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The application of SINUMERIK 840D CNC system in thread machining with multiple heads with accurate control, high measurement accuracy and flexible configuration

sinumerik 840D CNC system is still the mainstream CNC system in use today and the outstanding representative of Siemens CNC products. SINUMERIK 840D provides many creative technical functions. Various standard cycles of drilling, milling and turning processes greatly simplify frequent repetitive machining operations. Even for the most complex and accurate applications, such as the manufacturing of 5-axis standard setting milling machine for machining tools and molds, SINUMERIK 840D is also competent. In this paper, the author × Taking the machining of 16 head thread of 5210 groove roller on its 10 meter NC lathe as an example, the application of 840D cycle97 instruction in multi head thread machining is introduced

turning multi head threads on an ordinary lathe has always been a processing difficulty: after the first thread is turned, it is necessary to manually turn the small tool holder and calibrate it with a dial indicator to make the tool tip accurately move a pitch along the axial direction before processing the second thread; Or open the change gear box, adjust the gear meshing phase, and then process the threads of other heads in turn. The lead and pitch of multi head thread are difficult to achieve high accuracy due to the influence of the lead screw pitch error of ordinary lathe, the transmission error of change gear box, the movement error of small carriage and so on. Moreover, in the whole machining process, there are inevitably problems such as tool wear and even cutting. Once the tool is changed, the new tool must be accurately positioned on the unfinished thread line. All these require the operator to have rich experience and superb skills. However, in mass production, the production efficiency and product quality cannot be guaranteed only by the operator's personal experience and skills. Today, with the modernization of manufacturing industry, the application of high-precision CNC machine tools and high-performance CNC systems makes many problems that are difficult to be solved by ordinary machine tools and traditional processes relatively simple, and the production efficiency and product quality are also guaranteed to a great extent

I. program format, processing steps and parameter description of cycle97 instruction

1 Program format

the program format is as follows: cycle97 (pit, mpit, SPL, FPL, DM1, DM2, app, ROP, tdep, fal, iang, NSP, NRC, NID, vari, numth)

2. Machining steps

the turning tool moves quickly to the starting point (determined by DM1, DM2 and APP), and rough turning is started according to the feed cut in angle specified by iang and the stable feed mode or decreasing feed mode specified by vari. The times of rough turning are specified by NRC, and the total cutting depth of rough turning is obtained by subtracting the finish turning allowance fal from the tooth depth tdep. After rough turning, the fal machining allowance shall be cut off through one-time fine turning, and then the empty tool feeding and polishing shall be carried out according to the times specified by NID. Finally, the starting point shall be returned, and the cycle97 program shall be completed. When machining multi head threads, each thread (head) shall be turned according to the above steps before machining the next thread (head). The number of thread heads is specified by numth. The phase of the cutting point of the first thread in the circumferential direction of the end face of the part is specified by NSP, and the other threads are generated successively by automatically changing the phase of the cutting point of the tool tip in the circumferential direction of the end face

3. Parameter description

pit - pitch; Mpit - nominal diameter of metric coarse thread, range m3 ~ M60 (note that pit and mpit can only select one input in the cycle97 command. For example, M42 coarse thread, pit item does not need to be input, mpit item input value 42; m95x2 fine thread, pit item input value 2, mpit item is null); SPL -- axial coordinate value of thread starting point; FPL - axial coordinate value of thread end point; DM1 - thread starting point diameter; DM2 - thread end diameter; App - axial distance from the tool starting point to the thread starting point; ROP - axial distance from tool withdrawal point to thread end point; TDE - thread profile depth; Fal - machining allowance of the last tool feeding. The above parameters are shown in Figure 1

figure 1

iang - radial feed cut in angle of turning tool, The ang value should be less than or equal to half of the tooth angle (when cutting vertically from the radial direction, ang is 0, or no value can be entered, and the default value of the machine tool is 0. Ang is positive, which means that each cutting is always fed along the same side of the tooth profile. Ang is negative, which means that the tool is fed alternately along the two sides of the tooth profile. If ang is negative, it is only applicable to cylindrical thread processing. In taper thread processing, no matter whether ang is positive or negative, each cutting is always fed along the same side of the tooth profile), As shown in Figure 2 and figure 3

figure 2

figure 3

nsp - the phase of the thread entry point in the circumferential direction of the part end face (no value can be entered, and the default value of the machine tool is 0. When turning multiple threads, it indicates the phase of the first thread of multiple threads in the circumferential direction of the part end face, as shown in Figure 4)

figure 4

figure 5

nrc - times of rough turning tool path; NID - last empty tool travel times; Vari -- selection method of cutting depth for each tool feed (1 means machining external thread, stable feed, and equal cutting depth for each tool feed; 2 means machining internal thread, stable feed, and equal cutting depth for each tool feed; 3 means machining external thread, decreasing feed, and equal cutting area for each tool feed; 4 means machining internal thread, decreasing feed, and equal cutting area for each tool feed, as shown in Figure 5)

numth -- number of multi head threads. When turning ordinary single head thread, you can enter 0 or no value, and the default value of the machine tool is 0

II. Structural dimension and process of parts

1 Part sketch

part sketch is shown in Figure 6

Figure 6 part diagram

2 Process

(1) the model of tool

tool bar is Sandvik svvbn 3225p16; The blade model is Sandvik vbmt 160404-pm

(2) machining parameter

cutting speed vc=140m/min; Spindle speed n=75r/min

(3) process scheme

considering the large diameter and length of roll body, large machining allowance, easy wear of turning tool and other reasons, it is divided into two processes: rough and finish machining. The final thread profile dimension and accuracy shall be ensured by fine turning. During finish turning, the machining allowance is 0.1mm, which is divided into two times of cutting, one time of cutting to cut off the remaining machining amount, and the second time of empty cutting for polishing. During rough turning, the total cutting depth is 1.2mm, the feed cutting depth of each tool is 0.12mm, and the number of tool walking =10 times

(4) select the mode of feeding the cutting depth for each tool feed

since the selected clamping tool is a non-standard thread turning tool (35 ° tooth angle, non-standard), the front and rear angles of the blade are too large, and there is no spiral angle, resulting in large cutting force and poor blade strength, so the stable feed 5 Working wheel stroke: 20mm cutter mode, that is, the tooth depth is divided into several times of cutting, and the feed depth of each cutter is the same. In this way, good chip control can be obtained, and problems such as excessive cutting depth for the first time and easy edge collapse can be avoided when the cutter is operated in a decreasing way

(5) select

as the cutting angle for each tool feed. The cutting amount is small during fine turning. Radial vertical feed can be used to ensure the accuracy of thread profile, high precision and good surface roughness. During rough turning, the cutting amount is large. If radial vertical feed is adopted, the two edges shall be cut at the same time because the wall thickness of the roll body is small( δ 16mm), the rigidity of the roller is poor, and it is easy to produce vibration during processing; Radial vertical feed will form V-shaped chips, with large cutting heat and easy overload of tool tip fillet, so we adopt improved lateral feed. In this way, flat curled chips can be obtained, with good chip removal, small cutting heat and long tool life, as shown in Figure 7

figure 7

III. programming

cle97 new chemical materials and fine chemicals with high performance, special varieties, safety and environmental protection are still in short supply

pit. The pitch value of multi head thread is the lead of a single thread. Take 40 according to figure 6. Mpit, null, no need to enter. SPL, take 0 according to figure 6; FPL, take -5210 according to figure 6. DM1, take 600 according to figure 6. DM2, take 600 according to figure 6. App, the tool starting distance is generally 3 ~ 5 screw pitch. In order to facilitate the inspection of tool wear and tool change, it can be appropriately enlarged. Here, it is taken as 100. ROP, the tool withdrawal distance is generally 1 ~ 3 thread pitch, which shall be determined by referring to the width of the tool withdrawal groove in the drawing, and 30 is taken here. Tdep, thread profile depth, 1.2 in rough turning procedure and 1.3 in fine turning procedure. Fal refers to the machining allowance at the last tool feeding. According to the above process scheme, the actual machining allowance is cut off in the finishing turning program, so it is taken as 0 in the coarse turning and finishing turning cycle97 programs. Ang, radial cut in angle, modified lateral feed is adopted during rough turning, taking ang=15, as shown in Figure 7, and vertical feed is adopted during fine turning, taking 0. NSP, the phase of the cutting point of the first thread in the circumferential direction of the roll body end face, taken as 0. In actual machining, this value can be changed as required to specify the thread to be machined by the turning tool, as shown in Figure 8. Vari, as mentioned above, select the stable feeding mode, and take 1. Numth, number of thread heads, taking 16. All parameters are listed in the parameter list

2. Procedure

(1) rough turning procedure

cycle97 (40, 0, -5210600600100, 30, 1.2, 0, 15, 0, 10, 0, 1, 16)

(2) fine turning procedure

cycle97 (40, 0, -5210600600100, 30, 1.3, 0, 0, 1, 1, 16)

parameter list

IV. precautions and solutions to common problems

1 Tool wear and cutting

when NC lathes process threads, the program can generally be continuously optimized through trial run adjustment. The most common problems are tool wear and cutting. In order to improve the service life of the tool and prevent cutting, the following points should be paid attention to:

(1) for the precision turning process of the outer circle before turning the thread, certain dimensional accuracy, roundness, cylindricity and surface roughness should be ensured, and whether the roller surface has welding cracks, slag inclusions and other defects should be checked to ensure that the machining allowance is uniform and the turning is stable

(2) the spindle speed multiplying switch cannot be changed during tool walking

(3) good cooling and lubrication shall be ensured

(4) when turning low carbon steel, stainless steel and other materials, there will be long strip chips that are not easy to break. It should be prevented from being involved between the turning tool and the workpiece, so that the tool tip will be crushed and broken. The operator must pay attention to personal safety

(5) when it is necessary to change the tool midway, the spindle speed multiplying knob can be adjusted to "0" position until the turning tool returns to the starting point and has not been fed. At this time, the tool holder stops and the blade can be replaced. To facilitate operation, the app value can be set higher in cycle97 program

(6) in the actual processing, the blade and the tool body are damaged together due to cutting, so it is necessary to add a tool position as a backup. Note: during tool setting, it must be ensured that the coordinates of the tip points of the thread turning tool on the two tool positions are consistent to avoid disorderly screwing

2. Operation after cutting

in the process of turning 16 grooved roller threads, the coarse turning is performed for 10 times and the fine turning is performed for 2 times, that is, each thread requires a turning edge of 600 × The 5210 roll surface reciprocates 12 times, and a total of 192 times of tool feeding is required. About 2 minutes each time, and the total effective turning time is about 384 minutes. In such a long processing time, due to the wear of turning tools, the increase of cutting force, the material defects on the roll surface, the hardness changes in the weld area, etc., it is almost necessary to cut every 10 to 12 threads. After cutting, we can follow the following steps:

(1) press the "reset" key to stop after the cutting is completed and returns to the starting point (do not press the "emergency" emergency stop button, otherwise the turning tool will scratch the roll surface)

(2) take out the broken tool tip from the part surface, otherwise repeated punching will be caused at this position

Copyright © 2011 JIN SHI