How Do I Choose the Best Used Metal Lathe?

CNC lathe is one of the more widely used CNC machine tools. It is mainly used for internal and external cylindrical surfaces of shaft parts or disk parts, internal and external conical surfaces with arbitrary taper angles, complex rotating internal and external curved surfaces, and cylindrical and conical threads. Holes and boring. ^[1]

Numerical control (English name: Numerical Control for short: NC) technology refers to the use of numbers, characters and

Numerically controlled machine tool is an abbreviation of digitally controlled machine tool, which is an automatic machine tool equipped with a program control system. The control system can logically process and decode a program specified by a control code or other symbolic instructions, thereby causing the machine to operate and process parts.

Compared with ordinary machine tools, CNC machine tools have the following characteristics:

High processing accuracy and stable processing quality;

Multi-coordinate linkage can be performed, and parts with complex shapes can be processed;

When the processing parts are changed, generally only the NC program needs to be changed, which can save production preparation time;

The machine tool itself has high precision and rigidity. It can choose favorable processing amount and high productivity (generally 3 ~ 5 times of ordinary machine tools);

High degree of machine tool automation can reduce labor intensity;

Higher quality requirements for operators and higher technical requirements for maintenance personnel.

Preliminary preparation

Determine the process requirements and processing of typical parts

CNC lathe consists of CNC device, bed,

Lifting and transportation

The hoisting and positioning of the machine tool should use the special hoisting tools provided by the manufacturer, and other methods are not allowed. No special lifting tools are required, and wire ropes should be used for lifting and positioning in accordance with the specified parts of the instructions.

Foundation and location

The machine tool should be installed on a solid foundation and located away from the source of vibration; avoid sunlight and heat radiation; place in a dry place to avoid the effects of humidity and airflow. If there is a vibration source near the machine tool, an anti-vibration groove must be set around the foundation.

Installation of machine tools

The machine tool is placed on the foundation, it should be leveled in a free state, and then

The inspection and acceptance of CNC lathes shall be carried out in accordance with the "Technical Requirements for the Manufacturing and Acceptance of CNC Horizontal Lathes" promulgated and implemented by the state. During the acceptance process, if a dispute occurs, it shall be based on relevant national standards and resolved through negotiation.

Determine the processing route

The processing route is the movement trajectory and direction of the tool relative to the part during the process of the index-controlled machine tool.

1. It should be able to guarantee the processing accuracy and surface roughness requirements;

2. The processing route should be shortened as much as possible to reduce the idle travel time of the tool.

Relationship between machining route and machining allowance

Under the condition that numerical control lathes have not yet reached widespread use, generally, excessive allowances on blanks, especially those that contain forged and cast hard skin layers, should be arranged for processing on ordinary lathes. If the CNC lathe must be used for processing, you need to pay attention to the flexible arrangement of the program.

Key points for fixture installation

Hydraulic chuck and hydraulic clamping

The CNC car program can be divided into three parts: program start, program content and program end.

There are three methods for programming CNC machine tools: manual programming, automatic programming, and machining center CAD / CAM.

The main content of CNC machine tool programming

Analyze part drawings, determine processing technology, perform mathematical processing, write program lists, make control media, perform program inspections, enter programs, and test cut workpieces.

Steps for CNC machine tools

Analyze the parts drawings and process, analyze the parts' geometric shapes and technical requirements according to the drawings, determine the processing content and requirements, determine the processing plan, determine the processing order, design fixtures, and select

The mathematical processing of the part drawing is mainly to calculate the size of the machining track of the part, that is, to calculate the coordinates of the base point and the node of the machining contour of the part, or

The development of science and technology has led to the acceleration of product upgrading and the diversification of people's needs, and the production of products has also tended to be diversified in types and small to medium in batches. In order to adapt to this change, the role of numerically controlled (NC) equipment in enterprises is growing. As a national key vocational school, our school has purchased the BIEJING-FANUC Power Mate O CNC lathe in order to follow the trend of the times and focus on the construction of CNC majors. Compared with ordinary lathes, it has a significant advantage: it is highly adaptable to changes in parts. Replacement parts only need to change the corresponding program, simple adjustment of the tool can make qualified parts, and win the opportunity to save costs. . However, make the most of

Because CNC lathe machining is a high-precision job, and its processing procedures are concentrated and parts are clamped less frequently, higher requirements are placed on the CNC tools used. Dongguan Tongli Metal Products Co., Ltd. Introduction.

When selecting the tools for CNC machine tools, the following issues should be considered:

The type, specification and accuracy level of CNC tools should be able to meet the requirements of cnc lathe machining.

High precision. In order to meet the requirements of high precision of CNC lathe machining and automatic tool change, the tools must have high precision.

High reliability. To ensure that the accidental tool damage and potential defects will not affect the smooth processing of the CNC machining, the tool and its combined accessories must have good reliability and strong adaptability. Precision metal processing

High durability. The tools of CNC lathes, whether in roughing or finishing, should have higher durability than the tools used in ordinary machine tools, in order to minimize the number of times of tool replacement and reshaping and tool setting, so as to improve the processing of CNC machine tools. Efficiency and guarantee processing quality.

Good chip breaking and chip removing performance. In CNC lathe machining, chip breaking and chip removal can not be manually processed in time as ordinary machine tools do. Chips are entangled around the tool and the workpiece, which can damage the tool and scratch the processed surface of the workpiece, and even cause injuries and equipment accidents It affects the processing quality and the safe operation of the machine tool, so the tool is required to have better chip breaking and chip removing performance.

When the CNC lathe is started, the current of the motor will be 5-6 times higher than the rated one, which will not only affect the service life of the motor but also consume more power. The system will leave a certain margin in the selection of the motor during the design. The speed of the motor is fixed, but in actual use, sometimes it needs to run at a lower or higher speed, so it is necessary to carry out frequency conversion transformation. The inverter can realize the soft start of the motor, achieve the purpose of energy saving and speed regulation by changing the input voltage frequency of the equipment, and provide the equipment with protection functions such as overcurrent, overvoltage, and overload. country

If the ordinary lathes used and the lathes used for a long time are not modified, and only new CNC lathes are purchased, it will increase the cost of equipment of many manufacturers. Therefore, it is necessary for manufacturers to carry out numerical control transformation on ordinary lathes and lathes that have been used for a long time.

As the NC transformation is complicated and messy for the transformation manufacturers, how to control the quality of the transformed NC machine tools has been a problem we have always discussed. Here we talk about how to carry out the quality control of the transformation of NC lathes.

Ordinary lathe CNC transformation is divided into new machine transformation and old machine transformation. The new machine transformation is that users purchase ordinary lathes or ordinary light machines (referring to lathes with bedside boxes and vertical and horizontal guides only), and the transformation manufacturers perform numerical control according to their requirements. Makeover. Retrofitting of old machines refers to the refurbishment of conventional lathes or numerically controlled lathes that have been used by the user and the digital transformation. Among them, old machine transformation includes overhaul lathe transformation and user machine transformation. Here we talk about the mechanical quality control methods, focus on control points and inspection process of rebuilding CNC lathes.

Both new machine transformation and old machine overhaul lathe transformation must undergo the same transformation as follows

Replace the X-axis, Z-axis screws, bearings, and motors.

Add electric tool post and spindle encoder.

Increase the drive device of the axial motor, limit the travel switch for over-travel, install the inverter (customer needs), and the electrical parts required for processing and safety.

The scraping of the bearing surfaces at both ends of the X-axis and Z-axis screws, the scraping of the ball screw auxiliary bracket and the saddle, and the scraping of the bed and the saddle rail pair.

If necessary, increase the protection facilities, such as the protective cover of the directional screw, the safety protection door, and the protection device of the travel switch.

Differences between new machine retrofit and old machine overhaul lathe retrofit

The main shaft and tailstock of the new machine are not changed, and the main shaft and tailstock do not need to be rebuilt.

Due to the long-term use of the old machine overhaul lathe, the guide rail is worn. In order to ensure that it can continue to be used for a long time without deformation after overhaul, you must go through the quenching process, and then grind the guide rail, and after grinding the guide rail, the hardness of the guide rail must be HRC47.

The old machine overhaul lathe should be modified and adjusted according to the customer's needs.

The accuracy inspection of new machine renovation and overhaul machine transformation is an important item of inspection

The accuracy inspection is performed by JB / T8324.1-1996 "Accuracy of Simple CNC Horizontal Lathe".

The precision quality control of the new lathe transformation is as follows

Scraper inspection. The new lathe is transformed by scraping the bearing surfaces of the two ends of the screw shafts of the X and Z axes, scraping the ball screw auxiliary bracket and the saddle, and scraping the bed and the saddle rail pair. The main shaft and tailstock of the lathe are not disassembled. The inspection method is as follows: color the mating surfaces, combine the mating surfaces with each other, and rub them against each other, and then check the scraping points on the scraping surface, and use the feeler gauge to check the bonding degree of the joint.

Inspection of the parallelism of the screw and the guide rail: When assembling the screw, the parallelism of the screw and the guide rail must be 0.02mm.

The straightness (only convex) of the guide rail in the vertical plane in the G1 item of accuracy inspection shall be guaranteed by ordinary lathe manufacturers, and shall not be used as a key inspection item.

The accuracy of G4, G5, and G6 of the spindle part in the accuracy inspection should also be guaranteed by ordinary lathe manufacturers, and should not be used as a key inspection item.

The equal height of the two tops of the G11 headstock and tailstock is guaranteed by ordinary lathe manufacturers, and is not a key item for the quality control of the remodeling manufacturers.

Accuracy inspection of user overhaul lathe transformation

Because the guide rail has been ground and the reference surface has changed, all items in the precision inspection must be inspected and strictly controlled to ensure the performance after the transformation.

Other important quality control points for overhaul lathe transformation and new machine transformation

1. Corrosion inspection: each horizontal and vertical rail surface, main shaft, main shaft flange, hollow tailstock.

2. All exposed non-painted surfaces must be rust-proofed. For example, after cleaning, rust-proof inspection should be performed with grease, etc .: The shovel surface, lead screw and bearing must be cleaned before assembly, and no red powder, Iron shavings and other dirt; there is no dust or dirt on the inside of the electrical box and the inside of the protective cover.

3. Leakage inspection: The spindle bearings and gears of the overhaul lathe must be lubricated, and the axial leads and bearings of the overhaul lathe and the new lathe must be lubricated and must have a cooling device. There must be no leakage in oil, water tanks, etc.

4. Machine tool noise, temperature rise, speed, dry running test:

The spindle runs continuously for 4 minutes at various speeds, with the maximum speed running time not less than 2 hours. The dry running time of the whole machine is 16h. Simulated dry running tests are performed on circular turning such as arc, thread, outer circle and end face.

After the temperature of the main shaft bearing is stable, measure the bearing temperature and temperature rise. Rolling bearings: temperature 70 ° C, temperature rise 40 ° C; sliding bearings: temperature 60 ° C, temperature rise 30 ° C.

The noise pressure level of the machine tool is no more than 83dB (A) under dry running conditions, and the machine tool has abnormal screams and impact sounds. The feed motion in each axis direction should be smooth, without obvious vibration, chattering and crawling.

The continuous dry running test of the machine tool is trouble-free, reliable and stable during the specified continuous dry running time.

5. Reconstruction of user-replaced parts (including the maintenance of the machine tool part): As there are many reconstruction projects of lathe replacement parts, mainly the replacement of spindle bearings, axial screw rods, axial motors, axial bearings and systems.

Replace the spindle bearing: Because the replacement of the spindle bearing is to ensure the accuracy of machining the outer circle and the end surface, it is necessary to first check the noise of the spindle after the bearing is replaced. The sound pressure level of the whole machine must not exceed 83dB (A) , And then check the machining accuracy, and check the surface roughness of the workpiece.

Inspection of replacing the axial screw: Check the accuracy of the position in all directions to ensure that the treadmill runs within the specified range without abnormal impact sounds and noise during axial operation. Replacement of the axial motor: As other projects have not been modified, the inspection only checks the noise of the running machine, and there is no abnormal impact sound and noise in the axial operation. Check the axial backlash to prevent the reverse difference from meeting the requirements during assembly due to assembly.

Replace the axial bearing: For the case of replacing the axial bearing, it is necessary to ensure that the axial reverse difference value meets the requirements and check that there are no abnormal noises.

Replacement system inspection: In the case of replacing the system, only the system function is checked, whether the system has an alarm phenomenon, and whether the test thread is normal (for a lathe with an encoder).

In the hardware processing, all the rotating body parts that can be clamped on the ordinary lathe can be processed on the CNC lathe. However, the CNC lathe has the characteristics of high machining accuracy, linear and circular interpolation, and automatic speed change during hardware processing. Its process range is much wider than that of ordinary machine tools.

The CNC lathe has good rigidity, high manufacturing and tool setting precision, and can easily and accurately enter manual compensation and automatic compensation. Therefore, it can process parts with high dimensional accuracy requirements. In addition, the tool movement of CNC turning is realized by high-precision interpolation movement and servo drive. In addition, the machine tool has good rigidity and high manufacturing accuracy. Therefore, it can process shape accuracy such as straightness, roundness, and circularity of the bus bar. Demanding parts. For arcs and other curvilinear contours, the machined shape and the geometry required on the drawing are closer than those of a profiling lathe.

The CNC lathe has a constant linear speed cutting function, so the best linear speed can be used to cut the tapered surface and the end face, so that the surface roughness value after turning is small and consistent, and the parts with small and uniform surface roughness value are processed.

CNC lathes can not only turn any straight, tapered and end threads of equal lead, but also turn threads with a smooth transition between variable lead and variable lead. When turning a thread on a CNC lathe, the spindle rotation does not have to be changed alternately like a normal lathe. It can cycle from one knife to the next until it is completed, so the efficiency of the CNC lathe threads is very high.

The normal use of CNC lathes must meet the following conditions: the power supply voltage of the machine tool is small, the ambient temperature is less than 30 degrees, and the relative temperature is less than 80%.

CNC lathe is a kind of high precision and high efficiency automatic machine tool. Equipped with a multi-station turret or a powered turret, the machine tool has a wide range of processing performance. It can process linear cylinders, oblique cylinders, arcs, and various threads, grooves, worms and other complex workpieces. It has linear interpolation and arcs. Interpolation of various compensation functions, and played a good economic effect in the mass production of complex parts. The maintenance of the CNC lathe with inclined bed is analyzed as follows:

In order to ensure the working accuracy of the inclined bed CNC lathe and prolong its service life, reasonable maintenance work must be performed on the inclined bed CNC lathe. The quality of lathe maintenance directly affects the processing quality and production efficiency of the workpiece. After the Taiwan Taiyu Precision CNC lathe has been running for 500 hours, a first-level maintenance is required. The maintenance work of CNC lathes for inclined beds is mainly performed by operators and repair workers. During maintenance, you must first cut off the electric probe, and then perform maintenance according to the maintenance content and requirements.

NC lathe preparation function G code (JB3208-83), G code (or G instruction) is a technological instruction that needs to be specified in advance before interpolation operation of the CNC machine tool system, such as: coordinate plane selection, interpolation Designation of compensation methods, designation of fixed cycle functions such as hole processing, etc. The G code consists of the address G followed by two digits. Commonly used are G00 ~ G99. Some modern CNC machine tools have been extended to three digits. G code is divided into modal code and non-modal code according to function category. There are 9 groups a, c, d, ... j, k, etc. The G codes corresponding to the same group are called modal codes, which means that once a G code in the group (such as G17 in group c) is specified, the function is maintained until it appears It is invalid only when any other code in the same group (such as G18 or G19), otherwise it will remain valid. Therefore, when programming the next block, if you need to use the same G code, you can omit it, which can simplify the processing program. Non-modal code is only valid in this block.

Note: 1. All G codes indicated by lowercase letters a, b, c, d, ... are the same group of codes, which are called modal instructions;

2. "#" stands for special purpose, which must be stated in the program format description;

3. The letter (d) in the second column of the brackets can be cancelled or replaced by the letter d without brackets in the same column, or it can be cancelled or replaced by the bracketed letter (d);

4. "No designation" and "Never designate" codes indicate that when the standard is revised in the future, new functions and never specified functions can be assigned;

5. When the CNC system does not have G53 to G59, G63 functions, it can be designated for other purposes.

China is a big manufacturing country, and the domestic market for CNC lathes is huge. Domestic CNC lathe manufacturers also have their own characteristics and compete in the market. This resulted in two general types, one is a large producer, which is characterized by good quality and expensive; the other is a small producer, which is characterized by good quality and low price.

With the continuous improvement of China's R & D and manufacturing capabilities, China has gradually moved from importing CNC lathes to exporting, indicating the strong momentum of the development of China's CNC industry.

Programmable Logical Controller (PLC) is also a general-purpose automatic control device based on the tomb processor. It is used to complete various logic operations and sequence control of CNC machine tools, such as machine start-stop, workpiece Auxiliary actions such as clamping, tool change and coolant switch. The PLC also accepts instructions from the machine's operation panel: on the one hand, it directly controls the movement of the machine tool; on the other hand, it sends the relevant instructions to the CNC for use in the process of controlling innovation. The PLC in the CNC system has built-in and independent types.

The operation of CNC machine tools is realized through a man-machine operation panel, which is composed of a CNC panel and a machine tool panel.
The numerical control panel is an operation panel of a numerical control system, and is composed of a display and a manual data input (Manual Data Input, MDI for short) keyboard, also known as an MD panel. There is a menu selection button at the bottom of the display for selecting menus. In addition to various symbol keys, digital keys, and function keys, the keyboard can also be set with user-defined keys. Operators can implement system management through the keyboard and display. They can enter, store and edit NC programs and related data. During the process, the screen can dynamically display the system status, trouble diagnosis, etc. In addition, NC programs and data can also be boxed in via disk or communication interface.
The machine operation panel is mainly used to operate the machine tool in manual mode and to operate or predict the machine tool in automatic mode. There are various buttons and selection switches on it, which are used for machine tools and auxiliary equipment to start and stop, processing mode selection, speed override selection, etc .; there are digital tubes and signal display. The operation panel of small and medium-sized CNC machine tools is often integrated with the CNC panel, but there is a clear boundary between the two. The communication interface of the numerical control system, such as the serial interface, is standing and on the machine operation panel.

Since the beginning of the 21st century, with the continuous development of NC technology and the expansion of application fields, it has played an increasingly important role in the development of some important industries (IT, automotive, light industry, medical, etc.) of the national economy and people's livelihood, because these industries The digitization of the required equipment has become the general trend of modern development. In general, CNC lathes show the following three development trends:

High speed and high precision

High speed and precision are the eternal goals of machine tool development. With the rapid development of science and technology, the upgrading of mechanical and electrical products has accelerated, and the requirements for the accuracy and surface quality of parts processing have become higher and higher. In order to meet the needs of this complex and changeable market, the current machine tools are developing in the direction of high-speed cutting, dry cutting and quasi-dry cutting, and the machining accuracy is also continuously improved. On the other hand, the successful application of electro-spindles and linear motors, ceramic ball bearings, high-precision large-lead hollow internal cooling, and ball nut forced cold low-temperature high-speed ball screw pairs and linear guide pairs with ball cages and other machine tool functional components The launch of the market also created conditions for the high-speed and precision development of machine tools.

The CNC lathe uses an electric spindle, eliminating the links of belts, pulleys and gears, greatly reducing the moment of inertia of the main drive, improving the dynamic response speed and working accuracy of the main shaft, and completely solving the problems of belts and pulleys when the main shaft is running at high speed. Vibration and noise issues. The electric spindle structure can make the spindle speed reach more than 10000r / min.

The linear motor has high driving speed, good acceleration and deceleration characteristics, and excellent response characteristics and following accuracy. The linear motor is used for servo drive, eliminating the intermediate transmission link of the ball screw, eliminating transmission gap (including backlash), small motion inertia, good system rigidity, and precise positioning at high speed, which greatly improves Servo accuracy.

The linear rolling guide pair has zero friction in all directions and very small rolling friction, low wear, negligible heat generation, very good thermal stability, and improved positioning accuracy and repeatability. Through the application of linear motors and linear rolling guide pairs, the rapid moving speed of the machine can be increased from 10-20m / mim to 60-80m / min, up to 120m / min.

High reliability

The reliability of CNC machine tools is a key indicator of the quality of CNC machine tools. Whether CNC machine tools can exert their high performance, high precision and high efficiency, and obtain good benefits, depends on their reliability.

CAD design of CNC lathe and modular structure design

With the popularization of computer applications and the development of software technology, CAD technology has been widely developed. CAD can not only replace manual and tedious drawing work, but more importantly, it can select design schemes and analyze the static and dynamic characteristics, calculation, prediction and optimization of the large machine. It can also dynamically simulate the working parts of the machine. . On the basis of modularity, the three-dimensional geometric model and realistic colors of the product can be seen at the design stage. The use of CAD can also greatly improve work efficiency and increase the first-time success rate of design, thereby shortening the trial production cycle, reducing design costs, and improving market competitiveness.