Method for molding products made from metal or plastic materials

Abstract

A method for molding products made from metal materials is provided, which includes the following steps: heating a metal material to a melting temperature; and quenching the metal material from the melting temperature to a quenching temperature. The quenching temperature being 5˜20 degrees centigrade lower than room temperature. A method for molding products made from plastic materials is also provided, which includes the following steps: heating a plastic material to a melting temperature; decreasing temperature from the melting temperature to a glass transition temperature of the plastic material; quenching the plastic material from the glass transition temperature to a quenching temperature, with the quenching temperature being 5˜20 degrees centigrade lower than room temperature; tempering the plastic material from the quenching temperature to a tempering temperature; and decreasing temperature from tempering temperature to room temperature.

Description

TECHNICAL FIELD

The present invention relates to methods for molding products, in particular, to a method for molding products made from metal or plastic materials.

BACKGROUND

With the great development of technologies, market competition in the field of consumer electronic products becomes furious. For manufacturers, in order to sell out their products, efforts have been focused not only on functions of the products, but also on appearance of the products.

A shell of commonly used consumer electronic products is often made of metal or plastic materials. Shells with crude and tarnished surface will affect the appearance of the products. In addition, since shells are often touched by customers' hands, wear resistant properties are important to influence the appearance. Besides, impact resistant properties of shells are also important, which can prevent the appearance of the products from being destroyed by sudden impact or fall.

To improve surface properties of shells, particular treatment should be provided. Typically, heat treatments, such as quenching or tempering are widely used. While, during quenching, the shell will be naturally cooled down to room temperature. Sizes of crystal grains of the shells formed therefrom usually become large, whereby the surfaces of the shells become rough. This will not only influence brightness and smoothness of the surface, but also affect the toughness of the shell.

Therefore, a heretofore-unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.

SUMMARY

In a first preferred embodiment, a method for molding products made from metal materials includes the following steps: heating a metal material to a melting temperature; and quenching the metal material from the melting temperature to a quenching temperature. The quenching temperature is 5˜20 degrees centigrade lower than room temperature.

In a second preferred embodiment, a method for molding products made from plastic materials includes the following steps: heating a plastic material to a melting temperature; decreasing the temperature from the melting temperature to a glass transition temperature of the plastic material; quenching the plastic material from the glass transition temperature to a quenching temperature; tempering the plastic material from the quenching temperature to a tempering temperature; and decreasing the temperature from the tempering temperature to room temperature. The quenching temperature is 5˜20 degrees centigrade lower than room temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the molding methods can be better understood with reference to the following drawings.

FIG. 1 is a temperature—time graph of a method for molding products made from metals of a first preferred embodiment;

FIG. 2 is a flow chart of the method of FIG. 1;

FIG. 3 is a temperature—time graph of a method for molding products made from plastics of a second preferred embodiment; and

FIG. 4 is a flow chart of the method of FIG. 3.

DETAILED DESCRIPTION

A method of a first preferred embodiment is used for molding a metal shell. During dead-end molding step, temperature alteration of the metal shell should be controlled strictly as the method described, so as to get improved mechanical properties on a surface layer of metal products. Referring to FIGS. 1 and 2, T₁ represents a melting temperature of the metal. T_R represents room temperature. T_q represents a quenching temperature. First of all, when a metal shell raw product is made, metal material on surface layer of the metal shell row product is heated to the melting temperature (T₁) thereof. After maintaining the temperature at the melting temperature (T₁) for 10˜20 seconds, the melted metal is quenched rapidly from the melting temperature (T₁) to the quenching temperature (T_q). The quenching temperature (T_q) is 5˜20 degrees centigrade lower than room temperature (T_R). During this process, quenching rate from the melting temperature to the quenching temperature should be controlled fast, normally at a rate of 5˜100 degrees centigrade per second, preferably 20˜50 degrees centigrade per second. In order to prevent the metal shell from crisp, it is preferable to maintain the temperature at the quenching temperature for a long time, e.g., for about half-hour. Thus, finished metal product is manufactured.

During this process, the metal shell is treated with rapid quenching technology. Since the quenching rate is fast, and the quenching temperature is lower than room temperature, there's no time for grains of the metal material growing by diffusion mechanism. Thus sizes of crystal grains of the metals will be reduced, surface roughness will be decreased and brightness will be enhanced. Accordingly, compared with nature cooling process, the quenching process of the preferred embodiment could get a smaller grain size.

The metal materials which are suitable to the above rapid quenching process is selected from the following group comprising of aluminium magnesium alloy, magnesium aluminium alloy, aluminium magnesium titanium alloy, aluminium magnesium chromium alloy, iron carbon alloy, stainless steel, magnesium alloy and titanium molybdenum alloy.

A method of a second preferred embodiment is used for molding plastic shell, before a injection molding step. This method includes the following steps: heating a plastic material to a melting temperature thereof; decreasing the temperature from the melting temperature to a glass transition temperature thereof; dwelling or keeping pressure at the glass transition temperature; quenching the plastic material from the glass transition temperature to a quenching temperature; first heat insulating or keeping temperature at the quenching temperature; tempering the plastic material from the quenching temperature to a tempering temperature; second heat insulating at the tempering temperature; and decreasing the temperature from the tempering temperature to room temperature. Referring to FIGS. 3 and 4, T₂ represents the glass transition temperature of the plastic. T_R represents room temperature. T_q represents the quenching temperature. T_a represents the tempering temperature.

When manufacturing, plastic particles are firstly fed into a chamber of an injection-molding machine, and then heated to melt at a melting temperature. The melting temperature of a plastic is normally about 300 degrees centigrade, at which the plastic is flowable. Thus the melted plastics can flow from the chamber to a runner, and then into a cavity. When the cavity is filled with melted plastic material, decreasing the temperature from the melting temperature to the glass transition temperature (T₂) of the plastic material. During that step, the plastic material changes from a glassy state to a rubbery state. To different plastics, the melting temperature and the glass transition temperature are different. The glass transition temperature of plastics is normally about 100 degrees centigrade. In order to prevent plastic material from strong shrinkage due to sudden quencher, a dwell step is preferred, during that step, at the glass transition temperature, pressure in the cavity is maintained for about 10 seconds, referring to the first straight line in FIG. 2. Then quenching the glassy stated plastic material rapidly from the glass transition temperature (T₂) to the quenching temperature (T_q) at a quenching rate of 5˜100 degrees centigrade per second, preferably 2˜50 degrees centigrade per second. The quenching temperature is 5˜20 degrees centigrade lower than room temperature (T_R).

After maintaining temperature at the quenching temperature (T_q) for 10˜20 seconds, the plastic material undergoes a tempering step, that is, the temperature rises rapidly from the quenching temperature (T_q) to a tempering temperature (T_a) with a rising rate of 5˜80 degrees centigrade per second, preferably 10˜40 degrees centigrade per second. And then after maintaining temperature at the tempering temperature for 20˜60 seconds, the temperature is decreased rapidly to room temperature at a decreasing rate of 10˜20 degrees centigrade per second. Finally, followed with a rejection molding process, a plastic shell is formed.

Furthermore, in order to prevent melted plastic material from oxidating, during rapid quenching step and/or rapid tempering step, protective gases are introduced, which could be chosen from inert gases, such as nitrogen, argon or helium.

The plastic materials could be a composite material, such as a acrylonitrile butadiene styrene (ABS) resin added with fiberglass. The plastic could be used in mobile phone, notebook, desktop computer, DVD, liquid crystal display et al.

During molding of products made of metal or plastic materials, a rapid quenching process and/or a rapid tempering process are applied. Since the quenching rate is fast, quenching temperature is lower than room temperature, there is no time for the sizes of crystal grains of plastics growing at a diffusion mechanism. Thus sizes of crystal grains of the plastics will be reduced, furthermore, brightness, smoothness and surface toughness will be enhanced.

For metal alloy or plastic, particle size is an important factor which can affect fracture toughness of the materials. Fracture toughness (K_1c) is one of main mechanical parameters for metal alloy or plastic. Fracture toughness indicates an ability of the material for preventing micro crack extension. Generally, when the fracture toughness is high, the material exhibits a good mechanical property. The fracture toughness satisfies the following formula: $K_{1c}~{\sigma }_y·{\left(\frac{3.14159c}{d}\right)}^{0.5}$
wherein K_1c represents fracture toughnesss; σ_y represents yield strength, also known as yield limit; c represents crack length; and d represents particle size. It can be deducted from the above formula that the smaller the particle size, the larger the fracture toughness. Thus, when quenching at the temperature of lower than room temperature, sizes of crystal grains are reduced, thus fracture toughness will be enhanced.

In order to further improve the brightness of the shells made from metals or plastics, phosphorus or nano luminous materials could be added into the metals or the plastics. These nano luminous materials could be chosen from the following: ZnS, CdSe, CdS, Eu—ZnSiO_x, Eu—YBO₃ and Eu—BaMgAlO_x.

It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.

Claims

1. A method for molding products made from metal materials comprises the following steps:

heating a metal material to a melting temperature; and

quenching the metal material from the melting temperature to a quenching temperature, with the quenching temperature being 5˜20 degrees centigrade lower than room temperature.

2. The method as claimed in claim 1, wherein a quenching rate of quenching step is 5˜100 degrees centigrade per second.

3. The method as claimed in claim 2, wherein the quenching rate is 20˜50 degrees centigrade per second.

4. The method as claimed in claim 1, wherein the metal materials are chosen from the following group: aluminium magnesium alloy, magnesium aluminium alloy, aluminium magnesium titanium alloy, aluminium magnesium chromium alloy, iron carbon alloy, stainless steel, magnesium alloy and titanium molybdenum alloy.

5. The method as claimed in claim 4, wherein the metal materials further comprises nano luminous materials, chosen from the following group: ZnS, CdSe, CdS, Eu—ZnSiOx, Eu—YBO3 and Eu—BaMgAlOx.

6. A method for molding products made from plastic materials comprises the following steps:

heating a plastic material to a melting temperature;

decreasing the temperature from the melting temperature to a glass transition temperature of the plastic material;

quenching the plastic material from the glass transition temperature to a quenching temperature, with the quenching temperature being 5˜20 degrees centigrade lower than room temperature;

tempering the plastic material from the quenching temperature to a tempering temperature; and

decreasing temperature from tempering temperature to room temperature.

7. The method as claimed in claim 6, wherein a quenching rate from glass transition temperature to the quenching temperature is 5˜100 degrees centigrade per second.

8. The method as claimed in claim 7, wherein the quenching rate is 20˜50 degrees centigrade per second.

9. The method as claimed in claim 6, wherein the tempering temperature is 80˜100 degrees centigrade.

10. The method as claimed in claim 6, wherein a tempering rate from the quenching temperature to the tempering temperature is 5˜80 degrees centigrade per second.

11. The method as claimed in claim 10, wherein the tempering rate is 20˜50 degrees centigrade per second.

12. The method as claimed in claim 6, further comprising a step of processing a dwell step for 10 seconds after decreasing to the glass transition temperature.

13. The method as claimed in claim 6, wherein after decreasing to quenching temperature, maintain temperature at the quenching temperature for 10˜20 seconds.

14. The method as claimed in claim 6, wherein when rising to tempering temperature, maintain temperature at the tempering temperature for 20˜60 seconds.

15. The method as claimed in claim 6, wherein the plastic materials are ABS resin added with glass fiber.

16. The method as claimed in claim 1, wherein during quenching step and/or tempering step, inert gases are introduced.

17. The method as claimed in claim 6, wherein during quenching step and/or tempering step, inert gases are introduced.