In the design of NC machining process, the following aspects should be done well: the selection of NC machining process content; ? Process analysis of NC machining:? Design of NC machining process route.
A, the choice of NC machining process content
1, which is suitable for NC machining.
When choosing, you can generally consider it in the following order:
(1) The content that cannot be processed by general machine tools is preferred; ?
(2) The contents that are difficult to process and the quality of general machine tools is difficult to guarantee should be taken as the key selection contents; ?
(3) Generally, the processing efficiency of machine tools is low, and the manual operation of workers is labor-intensive, which can be selected when CNC machine tools still have rich processing capacity.
2, not suitable for the content of NC machining
(1) takes a long time to adjust. If the rough datum of the blank is used to locate and process the first fine datum, the content of special tooling is needed;
(2) The processed parts are scattered, and it is necessary to install and set the origin for many times. At this time, CNC machining is very troublesome and the effect is not obvious. Ordinary machine tools can be arranged for supplementary processing;
(3) The outline of the mold surface processed according to some specific manufacturing standards (such as templates, etc.). ). The main reason is that it is difficult to obtain data, which is easy to contradict the inspection basis and increases the programming difficulty.
Second,? Process analysis of NC machining
1, the dimension shall conform to the characteristics of NC machining.
2. The conditions in geometric features should be complete and accurate.
3. The positioning datum is reliable
4, unified geometric type and size
Third, the design of NC machining process route
1, division of processes
The division of NC machining process can generally be carried out in the following ways:
(1) One-time installation and processing is a process.
(2) according to the processing content of the same tool to divide the process.
(3) Dividing the working procedures according to the processing parts.
(4) The working procedure is divided into rough machining and finish machining.
2, the arrangement of the order
The sequence arrangement should generally be carried out in accordance with the following principles:
(1) The machining of the previous procedure cannot affect the positioning and clamping of the next procedure, and the machining procedures of general machine tools should also be considered comprehensively;
(2) processing the inner cavity first, and then processing the shape;
(3) In the process of machining with the same positioning and clamping method or the same tool, it is best to process continuously to reduce the times of repeated positioning, tool change and moving the platen.
3, CNC machining technology and common process of convergence
[2], CNC machining process design method
The main task of NC machining process design is to further determine the machining content, cutting amount, process equipment, positioning and clamping mode and tool motion trajectory of this process, so as to prepare for the preparation of machining program.
First, determine the feeding route and arrange the processing sequence.
Tool path is the movement path of the tool in the whole machining process, which not only contains the contents of each step, but also reflects the sequence of each step. Tool path is one of the foundations of programming. When determining the feed route, the following points should be noted:
1, find the shortest processing route.
2, the final contour is completed at one time.
3. Select the cut-in and cut-out direction.
4. Choose the route that makes the workpiece deform less after machining.
Second, determine the positioning and clamping scheme
When determining the positioning and clamping scheme, we should pay attention to the following issues:
(1) try to unify the design benchmark, process benchmark and programming calculation benchmark;
(2) Concentrate the working procedures as much as possible, reduce the number of clamping, and clamp all the surfaces to be processed at one time as much as possible;
(3) Avoid adopting a clamping scheme that requires manual adjustment of the machine for a long time;
(4) The action point of clamping force should fall on the part with good rigidity of the workpiece.
Thirdly, determine the relative position of the tool and the workpiece.
Tool alignment point refers to the datum point that determines the relative position between the tool and the workpiece through tool alignment. The tool alignment point is usually selected at the machining origin of the part. The principles for selecting tool points are as follows:
(1) The selected tool alignment point should make the programming simple;
(2) The tool setting point should be selected in a position where it is easy to find and determine the machining origin of the parts;
(3) The tool point should be located in a convenient and reliable position that is easy to check during machining;
(4) The choice of cutter points should be beneficial to improve the machining accuracy.
Tool changing points are set for machining centers, CNC lathes and other machine tools that use multiple tools for machining, because these machine tools will automatically change tools during machining. For CNC milling machines with manual tool change, the corresponding tool change position should also be determined. In order to prevent damage to parts, tools or fixtures during tool changing, the tool changing point is often set outside the contour of the machined parts, leaving a certain degree of safety.
Fourthly, determine the cutting parameters.
When determining the cutting parameters, programmers should choose the appropriate cutting speed according to the material, hardness, cutting state, back feed, feed rate and tool durability of the workpiece to be processed.
The following is a programming example (using Huazhong CNC system)
Cheng? Order? Say? bright
G92？ X80？ Z 100？ Establish the workpiece coordinate system (the origin is at the geometric center point of the left end face of the workpiece) and set the cutting point as (80, 100).
M03？ S500？ The spindle rotates forward at a speed of 500 rpm.
M06？ T0 10 1？ Replace the 1 tool (cylindrical rough turning tool) to prepare the rough turning of the cylindrical surface.
G00？ X32？ Z2？ The tool moves rapidly from the tool starting point to the cycle starting point (32, 2). (blank diameter Ф 30)
G7 1？ U 1？ R 1？ P 100？ Q200？ X0.6？ Z0.3？ F200？ G7 1 compound cycle roughing the cylindrical surface of the workpiece, with each feed 1mm (radius value), tool withdrawal 1mm (radius value) and 0.6 in the x direction. Mm allowance (diameter value), leaving 0.3 in the z direction? Mm allowance, finishing procedure from N 100 to N200.
G00？ X80？ Z 100？ After the rough turning of cylindrical surface is completed, quickly retract the tool to the starting point of the tool (that is, the tool change point).
T0 100？ Cancel the knife deviation value 1 knife.
M06？ T0202？ Replace the No.2 cutter (excircle finishing cutter) and prepare the excircle surface for finishing.
S800？ Increase the speed to 800 rpm. (When finishing, the rotating speed S should be increased and the feed F should be reduced. )
N 100？ G00？ X6？ Z2？ At the beginning of finish turning, the cutter moves from the starting point to (6, 2). Note: If the chamfer extends 2 in the z direction, then X= 12-2-4=6(X is the diameter value).
G0 1？ X 1 1.8？ Z- 1？ F 100？ Machining chamfering by linear feed. Note: The excircle of M 12 thread is machined to 1 1.8 (0.2 smaller than the thread outer diameter), and the feed rate is reduced to F 100.
Z-20？ Finish turning the thread excircle (thread relief groove will not be processed temporarily).
X 14？ Finishing end face
X 16？ Z-2 1？ Finishing chamfer
Z-28.5？ Finishing Ф16 excircle
X24？ Z-43.428？ Finish turning a 30-degree conical surface. Note: Node coordinates of the left end of the cone (24, -43.428)
N200？ Z-70？ Finish turning Ф 24 excircle to-70 (5mm longer than the workpiece). (The excircle and chamfer of the middle groove and the left end will not be processed for the time being). Finishing.
G00？ X80？ Quickly retract the tool to X80.
Z 100？ Quickly return the tool to the starting point.
T0200？ Cancel the knife deviation value of No.2 knife.
M06？ T0404？ Replace No.4 knife (grooving knife). Set the width of the cutter head to 3 mm (the width of the cutter head shall be measured during specific processing).
Prepare the threaded groove and the intermediate groove.
S500？ Adjust the speed to 500.
G00？ X 18？ Z-20？ Quickly move to the left of the thread groove (18, -20).
G0 1？ X9.3？ F50？ Machining thread groove to X9.3 (the groove bottom diameter is 9, leaving 0.3 allowance).
G00？ X 18？ Quickly retract the tool to X 18.
X 14？ Z- 17？ Quickly move to (14,-17). At this time, the right tool tip is at (14,-14), so prepare for chamfering.
G0 1？ X 10？ Z- 19？ Machining chamfer
X9？ Slot to the bottom of the slot
Z-20？ Machining to the left to remove the 0.3 margin left by the front groove, so that the whole groove bottom will not leave a knife mark because of two knives cutting the groove.
G00？ X26？ Quickly retract the tool to X26, and prepare to process the middle groove.
Z-55？ Move quickly to Z-35 (on the left side of the middle tank).
G0 1？ X20.3？ Cut the groove to X20.3 (the groove bottom diameter is 19.975, leaving a margin of 0.325). Note: Asymmetry tolerance takes the middle value.
G00？ X26？ Quick tool withdrawal to X26
Z-53？ Quickly move to Z-33 (to the right of the middle slot, and the right tool tip is at (26, -30).
G0 1？ X 19.975？ Grooving to the bottom of the groove (X 19.975)
Z-55？ Machining to the left removes the allowance of 0.325 left by the front grooving, so that the whole groove bottom will not leave knife seam marks because of the grooving of two knives.
G00？ X80？ Quickly retract the tool to X80.
Z 100？ Quickly return the tool to the starting point.
T0400？ Cancel the knife deviation value of No.4 knife.
M06？ T0303？ Replace the No.3 cutter (thread cutter) and prepare to process threads.
Note: thread M 12 is coarse thread. According to the look-up table, the pitch is 1.75, and the tooth depth = 1.75× 1.3=2.275 (diameter value). It is machined by four cutters, and the depth and diameter of each cutter are 1 and 0.
S400？ Adjust the speed to 400. Note: The rotational speed of thread processing is S= 1200/ pitch -80 (empirical formula).
G00？ X 14？ Z2？ Quickly move to the beginning of the thread processing cycle (14,2).
G82？ X 1 1？ Z- 17？ F 1.75？ For the first thread machining, the diameter value of cutting depth is:1mm.
G82？ X 10.2？ The second tool thread processing, the diameter value of tool depth is: 0.8 mm
G82？ X9.8？ For the third thread processing, the diameter value of the cutting depth is 0.4 mm
G82？ X9.62？ In the fourth thread processing, the diameter value of the cutting depth is 0.18 mm.
G82？ X9.62？ Take a thread to process an empty knife.
G00？ X80？ Z 100？ Quickly return the tool to the starting point.
T0300？ Cancel the knife deviation value of No.3 knife.
M06？ T0404？ Change the No.4 cutter (slot cutter), and prepare to process the left Ф 20 cylindrical surface, chamfer and cut off the workpiece.
S500？ Adjust the speed to 500.
G00？ X26？ Z-68？ Quickly move to (26, -68), and the right tool tip is at Z-65, that is, the right end face of the workpiece.
G0 1？ X 16？ F30？ Cut the groove to X 16 to prepare for chamfering.
G00？ X26。 Go back to X26.
Z-65？ Quickly move to Z-65 (that is, move one knife width to the right).
G0 1？ X20.3？ Cut the groove to X20.3 (the groove bottom diameter is 20.025, leaving a margin of 0.275). Note: Asymmetry tolerance takes the middle value.
G00？ X26？ Hurry back to X26.
Z-63？ Quickly move to Z-63, and the right blade is at Z-60, which is the shoulder.
G0 1？ X20.025？ Grooving to groove bottom X20.025
Z-67？ Turn left to Z-67. At this point, the right tool tip is in Z-64, ready for chamfering.
X 18？ Z-68？ Machining chamfer
X0？ Cut off workpiece
G00？ X80？ Go back to X80.
Z 100？ Go back to the beginning.
T0400？ Cancel the knife deviation value of No.4 knife.
M05？ Spindle stall
M02？ end of program