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Solutions to 30 of the most common CNC challenges

CNC machining often encounter some difficult problems, master the 30 points, I believe it will help your machining work.


1, the impact on the cutting temperature: cutting speed, feed rate, back draft amount.


The impact on the cutting force: back draft, feed rate, cutting speed.


The impact on tool durability: cutting speed, feed rate, back draft.


2、When the back draft is doubled, the cutting force is doubled.


When the feed rate is doubled, the cutting force increases by approximately 70%.


When the cutting speed doubles, the cutting force gradually decreases.


In other words, if you use G99, the cutting speed becomes larger, the cutting force will not change much.


3、You can judge the cutting force and whether the cutting temperature is within the normal range according to the chip discharge.


4、When the actual value of X and the diameter of the drawing Y are greater than 0.8, the R turned by a 52 degree sub-deviation tool (that is, a 93 degree main deviation tool with a 35 degree insert) may rub the tool at the starting position.


5、The temperature represented by the chip colour


White less than 200 degrees


Yellow 220~240 degrees


Dark blue 290 degrees


Blue 320~350 degrees


Purple-black greater than 500 degrees


Red greater than 800 degrees

6、FUNAC OI mtc general default G command


G69: not quite clear


G21:Metric size input


G25: spindle speed fluctuation detection disconnect


G80: Fixed cycle cancellation


G54: Coordinate system default


G18: ZX plane selection


G96 (G97): Constant linear speed control


G99: Feed per revolution


G40: Tool tip compensation cancellation (G41 G42)


G22: Store travel detection on


G67: Macro program modal call cancellation


G64: not quite clear


G13.1: Polar coordinate interpolation mode cancelled


7: 1.3P for external threads in general, 1.08P for internal threads


8、Thread speed S1200 / pitch * safety factor (generally 0.8)


9、Manual tool tip R compensation formula: chamfering from the bottom to the top: Z=R*(1-tan(a/2)) X=R(1-tan(a/2))*tan(a) . From top to bottom chamfering will be changed from minus to plus can be.


10, feed every increase of 0.05, the speed is reduced by 50 ~ 80 rpm This is because reducing the speed means that tool wear decreases, the cutting force increases more slowly, thus compensating for the increase in cutting force due to the increase in feed, the temperature increases and the impact.


11, cutting speed and cutting force on the impact of the tool is vital, cutting force is too big for the main reason of the tool chipped.


Cutting speed and cutting force relationship: the faster the cutting speed feed unchanged, the cutting force slowly decreases, while the faster the cutting speed will make the tool wear faster and faster, so that the cutting force is increasingly large, the temperature will be higher and higher, when the cutting force and internal stress is too large for the insert to withstand, it will collapse (of course, this also has the temperature change of stress and hardness decline and other reasons).


12, in the CNC turning process, the following points should be paid special attention to.


(1) For the current economy of China's CNC lathes are generally used in ordinary three-phase asynchronous motors through frequency converters to achieve stepless speed change, if there is no mechanical deceleration, often at low speeds when the spindle output torque is insufficient, if the cutting load is too large, it is easy to bore the car, but some machine tools with gear gears on the gears is a good solution to this problem.


(2) as far as possible so that the tool can complete a part or a work shift of processing work, large finishing especially to avoid changing tools in the middle to ensure that the tool can be processed once completed.


(3) When turning threads with a CNC lathe, a higher speed should be used wherever possible to achieve high quality and efficient production.


(4) Use G96 whenever possible.


(5) The basic concept of high speed machining is to make the feed exceed the speed of heat transfer so that the cutting heat is discharged with the chips to isolate the cutting heat from the workpiece and ensure that the workpiece does not heat up or heats up less, therefore, high speed machining is to select a very high cutting speed to match the high feed and to select a small back draft.


(6) Pay attention to the compensation of the tool tip R.


13、Some common tables.


Workpiece material cutting processability classification table


Commonly used thread cutting times and backlash table


Commonly used geometry calculation formula


Conversion table between inches and millimetres


14、Vibration and chipping are often produced when grooving, the root cause of all this is the cutting force and tool rigidity is not enough, the shorter the tool length, the smaller the back angle, the larger the area of the insert the better the rigidity, the greater the cutting force, but the greater the width of the groove tool can withstand the cutting force will also increase, but its cutting force will also increase, on the contrary, the groove tool is small it can withstand the force is small, but its cutting force is also small.

15, grooving when the cause of vibration.


(1) tool extension length is too long, resulting in lower rigidity.


(2) feed rate is too slow, resulting in the unit cutting force becomes large, thus causing substantial vibration, the formula is: P = F / back to eat the amount of tool * f P for the unit cutting force F for the cutting force, in addition to the speed is too fast will also vibrate the tool.


(3) machine tool rigidity is not enough, that is to say, the tool can bear the cutting force, and the machine tool can not bear, to put it bluntly, the machine tool can not move, generally new bed will not appear this kind of problem, the bed of this kind of problem is either a long time ago, or is often encountered machine tool killer.


16, in the car a goods, at the beginning found that the size are okay, but after doing a few hours found that the size has changed and the size is not stable reason may be that at the beginning because the knife are new, so cutting force are not very large, but car after a period of time tool wear, cutting force becomes large, resulting in the workpiece in the chuck shifted, so the size of the old run and unstable.


17、When using G71, the value of P and Q cannot exceed the number of sequences of the whole program otherwise there will be an alarm: G71~G73 instruction format is not correct, at least in FUANC.


18、There are two formats of subroutines in FANUC system.


(1) P000 0000 the first three digits refer to the number of cycles, the last four digits are the program number.


(2) P0000L000 the first four bits for the program number, L the next three bits for the number of cycles.


19、The starting point of the arc remains the same, the end point is offset by a mm in the Z direction, then the bottom diameter position of the arc is offset by a/2.


20、In playing deep holes when the drill does not grind cutting grooves to facilitate the drill chip discharge.


21、If the eye is made with the workpiece with the tool holder, the drill can be turned and the hole diameter can be changed.


22, in playing stainless steel centre eye, or playing stainless steel eye when the drill or centre drill centre must be small, otherwise it can not be played, in the use of cobalt drill eye without grinding groove to avoid annealing of the drill bit in the process of drilling the eye.


23, according to the process under the material is generally divided into three kinds: a material, two goods, the entire bar material.


24、When an oval appears during thread turning, it may be due to a loose material, so use a dental knife to make a few more cuts.


25、In some systems where you can input macro programs, you can use macro programs instead of subroutine cycles, which can save the program number and avoid a lot of trouble.


26、If the drill is used for reaming, but the runout of the hole is large, then the flat bottom drill can be used for reaming, but the twist drill must be short to increase the steel.


27、In the drill press if the drill bit is used directly to punch the hole, the hole diameter can be deviated, but if the drill press is used to ream the hole size generally will not run, for example, with a 10mm drill bit in the drill press to ream the hole, then the reamed out hole diameter is generally in about 3 wire tolerance.


28、When turning small holes (through holes) try to make the chips continuously roll chips and then discharge from the end.


Chip roll points.


(1) The position of the cutter should be appropriately placed high.


(2) the appropriate edge inclination, eat the amount of tool and feed, remember that the knife can not be too low, otherwise it is easy to break the chip, if the knife's sub-deviation angle is large, even if the broken chip will not card the tool bar, if the sub-deviation angle is too small, the chip will be broken after the chip will be stuck in the tool bar easy out of danger.


29, the larger the cross-section of the tool bar in the hole, the less likely to vibrate the knife, and can be tied to the tool bar can be a strong rubber band, because the strong rubber band can play a certain role in absorbing vibration.


30、When turning copper holes, the tip of the knife R can be appropriately large (R0.4~R0.8), especially in the lower taper of the car, iron parts may be nothing, copper parts will be very card chip.

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Contact: Jacky Wang

Phone: +86 14714816052

Tel: +86 14714816052

Email: [email protected]

Add: Floor 1, Shixi Industrial area, Canton, Guangdong, China. 510288

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