How to ensure the engraving accuracy in the process of cutting die processing?

In the process of die machining, the engraving accuracy directly determines the cutting quality (such as edge flatness and dimensional consistency) and service life of the die. It is necessary to control the whole process of equipment, materials, technology, operation and environment, and the core is to reduce all kinds of errors (such as positioning errors, cutting errors, vibration errors, etc.) in the machining process. The following are the key control points:

I. Equipment and Tooling: "Hardware Basis" of Accuracy

Select high-precision engraving equipment.

The engraving machine equipped with high-precision transmission system (such as ball screw and linear guide rail to reduce reverse clearance) and high-rigidity frame (such as cast iron/granite lathe bed to reduce cutting vibration) is preferred to ensure motion accuracy (positioning accuracy ≤0.01mm, repeated positioning accuracy ≤0.005mm).

Equipped with high-resolution servo motor/stepping motor (such as subdivision step angle ≤ 0.001) to avoid size deviation caused by motor "step loss"; At the same time, check the stability of spindle speed. For high-speed engraving (such as metal die), it is necessary to ensure that the spindle has no "jumping" (radial runout ≤0.003mm).

Precision tooling and positioning system

Adopt vacuum adsorption platform (for thin-plate die substrate) or precision fixture (such as vice and positioning pin) to ensure that the substrate has no displacement and deformation during processing. The adsorption platform should ensure uniform suction (to avoid local air leakage causing the substrate to tilt) and moderate clamping force of the fixture (to prevent the substrate from being pinched or the clamping is too loose).

Using datum positioning technology: Before machining, calibrate the X/Y axis datum of the substrate by "edge finder" and "tool alignment instrument" (such as taking the edge of the substrate or the pre-machined hole as the datum), and if necessary, use "multi-datum recheck" (such as diagonal positioning) to reduce the positioning error.

Second, cutting tools and consumables: the "execution key" of accuracy

Matching tool types and parameters

Choose the cutter according to the base material of the cutter die (such as steel plate, wood board and acrylic): for metal cutter dies, cemented carbide coated cutters are preferred (wear-resistant, high-temperature resistant, reducing the size drift caused by cutter wear), and for wood cutter dies, high-speed steel cutters can be used; The edge of the carving blade should be sharp (to avoid rough edges caused by "extrusion cutting"), and the extension length of the cutter should be shortened as much as possible (to reduce "cutter tremor").

Preset reasonable cutter parameters: set cutting speed (S), feed speed (F) and cutting depth (Z) according to cutter diameter and substrate hardness. For example, when machining 65Mn steel plate (a common material of cutter die), φ 3 cemented carbide cutter is recommended to have S=3000-4000rpm, F=500-800mm/min, and the cutting depth is ≤

Tool calibration and wear monitoring

After each tool change, the tool length and radius must be calibrated by the automatic tool alignment instrument (especially when carving deep grooves and steps, to avoid depth deviation caused by tool length error), and the manual tool alignment needs to be repeated for 2-3 times.

Check the tool wear regularly during machining (for example, by observing the shape of cutting debris: it is normal continuous debris, and it is powdery after wear; Or stop and observe the cutting edge with a microscope), and replace it in time when the wear exceeds the limit (generally, when the tool wear is more than ＞0.01mm, it needs to be replaced to ensure accuracy).

Third, the processing technology: the "process guarantee" of accuracy

Reasonable planning of machining path

Adopt "layered cutting": for deep grooves or steps (such as the "blade groove" of a knife die), cut for multiple times (each cutting depth is 0.1-0.3mm) to avoid machine tool vibration or substrate deformation caused by excessive single cutting force.

Optimize the feed mode:

"Forward milling" is preferred for contour carving (the rotation direction of the cutter is the same as the feed direction), which reduces cutting resistance, edge burr and size deviation;

Large-scale carving adopts "spiral cutting" and "diagonal cutting" to avoid the direct impact of the cutter on the substrate when cutting vertically, and reduce the cutter loss and positioning deviation;

Avoid "over-cutting": the end point and starting point of the machining path need to "overlap by 1-2 tool diameters" to ensure that the contour is closed without gaps.

Pretreatment and benchmark unification

Substrate pretreatment: the substrate of the knife die (such as steel plate) needs to be "leveled" first (the warpage is eliminated by grinder or press, and the flatness is ≤ 0.02 mm/m) to avoid unstable adsorption/clamping caused by uneven substrate; At the same time, clean up the oil stains and impurities on the surface of the substrate (to prevent slippage during positioning).

Unity of drawings and machining datum: CAD drawings should define the "design datum" (such as center and edge), and ensure that the machine tool coordinate system, substrate positioning datum and drawing datum are consistent during machining (to avoid the "datum misalignment error"). For complex tool dies, the "process datum hole" can be machined first, and then the datum hole is used for positioning and machining.

Iv. Operation and monitoring: "artificial control" of accuracy

Strictly carry out knife alignment and trial cutting.

Before formal machining, carry out "no-load operation" (run the machining path without tools) to check whether the path is consistent with the drawing, so as to avoid waste parts caused by program errors;

Trial cutting of the first piece: try cutting with scrap or substrate scraps, measure key dimensions (such as blade width, groove depth, hole position coordinates), and fine-tune tool parameters (such as compensating tool radius and correcting feed speed) after comparing with drawings until the trial cutting accuracy reaches the standard (error ≤0.01-0.02mm), and then batch processing.

Real-time monitoring and error compensation

Monitor the cutter position through the "real-time coordinate display" of the machine tool during machining, and stop the machine immediately for inspection if any abnormality (such as coordinate drift) is found; When high precision is required, an "on-line measuring system" (such as a laser probe) can be equipped to measure the machining dimension in real time and automatically compensate the error (such as the dimension becomes smaller due to tool wear, and the system automatically corrects the Z-axis depth).

In batch processing, the key dimensions are sampled every 5-10 pieces to avoid precision drift caused by continuous tool wear and temperature change of the machine tool.

V. Environment and Maintenance: "Stability Premise" of Accuracy

Control the processing environment

Temperature: keep the workshop at a constant temperature (20 2℃) to avoid thermal deformation of the machine tool guide rail and screw due to temperature changes (such as temperature difference between day and night, machine tool running fever) (the cast iron lathe bed may be deformed by 0.01mm/m for every temperature change of 1℃);

Humidity and vibration: the humidity should be controlled at 40%-60% (to prevent electrical components from getting wet or the base material from rusting). The machine tool should be far away from vibration sources (such as punching machines and air compressors), and "shockproof shim" should be installed if necessary to reduce the influence of external vibration on engraving accuracy.

Regular equipment maintenance

Daily inspection: clean the chips and oil stains on the guide rail and lead screw, and add lubricating oil (to ensure smooth transmission and reduce clearance); Check the tightness of the vacuum adsorption platform and the tightness of the fixture;

Periodic calibration: use "laser interferometer" to calibrate the positioning accuracy and geometric accuracy (such as verticality and parallelism) of the machine tool every month, and compensate the errors in time through machine tool parameters; Check the wear of spindle bearings every quarter to avoid the decline of spindle accuracy.

summary

The core of the engraving accuracy of the die is "reducing variables and stabilizing the process": controlling the "hardware error" through high-precision equipment and tooling, controlling the "cutting error" through matching the tools and optimizing the process, and controlling the "fluctuation error" through strict operation and environmental maintenance, and finally achieving the high-precision requirements of the die size, profile and depth (generally, the engraving accuracy of the precision die can be controlled within ±0.01-0.03mm).