What are the methods of precision calibration for the precision engraving machine of knife die?

The precision calibration of the precision engraving machine of the cutter die is the core link to ensure the machining quality of the cutter die, and it is necessary to adopt professional tools and methods for geometric accuracy, motion accuracy and machining accuracy. The following are the calibration methods and technical details of the system:

First, the geometric accuracy calibration method

1. Spindle verticality calibration

Tools: dial indicator (accuracy 0.001mm), magnetic meter base, 100mm standard test stick.

Steps:

Insert the inspection rod into the spindle taper hole, fix the dial indicator on the workbench, and the meter head contacts the edge of the end face of the inspection rod;

Manually rotate the spindle (360) and record the maximum difference of the dial indicator. The verticality error in the X/Y direction should be ≤ 0.02 mm/100mm;

In case of out-of-tolerance, the copper gasket (0.01-0.05mm in thickness) is installed between the headstock and the upright post for adjustment until it meets the requirements.

2. Table flatness calibration

Tools: 0-level precision level ruler (length 1000mm), feeler (accuracy 0.01mm) and adjustable support block.

Steps:

Put three adjustable support blocks on the workbench, and put the leveling ruler on the support blocks (span 800 mm);

Measure the clearance between the leveling ruler and the workbench with a feeler gauge, and the flatness error in the whole process is less than or equal to ≤0.03mm；;

Local high points can be ground by diamond grinding wheel (grinding amount ≤0.05mm), and low points can be filled with metal filler (such as epoxy resin+copper powder).

3. Alignment of guide rail

Tools: laser interferometer (such as Renishaw XL-80), mirror bracket.

Steps:

Fix that interferometer host in a stable position outside the machine tool, and installing the reflector on the slide block;

Move the slider all the way along the guide rail, and record the linearity error of X/Y axis (horizontal plane ≤0.02mm/1000mm, vertical plane ≤ 0.03 mm/1000 mm);

Adjust the mounting bolt of the guide rail (torque 80-100 nm) or add wedge-shaped shim between the guide rail and the mounting surface (thickness difference ≤0.01mm) when it exceeds the tolerance.

Second, the motion accuracy calibration method

1. Calibration of positioning accuracy and repeated positioning accuracy

Tools: laser interferometer, linear mirror assembly.

Calibration standard (taking X axis as an example):

Full positioning accuracy: ≤0.03mm(2000mm travel).

Repetitive positioning accuracy: ≤ 0.01mm.

Steps:

Five measuring points (such as 0mm, 500mm, 1000mm, 1500mm, 2000 mm) are evenly selected throughout the guide rail;

Each point moves back and forth five times, and the interferometer records the deviation between the actual position and the commanded position;

Through the correction of numerical control system parameters (such as pitch compensation and reverse clearance compensation), the compensation step is ≤100mm (such as setting a compensation point every 100mm).

2. Reverse clearance calibration of screw rod

Tools: dial indicator, precision gauge block (100mm)

Steps:

Let the slider move forward along the X axis to 500mm, and the dial indicator head contacts the side of the slider;

Move reversely at a speed of 0.1mm/s, record the offset of the meter head, and the reverse clearance shall be ≤ 0.005 mm;

Adjust the pre-tightening force of the lead screw nut when it is out of tolerance (the pre-tightening force changes by about 5N for every 0.01mm increase or decrease of the gasket through the thickness adjustment of the double nut gasket), or replace the worn lead screw nut pair.

Third, the machining accuracy verification method

1. Standard parts trial cutting method

Specimen materials: 45# steel (hardness HRC28-32) and aluminum alloy 6061(T6 state).

Trial cutting of workpiece and detection index:

Qualification standard of testing tools for workpiece type processing requirements

Rectangular groove (100×50×10mm): the flatness of the groove bottom is ≤0.02mm, the verticality of the side wall is ≤±0.03mm, and the dimension tolerance of the verticality detector is+/-0.03mm..

Circular arc profile (R50mm) roundness ≤0.02mm, surface roughness Ra≤1.6μm, and CMM profile error ≤ 0.02mm.

The uniformity of the slot width of the narrow slot (width 0.1mm) is ≤0.01mm, and the edge roughness Ra of the optical projector without chipping (50 times) is ≤ 3.2 μ m.

2. Machining verification of the die specimen

Typical tool die workpiece: cutting edge of stamping die (material Cr12MoV, hardness HRC58-62)

Key points of calibration:

Proces a linear cutting edge with a length of 100mm, and detect that straightness by a tool microscope to be less than or equal to ≤0.01mm/100mm；;

Machining R0.2mm fillet, scanning with 3d scanner (such as HandySCAN 700), and the contour error is ≤ 0.005 mm;

10 identical cutter dies are processed continuously, and the dimensional consistency (deviation ≤0.015mm) between the first piece and the last piece is detected.

Four, dynamic precision calibration (for high-speed machining)

1. Spindle dynamic balance calibration

Tools: dynamic balance instrument (such as Schenk VAD-6), counterweight (accuracy 0.1g).

Steps:

The spindle idles at 15000rpm, and the vibration amplitude (allowable value ≤ 0.1 mm/s) is measured by the dynamic balance instrument;

Mark the unbalanced position on the end face of the spindle and install a counterweight (mass calculation: m = e× g/(ω× r), where e is the allowable eccentricity and g is the spindle weight);

Repeat calibration until the vibration value is ≤0.05mm/s (≤0.03mm/s for high-speed machining).

2. Optimization of dynamic characteristics of feed shaft

Tools: servo debugging software (such as FANUC SERVO GUIDE) and oscilloscope.

Parameter adjustment:

Speed loop gain: set 200-300rad/s for low-speed machining (≤1000mm/min) and 400-500 rad/s for high-speed machining (≥5000mm/min);

Position loop gain: adjust according to machining accuracy (generally 5-10rad/s, high accuracy should be ≥15rad/s, but system oscillation should be avoided);

Acceleration and deceleration time constants: set it to 100-200ms for linear machining and 50-100ms for circular machining to prevent corner overshoot (overshoot ≤0.01mm).

V. Special calibration tools and technologies

1. Club instrument calibration (contour accuracy)

Principle: By measuring the roundness of the relative motion between the spindle and the workbench, the accuracy of two-axis linkage is evaluated.

Parameter requirements:

200mm diameter circle profile ≤ 0.03 mm.

Quadrant deviation ≤ 0.015mm.

Application scenario: correct the "ellipticity" problem in arc machining (such as long axis deviation caused by mismatch of X/Y axis gain).

2. Thermal deformation compensation calibration

Environment: After continuous operation for 4 hours, detect the temperature rise of the spindle (≤40℃) and the thermal elongation of the screw (about 1.2μm/m per 1℃).

Compensation method:

Input the thermal deformation coefficient in the numerical control system (for example, the length of the X-axis lead screw is 2m, and the compensation is 2.4μ m for every temperature change of 1℃);

Install a temperature sensor (accuracy 0.5℃) to monitor the temperature of the screw rod in real time and automatically compensate (compensation frequency 1 time/minute).

Six, calibration cycle and record management

Periodic calibration frequency:

Acceptance of new machine: all project calibration (including laser interferometer detection)

Daily production: calibrate the verticality of the spindle and the flatness of the workbench every month.

Quarterly calibration: positioning accuracy, reverse gap (using laser interferometer)

Annual calibration: overall geometric accuracy+dynamic accuracy (including club instrument and dynamic balance)

Calibration record requirements:

Establish calibration files for each equipment, including calibration date, tool number, measured data and adjustment contents;

Waveforms (such as positioning error curve and reverse gap curve) should be attached to the calibration report of laser interferometer as the basis for precision traceability.

summary

The precision calibration of the precision engraving machine of the knife die needs to integrate static geometric measurement (such as dial indicator and leveling ruler), dynamic performance test (laser interferometer and club instrument) and machining demonstration verification (standard part trial cutting). The key point is to adopt customized calibration scheme for the special requirements of tool die machining (such as straightness of cutting edge and precision of small fillet), and at the same time, ensure the precision stability of equipment in long-term operation (such as precision attenuation ≤0.01mm after 8 hours of continuous machining) by means of thermal deformation compensation and servo parameter optimization.