Fine machining of the most popular stamping die su

2022-07-25
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With the rapid development of China's mold manufacturing industry, especially driven by the car industry, the development of car panel mold has also entered a new stage. This new stage has two meanings:

first, as a car mold, the quality requirements are getting higher and higher, Both appearance quality, internal quality and dimensional accuracy are becoming more and more demanding

second, the competition in the automotive industry determines that the mold development cycle is becoming shorter and shorter. The fine machining of the profile and trimming edge introduced in this paper is one of the most effective machining methods to improve the internal and external quality of the die and shorten the manufacturing cycle

overview

surface machining

according to the traditional manufacturing method of stamping die, the surface machining is: rough machining → semi finishing finishing finishing → root cleaning. After assembly, the fitter usually uses a grinder to polish first, then uses a coarse oilstone to polish, and finally uses a fine oilstone to polish. This often leads to two problems. One is the problem that the profile is damaged. Generally, it is normal for the profile to have an error of 0.1 ~ 0.2mm due to grinding machine repair. On the other hand, the fitter's repair and assembly cycle will be longer

cutting edge processing of repair and punching dies

the cutting edge of repair and punching dies is usually processed first, quenched, and then repaired and grinded by fitters one by one. As a result, the assembly accuracy and cycle cannot be guaranteed. There are some differences in dimensional accuracy due to repair and grinding, which often leads to uneven clearance and large trimming burr

introduction to fine machining of profile and trimming edge

the fine machining process has been greatly improved on the basis of inheriting the traditional machining methods. The quality of the profile has been greatly improved. The parts can be pressed without research and fitting, and the clearance qualification rate of trimming edge reaches more than 75%. Reduce the fitter assembly repair and research time by 30% ~ 40%, and greatly improve the quality and efficiency. Directly reduce the cost by 548 yuan/standard set (one standard set of drawing and grinding die for the outer door panel)

surface fine machining

surface fine machining process route: rough root cleaning 50 - rough machining 50 - semi fine root cleaning 32 - semi fine machining 32 - fine root cleaning 30 - fine root cleaning 20 - fine root cleaning 16 - fine root cleaning 12 - fine root cleaning 10 - fine root cleaning 8 - fine root cleaning 6 - fine root cleaning 4

the processed profile can be directly pressed without polishing

processing example

processing workpiece Name: drawing punch for car door outside panel

workpiece material: mocr cast iron alloy

stable medium to strong hardness in the domestic coke spot market after the festival: about hrc28

spindle speed: 6000 rpm

cutting line speed: 400m/min

feed speed: f=4000mm/min

feed per tooth: fz=0.5mm/rev

cut depth : ap=0.2mm

step length: AE (step) =0.4mm

cooling method: dry

processing tool: Daijie mirror ball cutter

tool diameter: φ 30

processing time: 12 hours

after 12 hours and its application in a wide range of industries: scientific research institutes, commodity inspection and arbitration institutions, colleges and universities, and rubber, tire, plastic, wire and cable, shoemaking, leather, textile, packaging, building materials, petrochemical, aviation and other industries, it can be seen that the surface roughness is very good, and there is no need to connect the knife. The tool wear is only about 0.015mm after inspection, and it is also very sharp, The mold surface feels smooth. If the user doesn't have the requirements for polishing the surface, he can directly pull the parts without polishing. If the user has the requirements, he can directly use 150

fine machining of trimming die edge

the clearance and dimensional accuracy of the trimming edge are very important. The dimensional accuracy is often affected by the burr or too short service life of the edge due to unreasonable clearance and out of tolerance of dimensional accuracy. In this regard, the process route is as follows: rough milling of trimming contour (stock=1mm with 10mm left) → fine milling of trimming contour (stock=0.3mm) → R angle cleaning (stock=0.3mm) → disassembly and quenching → assembly → φ 20 superhard tool machining → φ 16 corner clearing → φ 10 corner clearing → φ 8. Corner cleaning (generally, R4 is reserved for the process fillet without special requirements in the design)

in the process of machining, the qualified rate of trimming edge clearance can reach 75% ~ 80% after this processing process. If the angle design is reasonable, it can reach 100%, δ= The repair and punching dies above 0.8mm can reach 100%. In this regard, the selection of cutting tools is very critical. The difficulty is the processing after quenching, which is a key part of the whole process. In this regard, there are several cutting tools to choose from:

(1) superhard cutting tools

(2) integral carbide end milling cutter of Daijie dajet

(3) Hitachi integral superhard end milling cutter + superhard coating

in this example, we select the Hitachi integral superhard end milling cutter. The parameters of this cutter are as follows:

speed: 1500rpm

feed: 2500mm/min

factors affecting the dimensional accuracy and surface roughness of ultra precision machining

it should be said that for NC machining, there are many factors affecting the machining accuracy, It can be summed up as follows:

(1) the geometric precision of the equipment is due to the creep and hysteresis characteristics of the sensor, linear accuracy, interpolation performance, etc

(2) the influence of machine tool structure and rigidity on machining

(3) thermal deformation during cutting

(4) size of machining allowance

(5) selection of tool material and cutting parameters

(6) influence of ambient temperature change

(7) clamping, secondary alignment, positioning, etc

(8) operator's heart

★ influence of equipment structure on superfinishing

first of all, the structure of the equipment determines the weight of the equipment itself. According to the law of conservation of acceleration energy, ft=mv is directly transformed into the dynamic response capability of the equipment. This is the intuitive so-called servo control time. Generally, this requirement can be achieved only when it is controlled within 4 milliseconds. Second, the structure of the equipment determines the rigidity of the equipment. The rigidity of the equipment determines whether the equipment operates at full load, including whether it vibrates in the full range of rotation after the spindle is equipped with a tool handle. The rigidity of the light milling machine or the movable door bridge is often poor, and it often vibrates at speed=6000 ~ 8000rpm. This vibration is what we call the orange peel phenomenon on the mold

★ the accuracy of the equipment is also very critical

according to the national industrial standards, the accuracy of NC test and bar inspection must meet the requirements. In addition, the requirements for the positioning accuracy, repeated positioning accuracy and reverse clearance of the equipment are also very strict. Generally, P ≤ 0.015/l, Max ≤ 0.005/l mm, and backlash ≤ 0.006 (vdi3441 standard) (tenpure 25 ° ± 4). If this standard is not met, the finishing effect will be reduced. Our factory has adopted two Japanese Okuma machine tools in the process of realizing this operation

★ tool wear has a great impact on both profile and profile

in the process of machining the worn profile, the linear speed gradually increases from vc=0 to vc= π n/1000*m at the tool tip, so the side wear is large. In this way, especially the side wall is easy to produce a knife. The wear of our mirror ball cutter within 17 hours is 0.015mm after measuring with the tool setting block and three coordinates. Do not underestimate this 0.015mm, its wear process is divided into three stages

the first stage: sharp wear stage, which lasts about 20 minutes

second stage: constant stage, in which the tool runs smoothly

the third stage: it is a slow wear stage. The above two stages are only physical changes. In the third stage, the chemical changes of denaturation. With the passage of time, this kind of wear is accelerated. Finally, it is a vicious cycle, resulting in a rapid decline in surface roughness. The hand feels like a file. Usually, this change is the main factor

★ thermal deformation also has a great impact on superfinishing, and the main source of heat is cutting heat

generally, cutting heat exists in three aspects: workpiece accounts for about 20%, iron filings accounts for about 70%, and cutting tools account for about 10%. For ultra precision machining, do not underestimate the 10% heat carried by the tool. In the whole clamping system, 10% heat can make the tool and the clamping system extend about 0.015 ~ 0.02mm. If the cutting depth is more than 0.5mm, this phenomenon will be very obvious. That is, it is often found that a tool suddenly feels that the profile is deeper than before after changing the blade

★ the selection of material, allowance and cutting parameters is very important

the material and allowance of the processed material are very important. For different materials, the hot place machine should be placed on the prefabricated 720mmx600mm cement foundation 300mm above the ground. Different treatment methods and hardness make the cutting amount different. When the allowance is large, for the machining of the profile, especially for the side cutting, it will be very serious. Generally, if the side allowance reaches 0.5mm, the maximum oversize of the side cutting is about 0.06 ~ 0.08mm. If the side allowance is 0.2mm, the side clearance is 0.02 ~ 0.04mm. Therefore, the size of allowance is very critical, and the selection of parameters is also very critical

★ the influence of ambient temperature is also crucial

from the working principle of CNC machine tools, the counting methods of semi closed loop and closed loop are different. The counter of (semi closed loop) is rotary encoder or circular grating, while the encoder of (closed loop) is linear grating, magnetic grating, spherical grating, etc. Due to the influence of temperature, the linear grating has a line length coefficient, that is, it expands or contracts with the temperature rising or falling. Taking Heidenhain linear grating ruler as an example, the error at the same temperature is basically a repetitive error, but at different temperatures, its error will be very large. For example, in a workshop without constant temperature device, the change of temperature is 10 ℃, and the change of positioning accuracy is 0.0807mm ~ 0.11mm, Especially for the trimming edge, the trimming clearance of sheet metal is generally 5% ~ 7%* δ Mm. Therefore, the result of such a large error must be inaccurate. The key to solving this problem is: first, keep the temperature constant. If there is no condition, try to control the temperature difference of punch or die within 1 ~ 3 ℃. If it exceeds this range, the result will be unqualified

★ the operator's heart is also the key factor to determine whether the fine processing can meet the requirements

the so-called operator's heart specifically includes the quality when making the three reference pin holes, the precision of clamping and alignment, the number of sizing blocks, the preciseness when executing the processing technology, and the error when setting the tool

the layout of general sizing blocks is shown in Figure 6: the number of sizing blocks is Δ= 7+(L-1.5m)/1.5m*2。

the selection of cutting tools is the key to the fine machining of trimming edges. During the machining process, we selected the following manufacturers' cutting tools

a common feature of these tools is their high machining hardness, good wear resistance and high precision. Take Hitachi tools as an example, φ 20. The cutting tool has 6 teeth, the spiral rise angle is 40 °, and the coating is tinai. When cutting, the edge hardness can be machined above 65 °, the feed is 1800 ~ 2500mm/min, the rotating speed is s=2500rpm, and the cutting side edge is 0.3 ~ 0.5mm. However, the smaller the margin, the better the effect