Product picture of bearing housing of output station is shown in Figure 1. Maximum external dimensions of product are 170.5mm * 102.2mm * 32mm, average plastic thickness of plastic parts is 3.0mm, material of plastic parts is PC+ABS, shrinkage rate is 1.005, weight of plastic parts is 73.92 grams. Technical requirements for plastic parts are that there must be no defects such as peaks, injection dissatisfaction, flow lines, pores, warpage, silver lines, cold materials, spray lines, etc. Plastic parts must ensure geometric tolerances of drawing.

 

Detailed technical requirements are included in plastic parts drawing, which is briefly translated as follows:
1. Adopt GE's black raw material PC+ABS, model 23-931J;
2. Surface marked 2 is etched surface, according to general requirements of American guests, etched texture is model MT-11040;
3. Designated area sinks 8mm, and the rest is 9mm;
4. Make IBM inserts;
5. Maximum draft angle is 1 degree;
6. Draft angle must be reduced;
7. Typical wall thickness is 3mm, and thickness is reduced for insert;
8. Material is fireproof material, level V0;
9. Surface marked 12 must not have a draft angle.

 

 

Plastic parts are door bearing housing products of output station of I/O network base station of IBM Corporation. Product functions require that plastic parts have strength and no deformation. Mold design style book is shown in Figure 2. Mold design style book is basis for mold design, manufacturing and delivery. Mold steel is specified as S-7. S-7 cold work tool steel belongs to high-toughness wear-resistant non-deformable chromium-molybdenum steel. Chromium content is about 5%, excellent corrosion resistance, strong ductility, good damage resistance of die edge, good hardenability, uniform carbide distribution, good wear resistance and air quenching performance. After air quenching, dimensional deformation is small, carbides are uniform and fine, so wear resistance is very good. Therefore, use of S7 to make molds rarely cracks and cracks, it has characteristics of high strength, high wear resistance, high impact, low deformation and good finish. Therefore, using S7 can increase mold life and reduce processing steps. Mold made with S-7 cannot be replaced by 8407 and 1.2344, otherwise mold cannot meet performance requirements. While front and rear mold cores are heat-treated, front mold cores are etched and rear mold cores are polished SP1-B3. Mold style book specifies mold grade 102 and corresponding mold life is 500,000 times. Mold cavity is layout 1 cavity and there are 3 places where slider core needs to be designed. Mold is exported to United States. Overall design style adopts American mold standard, and standard mold parts adopt DME standard. Positioning ring is ø3.99"; sprue sleeve spherical surface R1/2"; design of mold gating system is a latent gate with two points injection; mold base is a straight mold base 3545; four sides of mold base are designed with a zero degree positioning block to ensure accuracy of mold clamping; U-shaped skid grooves are designed between each two adjacent templates of mold base. U-shaped skid grooves are processed on long side of mold plate by milling machine and close to corners. Advantage is that it will not slip during skid and cause unsafe accidents, so it is widely used in European and American molds.

 

Fig. 1 Product drawing of bearing housing of output station door

There is no draft angle on the surface, and design slider. With regard to accuracy of mold processing, S-7 cold work tool steel is a hard mold steel and requires heat treatment. Machining accuracy is related to CNC machine tools, cutting tools and steel. Best processing performance of milling is related to heat treatment hardness of steel. Steel has the best processing performance at 38HRC hardness. Hardness of S-7 cold work tool steel is HRC55~57. With development of tool industry, milling of this hardness is no longer difficult. Processing accuracy of injection mold is reflected in mold clamping precision. Mold clamping precision is high, mold core processing precision is required to be high, and vice versa; American customer propose to reduce gap at mold parting surface to 0.0015", which is 0.04mm. It is clearance of AB plate at parting surface, see mold design picture 3, such a high mold clamping gap requires high mold processing accuracy. During injection, when mold is over-pressured, mold bases contact each other, which can increase contact area and and protect parting surface. Some mold manufacturers think that gap of AB plate at parting surface is 1 or 2, it seems to be indifferent. I don’t know if this is because precision of machine is not enough, there is no way. In a modern mold manufacturer with excellent equipment, with cooperation of a mold clamping machine, zero clearance can be achieved.

 

Figure 2 Style book of door bearing housing of output station

Three slides are all rear-mold slides, which are driven by inclined guide columns, which is the most safe and reliable core pulling mechanism. Slider is designed as an insert and fixed on slider seat. Ejection of plastic parts depends on ejection of flat thimble and is designed on bone position. Remaining parts are ejected with dome needles. Cooling circuits are designed for front and rear molds, large slider on the left.

 

 

 

 

 

Figure 3 Die drawing of door bearing housing of output station

 

Figure 4 3D drawing