Views:0 Author:Site Editor Publish Time: 2020-09-23 Origin:Site
Cutting Technology of High Quality Tungsten Carbide Lithium Battery Blade Pole Piece
Production of pole pieces is the basic process for manufacturing lithium-ion power batteries, which requires very high equipment accuracy, intelligence level, and reliability of production performance. Pole piece slitting machine is an equipment for slitting rolled battery pole pieces according to battery specifications. Main technical requirement is that pole pieces after slitting must not appear wrinkled or de-powdering, and slitting size is required to have high precision. Burrs on the edge of chip are small, otherwise dendrites will pierce diaphragm on burrs and cause a short circuit inside battery. Disc slitting knives mainly include upper and lower disc knives, which are installed on cutter shaft of slitting machine, and use rolling shear principle to slit aluminum foil, copper foil, and positive and negative pole pieces with a thickness of 0.01~0.1mm. Here, we will sort out basic knowledge of lithium battery pole piece disc slitting process, share and learn with everyone.
Principle of pole piece disc slitting
Refer to sheet metal disc slitting process, first introduce the basic principle of pole piece disc slitting. First, when plate is in contact with upper and lower blades, plate will be elastically deformed by pressure of upper and lower blades, and due to existence of moment, plate will bend, and shear stress will be generated in material near the gap. . With rotation of blade point, plastic deformation occurs when internal stress state meets plastic conditions. As shearing process continues, shearing force on plate becomes greater and greater, and it enters shear yield state. Shear deformation zone begins to produce macroscopic slip deformation, and upper and lower round blades begin to cut into material. At this time, material of edge attachment produces plastic deformation, shear plastic slip is formed, and section is bright. As cutter head continues to rotate, degree of plastic deformation of material intensifies, material will undergo work hardening, and its stress state will also change, resulting in microscopic cracks inside material. As deformation continues, these microcracks merge into main. Crack transforms into crack propagation and separation, and section forms a tear zone.
Compared with sheet metal slitting processing, cutting method of lithium battery pole piece disc cutter has completely different characteristics:
(1) When cutting pole piece, upper and lower disc knives have a back angle, which is similar to blade of a scissors, and width of blade is very small. There is no horizontal gap between upper and lower disc knives, but upper and lower knives are in contact with each other and there is lateral pressure.
(2) Basically, there are rubber rollers on upper and lower sides of sheet when slitting, which balances shearing force and shearing moment generated by upper and lower knives during cutting and avoids substantial deformation of sheet. The pole piece slitting has no upper and lower rollers.
(3) The pole piece coating is a composite material composed of particles, which has almost no plastic deformation ability. When internal stress generated by upper and lower disc cutters is greater than bonding force between coating particles, coating will crack and expand and separate.
The main failure mode of disc cutter
In pole piece slitting process, quality of slitting disc blade directly affects pole piece slitting performance. Slitting machine needs to run for a long time, so it is necessary for slitting blade to have good mechanical properties, such as hardness, manufacturing technology and wear resistance. Disc cutter has a certain life span during continuous operation, and cutter life needs to be managed in cutting process. Generally, main failure mode of pole piece disc cutter is tool wear, which includes:
(1) Fatigue failure
Pole piece slitting disc cutter has lateral pressure. Upper and lower cutters overlap each other on side of cutting edge. During continuous slitting process, stress on cutting edge is large and concentrated. Due to frequent extrusion, shearing, friction and cyclic crossover The effect of variable mechanical load is prone to fatigue micro-cracks in cutting edge area, and then under action of cyclic stress, it will expand along the side of disc cutter to center. When crack grows to a certain extent, stress reaches strength limit of tool material It will cause local micro-breakage of cutting edge of tool.
(2) Adhesive wear
Adhesives with squeezing marks can also be found in wear area of tool. These adhesives are formed by sticking of pole piece debris on tool. This is because the side of disc cutter is in contact with pole piece cutting surface, and there is a large contact pressure, so that part of cutting material is cold welded to side of disc cutter. These bonding layers continuously fall off during cyclic slitting process and then re-form. The fall off process may cause hard phase of tool to fall off, and aggravate wear process. This situation is easiest to form when slitting aluminum foil. Due to low melting point of aluminum, cutting chips and side of tool stick together to cause tool wear and shorten life.
(3) Abrasive wear
Although the hardness of cutting chips and pole pieces is lower than the hardness of tool, they often contain some extremely high hardness tiny hard points, which can engrave grooves on tool surface, which is abrasive wear.
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