Development of LED spotlight lenses has led to development of optical molds, and quality of mold structure directly affects control of injection moulding process and product cost. This paper analyzes structure of a spotlight led lens molding. For problem that mold flow path is too long, raw materials are wasted and parameters of injection process are affected, objective factors of mold structure are analyzed and a new nozzle structure is designed. Positioning ring and sprue bushing are made into an integral structure, die structure is optimized according to nozzle of injection moulding machine. Optimized mold shortens length of main runner, reduces cost and difficulty of tuning. After being put into production, it proves that its structure is efficient, stable and reliable.

Figure 1 shows a 35 mmX 17 mm spotlight lens. This lens is used as an example to illustrate structural optimization of this type of lens mold. Maximum installed diameter is ≯35 mm, total height is 17 mm, overall mass is 8 g, minimum wall thickness is only 0.27 mm, and maximum wall thickness is about 11 mm. There are openings on upper and lower sides of product, and on the center, and it is not suitable for opening gate. Therefore, only side gate can be selected. Due to small overall weight of product, considering utilization rate and production efficiency of injection moulding machine, a led lens molding of eight cavities is opened. Parting surface is selected on the largest mounting side and can be pushed out around mounting ring. Product has a high optical requirement, so polishing performance is excellent at $136. Due to high cost of materials and commonality of products, in order to share mold base, it is necessary to select structural form of molded parts as a whole. Customers have requirements, only cold runner molds can be selected to control mold costs. Therefore, final mold plan is shown in Figure 2.

 

 

As can be seen from Fig. 2, thickness of fixed seat plate is 25 mm, thickness of fixed plate is 60 mm, and total thickness of template is 85 mm. One design principle of gating system is that gating system should be as short as possible. Length of main runner is thickness of template and length is preferably not more than 60 mm. Therefore, hole of positioning ring is opened into a tapered hole, small end of main runner is minimized, and length of main channel in fixed plate can be omitted, but length of main runner is still about 65 mm.

Mold of long runner has many drawbacks, mainly reflected in following two aspects.
(1) Waste of raw materials. In cost control of lens mold, control of raw material is a large part, and for mold of cold runner, main waste of raw material is reflected on aggregate of casting system. Diameter of small end of main runner is constant with diameter of nozzle, and taper is determined by fluidity of material, Diameter of runner is also affected by main runner. So in mass production, length of main runner is a great waste of materials.
(2) Process ratio is too large to affect injection molding process parameters and increase difficulty of mold trial. Three process parameters of mold forming are time, temperature and pressure. Temperature includes mold temperature and material temperature, temperature of material and mold are mainly determined by viscosity of material, and influence of flow path structure is relatively small. Molding time, injection time and cooling time are mainly affected by factors such as product size, thickness, mold temperature and gate number. However injection pressure is largely affected by length of flow path. P is used to indicate injection pressure, 7" / means material constant (generally 0.15 ~ 0.36), and injection pressure is proportional to flow length as can be seen from equation (1). As flow length increases, required injection pressure increases accordingly. Injection is usually carried out with medium pressure, because too high injection pressure easily causes machine to overload, which will cause excessive energy consumption and increase injection cost.

Due to problems of long-flow runner molds during molding, optimization method is to shorten flow path. Flow path refers to length from nozzle of injection moulding machine to gate position. Therefore, core idea of improvement is to change length of flow path by changing position of nozzle of injection moulding machine.

Design of mold casting system has a great relationship with injection moulding machine. Many parts of mold are determined by size of injection moulding machine. Diameter of small end of main channel of mold is 0.5~1 mlTl larger than nozzle size of injection moulding machine, ball nose radius of main runner bushing is 1~2 1Tin2 larger than ball nose radius of injection moulding machine nozzle. Diameter of positioning ring should be less than or equal to aperture of injection moulding machine, height is 8 to 15 1 TTITI higher than surface of mold fixing plate. Considering these two conditions that must be met, locating ring and main runner bushing can be designed as a single structure. Regular structure will make main runner very long. Nozzle structure and dimensions of injection moulding machine are shown in Fig. 3. Positioning ring structure of mold and structure of main runner bushing are designed as shown in Fig. 4, which is referred to herein as a machine nozzle. Nozzle is designed with an inner hole d, which is 701Tlln and much larger than outer diameter 30 l'nlTl of injection moulding machine. During injection moulding, nozzle of injection moulding machine is directly placed into inner hole of positioning ring, and nozzle is assembled into mold to obtain the structure as shown in FIG. From structure of nozzle, it can be clearly seen that length of flow path has been reduced to 40 mm.

 

 

Machine sprue requires a certain strength and rigidity. Since life expectancy of led lens molding is high now, it is made of Crl2MnV. Following processing route is adopted: blanking, turning shape, drilling screw hole, heat treatment, grinding shape and matching size, a small hole machined through wire hole to cut flow channel taper.

Size of nozzles of different injection moulding machines is different, but lens mold are mostly of a monolithic structure. Different sizes of products have different layouts, but structure of molded parts is similar. For different injection moulding machines and different sizes of mold bases, it is only necessary to change outer diameter D and height L of machine according to size of mold base. Derivative structure after changing outer diameter D and height L of machine sprue can basically solve structural problem that main flow path of led lens molding is too long.

 

This paper analyzes structure of an spotlight led lens molding and comprehensively evaluates its structure. Long flow path is not only waste raw materials and increase difficulty of injection moulding. According to analysis of objective factors, an integrated nozzle was designed, which directly shortens length of main runner, saves raw materials and reduces difficulty of adjusting injection moulding parameters. It is used in actual production to prove that its structure can ensure stable and reliable production. It can also be applied to other long runner molds, which fundamentally solves problem of excessive flow passage.