chengcg – Page 25 – CNC Machining & Turning, Milling, Metal parts

Precision of computer gong forming

The content of mold precision includes four aspects: dimension precision, shape precision, position precision and appearance precision. Because the mold is divided into two parts: upper mold and lower mold, the position accuracy between the upper mold and the lower mold is the most important among the four kinds of accuracy.

3。 Mold precision is to serve the precision of products, high-precision products must be guaranteed by higher precision mold, mold precision generally must be higher than the precision of parts 2 or above.

Methods of improving die precision

1。 Precision guarantee of mould processing equipment

2。 Precision requirement of parts in mould manufacturing

①。 Mold material accuracy requirements

The processing tolerance of die steel shall be controlled within 300×300 + 0.005-0 ± 0.005300×500 + 0.01-0 ± 0.01500×800 + 0.01-0.01 ± 0.015800×1200 + 0.02-0.02 ± 0.02 ②. The accuracy requirement of die parts is a. Misumi guide pillar and guide sleeve series are used for guide parts affecting die precision, and the tolerance of superfinishing can be controlled within 0.002mm.

b。 The edge forming punch is made of Misumi standard material: SKD-11, hardness: 60-62hrc, edge shape: dregth punch is usually used for forming inner hole or cylinder shape of products. The precision of punching needle can be controlled within ± 0.01mm, and it can be about 2um for special requirements, and keep the mirror.

3。 The size of die gap is the main basis of die design and manufacturing accuracy. In order to ensure the product size accuracy, shape and position accuracy, and product quality (such as the quality of punch section and burr height), it is necessary to ensure the gap between the concave and convex dies.

4。 The construction precision of the mould is required. From the perspective of processing and assembly, the accuracy of mold base mainly includes the following aspects: a. The consistency of plane dimension and guide hole position of upper and lower formwork; B. Flatness and parallelism of large plane of formwork; C. Perpendicularity of guide hole to large plane; D. Perpendicularity between adjacent sides of formwork; e. The fitting accuracy between guide post and guide sleeve.

The main methods to ensure the accuracy of the mold base are as follows:

a。 One time processing method is that after the large plane of the template is processed, the upper and lower templates are clamped together, and the plane size and guide hole of two templates are processed at one time.

b。 One of the four guide holes is deviated from the symmetrical position to ensure the assembly orientation of the die.

c。 Datum is used for surface calibration.

d。 High precision guide post and guide sleeve are adopted.

e。 Improve the machining accuracy of parts.

②。 In order to ensure the accuracy of punch, from the perspective of processing and assembly, the accuracy of punch mainly includes: a. The shape and dimension accuracy of punch; B. Perpendicularity between adjacent sides of punch.

③。 From the perspective of processing and assembly, the accuracy of the die mainly includes: a. The shape and dimension accuracy of the die; B. Perpendicularity between adjacent sides of die; C. Perpendicularity of die side to large plane; D. Die position.

5。 The precision of forming processing is guaranteed. When processing the forming structure, whether it is processed by computer gong, EDM, WEDM or ordinary milling machine, coordinate processing method is adopted. The guarantee of the accuracy mainly depends on the accuracy of the machine tool and the accuracy of the operator’s calibration. It is considered that the concept of die precision should also run through the whole process of die design and manufacturing, just like the guidelines and guiding ideology of establishing enterprise product quality assurance and management system. In order to ensure the accuracy requirements of the closed loop of the die assembly dimension chain, strict control and management must be carried out on the key links and key factors affecting the accuracy of the die in the process of die manufacturing, outsourcing (including materials and standard parts) and the whole process of die assembly, die test, acceptance, packaging and transportation.

The most efficient computer gong processing method

The so-called most efficient processing method is that when reprocessing, it can be completed quickly. Its completion effect can not be underestimated. All kinds of complex products can be completed. So what is the most efficient processing method for computer gong processing?

The machining center is an efficient and high-precision CNC machine tool. The workpiece can be processed in multiple processes in one clamping. At the same time, it is equipped with a tool library and has the function of active tool change. These abundant functions of machining center determine the disorder of programming of machining center.

The machining center can realize the linkage control of three or more axes, so as to ensure the tool to process the disordered surface. In addition to linear interpolation and circular interpolation, the machining center also has various functions, such as processing fixed cycle, active compensation of tool radius, active compensation of tool length, graphic display of machining process, man-machine dialogue, active fault diagnosis, off-line programming, etc.

Machining center is developed from CNC milling machine. The biggest difference with CNC milling machine is that the machining center has the ability to exchange machining tools actively. After installing different tools in the tool magazine, the machining tools on the spindle can be changed through the active tool changing equipment in one clamping, so as to realize a variety of processing functions.

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.

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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.

About CNC Turniing

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.

About CNC Turniing

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.

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ken.tang @ chengcg.com

CNC computer gong processing method (Part 2)

CNC with EDM, copper way:

Under what circumstances do you need to be a copper company

If the knife can’t go down completely, it needs to be a copper Gong. In a copper Gong, there are still some that can’t go down. The shape is convex and needs to be subdivided.

The knife can go down, but the one that is easy to break also needs to be made of copper, which depends on the actual situation.

Products requiring spark pattern shall be made of copper.

If the copper alloy can’t be made, the bone position is too thin and too high, and the alloy is vulnerable to deformation. During machining, the alloy will deform and spark will deform. At this time, the insert is needed.

The East-West surface (especially the surface will be smooth and even) produced by copper Gong can overcome many problems in fine Gong and drawing.

When accurate shape is required or there is a lot of allowance, rough copper must be made.

The practice of tonggong

Select the surface to be made, complete the surface to be made, or extend the surface to be made, ensure that all edges of the copper are larger than the edges to be made, and do not damage the surface of other products at the same time, remove the unnecessary plane angle (the intersection with the plane angle is the deeper glue position), and make up the regular shape; find out the maximum shape of the copper, use one side boundary, and then project it to the supporting surface; Determine the size of the reference frame, cut off the supporting surface, and this copper map is basically completed; material preparation: length * width * height, length and width ≥ ymax and xmax as the reference frame, the actual length and width of copper material must be greater than the reference frame on the map. The height is equal to or greater than the theoretical dimension of the copper male + the height of the reference frame + the clamping height.

Drawing number determination:

When there is no ready-made machining surface, the center of the plane is to * *, the top is to zero, and the top surface is irregular (for copper), leaving a margin of 0.1, that is, when the collision number is 0 (z), the actual value is 0.1 lower than the figure.
When there is a ready-made processing surface, make the ready-made surface on the drawing 0 (z), the plane can be divided into the middle, otherwise with the ready-made edge collision number (unilateral) processing surface, check the actual height, width, length and drawing differences, according to the actual material to program. In general, the size on the drawing is processed first, and then the shape on the drawing is processed.
When you want to process more than one bit, the first bit (standard bit) needs to set the reference gongs of other bits well. The length, width and height need to be set. All the next processing datum should be based on the surface that has been processed for the last time. Thank you for your attention to CNC automation wechat: cncaut.
Positioning of the insert: put it in the whole, pad the lower part with a certain height, and then raise the height of the drawing. The plane is divided according to the whole, and the height is locked with screws according to the figure. If it is square, it can be divided directly. If it is rough, it can be divided by the maximum shape. Cut a fixture, and determine the relative position of the insert drawing and the fixture according to the fixture, and then put the drawing * * in the center of the fixture.

Tool path selection for roughening:

Surface trenching

The key is the selection of range and surface.

The area of tool path processing is: the selected surface in the selected range is the end surface, and all the places that the tool can go down from the highest point to the lowest point is the principle. The selected face should be the full face, and the boundary should only be the area to be processed. The distance of the non face should be less than half the tool diameter, because other faces have enough margin, so it is automatically protected. It is better to extend the lowest line, because there is an R Gong at the lowest point.

Selection of cutter: if the cutter can’t feed in helix or oblique line or the area that can’t be machined, the area that can’t feed in the cutter will be sealed and left for secondary roughening.

Before using the light knife, make sure to cut all the uncut areas, especially the small angles, including the two-dimensional angle, the three-dimensional angle and the sealed area, otherwise the knife will be broken. Secondary roughening: generally use three-dimensional trenching to select the range, flat bottom cutter, and use plane trenching and contour cutter path. In the case of no damage to other surfaces, the center of the tool is to the selected boundary. Generally, the boundary is not refined. The fast two-way angle depends on the situation. The angle of spiral feed is 1.5 degrees, and the height is 1. When the groove shape is strip, the oblique feed is used. Generally, the filter is turned on. Especially for the rough surface, the feed plane should not be low to avoid tool collision, and the safety height should not be low.

Back knife: generally, relative back knife is not used, but absolute back knife is used. When there is no island, relative back knife is used.

Plane trenching

Milling all kinds of plane, concave slot, when milling part of the open plane, you need to define the boundary, the principle can feed (more than one tool diameter), the open part is more than half a tool diameter, close the periphery.

Shape

When the selected plane is suitable for contour layering, lift the cutter by contour layering (plane contour). When the lifting point and the cutting point are one point, it is not necessary to lift the cutter. Generally, lift the cutter on z plane, and do not use the relative height as far as possible; the direction of correction is generally right correction (along the cutter).

Tool path setting of mechanical correction

The correction sign is 21, the computer correction is changed, the mechanical correction is changed, the feed is vertical, and where the knife can not pass, the R is increased, leaving no allowance.

Contour contour

It is suitable for closed face, open face, if it has four circles, it needs to seal the surface, if it has four circles or not, it needs to choose the range and height (certain arc feed roughening). It is used for roughening: the machining distance in any plane is less than one tool diameter, if it is greater than one tool diameter, it needs to use a larger tool or two contour.

Surface streamline

With the best uniformity and dry brittleness, it is suitable for light knife and can replace contour in many cases.

Radial knife path

It is suitable for large hole in the middle. Note: the knife is not sharp, the knife is too long, the workpiece is too deep to walk around, not up and down; the sharp corner of the workpiece on both sides of the surface should be divided into two paths, not over the past, the edge of the light knife is best extended (with arc forward and backward knife).

About CNC Turniing

ken.tang @ chengcg.com

Significance of dividing CNC machining into stages

Experienced CNC processing masters all know that CNC processing needs to be carried out in stages, so what is the significance of doing so? The main points are as follows:

(1) Rational use of CNC processing equipment

With large rough machining allowance and large cutting amount, the machine tool with high power, good rigidity, high efficiency and low precision can be used. High precision machine tool is used because of small cutting force and small damage to machine tool. This gives full play to the respective characteristics of the equipment, which can not only improve productivity, but also extend the use of precision equipment.

(2) It is convenient to find the defects of CNC blank in time

All kinds of defects (such as porosity, sand inclusion and insufficient allowance) of the blank can be found after rough machining, which is convenient for timely repair or scrapping, so as to avoid unnecessary waste caused by continuous machining.

(3) Easy to arrange heat treatment process

After rough machining, stress relief heat treatment is usually arranged to eliminate internal stress. Before finishing, quenching and other final heat treatment should be arranged. The deformation caused by heat treatment can be eliminated by finishing.

(4) Guarantee CNC machining quality

In the rough machining of CNC parts, the metal layer cut out is thicker, the cutting force and tightening force are larger, and the cutting temperature is also higher, which will cause greater deformation. According to the processing stage, the machining error caused by rough machining can be corrected by semi finish machining and finish machining, so as to ensure the machining quality of parts.

About CNC Turniing

ken.tang @ chengcg.com

CNC machining center spindle fault

The spindle is the power auxiliary device of CNC machining center. The spindle drives the workpiece to rotate to process the workpiece of the rotating body. Spindle is an important guarantee for high-speed and high-precision machining of CNC machining center, so the maintenance methods and skills of spindle fault are the basic knowledge that operators and maintenance personnel of CNC machining center must master. In the operation of CNC machining center, the spindle will inevitably have some faults. What is the specific reason?

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 transmission spindle with variable speed gear, the main transmission spindle with belt transmission, the dual motor drive spindle and the motor spindle integrated spindle. No matter what type of spindle application, the common faults in use are as follows:

Overload.

Fault causes: excessive cutting amount, frequent forward and reverse rotation, spindle motor fault, spindle drive device fault.

The spindle does not rotate

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

The spindle speed deviates from the command value

Fault causes: motor overload, CNC system output spindle speed command output problem, speed measuring device failure or speed feedback signal disconnection.

Abnormal noise and vibration of spindle

Cause of failure: it usually occurs in the process of deceleration, and there is something wrong with the spindle drive device, such as the regeneration circuit fault in AC drive.

Computer gong processing to prevent collision

Under the condition of such high speed and structure, once the operator has no time to press the emergency stop button due to programming and operation errors, the tool has collided with the workpiece. In order to prevent machine tool and personal troubles, the following methods can be adopted in programming and operation (take FANUC system as an example).

The origin of the workpiece coordinate system set by the programmer should be outside the workpiece blank, at least on the workpiece surface.

Under normal conditions, the origin of workpiece coordinate system can be set anywhere, as long as the origin has a certain connection with the origin of machine coordinate system. But in practice, if the command value is zero or close to zero, the tool will point to zero or close to zero. In milling, the cutter will run to the table or fixture base surface; in turning, it will run to the chuck base surface. In this way, the tool will penetrate the workpiece and point directly at the reference plane. At this moment, if you want to move quickly, you will have trouble.

FANUC system generally set: when the decimal point is omitted, it is the minimum input unit, generally μ M. When the decimal point is omitted, the input value will be reduced to one thousandth. At this moment, the input value will be close to zero. Perhaps, due to other factors, the tool should be separated from the workpiece, but the practice is not separated from the workpiece and into the workpiece. In this case, the zero point of the workpiece coordinate system should be set outside the workpiece or on the base surface of the worktable (or fixture), and the result will be different.

Programmers and operators should be more careful about decimal points when writing programs.

FANUC system is the minimum setting unit when the decimal point is omitted, while most domestic systems and some European and American systems are mm when the decimal point is omitted, which is the input method of calculator. If you are used to calculator input method, there will be problems in FANUC system. Many programmers and operators may use both systems. In order to prevent the scale from getting smaller due to decimal point, decimal point should be added to the input program of calculator. But it’s not because of the habit of doing something like this.

In order to make the decimal point eye-catching, the isolated decimal point is usually written as “. 0” in programming. Of course, when the system is executed, the zero after the decimal point of the value is ignored.

When adjusting the workpiece coordinate system, the operator should set the reference point beyond the physical (geometric) length of all tools, at least on the tool position of the longest tool.

For the workpiece coordinate system on the workpiece installation drawing, the operator obtains it by setting the machine coordinate system offset on the CNC machining center. In other words, the operator sets a reference point on the CNC machining center, finds the scale between the reference point and the zero point of the workpiece coordinate system set by the programmer, and sets this scale as the workpiece coordinate system offset.

On the lathe, the datum point can be set on the base of turret rotation, the datum tool tip or other directions. If there is no additional movement, the zero of the programmer’s instruction is the zero position of the tool rest (CNC machining center) moving to the offset. At this moment, if the datum point is set at the base of turret rotation, the turret must collide with the workpiece. In order to avoid collision, the datum point of CNC machining center should not only be set outside the tool holder, but also outside all tools. In this way, even if the tool is installed on the tool holder, the datum point will not collide with the workpiece.

In CNC machining center, the datum points of X and Y axes are on the axis line of spindle. However, the reference point of the z-axis can be set at the spindle end or at a point other than the spindle end. If it is at the spindle end, when the command is zero, the spindle end will reach the zero position specified in the coordinate system. At this moment, the end key of the spindle end will collide with the workpiece: if the spindle is equipped with a tool again, it will collide with the workpiece. To ensure that there is no collision, the reference point on the z-axis should be set beyond all tool lengths. Even if no other motion is attached, the reference point will not hit the workpiece.