CNC machining how to choose the tool
Article Source: SHENZHEN SITEMPO TECHNOLOGY CO., LTD.Popularity：232Issuing time:2017-08-10 11:05:35【smallinBig】
The letter is treasure, focusing on CNC machining, mainly to
provide precision parts processing CNC precision machining CNC machining
machine processing computer gong processing complex parts processing
custom parts processing.
CNC machining in the scientific choice of how to control the
tool, the letter in the long-term production practice, summarized as
follows:
1, the principle of choice of CNC tool tool life and cutting the amount of closely related. In
the development of cutting the amount, should first select a reasonable
tool life, and reasonable tool life should be based on the optimal
target. Generally the highest productivity of the tool life and the
lowest cost of the tool life of two, the former according to the minimum
single-person work to determine the target, according to the lowest
cost of the process to determine the target.
Select
the tool life can be considered the following points according to the
complexity of the tool, manufacturing and sharpening to choose the cost. Complex and high precision tool life should be higher than single-blade tools. For
the machine can be indexable tool, due to tool change time is short, in
order to give full play to its cutting performance, improve production
efficiency, tool life can be selected lower, generally take 15-30min. For
the knife, tool change and adjust the knife more complex multi-knife
machine tools, combined machine tools and automated processing tools,
tool life should be selected higher, especially to ensure tool
reliability. The
productivity of a process in the workshop limits the productivity of
the entire workshop, the tool life of the process to be selected lower
When a process unit time to share the full cost of the plant, the tool
life should also be selected Lower Large
pieces of finishing, in order to ensure that at least one time to
complete the knife, to avoid cutting the middle of the tool change, tool
life should be part of the accuracy and surface roughness to determine. Compared
with the ordinary machine tool processing methods, CNC machining on the
tool put forward a higher demand, not only need good grass, high
precision, and requires dimensional stability, high durability, broken
and row of the altar at the same time require easy installation and
adjustment, so to To meet the high efficiency of CNC machine tools. CNC tools used in the machine tool often used to adapt to
high-speed cutting tool materials (such as high-speed steel,
ultra-fine-grained carbide) and the use of indexable blade.
2,
the choice of CNC turning tools CNC turning turning tools commonly used
in the general sub-forming turning tools, sharp-shaped turning tools,
arc-shaped turning tools and three categories. Molded
knives are also known as molds, and the contours of their machined
parts are entirely determined by the size and size of the tool edge. CNC
turning, the common molding tool has a small radius of circular turning
tools, non-rectangular slot knife and thread knife and so on. In CNC machining, should be used with or without the use of turning tools. A sharp turning tool is a turning tool characterized by a linear cutting edge. The
tip of this type of turning tool is made up of straight main and minor
cutting edges, such as 900 internal and external circular turning tools,
left and right end turning tools, grooving (cutting) Hole knife. The
geometric parameters of the geometric tool (mainly geometric angle) are
chosen in much the same way as ordinary turning, but should be taken
into account in conjunction with the characteristics of CNC machining
(eg, machining routes, machining interventions, etc.) and taking into
account the tool tip itself strength.
Second, arc-shaped turning tool. An
arc-shaped turning tool is a turning tool characterized by a circular
arc-shaped cutting edge with a small roundness or a line profile error. The
arc of the turning edge of the arc is the tip of the arc-shaped turning
tool, and the knife point is not on the arc, and on the center of the
arc. The
arc-shaped turning tool can be used to turn inside and outside the
surface, especially suitable for turning a variety of smooth connection
(concave) molding surface. Select
the radius of the radius of the knife should be considered two arc
cutting edge of the arc radius should be less than or equal to the
concave surface of the smallest radius of curvature, in order to avoid
the formation of dry and shallow The radius should not choose too small,
otherwise not only difficult to manufacture, But also because the tip strength is too weak or the knife body cooling capacity caused by poor damage to the car.
3,
the choice of CNC milling tools in CNC machining, milling and internal
parts of the plane contour and milling plane commonly used flat end
mill, the tool parameters of the empirical data are as follows: First,
the milling radius of RD should be less than the minimum curvature of
the plane Radius Rmin, generally take RD = (0.8 a 0.9) Rmin. Second, the processing height of parts H <(1 / 4-1 / 6) RD, to ensure that the knife has enough rigidity. Third,
with the flat end mill milling the bottom of the inner slot, due to the
bottom of the groove at the end of the need to overlap, and the tool
edge of the role of the radius of the Re = Rr, the diameter of d = 2Re =
2 (Rr) Take the tool radius as Re = 0.95 (Rr). For some of the three-dimensional and variable-angle profile
contour processing, commonly used spherical cutter, ring cutter, drum
cutter, tapered cutter and disk cutter.
At
present, most of the CNC machine tools using a series of standardized
tool, on the translatable machine folder outside the turning tool, the
end of the knife and so on the knife handle and the head has a national
standard and serialized models for the processing center and automatic
tool change The
machine tool, the tool handle of the tool has been serialized and
standardized, such as taper shank tool system standard code for the
TSG-JT, straight handle tool system standard code for the DSG-JZ, in
addition to the selected tool ,
In the use of the tool size before the need for rigorous measurements
to obtain accurate data, and by the operator of these data into the data
system, the program calls to complete the processing process, which
processed a qualified workpiece.
Set the knife point and tool change point
Therefore,
at the beginning of the program execution, it is necessary to determine
the position at which the tool starts to move in the workpiece
coordinate system. This position is the starting point of the tool
relative to the movement of the workpiece when the program is executed.
In this case, So called the program starting point or knife point. This starting point is generally determined by the knife, so the point also known as the knife point. In the preparation of the program, to correctly select the location of the knife point. The principle of setting the tool point is: to facilitate numerical processing and simplify the programming. Easy to find and in the processing process to facilitate inspection; caused by the processing error is small. The
tool point can be set on the machined part, or it can be set on the
fixture or machine tool. In order to improve the machining precision of
the part, the point should be set on the design basis or technology base
of the part. When
the machine is actually operated, the tool point of the tool can be
placed on the tool point by manual tool setting, that is, the
coincidence of "knife point" and "knife point". The
so-called "knife point" refers to the positioning of the tool reference
point, turning tool point for the tool nose or tool nose arc center. Flat
end mill is the intersection of the tool axis and the bottom of the
tool; the ball end mill is the ball of the ball, the drill is the drill
tip and so on. With manual knife operation, the knife is low, and low efficiency. And
some factories using optical knife on the knife, knife, automatic knife
set, etc., to reduce the knife time, improve the accuracy of the knife. During the machining process, the tool change point should be specified. The so-called "tool change point" refers to the position of the
tool holder when the tool change, the tool change point should be set
in the workpiece or fixture outside, to change the workpiece when the
workpiece and other parts.
Determine the amount of cutting
In NC programming, the programmer must determine the amount of cutting per process and write it as an instruction. Cutting the amount of spindle speed, including the amount of knife and feed speed. For different processing methods, the need to use a different amount of cutting. The principle of cutting the amount of choice is: to ensure the
accuracy of parts and surface roughness, give full play tool cutting
performance, to ensure a reasonable tool durability, and give full play
to the performance of the machine to maximize productivity and reduce
costs.
1, to determine the spindle speed
The spindle speed should be selected according to the permissible cutting speed and the workpiece (or tool) diameter. The
formula is: n = 1000 v / 7 1D where: v? Cutting speed, the unit is m / m
dynamic, determined by the durability of the tool; n one spindle speed,
the unit r / min, D for the workpiece diameter Or tool diameter in mm. Calculate the spindle speed n, and finally to select the machine or some of the speed closer.
2, to determine the feed rate
Feeding
speed is an important parameter in the cutting amount of CNC machine
tools. It is mainly selected according to the machining precision and
surface roughness requirements of the parts and the material properties
of the tool and workpiece. The maximum feed rate is limited by the machine stiffness and feed system performance. The
principle of determining the feed rate: When the quality requirements
of the workpiece can be guaranteed, in order to improve production
efficiency, you can choose a higher feed rate. Generally
in the range of 100 to 200mm / min; in cutting, processing deep hole or
high-speed steel cutting tool, it is appropriate to choose a lower feed
rate, generally in the range of 20 to 50mm / min selected; when the
processing accuracy, the surface Roughness
requirements are high, the feed rate should be selected smaller,
generally in the range of 20 - 50mm / min selected; tool empty trip,
especially the long distance "back to zero", you can set the machine CNC
system settings The maximum feed speed.
3, to determine the amount of back to eat knife
The
amount of kneading knife according to the machine, the workpiece and
the stiffness of the tool to decide, in the rigidity of the conditions
allowed, should be as much as possible to make the amount of knife back
to the workpiece allowance, which can reduce the number of passes and
improve production efficiency. In order to ensure the quality of the processing surface, a
small amount of finishing allowance can be retained, generally 0.2 to
0.5 m m. In summary, the specific value of the cutting amount should be
determined by analogy according to the machine performance, the relevant
manual and the actual experience.
At the same time, the spindle speed, cutting depth and feed
speed can be adapted to each other to form the best amount of cutting.
The
cutting amount is not only an important parameter that must be
determined before the machine is adjusted, but also its numerical value
is very important to the processing quality, processing efficiency and
production cost. The
so-called "reasonable" cutting amount refers to the full use of tool
cutting performance and machine power performance (power, torque), in
ensuring the quality of the premise, to obtain high productivity and low
processing costs of cutting costs.
