)", so it is necessary to select tools accordingly:

Roughing: using carbide end milling cutter (4 blades, blade length > machining depth 1-2mm) to improve cutting efficiency and avoid tool breakage caused by insufficient tool rigidity;

Carving cutting edge: Use single-edge or double-edge coated milling cutter (TiAlN coating is optional, which is resistant to high temperature and wear), the sharpness of the cutting edge should be high (avoiding burr on the cutting edge caused by "extrusion"), and the extended length of the cutter should be as short as possible (the shorter the hanging length, the stronger the rigidity and the smaller the cutting vibration).

Accuracy of tool installation: when loading the tool, use the cleaning brush of the handle to remove the dust in the chuck, and the depth of the tool inserted into the chuck should be consistent (the recommended extension length error is less than or equal to ≤0.1mm), and the tool length should be calibrated by the "tool alignment instrument" (the repeated tool alignment error is less than or equal to ≤0.002mm), so as to prevent the depth of the cutting edge from being insufficient or over-cut due to the tool length deviation.

Second, in process: process parameters and quality control

Optimization of cutting parameters (core affects cutting edge quality)

Adjust the parameters according to the material: different die steels have different hardness (such as hardness HRC58-62 after quenching of SKD11 and HRC20-25 before quenching), so the parameters need to be set differently:

Tool type in machining stage: spindle speed (SFM), feed speed (f), cutting depth (AP) Matters needing attention

Rough 4-edge carbide cutter 800-1200 rpm 500-800 mm/min 0.5-1 mm, leaving 0.1-0.2mm allowance to avoid excessive tool load during fine carving.

Single-edge coated milling cutter with carved cutting edge 1500-2000 rpm 200-400 mm/min 0.05-0.1 mm to reduce the feed speed and ensure the smoothness of cutting edge (Ra≤0.8μm).

Avoid "over-cutting" and "under-cutting": the cutting edge of the die is usually "acute angle" or "inclined edge", and it is necessary to set "layered cutting" (the depth of each layer is ≤0.05mm) in fine carving, especially at the tip of the cutting edge, the path of "arc transition" can be adopted to prevent the cutting edge from collapsing due to the direct impact of the cutter; At the same time, the "constant linear speed cutting" function of the engraving machine is turned on to ensure that the cutting speed at different diameters of the cutting edge is consistent and avoid local overheating leading to annealing of the cutting edge (affecting hardness).

Machining path planning

Optimization of path direction: adopt "spiral cutting" or "oblique feeding" when roughing (to avoid the cutter edge directly impacting the workpiece when cutting vertically, resulting in cutter collapse); When the cutting edge is finely carved, it follows the "forward milling" direction (the rotation direction of the cutter is the same as the feed direction), which reduces the cutting resistance and the burr of the cutting edge (reverse milling is easy to produce "tearing" cutting, resulting in rough cutting edge).

Avoidance of easy-to-deform areas: the die is often designed with "hollowed-out grooves" and "narrow slits" (such as the thin cutting edge of the die for electronic parts). When processing, the outer rigid areas should be processed first, and then the inner weak areas should be processed to avoid the deformation of the workpiece due to local stress release; For narrow seam (width < 1 mm), it is necessary to select small-diameter cutter (such as φ0.8mm milling cutter) and reduce the feed speed (≤150mm/min) to prevent the "chatter" of the cutter from causing the seam wall to be rough.

Real-time monitoring and exception handling

Observation of cutting state: During machining, the working condition can be judged by hearing (normal cutting is "uniform rustling", and if "harsh screaming" occurs, it may be tool wear or improper parameters) and vision (observing chip shape: continuous curling chip is normal, if chip is "broken", it may be too fast feeding, and if it is "banded", it may be too low rotating speed).

Handle the abnormality in time: if "edge collapse" occurs on the cutting edge (which may be caused by tool passivation or excessive feed speed), stop the machine immediately to replace the tool and adjust the parameters; If there is a "broken knife" in machining, it is necessary to clean up the residual knife first (to avoid secondary damage to the workpiece), and then re-align the knife and continue machining from the path node before the broken knife (depending on the "breakpoint carving" function of the engraving machine).

Third, after processing: quality inspection and equipment maintenance

Key indicators of quality acceptance of knife die

Dimensional accuracy: the key dimensions (such as the diameter of the inner hole and the outline) of the cutting edge of the knife die are detected by a three-coordinate measuring instrument, and the error should be ≤±0.01mm (to meet the requirements of high-precision die cutting, such as small hole die cutting of electronic components); Check the blade spacing (multi-blade die), and the error between adjacent blades is ≤0.005mm to avoid "missing cutting" and "offset" during die cutting.

Quality of the cutting edge: when observing the cutting edge with a tool microscope (magnification of 20-50 times), it should be free of burrs, chipping and curling, and the deviation of the cutting edge angles (usually 30, 45 and 60) should be ≤ 1; When the surface roughness meter is used to detect the surface of the cutting edge (Ra≤0.4μm), the lack of smoothness will lead to "material sticking" during die cutting (such as paper and film sticking to the cutting edge).

Flatness and verticality: use marble platform+dial indicator to detect the flatness (≤0.02mm/200mm) of the bottom surface of the knife die, so as to ensure that it fits with the press table during die cutting; Check the perpendicularity between the cutting edge and the bottom surface (≤0.01mm/100mm) with a square ruler and a feeler gauge to avoid uneven die cutting depth.

Postoperative maintenance of equipment

Cleaning and protection: clean the workbench in time after machining (blow away the iron filings with a high-pressure air gun to avoid residual iron filings scratching the workbench or affecting the next clamping accuracy), and blow off the dust of the tool holder and chuck after the spindle stops; If it is not used for a long time, it is necessary to apply anti-rust oil on the surface of the guide rail and the lead screw, and turn off the cooling system before turning off the main power supply of the equipment (drain the cooling liquid to prevent the pipeline from being damaged by freezing at low temperature).

Consumables replacement record: establish the replacement account of tools and cooling liquid (commonly used emulsion and cutting oil, the concentration of which needs to be tested regularly, and the emulsion concentration should be kept at 5%-8% to prevent rust or bacterial growth), and the tools should be scrapped immediately after reaching the service life (for example, in SKD11 machining, the single-edged milling cutter needs to be replaced after continuous cutting for more than 2 hours) to avoid affecting the machining accuracy.

Fourth, safety and environmental norms

Personnel safety protection

When operating, you must wear protective glasses (to prevent iron filings from splashing), non-slip labor protection shoes (to prevent heavy objects from being injured) and dust masks (to prevent dust when processing cast iron knives). It is forbidden to wear gloves (to avoid being involved in the spindle or knives).

Before starting the machine, make sure that the emergency stop button and the protective cover (to prevent cutting fluid from splashing and iron filings from hurting people) are functioning normally. It is forbidden to open the protective cover during machining and touch the rotating tool or the moving workbench with your hands.

Environmental adaptation

The engraving machine should be placed in a constant temperature (20-25℃, with a temperature difference of ≤ 2℃, so as to avoid thermal expansion and cold contraction of machine parts caused by temperature changes), constant humidity (humidity 40%-60%, so as to prevent electrical components from getting wet or metal parts from rusting) and vibration-free environment (away from vibration sources such as punching machines and air compressors, and install shock-proof pads if necessary).

Power supply should be stable: equipped with voltage regulator (voltage fluctuation ≤ 5%) to avoid overload of spindle motor or control system failure caused by sudden voltage rise and fall; Grounding resistance ≤4Ω to prevent electrostatic interference (especially affecting the signal transmission accuracy of electronic control system).

summary

The core of high-precision die processing is "millimeter design and micron control", which needs to be controlled through the whole process of "pre-calibration (equipment+material), medium-optimization (parameters+path) and post-detection (precision+cutting edge)", and at the same time, combined with strict safety and environmental norms, in order to ensure that the die can meet the high adaptability of the subsequent die-cutting process (such as no burr and long die-cutting life), and finally improve the downstream products.