CNC Technology – Page 38 – CNC Machining & Turning, Milling, Metal parts

CNC machining non-standard parts

In the machining process of parts, the surface as the positioning datum should be processed first, and the computer gong processing can provide precise reference for the subsequent processing as soon as possible.
The machining stage is divided into three stages: rough machining, semi finishing and finishing. It is mainly to ensure the quality of processing; it is conducive to the scientific application of equipment; it is convenient to arrange the heat treatment process; and it is convenient to find the blank defects.
For parts such as box, bracket and connecting rod, the plane should be machined first and then the hole should be processed. In this way, the hole can be processed by plane positioning, which ensures the position accuracy of plane and hole, and brings convenience to the processing of hole on the plane.
Finishing the main surface finishing, such as grinding, honing, finishing and rolling, should be placed at the end of the process route. The general principle of drawing up the process route of precision parts and the formulation of the process regulation of precision parts can be roughly divided into two links. First of all, it is to draw up the process route of parts processing, and then determine the process size of each process, the equipment and process equipment used, as well as the cutting specifications, man hour quota, etc. In the machining process of non-standard parts, the foundation is the most important, and the same is true for precision mechanical parts processing. The precision datum is always processed first, and then the other surfaces are positioned and processed by the precise datum. Next, we’ll go into details about me. For box parts, the main hole is generally used as the rough datum to process the plane, and then the plane is used as the precision datum to process the hole system; for the shaft parts, the outer circle is generally used as the rough datum to machine the central hole, and then the center hole is used as the fine datum to process the outer circle, end face and other surfaces. If there are several precision datum, the machining of base surface and main surface should be arranged according to the sequence of datum transformation and the principle of gradually improving machining accuracy.

For the box, bracket and connecting rod, the plane should be machined first and then the hole should be processed. Because of the flat contour and large area of the plane in high-speed CNC machining, machining the plane first and then machining the hole by plane positioning can not only ensure that the hole has a stable and reliable positioning reference, but also is conducive to ensuring the position accuracy requirements between the hole and the plane. A part is usually composed of multiple surfaces, and the machining of each surface generally needs to be carried out in stages. In high-speed CNC machining, when arranging the machining sequence of precision mechanical parts, the roughing of each surface should be arranged first, then the semi finishing should be arranged in turn according to the needs, and finally the finishing and finishing should be arranged. In order to reduce the influence of deformation caused by rough machining on finish machining, roughing and finishing should not be carried out continuously, but should be carried out in stages and at appropriate intervals. The general principle of machining non-standard parts is: the front work must be prepared for the later work, lay a good foundation, and do a good service.

The specific working principle of CNC machining non-standard parts can be divided into four aspects: the main surface of parts is generally the surface with high machining accuracy or surface quality requirements. Their processing quality has a great impact on the quality of the whole part, and its processing procedures are often more. Therefore, the processing of main surface should be arranged first, and then other surface processing should be properly arranged in them In the middle. Generally, the assembly base surface and working surface are regarded as the main surface, while the keyway, smooth hole and screw hole for fastening are regarded as the secondary surface.

Computer gong processing programming

CNC machine tool is a machine tool manufacturing industry, the revitalization of each field needs a large number of advanced CNC machine tools. In recent years, the production of CNC machine tools in China continues to grow, and the industry of CNC machine tools and CNC systems will develop rapidly.

Reader: in this case, many production plants are placed on CNC machine tools, we can imagine the importance of CNC machine tools. I want to know, how do we master NC machine programming technology, NC machine programming experts?

Editor: NC machine programming technology is not a very short period of time can learn, need to learn step by step, and slowly accumulate experience. Master this technology, small editor is not only the theoretical level of engineers, but also the practical experience and practical ability of senior technicians. How to become the master of NC machine programming?

1, the process is the basis of programming. If you don’t know the technology, it can’t be called programming. Therefore, to master the programming technology of CNC machine tools, you must first become a craftsman.

Proficient in CNC programming and computer software application.
Proficient in CNC machine tools. It takes 2-3 years to study. In this process, we need to learn how to operate the system, fixture installation, part datum alignment, tool presetting, zero point offset setting, tool length compensation, radius compensation, tool and handling handle, cutting tool grinding, part measurement (skilled use of vernier caliper, micrometer card, micrometer, diameter bar gauge), etc.
There must be good fixture foundation and measurement technology.
Familiar with CNC machine tools. Proficient in the maintenance of CNC machine tools.
Cultivate good habits and adapt to the characteristics of CNC processing. In this case, suitable for CNC machining master should be humble, rigorous, calm, serious thinking, orderly and persuasive people.

CNC machining repeatability of CNC lathe

CNC CNC lathe processing repetitive production of parts: the use of CNC grinding machine process preparation time occupies a high proportion. For example Process analysis preparation, programming, adjustment and trial cutting of the first part of the part, the sum of these comprehensive working hours is often dozens to hundreds of times of the working hours of a single part of the part. However, the work contents of these CNC lathes can be saved and reused. Therefore, when a part is successfully trial produced on a CNC grinder and put into production again, the production cycle is greatly reduced, and the cost is also less, which can achieve better results The economic benefits of.

It is required to focus on ensuring the processing quality and producing the key parts in small and medium batches: CNC grinder can realize high precision, high quality and high efficiency grinding under the control of computer. Compared with the special grinding machine processing, it can save a lot of special process equipment, has strong flexible manufacturing ability and obtains better economic benefits. Compared with ordinary grinding machine, it can eliminate many artificial interference factors in the long process of complex machining, and has good precision consistency and interchangeability, and high processing efficiency.

The parts processed by CNC CNC lathe should conform to the process characteristics that can give full play to the multi process centralized processing of CNC grinder. When CNC grinding machine processes parts, the situation of grinding wheel cutting workpiece is exactly the same as that of corresponding non CNC grinder, but it can carry out some complex processing with processing accuracy requirements. For example, in the grinding range, ordinary grinder is mainly used for grinding cylindrical surface and circular CNC lathe In addition, it can also grind toroidal surface and complex combined surface of various forms mentioned above.

The processing batch size of parts should be larger than that of economic batch of parts by ordinary lathe. When NC lathe is used to process medium and small batch parts by non CNC grinder, due to various reasons, the pure cutting time only accounts for 10% – 30% of the actual working hours. When CNC machining is carried out on the CNC grinding machine with multi process concentration, such as grinding center, the proportion may rise to 70% – 80%, but the man hour to be adjusted is often much longer, so it will be uneconomical if the parts batch is too small.

Some special parts processed by CNC lathe are considered to be processed. Although some parts are processed in small batches, ordinary lathes have complex shapes, high quality and good interchangeability, which can not meet the above requirements on non CNC grinding machines. CNC machining can only be arranged on CNC grinding machines, such as parabola, cycloid cam and special surface mirror mirror.

Computer gong processing and knife loading

1、 Try to install the clamping material first and then the cutting tool,

In order to prevent the hand from touching the tool when loading the material. If the tool has been installed, the worktable should first be moved to the outside to ensure that the clamping material will not interfere with the tool, so as to avoid injury or breakage of the tool.

2、 When disassembling the tool, you must first observe whether the spindle stops rotating.

4、 The wrench should be placed in the tool storage area after use.

In the process of CNC machining, operators are not allowed to observe the cutting position closely to prevent chips from falling into eyes.

6、 Before processing, check the position of the oil nozzle before opening the oil pump switch to avoid spraying to other positions when flushing oil.

7、 When the machining gap is suspended for observation, the worktable must be moved away from the cutting position.

8、 After the machining is completed and before the workpiece is disassembled, we should first conduct the preliminary inspection of the necessary size or appearance. Only after the inspection is qualified can the workpiece be disassembled, so as to avoid the positioning problem of secondary processing and the scrapping of the workpiece.

CNC computer gongs machine tool debugging

Before the commissioning of CNC computer gong machining machine tool, the debugging method of CNC computer gong machining machine precision and function is as follows:

Using precision level instrument and other detection tools, mainly by adjusting the pad iron way to fine adjust the level of the main bed of the computer gong processing machine tool, so that the geometric accuracy of the machine tool can reach the allowable tolerance range;
For the automatic tool change device, adjust the position of the tool magazine, manipulator, travel parameters, etc., and then check the action with the command, which is required to be accurate;
For the machine tool with APC automatic exchange table, after adjusting the relative position, carry out automatic load exchange;
After the adjustment of the machine tool, carefully check whether the parameter setting values in the numerical control system and the programmable controller conform to the data specified in the random index, and then test the main operation functions, safety measures, execution of common instructions, etc.
Check the auxiliary functions and accessories of the machine tool. CNC machining is the basis of modern manufacturing technology. This invention has epoch-making significance and far-reaching influence for the manufacturing industry.

CNC machining to prevent deformation of parts

Computer gong processing is an automatic numerical control machine,

Now many processing enterprises need this kind of mechanical equipment, but due to the fierce market competition, computer gongs processing chaos. The author suggests that before purchasing computer gong equipment, we must have a detailed understanding and investigation of the manufacturer.

Computer gong processing in the process of use will encounter some common faults, such as computer gongs can not return to zero, computer gongs positive and negative hard limit alarm, so what are the causes of these failures?

Cause analysis of computer gong can not return to zero

The contact of origin switch is stuck and cannot act;
The origin stop can not press the origin switch to the switch action position;
The water in the origin switch causes the contact rust and poor contact;
The line of origin switch is disconnected or the input signal source is faulty;
PLC input point burned out.

Cause analysis of positive and negative hard limit alarm of computer gong

In this case, what is the cause of this normal situation?

The contact of travel switch is pressed and stuck (over travel);
The travel switch is damaged;
There is open circuit, short circuit and no signal source in the travel switch circuit;
The limit stop can not press the switch contact to the action position;
PLC input point burned out.

Most of the time, due to the improper use of technical personnel, or work handover is not in place, computer gong processing will cause some problems.

Precision CNC machining criteria

CNC machining can change the shape and size of products, which plays a very important role.

Many friends do not understand the high-speed CNC machining process benchmark.

The broad meaning of benchmark is the meaning of “basis”. In mechanical manufacturing, the datum refers to the points, lines and surfaces used to determine the geometric relationship between geometric elements on the production object. According to the different functions and applications, the datum can be divided into two categories: design datum and process datum. Process datum can be divided into process datum, locating datum, measuring datum and assembling datum.

High speed CNC machining technology is the premise to ensure the production of high-quality parts.

On the lathe, the shape and size of the blank can be changed by the rotary motion of the workpiece and the linear or curvilinear motion of the cutter, so that it can be processed to meet the requirements of the drawing.

Ordinary machine tools are more and more difficult to meet the needs of machining precision parts,

At the same time, due to the improvement of production level, the price of CNC machine tools is falling from time to time. CNC precision parts processing mainly includes ultra precision turning, mirror grinding and grinding.

The primary premise of CNC precision parts processing is the accuracy of process datum. The datum on mechanical drawings are all represented by capital letters a, B, C, D, etc. with a specific ring datum symbol. When the datum symbols are aligned with the surface and the extension line of the surface or the dimension limit of the surface, the indication is based on the surface. When the datum symbol is aligned with the dimension line, it is indicated that it is based on the solid center line of the dimension. It is a more general statement that the accuracy of the technology mentioned above is mentioned for you.

Assembly benchmark refers to the accuracy of the position of parts in parts or products during assembly. Measurement benchmark refers to the specification for the size and position of the measured processing surface when the parts are inspected. Positioning reference, refers to the processing, the workpiece in the machine tool or fixture positioning with the reference.

Reasons for uneven machining of CNC parts

In the process of using computer gong machining center, the tool imbalance may appear. If not adjusted in time, it will affect the processing effect. Therefore, we should always pay attention to the tool balance of the computer gong machining center. What are the main reasons for the imbalance of the handle?

The main reasons are that the design of the tool is asymmetric, there are defects in the tool body, and all the adjustments on the tool. The correct balance of the tool can significantly reduce noise and vibration, which increases the tool life and improves the accuracy consistency of parts.

The centrifugal force of computer gong machining center magnifies the vibration caused by unbalance in proportion to the square of velocity. The vibration increase of CNC machining center caused by the machining center minimizes the service life of bearing bush, bearing, shaft, spindle and gear.

It is necessary to measure the magnitude of the unbalance and the angle position of each selected correction plane before balancing the tool on the computer gong machining center. These variables are measured on two general types of balancing machines: non rotating or gravity machines are used to measure single plane unbalance, while rotary or centrifuge is used to measure single plane or two plane unbalance.

After measuring the magnitude and angle of the unbalance in the correct plane, you can correct it by adding or removing material from the workpiece. For the components which are not tools, the most widely used material adding method of drilling center is welding counterweight on the components.

For components with slight unbalance, other methods include adding solder on the assembly body or increasing weight in pre drilling. For tools, when you determine that the unbalance must be removed in order to get the correct balance, the easiest and most effective method is drilling.

Check the condition of lubrication system and pressure gauge, clean the filter screen of lubrication system, change lubricating oil and dredge oil circuit. machining center
Check the gas system, clean the air filter screen and eliminate the leakage of pressure gas.
Check the fluid system, clean the filter, clean the oil tank, replace or filter the oil. If possible, replace the seal.
Fasten the transmission parts and replace the defective standard parts.
Grease lubrication parts, according to the requirements, add grease
Clean and clean all driving surfaces,
Check the status of tool magazine and manipulator for computer gong processing, analyze the wear status of manipulator, and propose replacement suggestions to customers.
Repair and repair the damaged parts of external components.
Check the condition of the protective cover.

CNC cutting technology

When high speed milling is used to finish hardened die steel, one of the main factors to be observed is to use shallow cutting. The cutting depth shall not exceed 0.2/0.2 mm (AP / AE: axial cutting depth / radial cutting depth). This is to avoid excessive bending of the toolholder / cutting tool and to keep the machined die with small tolerance and high accuracy.

It is also important to choose a clamping system and tool with good rigidity. When using monolithic cemented carbide tools, it is very important to use tools with the largest core diameter (maximum bending rigidity). A rule of thumb is that if you increase the diameter of the tool by 20%, for example from 10 mm to 12 mm, the bending of the tool will be reduced by 50%. It can also be said that if the tool overhang / extension is shortened by 20%, the tool bending will be reduced by 50%. The tool holder with large diameter and taper further improves the stiffness. When ball end mills with indexable inserts are used (see mold manufacturing sample c-1102:1), if the handle is made of integral cemented carbide, the bending rigidity can be increased by 3-4 times.

When high speed milling is used to finish the hardened die steel, it is also very important to select the special groove and grade. It is also important to select coatings with high thermal hardness such as TiAlN.

11) When should forward milling be used and when should reverse milling be used?

The main suggestion is: use down milling as much as possible.

When the cutting edge is just cutting, the chip thickness can reach its maximum value in down milling. In the reverse milling, it is the minimum value. Generally speaking, the tool life in up milling is shorter than that in down milling because the heat generated in up milling is significantly higher than that in down milling. When chip thickness increases from zero to maximum in up milling, more heat will be generated because the friction of cutting edge is stronger than that in down milling. The radial force is also obviously high in up milling, which has a negative effect on the spindle bearing.

In down milling, the cutting edge is mainly subjected to compressive stress, which is much better than the pulling force produced in up milling on cemented carbide blade or integral carbide tool. There are exceptions, of course. When using solid carbide end mills (see tools in die sample c-1102:1) for side milling (finish machining), especially in hardened materials, the top milling is preferred. It’s easier to get a better straightness and a smaller wall angle of 90. If there is no coincidence between different axial feed, the tool mark is also very small. This is mainly due to the direction of the cutting force. If a very sharp cutting edge is used in cutting, the cutting force tends to “pull” the knife toward the material. Another example that can be used for up milling is the use of an old manual milling machine, which has large lead screw clearance. Up milling produces cutting force to eliminate clearance, which makes milling action more stable.

12) Profile milling or contour cutting?

In cavity milling, the best way to ensure the success of down milling tool path is to use contour milling path. Milling the outer circle of a milling cutter (e.g. ball end mill, see die manufacturing sample c-1102:1) along contour lines often yields high productivity because more teeth are being cut on larger tool diameters. If the speed of the machine spindle is limited, contour milling will help to maintain the cutting speed and feed rate. With this tool path, the change of working load and direction is also small. This is particularly important in high-speed milling applications and hardened material processing. This is because if the cutting speed and feed rate are high, the cutting edge and cutting process will be more vulnerable to the adverse effects of working load and direction changes, which will cause changes in cutting force and tool bending. Profiling milling along the steep wall should be avoided as far as possible. The chip thickness is large at low cutting speed when profile milling is carried out. In the center of the ball knife, there is also the danger of breaking the edge. If the control is poor, or the machine tool has no pre reading function, it can not decelerate fast enough, and it is most likely to cause the edge breakage in the center. The reason is that the chip thickness is the maximum under the favorable chip speed.

In order to obtain the longest tool life, the cutting edge should be kept continuous cutting as long as possible in the milling process. If the tool enters and exits too frequently, the tool life will be significantly shortened. This will aggravate the thermal stress and thermal fatigue on the cutting edge. It is more advantageous for modern cemented carbide tools to have uniform and high temperature in the cutting area than large fluctuation. Profiling milling path is often a mixture of up milling and down milling (zigzag), which means that the cutter will be frequently fed and withdrawn during cutting. This kind of tool path also has bad effect on the quality of die. Every time you eat a knife, it means that the tool is bent, and there is a mark of lifting on the surface. When the tool exits, the cutting force and tool bending decrease, and there will be a slight “over cutting” of the material in the exit part.

PMM alarm of computer gong machining center system

If there is no emergency stop and alarm, the alarm will be sent out if there is no emergency stop and alarm. Therefore, all channels of the above CNC machining center are fault points.

Check whether the plugs of CNC machining center are in poor contact, including command line and feedback line.
Check whether the LED has display, if not, it is the board is not powered on or the power circuit is broken.
Check whether the AC voltage of external CNC machining center is normal.
Check whether the DC voltage on the control board is normal. If there is any abnormality, the CNC machining center shall check whether the fuse on the board and the power circuit on the board are burnt out. If it cannot be repaired by itself, replace the amplifier or send it back to the manufacturer for repair.
Carefully observe whether the green light of pay in CNC machining center turns on and off, or it doesn’t pull in at all. If it is closed and then disconnected, it may be that the contact of the relay is not good. Replace the relay. If it is a working environment with woodworking machinery or dust, it can be basically judged that the contact of the relay is not good. If it doesn’t pull in at all, the relay coil of the unit is not good or the control board is not good or there is a broken line, which can be judged by measuring the coil resistance of the relay.

How to deal with scratches after machining holes in computer gong machining center

See if you can change the next processing parameters, it may be unreasonable to set the parameters.
On the other hand, the effective way to avoid scratch is to use boring instead of drilling, and the process selection is wrong.
First of all, you need to see the processing drawing to know that if the thickness of the workpiece processed by the CNC machining center is not very thick, reamer can be used.
It’s also possible that your coolant water speed is slow and the amount of water is not enough, and the chips can’t be discharged.
CNC machining bit angle grinding point, and your penetration rate is too high