Development and use of CNC machining process

The cutting of small pitch thread is mainly completed by the fixed cycle program of the CNC machine. The feeding mode includes vertical feed, lateral feed and alternate feed.

The vertical feed lateral feed is alternately fed. The defect is that the blade is unevenly stressed during cutting and is easy to vibrate. As the amount of back-feeding knife increases, the cutting area gradually increases. When the tool tip approaches the large diameter of the thread, the tool is subjected to the greatest resistance. At this time, if the rigidity of the tool, the workpiece, and the machine tool is not good, it is easy to cause resonance when the workpiece is cut, which affects the surface roughness of the thread. Reducing the amount of back-feeding can alleviate vibration, but this will affect production efficiency.

Efficient machining of large pitch and large internal threads away from the end face must meet the rigidity requirements of the tool, workpiece and machine tool. The tooth types of the various threads are different from each other, and the corresponding processing procedures are also different. For example, the programming is performed in a general manner, and the program needs to be written one by one, the program is tedious, and the versatility is poor and error-prone. The general procedure of the large pitch thread provided below uses the calculation and circulation function of the numerical control system to control the tool to divide the cutter in the transverse direction and the radial direction of the thread respectively, which greatly reduces the cutting resistance and can be used without changing the rigidity of the hardware. Through the change of the cutting method, the processing of various types of threads is completed.

2 The process route uses a forming blade, the material to be processed is 42CrMo, the quenched and tempered hardness HB230, and the numerically processed car is processed with a zigzag thread as an example. The thread is diametrically oriented in the diameter direction (ie, the X axis), and the depth of each layer is 0 9 mm; the longitudinal direction (ie, the Z axis) is alternately fed, offset from the center line of the bottom of the tooth to the left and right sides. With a small straight line approaching, it is necessary to calculate the starting point position and the number of feeds for the lateral pass at each cutting.

Other types of threads are typically offset to the left and right by centering the midpoint of the tooth width.

(1) Determination of the number of transverse (Z-axis) passes: the number of transverse passes = the number of feeds to the left of the initial edge of the transverse feed + the initial point of the transverse feed, the number of feeds to the right, the initial angle of the feed, the left of the feed Number of knives = < (tooth height - finishing amount) - Radial infeed times per radial feed amount > TAN (left corner) / each lateral feed value lateral feed initial point to right right feed = TAN (right angle) / each lateral feed value (2) machining step Z axis is positioned to the initial edge of the transverse feed centered on the center of the arc of the tooth, and the X axis is positioned to the depth of the first layer; After the thread P is threaded, the Z axis returns to the initial point of the feed; the X axis is still positioned to the depth of the infeed under the current layer, and the tool is shifted left along the Z axis to the next thread starting point, and the steps are repeated until the The thread center line of the radial value is formed with the left profile; the radial coordinate is constant, the tool is offset to the right by a certain distance along the Z axis, and the thread P is threaded until the radial center line is right. Profile forming; radial coordinate changes, X-axis positioning to the depth of the second layer; repeat steps, %,; cycle until the X-axis coordinate reaches the programmed thread roughing contour; (the tool is positioned to the Z-axis feed initial point, and the thread is finished in the straight line along the X-axis until the thread diameter In size, the margin in all contours is cut off.

Block diagram of the thread processing program. It should be noted that at the beginning and end of the threading process, due to the need to add or decelerate the Z-direction motor (), an incomplete tooth shape will occur, so sufficient speed-increasing infeed section and deceleration retracting section should be set. In order to eliminate the pitch error caused by servo lag.

3 machining program takes Siemens numerical control system as an example R10=pitch R11=X coordinate (diameter) of thread starting point R12=Z coordinate of thread starting point R14=thread tooth height (ie total cutting depth), the value has positive and negative points R15=Finishing amount (positive value) R16=Rising speed distance The distance between the starting point of the transverse infeed and the starting point of the thread R17=Deceleration distance The distance between the end point of the transverse infeed and the end point of the thread R18=The radial infeed depth of each layer (positive value) R21=X coordinate (diameter) of thread end point R22=Z coordinate of thread end point R23=left corner of thread profile R24=right corner of thread profile R31=lateral feed initial value (positive value) Subroutine: R19= ABS( ( R14- R15) / R18)R19= TRUNC( R19+ 0. 7)R18=(ABS( R14) - R15) / R19 R27= 1 Record the number of feed sequence variables R36= R21+ 3 ( R21- R11) / ABS ( R21- R11) Safe tool diameter when retracting R41= R22+ R17 ( R22- R12) / ABS ( R22- R12) Z coordinate when retracting A: R26= R11+ ((R21- R11)/(R22- R12) R16+ R14/ ABS( R14) R27 R18 2) Tool diameter of the infeed point G00 X= R26 Z= R12+ R16 R28= R26+ ( R11- R2 1) / ( R22 - R12) (R16+ R17+ ABS( R22- R12) ) Tool diameter G33 X= R28 Z= R41 K= R10 (thread machining) G00 X= R36 Z= R12+ R16 IF R27= = R19 GOTOFD (Determine whether it is finishing) R29= (ABS( R14) - R15- R27 R18) TAN( R23) / R31 R29= TRUNC( R29+ 0. 5) (Z-axis feed rounding rounding operation) R31= ( ABS( R14) - R15- R27 R18) TAN( R23)/ R29 (distance of the thread center line to the left Z axis) R30= 1 (the initial value of the Z-axis feed) B: G00 X= R26 Z= R12+ R16- R30 R31 R28= R26+ ( R11- R21) / ( R22 - R12)(R16+ R17+ ABS( R22- R12) - R30 R31)G33 X= R28 Z= R41 K= R10 G00 X= R36 Z= R12+ R16 R30= R30+ 1 Z-axis feed increments 1 time IF R30 < = R29 GOTOBB judges whether the number of feeds is enough R31= 0. 8 Z-axis feed initial value (positive value) R29= ( ( ABS( R14) - R15) - R27 R18) TAN( R24) / R31 R29= TRUNC( R29+ 0. 5)R31=(ABS( R14) - R15- R27 R18) TAN( R24) / R29 (The thread center line moves to the right Z axis every time Value) R40= 0 C:G00 X= R26 Z= R12+ R1 6+ R30 R31 R28= R26+ ( R11 - R21)/(R22- R12)(R16+ R17 + ABS( R22- R12) + R30 R31)G33 X= R28 Z= R41 K= R10 G00 X= R36 Z= R12+ R16 R30= R30+ 1 Z-axis feed increments 1 time IF R30 < = R29 GOTOB C Determines whether the Z-axis feed is enough R27= R27+ 1 GOTOB A: D: Finishing part G00 X= R11+ R14 2+ R16 ( R21- R11) / ( R22- R12)Z= R12+ R16 G33 X= R21+ R14 2+ R17 ( R21- R11)/(R22- R12)Z= R41 K= R10 G00 X= R36 Z300 M30 4 Conclusion Processing program is modular Design, just put a few simple parts information, such as thread start, end point diameter, tooth height, etc., into the corresponding position to complete all programming work. This reduces the technical requirements of the operator and improves the processing efficiency. This program is not limited by the thread type, has good versatility, and has broad application prospects in production.

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