Monthly Archive September 14, 2020

The following problems should be paid attention to in the process of CNC hand board processing

(1) Determine the processing content of CNC machining center, determine the installation base surface, processing base surface and machining allowance of workpiece, and organize the machining process with the intention of giving full play to the power of CNC machining center.

(2) As for complex parts, due to thermal deformation during processing, internal stress after quenching and deformation after parts clamping, it is difficult to complete the whole process after one clamping. At this time, it can be considered to clamp twice or repeatedly.

(3) The principle of “from rough to fine” should be followed in the organization of machining process. First, organize heavy cutting, rough machining, remove the machining allowance on the blank, and then organize the content with low machining accuracy.

(4) In order to reduce the influence of a large amount of heat on the machining accuracy, and to improve the tool life, large flow cooling method should be used actively.

CNC machining method and tool selection.

1. Try to use a big knife to cut thick, and then use a small knife to clear the corner. For example, the diameter of? 32 tool is 4 times that of? 8 tool, while the processing area is 16 times. Moreover, the large diameter tool has good rigidity, and the cutting depth and feed speed are significantly greater than those of the small diameter tool.
2. Try to use the fillet knife for roughening and flat bottom knife for corner cleaning. Because of the better force on the round blade, and it can be used repeatedly, the square grain can only be used twice.
3. Generally, the plane should not be processed with ball cutter, but with flat bottom knife. It is better to leave 0.2mm for polishing.
4. For straight wall groove processing, first finish the bottom surface of the workpiece, and then finish the side surface. For the side surface with height less than 50 mm, large number of reciprocating machining with carbide grain cutter shall be avoided as far as possible, and all straight shank cutters shall be selected for contour processing. (the depth of each tool is about the tool radius. )

CNC machining

1. Proper selection of forming tools to process regular shaped workpieces to improve power. For example: taper cutter milling slope, finger knife milling rib, fillet cutter (r0.3-r1) small fillet, etc.
2. In order to ensure the constant cutting load of the cutting tool, the layer by layer winding processing method should be selected as far as possible to avoid the upper and lower tool feeding.
3. The rigidity of the tool should be enough. Generally, the length diameter ratio (measured by the ratio of tool length to diameter) should not exceed 5. For example, the extension length of a 16mm diameter cutter should not be greater than 80mm, and a clamping length of 25-45mm should be reserved. Please refer to the tool specification table (Appendix 2) to select the machining tool to avoid over cutting due to lack of rigidity in the process of machining.
4. According to the shape of the workpiece, the programmer can select the self-made taper shank cutter or small cable head clamp to enhance the rigidity; for narrow groove and deep cavity dead angle, please use EDM, and do not have to force milling out.
5. If there are upper boss and pits in multi curved surface machining, please use a tool with small diameter to partially clean the corner, or make a protective surface to avoid bouncing.
6. Please process from center to corner. If the flat bottomed cutter is used for downward machining, please first use the ball cutter to cut the lower edge, or the horizontal feed part should be processed layer by layer to avoid the excessive allowance of the first cutter, resulting in over cutting of the “top and bottom”.
7. For the molding of the surrounding inclined plane and the bottom fillet, it is usually wound layer by layer with a ball cutter, and the fillet will appear “undercut” and affect the quality. Please use a flat bottomed cutter for semi finishing, and then use a ball cutter with a radius less than 1-2mm for finishing, or use a flat bottomed cutter to go back and forth for machining.
8. For the vertical or steep surface, please use the unidirectional cutting method to process from top to bottom, or use the winding method to process layer by layer downward.
9. For deep cavity or high column machining, please use ball cutter or R6 fillet cutter for winding and finishing layer by layer. Avoid using

When machining flat bottomed cutter or fillet cutter without R1, the tool tip of flat bottomed cutter is easy to wear, resulting in inaccurate shape, while the position of cutting contact point of ball cutter and fillet cutter changes with the change of machining position, and the wear is more uniform, which can ensure the machining quality.

1. For deep cavity or high column position (greater than 200 mm), please use square cutter for roughening, do not use R6 fillet cutter for roughening, because the contact surface of fillet cutter is large, it is easy to vibrate and spring the cutter.

In the process of work, mold failure is also a common thing. In general, when we encounter failure problems, we first need not to solve the problem, but to find out what causes the failure. In this way, we can better solve the fundamental problem. If the cause is not found, then even if it is solved, it is basically a temporary cure rather than a root cause. So let’s To understand the CNC machining center spindle abnormal noise causes what is it?

CNC machining

1. Overload.

Fault causes: excessive cutting amount, frequent positive and negative rotation, spindle motor failure, spindle drive device failure.

1. The spindle does not rotate

Fault causes: spindle drive device failure, CNC device can not output speed signal, spindle motor fault, spindle drive device fault, drive belt fracture.

1. Spindle speed deviates from the command value

Fault causes: motor overload, problems with spindle speed command output from CNC system, fault of speed measuring device or disconnection of speed feedback signal.

1. Abnormal noise and vibration of spindle

Different types of CNC machining centers adopt different types of spindles. According to the different transmission systems, the spindle system can be divided into the main drive spindle with variable speed gear, the main transmission spindle through belt drive, the spindle driven by dual motors and the spindle integrated by motor and spindle

What are the problems of computer gong processing?

1. In the process of processing products, when the size of height direction changes greatly, do not adjust the depth of wear tool compensation, first check whether there is aluminum slag in the handle and spindle, and then add wear cutter compensation after admitting that there is no slag.
2. When using the jaw to clamp the products, the thickness is different, the outer dimension is thinner and the inner dimension is thicker. This is when the product is jacked up by clamping the external jaw. It is necessary to pay attention to whether the movable parts of the jaw are too loose, and the problem of different product thickness can be handled after locking it.
3. When CNC machining deep hole has accuracy requirements, it simply presents taper, especially when the hole depth is longer, it is difficult to ensure that the upper and lower are reached. It can be rough first and leave a small amount of allowance before boring.
4. When processing products with high surface finish requirements, the rough blade pattern is difficult to meet the requirements of customers. At this time, the flying cutter can be used to install PCD cutter grain for large surface, and PCD flat cutter can be customized for small surface to improve the surface finish.

CNC machining

1. 304 stainless steel material, it is very simple to wear the tool during processing, cold cutting fluid can be changed to oil cooling, oil cooling can improve the service life of the tool. The tapping diameter of aluminum material is small, the wire tapping is simple, and the oil cold cutting is also available.
2. Corner flick knife

When it is found that there is a product corner spring knife, the first analysis of the product corner size, the use of less than corner R angle of the tool. It can also be handled by reducing the spindle speed.

1. Burr on chamfering

When there are burrs after chamfering, the first thing to check is whether the tool is worn. If the tool is intact, then check the depth and range of chamfering. Generally, these two aspects can deal with the problem of chamfering burr.

1. Pinch injury

Pinch injury is a common problem in CNC machining. On the one hand, it may be that the operator is clamping the product or the tooling is not blown clean, which can be completed by strengthening training. On the other hand, it may be that the contact surface of clamping products is large, which can be treated by replacing the steel jaw. The tooling can also be placed in the direction of the oil pipe when adjusting the machine, so as to clean up the residual materials and reduce the formation of clamping injury.

Matters needing attention before CNC machining

① Cutter path sequence: large cutter curved surface grooving cutter path opening, small cutter contour contour cutter opening rough, large cutter (ball cutter) parallel milling cutter path smooth cutter, small cutter parallel milling cutter path smooth cutter. When the front die is manufactured, there is usually a matching copper male, mainly with a rough cutting path, supplemented by a local curved surface smooth knife.

② With parting surface and pillow surface, it is necessary to add time together. The parting surface pillow surface shall be machined in place without allowance, and the allowance of 0.2-0.5 shall be reserved at the cavity for spark. If only the young male is needed, a margin of 0.3 can be left. The allowance is 0.5. The allowance of 0.1 can be reserved at the position of collision and wear of front die, which is used for front and rear die matching.

③ When the diameter is too small, it is easy to break and snap the knife. It should also be selected as far as possible.

CNC machining

④ The tool path size in curved surface machining is calculated according to the moving track of the tool center axis, that is, the actual machining area is one more tool radius value than the one side of the selected tool path size constraint box, so the parameters of tool path size constraint frame should be set reasonably. To prevent the processing scale beyond the practical processing needs.

⑤ The data of the front die is hard. Check carefully before processing to reduce mistakes and not easy to weld!

Precautions after CNC machining

① Sequence of tool path of back die: large tool surface grooving, cutter path opening, small tool constraint scale, curved surface grooving and opening, angle cleaning, large cutter (ball cutter) parallel milling path smooth surface, small cutter (ball cutter) parallel milling path constraint scale, angle cleaning, smooth cutter, flat cutter and other high profile tool path angle cleaning.

② The data of the back die is the same as that of the front die, and the round nose knife (handle) should be used as far as possible.

Some skills in NC machining

How to prepare NC programming

After determining the processing technology, the following should be understood before programming:

1、 Workpiece clamping method;

2、 Workpiece rough blank size – determine the processing range or whether multiple clamping is required;

3、 Workpiece material: select the tool for processing;

4、 What are the tools in stock? Avoid modifying the program due to the lack of this tool during processing. If you have to use this tool, you can prepare it in advance.

What are the programming principles for safe height setting?

Precision machining

Safety height setting principle: generally higher than the highest height on the island. Or set the programming zero point to the highest plane to avoid the risk of knife collision as much as possible.

Why do tool paths need post-processing?

Since different machine tools can identify different address codes and NC program formats, it is necessary to select the correct post-processing format for the machine tools to ensure that the program can run.

Reasonable selection of cutting parameters

For high efficiency metal cutting, the material to be processed, cutting tools and cutting conditions are the three major elements. They determine the processing time, tool life and machining quality. The economical and effective machining method must be the reasonable choice of cutting conditions.

The three elements of cutting conditions: cutting speed, feed rate and cutting depth directly lead to tool damage. With the increase of cutting speed, the tool tip temperature increases, resulting in mechanical wear, chemical wear and thermal wear. If the cutting speed is shortened by 2%, the tool life will be increased.

The relationship between feed condition and tool wear is very small. However, when the feed rate is large, the cutting temperature increases and the wear is large. It has less effect on cutting tool than on cutting speed. Although the influence of cutting depth on the tool is not as great as the cutting speed and feed speed, when the cutting depth is small, the hardened layer of the material to be cut will also affect the tool life. The user should select the cutting speed according to the processing material, hardness, cutting state, material type, feed rate, cutting depth, etc.

On this basis, the most suitable process conditions were selected. Regular and stable wear is the ideal condition for service life. Don’t want to work at the bottom, want to get rid of the status quo.

But in practice, the choice of tool life is related to tool wear, change of machining size, surface quality, cutting noise, processing heat and other factors. When determining the processing conditions, it is necessary to study according to the actual situation. For difficult to machine materials, such as stainless steel and heat resistant alloy, coolant or rigid blade can be used.

Universal threading method for CNC machining

There are generally four ways to process thread on CNC lathe. There are four cutting methods: direct cutting, oblique cutting, left and right cutting and rough cutting.

1. Direct development method; as shown in Fig. 1 (the depth of thread turning tool intermittently feeding to the teeth), when the trapezoidal thread is processed (all three parties are involved in cutting), the chip removal is difficult (increasing the cutting force and cutting heat), the tool tip of severe wear (too much feed), and the possible phenomenon of thorn. Obviously, machining large pitch trapezoidal thread and worm is not advisable.
2. Oblique method; as shown in Figure 2 (thread turning tool is the phenomenon that the Federal Reserve uses the depth of helical teeth and intermittent way along the direction of tooth angle) (when trapezoidal thread processing is in this way (thread turning tool always has only one edge to participate in cutting (so the chip discharge is relatively smooth) (the skill of force and thermal conditions is improved (not easy to cause tool turning).
3. Left and right cutting mode; as shown in Fig. 3 (the thread turning tool enters the tooth depth through the staggered gap in the direction of tooth profile angle).

CNC machining

1. Groove cutter rough groove cutting method: as shown in Fig. 4, (this method first uses slotting cutter to rough groove (then uses trapezoidal thread turning tool to process both sides of thread).

Characteristics and processing method of worm and trapezoidal thread with large pitch

The cutting resistance of turning worm and large guide wire (either oblique or left-right cutting mode) is very high (previously only high-speed steel turning tool is used for low-speed turning (production efficiency is very low). In order to be able to use carbide tools, I had to find a way to reduce the cutting depth of the blade.

The groove of thread or worm is divided into several layers (converted into several shallow trapezoidal grooves) for cutting.

Since the depth of the left cutting groove remains unchanged (the tool only needs to do left direction!) and feed along the guide rail direction (thus organically combining the left and right cutting methods with the oblique cutting method), the cutting edge can be cut once (and the cutting margin can be effectively controlled), which can guarantee the surface quality and tool life