Problems In The Design Of Die-Casting Molds
Due to the long production cycle, large investment, high manufacturing precision and high cost, the die-casting mold has harsh working conditions. When the die-casting is produced, the surface of the die-casting cavity is not only subjected to the high pressure and high-speed erosion of the molten metal, but also in the intense heat. Exchange, metal flow is complicated, and many factors affect the quality of die castings and die life. Therefore, designing and manufacturing a pair of die-casting molds that can ensure the quality of die-casting parts and durability can become the goal pursued by mold design and manufacturing enterprises.
According to the characteristics of the die casting production process, as well as the production practice summary. Factors such as mold design, part machining, part heat treatment, mold assembly, mold use, etc. are the main factors affecting the quality of die castings and the service life of the mold.
1. Ensure the quality of die castings is stable
When designing the mold, the main purpose of the die casting and the assembly relationship with other structural parts should be fully understood, so as to distinguish the primary and secondary, highlight the key points of the mold structure, and obtain the die castings that meet the technical requirements and requirements. The mold design should fully reflect the superior performance of die-casting, and die-casting the structure conforming to the die-casting process, such as holes, grooves, undercuts, side protrusions, etc., to avoid unnecessary post-processing.
When necessary, discuss the rationality of die casting design with the design of die casting: if consistent wall thickness is used; draft angle; sidewalls, ribs, raised parts, etc., with large rounded corners; sharp outer corners Apply rounding or chamfering to eliminate the possibility of mold failure and reduce maintenance; barbs should be avoided as much as possible, as they require machining of the part or the use of a reciprocating core slide in the mold; Let the main dimensions be related to the die-casting part, not the parting line. Since the parts are asymmetrical in the two parts of the ejector die and the fixed die, it is very difficult to achieve the same accuracy on both sides of the die-casting die boundary.
Therefore, the mold designer should give full play to the technical functions and production capacity of the die casting machine according to the technical characteristics of the die casting machine. Mold installation should be convenient and reliable.
2. Reasonable structure
The structure is advanced and reasonable, the operation is convenient, and the high die-casting efficiency has the characteristics of fast filling, quick mold opening, flexible and reliable demoulding mechanism and high degree of automation.
(1) Arrangement of gating system and drainage system
In the process of filling and pressing the mold cavity, the pouring system and the drainage system are an inseparable whole, which together play a controlling role in the filling process and are an important factor in determining the quality of the die casting.
The overall layout of the gating system and the drainage system shall be based on the structural characteristics of the die casting, the geometry, the exhaust conditions of the cavity, etc., and in combination with the form of the die casting machine selected, for the sprue, sprue and inner The location, form, size, direction of the diversion, and the setting of the drainage system are considered comprehensively and initially determined. In particular, the position and form of the ingate are important factors in determining the filling effect of the molten metal and the quality of the die casting.
When designing the gating system, it is necessary to prevent the metal liquid from impacting or flushing the core at the front and reducing the erosion of the gate inflow. Try to avoid the gate, overflow trough, and exhaust trough close to the guide post, guide bushing and core-pulling mechanism to prevent metal liquid from entering.
The die casting analysis software application of the die casting mold contributes to the design and layout of the gating system and the drainage system. Through CAE mold flow analysis, it is possible to analyze whether the design of the gating system is reasonable, analyze the balance of the mold temperature and the existence of thermal stress, and analyze the position of the defect and the cause of the die casting defect. According to the analysis results, the casting system is modified to effectively improve the mold design and product quality level.
(2) Demoulding mode selection
Under normal circumstances, after die-casting, the die-casting part remains on the side of the movable mold during the parting. In order to smoothly release the die-casting part without damage or deformation, the correct and reasonable demoulding method should be selected according to the structural characteristics of the die-casting part, and the position and size of the pushing part and the resetting rod should be determined.
For complex die-casting parts, after one ejection operation, when the mold cannot be completely demolded, two or more demolding mechanisms should be used, and the number of times and the structure and sequence of the multiple demouldings should be determined.
The side of the side of the die casting shall be a side core pulling mechanism. The side core pulling mechanism should be selected on the basis of economy and practicality. If the product batch size is not large, a simple side core type can be used; if the manual core pulling mechanism and the movable core core are used, the core can be manually removed after the mold is opened.
When the side core pulling mechanism driven by the mold opening force or the external force must be borrowed, after calculating the core pulling force, an appropriate side core pulling mechanism can be selected and the size of the main structural member can be determined.
(3) Reasonable selection of the parting surface of the mold
According to the shape and structural characteristics of the die-casting parts, it is an important part of the mold design to determine the parting surface reasonably. The choice of the parting surface largely affects the complexity of the mold structure. Parting surface selection principle:
1) The parting surface is simple and easy to process.
2) It is beneficial to simplify the mold structure.
3) The accuracy requirements of die castings should be easily ensured.
4) The parting surface should be suitable for filling and forming.
5) Keep the die casting on the side of the movable mold as much as possible when opening the mold.
(4) Structure and size of parts
According to the properties of the die-casting alloy and the structural characteristics of the die-casting part, the specific pressure of the injection is determined, and combined with the projected area of the die-casting part and the depth of the cavity, the calculation and determination are made:
1) the thickness of the sidewall of the cavity;
2) the thickness of the support plate;
3) Determine the thickness of the cavity plate, the movable platen, the movable plate seat plate, the fixed mold seat plate and related dimensions;
4) determining the position and main dimensions of the mold guiding form;
5) determining the positioning mode, installation position and fixing form of the die-casting mold;
6) determining the connection and fixing form of each structural member, and combining the various structural members into one body;
7) Determine the mold temperature adjustment method, and arrange the position and size of the cooling or heating pipe.
For more complex molded parts, it is important to consider the actual processing method, whether it is a common processing method or a special processing method. When the traditional processing method must be adopted due to the limitation of processing equipment, it should be considered how to separate and inlay to make it easier to process and polish, and to avoid deformation of heat treatment to ensure the dimensional accuracy of assembly.
The accuracy of the relative moving parts should be considered in consideration of the influence of the mold temperature change. Appropriate movement tolerances should be selected to achieve smooth, flexible and reliable movement in a die-casting environment with high mold temperatures.
The radial matching precision of the die-casting structure parts, the tolerance matching and surface roughness of various parts are correctly selected, so that the working part does not bite and smash the metal liquid at the working temperature, and the fixed parts are not loosened. Reasonable use of the combination of inserts to avoid sharp corners and sharp edges to meet the heat treatment process requirements. When setting the push rod and core hole, keep a certain distance from the edge of the insert, and the overflow groove should also be kept at a certain distance from the edge of the cavity.
Due to the design of the die-casting part, the inevitable vulnerable parts of the mold, especially the boss core of the smaller cross-section, should be inlaid as much as possible to facilitate replacement when damaged. The mold design should use standardized common parts as much as possible to shorten the mold manufacturing cycle.
3. Material selection is appropriate
The mold structural parts should meet the requirements of the mechanical processing technology and the heat treatment process. When selecting the materials of the molded parts and the casting system parts, the manufacturing cost of the mold should be considered and rationally selected. Appropriate material selection, especially for molded parts and other parts in direct contact with molten metal, should be made of high-quality heat-resistant steel and hardened to have sufficient mechanical properties and resistance to thermal deformation, fatigue strength and hardness. Corrosion performance.
(1) Material requirements for die-casting molds for formed parts and gating system parts
1) Good forgeability and cutting performance.
2) It has high red hardness and high high temperature strength at high temperature.
3) It has good thermal conductivity and thermal fatigue resistance, and has a small thermal expansion coefficient.
4) Has sufficient high temperature oxidation resistance.
5) High wear resistance and corrosion resistance.
6) Has good hardenability and a small heat treatment deformation rate.
(2) Requirements for materials used for sliding fit parts
1) Has good wear resistance and strength.
2) Appropriate hardenability and less heat treatment deformation rate.
(3) Requirements for materials used for sets and support plates
1) Should have sufficient strength and rigidity.
2) Easy to cut.
4. Software application and drawing specifications
The shape of die-casting products becomes more and more complicated while meeting the performance requirements. Only the CAD/CAE/CAM software can be used for mold design and manufacturing, so that the fastest speed, lowest cost and highest quality can be achieved. Design and produce molds.
The mold design engineering drawing should conform to the relevant standards. Since the 3D design software conversion engineering drawings such as PRO/E and UG are quite different from the relevant standard regulations, the application software can be converted and edited into engineering drawings conforming to relevant standards.