CNC Technology – Page 17 – CNC Machining & Turning, Milling, Metal parts

Selection of cutting tools for CNC machine tools

1、 Selection of blade (cutter)

The following aspects should be considered when selecting a blade or cutter

The workpiece materials are steel materials (carbon steel, low alloy steel, tool steel, stainless steel). And other complex materials, such as copper, iron and non-metallic materials.
The material properties of machined parts include properties, toughness, microstructure, etc.
The categories of cutting technology include turning, milling, boring, drilling; machining, superfinishing; inner hole, outer circle, plane, groove; cutting flow state, tool displacement time interval, etc.
The geometric shape of the workpiece affects the continuous cutting or intermittent cutting, the cutting in or out angle of the tool. Part accuracy (dimensional tolerance, geometric tolerance, surface roughness) and machining allowance.
Cutting parameters of blade (tool) (back feed, cutting speed)
Production site conditions (operation interruption time, feed rate, cutting speed)
Processing of workpieces and production batch. Economic life of blade (cutter)

2、 Selection of boring tools:

In the selection of boring tools, the main problem is the rigidity of the tool bar, and the vibration should be prevented or eliminated as far as possible. The main points for consideration are as follows;

The diameter of the reverse bar should be as large as possible, close to the boring diameter.
Select the short arm (working length) as far as possible. When the working length is less than 4 times the diameter of the tool bar, steel tool bar can be used. When machining holes with high requirements, cemented carbide tool bar is best used. When the working length is 7-10 times the diameter of the arbor, the small hole is made of cemented carbide arbor, and the drilling is made of shock absorber arbor. When the working length is 7-10 times the diameter of the cutter bar, the damping cutter bar should be used.
The main deflection angle is more than 75 ° and close to 90 °
Select the blade without coating to reduce the radius of cutting arc and tool tip.
The positive cutting edge (positive rake angle) blade and tool are used for finish machining, and the negative cutting edge (negative rake angle) blade and tool are used for rough machining.
When boring deep through holes, cooling measures should be taken. Compressed air (air cooling) or cutting fluid (chip removal and cooling) can be used.
Choose the right and fast boring tool holder.

3、 Selection of milling cutter:

Indexable carbide milling cutter should be used when milling plane on CNC machine tool. It can be divided into two steps. One rough milling and one finish milling. When continuous cutting. The diameter of rough milling cutter should be reduced. The diameter of the finishing cutter should be larger, and it is better to contain the whole width of the surface to be machined. When the machining allowance is large and the machined surface is uneven, the tool diameter should be selected smaller. Otherwise, when rough machining, it will affect the machining quality due to the deep tool mark.
High speed steel end mills are mostly used to process boss and groove, so it is better not to use them to process blank, because there are hardening layer and cracks in the blank. It will accelerate the tool wear.
The machining allowance is small and the surface roughness is required to be low, so the CBN end mill or ceramic end mill should be used.

The end milling cutter with carbide insert can be used for machining groove, concave surface, convex surface and blank surface.

The end milling cutter with cemented carbide can be used for powerful cutting. Milling the surface of the blank and rough machining the hole.
When machining the groove with high accuracy requirements, the end milling cutter with diameter smaller than the groove width can be used. Firstly, the middle part of the groove is milled, and then the two sides of the groove are milled by using the radius compensation function of the cutter until the accuracy requirements are met.
When drilling on CNC milling machine, the drill die is generally not used. When the depth of the hole is about 5 times of the diameter, it is easy to break the drill bit. Fixed cycle program can be used to advance and retreat automatically for many times to facilitate cooling and drainage. Before drilling, it is better to drill a central hole with a central drill or to drill the bottom hole with a section drill with good rigidity for positioning

When drilling on the milling machine, the drilling die is not generally used. When the depth of the hole is about 5 times of the diameter, it is easy to break the drill bit, and fixed circulation can be used

ken.tang @ chengcg.com

Key operation points of CNC machining center

As a skilled operator, you must understand the requirements of processing parts, process route, machine characteristics before you can operate the machine to complete the processing tasks. Operation points:

1) In order to simplify the positioning and installation, each positioning surface of the fixture should have accurate coordinate dimensions relative to the machining origin of the machining center.

2) In order to ensure that the orientation of the parts is consistent with the orientation of the workpiece coordinate system and the machine coordinate system selected in the programming, and the directional installation.

3) After a short time of disassembly, it can be changed into a fixture suitable for new workpiece. As the auxiliary time of machining center has been compressed very short, the loading and unloading of supporting fixture can not take up too much time.

4) The fixture should have as few components as possible and high stiffness.

5) The fixture should be open as far as possible, the space position of the clamping element can be low as possible, and the installation fixture should not interfere with the tool path of the working step.

6) Ensure that the processing content of the workpiece is completed within the stroke range of the spindle.

7) For the machining center with interactive worktable, due to the movement, up support, down support and rotation of worktable, the fixture design must prevent the space interference between fixture and machine tool.

8) Try to finish all the processing contents in one clamping. When it is not necessary to replace the clamping point, special attention should be paid not to damage the positioning accuracy due to replacing the clamping point. If necessary, it should be explained in the process documents.

9) For the contact between the bottom surface of the fixture and the worktable, the flatness of the bottom surface of the fixture must be within 0.01-0.02MM, and the surface roughness shall not be greater than ra3.2um.

ken.tang@chengcg.com

The importance of CNC machine tool spindle

Machine tool spindle refers to the machine tool to drive the workpiece or tool rotation axis. It is usually composed of spindle, bearing and transmission parts (gear or pulley). In addition to planer, broaching machine and other machine tools whose main motion is linear motion, most machine tools have spindle components. The motion accuracy and structural stiffness of spindle components are important factors to determine the machining quality and cutting efficiency. The main indexes to measure the performance of spindle components are rotation accuracy, stiffness and speed adaptability.

For the modular design of CNC machine tools, simplify the structure of machine tools, improve the performance of machine tools

a. Simplify the structure and promote the modularization of machine tool structure

Motorized spindle can form standardized and serial products according to the use, structure, performance parameters and other characteristics, which can be selected by the host machine, so as to promote the modular structure of the machine tool.

b. Reduce the cost of machine tools and shorten the development cycle of machine tools

The development of motorized spindle is changeable and easy to form a series of standardized products.

c. Improve machine performance and reliability

The reliability of CNC machine tools with motorized spindle structure is improved due to its simplified structure and reduced transmission and connection links; the motorized spindle functional parts with mature technology, perfect function, excellent performance and reliable quality make the performance of the machine tools more perfect and the reliability further improved.

d. Realize the special requirements of some high-grade CNC machine tools

Some high-end CNC machine tools, such as parallel motion machine tools, pentahedral machining centers, small hole and super small hole machining machines, must use motorized spindle to meet the perfect functional requirements.

ken.tang @ chengcg.com

Safe operation of CNC machining

No matter what products we process or what operations we carry out, the most important thing is our safety. We can’t underestimate this aspect. Its influence is very big, and so is CNC processing. So how should we do the safe operation of CNC processing?

1) Try to install the material first and then the cutter, so as to prevent the hand from touching the cutter when installing the material. If the cutter has been installed, when loading the material, the worktable should be moved to the outside to ensure that the material will not interfere with the cutter, so as to avoid injury or breaking the cutter.

2) When disassembling the tool in CNC machining, we must first observe whether the spindle stops rotating.

3) Don’t hold or pinch the edge of the tool when unloading the tool to avoid the blade scratch.

Dongguan CNC processing

4) The spanner should be placed in the tool storage area after use, and it is not allowed to be placed on the y-axis shield or crossbeam.

5) In the process of machining, the operator is not allowed to observe the cutting position closely to prevent chips from crashing into the eyes.

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

7) When pausing to observe the gap of CNC machining, the worktable must be moved away from the cutting position.

ken.tang @ chengcg.com

CNC machining center spindle does not rotate solution

Many CNC machining center friends do not know much about mechanical equipment, so in the work will encounter some problems, if you encounter CNC machining center spindle computer gongs do not turn, how to deal with it? In addition, the machine has not prompted any alarm information. What should you do at this time?

CNC machining center of computer gongs, in use, the spindle of CNC machining center of computer gongs does not rotate, which is a knife arm type tool magazine. When processing, the spindle does not rotate suddenly, and there is no alarm signal. And all the three axes can move normally. After giving a speed command in MDI mode, the spindle will not move a bit. At first, it was suspected that the shift signal was incorrect. After disassembling the z-axis gearbox, it was found that the shift of the spindle gear was normal and in place, and the in place signal was correct. But the spindle doesn’t rotate. In principle, if the spindle encoder or spindle is not powered on, it will cause an alarm. Therefore, the above two suspicions are eliminated, and the solutions to such problems are as follows:

Solution 1: first of all, you need to know whether you can see the parameters after 9000, and if you can, whether the parameters have been changed. I have encountered such a situation, is 0i-MC system, each axis is normal, that is, the spindle does not rotate. Later, the parameters after 9000 were changed.

Solution 2: there was an oi-m in the company before. It was found that the pneumatic valve of the knife arm was stuck. After the tool change, the knife arm should be ready for the next knife, but the knife arm was not put down, and there was no alarm. After the valve change, it was ready. And whether there is a hydraulic fixture, the fixture is not tightened, or the clamping signal is disconnected.

Solution 3: first take a look at the spindle monitoring, and turn the spindle manually to see if there are any values? Is the value right? The main shaft doesn’t rotate. There is no monitoring value, adjust the distance, or replace it with a new speed detection.

ken.tang @ chengcg.com

Influence of CNC machining tool material on quality

Over the years, users in accordance with the standard, interchange the use of a variety of tool manufacturers produced by the milling cutter and blade. However, these standards make various restrictions on milling cutters and inserts, including the shape and thickness of the inserts, the inscribed circle of the cutting inserts, the size of the holder and wedge clamping parts, and the size of the cutter body. Due to the limited design range of blade material, edge and chip breaking groove, the tool suppliers and users who abide by the standard are limited by the machining function.

However, today, the concept of milling cutter tends to be flexible, which provides tool developers with the freedom to adopt new tools and blade design. These designs can be optimized, and the use of new tool concept can better solve the problems of machining safety, accuracy, appearance quality, metal removal rate, tool overhang, high-speed cutting, and the ability of different cutting paths.

Today’s milling tools are constantly optimized to meet the needs of modern production, machine tools and data, and are widely accepted by all industries. The new tool can remove metal several times faster, with smaller cutting force and better orientation. Its typical runout is only a fraction of the old standard tool. Therefore, the machining tolerance can always be controlled in a smaller range, and the loss of cutting edge is also smaller and more ideal. The axial and radial runout are very small, which means that the accuracy of the cutting edge is improved, so the appearance quality of the workpiece is better, the tolerance is smaller, the tool life is longer, and the cutting load is more uniform, so as to improve the cutting speed and reduce the noise, vibration and loss.

The use of tools also helps to increase spindle speed, high-speed feed and hard part milling, and expands the opportunities for dry cutting. The design of these cutting tools is more concise, and the workload and time required for adjustment and maintenance are very small. The cutter body is rigid and accurate in size. It is made of pre hardened steel, which ensures that the blade is accurately and firmly installed on the milling cutter body, and the appropriate pitch can be selected according to different applications.

The new milling tools use the blade material and groove type developed for specific data or process. The functions and achievements of the new milling tools with these blades are far better than those of ISO or ans standard tools and blades. Compared with most standard inserts, modern new inserts and tools can provide larger rake angle and more complex groove, thus reducing the cutting force and forming the synergistic effect of faster and more stable metal removal.

ken.tang @ chengcg.com

Deformation of CNC machining machine parts

Mechanical parts processing usually have some problems, such as the workpiece deformation in the processing process, how to do, how to do well?

In order to avoid this kind of deformation, it is necessary to select the appropriate clamping point, and then select the appropriate clamping force according to the position of the clamping point. Therefore, the clamping point and supporting point of the workpiece should be kept as far as possible to make the clamping force act on the supporting part and make the clamping point closer to the processing surface, so as to avoid deformation.

What are the requirements for machining mechanical parts

When the clamping force acts on the workpiece, the order of the clamping force should be considered, and the clamping force should not be too large. In order to balance the cutting force, the clamping force should be applied at the end. It is also necessary to increase the contact area between workpiece and fixture or use axial clamping force. The most effective way to solve the clamping deformation is to improve the stiffness of the parts. The increase of contact area between workpiece and fixture is helpful to reduce the deformation of workpiece in the process of clamping.

What are the requirements for machining mechanical parts

Workpiece deformation caused by material and structure of workpiece

The deformation is directly proportional to the shape complexity, aspect ratio and wall thickness, and to the stiffness and stability of the material. Therefore, in the design of parts, the influence of these factors on the deformation of the workpiece should be reduced as far as possible. Especially the structure of large parts should be more reasonable. Before machining, the hardness, porosity and other defects should be strictly controlled to ensure the quality of the blank and reduce the deformation of the workpiece.

ken.tang @ chengcg.com

CNC computer gong processing feed parameter setting

1、 Varieties and characteristics of tools commonly used in CNC computer gong processing

CNC computer gong machining tool has the characteristics of high speed, high efficiency and high degree of automation. It usually includes general tool, general connecting tool holder and a small number of special tool holders. The tool holder needs to be connected with the tool and installed on the power head of the machine tool, so it has been gradually standardized and serialized. There are many ways to classify CNC tools.

According to the tool structure, it can be divided into three parts

Integral type;
Mosaic type, welding or clip type connection, clip type can be divided into two situations: non transposable and transposable;
Special type, such as compound cutting tool, shock absorption cutting tool, etc.

According to the data used to make the cutting tool, it can be divided into:

High speed steel cutting tools;
Cemented carbide tools;
Diamond tools;
Other information tools, such as CBN tools, ceramic tools, etc.

From the cutting process can be divided into

Turning tools, extra round, inner hole, thread, cutting tools, etc;
Drilling tools, including drill, reamer, tap, etc;
Boring tools;
Milling tools, etc.

In order to get used to the requirements of CNC machine tools for tool durability, stability, easy adjustment, replaceability, etc., in recent years, the clip type indexable tool has been widely used, with the number reaching 30% – 40% of all CNC tools, and the metal removal amount accounting for 80% – 90% of the total.

2、 CNC computer gong processing tool selection

Tool selection is carried out in the state of human-computer interaction of CNC programming. The tool and tool holder should be selected accurately according to the processing capacity of the machine tool, the function of workpiece data, processing procedures, cutting parameters and other relevant factors. The general criteria for tool selection are: convenient adjustment, good rigidity, high durability and accuracy. On the premise of satisfying the machining request, the shorter tool holder should be selected as far as possible to improve the rigidity of tool processing.

When selecting the cutting tool, the dimension of the cutting tool should be used to the external dimension of the workpiece to be processed. In production, the end mill is often used for the processing of plane parts; when milling plane, the cemented carbide cutter should be selected; when machining boss and groove, the high speed steel end mill is selected; when machining rough surface or rough hole, the corn milling cutter with cemented carbide cutter can be selected; when machining some three-dimensional surface and variable bevel angle, the ball end mill and ring mill are often selected Cutter, taper cutter and disc cutter.

In free-form surface machining, because the end cutting speed of the ball head tool is zero, in order to ensure the machining accuracy, the cutting line spacing is usually very close, so the ball head is often used for surface finishing. The flat head tool is superior to the ball head tool in terms of surface processing quality and cutting power. Therefore, as long as it can not be cut, whether it is rough or finish machining of curved surface, the flat head tool should be selected first. In addition, the durability and accuracy of cutting tools are closely related to the quotation of cutting tools. It is necessary to pay attention to that in most cases, although the cost of cutting tools is added to the selected cutting tools, the improvement of processing quality and processing power can greatly reduce the total processing cost.

In the machining base, all kinds of tools are separately installed on the tool magazine, and the tool selection and tool change actions are carried out at any time according to the program rules. Therefore, it is necessary to select the standard tool holder, so that the standard tools used in drilling, boring, expanding, milling and other processes can be quickly and accurately installed on the machine tool spindle or tool magazine. The programmer should know the structural dimension, adjustment method and adjustment scale of the tool holder used on the machine tool, so as to determine the radial and axial dimension of the tool when programming. At present, China’s processing base adopts TSG East-West system, with straight shank (three standards) and taper shank (four standards), including 16 different kinds of toolholders.

ken.tang @ chengcg.com

Environment temperature and humidity of CNC machining

When working, we need to see whether the surrounding environment is suitable for processing, and whether its requirements are up to standard. These are the things we should pay attention to,

Environmental temperature and humidity requirements. CNC machining CNC lathe generally requires the use of constant temperature environment, in order to ensure the working accuracy of CNC machine tools, generally requires a constant temperature of about 20 ℃. A large number of practices have proved that the failure rate of CNC system increases greatly in summer high temperature period, which is easy to cause collision accidents.

Humid environment will also reduce the reliability of CNC lathe operation, so we should take dehumidification measures to avoid circuit short circuit, causing CNC system misoperation and collision accidents.

At the same time, the CNC lathe is required to keep away from the vibration sources such as forging equipment, electromagnetic interference, electric welding machine, wire cutting machine and EDM machine.

ken.tang @ chengcg.com

CNC computer gong processing method (Part 3)

Clear corners:

The corner clearing here is the two-dimensional dead corner, which is the part that has not been reached in the previous process. If the light knife needs to go to the place, it should clear the corner first and then the light knife. If the angle is too small and deep, it can be divided into several knives. Don’t use a small knife to clear too many places.
Clear three-dimensional corner: open some small slots, some three-dimensional corner.
Easy to break the knife, we must consider such as thin knife, too long, processing capacity is too large (mainly Z direction, depth direction).
Tool path: only small angle (r0.8) and two-dimensional plane angle can be cleared by using two-dimensional shape; parallel tool path can be used; contour contour can be used; there is a kind of surface that can not be reached by the tool and dead angle that can not be reached by the shape, it is necessary to seal the tool first and clear the angle finally, and small gap in large surface is usually sealed first.

Medium light:

Zhongguang: as a curved surface of steel and fine Gongcai Zhongguang.
Principle: when the big knife is rough, there is more margin between layers, which is a process to get better effect when the light knife is used. Thank you for your attention to CNC automation wechat: cncaut.
Features: fast cleaning, big knife flying, large feed and large spacing; no need to worry about the surface quality; flat workpieces do not need to be polished; workpieces with equal height profile do not need to be polished; when the contour is rough, the two processes can be put together in a smaller way, and the smaller one refers to the surface allowance and the distance between layers; The more hard the material is, the more medium light will be considered. The processing direction of medium light is better than that of light knife. In this way, the processing effect will be good and uniform.

Light knife:

Light knife is to meet the assembly requirements of various products and molds, so we should be very careful, according to different requirements to give different tool path settings and parameter settings.

The cutting height and the final height of the light knife are changed to 0, and the tolerance is designed within 1 thread, without filtering (the smaller the workpiece, the smaller the tolerance, and the tolerance will affect the appearance).
The front mold and parting surface should achieve the best finish, the back mold can be used twice, and other non matching and avoiding positions can be rough.
Tool path design is determined by the following factors:

Specific shape (such as plane and other surfaces), steep surface and flat surface.

Whether there is a sharp angle between the two sides (the sharp angle is separated).

Whether the requirements of the two parts are different (whether to leave allowance, the amount of allowance and the requirements of finish are different).

The problem of protecting surface in the light knife is a big problem. The machined surface must be protected according to the requirements of protecting surface. Range protection, zero protection regardless of error, height range and plane range; protection surface protection.

For the extension of the tool path, when the tool path is machined to the edge, it is better to make circular arc advance and retreat, otherwise the face will be slightly extended in advance.

The problem of lifting the knife in the light knife. It’s a waste of time to lift the knife, so try to avoid it.

Method 1: set the clearance (small gap) of knife lifting

Method 2: cover, seal the knife (small gap)

Method 3: avoid gap (large gap)

Method 4: extend to the same height in contour

For the problem of feed in the light knife, the first feed must be from the outside of the workpiece to avoid vibration and damage to the workpiece. All light knives must be equipped with feed.

Tool wear: when the workpiece is large, more tools are needed to finish the same workpiece.

The above is for you to share the content, I hope to help you.

ken.tang @ chengcg.com

Category Archive CNC Technology

Selection of cutting tools for CNC machine tools

Key operation points of CNC machining center

The importance of CNC machine tool spindle

Safe operation of CNC machining

CNC machining center spindle does not rotate solution

Influence of CNC machining tool material on quality

Deformation of CNC machining machine parts

CNC computer gong processing feed parameter setting

Environment temperature and humidity of CNC machining

CNC computer gong processing method (Part 3)

CNC Machining parts

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