Key points of injection mold design for inner and outer casing of spotlights

Time：2023-11-24 19:31:11 / Popularity： / Source：

Inner and outer casing products of spotlights are shown in Figure 1. Maximum outer dimension of product is ø129.75 mm * 29.20 mm; average glue thickness of plastic parts is 3.00 mm, plastic part material is ABS, shrinkage rate is 1.005, plastic part weight is 42.8 grams and 47.06g. Technical requirements for plastic parts are that there must be no defects such as peaks, uderfilling, flow lines, pores, warping deformation, silver streaks, cold materials, jet lines, etc. and they must comply with ROSH environmental requirements.

Figure 1 Product diagram of inner and outer casing of spotlight
Spotlights are mostly used outdoors, and some can be placed underwater. They are commonly used lamps for landscaping and decoration places, and can play a refreshing role. Spotlights can be used as both main lighting and auxiliary light sources. Shapes of spotlights are ever-changing and overwhelming, but most of them are round. This article introduces 1+1 mold for spotlight mounting bracket and waterproof housing.
Plastic part is a round plastic part with a deep bone on the back. It is a 1+1 mold of spotlight mounting bracket and waterproof shell. It is often called a family mold abroad. Family-style molds can reduce costs during product trial production or small batch production. However, in high-precision products, due to inconsistent shape and size of each plastic part, runner is difficult to balance, which brings difficulties to the injection molding machine. In actual mold design, the two plastic parts use 2-point and 3-point glue feeding respectively, gate is a point gate, and mold is a three-plate mold. Mold base is standard mold base FCI2740 - A60 -B90 -C80 -L250. In order to improve mold closing accuracy of front and rear mold cores, positioning tabs are designed at the four corners of front and rear mold cores, with a single side angle of 10゜.
Obviously, mold is a simple mold, without complex mold opening motion analysis, and there is no slider or lifter. Parting surface of mold is also a simple plane. Mold parting surface is shown in Figure 3. There are 6 sunken insertion positions on the top surface of mounting bracket, which are prone to sharp edges. Certain measures need to be taken when designing mold.

Figure 2 3D diagram of mold

Figure 3 Mold parting surface view
Molds usually have chipping problems, such as: chipping on parting surface, chipping at runner nozzle, chipping at penetration position, chipping at rubbing position, chipping on thimble barrel, chipping on the joint of inserts, chipping on lifter, and chipping on sliders, etc. Problem of mold chipping needs to be solved from two aspects: mold design and mold production:

1. Mold design:

1) Reasonable design of three-level positioning of mold can effectively solve problem of mold tipping. The first level is positioning of guide posts and bushings, and second level is zero-degree positioning parts, taper positioning parts or cone positioning parts on mold base. Third level is positioning corner at four corners of mold.
2) Designing a hard mold, that is, heat treatment of front and rear mold cores, can increase life of mold and reduce occurrence of chipping.
3) Properly designed inserts, well vented molds, and reduced injection pressure can reduce occurrence of glitches.
4) Front and rear molds should be rigidly designed, especially for large and medium-sized molds with thick mold plates and heavy weight. Design positioning pins between fixed mold plates to increase mold rigidity.

2. Mold manufacturing

1) When trying out mold, if product has a chip, apply a thin and even layer of red paint on machine table to check whether FIT mold is in place. If red core does not arrive or arrives unevenly, you need to re-FIT mold.
2) Red core has arrived evenly. Check whether machine is not strong enough, or mold base is too thin, strength of mold base is not enough, and whether support head is 0.15~0.25mm higher than square iron.
3) Red core reaches evenly, but there are still ridges at gate and water pinch area. Whether gate runner is too small and difficult to fill, injection pressure needs to be increased. Then check whether gate runner meets injection molding requirements and whether it is necessary to increase water inlet or increase water inlet point. Water trap should be vented.
4) If material has good fluidity, it is easy to have edges. Check whether ejector pin hole and cylinder hole are too loose.
5) Whether FIT mold of sloping top cape is not in place, there is a gap in sealing position or screws are not tightened.
6) Whether slider strip is not firmly locked, and whether red rubber sealing position is not in place or uneven.
7) There are sharp edges at joints of inserts. Is insert too loose or sealant position has been excessively polished? Or verticality of insert is not good and there is a gap in contact surface. Or insert is too thin and deformed.
8) Sealing side of ejector block is straight, there will be scratches when it is pushed out and reset.
9) Top block is not nitrided and is scratched when it is pushed out and reset.
10) It was not installed properly during assembly and the top block screws were not tightened.
11) When tonnage of injection molding machine is not enough, mold clamping force is insufficient, which will also cause chipping. At this time, you need to pay attention to replacing machine.
If precision of mold processing machine tool is not high, accuracy of front and rear mold closing cannot be guaranteed, and parting surface will produce a large clamp line. If clamp line is combined with edge, it will seriously affect quality of mold, and should be avoided as much as possible. Careful inspection is required during mold trial to determine cause of ridge formation so that correct corrections can be made.

Gud Mould Industry Co., Ltd