In controlled machining, the path of the tool position relative to the workpiece is called the machining route.
When programming, the main principles for determining the machining route are as follows:- 1) The machining route should ensure the accuracy and surface roughness of the processed parts, and the efficiency is high.
- 2) Make numerical calculation simple to reduce programming workload.
- 3) The machining route should be the shortest, which can reduce the program segment and the time of empty tool. To determine whether it is a single pass or multiple passes to complete the machining, and whether to use down milling or up-cut milling in the milling process.
For point-controlled CNC machine tools, only
high positioning accuracy is required, and the positioning process is as fast
as possible, and the movement path of the tool relative to the workpiece is
irrelevant. Therefore, this type of machine tool should arrange the tool path
according to the shortest idle distance. In addition, the axial movement size
of the tool must be determined. The size is mainly determined by the hole depth
of the machined part, but some auxiliary dimensions should also be considered,
such as the introduction distance and overrun of the tool.
When threading on a CNC machine tool, the
z-direction feed along the pitch direction should maintain a strict speed ratio
relationship with the rotation of the machine tool spindle, so it is necessary
to avoid cutting during the acceleration or deceleration of the feed mechanism.
To this end, it is necessary to introduce a distance δ1 beyond the distance δ2.
The value of and is related to the dynamic characteristics of the machine tool
drag system, and is related to the thread pitch and thread accuracy. It is
generally 2-5mm, and the larger value is used for the large pitch and
high-precision thread; generally it is about 1/4. If there is no undercut at
the end of the thread, the shape of the end is related to the CNC system, and
the end is generally 45o. String 8
When milling flat parts, the side edge of
an end mill is generally used for cutting. In order to reduce the traces of the
knife and ensure the surface quality of the parts, the cutting-in and
cutting-out procedures of the tool need to be carefully designed. When milling
the outer surface contour, the cutting-in and cutting-out points of the milling
cutter should cut into and out of the part surface tangentially along the
extension line of the part contour curve, instead of directly cutting into the
part along the normal direction to avoid scratches on the machined surface.
Ensure that the contour of the part is smooth.
When milling the inner contour surface, the
cut-in and cut-out cannot be extended. At this time, the milling cutter can cut
in and cut out along the normal direction of the part contour, and select the
cut-in and cut-out points at the intersection of the two geometric elements of
the part contour. In the state of balanced elastic deformation of the
workpiece, tool, fixture, and machine tool system, when the feed is stopped,
the cutting force will decrease, which will change the balance of the system.
The tool will leave scratches on the surface of the part where the feed is
stopped. Avoid feed stalls during contour machining.
When it comes to curved surfaces, the
ball-end knife is commonly used for machining with the "line cutting
method". The so-called line cutting method means that the tangent track of
the tool and the part contour is line by line, and the distance between the
lines is determined according to the requirements of the machining accuracy of
the part.
