CNC milling machine or router?

Milling Router BPF2161

What is the difference between a milling machine, a milling plotter and an engraving machine? Different people interchangeably use these terms often for the same machine. Indeed, the tasks of these machines often overlap, but this is not always the case.

We used to describe a milling machine as a heavy machine, most often cast from cast iron, with a coordinate table and a spindle with a speed range from several dozen to several thousand revolutions per minute, enabling milling with large-size milling heads. Torques achieved thanks to gears (most often toothed) are in the order of several hundred Newton meters. These gears are one of the reasons for the relatively low maximum speed of the milling machine spindles. Milling machines and milling machining centers are mainly used for milling with multi-plate heads with diameters up to 300 mm, milling with end mills with diameters of 3-50 mm, drilling with drill bits with diameters of 3-40 mm, reaming, countersinking, boring. They are used primarily for rough and medium-precision machining of bodies, molds, dies, dies, dies.

The milling and engraving machine is a light milling machine with a spindle speed of 18,000, 24,000 or 40,000 rpm. This is dictated by the necessity to use tools with much smaller diameters (from 0.05mm) in the engraving work, which require much higher spindle speeds due to the need to achieve the appropriate cutting speed. They do not use a conventional motor-spindle system with a gear as a spindle, but electro-spindles integrating a spindle and a drive motor, most often induction, in one housing and on one axis. The advantage of this solution is smooth and quiet operation at high revolutions and the lack of brushes, and the disadvantage is relatively low torque, which is caused by the lack of a gear. Therefore, the diameters of the tools used in milling and engraving machines do not exceed 16mm in metals and 100mm in other materials. The solution to the inconvenience associated with the low torque of the electro-spindle is the use of a significant excess of its rated power (at least 9kW with a 10 mm cutter in steel), which often causes surprise to a potential buyer, but the matter needs to be clarified in depth.

Induction electrospindles, in addition to many undeniable advantages, have one serious drawback – constant torque. In spindles with a gear, in order to reduce the speed (e.g. for a large head), we change the gear ratio to a lower one, which at the same time increases the torque. In induction electro-spindles, the rotation is regulated by an inverter. The u / f characteristics of the motor show that the torque is almost independent of the revolutions (there are inverters that enable the torque boost at low revs, but not more than 200% of the nominal value). Therefore, the electrospindle, which has, for example, 7kW written on the nameplate, means that it achieves this power at a specific rotational speed (not necessarily the maximum one found on the nameplate), called the nominal speed. Let’s say it’s 18. 000 rpm The power is the product of the torque and the revolutions, which means that if we set the revolutions to 9.000 rpm, the power we have at our disposal is 3.5 kW, and at 1800 rpm only 700W.

It is comforting, however, that during operation, the average power consumed by an exemplary electrospindle does not exceed several hundred watts. Since high revolutions, which enable the transfer of high power, are used only with tools of small diameters, they are not consumed of such power, while at low speeds and large tools, the power achieved by the electrospindle is small, which also results in low power consumption from the network. Summarizing the above observations, one should always choose an electrospindle with a rated power much higher than it would result from the calculated power demand for a specific tool.

Milling and engraving machines equipped with electrospindles are increasingly used in the production of injection molds, dies, dies, dies, stamps, copper and graphite electrodes thanks to the availability of a wide range of tools made of monolithic sintered carbides. These tools are capable of cutting at speeds many times higher than the previously used HSS tools, which, combined with the possibility of obtaining high revolutions on machines equipped with induction electrospindles, becomes an ideal tool for many applications in every machining workshop.

Computer engravers are even lighter milling machines than milling and engraving machines. They are used primarily for work with very small tools (up to 6mm), most often with a conical geometry with a foot diameter from 0.02mm. Due to the very small diameter of the working part of the engraving tool, the spindle power does not have to be high (up to 2.2kW), but the stability, stiffness, positioning resolution and dynamic properties of the control system should be at the highest level. Positioning resolution is particularly important in this case, because engraving often involves jobs that are invisible to the naked eye. The smallest unit increment of position, called the positioning resolution, should not exceed 0.001mm, with the reverse play of the entire drive system not exceeding 0.005mm.

In computer engraving machines, one of the functions of the control system is also indispensable at work, rather unavailable in other machines. It is about the possibility of automatic cutting of corners with an engraving cutter. This is especially important if we are doing a jump job, i.e. we choose the background and the inscription stays sticking out. In the absence of this function, each sharp internal angle will be cut only at the bottom, while on the surface, an arc with the tool radius at the height of the mark top will be uncut.

Milling plotters, often called milling tables, probably owed their name to the first structures that were built on the basis of ordinary tables. But that’s all in the past. Today, milling plotters are modern, universal CNC machines that have found the greatest use in the advertising industry, for cutting, notching, drilling, engraving in plastic, aluminum, composite boards, foil, cardboard and paper cutting. In 3D versions, plotters are used to make casting models, thermoforming or laminating, modeling bas-reliefs, spatial mock-ups, three-dimensional presentations. They are the cheapest computer-controlled machine tools available on the market. They are most often made in the version with a movable gate, which with relatively large working areas (up to 3 x 8m),
The tables of milling plotters are most often equipped with tables with T-slots, which gives great versatility, or with vacuum material clamping systems, which makes it much easier to attach large and thin boards. A hybrid version is also available, a table covered with T-slots, additionally equipped with a vacuum clamping system, depending on the processing, we can use one or the other system. Milling plotters use 0.8k – 18 kW spindles. Optionally, they can be equipped with a homing system, a laser or touch scanner, a rotary axis, additional cutting, drawing and pouring heads, angular aggregates for cutters and circular saws, etc.

Light Portal Milling Machines are devices similar to milling plotters, but they are much stiffer, heavier and more accurate. They are primarily used in industrial conditions, or where there is a need to process large surfaces with large tools and with high efficiency. Power of spindles installed on light gantry milling machines start from 7kW and reach up to 20kW.