Pitch diameter tolerance of external thread of plastic parts Manufacturing tolerance of threaded ring cavity, for pitch diameter, =475 and for major and minor diameters, 8=A/4 Computation for the Dimension of Threaded Core dn=[dm(1+k)-△]- d=d(1+k)-△] d=[dn(1+k)-A]。 Wherein: d-D n of pitch diameter of threaded core; d diameter of threaded ds- Dimension of minor diameter of threaded core dpm-Nominal dimension of pitch diameter of plastic parts'internal thread dpl-Nominal dimension of major diameter of plastic parts'internal thread: dps ts’ internal thread Tolerance of pitch diameter of plastic parts'internal thread Manufacturing tolerance of threaded core, for pitch diameter, S =A/5,and for major and minor diameters, 8=A/4 3)Computation for Working Dimension of Screw Pitch P=P(1+k)±6/2 (2-8) Wherein: Pp- Nominal dimension of screw pitch of plastic thread parts; 6 ng P-Dimension of screw pitch of threaded ring cavity or threaded core Usually, when the number of threads is less than 7-8, it is not necessary to count the working dimension of screw pitch; instead it can be redeemed through the engagement clearance of thread Table 2-1: manufacturing tolerance of threaded core or threaded ring cavity Diameter of Thread Length of Fit oor ng toleranced Manufactu 12~22 >12~20 24~66 4. Examples of Computation Refer to Fig2-8 for the structural dimension of plastic parts and corresponding cavity structure, wherein the plastic parts are made from polypropylene, the shrinkage is 1%-3%. The dimension of cavity and core is to be calculated ig 2-8: plastic parts and corresponding cavity and core
Δ —— Pitch diameter tolerance of external thread of plastic parts; δ —— Manufacturing tolerance of threaded ring cavity, for pitch diameter,δ = Δ / 5 , and for major and minor diameters, δ = Δ / 4 . 2）Computation for the Dimension of Threaded Core δ δ δ − − − = + − Δ = + − Δ = + − Δ [ 1 ] [ 1 ] [ 1 ] （ ） （ ） （ ） d d k d d k d d k s ps l pl m pm （2-7） Wherein: dm —— Dimension of pitch diameter of threaded core; dl —— Dimension of major diameter of threaded core;； ds —— Dimension of minor diameter of threaded core; dpm —— Nominal dimension of pitch diameter of plastic parts’ internal thread; dpl —— Nominal dimension of major diameter of plastic parts’ internal thread; dps —— Nominal dimension of minor diameter of plastic parts’ internal thread; Δ —— Tolerance of pitch diameter of plastic parts’ internal thread; δ —— Manufacturing tolerance of threaded core, for pitch diameter,δ = Δ / 5 , and for major and minor diameters, δ = Δ / 4 . 3）Computation for Working Dimension of Screw Pitch P = P（p 1+ k）± δ / 2 （2-8） Wherein: Pp —— Nominal dimension of screw pitch of plastic thread parts; δ —— Refer to Table 2-1 for the manufacturing tolerance of screw pitch; P —— Dimension of screw pitch of threaded ring cavity or threaded core. Usually, when the number of threads is less than 7~8, it is not necessary to count the working dimension of screw pitch; instead it can be redeemed through the engagement clearance of thread. Table 2-1: manufacturing tolerance of threaded core or threaded ring cavity Diameter of Thread Length of Fit Manufacturing Toleranceδ 3 ~10 12 ~22 24 ~ 66 ~ 12 >12 ~ 20 >20 0.01 ~ 0.03 0.02 ~ 0.04 0.03 ~ 0.05 4. Examples of Computation Refer to Fig.2-8 for the structural dimension of plastic parts and corresponding cavity structure, wherein the plastic parts are made from polypropylene, the shrinkage is 1％-3％. The dimension of cavity and core is to be calculated. Fig.2-8: plastic parts and corresponding cavity and core
Answer: Average shrinkage of plastic is 2% O Computation of relevant dimension of cavity Radial dimension:L=[Ln(1+k)-(3/4)△° =[10+0.02)-(3/4)×0.8]6 =1116+013 Depth Dimension: H=H1+k)-(2/3)△° [301+002)-(2/3)×0.3]3×16 304 Computation of relevant dimension of core Radial Dimension: 1=[, (1+k)+(3/4)Al-2 =[801+0.02)+(3/4)×06]06x 82.05 Depth Dimension: h=[h, (1+k)+(2/3)Als =[15(1+0.02)+(2/3)×0.2]025 =15430 Core Diameter: d=[d, (1+k)+(3/4)A] =[8(1+0.02)+(3/4)×0.1a:ss =8.240 3 Computation of position dimension of core C=Cn(1+k)±6/2 =30(+0.02)±(0.3×1/6)/2 =30.6±0.025 2. 1.3 Simplifying Method for Dimension Design Presently, almost all mold enterprises adopt three-dimension CAD/CAM to design mold, which turns out to be inconvenient. Therefore, they usually use simplifying method to calculate
Answer: Average shrinkage of plastic is 2% ① Computation of relevant dimension of cavity Radial Dimension: +δ L = [L（1+ k）− (3/ 4)Δ] p 0.8 1/ 6 [110(1 0.02) (3/ 4) 0.8] × = + − × 0.13 111.6+ = Depth Dimension: +δ H = [H（1+ k）− (2 / 3)Δ] p 0.3 1/ 6 [30(1 0.02) (2 / 3) 0.3] × = + − × 0.05 30.4+ = ② Computation of relevant dimension of core Radial Dimension: = + + Δ −δ l [l（1 k） (3/ 4) ] p 0.6 1/ 6 [80(1 0.02) (3/ 4) 0.6] = + + × − × 05 0.1 82. = − Depth Dimension: = + + Δ −δ h [h（1 k） (2 / 3) ] p 0.2 1/ 5 [15(1 0.02) (2 / 3) 0.2] = + + × − × 43 0.04 15. = − Core Diameter: = + + Δ −δ d [d（1 k）（3/ 4） ] p 0.1 1/ 5 [8 1 0.02 3/ 4 0.1] = （ + ）+（ ）× − × 24 0.02 8. = − ③ Computation of position dimension of core C = C（p 1+ k）± δ / 2 = 30(1+ 0.02) ± (0.3×1/ 6)/ 2 = 30.6 ± 0.025 2.1.3 Simplifying Method for Dimension Design Presently, almost all mold enterprises adopt three-dimension CAD/CAM to design mold, which turns out to be inconvenient. Therefore, they usually use simplifying method to calculate
the forming design of mold, of which the following is a commonly-used one L=L×k erein L-Working dimension of molds forming parts Lp--Nominal dimension of plastic parts external shape, k Average shrinkage of plastic Dimension tolerance of plastic parts Manufacturing tolerance of molds usually taking 50% When the upper and lower tolerance are either positive or negative value, it is a seldom-used tolerance, which can easily result in faulty calculation; thus, it needs to be modified during design before calculating the working dimension and tolerance, for example Dimension of plastic parts 1002, re-defined as the medium value.3-01, dimension and tolerance of its molds: 10.35 Dimension of plastic parts 10_04, re-defined as the medium value 9.7_0,1, dimension and tolerance of its molds: 9.75-0 05 This principle is very important, since when modifying the product chart of plastic parts, it must be modified into the medium dimension in accordance with the requirements of dimension and tolerance of drawings. Several instances of such dimension and tolerance see Table 2-2 Table 2-2: several instances of dimension and tolerance Dimension and Plastic Shrinkag Working Manufacturing Dimension and Tolerance of plastic Dimension Tolerance Tolerance of mold 10±0.1 HIPS 0.5% 1005 ±0.05 10.05±0.05 1005 HIPS 0.5% 1005 0025 10.050 10 HIPS 0.5% 10.35 9.75 2.2 Side Core-pulling Mechanism The flanks of plastic parts are usually provided with holes or flutes, as indicated in Fig. 2-9 Under such cases, side-direction forming cores must be employed to form plastic parts. However, Ich forming cores must be fabricated into active parts so that they can be pulled out prior to the stripping of plastic parts. The mechanism for pulling out and restoring such active forming cores called core-pulling mechanism
the forming design of mold, of which the following is a commonly-used one: L = L × k p (2-9) δ = Δ× p Wherein: L—— Working dimension of molds’ forming parts; Lp —— Nominal dimension of plastic parts’ external shape; k —— Average shrinkage of plastic; Δ —— Dimension tolerance of plastic parts; δ —— Manufacturing tolerance of molds; p —— Proportion, usually taking 50%. When the upper and lower tolerance are either positive or negative value, it is a seldom-used tolerance, which can easily result in faulty calculation; thus, it needs to be modified during design before calculating the working dimension and tolerance, for example: Dimension of plastic parts 0.4 0.2 10+ + , re-defined as the medium value 0.1 0.1 10.3+ − , dimension and tolerance of its molds: 0.05 0.05 10.35+ − ; Dimension of plastic parts 0.2 0.4 10− − , re-defined as the medium value 0.1 0.1 9.7+ − , dimension and tolerance of its molds: 0.05 75 0.05 9. + − . This principle is very important, since when modifying the product chart of plastic parts, it must be modified into the medium dimension in accordance with the requirements of dimension and tolerance of drawings. Several instances of such dimension and tolerance see Table 2-2. Table 2-2: several instances of dimension and tolerance Dimension and Tolerance of Plastic Parts Plastic Shrinkage Working Dimension Manufacturing Tolerance Dimension and Tolerance of Molds 10 ± 0.1 HIPS 0.5% 10.05 ± 0.05 10.05 ± 0.05 0.05 100 + HIPS 0.5% 10.05 0.025 0 + 0.025 050 10. + 0 10−0.05 HIPS 0.5% 10.05 0 −0.025 0 05 0.025 10. − 0.4 10 0.2 + + HIPS 0.5% 10.35 0.05 0.05 + − 0.05 35 0.05 10. + − 0.2 10 0.4 − − HIPS 0.5% 9.75 0.05 0.05 + − 0.05 75 0.05 9. + − 2.2 Side Core-pulling Mechanism The flanks of plastic parts are usually provided with holes or flutes, as indicated in Fig.2-9. Under such cases, side-direction forming cores must be employed to form plastic parts. However, such forming cores must be fabricated into active parts so that they can be pulled out prior to the stripping of plastic parts. The mechanism for pulling out and restoring such active forming cores is called core-pulling mechanism
Fig 2-9: plastic parts with side holes and side flutes 2.2. 1 Classification of Core-pulling mechanism Core-pulling mechanism usually comprises the following types Manual Pulling Manual pulling refers to the pulling of side-direction cores with hand or hand tools. Such mechanism is simple in structure yet low in productivity and large in labor intensity, See Fig 2-10 Fig 2-10: screw mandril manual side core-pulling mechanism 2. Hydraulic or Pneumatic Core-pulling Use pressure oil or compressed air as power, equipped the molds with special hydraulic or pneumatic tank, and achieve core-pulling through the to-and-fro movements of piston. The pulling force under such structure is large yet the cost is relatively higher. See Fig 2-11, 2-12 and 2-13 Fig 2-11: hydraulic(pneumatic)side core- Fig 2-12: hydraulic(pneumatic)side core- pulling mechanism for fixed half mold pulling mechanism for
Fig.2-9: plastic parts with side holes and side flutes 2.2.1 Classification of Core-pulling Mechanism Core-pulling mechanism usually comprises the following types: 1. Manual Pulling Manual pulling refers to the pulling of side-direction cores with hand or hand tools. Such mechanism is simple in structure yet low in productivity and large in labor intensity. See Fig.2-10. Fig.2-10: screw mandril manual side core-pulling mechanism 2. Hydraulic or Pneumatic Core-pulling Use pressure oil or compressed air as power, equipped the molds with special hydraulic or pneumatic tank, and achieve core-pulling through the to-and-fro movements of piston. The pulling force under such structure is large yet the cost is relatively higher. See Fig.2-11, 2-12 and 2-13. Fig.2-11: hydraulic (pneumatic) side core- Fig.2-12: hydraulic (pneumatic) side corepulling mechanism for fixed half mold pulling mechanism for moving half mold
Fig. 2-13: hydraulic long-core-pulling mechanism I -fixed plate, 2- long core, 3- moving plate 3. Power-driven Core-pulling Such mechanism pulls out the active cores by utilizing the mold opening force of injection machine and through the driving of parts. Such mechanisms as angle pin core-pulling, gear and rack core-pulling etc have been extensively applied in production 4. Side Core-pulling Mechanism Driven by Spring When the side concave of plastic parts is shallow and requires relatively smaller pulling spring or ebonite can be used to achieve core-pulling. See Fig 2-14, 2-15 and 2-16 Fig2-14: ebonite core-pulling Fig 2-15: spring core-pulling (a)close mold; (b)open mold core-pulling (a)close mold; (b)open mold core-pulling P区 Fig 2-16: spring core-pulling fixed mold (a)close mold; (b)open mold core-pulling 2.2.2 Design of Angle Pin Core-pulling Mechanism 1. Principle of Design
Fig.2-13: hydraulic long-core-pulling mechanism 1- fixed plate; 2- long core; 3- moving plate 3. Power-driven Core-pulling Such mechanism pulls out the active cores by utilizing the mold opening force of injection machine and through the driving of parts. Such mechanisms as angle pin core-pulling, gear and rack core-pulling etc. have been extensively applied in production. 4. Side Core-pulling Mechanism Driven by Spring When the side concave of plastic parts is shallow and requires relatively smaller pulling force, spring or ebonite can be used to achieve core-pulling. See Fig.2-14, 2-15 and 2-16. Fig.2-14: ebonite core-pulling Fig.2-15: spring core-pulling (a) close mold; (b) open mold core-pulling (a) close mold; (b) open mold core-pulling Fig.2-16: spring core-pulling fixed mold (a) close mold; (b) open mold core-pulling 2.2.2 Design of Angle Pin Core-pulling Mechanism 1. Principle of Design