Chapter 2 Mold design 2.1 Molding parts Molding parts refer to those in direct contact with plastics to form the shape of plastic parts, wherein those constituting the contour of the plastic parts are called cavities and those constituting the internal shape of the plastic parts are called cores. Since the cavity and core directly contact the plastics of high temperature and pressure and rub with the plastic parts when protruding, it is thus required that they are provided with sufficient intensity, rigidity, hardness, abrasion resistance corrosion resistance as well as low enough surface roughness 2.1.1 Structural design 1. Cavity Structural Design 1)Integral Cavity Directly cut cavity in the die set plate as indicated in Fig. 2-1. The advantage thereof is that the processing cost is relatively low. Yet the molding board material for making the die set is usually common medium carbon steel which is short in service life if used as cavity parts, whereas selecting materials with high performance shall result in high production cost. Usually, for the mold and precision of plastic parts which are less than 10000 times of molding, relatively low requirements are made; therefore, for molds of simple shape, integral structure can be adopted ig.2-1: integral ca 2) Integral Embedded Cavity Use high quality materials(high-carbon steel or alloy tool steel)which are slightly larger than the external shape of the plastic parts(wall thickness of sufficient intensity must be ensured)to make the cavity parts and embed them into the molding plate thereafter, as indicated in Fig. 2-2 The advantage is that the service life of the cavity parts can be ensured and meanwhile the material cost is reduced. Furthermore, it is easy and convenient to repair and replace the cavity parts if they are damaged
Chapter 2 Mold Design 2.1 Molding Parts Molding parts refer to those in direct contact with plastics to form the shape of plastic parts, wherein those constituting the contour of the plastic parts are called cavities and those constituting the internal shape of the plastic parts are called cores. Since the cavity and core directly contact the plastics of high temperature and pressure and rub with the plastic parts when protruding, it is thus required that they are provided with sufficient intensity, rigidity, hardness, abrasion resistance, corrosion resistance as well as low enough surface roughness. 2.1.1 Structural Design 1. Cavity Structural Design 1) Integral Cavity Directly cut cavity in the die set plate as indicated in Fig. 2-1. The advantage thereof is that the processing cost is relatively low. Yet the molding board material for making the die set is usually common medium carbon steel which is short in service life if used as cavity parts, whereas selecting materials with high performance shall result in high production cost. Usually, for the mold and precision of plastic parts which are less than 10000 times of molding, relatively low requirements are made; therefore, for molds of simple shape, integral structure can be adopted. Fig.2-1: integral cavity 2) Integral Embedded Cavity Use high quality materials (high-carbon steel or alloy tool steel) which are slightly larger than the external shape of the plastic parts (wall thickness of sufficient intensity must be ensured) to make the cavity parts and embed them into the molding plate thereafter, as indicated in Fig. 2-2. The advantage is that the service life of the cavity parts can be ensured and meanwhile the material cost is reduced. Furthermore, it is easy and convenient to repair and replace the cavity parts if they are damaged
H7/m6 7/m6 egral e 3)Insertion and Splice Cavity For cavities which are of complicated shapes or are damageable in certain parts, design the parts hard to be processed or easily damaged into insert form and embed them into the basal body he cavity, as indicated in 2-3 Fig 2-3: local insertion and splice cavity For large and complicated cavity mold, the four walls of the cavity can be separately processed and inlaid into the mold sleeve and finally fitted with the soleplate, as indicated in 1g. 2-4: split-type cavit
Fig.2-2: integral embedded cavity 3) Insertion and Splice Cavity For cavities which are of complicated shapes or are damageable in certain parts, design the parts hard to be processed or easily damaged into insert form and embed them into the basal body of the cavity, as indicated in 2-3. Fig.2-3: local insertion and splice cavity For large and complicated cavity mold, the four walls of the cavity can be separately processed and inlaid into the mold sleeve and finally fitted with the soleplate, as indicated in Fig.2-4. Fig.2-4: split-type cavity
4)Threaded Ring Cavity Threaded ring cavity is a kind of active insert used to mold the outer thread of the plastic parts, which shall be protruded together with the parts after molding and dismounted outside the mold. Fig 2-5 shows an integral threaded ring cavity whose length of fit is 5mm-8mm. To make it easy for assembly, the remaining parts are made into 3.5obliquity, and a four-sided plane is modified at the lower extreme so that it will be convenient to screw it from the plastic parts with To sum up, cavity structures in more common application are integral embedded cavity and insertion and splice cavity 8/8 2. Core Structural Desi Integral punch costs too many materials and the working load for cutting and processing amounts too high. Therefore, hardly any such structure exists in modern mold structures which is instead preoccupied with integral embedded punch and inlaying modular punch, as indicated in Fig 2-6 and 2-7 多
4) Threaded Ring Cavity Threaded ring cavity is a kind of active insert used to mold the outer thread of the plastic parts, which shall be protruded together with the parts after molding and dismounted outside the mold. Fig.2-5 shows an integral threaded ring cavity whose length of fit is 5mm~8mm. To make it easy for assembly, the remaining parts are made into 3°~ 5° obliquity, and a four-sided plane is modified at the lower extreme so that it will be convenient to screw it from the plastic parts with tools. To sum up, cavity structures in more common application are integral embedded cavity and insertion and splice cavity. Fig.2-5: threaded ring cavity 2. Core Structural Design Integral punch costs too many materials and the working load for cutting and processing amounts too high. Therefore, hardly any such structure exists in modern mold structures which is instead preoccupied with integral embedded punch and inlaying modular punch, as indicated in Fig.2-6 and 2-7. Fig.2-6: core structure
Fig 2-7: inlaying modular core 2.1.2 Dimension Design The working dimension of molding parts refers to the dimension in direct contact with plastic parts in the cavity and core. Its precision directly influences the precision of plastic parts 1. Factors Relating with Working Dimension 1)The Shrinkage of Plastic Parts Due to the nature of plastic(to expand when hot and to shrink when cold), the dimension of plastic parts after molding and cooling is smaller than that of the cavity 2)Manufacturing Tolerance The manufacturing tolerance directly influences the dimension tolerance of plastic parts 3-1/6 of the tolerance of plastic parts is usually taken as the manufacturing tolerance of cavity and core and the surface roughness ra is0.8 um.4 um 3)Abrasion loss during Use The abrasion and restoration during production can lessen the dimension of cores and enlarge the dimension of cavities Therefore, shrinkage plays a more important part in the dimension of plastic parts when molding large parts, whereas when molding small parts, the influence of manufacturing tolerance ly gre between several percent and parts per thousand. For specific shrinkage of plastic please refer to relevant manuals or instructions to plastic products Usually, the working dimension of cavities and cores is determined according to such three factors as the shrinkage of plastic, the manufacturing tolerance of cavity and core parts as well ) Computation of Cavity Working DimensioN Cavities are mold parts for forming the external shape of plastic parts. Its working dimension is a kind of containment dimension which can gradually get larger due to the abrasion of cavity in use.Hence, to leave some space for mold-repair after abrasion and for the convenience of fitting and assembly, when designing mold, it might as well take the lower limit as the containment dimension and take the upper deviation as dimension tolerance. The specific formula is as follows
Fig.2-7: inlaying modular core 2.1.2 Dimension Design The working dimension of molding parts refers to the dimension in direct contact with plastic parts in the cavity and core. Its precision directly influences the precision of plastic parts. 1. Factors Relating with Working Dimension 1) The Shrinkage of Plastic Parts Due to the nature of plastic (to expand when hot and to shrink when cold), the dimension of plastic parts after molding and cooling is smaller than that of the cavity. 2) Manufacturing Tolerance The manufacturing tolerance directly influences the dimension tolerance of plastic parts. 1/3~1/6 of the tolerance of plastic parts is usually taken as the manufacturing tolerance of cavity and core, and the surface roughness Ra is 0.8 um ~0.4 um . 3) Abrasion Loss during Use The abrasion and restoration during production can lessen the dimension of cores and enlarge the dimension of cavities. Therefore, shrinkage plays a more important part in the dimension of plastic parts when molding large parts, whereas when molding small parts, the influence of manufacturing tolerance and abrasion loss is relatively greater. Commonly-used shrinkage of plastic parts is usually between several percent and parts per thousand. For specific shrinkage of plastic please refer to relevant manuals or instructions to plastic products. 2. Computation of Working Dimension Usually, the working dimension of cavities and cores is determined according to such three factors as the shrinkage of plastic, the manufacturing tolerance of cavity and core parts as well as the abrasion loss. 1) Computation of Cavity Working Dimension Cavities are mold parts for forming the external shape of plastic parts. Its working dimension is a kind of containment dimension which can gradually get larger due to the abrasion of cavity in use. Hence, to leave some space for mold-repair after abrasion and for the convenience of fitting and assembly, when designing mold, it might as well take the lower limit as the containment dimension and take the upper deviation as dimension tolerance. The specific formula is as follows: Formula for radial dimension of cavity:
L=[L21+k)-(3/4)△° Wherein Nominal dimension of the external shape of plastic parts k Average shrinkage of plastic; plastic of molds taking 1/3 1/6 of the dimension olerance of corresponding plastic par Formula for depth dimension of cavity H=[Hn01+k)-(2/3)△]° (2-2) Wherein: Hp-Nominal dimension in the altitude-direction of plastic parts 2)Computation of Core Working Dimension to contained dimension which gradually decreases due to the abr orking Cores are used to mold the internal shape of plastic parts. Its working dimension also belongs leave some space for mold-repair after abrasion and for the convenience of fitting and assembly when designing mold, it might as well take the upper limit as the contained dimension and take the lower deviation as dimension tolerance. The specific formula is as follows Formula for radial dimension of core =[(+k)+(3/4)△ (2-3) Wherein: p-Radial nominal dimension of the internal shape of plastic parts Formula for altitude dimension of core h=[bn(1+k)+(2/3)4] Wherein: hp--Nominal dimension in the depth-direction of plastic parts 3)Computation of the Position Dimension of Molds(such as dimension of center-to-center distance of holes) The formula is C=C.(1+k)±δ/2 Wherein: Cp--Position dimension of plastic parts 3. Computation for the Dimension of Threaded Ring Cavity and Threaded Core 1)Computation for the Dimension of Threaded Ring Cavity Dn=[Dm(1+k)-△]° D=[D(+k)-4 [Dn(1+k)-△]° Wherein: Dm-Dimension of pitch diameter of threaded ring cavity D-Dimension of major diameter of threaded ring cavity D Dimension of minor diameter of threaded ring cavity Dpm--Nominal dimension of pitch diameter of plastic parts' external thread; D Nominal dimension of major diameter of plastic parts external thread D ominal dimension of minor diameter of plastic parts' external thread
+δ L = [L（1+ k）− (3/ 4)Δ] p （2-1） Wherein: Lp —— Nominal dimension of the external shape of plastic parts; k —— Average shrinkage of plastic; Δ —— Dimension tolerance of plastic parts; δ —— Manufacturing tolerance of molds, taking 1/3 ~ 1/6 of the dimension tolerance of corresponding plastic parts. Formula for depth dimension of cavity: +δ H = [H（1+ k）− (2 / 3)Δ] p （2-2） Wherein: Hp —— Nominal dimension in the altitude-direction of plastic parts. 2) Computation of Core Working Dimension Cores are used to mold the internal shape of plastic parts. Its working dimension also belongs to contained dimension which gradually decreases due to the abrasion of core in use. Hence, to leave some space for mold-repair after abrasion and for the convenience of fitting and assembly, when designing mold, it might as well take the upper limit as the contained dimension and take the lower deviation as dimension tolerance. The specific formula is as follows: Formula for radial dimension of core: = + + Δ −δ l [l（1 k） (3/ 4) ] p （2-3） Wherein: lp —— Radial nominal dimension of the internal shape of plastic parts. Formula for altitude dimension of core: = + + Δ −δ h [h（1 k） (2 / 3) ] p （2-4） Wherein: hp —— Nominal dimension in the depth-direction of plastic parts. 3) Computation of the Position Dimension of Molds (such as dimension of center-to-center distance of holes) The formula is: C = C（p 1+ k）± δ / 2 （2-5） Wherein: Cp —— Position dimension of plastic parts. 3. Computation for the Dimension of Threaded Ring Cavity and Threaded Core 1）Computation for the Dimension of Threaded Ring Cavity δ δ δ + + + = + − Δ = + − Δ = + − Δ [ 1 ] [ 1 ] [ 1 ] （ ） （ ） （ ） D D k D D k D D k s ps l pl m pm （2-6） Wherein: Dm —— Dimension of pitch diameter of threaded ring cavity; Dl —— Dimension of major diameter of threaded ring cavity; Ds —— Dimension of minor diameter of threaded ring cavity; Dpm —— Nominal dimension of pitch diameter of plastic parts’ external thread; Dpl —— Nominal dimension of major diameter of plastic parts’ external thread; Dps —— Nominal dimension of minor diameter of plastic parts’ external thread;
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
