chengcg – Page 43 – CNC Machining & Turning, Milling, Metal parts

Surface accuracy of CNC computer gong machining

In a broad sense, it refers to the process that all products can be manufactured by mechanical means; in a narrow sense, it refers to the process of making parts by special machinery such as the lathe, milling machine, drilling machine, grinding machine, stamping machine, die-casting machine, etc.

There will be some errors in machining. Let’s talk about the original error related to the initial state of the process system itself

① Principle error is the error of machining method.

② Geometric error of process system

The relative position errors between workpiece and tool exist in static state, such as manufacturing error of tool and fixture, adjustment error and installation error;

The relative position error of workpiece and cutter exists in the motion state, such as the spindle rotation error of machine tool, the guide error of guide rail, the transmission error of transmission chain, etc.

① The deformation caused by the force effect of the process system, such as the deformation caused by the stress deformation of the process system and the deformation caused by the generation and disappearance of the internal stress of the workpiece.

② Deformation caused by thermal effect of process system, such as the error caused by thermal deformation of machine tool, cutting tool and workpiece.

In the machining process, when the position relationship between the tool and the workpiece processing surface is reasonable, the machining surface accuracy can meet the processing requirements, otherwise it can not meet the processing requirements. CNC machining accuracy analysis is to analyze and study various factors when the machining accuracy cannot meet the requirements, that is, the possibility of various original errors, and take effective technological measures to overcome them, So as to improve the machining accuracy.

Common problems of CNC computer gong processing

First question:

The injection head is stuck in the gooseneck

Solution:

When the equipment is at normal temperature, try to rotate the hammer head. If it cannot be rotated, replace the sleeve and take out the hammer head.

If you want to quickly solve the problem of jamming, the best is the refueling pot. Precision mold processing

Second question:

In the process of punching, it will not be able to produce dozens of die materials. It will take a few minutes to continue to punch the precise mold processing

Solution:

Check whether there are bright spots on the top of the blanking head. If the cross-section is gray, it indicates that the nozzle is blocked. The temperature of the nozzle can be moderately increased. The time of leaving the nozzle can be reduced by 0.1 to 0.2 seconds, and the cooling water of the fixed mold is slightly turned down.

Third question:

It is easy to crack when casting thin-walled products

Solution:

This problem may be due to material problems, poor mold setting or improper selection of process parameters,

The proportion of waste material should not exceed 30%. The mold retention time should not be too long, about 3S per mm wall thickness, and the ejection delay should not be long, generally 0.5-2s.

Fourth question:

The material is hard and the tool is easy to wear

Solution:

The raw material ratio is used, and the gem blade specially produced for cemented carbide is used instead of recycled material.

Advantages of CNC computer gong processing

CNC computer gongs processing refers to the processing with CNC tools. CNC index controlled machine tool is programmed by NC machining language, usually G code.

The accuracy of the work is relatively high, and the quality of the processed products is guaranteed.
Even if there are multiple coordinates, there is no need to worry, because it can realize the linkage between the coordinates, and can process parts with complex geometry structure.
It is necessary to replace the processed parts, but only need to change the relevant data to realize the work and simplify the work
Because the computer gong is automatic, it can reduce the labor force and increase the productivity

Formulation of machining process flow

The technological process of machining includes, generally speaking, the process of changing the overall dimension and performance of the workpiece through a kind of mechanical equipment.

The working principle of machining process regulation is high quality, high yield and low cost, that is, under the premise of ensuring product quality, labor productivity can be improved and cost can be reduced as much as possible. What problems should be paid attention to in the process planning? Let’s take a look at it

1., the advanced technology.

When working out the machining process specification, we should make full use of the existing production conditions of the enterprise, adopt the advanced technology and experience at home and abroad as far as possible, and ensure good working conditions.

Economic rationality

Under the specified production program and production batch, there may be several process schemes that can meet the technical requirements of parts. At this time, the process cost is generally required to be the lowest through accounting or comparison with each other.

Computer gongs processing how to score

Confirm the model, size and allowance of processing blank according to the program sheet before operation, and sand and grind the blank

After operation, confirm the position of the workpiece and the processing sequence, and complete the table comparison

In the process of centring, if it is necessary to “split the rod”, the rotating speed is 501r / m. if the tool is used to divide the center, the speed depends on the tool. In this process, it should be noted that the data must be taken at the same height to ensure the accuracy of the split. After the separation, the “g0g54 x0y0” can be used for inspection

Before the formal processing, check and confirm whether the position of the workpiece is placed and whether the fetching is correct

C. Precautions in CNC machining

Check whether the tool is consistent with the machining procedure

When installing the tool, confirm whether the length of the tool and the selected tool holder are suitable
In the same workpiece, each tool setting should be kept in the same area to ensure the accuracy of tool connection

In the program, use the gas blowing knife as much as possible

Clean the aluminum slag in the machine tool before the smooth knife oil injection to prevent the aluminum slag from absorbing oil
During the operation of the machine tool, the operator shall not leave the machine tool or regularly check the operation status of the machine tool. If it is necessary to leave midway, relevant personnel must be designated to check
If too much machining allowance is found during machining,

You must use “single section” or “pause” to clear x, y, Z values, and then manually mill them off, and then swing back to “zero” to let them run on their own

Key points in computer gong processing

Try to install the clamping material first and then the cutting tool, so as to prevent the hand from touching the tool when installing the clamping 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.
When disassembling the tool, you must first observe whether the spindle stops rotating.
When unloading the knife, do not hold or pinch the edge of the knife with force to avoid scratching.
The wrench should be placed in the tool storage area after use, not on the y-axis shield or beam.
In the process of machining, operators are not allowed to observe the cutting position closely to prevent chips from falling into the eyes.
Before processing, check the position of the oil nozzle before opening the oil pump switch to avoid spraying to other positions when flushing oil.
When the machining gap is suspended for observation, the worktable must be moved away from the cutting position.
Inspection: after the machining is completed and before the workpiece is disassembled, we should first carry out 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

Computer gong processing reduces tool change times

In order to improve the accuracy of the groove width and reduce the number of tool changes, the milling cutter with a diameter of 7 than the groove width can be used to mill the middle part of the groove first, and then use the tool radius compensation function to mill the two sides of the groove.

Ball end milling cutter, ring milling cutter, drum milling cutter, cone milling cutter and disc milling cutter are often used in machining solid curved surface or variable bevel profile.

When the machining allowance is small and the requirement of surface roughness is high, the face milling cutter with cubic boron nitride blade or ceramic insert blade can be selected for high-speed cutting.

According to the principle of NC machining, the overall consideration is made according to the requirements of workpiece processing drawings, the format specified by the CNC milling machine is used for editing, and the processing program input is carried out according to the action sequence. Thus, it is necessary to know the precision machining technology of CNC lathe while compiling the NC program.

Determine the process flow. The processing technology of CNC milling machine is very similar to that of ordinary machine tool. Through analyzing the workpiece, specify the processing route, select the processing procedure, select the machine tool, fixture and cutter. Determine the equipment baseline position and cutting amount. The difference is that CNC machine tools need to program the operation process.
Calculate the tool coordinate value. In order to facilitate the programming and calculation of tool path coordinates. The coordinates of the workpiece and the size and shape of the part must be calculated first, so as to determine the whole machining path of the tool.
Write processing program, for simple workpiece can be written manually, but for complex processing workpiece, automatic programming is needed.
There are many ways to input programs into CNC system, which are mainly accomplished by the operation panel of CNC control system. In addition, the interface between computer and CNC system can be connected to input program by computer.
Comprehensive inspection of procedures. Through the function of graphic magic shadow display or NC milling machine equipment running without load, the running track of machine tool is checked, and whether the cutter movement meets the requirements of capping

CNC machining method of plane peripheral contour

The end mill C is often used when machining the peripheral contour of a plane workpiece.

Ball end milling cutter, ring milling cutter, drum milling cutter, cone milling cutter and disc milling cutter are often used in machining solid curved surface or variable bevel profile.

Determine the process flow. The processing technology of CNC milling machine is very similar to that of ordinary machine tool. Through analyzing the workpiece, specify the processing route, select the processing procedure, select the machine tool, fixture and cutter. Determine the equipment baseline position and cutting amount. The difference is that CNC machine tools need to program the operation process.
Calculate the tool coordinate value. In order to facilitate the programming and calculation of tool path coordinates. The coordinates of the workpiece and the size and shape of the part must be calculated first, so as to determine the whole machining path of the tool.
Write processing program, for simple workpiece can be written manually, but for complex processing workpiece, automatic programming is needed.
There are many ways to input programs into CNC system, which are mainly accomplished by the operation panel of CNC control system. In addition, the interface between computer and CNC system can be connected to input program by computer.

Standard of computer gongs processing

Design datum: the datum used to determine the position of other points, lines and planes on the part drawing, which is called design datum.

Process datum: the datum used in the process of machining and assembling parts, which is called process datum. According to different uses, the process datum of die and mould can be divided into assembly datum, measuring datum and locating datum.

(1) Assembly datum: the datum used to determine the position of parts in parts or products during assembly, which is called assembly datum.

(2) Measurement datum: the datum used to check the size and position of machined surface, which is called measuring datum.

(3) Positioning datum: the datum used for workpiece positioning during machining, which is called positioning datum. For the surface (or line, point) as positioning reference, only the rough surface can be selected in the first working procedure. This positioning surface is called rough datum. The machined surface can be used as the positioning datum in the following processes, and the positioning surface is called the precise datum. Process datum: the datum used in the process of machining and assembling parts, which is called process datum. According to different uses, process datum can be divided into assembly datum, measuring datum and locating datum.

(1) Assembly datum: the datum used to determine the position of parts in parts or products during assembly, which is called assembly datum.

(2) Measurement datum: the datum used to check the size and position of machined surface, which is called measuring datum.

In the process of turning a blank into a finished product, the total thickness of the metal layer cut off on a machining surface is called the total machining allowance of the surface. The thickness of the metal layer cut by each process is called the machining allowance between processes. For the rotating surface such as outer circle and hole, the machining allowance is considered from the diameter, so it is called symmetrical allowance (i.e. bilateral allowance), that is, the actual thickness of the metal layer cut off is half of the machining allowance on the diameter. The machining allowance of the plane is the unilateral allowance, which is equal to the actual thickness of the metal layer removed. The purpose of leaving machining allowance on the workpiece is to remove the machining errors and surface defects left by the previous process, such as the surface cold and hard layer, air hole and sand inclusion layer on the casting surface, oxide scale, decarburization layer and surface crack on the forging surface, internal stress layer and surface roughness after cutting. The precision and surface roughness of the workpiece are improved. The size of machining allowance has great influence on machining quality and production efficiency. If the machining allowance is too large, it not only increases the labor of machining, reduces the productivity, but also increases the consumption of materials, tools and power, and increases the processing cost. If the machining allowance is too small, it can not eliminate the defects and errors of the previous process.

Precision form grinding technology

Precision form grinding technology, and realize the precision coordinate grinding technology of round hole and mold hole with precision hole spacing. EDM and NC WEDM are widely used, which provide the key processing technology for high hard materials. The specialization, serialization and standardization of die materials are realized. During this period, the high development of mold standardization, the full use of standard parts and components in mold production is not only a major achievement and feature of mold industrial production mode, but also an important technical basis for realizing modern mold production mode. With the progress and development of computer and machine tool industry, die CAD / CAM and CAD / CAM / CAE have become widely used production technologies. They are combined with high standardization to form a modern mold production mode, that is to realize the informatization and digital mold production mode of mold design and manufacturing.

Design: during the period of manual workshop mold making and the early stage of industrial mold manufacturing, mold design was not carried out, and mold manufacturing was completely dependent on the experience and skills of mold makers. With the development of industry, the application of die and mould is becoming more and more extensive, the requirement of mould performance and quality is getting higher and higher, and the production technology is constantly improving. Designing and drawing the die structure system diagram and parts drawing, defining the design requirements and manufacturing technical conditions are the first task and core technology in the mold production process, which has been evolving until now.

However, with the progress of computer and CNC machine tool industry, and the wide application of CNC machine tools such as machining center, the mold design method and method have produced substantial and breakthrough progress. Mold design includes the following three aspects: mold part modeling and structure design, mold structure system design, mold structure parameter calculation and setting. Mold design process and content. The die with high precision needs to be processed by high-precision CNC machine tool, and the die material and forming process have strict requirements, and CAD / CAE / CAM die technology is also needed to design and analyze. Due to the special requirements of some parts, the mold also needs to use advanced technology such as hot runner, gas assisted molding, nitrogen cylinder and so on. The manufacturer shall be equipped with CNC, EDM, WEDM and NC profiling milling equipment, high-precision grinder, high-precision CMM, computer design and relevant software. Generally, large stamping dies (such as automobile cover parts mould) should consider whether the machine tool has blank holder mechanism, or even edge lubricant, multi position progressive, etc. In addition to stamping tonnage, punching times, feeding device, machine tool and die protection device should be considered.

Not every mold manufacturer and manufacturer has the means to master the above mold. When choosing a cooperative manufacturer, we must understand its processing ability, not only depending on the hardware equipment, but also combining the management level, processing experience and technical strength. For the same set of mould, there is sometimes a big gap between quotations from different manufacturers. You should not pay more than the value of the mold, at the same time, should not be less than the cost of the mold. Mold manufacturers like you, to make a reasonable profit in the business. Ordering a set of molds with a much lower price would be the beginning of trouble. Users should start from their own requirements and comprehensively measure. Avoid multi cooperation, try to make mold and product processing one-stop, with qualified mold (test piece qualified), not necessarily can produce a batch of qualified products. This is mainly related to the machine tool selection, forming process (forming temperature, forming time, etc.) and the technical quality of the operator.