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2 Determination of the transformation plan
The purpose of the transformation of the machining center is to configure, design and debug the control part so that it can fully comply with the technical specifications and accuracy standards of the original machine tool. After comprehensive analysis and analysis, the Siemens 840C system was used to transform it, and the motors of all feed axes except the spindle were changed from DC servo motor to AC motor, driven by 611A.
3 system transformation and debugging
3.1 Basic configuration of machine tool transformation (1) Hardware configuration includes operation display part, host frame and input and output equipment. Since the machine has six analog axes, the main frame uses three sub-frames. Each sub-frame has a fan and 6 template slot locations. The mainframe is equipped with a power module, CSB (central service) board, position measuring board, MMC-CPU board, NC-CPU board, PLC-CPU board, etc.
(2) The software configuration is based on its hardware configuration and mechanical structure to set the relevant parameters. Here set two mode groups, two channels.
The first channel belongs to the first mode group, and the second channel belongs to the second mode group; sets the command values ​​of X, Y, Z, B, Q, S, the actual value interface address and the weight value of the actual position; defines X, Y, The Z axis is the linear axis and B, the Q axis is the rotation axis and the B axis is the bisector; the X, Y, Z, B, Q, and S axes are defined as the first channel; the DMP module address is also defined.
The control mechanism NCK of Siemens 840C system is mainly used to control the interpolation of the axis; PLC mainly controls the operation panel of the machine tool and completes the motion logic of the machine tool; MMC is a personal microcomputer, which mainly completes the man-machine dialogue.
3.2 Design and commissioning of machine tool transformation
(1) NC and PLC system In the CNC machine tool, the core component of the electrical system is the NC and PLC system. The NC control system controls the tool movement trajectory according to the NC program through a certain algorithm. The PLC is a programmable controller that controls the execution components according to the input control signals according to the input control logic. The NC works under the supervision of the PLC. The PLC not only monitors the NC, but also monitors externally executed components (such as tool magazines, hydraulic systems, etc.).
The measurement system of the X, Y, Z linear axes in the NC system is a linear scale with full closed loop position control; B and Q axes are rotary axes, and the measurement system is a circular encoder with semi-closed loop position control. The adjustment of this system is mainly to complete the matching of the feed axis, spindle, channel, mode group and other parameters, and use the laser interferometer to make the pitch compensation to improve the machining accuracy of the machine tool.
The design of the PLC system is mainly the design of the PLC program. The PLC program adopts the STEP5 programming language (compatible with the original Siemens 8 system). The standard interface (OB block) is designed in the system, and the FB, PB called by the OB block is also designed. , SB, DB, FX, DX blocks, the user's control software is in these blocks. In addition, the PLC program that realizes the handwheel control and the original PLC program are adjusted by the programmer and then transplanted to the current PLC to complete the debugging of the PLC program.
(2) Debugging of the 611A drive system The commissioning of the drive system is directly related to the stability of the machine tool movement and the accuracy of the machined parts. There are 4 potentiometers on the system module, which mainly adjust the speed control gain and drift compensation. When adjusting the speed control gain, you can first increase the potentiometer more, let the motor oscillate, and then slowly adjust back until you can only hear a slight sound. The method of adjusting the drift compensation is to disconnect the command voltage and let the motor stop rotating.
(3) Custom alarm system Sets the all-round alarm text function. In addition to the corresponding protection actions, the system displays the alarm number and alarm text.
4 transformation effect
After the completion of the transformation, the functions of the CNC system of the center are complete, the operation is reliable, and the temperature rise of the moving parts and the heating unit is normal. Since the equipment has been running for nearly 2 years, there has not been any partial failure of the drive unit. The newly added handheld features also greatly facilitate operation. In addition, the servo shaft drive is changed from the original DC servo motor to the AC servo motor, which greatly shortens the abnormal downtime and improves the working efficiency. The precision of the machined parts and other technical requirements can be met.
(Finish)
"Gravity Die Casting. A permanent mould casting process, where the molten metal is poured from a vessle of ladle into the mould, and cavity fills with no force other than gravity, in a similar manner to the production of sand castings, although filling cn be controlled by tilting the die."
Gravity Die Casting
Sometimes referred to as Permanent Mould, GDC is a repeatable casting process used for non-ferrous alloy parts, typically aluminium, Zinc and Copper Base alloys.
The process differs from HPDC in that Gravity- rather than high pressure- is used to fill the mould with the liquid alloy.
GDC is suited to medium to high volumes products and typically parts are of a heavier sections than HPDC, but thinner sections than sand casting.
There are three key stages in the process.
- The heated mould [Die or Tool] is coated with a die release agent. The release agent spray also has a secondary function in that it aids cooling of the mould face after the previous part has been removed from the die.
- Molten metal is poured into channels in the tool to allow the material to fill all the extremities of the mould cavity. The metal is either hand poured using steel ladles or dosed using mechanical methods. Typically, there is a mould [down sprue" that allows the alloy to enter the mould cavity from the lower part of the die, reducing the formation of turbulence and subsequent porosity and inclusions in the finished part.
- Once the part has cooled sufficiently, the die is opened, either manually or utilising mechanical methods.
Advantages
- Good dimensional accuracy
- Smoother cast surface finish than sand casting
- Improved mechanical properties compared to sand casting
- Thinner walls can be cast compared to sand casting
- Reverse draft internal pockets and forms can be cast in using preformed sand core inserts
- Steel pins and inserts can be cast in to the part
- Faster production times compared to other processes.
- Once the tolling is proven, the product quality is very repeatable.
- Outsourced Tooling setup costs can be lower than sand casting.
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