How to judge whether the accuracy of vertical machining center machine is up to standard?

The core of judging whether the accuracy of the vertical machining center machine reaches the standard is to pass the four-layer detection of "geometric accuracy+positioning accuracy+dynamic accuracy+trial cutting verification", and comprehensively verify from static state to dynamic state and from no-load to load in combination with the factory standards and industry specifications (such as ISO 230). The specific methods are as follows:

1. Geometric accuracy detection: verify the static foundation accuracy of the equipment.

Geometric accuracy is the core benchmark of machine tools, and it needs to be tested when the equipment is horizontally calibrated and cold under no-load condition, and checked one by one with professional measuring tools.

Straightness detection: measure the straightness of the full-stroke movement of X, Y and Z axes with a laser interferometer or a leveling ruler plus a dial indicator, and the error shall be ≤0.01mm/m (the total accumulated error shall be ≤0.02mm).

Verticality detection: use a square ruler+dial indicator or laser interferometer to detect the verticality between X-Y, Y-Z and X-Z axes, and the error shall be ≤0.015mm/m to avoid inclined plane or verticality deviation during processing.

Accuracy of the workbench: use a level to detect the flatness of the workbench, and the error is ≤ 0.01 mm/m; Use a dial indicator to detect the rotary accuracy of the workbench (if it has rotary function), and the end face circular runout is ≤ 0.005 mm..

Geometric accuracy of the spindle: measure the end-face circular runout (≤0.003mm) and radial circular runout (≤0.003mm) of the spindle with a dial indicator to ensure that there is no eccentricity when the spindle rotates.

2. Detection of positioning accuracy and repeated positioning accuracy: to verify the accuracy of movement.

These two kinds of accuracy directly affect the consistency of machining dimensions, and need to be completed by laser interferometer (high-precision detection) or club instrument (convenient detection).

Positioning accuracy: to detect the deviation between the actual positioning value and the theoretical value of multiple target positions of each axis in the whole stroke, the common vertical machining center should be ≤0.015mm, and the high-precision model should be ≤ 0.008 mm.

Accuracy of repeated positioning: the same shaft is repeatedly positioned at the same position for 10 times, and the maximum deviation value is required to be ≤0.008mm (high-precision models ≤0.005mm) to ensure the dimensional stability during batch processing.

Reverse clearance detection: Measure the clearance (commonly known as "back clearance") when each shaft moves in the reverse direction. If it is detected by laser interferometer or dial indicator, the error should be ≤0.003mm, which will easily lead to machining steps or size fluctuation.

Third, dynamic accuracy detection: verify the stability in the moving state.

The dynamic accuracy reflects the accuracy maintenance ability of the equipment when it is running at high speed, and it needs to simulate the actual processing condition detection.

Dynamic accuracy of spindle: When the spindle runs at different rotational speeds (low speed, medium speed and high speed), the vibration value of the spindle (≤0.2mm/s) is measured by a vibration detector, and the temperature rise of the spindle (≤20℃) is monitored by an infrared thermometer, so as to avoid the influence of vibration or overheating during high-speed rotation on accuracy.

Accuracy of axis linkage: Carry out circular interpolation test (such as drawing a circle with a diameter of Φ100mm) with the club instrument, and detect the trajectory deviation when the axes such as X-Y and X-Z are linked, and the roundness error should be ≤0.01mm to ensure smooth surface processing.

Dynamic accuracy of tool change: automatically change the tool for 10-20 times, and use a dial indicator to detect the coaxiality (≤0.01mm) between the tool tip and the spindle center line after tool change, and observe whether the tool change process is smooth without collision or positioning deviation.

Fourth, trial cutting verification: intuitive judgment through actual processing.

Trial cutting is the final verification means, and whether the actual processing effect is up to standard is detected by processing standard specimens.

Standard specimen selection: 45 # steel or aluminum alloy blocks (recommended size ≥100mm×100mm×50mm) are commonly used to facilitate the detection of dimensional accuracy and surface quality.

Inspection of key processing items:

Milling plane: process the upper surface of the specimen, measure the flatness (≤0.01mm/100mm) with a leveling ruler and a dial indicator, and measure the surface roughness (Ra≤1.6μm) with a roughness meter.

Drilling+boring: drill a φ 10 mm through hole on the specimen, and then bore it to φ Φ10H7 (tolerance+0.015mm). Check the tolerance of aperture size with an inner diameter dial gauge, the roundness of the hole (≤0.005mm) with a roundness meter, and check the verticality of the hole with the plane (≤0.01mm/100mm).

Milling groove: process a straight groove with a width of 5mm and a depth of 10mm, check the groove width tolerance (≤ 0.01 mm) with a plug gauge, and check the groove straightness (≤0.01mm/100mm) with a dial gauge.

Multi-faceted processing: clamp the test piece on the fixture, and process three end faces in X, Y and Z directions in turn, and check the verticality (≤0.015mm) and dimensional consistency (cumulative error ≤0.02mm) between the faces.

V. Auxiliary judgment: Combined with the running state of the equipment.

In addition to quantitative detection, the operating state of the equipment can also assist in judging the accuracy:

During operation, there is no abnormal vibration or abnormal sound, and each axis moves smoothly, without jamming or crawling.

In the process of machining, the cutting force is stable, the tool wears evenly, and there is no machining grain caused by obvious chatter.

Batch processing of 3-5 identical specimens shows that the size dispersion is small (range ≤0.01mm), which shows that the precision stability is good.

Key reference standard

Ordinary vertical machining center: following ISO 230-2/3 standard, the positioning accuracy is ≤0.015mm, the repeated positioning accuracy is ≤0.008mm, and the trial cutting dimension tolerance is ≤±0.02mm.

High-precision vertical machining center: positioning accuracy ≤0.008mm, repeated positioning accuracy ≤0.005mm, trial cutting dimension tolerance ≤±0.01mm, surface roughness Ra ≤ 0.8 μ m..