CNC Technology – Page 20 – CNC Machining & Turning, Milling, Metal parts

The standard of CNC programming program

It takes 1-2 months to be very familiar with. The automatic programming software is a bit complicated and needs to be learned. But it is not difficult for CAD.

In practice, one is:

Readable, well organized, and understood by everyone in the operator.
The program instructions should be as few as possible for the purpose of simple, practical and reliable. From the point of view of programming, I think that the instruction G00 G01 and other auxiliary instructions are convenient for programming.
Easy to adjust. Parts machining accuracy need to be fine tuned is the best without changing the plan. Tool wear, for example, adjustment, just change the tool offset table length, radius.
Easy to operate. Programming will be based on the characteristics of machine operation, conducive to observation, inspection, measurement, safety, and so on. The same parts, for example, the same processing content, in the vertical machining center and horizontal machining center processing, are certainly not the same.

In machining, the simplest method is the best. As long as there is practical experience of the peer, will certainly agree with this sentence!

Skillfully operate CNC machine tools

This requires 1 – 2 years of research, operation delicate feeling, beginners, especially college students, know how to do, can not listen. Learn in this process: operation mode of installation system, clamp, datum alignment, knife, setting zero point offset, setting tool radius, length compensation, compensation, handling of tool and loading and unloading, grinding tools, measurement, skilled use of vernier caliper, micrometer, dial indicator, dial indicator, rod diameter indicator, etc.

CNC machining process of complex parts

It is difficult to guarantee the size of the curve groove at the lower end of the front side of the part, and the two 90 ° notches are not closed, so it is necessary to close the auxiliary line before programming.

There are two ellipses in different directions on the inner contour edge of the back, inner and outer hexagonal petals composed of arcs in the center, and two arc curve islands at the top and bottom. These elements need to be rounded in processing, so it is more convenient to choose a reasonable shape.

Analysis of parts processing technology

Using CAXA to manufacture engineering parts, there is no need to draw a complete part for reprocessing. Firstly, the downtime is long and the processing time is wasted. Secondly, when selecting local processing, the elements between parts will interfere, which is not convenient to draw the program track.

The software supports rough and finish machining only by drawing the contour line of the part when machining the plane contour elements. Surface machining can be programmed by solid or surface. In order to realize local machining, curved surface must be used, and some finishing commands can only be selected by curved surface.

The rough machining command can not only realize rough machining, but also be used as finish machining command.

The finishing command can use the track translation to form multiple levels and connect the tracks into a whole rough machining command; the rough machining command can change a layer of processing track into a finishing command by setting the layer height.

The plane contour elements of CAXA Manufacturing engineer can use the plane area rough machining and contour finish machining to complete the rough and finish machining of parts, and can also use the contour finish machining to do the rough machining. Surface roughing can use contour roughing, parameter line finishing and three-dimensional offset surface finishing commands for roughing and finishing.

Due to the high dimensional accuracy in the drawing, it is decided to adopt rough machining, semi finishing and finishing to achieve dimensional accuracy. Semi finishing and finishing adopt the same cutting tools and cutting parameters, which can correct various geometric errors of the cutting tools and elastic deformation of the parts. It is easy to ensure the size, and finish machining is also required for the important bottom surface.

The part is processed by FANUC CNC machining center, all tool paths are generated according to FANUC post format, and transmitted by CAXA’s own communication function according to FANUC settings, and large surface programs are processed online; the later processing programming ends with tool path.

Methods of improving CNC machining

(1) The size and structure of all kinds of parts are very different, and the universality of machine tools and other process equipment is not high.

(2) Many companies are usually faced with the production task of multi variety, small batch and short production cycle, so the process system is required to have a higher response speed.

(3) The structure of product parts is complex and the processing is difficult.

(4) Thin wall, easy to produce processing deformation. There are a lot of thin-walled and deep cavity structures, which are typical weak rigid structures.

(5) It is difficult to select cutting tools and cutting parameters. Because the development of tool industry can’t catch up with the development and application of new materials, and lack of the support of machining database.

So how to improve the efficiency of CNC machining? Generally speaking, the methods to improve the machining efficiency of CNC machine tools are as follows:

1、 Change the understanding of numerical control technology.

Numerical control technology is a comprehensive technology, in addition to the numerical control machine tool, there must be corresponding supporting technology and personnel support, especially in the numerical control processing process, people play a decisive role, the technical ability of management personnel, engineering and technical personnel, engineering maintenance personnel and operators will affect the production efficiency of numerical control machine tool.

2、 Develop effective tool management measures.

For example, the tool is pre adjusted to reduce the installation and adjustment time of the tool on the machine tool, and the tool is managed through the management system to reduce the errors caused by manual management.

3、 Fixture management.

Because the selection of fixture is directly related to the installation time and measurement time of workpiece, the management of fixture should be realized.

Computer gong processing workpiece collision number

After the workpiece is placed on the pad iron, it is necessary to pull the table for the workpiece datum according to the drawing requirements. For the workpiece that has been ground on six sides, it is necessary to check whether its verticality is qualified.

The nut must be tightened after the work-piece is pulled to prevent the work-piece from shifting during the processing due to the loose clamping; pull the work-piece again to ensure that the error does not exceed the tolerance after the clamping.

Number of workpieces touched

For the clamped workpiece, the contact head can be used to set the processing reference zero position. The contact head can be used in photoelectric type and mechanical type. There are two kinds of methods: middle collision number and unilateral collision number

Photoelectric static, mechanical speed 450 ~ 600rpm. Manually move the x-axis of the worktable according to the collision number to make the collision number head touch one side of the workpiece. When the collision number head just touches the workpiece and the red light is on, set the relative coordinate value of this point to zero. Then manually move the x-axis of the worktable to make the collision number head touch the other side of the workpiece. When the collision number head just touches the workpiece, record the relative coordinate at this time.

According to the relative value minus the diameter of the collision head (i.e. the length of the workpiece), check whether the length of the workpiece meets the requirements of the drawing.

Batch conditions of computer gong processing

The type of blank should be determined according to the material, shape and size of the parts, and the batch and production conditions of the parts should also be considered in the computer gong processing. Transmission shaft, small diameter, the diameter of each section of the outer circle is not big, optional round steel blanking. In order to save materials and processing time, if the gear shaft has large quantity and forging conditions, the forging blank should be selected; otherwise, round steel cutting should be selected. The material of bearing cover is cast iron, and the blank should be cast. Processing gear, its material is 40 steel, and the outer circle diameter is small, small outer circle is short, optional round steel blanking. Due to the large diameter of the outer circle and hole of the gear, the gas cutting of the steel plate with the corresponding thickness can be selected for a single piece, and the forging can be selected for a large batch to forge the ring-shaped blank. In this way, the material can be saved, the processing time can be reduced, and the mechanical properties of the forging blank are better.

Determine the processing sequence of parts

The processing sequence should be determined according to the type, structure, size, processing accuracy, surface roughness, heat treatment and other technical requirements of the blank.

Determine the processing procedure

Determine the machine tool, workpiece clamping method, processing method, processing size and detection method used in each process, including the allowance for the next process. Generally, for small and medium-sized parts, the outer cylinder and the inner cylinder and the plane in CNC machining all refer to the unilateral allowance. In the small batch production of a single piece, the larger the blank size is, the smaller the blank size is. Total allowance: 3-6 mm for hand molded castings, 3-7 mm for free forging or gas cutting parts and 1.5-2.5 mm for round steel. Process: semi finish turning is 0.8-1.5mm; high speed finish turning is 0.4-0.5mm.

Determine the cutting amount and man hour quota

The cutting parameters of single piece and small batch production are generally selected by the producers themselves, and the man hour quota is set by the management personnel.

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 of spindle in CNC machining

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.

CNC machining center spindle abnormal noise is most operators will encounter things, understand the cause of the failure, we should take what measures to solve it?

When the machining center is in use, some customers often find that the spindle is transported by belt. After a long time of use, there will be abnormal noise. When the forward transmission and reverse transmission are switched, there will be noise. According to years of assembly experience, it is determined that most of the problems are caused by the belt, The belt tension at the joint of servo motor and spindle is too tight, which leads to the phenomenon of belt slipping, so the spindle will make abnormal noise.

Another situation is that the tension of the belt connecting the servo motor is not enough, so it will appear that the belt of the motor is too loose, which can be seen intuitively. When the machining center is used for heavy chip, it will slip and make abnormal noise. After the machining center is used for a long time, the belt will be worn, which is part of the cause of abnormal noise.

After the abnormal noise of CNC machining center spindle occurs, some economical customers will choose to replace the drive wallet. After the replacement, the belt drive gear and the tooth profile of the motor and the spindle do not match, and they can make do with it. However, there will be a lot of abnormal noise during use, which seriously causes the wear and damage of the gear of the servo motor and the spindle. It is suggested to observe whether the belt model purchased is the same as that replaced. 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?

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

Computer gong processing tool

The main matching dimensions of parts are guaranteed by computer processing, so it is very important to choose a reasonable tolerance, especially some product design drawings do not consider the matching problem. Bottom, surface, shell fit, shape is no doubt 0 to 0 fit, positioning is guaranteed by the mouth, concave mouth and convex mouth tolerance is generally 0.1 mm, unilateral. The fit on the big body is like a transparent mirror. The shape of the general accessories is 0.1 ~ 0.2 smaller than the size on the big body. The shape of the movable accessories on the big body, such as buttons, is 0.1 ~ 0.5 smaller than the shape on the big body. The surface shape of the accessories on the big body is generally consistent with the surface shape on the big body, which can be removed from the big body.

1、 Exit angle (draft angle)

All plastic molds should have a mold angle, otherwise they will be scratched. If it is not indicated in the drawing, you can discuss with the mold maker. The mold angle is generally 0.5 ~ 3 degrees. If the mold is etched, the mold angle should be larger, 2 ~ 5 degrees, depending on the thickness of the etched pattern.

2、 Cutting problem

Most of the time, when the cutter is just milled, the amount of cutting is relatively large, which is easy to cause the cutter to break and bounce. At this time, you can first roughen the lower cutter position, or lift the cutter away, or lower the cutter outside the material in the daytime. In a word, this problem should be fully considered. Grab the knife, spring the knife, drop the knife, when the processing capacity is relatively large, the knife clip is too long, the knife is too small, this often happens. When the processing capacity is relatively large, especially when the concentration feed is large, it is easy to occur. For example, when the depth of the smooth side is 50 mm and the diameter is 3 / 4, we can process it in 25 mm twice, so it is not easy to occur. Tool clamping is too long, the length of the tool is very important for processing, should try to clamp short, beginners are easy to ignore this problem, the program paper must indicate the length of the tool clamping. It’s easy to grab the knife when turning the corner. The solution is to use a smaller knife to clear the corner layer by layer, and then change the larger knife to smooth the side.

3、 Sharpen a knife

The shapes of computer gongs are different, so we often need to grind all kinds of knives. When all kinds of molding knives are worn out, we also need to grind them. Only when we reach the following points can we grind a usable knife.

The four corners of the tool should be the same height.
A is higher than D.
The forward (tool face) of the tool is higher than the back, that is, it has a certain back angle.

4、 Milling direction

The reason is that the rigidity of the computer gong is relatively good, it is not easy to let the cutter, the back clearance is small, and the milling shape or inner groove is left compensation. When machining left and right symmetrical shapes, the profile tool path cannot be mirrored, otherwise the processing effect of the mirrored side is not good. In order to communicate with the operator of the machine tool, the program paper should include:

Program name
Tool size and length
Method of machining tool path
Machining allowance
Rough or light knife

Computer gong processing vertical processing

The height of the vertical machining center is limited, which reduces the processing range of the workpiece, which is the disadvantage of the vertical machining center. However, the workpiece clamping and positioning is convenient for vertical machining center; the cutting path is easy to observe and debug, the program inspection and measurement is convenient, the problems can be found in time, and the treatment or modification can be stopped; the cooling conditions are easy to establish, and the cutting fluid can directly reach the cutting tool and machining on the surface; the three-axis and Cartesian coordinate system, intuitive feeling, conforms to the design point of view, and the chip is easy to eliminate, Surface treatment to avoid scratches.

Vertical machining center

Mainly used for:

Using grease and oil circulation in machining center will produce abnormal heating.
Spindle, need high-definition washing, high-speed bearing sealing place

working principle:

The use of compressed air flow pipe, transmission oil along the pipe caused by continuous flow, stirring and transportation of oil and gas processing center spindle part and other parts of the screw need lubrication. The constant pressure dry compressed air (bar) 5 – 8 continuous supply, according to the spindle and lubricating oil lubrication, screw oil and other parts of the fuel consumption different quantitative supply. Therefore, each lubrication circuit must use a separate micro pump power supply of oil. After the oil pump, it must enter the oil and natural gas mixing valve. In the oil and natural gas mixing valve, the compressed air flow blows into small oil drops and adheres to the wall to form an oil film. The flow direction of the air flow between the oil film and the pipe wall, and the thickness of the medium oil film gradually becomes thinner, but not together.

CNC machine tool processing principle, all kinds of processing tools, all kinds of workpiece processing tool path method, all kinds of workpiece feed and speed, cutting amount.

Maximum depth allowed for each cutting, actual m auxiliary function, s speed, t tool change, R radius, u, W are relative G: preparation command M: auxiliary command T: tool s: spindle speed, R: arc radius, and then p q R, where R means different.

What is the benchmark of computer gong processing

The broad meaning of benchmark is “basis”. The datum in mechanical manufacturing refers to the points, lines and surfaces used to determine the geometric relationship between the geometric elements on the production object. According to different functions and applications, datum can be divided into design datum and process datum, and process datum can be divided into process datum, positioning datum, measurement datum and assembly datum.

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

The movement of the workpiece and the movement of the tool on the drawing are used to change the shape and shape of the workpiece.

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

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. Datum on mechanical drawings are represented by capital letters a, B, C, D, etc. with a specific reference symbol with circle. When the reference symbol is aligned with the surface and its extension line or the dimension limit of the surface, the surface is taken as the datum. When the datum mark is aligned with the dimension line, it means that the solid center line of the dimension is taken as the datum.

Assembly benchmark refers to the precision used to determine the position of parts in components or products during assembly.

Measurement datum refers to the specification for the size and position of the machined surface to be measured during the inspection of parts. Positioning datum refers to the datum used for positioning the workpiece in the machine tool or fixture during machining.