In the mold processing, WEDM technology has been widely used, but during the process of WEDM, the mould is easy to produce deformation and crack, cause parts scrapped, that increase the cost of frequent occurrence. So, the problem of deformation and cracking in WEDM mold, people pay more and more attention, for many years, cracking and deformation of cutting line of people understanding is insufficient, often caused by cutting between departments and incoming processors mutual shirk responsibility, conflict. In fact, the causes of deformation and cracking are many aspects, such as material, heat treatment, structure design, process planning and the choice of the workpiece clamping and cutting line. In this many factors, can find the line cutting processing deformation and the law of crack? Through years of in-depth study, the author puts forward the following measures to prevent deformation and cracking.
1 deformation and crack of the main factors
In the production practice, the author has found that the deformation and crack of the wire cutting process are related to the following factors through a large number of examples.
1.1 and parts of the structure
1) where a narrow long shape of the concave die, the convex die is easy to produce deformation, the size of its deformation and shape complexity, length and width ratio, the width ratio of the cavity and the border. The more complex shape, the ratio of length to width and cavity and the border width ratio is larger, the greater the amount of the mold deformation. The rule of deformation is that the middle cavity of the cavity is flat, and the convex die is usually warp;
2) quenching cavity any complex shape angle, easy to crack in the corner, and even prone to breakage. The frequency of the material and the composition of the material, the heat cylinder wall thickness than the book parts, if the inner wall for cutting, easy to produce deformation, generally by the round into oval shape. If the cutting gap, the bursting phenomenon is easy to produce in the upcoming cut through time;
3) cylindrical wall thickness than the book parts, if the inner wall for cutting, easy to produce deformation, generally by the circular into oval shape. If the cutting gap, the bursting phenomenon is easy to produce in the upcoming cut through time;
4) by external parts cut deep groove, easy deformation, deformation law of mouth closed, the deformation of the size and amount of the relevant properties of notch depth and material.
1.2 and the hot processing technology
1) die blank forging temperature is too high or too low, and the final forging temperature is low;
2) the final forging temperature is too high, the grain grows up, the cooling rate is too slow after the final forging;
3) the blank annealing process is not carried out in accordance with the ball annealing process, the ball of pearlite more than 5 parts;
4) the quenching heating temperature is too high, the austenite grain is coarse, the material toughness is reduced, and the brittleness is increased;
5) quenched parts without timely tempering and tempering parts.
1.3 and mechanical processing technology
1) die area of large, middle and large area excision without hollowing out, because of large size of the trim frame, the frame size will have a certain deformation;
2) where there is no contour starting point in the blank through the wire hole, had to cut from the blank, regardless of the convex die tempering and shape, generally easy to produce deformation, especially
The hardened parts are deformed seriously, even in the cutting process;
3) of workpiece after heat treatment, no grain size, amount of feed and cooling process requirements, grinding surface burn and micro crack defect parts.
1.4 related to materials
1) the raw material has the serious carbide segregation;
2) the poor permeability, easy deformation of the materials, such as T8A, T10A, etc..
1.5 related to the wire cutting process
1) the line cutting path selection is improper, easy to produce deformation;
2 the workpiece clamping pressure is not reliable, the pinch point of the choice of improper, are prone to deformation;
3) electric gauge is not properly selected, easy to crack.
2 measures to prevent deformation and cracking
To find the causes of deformation and cracking can be an antidote against the disease, take the appropriate measures to avoid and prevent deformation and cracking. Specific measures can be started from the following aspects:
2.1 select materials with less deformation and adopt proper heat treatment process.
In order to prevent and reduce deformation, cracking, the need for wire cutting processing of the mold, the choice of materials, processing, heat treatment, heat treatment until the finished product in all aspects should be fully concerned about and attention;
1) strict examination of the chemical composition of raw materials, metallographic structure and testing, for the unqualified raw materials and coarse grain steel and harmful impurities content exceeding the standard steel should not be selected;
2) as far as possible the use of vacuum smelting, furnace refining or electro slag remelting steel;
3 to avoid the selection of poor permeability, easy deformation materials;
4) should comply with reasonable blank forging, upsetting, stretching, forging forging and other raw materials than the code of length to diameter ratio is the best selection of forging ratio between 2-3;
5) improvement of heat treatment process, using vacuum heating, protective atmosphere heating and bath furnace heating and deoxidation full quenching and isothermal quenching;
6) select the ideal cooling rate and the cooling medium;
7) quenched steel should be tempered in time, as far as possible to eliminate quenching stress, reduce brittleness;
8) for a long time to temper, improve the mold resistance to fracture toughness value;
9) fully tempered, to get the stable performance of the organization;
10) the transformation of the retained austenite to the full and the elimination of the new stress;
11) for second types of temper embrittlement die steel after high temperature tempering should be fast cooling (water cooling or oil cooling), can eliminate the two types of temper brittleness;
12) prior to the chemical treatment of die steel diffusion annealing, the ball back