Size analysis of 1 wire drawing dies
1.1 mold processing and production level
The influence of the level of mold processing on the quality of the mold is mainly reflected in two aspects. One is the hole size of the drawing die, the two is the surface finish of the die.
High-speed lapping machine is widely used in the grinding process in the foreign drawing die, and plated with metal grinding of diamond, the equipment running smoothly, grinding specifications and the use of standardized, product precision. The groove dimensions of the mold using outline recorder and aperture measuring instrument to detect, and with the special inspection of the drawing die microscope to check the surface is bright and clean degree.
And many domestic manufacturers are still using outdated equipment, use manual operation to grinding pass. Therefore, there is a the following problems: pass parameters fluctuation is large, it is difficult to process the straight cone; sizing area and work, shorten the handover easy grinding angle transition, the wire in generates secondary compression to increase the friction, shortening the service life of the path length of die; wear of grinding repair frequency is different from person to person, the use of non-standard, which pass the consistency difference size area. Detection methods are backward, can only rely on visual or zoom lenses, microscopes and other simple tools to detect and attention is mold surface finish, to pass dimension is not effective in detecting, not to mention the control. Therefore, the level of processing and production of the mold is one of the reasons for the size of the mold.
1.2 improper use of drawing die in the process of drawing
(1) drawing area is too large, resulting in cracks or breaking the mold. The vast majority of cracks or broken lines are generated by internal stress release. In any material structure, the existence of stress is inevitable and the internal stress of the wire drawing could have enhanced diamond microcrystalline structure, but when the drawing surface shrinkage is too large, can not be timely lubrication and temperature rise is too high it will lead to diamond die that portion of the material is removed, the microcrystalline structure to withstand the stress is greatly increased, making it more prone to cracks or broken.
(2) wire tensile axis and the die hole center line asymmetry, resulting in of wire rod and wire drawing die stress is not uniform, and mechanical vibration impact will cause of wire rod and wire drawing die very high peak stress, both will accelerate mold wear.
(3) the hardness of the wire caused by uneven annealing is easy to cause the fatigue damage of diamond wire drawing die prematurely, and the ring groove is formed, which aggravate the wear of die hole.
(4) rough surface, surface adhesion oxide, sand or other impurities will cause excessive wear and tear. When the wire passes through the die orifice, hard, brittle oxide layer and other adhesive impurities would like abrasive caused by wire drawing die hole soon wear and abrasion of wire rod surface.
(5) lubrication is not smooth or wire drawing powder containing metal debris impurities lead to wear and tear. Poor lubrication can make the surface temperature rise too fast, diamond grains fall off, leading to mold damage. When the lubricating oil is not clean, especially when the metal fragments which fall off in the drawing, it is easy to scratch the mold and wire surface.
(6) frequent stop at the wire drawing process will also be increasing the die wear. This is because of the drawing started when the tensile stress caused by the friction than the normal pull-out friction to much larger.
2 effectively reduce the size of wire drawing die in the use of the method of fluctuations
2.1 as far as possible the use of advanced mold processing technology to produce high-quality drawing die
2.2 select good pass design of wire drawing die
The drawing die pass is generally divided into the curve (i.e., R Series) and the straight line type (that is, the cone type series). As shown in figure:
The type of cable of die hole
From the wire in the wire drawing die deformation uniform angle analysis, seems to curve than linear type, this pass is designed under the guidance of the theory of "smooth transition", the hole structure according to the nature of work can be divided into "population", "lubrication", "working area", "sizing area", "the day of the" five parts, the junction for chamfer, smooth transition, the pass grinding of the whole into a large, with different curvature of the arc surface of this groove mold in when the drawing speed conditions, or can be applied. To the 70's of the last century to the beginning of the 80's, with the drawing speed increased, the service life of the die has become a prominent problem. In order to adapt to the requirements of high speed wire, American T.Maxwall and E.G.Kennth proposed the "linear" theory. The theory focuses on the process of drawing lubrication and wear factors, it is pointed out that the improvement of linear type wire drawing die hole should have the following characteristics:
(1) profile of each part of the pass must be straight, straight cone working drawing force minimum;
(2) the junction of each part of the mold must be clear, so that each part can fully play its role, to avoid the transition angle of the actual length of the fixed diameter area decreases;
(3) extend the height of the entrance area and work area, the wire into the middle of die hole cone, the inlet cone angle and cone angle on the upper part of the formation of wedge-shaped area, to establish a "wedge effect, online material is formed on the surface of the more dense solid lubricating film, reduce wear, suitable for high speed drawing;
(4) the sizing area must be straight and the length is reasonable. Sizing area is too long, cable friction increases, wire out of the die hole often cause shrinkage or disconnection, sizing area is too short, it is difficult to obtain stable shape, accurate size and good surface quality of wire rod, also die hole will soon wear the ultra poor.
2.3 the installation and use of wire drawing machines should be reasonable
(1) the installation foundation of wire drawing machine is very stable and avoid vibration;
(2) to be installed by debugging the wire drawing die hole and the axis of symmetry for the center line, the wire drawing dies and uniform stress;
(3) during pulling to avoid frequent start stop, because drawing started when the tensile stress caused by the friction than the normal pull-out friction to much larger, which is bound to increase in die wear.
2.4 used for drawing wire to go through pretreatment
(1) surface pre treatment: for the surface dirt, adhesion more impurities in the wire, to first after cleaning, drying and then drawing; for more oxide wire surfaces are, to first after acid fine, after drying and then drawing; for the surface of skin, pits, heavy skin phenomenon of wire, but also through the grinder for grinding of drawing;
(2) heat treatment: the hardness is too large or uneven hardness of the wire, first by annealing or tempering to reduce the hardness, and make the wire to maintain good hardness uniformity and then drawing.
2.5 keep drawing area suitable
If for large shrinkage reducing drawing, can easily lead to die that can withstand stress and scrapped broken. Therefore, we should according to the different mechanical properties of wire, select the appropriate surface shrinkage is used for drawing wire drawing die itself has a hard, brittle characteristics.
2.6 regular maintenance and repair of wire drawing die
Drawing die in the long-term use process and die wall by metal wire strong friction and scouring effect, inevitably will produce wear phenomenon, the most common is annular groove (dent) at the entrance of the wire. Wire drawing die ring groove, exacerbated by the wear of die hole, because ring groove for loosening and spalling of the core material of small particles is metal wire into the die hole area and sizing area, plays a role of abrasive, and into the wire hole die is like grinding as aggravate the die hole wear. If not replaced in time to repair, then the ring will continue to accelerate the expansion of the expansion, so that the repair increased, and even more likely to appear in the ring groove crack, so that the mold completely broken scrap.
To develop a set of norms and standards, to strengthen routine maintenance, regular maintenance of the mold is a very cost-effective thing. In the event of any slight wear and polishing in a timely manner, the mold will be restored to the original state of polishing and the size of the hole of the mold will not change significantly.
In summary, in order to remain in the wire drawing process to avoid drawing die size fluctuations in addition to select a suitable mold material, reasonable design of pass dimension and improve the level of drawing die manufacturing, the die hole surface finish to achieve technological requirements, must also determine a reasonable compression ratio, improve the conditions for the use of drawing die. In the use of the process to pay attention to the mold of daily maintenance, should wash frequently change, and to ensure that the tensile process has good lubrication effect.
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