Picture of multi-function watch case is shown in Figure 1. Maximum size of product is 54.82 mm * 36.40 mm * 17.47 mm, average thickness of plastic part is 1.30 mm, material of plastic part is ABS, shrinkage rate is 1.005, and weight of plastic part is 7.5. Grams. Technical requirements for plastic parts are that there must be no defects such as peaks, underfilling of injection molding, flow lines, pores, warpage deformation, silver streaks, cold materials, jet lines, bubbles and so on.

 

Figure 1 Product picture of multifunctional watch case
It can be seen from Figure 1 that structure of plastic part is a complex structural part. See attached file for 3D drawing of plastic part. There are 3 side holes on two side faces that are directly opposite at 3 o'clock and 9 o'clock respectively. Three side holes need slider to pull core and have an angle between each other. A square hole on the inside of plastic part communicates with oblique hole on the front. There is a watchband connection pinhole at each end of plastic part, diameter of this hole is ø1.92, and core pulling length is 12 or more. These holes and grooves need to design 11 slider cores. Due to small space position, there is interference between sliders, which brings difficulties to mold design. Mold design drawing is shown in Figure 2.
Mold is a complex mold. Product size is small, but sliders occupy a lot of space. Therefore, mold design cavity ranks 1 cavity. In order to facilitate design of front mold oblique slider, mold base uses standard mold base EDI3335; shape of part is all appearance surface, so gate is selected inside circumference of plastic part. After molten plastic enters parting surface from sprue bushing sprue, it is divided into 4 channels, latent gates, and 4 points of glue.
Two pits at both ends of plastic part need to be designed with front mold sliders, which are driven by 25° inclined guide posts. Square hole on the inner side of plastic part adopts form of a sliding block in rear mold, and oblique guide post is fixed on back mold backing plate. There are 3 side holes on two sides facing 3 o'clock and 9 o'clock respectively, and a small sliding block of rear mold is designed, all of which are driven by inclined guide posts. There is a strap connection pinhole at both ends of plastic part. Two holes also need to be designed with back mold slider. Due to small space position, two-hole slide block is designed at the bottom of side-hole core-pulling slide block, and position is staggered. See 3D drawing of mold design.

 

Inner sliding block adopts rear mold floating mpld plate to achieve core pulling, this sliding block and front mold inclined sliding block need to collide. Therefore, a first reset device is designed. This first reset device is the first resetting sleeve resetting after straight rod of front mold hits mold, which has advantages of simple structure and small mold space occupation. This kind of first reset mechanism has standard components to buy. It is widely used in European and American molds.
Both front and back molds of mold are designed for direct water transport to ensure stable progress of injection molding process.

 

 

 

 

 

Figure 2 Die diagram of multi-function watch case

Study performance or status of injection molding machine and gradually decline with passage of time. Many failures have some signs before they occur. This is so-called latent failure. Its identifiable physical parameters indicate that a functional failure is about to occur, a functional failure indicates that injection molding machine has lost specified performance standards.　
Failure rate of an injection molding machine changes with time, which is often called a bathtub curve. Failure rate of an injection molding machine changes with time roughly divided into three stages: early failure period, occasional failure period and wear failure period.

Injection molding machine is in the early failure period, with a high initial failure rate, but failure rate drops rapidly with passage of time. Early failure period is also called running-in period for mechanical products. Length of this period of time varies with product, system design and manufacturing quality. Failures occurred during this period are mainly caused by defects in design and manufacturing, or caused by improper use environment.

Injection molding machine enters a period of sporadic failure, and failure rate is roughly in a stable state, tending to a fixed value. During this period, failures occur randomly. During occasional failure period, failure rate of injection molding machine is the lowest and stable. Therefore, it can be said that this is the best period or normal working period of injection molding machine. This section is called effective life.
Failures during occasional failure period are mostly caused by improper design, improper use and poor maintenance. Therefore, failure rate can be reduced to the lowest level by improving design quality, improving use management, strengthening monitoring, diagnosis, and maintenance.

In later stages of injection molding machine's use, failure rate began to rise. This is caused by wear, fatigue, aging, corrosion, etc. of parts of injection molding machine. If overhaul is carried out at inflection point, that is, when wear-out failure period begins, failure rate can be economically and effectively reduced.
Three stages of change of failure rate curve of injection molding machine truly reflect law of failure rate of injection molding machine from running-in, debugging, normal operation to overhaul or scrapping. Strengthening daily management and maintenance of injection molding machine can extend occasional failure period. Accurately find inflection point to avoid excessive repairs or expansion of repair scope to obtain the best investment benefits.