How linear guideways affect CNC machine performance

Analysis of the key impact of linear guide on the performance of CNC machine tools

I. Positioning accuracy: a direct correlation from micron-level error to the quality of the workpiece

Linear guide's straightness and rigidity directly determines the movement accuracy of the machine tool table. For example, a vertical machining center using high-precision roller guideway, machining 100 mm long workpiece, the size deviation from 0.02 mm to 0.01 mm, this is because the guideway straightness will lead to table offset, and high-precision guideway (such as THK's HRW series) can control the straightness of 0.003 mm per meter or less. In addition, the repetitive positioning accuracy of the guideway is especially critical - when the guideway is worn out and has a gap, the dimensional consistency of the milling of cell phone housings will be reduced, and by replacing the guideway with a pre-tensioned design, the accuracy can be increased to ±0.003 mm, which can satisfy the demand for precision machining of 3C products.

Second, rigidity and cutting capacity: the core elements of the decision processing efficiency

The rigidity of the guideway directly affects the stability of cutting. Roller guideway than ordinary ball guideway rigidity is about 40% higher, in the gantry milling machine machining cast iron, the former can withstand 5000 Nm radial cutting force, the surface of the workpiece is smooth (roughness Ra ≤ 1.6 microns), while the latter in the 3,000 Nm will be vibration lines. Part of the guideway with damping structure (such as THK's SRG series), the spindle vibration amplitude can be reduced from 0.02 mm to 0.008 mm, doubling the life of the tool, especially suitable for molds and other high-demand machining scenarios.

Third, the speed and smoothness of movement: the bottleneck of high-speed machining breakthrough point

The upper speed limit of different types of guideway varies significantly: the maximum speed of standard ball guideway is about 60 m / min, suitable for ordinary milling; roller guideway due to the coefficient of friction is 30% lower, the speed of up to 120 m / min, suitable for automotive coverings of high-speed cutting; and air-floating guideway through the air film of 0.01 mm to achieve zero friction, the speed of up to 200 m / min, a lithium ion lithium-ion coating, the speed of up to 200 m / min. 200 m / min, a lithium battery wafer cutting equipment, cutting speed increased to 180 m / min, burr height reduced by 70%, to meet the semiconductor and new energy field of high-speed precision needs.

Fourth, life and maintenance costs: the key to long-term operation of the economy

The wear characteristics of the guideway directly affect the frequency of equipment maintenance. Roller guide because of the larger contact area, life than ball guide 2.6 times longer -- a 24-hour running production line using roller guide (life 8000 hours), the annual maintenance cost reduced by 60,000 yuan. In addition, fully sealed guide (such as NSK's LE series) with automatic lubrication system, in a dusty environment, the maintenance cycle is extended from 3 months to 1 year, so the photovoltaic production line to reduce downtime losses of 150,000 yuan / year, a significant improvement in the economy.

V. Thermal deformation and precision maintenance: performance stability under temperature fluctuations

The coefficient of thermal expansion of the guideway material determines the ability to maintain precision when the temperature changes. Steel guide in the temperature difference of 20 ℃, each meter length will be deformed 0.023 mm, while the granite guide (coefficient of thermal expansion is very low) can be deformed to control within 0.0016 mm, a precision grinder changed to use the consistency of the size of the workpiece to improve 90%. Part of the high-end guide rail built-in cooling channels (such as Germany Rexroth temperature-controlled guide rail), the temperature fluctuations can be controlled at ± 1 ℃, 4 hours of continuous processing after the size deviation is still less than 0.005 mm.

Sixth, the installation accuracy: a prerequisite for the performance of the guide rail

The installation error of the guide rail will seriously affect the performance: if the parallelism is more than 0.02 mm, the table will appear to run stagnant, the motor current fluctuations of up to 20%, you need to use a laser alignment instrument calibration and pad into the 0.01 mm shims to adjust; the support base of the perpendicularity of excessively poor (such as >0.01 mm) will lead to abnormal wear and tear of the guide rail, the noise rises from 65 dB to 80 dB, you need to grind the mounting surface. The noise level rises from 65 dB to 80 dB and the mounting surfaces need to be ground to within 0.005 mm. A gear processing machine had a pitch error of 0.03 mm due to mounting error, and after recommissioning, the accuracy reached the standard and met the high precision requirements of gear processing.

Summary: the core strategy of guide selection

High-precision scenarios: select roller guide with granite base, suitable for aviation molds and other precision machining;

High-speed scenarios: with air-floating guide or linear motor drive, suitable for high-speed cutting of 3C products;

Heavy-duty scenarios: with a double-row roller guide and configure the mandatory lubrication, suitable for heavy-duty lathes.

Linear guide as a machine tool "motion spine", its performance is directly related to the machining accuracy, productivity and maintenance costs, need to be based on the workpiece material, process requirements and environmental conditions of the comprehensive selection, in order to maximize the performance of the equipment.