2. There should be an area larger than 0.5 mm without screw on its end, to facilitate manufacturing avoid burr, and effect guidanc ce at use. as shown in Fig. 1-12 3. For a plastic part which has two screws located along the same axis, the pitch and tightening irection should be the same. It simples mold structure design and the part production 1. 2. 8 Gear Fig 1-13: dimensions of a plastic gear The following principles are followed for plastic part design with gears The same material should be used for gears that match, to avoid problems caused by thrinkage 2. Follow the dimensional relations as below. H=D D1>1.5D t1=3m where H- the spoke thickness, mm D-the hub hole diameter, mm Di-the hub diameter, mm: tI-the spoke width, mm m-the gear modulus 3. Adopt the transition fit between the hole and shaft on a plastic gear. Avoid the key and key way design. Use the fastening method as shown in Fig. 1-13 1.2.9 Structure of Inserts Inserts are a metal part permanently inserted into a plastic part. They are used for various purposes. Some are used to enhance local strength, hardness, or wear of a plastic part. Some are used for electricity reasons, while others are used to improve the stability of its shape and dimensional precision. Though most inserts are typically made of metal, other materials may also be used Fig 1-14 shows some commonly used inserts. Fig 1-14(a) shows tubular inserts, with through holes blind holes, screw inserts, shaft inserts, and thin-walled tube inserts. Fig 1-14(b) shows cylindrical inserts such as screw bolts, pins, and connection pole and so on. Fig 1-14(c)shows non-cylindrical inserts such as conductive sheets and weld pieces. Fig 1-14(d)shows the small rod-shaped cross-cutting inserts of the car steering wheel. Fig 1-14(e) illustrates a PMMA housing inlaid with ABS plastic
2. There should be an area larger than 0.5 mm without screw on its end, to facilitate manufacturing, avoid burr, and effect guidance at use, as shown in Fig.1-12. 3. For a plastic part which has two screws located along the same axis, the pitch and tightening direction should be the same. It simples mold structure design and the part production. 1.2.8 Gear Fig.1-13: dimensions of a plastic gear The following principles are followed for plastic part design with gears. 1. The same material should be used for gears that match, to avoid problems caused by thrinkage. 2. Follow the dimensional relations as below. H = D D1 >1.5D t1 = 3m where H – the spoke thickness，mm； D – the hub hole diameter，mm； D1 – the hub diameter，mm； t1 – the spoke width，mm； m – the gear modulus。 3. Adopt the transition fit between the hole and shaft on a plastic gear. Avoid the key and key way design. Use the fastening method as shown in Fig.1-13. 1.2.9 Structure of Inserts Inserts are a metal part permanently inserted into a plastic part. They are used for various purposes. Some are used to enhance local strength, hardness, or wear of a plastic part. Some are used for electricity reasons, while others are used to improve the stability of its shape and dimensional precision. Though most inserts are typically made of metal, other materials may also be used. Fig.1-14 shows some commonly used inserts. Fig.1-14(a) shows tubular inserts, with through holes, blind holes, screw inserts, shaft inserts, and thin-walled tube inserts. Fig.1-14(b) shows cylindrical inserts such as screw bolts, pins, and connection pole and so on. Fig.1-14(c) shows non-cylindrical inserts such as conductive sheets and weld pieces. Fig.1-14(d) shows the small rod-shaped cross-cutting inserts of the car steering wheel. Fig.1-14(e) illustrates a PMMA housing inlaid with ABS plastic
thereby forming a nonmetal insert For design of a plastic part with inserts, the first concerns are the stability of fastening the insert, the strength of the plastic part, and the stability of the locating the insert during injection molding. The solution depends on the structural design for the insert and its fit with the plastic part design The expansion coefficient of the materials for insert plastic part should be as similar as possible. It should assure that the insert does not rotate or p when it is under load. There are several structural designs. Fig Fig 1-14 shows the use of knurling and notching. Only knurling is applicable to small part designs, as shown in Fig. 1-14(b). Fig. I-15(a)shows flattening of the inserted portion of the insert. It applies to the conductive part to assure a certain area exists on its section Fig 1-15(b)shows the use of cut, hole-punching, and bending on the planer end of the insert. Fig 1-15(c) shows the use of flanging on the edge of the insert to fix. Fig 1-16 recommends sizes for cylindrical and tubular inserts where H=D. h=0.3H. h1=0.3H. d=0.75D. In extreme cases the maximal h cant exceed 2D. All corners along the insert should be rounded 应唧中 Fig 1-14: types of common screw inserts Fig 1-15: inserted structures Fig 1-16: dimensions of an insert 2)The location of the insert inside the mold must be accurate and secure, to avoid disorientation or deformation during injection molding. In addition, it needs to prevent the plastic material from leaking into other parts of the insert such as hole or thread. Cylindrical inserts are usually inserted into a corresponding hole on the mold to fix it. Fig 1-17 shows a structure used to enhance the stability of the insert on the mold and prevention of the material from leaking. Inserts with threaded blind holes and threads are usually inserted onto a cylindrical shaft on the mold, as shown on Fig. 1-18(a). Fig. 1-18(b), (c), and (d) show the use of external bulges or internal steps to further improve the inserts stability in the
thereby forming a nonmetal insert. For design of a plastic part with inserts, the first concerns are the stability of fastening the insert, the strength of the plastic part, and the stability of the locating the insert during injection molding. The solution depends on the structural design for the insert and its fit with the plastic part design. 1) The expansion coefficient of the materials for insert and the plastic part should be as similar as possible. It should assure that the insert does not rotate or pop out, when it is under load. There are several structural designs. Fig Fig.1-14 shows the use of knurling and notching. Only knurling is applicable to small part designs, as shown in Fig.1-14(b). Fig.1-15(a) shows flattening of the inserted portion of the insert. It applies to the conductive part to assure a certain area exists on its section. Fig.1-15(b) shows the use of cut, hole-punching, and bending on the planer end of the insert. Fig.1-15(c) shows the use of flanging on the edge of the insert to fix. Fig.1-16 recommends sizes for cylindrical and tubular inserts where H=D, h=0.3H, h1=0.3H, d=0.75D. In extreme cases, the maximal H can’t exceed 2D. All corners along the insert should be rounded. Fig.1-14: types of common screw inserts Fig.1-15: inserted structures Fig.1-16: dimensions of an insert 2) The location of the insert inside the mold must be accurate and secure, to avoid disorientation or deformation during injection molding. In addition, it needs to prevent the plastic material from leaking into other parts of the insert such as hole or thread. Cylindrical inserts are usually inserted into a corresponding hole on the mold to fix it. Fig.1-17 shows a structure used to enhance the stability of the insert on the mold and prevention of the material from leaking. Inserts with threaded blind holes and threads are usually inserted onto a cylindrical shaft on the mold, as shown on Fig.1-18(a). Fig.1-18(b), (c), and (d) show the use of external bulges or internal steps to further improve the insert’s stability in the
old. Fig. 1-18(e) shows an insert with threaded through holes is mounted on a component with external threads. Smooth shafts can be applied to the type of small insert designs(M3.5 or less), when the injection force is not high. For both cylindrical and ring-shaped inserts, their stick-out portion cannot be more than twice the inserted portion, or the flow pressure may dislocate or deform the insert. Additional support from the mold should be considered for inserts which have a thin, plate shape or exceeds the ratio, as shown in figure Fig 1-19. However, the hole left by the support cannot affect the use of the plastic part. Figure Fig 1-19(c)shows holes are added to the thin insert part to ease the material flow and thus reduce the pressure on the insert Fig 1-17: fixation of cylindrical inserts in molds Fig. 1-18: fixation of ring-shaped inserts in molds 型料→海方内 Pillar Plastic flow direction Fig 1-19: support methods for thin inserts in molds Fig 1-20: location and dimensions for inserts 3)Residual force may linger in the plastics around the insert. The amount depends on the plastic
mold. Fig.1-18(e) shows an insert with threaded through holes is mounted on a component with external threads. Smooth shafts can be applied to the type of small insert designs (M3.5 or less), when the injection force is not high. For both cylindrical and ring-shaped inserts, their stick-out portion cannot be more than twice the inserted portion, or the flow pressure may dislocate or deform the insert. Additional support from the mold should be considered for inserts which have a thin, plate shape or exceeds the ratio, as shown in figure Fig.1-19. However, the hole left by the support cannot affect the use of the plastic part. Figure Fig.1-19(c) shows holes are added to the thin insert part to ease the material flow and thus reduce the pressure on the insert. Fig.1-17: fixation of cylindrical inserts in molds Fig.1-18: fixation of ring-shaped inserts in molds Fig.1-19: support methods for thin inserts in molds Fig.1-20: location and dimensions for inserts 3) Residual force may linger in the plastics around the insert. The amount depends on the plastic Pillar Plastic flow direction
material type, insert material, insert structure, and the difference in expansion coefficients between the two materials. Some may cause cracking on the plastic part. To avoid cracking, inserts are usually located in the part area where there is a sufficient thickness as shown in Fig. 1-20 1.2.10 Surface Marking Markings of protrusions, depressions, or leather-like wrinkles may exist on a plastic part as shown in Fig. 1-21. Some are for functional requirement, while others are for decoration. Markings should be easy for molding, ejection and mold making. Usually the marking should be in parallel to the ejection direction. A side draft must be considered to assure the wrinkle design on the side of the plastic part can be properly ejected AA④ Fig 1-21: structure of characters on plastic parts Markings,symbols,and characters on a plastic part can be classified into three structures.The first is protrusion as shown in Fig. 1-21(a). It is easy to make the mold but also easy to wear off. The second is a depression as shown in Fig. 1-21(b). Various paints can be added to the depression to create right markings. Its drawback is the difficulty of making the mold by traditional machining, unless a non-traditional machining approach such as ECM, EDM or cold extrusion is used. The third is depression on a boss as shown in Fig. 1-2I(c). An insert is usually used in this type of structure Characters are made on the insert, which is in turn inserted into the mold Wear resistance and ease of 1.3 Mold Specification 1.3.1 Basic mold Structure Two-plate molds are molds whose sprue, runners, gates, and cavities are all on the same side of the mold as shown in Fig. 1-22, divided by the parting line into moving half and fixed half. Their features 1) Simple structure, easy to operate, and satisfactory to have the plastic part to drop off freely 3) 4) Easier to choose gate 5)Other than direct gates, gate location is limited to the side of the plastic part, with certain
material type, insert material, insert structure, and the difference in expansion coefficients between the two materials. Some may cause cracking on the plastic part. To avoid cracking, inserts are usually located in the part area where there is a sufficient thickness as shown in Fig.1-20. 1.2.10 Surface Marking Markings of protrusions, depressions, or leather-like wrinkles may exist on a plastic part as shown in Fig.1-21. Some are for functional requirement, while others are for decoration. Markings should be easy for molding, ejection and mold making. Usually the marking should be in parallel to the ejection direction. A side draft must be considered to assure the wrinkle design on the side of the plastic part can be properly ejected. Fig.1-21: structure of characters on plastic parts Markings, symbols, and characters on a plastic part can be classified into three structures. The first is protrusion as shown in Fig.1-21(a). It is easy to make the mold but also easy to wear off. The second is a depression as shown in Fig.1-21(b). Various paints can be added to the depression to create bright markings. Its drawback is the difficulty of making the mold by traditional machining, unless a non-traditional machining approach such as ECM, EDM or cold extrusion is used. The third is depression on a boss as shown in Fig.1-21(c). An insert is usually used in this type of structure. Characters are made on the insert, which is in turn inserted into the mold. Wear resistance and ease of mold making are both its advantage. 1.3 Mold Specification 1.3.1 Basic Mold Structure 1． Two-plate Mold Two-plate molds are molds whose sprue, runners, gates, and cavities are all on the same side of the mold as shown in Fig.1-22 ,divided by the parting line into moving half and fixed half. Their features are: 1) Simple structure, easy to operate, and satisfactory to have the plastic part to drop off freely. 2) Minimal operational problems, long lifespan, and shortened molding cycle. 3) Inexpensive mold cost. 4) Easier to choose gate shape and location. 5) Other than direct gates, gate location is limited to the side of the plastic part, with certain exceptions
6) After molding, there is a need to cut off the gate from the part 9 76 1. sprue bush: 2.guide pin: 3. cavity-retainer plate: 4.core: 5. core-retainer plate: 6.support plate 7. sleeve: 8. stop pin: 9. spacer block: 10.core: 1l.screw: 12 clamping plate of the moving half: 13. ejector-retainer plate: 14. sprue puller pin: 15.ejector-support plate: 16. returm pi Fig 1-22: two-plate injection mold Fig. 1-23 is the photos of two-plate injection mold with one cavity for a plastic ear rack of Bluetooth product which has been installed on a plastic injection molding machine a) fixed half mold alf mold Fig. 1-23: two-plate injection mold with one cavity for a plastic ear rack of Bluetooth product 2. Three-plate Mold Three-plate mold is a mold which has a runner plate in between moving half and fixed half. The unner exists between the runner plate and the fixed half as shown in Fig. 1-24. The cavity is located in between the runner plate and moving half of the mold. Pin-point gates typically locate at the middle of the plastic part, away from its edge, satisfying the aesthetic requirement and eliminating the process for cutting off the gates A three-plate mold has the following features 1)Its gates can be located at the middle of the plastic part 2) It allows pin-point gates 3) It may eliminate cutting off the gates manually, when pin-point gates or submarine gates are used 4) It has to take out both the part and the runner respectively 5) The injection molding machine should have sufficient mold opening distance 6) It has a complex structure, more problematic and less durable 7) It carries a higher mold cost
6) After molding, there is a need to cut off the gate from the part. 1. sprue bush；2.guide pin；3. cavity-retainer plate；4.core；5. core-retainer plate；6.support plate； 7. sleeve；8. stop pin；9. spacer block；10.core；11.screw；12. clamping plate of the moving half； 13.ejector-retainer plate；14. sprue puller pin；15.ejector-support plate；16. return pin Fig.1-22: two-plate injection mold Fig. 1-23 is the photos of two-plate injection mold with one cavity for a plastic ear rack of Bluetooth product which has been installed on a plastic injection molding machine. a) fixed half mold b) moving half mold Fig. 1-23: two-plate injection mold with one cavity for a plastic ear rack of Bluetooth product 2． Three-plate Mold Three-plate mold is a mold which has a runner plate in between moving half and fixed half. The runner exists between the runner plate and the fixed half as shown in Fig.1-24. The cavity is located in between the runner plate and moving half of the mold. Pin-point gates typically locate at the middle of the plastic part, away from its edge, satisfying the aesthetic requirement and eliminating the process for cutting off the gates. A three-plate mold has the following features: 1) Its gates can be located at the middle of the plastic part 2) It allows pin-point gates 3) It may eliminate cutting off the gates manually, when pin-point gates or submarine gates are used. 4) It has to take out both the part and the runner respectively. 5) The injection molding machine should have sufficient mold opening distance. 6) It has a complex structure, more problematic and less durable. 7) It carries a higher mold cost