The content of numerical control transformation of machine tools

In the following, according to the third modification method, the numerical control transformation of the lathe is taken as an example, and the main contents and main structural forms of the transformation are introduced in combination with the actual operation of the company in the machine tool transformation.

1. Transformation of the feed shaft

The X-axis and Z-axis of the ordinary lathe are driven by the same motor. The movement of the cutter passes through the cutter box drive screw and the slide box to obtain different workpiece pitches, that is, the Z-axis movement; the movement of the cutter passes through the cutter box to transmit the polished rod and slide. Crate, get different feeds, ie X-axis movement. When the CNC lathe is modified, the cutter box and the slide box are generally removed, and the feed servo (or stepping) drive chain is used instead, which is embodied as:

Z axis: longitudinal motor → reduction gearbox (or coupling) → longitudinal ball screw → large carriage, longitudinal control by CNC command to obtain different clearance and pitch.

X-axis: transverse motor → gearbox (or coupling) → transverse ball screw → cross-slide, horizontally press the CNC command to obtain different passes.

After the transformation, the transmission precision of the whole transmission chain has a great relationship with the selection and arrangement structure of the ball screw pair and the accuracy of the machine guide rail under the condition of ensuring the rigidity of the machine tool.

1), the selection and arrangement of the ball screw pair

Most of the ordinary lathes use a sliding screw pair such as a T-type screw. Compared with the ball screw pair, the frictional resistance is large and the transmission efficiency is low, which cannot be adapted to high-speed motion. In addition, due to the rapid wear, resulting in its precision retention and low life, etc., it is often replaced with a ball screw pair when performing numerical control transformation of ordinary machine tools. The ball screw pair has the following characteristics: low friction loss and high transmission efficiency, up to 0.90~0.96; if the screw nut used is pre-tightened, the gap can be completely eliminated, the transmission stiffness is improved; the friction resistance is small, almost the speed of movement Irrelevant, the difference in friction of the message is extremely small, which can ensure smooth movement and low creep phenomenon; low wear, long life and good precision retention. However, it should be noted that since the ball screw pair cannot be self-locking, it is reversible, that is, it can convert the rotary motion into a linear motion or convert the linear motion into a rotary motion. Therefore, when the lead screw is used vertically and tilted, the brake should be increased. Device or balancing device.

2), machine tool guide

Most of the ordinary lathe rails use sliding guide rails, which have large dynamic and static friction coefficients. They will have different degrees of wear after a period of use, which will have a great impact on the accuracy and maintainability of the machine tool. Therefore, in the process of numerical control transformation, it is necessary to carry out the necessary inspection and treatment for the condition of the machine guide rail. For the more serious wear, it is necessary to carry out overhaul, that is, grinding, quenching, plasticizing, shaving, etc., while adopting fairness. Lubrication, fully guarantee its accuracy.

3), the connection between the motor and the lead screw

Under the condition of meeting the requirements of the machine tool, in order to reduce the transmission error caused by the intermediate link, we will directly connect the motor and the screw pair through the coupling, which is determined according to the actual situation in the transformation. Generally for small lathes such as C6116, due to limited space, especially the X-axis, the motor and the screw pair can not be directly connected, and the gear pair or synchronous belt is used for transmission. For large lathes such as C6150, the bed is 5 meters long. Since the lead screw is long and the diameter is large, in addition to the problem of the transmission force, the low speed performance and the acceleration/deceleration inertia matching problem must be considered. The motor is often driven by several stages of deceleration. Whether using gear or synchronous belt drive, the elimination of the transmission clearance is more critical. Commonly used methods in gear transmission include the wrong tooth backlash method, the eccentric shaft adjustment method, etc. In the synchronous belt theory transmission, the adjustment center distance or the tension wheel anti-backlash method is often used.

2. Transformation of the main shaft part

The spindle of the lathe drives the workpiece to rotate at different speeds. It is the main motion in the turning process and consumes most of the power of the machine. The ordinary lathe is driven by the main motor via the belt, and the spindle is rotated by the main shaft gearbox. The main shaft box is obtained by manual or automatic shifting (9~24) speed, and the shifting and reversing of the main shaft are controlled by electromagnetic or hydraulic clutch; and the CNC lathe spindle The box consists of an electric spindle or a conventional mechanical spindle unit plus a variable frequency motor and a frequency converter. In the case of numerical control, the ordinary lathe will save the original headstock in most cases without modification or minor changes.

3, the transformation of the knife holder part

At present, the CNC lathe tool holder is basically an electric tool holder, which is characterized by more accurate and rapid positioning. Old-fashioned traditional lathe tool holders are mostly manual, hydraulic or a small part of the electric, which can be replaced as needed.

The electric knife holder can be divided into a horizontal turret tool holder (generally 8 to 12 knives are installed) and a vertical electric knife holder. The vertical electric turret has four stations (or six stations), each of which is provided. There are also points for lifting the knife holder (the both ends of the toothed disc) and the lifting-free knife holder (the three-ended toothed disc). The horizontal turret tool holder is relatively expensive, and the vertical four-station electric knife holder is often used in the transformation.

4, the transformation of the lubrication part

In addition to the spindle box, the old-fashioned lathes are regularly lubricated with grease guns and grease lubricated by guide rails, screw rods, polished rods, etc. This maintains the accuracy of the guide rails and lead screws of the machine tool, and the stability of the machine tool under the same drive. Sex and flexibility are also poor.

5, machine protection

After the machine tool is rebuilt, the whole protection is divided into three types: partial protection, semi-protection and full protection.

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