12 lessons learned in CNC machining!

Due to the complexity of CNC machining (such as different tooling machines, different materials, different tungsten steel end mills, different cutting methods, different parameter settings, etc.), it is determined that a relatively long period of time is required to reach a certain level of CNC machining (whether machining or programming). The following is a summary of the experience of engineers in the long-term actual production process, related to digital control of cutting technology, process, selection of common tungsten cutter parameters, monitoring during the cutting process, etc. for your reference.

I. How are the cutting processes classified?

The classification of digitally controlled cutting processes can generally be carried out in the following ways.

1. Solid carbide end mill centralized sequencing method is the solid carbide end mill used to divide the process, with the same solid carbide end mill cutting parts on all parts can be completed. Finish the rest as they can with the second knife, the third. This reduces the number of cutting tool changes, compresses the clearance time and reduces unnecessary positioning errors..

2. Base on the cutting parts divided cutting accessories, according to its structural characteristics of the cutting part into several parts, such as internal shape, shape, surface or plane, etc. Generally, it cuts the plane and positioning surface first, then the hole; it cuts the simple geometry first, then the complex geometry; it cuts the parts with lower precision first, then the parts with higher precision.

3. Roughing, finishing methods for parts prone to cutting deformation, due to roughing cutting may occur after the deformation and need to be calibrated, so generally speaking, where to carry out roughing, finishing is to separate the process. In summary, in the delineation of the process, must be based on the structure and technicality of the parts, the function of the tool machine, the number of parts of the CNC cutting content, the number of installations and the unit of the production organization of the state of flexible mastery. Whether the principle of process concentration or process decentralization is to be adopted is to be determined in the light of the actual situation, but it must be as reasonable as possible.

II. What principles should be followed while cutting?

The cutting sequence should be considered according to the structural and blank condition of the part, as well as the need for positioning clamping, without destroying the rigidity of the part. The sequence should generally be based on the following principles.

1. The cutting process cannot affect the positioning and clamping of the next process, interspersed with the cutting process of the general-purpose machine tool should also be considered.

2. Advanced inner cavity cutting sequence, then shape cutting process.

3. The same positioning, clamping or the same tool cutting process is best connected to reduce the number of repeated positioning, the number of tool changes and the number of moves of the pressure plate.

III. Which aspects should be taking care of while clamping the workpiece?

The following three points should be noted when determining the positioning benchmark and clamping scheme.

1. Strive to unify the design, process, and benchmarks of programming calculations.

2. Reduce the number of clamps as much as possible, so that all the surface to be cut can be cut out after one positioning.

3. Avoid using the manual adjustment scheme.

4. The clamping tool should be open, the positioning and clamping mechanism should not affect the cutting tool (such as collision), when encountering this kind of situation, the clamping can be installed by means of vise or with bottom plate extraction screws.

IV. How to determine the reasonable alignment point? What is the relationship between the workpiece coordinate system and the programming coordinate system?

1.   The counterpoint can be set on the part to be cut, but pay attention to the counterpoint must be the reference position or the part that has been finely cut. Sometimes the counterpoint is destroyed by cutting after the first process, which will cause the second process and the subsequent counterpoint to be impossible to find. This relative counterpoint position is usually located on a tool machine work table or clamp. Its selection principles are as follows.

1) It's easy to adjustment.

2) Easy programming.

3) Small error on the cutting tool.

4) Convenient and checkable during cutting.

2. The workpiece coordinate system home position is set by the operator himself, it is after the workpiece clamping, through the knife to determine, it reflects the distance between the workpiece and the zero point of the tool machine position relationship. Once the workpiece coordinate system is fixed, it is generally not changed. The workpiece coordinate system and the programming coordinate system must be unified, i.e. the workpiece coordinate system and the programming coordinate system are the same when cutting

V. How to choose the cutting path?

The cutting path is an index that controls the trajectory and direction of the movement of the tungsten end mills in relation to the part being cut. The rational choice of cutting route is very important as it is closely related to the cutting accuracy and surface quality of the part. In determining the route of the tool is the main consideration of the following points:

1. Guarantee the cutting accuracy of the parts.

2. Convenient numerical calculation to reduce programming workload.

3. Seek the shortest cutting route and reduce the empty cutter time to improve cutting efficiency.

4. Reduce the number of program segments as much as possible.

5. To ensure that the workpiece contour surface roughness after cutting requirements, the final contour should be arranged for the last cutter to cut out continuously.

6. The incoming and outgoing cutter of solid carbide end mill should also be seriously considered to minimize the stopping of the cutter at the contour (sudden change in cutting force caused by elastic deformation) and leave cutter marks, but also to avoid the vertical cutter in the contour surface and scratch the workpiece.

VI. How to monitor and adjust during the cutting process?

After the workpiece has been straightened and debugged, it is ready for automatic cutting. During automatic cutting, the operator monitors the cutting process to prevent workpiece quality problems and other incidents caused by abnormal cutting.

The main considerations for the monitoring of the cutting process are as follows.

1. Cutting process monitoring coarse cutting mainly considers the rapid removal of the excess of the workpiece surface. In the automatic cutting process of the tool machine, the tungsten carbide end mills automatically cut at a predetermined cutting trajectory based on a set amount of cutting. At this time, the operator should pay attention to observe the change of cutting load during automatic cutting through the cutting load table, adjust the cutting amount according to the load-bearing condition of the tungsten cutter to maximize the efficiency of the tool machine.

2. Monitoring of cutting sound during cutting In the automatic cutting process, the sound of tungsten carbide milling cutter cutting workpiece is stable, continuous, light and fast when the automatic cutting process is started. As the cutting process progresses, when there are hard points on the workpiece or when the tungsten end mills wear out or the tungsten end mills feed clips, the cutting process appears unstable, the unstable manifestation is that the cutting sound changes, the tungsten end mills and the workpiece will have a mutual impact sound, the tool will appear to vibrate. At this time, the cutting amount and cutting conditions should be adjusted in a timely manner. When the adjustment effect is not obvious, the tooling machine should be suspended to check the solid carbide end mill and workpiece condition.

3. Finishing monitoring finishing, mainly to ensure the cutting size and cutting surface quality of the workpiece, higher cutting speed and larger feed. At this time, attention should be paid to the effect of the accumulation of psoriasis on the cutting surface, and for cavity cutting, attention should also be paid to the corner overcutting and giving way. For the solution of the above problems, one is to pay attention to adjust the spray position of the cutting fluid, so that the cutting surface at all times in the cooling conditions; two is to pay attention to observe the quality of the cutting surface of the workpiece, by adjusting the cutting amount, as far as possible to avoid changes in quality. If the adjustment still has no significant effect, the machine should be stopped to check whether the original programming is reasonable.

In particular, pay attention to the position of the tungsten steel end mills when pausing or stopping for inspection. If the solid carbide end mill is stopped during cutting, a sudden spindle stop will cause cut marks on the workpiece surface. Generally, stopping the machine should be considered when the tungsten cutter leaves the cutting state.

4. The quality of tungsten steel end mills to monitor the quality of tungsten steel end mills determines the cutting quality of the workpiece to a large extent. In the automatic cutting process, the normal wear condition and abnormal breakage condition of tungsten steel end mills should be judged by sound monitoring, cutting time control, pause inspection during cutting, workpiece surface analysis and other methods. The cutting quality problem caused by the untimely treatment of the carbide cutter should be prevented by timely treatment of the carbide cutter according to the cutting requirements.

VII. How to choose a reasonable cutter for cutting tungsten steel end mills? What are the major elements of cutting usage? How many materials are there for carbide end mill? How to determine the RPM, cutting speed, cutting width of the tungsten carbide cutter?

1. Use non-regrind carbide end mills or end mills for surface milling. In general milling, try to use a second cutter, the first cutter is better to use an end mill for rough milling, continuous cutting along the workpiece surface. The recommended width per tool travel is 60% to 75% of the diameter of the carbide end mill.

2. Stand milling cutters and end mills with carbide inserts are mainly used for cutting the face of the tabs, grooves and box mouths.

3. Ball cutter, round cutter (also called round nose cutter) is commonly used to cut curved surface and beveled profile shape. The ball cutter is mostly used for semi-fine cutting and fine cutting. Round cutters with carbide carbide end mills are mostly used for roughing.

VIII. What is the purpose of the cutting program list? What should be included in the cutting program list?

1. the cutting program is a single digital control cutting process design content, but also requires the operator to comply with the implementation of the regulations, is a specific description of the cutting program, the purpose is to allow the operator to clarify the content of the program, the clamping and positioning of the various cutting procedures chosen by the tungsten carbide cutter should be aware of the problem.

2. In the cutting program list, it should include: drawing and programming file name, workpiece name, clamp sketch, program name, tungsten cutter used for each program, maximum depth of cutting, cutting nature (such as rough cutting or fine cutting), theoretical cutting time, etc.

IX. What should I do before CNC programming?

After determining the cutting process, it is important to understand before programming.

1. Workpiece clamping method.

2. The size of the workpiece blank - In order to determine the range of cutting or whether the need for multiple clamping.

3. Material of the workpiece --- To select the type of solid carbide end mill used for cutting.

4. What are the stock of tungsten carbide end mills --- Avoid modifying the procedure when cutting without this tungsten carbide end mills, if you must use this tungsten carbide end mills, you can prepare in advance.

X. What are the principles for setting the safety height in programming?

Principle for setting the safety height: generally higher than the highest surface of the island. Or set the programming zero point on the highest side, which also minimizes the risk of knife bumping.

XI. After the path of tungsten milling cutter has been programmed, why do we still need to carry out post-processing?

Because different tools recognize different address codes and NC program formats, it is necessary to choose the correct post-processing format for the tool used to ensure that the program will run.

XII. What is DNC communication?

CNC means that the program is transferred to the memory of the tool machine through media (such as floppy disk, tape reader, communication cable, etc.) for storage, and the program is removed from the memory during cutting. Since the capacity of the memory is limited by the size, it can be cut by DNC when the program is large, and since the DNC cutting machine reads the program directly from the control computer (i.e., it does it while feeding), it is not limited by the capacity of the memory.

1. The amount of cutting has three main elements: depth of cutting, spindle speed and feed speed. Cutting amount of choice of the overall principle is: less cutting, fast feeding (that is, cutting depth is small, fast feeding speed)

2. According to the material classification, carbide end mills are generally divided into ordinary HSS, coated carbide end mill (such as titanium plating, etc.), alloy carbide end mill (such as tungsten steel, boron nitride carbide end mill, etc.).