Printer guide bracket products are shown in Figure 1. Maximum dimensions of product are 235.00 mm * 60.05 mm * 50.00 mm, average thickness of plastic part is 1.50 mm, material of plastic part is HIPS, shrinkage rate is 1.0045, and weight of plastic part is 68.18 grams. Technical requirements for plastic parts are that there should be no defects such as peaking, underfilling, flow lines, pores, warping deformation, silver streaks, cold material, and spray lines.

 

Figure 1 Printer Guide Bracket Product Map
Guide bracket of printer is a guide bracket in a printer of a famous Japanese brand. Middle of plastic part is a roof-like protrusion, two upper surfaces are smooth and curved, and one side has guide ribs passing through paper surface. Guide bracket is supporting part inside printer, and it is substrate for installation of electronic imaging system, paper passing motor, PCB board and control components, and is also an important functional part. There are three horizontal small holes on two end faces of plastic part. Dimensional accuracy of these holes is very high, and slider core puller needs to be designed. It can be seen from Figure 1 that structure of plastic part is unique, difficulty in mold design is mosaic structure of front and rear mold cores.

 

 

Figure 2 Tolerance requirements for plastic parts
Guide bracket of printer has high dimensional accuracy, and its tolerance is shown in Figure 2. In order to make product run smoothly after assembly without paper jams, there are also high requirements for 6 small holes at both ends. Bending deformation of plastic part body in both directions must not exceed 0.3. Design requirements for parts on paper surface of printing machine are flat, smooth, no burrs, no thimble marks, and no gate marks. Inserts are not allowed on paper surface, step difference between movable and fixed molds is less than 0.03 or less. Appearance is required to be free of defects such as shrinkage marks, white top, burnt, air marks, color difference and material flowers, etc. Products must not be stained with oil and dust, and no mold release agent should be used in injection molding process. Since product is tilted after natural placement, it is difficult to measure the size, so measurement of product size requires use of specially designed fixtures.

 

Figure 3 3D mold design drawing
Mold design cavity layout is 2 cavities, and mold base is edge gate mold base 4045. 3D mold design drawing is shown in Figure 3, and 2D drawing is shown in attachment. Due to structural characteristics of plastic parts, mold adopts method of breaking up and making inserts. Due to large open frame size of mold base, it is very difficult for fitter to assemble frame. Use of wedge blocks in full inlaid design can solve problem of assembly accuracy of mold core. It is difficult to really improve processing technology by adopting design of partial inlays for large and medium-sized molds. All-inlaid structure is a mold design method that takes manufacturing process of mold core into consideration, shortens mold manufacturing cycle, improves manufacturing precision, and improves injection molding process. For above-medium, large or extra-large injection molds, in order to shorten processing cycle and facilitate processing, a full-inlay structure design is adopted, commonly known as design of scattered inserts. Idea is to divide the entire mold core (usually mainly refers to rear mold core) into multiple inserts for simultaneous processing, which not only simplifies processing time of inserts, but also saves a lot of mold steel. Therefore, fully inlaid mosaic structure has been widely used in Japanese mold design.
Key point of this set of molds is design of inserts. Inserts are skillfully cut to make the whole set of molds have good injection molding processability.
Mold gating system uses side gates to feed glue, front and rear molds are positioned with 4 conical positioning parts 05. In order to facilitate molding, front and rear mold panels and edges of bottom plate have been milled, leaving only 30 thickness, which is conducive to pressing of pressure plate.
Slider of mold is locked with an inlaid wedge. Slider is wider and driven by two inclined guide posts. Wear-resistant plates are designed on the bottom surface and slope of slider, which is convenient for mold assembly and maintenance, maintains mold precision. Lifter adopts lifter with pin structure. Note that diameter of pin should not be less than 4mm, but it should not be too large, so as not to damage strength of tail of lifter. Tail of lifter is made of arc, bottom is made of wear-resistant plate, moving part of lifter is made of oil groove, and the whole is nitrided to improve service life. Back of B board is designed with a guide block for lifter to increase stability of lifter movement.
Bottom of support head is connected to bottom plate with screws, and positioning pins are added between top and B plate to facilitate mold assembly. Ejection insert 17 is designed at the bottom of thimble base plate in the K.O hole, which reduces ejection stroke of ejector rod of injection molding machine, shortens injection molding cycle, and is also conducive to improving force condition of thimble plate and preventing deformation of thimble plate.

 

Figure 4 3D explosion diagram

 

Figure 5 Parting surface diagram
Front and rear molds of mold are designed to be cooled by ponds, and slider is designed to transport water through. Good cooling can ensure stability of injection molding process.
Details make a difference. Life of an injection mold depends on every detail. Common mold failures are lifter wear, breakage, and burning. Slider is stuck, inclined guide column is bent, etc., thimble is also burned and broken. Every small improvement has potential to greatly increase die life. Design ejection insert 17 in K.O hole is exactly an example. This insert can avoid deformation of ejector plate, coupled with center support guide post and guide sleeve, ejection of mold is stable, life of lifter and ejector pin is greatly improved.