Use of machining centers

1. The object to be processed is selected

Before determining the object to be purchased, the object to be machined should be clearly defined. Generally speaking, parts with the following characteristics are suitable for machining on a machining center.

Workpieces with cumbersome positioning For example, multi-hole machining with a certain hole spacing accuracy requirement is easy to implement by using the machine tool with high positioning accuracy.

Repetitive workpieces Suitable for machining small batches of single pieces. Small batch means in 1-100 pieces, the number of each batch is small, but also need to repeat production. Also, parts that are similar workpieces even though the shape and size of the workpieces are different, and are easy to implement in group processing (gt) processes.
Complex-shaped parts Mold, aerospace parts and other complex-shaped workpieces, can be processed on the machining center with the help of automatic programming technology for various shaped parts.

Box type, plate type parts In the horizontal machining center using rotary table, the box parts for multi-surface processing, such as spindle box, pump body, valve body, internal combustion engine block, etc.. If even the top surface should also be processed in one clamping, five-sided machining center can be used. Vertical machining center is suitable for processing box head cylinder head, plane cam, etc. Gantry machining center for processing large box, plate parts, such as internal combustion engine cylinder, machining center column, bed, printing wall plate machine, etc..

2. Selection of machine specifications

According to determine the size of the processing workpiece size, corresponding to determine the required machine table size and three linear coordinate system travel. Table size should ensure that the workpiece in its top can be smoothly clamping workpieces, processing size must be in each coordinate stroke, in addition to consider the tool change space and the limits of each coordinate interference zone.

3. Machine accuracy selection

The accuracy of the machining center is classified as ordinary and precision type, and its main accuracy items are shown in the following table.

  • Machining center main precision items
  • Accuracy items Ordinary type (mm) Precision type (mm)
  • Linear positioning accuracy ±0.01/whole ±0.005/whole
  • Repeat positioning accuracy ±0.006 ±0.002
  • Rounding accuracy 0.03-0.04 0.015

According to the processing accuracy requirements of the workpiece, the user chooses the machine tool with the corresponding accuracy level. For mass-produced parts, the actual accuracy value may be 1.5-2 times of the positioning accuracy. Ordinary machine tools batch processing 8 precision workpiece, precision machine tools processing accuracy of up to 5-6, but to have constant temperature and other process conditions, so precision machine tools use strict, high prices.

4 tool magazine capacity selection

Machining center manufacturers of the same specification of the machine tool, usually set up 2-3 different capacity tool magazine, such as horizontal machining center tool magazine capacity of 30, 60, 80, etc., vertical machining center has 16, 24, 32 capacity of the tool magazine.

Users can determine the required quantity according to the process analysis result of the machined workpiece when selecting, and usually determine the capacity of the tool magazine by the number of tools required for a part in one clamping, because when changing another part for processing, the tools need to be rearranged, otherwise the tool management is complicated and easy to make mistakes.

From the statistical data of the vertical machining center to choose about 20 tools of the tool magazine, the horizontal machining center to choose about 40 tools of the tool magazine is appropriate. Of course, according to the actual needs of the final determination. For flexible manufacturing cell (fmc) or flexible manufacturing system (fms) of the machining center machine tool, its tool magazine capacity should be selected for large-capacity tool magazine, or even configure the exchangeable tool magazine.

5 machine selection function and the selection of accessories

Selected machining center machine tools, in addition to the basic functions and basic parts, there are provided to the user according to their own requirements for the selection of functions and accessories, known as the selection of functions, selection of accessories (optional accessories). With the development of CNC technology, the choice of more and more content, the price of its composition in the host of a larger and larger proportion, so it is not clear purpose of a large number of optional accessories is also uneconomical, the so-called “preparedness” ordering guideline is essentially a waste. So choose to order a comprehensive analysis, but also give due consideration to long-term factors.
Select the function of the main for the CNC system, the kind of price increase is not much, but the use of many convenient features, should be properly configured to complete a little, and can be more than one machine common accessories, you can consider a machine, but must consider the interface is common.

6 processing tempo and the number of machines estimated

According to the workpiece has been selected, and then analyze the process route, in this process route to select the process ready to be processed on the machining center, these processes for the work time beat estimates.

According to the existing process parameters, estimate the cutting time of each process, and the auxiliary time is usually taken from 10%-20% of the cutting time. In addition, small and medium-sized machining centers require about 10-20 seconds per tool change, so that the single process time is: t single process = t cut + t auxiliary + (10-20s) = t cut + (10% -20%) t cut + (10-20s)

With the single process time it is not difficult to calculate the annual production. 300 working days a year, the machine tool start rate calculated at 75%-85%, if the calculated output does not reach the target value, but similar, modify the process parameters; if the gap is large, should consider increasing the number of machine configuration.

Machining center commissioning and acceptance

I. Machining center debugging

The purpose of machine debugging is to assess whether the installation of the machine is stable, the transmission, manipulation, control systems are normal and sensitive and reliable.
Commissioning test run in accordance with the following steps.

According to the requirements of the manual to a lubrication point oil, to the hydraulic oil tank filled with hydraulic oil to meet the requirements, connected to the air supply.
Power on the machine, supply power to each part separately or test each part once, then supply power to all parts. Observe whether each part has an alarm, manual observation of each part is normal, each safety device is working. Even if all parts of the machine tool can operate and move up.
Grouting, after the initial operation of the machine tool, rough adjustment of the geometric accuracy of the machine tool, adjust the relative position of the main moving parts and the host after disassembly. The manipulator, tool magazine, exchange table, position finding, etc. After these jobs are done, you can use fast-drying cement to fill the host and each accessory foot bolt, will be all over the foot bolt reserved hole filling flat.

Commissioning, ready for a variety of testing tools, such as precision level, standard square ruler, parallel square tube, etc..
Fine tune the level of the machine tool so that the geometric accuracy of the machine tool reaches the range of the allowable error, use multi-point pad support to level the bed in the free state to ensure the stability of the bed after adjustment.

Adjust the position of the manipulator relative to the spindle by manual manipulation, using an adjusting mandrel. When installing the maximum weight toolholder, make several automatic exchanges of tool magazine to spindle position to achieve accuracy and no impact… Move the table to the exchange position, adjust the relative position of the pallet station and the exchange table to achieve smooth automatic table exchange action, and install the maximum load of the table for multiple exchanges.
Check whether the set parameters of CNC system and programmable controller plc device are in accordance with the data specified in the random information, and then test each main operation function, safety measures, the execution of common instructions, etc.

Check the working condition of accessories, such as machine lighting, cooling shields, various guards, etc.

After the installation and commissioning of a machining center, due to its wide range of functions, after installation, can be under a certain load after a long period of automatic operation, a more comprehensive check of the machine’s functionality is complete and stable. The running time can be 8 hours a day for 2 to 3 days of continuous operation or every 24 hours for 1 to 2 days of continuous operation. Continuous operation can be used to test the machine program.

II. Acceptance of the machining center

Acceptance of the machining center is a complex inspection technology work. It includes the machine tool, electricity, liquid, gas parts of the comprehensive performance testing and machine tool static, dynamic accuracy testing. In China, there are special institutions, namely the National Machine Tool Quality Inspection Center. User acceptance work can be in accordance with the acceptance methods of the institution, but also can ask the above institutions for acceptance. The main focus is on two aspects.

Machining center geometric accuracy check

The geometric accuracy of the machining center is the geometric shape error after assembly, the inspection content is as follows.

  • The flatness of the working table
  • Mutual perpendicularity of movement in each coordinate direction
  • Parallelism of the table surface in the x-axis direction
  • Parallelism of the table surface in the y-axis direction
  • Parallelism of the x-axis direction movement on the side of the upper and lower groove of the table
  • Axial runout of the spindle
  • Radial runout of spindle bore
  • Parallelism of the spindle box to the axis of the spindle when moving in the z-direction
  • Perpendicularity of the axis of rotation of the spindle to the table surface
  • Straightness of the spindle box in the z coordinate direction
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