With the development of science and technology, the demand for the safety of die-casting products and the beautiful appearance are continuously increasing. The evaluation of the quality of the parts is different depending on the use. Xiaobian today to tell you how die design affects the quality of aluminum die-casting.
How to produce high-quality parts, to save materials, energy and shorten the manufacturing man-hours, improve economic efficiency are of great significance.
One. Affect the quality of die-casting parts
There are many factors that affect the quality of die-casting parts, such as the type and quality of die-casting machine, die-casting geometry and technical requirements of the rationality, mold structure and operator skills.
Die casting design
Designers should first fully understand the user's requirements and working conditions, die-casting force, and then use the requirements and work environment, select the appropriate material to understand the material die-casting properties. In the design, pay special attention to meet the requirements of the premise, as far as possible to make die-casting structure is simple. Wall thickness properly, and leave the necessary draft, otherwise it will lead to die-casting pit, porosity, shrinkage, cast, pull marks, cracks, deformation and other defects.
Die-casting dimensional accuracy requirements should be reasonable, otherwise the mold design, mold processing, process conditions and the management of the formation of unnecessary trouble, will result in a large number of substandard products.
2 die structure, machining accuracy and mold material selection
Die-casting is die-casting mold, no doubt mold design, processing, mold material selection and product quality are closely related. Die structure is irrational, no matter what kind of measures taken from the process, it is difficult to make the product qualified.
In addition, the mold material, mold machining accuracy, surface roughness, processing marks, heat treatment of tiny cracks, nitride layer thickness and improper assembly of the mold, etc., will affect the product quality and mold life.
3. Casting material shrinkage
Shrinkage of casting materials, usually in the average percentage or a certain percentage of the range of change is given, the material is usually selected the average shrinkage rate. For high-precision die-casting parts, mold design, the choice of material shrinkage should pay special attention, if necessary, can be the first test mold, the test mold to obtain the required data, and then proceed to the design and manufacture of molds for mass production.
4. Die casting process development and implementation
Die-casting process of the formulation and implementation, and die, die-casting equipment, the quality of the technical level of the operator. Diecasting equipment in the country under the conditions of the die-casting process parameters are also difficult to achieve stable, reliable and accurate control. To achieve the basic control Die-casting process is the die-casting equipment, die-casting materials and mold and other elements combined and applied process. The lax implementation of the process and the main parameters will lead to shrinkage casting, deformation, casting, size and other unqualified.
Second, the quality of die-casting mold and the relationship
Die is the main tool for die-casting, die, mold design, should try to make the overall structure of the mold and mold parts structure is reasonable, easy to manufacture, easy to use, safe and reliable. To make the mold in the die-casting is not deformed, liquid metal flow stability in the mold, the casting can be evenly cooled, fully automatic die-casting without fault. In addition, according to the production volume, material and other reasonable selection of appropriate mold material.
1. Die and mold parts of the structure to be reasonable
From the strength point of view, the mold parts designed as a whole good, durable, easy to use in the damaged, not easy to deformation. However, if the die-casting shape is complex, mold parts are complex, the mold will be difficult to process, processing accuracy is not high. If the mold parts made of a combination, the processing greatly simplified, easy access to high precision machining, and thus access to high-quality die-casting.
2 cavity number decision
Determine the number of cavities, to consider the equipment capacity, the difficulty of mold processing, production batch size, precision casting requirements. Especially the multi-cavity mold, due to the mold processing difficulty, dimensional error, channel configuration is not easy to achieve balance, the performance of the cavity casting is inconsistent. Die casting requires high precision, complex geometry, the best mold cavity. Small castings depending on the situation.
3 pouring system design
Casting system is not only liquid metal filled die-casting channel, but also on the melt flow rate and pressure transmission and exhaust conditions, die-casting thermal stability and other factors have a regulatory role, therefore, the design of the casting system must analyze the structural features of the casting, Technical requirements, alloy types and their characteristics, but also consider the type and characteristics of die-casting machine, etc., in order to design a reasonable pouring system.
Exhaust system design
The mold should be provided with overflow tank and exhaust passage with sufficient overflow range, which is very important to ensure product quality. It is often overlooked that the overflow channel is prematurely blocked by incoming liquid metal. To adopt a reasonable structure, the liquid metal flow into the deeper part of the overflow tank, to ensure that the vent has been through for the longest time. In addition, the overflow tank should be provided with ejector rods to exclude the metal in the overflow tank.
Die casting mold temperature is an important factor affecting the quality. Mold temperature is not appropriate, not only affect the internal and external quality of die-casting (such as casting porosity, shrinkage, loose, mucous membrane, coarse grains and other defects), but also affect the dimensional accuracy of castings, and even deformation of castings, die- The surface is difficult to remove the net-shaped burr, affecting the appearance of die-casting quality. Taking aluminum alloy as an example, the alloy temperature is poured into the mold at 670-710 ° C. In the long-term production practice, concluded that the best mold temperature should be controlled at casting mold temperature of 40%. Aluminum die-casting mold temperature of 230-280 ℃, mold temperature within this range is conducive to obtain high-quality castings.
Molds are generally not gas or electric heating, and the use of preheating cooling device, these devices are in accordance with the requirements of oil as a medium, the mold preheating and cooling.
6 forming the size of the decision
Calculate the size of die-casting parts, the choice of die-casting material shrinkage to be realistic, otherwise it will lead to the production of substandard products. When necessary, after the test mold measured, and then calculate the size of die-casting. For high-precision products, die-casting parts and materials even to the thermal expansion and product die-casting preservation, the use of the environment to take into account the impact of dimensional accuracy.
7. Parting surface position decision
Sub-surface location, will affect the mold processing, exhaust, product release and so on. Usually, the parting surface will leave a trace on the product, affecting the surface quality and dimensional accuracy of the product. Therefore, the design sub-surface location, in addition to taking into account product demoulding, mold processing, exhaust and other issues, the sub-surface location on the product surface quality is not demanding, or the size of the place is not high precision.
8. Mold can not be deformed
Often due to unreasonable mold structure or improper selection of mold materials, resulting in the use of mold in the mold, deformation, and thus lead to product failure, therefore, in the design of the mold, we must take appropriate measures to ensure product quality.
Normally, when die-casting, the pressure in the mold is 70-100MPa. In order to make the mold not distorted, the cavity should be thick enough and the plate and the pad to install the core should be thick enough. Under the pad, the pad can be added if necessary. Core and cavity to be installed reliably, the core and the mounting hole side roughness to be appropriate, the roughness can not be too low, through-hole core should be fixed on both sides to prevent the product side wall thickness, while thin wall. Blind hole on the product core, but also from the feed port site, the number and core reinforcement on the way to make the core force balance.
The die-casting mold cavity, backing plate for strength check. The wall thickness of the cavity strength, stiffness check, check the stiffness of the pad. In addition to the mold structure to take certain assurance measures, but also have to use small deformation, high strength mold material. In addition, the gap between the mold guide and the guide sleeve, or guide post, the guide sleeve in the course of wear and tear will affect the quality of the product. Especially for the product with high dimensional accuracy, in order to ensure the accuracy of the product, the parting surface can be set on the parting surface with the matching part of the conical surface or in the proper place around the cavity to set the positioning and enhancing effect , In order to prevent moving, fixed mold misplaced, which is more important for large-scale, high-volume production of mold.
The introduction of the system should be set guide column to prevent the push rod and other work is not stable, subject to unilateral wear and tear to ensure that the product force evenly, the top does not make the product deformation. 【Suzhou mold design】