2. Blanking is a stamping process that separates the sheet metal through the die, and blanking is the most basic stamping process. Blanking is the general name of separation processes, including blanking, punching, cutting, trimming, tongue cutting, bending and other processes. Generally speaking, blanking mainly refers to blanking and punching processes.
3. Blanking deformation process: 1. Elastic deformation stage (material stress in deformation zone is less than yield stress); 2. Plastic deformation stage (material stress in deformation zone is greater than yield stress); 3. Fracture separation stage (the material stress in the deformation zone is greater than the strength limit).
4. The blanking part can be divided into four obvious parts: corner collapse, brightness, rough surface and burr.
5. Quality of blanking parts: refers to section condition, dimensional accuracy and shape error. Clearance is one of the main factors affecting the quality of blanking parts. The section quality of blanking parts mainly refers to the size of collapse angle, the ratio of glossy surface to the thickness of sheet, the bevel angle and burr of rough surface. When the clearance is appropriate, the shear cracks at the upper and lower cutting edges basically overlap, and the time plane accounts for about 1/2~ 1/3 of the thickness of the sheet, and the collapse angle, burr and inclination of the cutting surface are very small, which fully meets the requirements of general blanking parts. When the clearance is too small, the cracks at the cutting edge of the punch are staggered outward by a certain distance than when the clearance is reasonable; When the gap is too large, the cracks at the punch edge are staggered inward by a certain distance than the reasonable gap, the bending and stretching of the material increase, the tensile stress increases, and the plastic deformation stage ends ahead of schedule, which leads to the decrease of section smoothness, the increase of collapse angle and inclination angle, and the formation of thick and slender burrs, which are difficult to remove. At the same time, the warping phenomenon of blanking parts is serious, which affects normal production. The greater the relative thickness of the material, the smaller the elastic deformation, so the higher the accuracy of the parts. The smaller the size of the blanking part, the simpler the shape and the higher the accuracy. )
The basis and criterion for calculating the cutting edge size of stamping die: in the measurement and use of the size of blanking parts, the smooth surface size is taken as the benchmark. The smooth surface of the blanking part is produced by the extrusion of material by the cutting edge of the female die, while the smooth surface of the hole is produced by the extrusion of material by the cutting edge of the male die. Therefore, when calculating the cutting edge size, blanking and punching should be carried out according to the following principles: 1. Blanking: the smooth size of blanking parts is equal to the size of the die, so the size of the die shall prevail (the basic size of blanking die is smaller within the tolerance range of workpiece size). ); 2. Punching: The aperture of the smooth surface of the workpiece is equal to the punch size, so the punch size shall prevail. (Because the size of punching hole will decrease with the wear of punch, the basic size of punching punch should be larger than the tolerance range of workpiece hole size); 3. Hole center distance: When multiple holes need to be punched on the workpiece, the dimensional accuracy of the hole center distance is guaranteed by the hole center distance of the female die. 4. Manufacturing tolerance of die cutting edge: the selection of the dimensional accuracy of punch and die cutting edge should be based on the requirements of ensuring the workpiece accuracy, ensuring a reasonable gap value between punch and die and ensuring a certain service life of the die. 5. In principle, the dimensional tolerance of the workpiece and the manufacturing deviation of the die cutting edge size should be marked as one-way tolerance according to the principle of "into the body". However, for the size that has not changed after wearing, the two-way deviation will generally be marked.
7. The layout method of strip, strip or sheet blanking parts is called layout. The percentage of the actual area of blanking parts to the area of used sheet metal is called material utilization rate, which is a technical and economic index to measure the rational use of materials.
8. The waste produced by blanking can be divided into two categories: one is structural waste, which is produced by the shape characteristics of stamping parts; Second, the wastes generated by the overlapping of stamping parts, stamping parts and the side edges of the strip, and the head, tail and edge materials are called process wastes.
9. Layout method: waste layout, less waste layout and no waste layout.
10. Determination of overlap value: The process wastes left between blanking parts and between blanking parts and the side of strip during layout are called overlap. Grinding has two functions: one is to compensate the positioning error and shearing error, and to ensure that qualified parts are punched; Second, it can increase the rigidity of the strip, facilitate the feeding of the strip and improve the labor productivity.
1 1. Determination of die pressure center: The action point of the resultant force of blanking force is called the die pressure center. The pressure center of the die should be the center line of the press slider.
12. Classification of blanking dies: 1. Single-process die: single-process die without guide, single-process die with guide plate and single-process die with guide column; 2. Progressive die is a progressive die that completes several stamping processes at different positions of the die in one stroke of the press: the progressive die that fixes the stop pin and the guide pin, and the progressive die that measures the edge and sets the distance; 3. Compound die is to complete several stamping processes at the same position of a pair of dies in one stroke of the press: according to the different installation positions (male die and female die), compound die is forward and compound die is turned over;
13. Requirements of layout for die strength: for stamping parts with small hole spacing, holes should be punched out step by step; If the wall thickness of the die between stations is small, empty steps should be added; Stamping parts with complex shapes should be stamped step by step to simplify the shapes of punch and die, enhance strength and facilitate processing and assembly. The position of measuring edge shall be as far as possible to avoid causing local workpiece of convex-concave die and damaging cutting edge.
14. From the structural analysis of forward and backward compound dies, we can see that they have their own advantages and disadvantages. The progressive type is more suitable for stamping parts with soft stamping materials or high straightness requirements of thin plates, and can also punch stamping parts with small hole edge distance. But it is not suitable for punching blanking parts with small hole edge distance by flip chip method. The flip-chip compound die is simple in structure, can be directly recommended by the punch device of the press, has reliable discharging and convenient operation, and provides favorable conditions for mechanized discharging, so it is widely used. In a word, the compound die has high production efficiency, high relative position accuracy between the inner hole and the outer circle of the blanking part, lower positioning accuracy of the sheet metal part than that of the progressive die, and smaller blanking outline size. However, the composite die has complex structure, high manufacturing accuracy and high cost. The compound die is mainly used to produce blanking parts with large batch and high precision.
15. Initial stop device: In order to solve the positioning problem of the first part in the progressive die, it is necessary to set an initial stop device.
16. Unloading equipment: 1. Fixed unloading device; 2. Elastic discharging device (discharging and pressing, good stamping quality, high straightness, strong applicability and high quality requirements); 3. Waste cutter device.
17. Bending: it is a stamping process that bends parts such as plates, bars, profiles or pipes into a certain shape and angle.
18. Strain neutral layer: There must be a layer of metal fiber with the same length before and after deformation between the shortened and elongated deformation zones.
19. The cross-sectional shape of sheet metal in bending deformation zone can be divided into: 1. When the wide plate is bent, the cross-sectional shape is almost unchanged, and it is still rectangular; 2. When the narrow plate is bent, the original rectangular section becomes a fan. Wide plate bending is generally used in production.
20.r/t is called the relative bending radius of sheet metal, which is an important parameter to indicate the bending deformation degree of sheet metal. The smaller the relative bending radius, the greater the bending deformation.
2 1. Deformation characteristics of plastic bending of sheet metal: 1. Internal displacement of strain neutral layer; 2. Thinning and growth of metal sheet in deformation zone:
3. Distortion, warping and fracture of metal profile in deformation zone.
22. Minimum bending radius: The minimum radius of the fillet on the inner surface that the workpiece can be bent into is called the minimum bending radius without damaging the fibers on the outer surface of the workpiece blank. It is used in production to indicate the forming limit of materials when they are bent.
23. Factors affecting the minimum bending radius: 1. Mechanical properties of materials; 2. The size of the bending center angle of the parts; 3. The relationship between the rolling direction of plate and the included angle of bending line; 4. Quality of sheet metal surface and blanking section; 5. The relative width of materials; 6. Plate thickness
24. Rebound phenomenon: Rebound phenomenon occurs during unloading after bending deformation.
25. Factors affecting springback: 1. Mechanical properties of materials; 2. Relative bending radius r/t; 3. Bending center angle; 4. Bending mode and correction force; 5. Workpiece shape; 6. Mold clearance.
26. Deep drawing: it is a stamping process that uses a die to make a flat blank into an open hollow part.
27. Wrinkling and cracking are two main factors affecting the deep drawing process:
28. Wrinkling: In the process of drawing, the blank flange may arch due to plastic instability under the action of tangential compressive stress.
29. Causes of wrinkling: The tangential compressive stress of the blank flange is too large, and the maximum tangential compressive stress occurs at the outer edge of the blank flange, so the wrinkling starts from the outer edge first.
30. Cracks: The factors affecting friction resistance are: 1. Influence of BHF; 2. The influence of relative fillet radius; 3. The influence of lubrication; 4. The influence of the gap between convex and concave dies; 5. Influence of surface roughness.
3 1. Drawing coefficient: refers to the ratio of the diameter of the cylindrical part after each drawing to the diameter of the blank before drawing, m indicates.
32. Ultimate tensile coefficient: the minimum tensile coefficient that a material can be stretched without breaking.
33. Factors affecting the tensile coefficient: 1. Influence of mechanical properties of materials; 2. The influence of material relative thickness; 3. The influence of the painting era; 4. the influence of 4.BHF; 5. The influence of fillet radius and clearance on the working part of the die.
34. Classification of plastics: 1. According to the molecular structure and behavior of synthetic resin when heated, it can be divided into thermoplastic and thermosetting plastics. 2. Classification according to the application scope of plastics: general plastics, engineering plastics and special plastics.
35. Thermodynamic properties of polymers: The physical and mechanical properties of polymers are closely related to temperature. When the temperature changes, the mechanical behavior of the polymer changes, showing different mechanical States, showing the characteristics of mechanical properties in stages. When the temperature is low (below the temperature), the curve is basically horizontal and the deformation is very small. When the temperature rises, the () curve begins to change sharply and soon tends to be horizontal. If the temperature continues to rise, the change develops rapidly, the elastic modulus decreases rapidly, and the polymer produces viscous flow, which becomes a viscous state. At this time, the irreversibly changing object becomes liquid.
36. The injection process generally includes feeding, plasticizing, injection, cooling and demoulding.
37. Post-treatment of products: After plastic products are demoulded, proper post-treatment (annealing and debugging) is often needed to improve and improve the performance and dimensional stability of products.
38. Pressure: The pressure during injection molding includes plasticizing pressure and injection pressure. Plasticizing pressure, also known as back pressure, refers to the pressure generated by the melt at the top of the screw of injection molding machine under the condition that the screw does not retreat. Injection pressure: used to overcome the flow resistance of the melt from the barrel to the cavity, improve the mold filling speed and compact the melt.
39. According to the relevant requirements of the process, the wall thickness of each part of the product should be as uniform as possible, so as to avoid being too thick and too thin locally, otherwise the uneven shrinkage after molding will deform the product or produce defects such as shrinkage cavity, depression and insufficient filling. P83
40. The injection mold consists of two parts: the moving mold and the fixed mold.
4 1. According to the different functions of each part in the mold, the injection mold can be composed of the following seven systems and mechanisms: 1. Molded parts; 2. Pouring system; 3. Guiding and positioning mechanism; 4. demoulding mechanism; 5. Lateral parting and core-pulling mechanism; 6. Temperature regulation system; 7. Exhaust system.
42. According to the overall structural characteristics of the mold, it is classified as 1. Single parting injection mold: 2. Double parting injection mold; 3. Injection mold with lateral parting and core-pulling mechanism: 4. Injection mold with movable molding parts; 5. Injection mold with motor thread removal; 6. Runner-less injection mold.
43. Parting surface: it is a separable contact surface on the mold, which is used to take out the condensate of plastic parts and gating system.
44. Selection principle of parting surface: Basic principle-the parting surface should be selected at the position with the largest outline of the plastic part, so as to demould by the way. There are other factors to consider: 1. The selection of parting surface should facilitate the demoulding of plastic parts and simplify the mold structure; 2. The selection of parting surface should consider the technical requirements of plastic parts; 3. The parting surface should be selected as far as possible in a position that does not affect the appearance of plastic parts; 4. The choice of parting surface should be conducive to exhaust; 5. The choice of parting surface should be convenient for the processing of die parts; 6. The selection of parting surface should consider the technical parameters of the injection machine.
45. Composition and function of injection system: Gating system refers to the feeding channel of plastic melt in the mold from the nozzle of injection machine to the cavity. Its function is to fill the cavity with plastic melt and transfer the injection pressure to all parts of the cavity, so as to obtain plastic parts with compact structure, clear outline, smooth surface and accurate size.
46. The composition of the gating system: main runner, branch runner, gate and cold cavity (it can be arranged at the end of the main runner, at the turning point of each branch runner, or even at the end of the cavity material flow).
47. runner design: 1. The main channel is generally designed as a cone with a cone angle of 2 ~ 4 and an inner wall roughness of 0.4.
0.8 um2. In order to ensure the close contact between the main channel and the nozzle of the injection molding machine and prevent material leakage, the joint between the main channel and the nozzle is generally made into a spherical pit with the smallest radius and diameter. Pit depth h = 3 ~ 5mm；; 3. In order to reduce the pressure loss and plastic loss in the melt mold, the length of the main runner should be shortened as much as possible, and the length of the main runner should generally be controlled within 60 mm ..
48. Structural design of concave die: The concave die can also be called cavity and concave model cavity, which is used to shape the outline of plastic parts. According to the different structural forms, it can be divided into four types: integral type, integral embedded type, mosaic type and flap type.
49. The structural forms of punch and core can be divided into: integral type, integral embedded type, embedded type and movable type.
50. Role of guiding mechanism: The guiding and positioning mechanism of injection mold is mainly used to ensure the accurate cooperation and reliable separation between the moving mold and the fixed mold and other parts in the mold, so as to avoid the collision and interference of parts in the mold and ensure the shape and dimensional accuracy of plastic parts.
5 1. Design of guiding mechanism: The function of guiding mechanism: guiding, positioning and bearing certain lateral pressure. The guide mechanism of guide post is a combination of guide post and guide sleeve, and the clearance fit between guide post and guide post hole is used to ensure the matching accuracy of die.
52. Classification of demoulding mechanism: 1. The push rod pushes out the plastic part; 2. A push rod fixing plate for fixing the push rod; 3. A push plate guide sleeve which guides the movement of the push plate; 4. The guide post of the push plate is the movement guide of the push plate; 5. The material pulling rod makes the condensate of the gating system escape from the mold; 6. Push plate; 7. Support nails; 8. After ejecting the plastic parts, the reset lever will reset the push plate.
53. Design principle of demoulding mechanism: 1. The power of the demoulding mechanism generally comes from the ejection mechanism of the injection molding machine, so the demoulding mechanism is generally arranged in the moving mold of the injection mold; 2. The demoulding mechanism should ensure that the plastic parts will not be deformed and damaged during ejection; 3. The demoulding mechanism should be able to ensure that the plastic parts stay in the moving mold with the ejection mechanism during the ejection and mold opening process; 4. The demoulding mechanism should be as simple and reliable as possible with appropriate pushing distance; 5. If the plastic parts need to stay in the moving mold, the demoulding mechanism should be set in the fixed mold.
54. Simple demoulding mechanism forms: push rod pushing mechanism, push tube pushing mechanism, push plate pushing mechanism, push block pushing mechanism, combined pushing mechanism and compressed air pushing mechanism.
55. Design of reset mechanism: In order to carry out the molding of the next cycle, after the ejection of plastic parts is completed, the demoulding and pushing mechanism must return to the initial position. Common reset mechanisms: spring reset (installing compression spring between push plate and moving die support plate) and reset rod reset. Ejection forms: ejector plate ejection, push rod ejection, and push tube ejection, which generally require a reset mechanism.
56. Classification of inclined column core-pulling mechanism: inclined column in fixed mould and slider in moving mould, inclined column and slider in fixed mould, inclined column in moving mould and slider in fixed mould, inclined column and slider in moving mould.
57. Inclination angle of inclined column: when the tension Q is constant, the inclination angle decreases and the bending force P on inclined column is also small; However, when the effective working length of the guide pillar is fixed, if the inclination angle decreases, the core-pulling distance S will also decrease, which is not good for core-pulling. Therefore, when determining the inclination angle of the inclined guide post, the core-pulling distance and the bending force on the inclined guide post should be considered, and 15 ~ 20 is usually adopted, generally not exceeding 25.
58. The wedge angle of the compaction block, the wedge angle of the compaction block is usually 2 ~ 3 larger than the inclination angle of the inclined guide post. This can ensure that the briquette can be separated from the slider as soon as the mold is opened, otherwise the inclined guide pillar can't drive the slider to do side core-pulling action.
59. Design of the first reset device: 1. Interference phenomenon in mold design, when the projection of the side core and the push rod perpendicular to the mold opening direction coincides, the side core may collide with the push rod during the mold closing process, which is the interference phenomenon in abrasive design.
60. Measures to avoid interference: 1. Try to avoid putting the push rod in the projection range of the transverse centroid on the plane perpendicular to the mold opening direction. 2. Make the push-out distance of the push rod smaller than the lowest surface of the movable core. If the structure does not allow, h-scot >; 0.5 mm. When H is only slightly smaller than scot, interference can be avoided by increasing the angle appropriately; 3. When the above two points cannot be realized, the push rod can be reset first, and then the slider can be reset.
6 1. Common push rod reset mechanisms are: spring reset mechanism, triangle slider reset mechanism, lever reset mechanism and pendulum reset mechanism.
1-4 Description: The drawing wall thickness is uneven, and it is easy to generate bubbles to deform plastic parts. The wall thickness on the right is uniform, which improves the molding process conditions and is conducive to ensuring quality. 5 Note: In order to avoid leaving weld marks on the plane when feeding flat-topped plastic parts with side gates, it is necessary to ensure smooth plane feeding, so a> B. Note: For plastic parts with uneven wall thickness, ripples can be used on the surface where dents are easy to occur, or process holes can be opened at the wall thickness to cover or eliminate dents.
1 Description: After adding reinforcing ribs, the strength of plastic parts can be improved and the material flow conditions can be improved. 2. Description: The use of reinforcing ribs will not affect the strength of plastic parts, but also avoid shrinkage caused by uneven wall thickness. Note: For flat plastic parts, the reinforcing ribs should be parallel to the direction of material flow, so as not to cause excessive mold filling resistance and reduce the toughness of plastic parts. 4. Note: For uneven plastic parts, the reinforcing ribs should be staggered to avoid warping and deformation of plastic parts. Note: The reinforcing ribs should be designed to be short, and there should be a gap greater than 0.5 mm between them and the supporting surface.
Flip chip composite die
1- drive rod 2- die 3- push plate 4- push rod 5- discharge screw 6- die 7- discharge plate 8- blanking die 9- ejector 10- shoulder ejector pin 1 1- punching punch 12- stop pin
Forward compound mode
1- guide pin 2- stop pin 3- concave-convex die 4- ejector plate 5- female die 6- punch 7- punch 8- push plate 9- push rod 10- push plate
Forward compound mode