When plastic part has holes, cavities or bosses on inner or outer side different from opening and closing direction of mold, parts formed on mold must be made into a laterally movable structure, so that laterally molded part can be drawn out before plastic part is ejected, otherwise cannot be demolded. Whole mechanism that drives lateral parting, core-pulling and resetting of laterally formed parts is called lateral parting and core-pulling mechanism. In study, you should master design skills of lateral parting and core-pulling mechanism through comparative analysis of structural forms, operating principles, advantages and disadvantages of manufacturing and application processes of various typical structures.

According to different sources of lateral core-pulling power, lateral parting and core-pulling mechanisms can generally be divided into three categories: manual, hydraulic (or pneumatic) and motorized.

Manual lateral parting and core-pulling mechanism is to manually perform lateral parting and core-pulling of mold, which can be divided into two types: mold inner parting and core-pulling, mold outer parting and core-pulling. This kind of mechanism is inconvenient to operate, labor intensity of workers is high, production efficiency is low, and it is difficult to obtain a large core pulling force due to limitation of manpower, but mold structure is simple, cost is low, and is often used for product trial production, small batch production or occasions where other lateral core-pulling mechanisms cannot be used. Because screw nut drive pair can obtain a relatively large core pulling force, this core pulling method is often used in manual lateral core pulling.

Hydraulic (or pneumatic) lateral parting and core pulling mechanism uses pressure oil (or compressed air) as power, and a special core pulling hydraulic cylinder (or air cylinder) is prepared on the mold, relying on back and forth movement of piston of hydraulic cylinder (or air cylinder) to realize lateral parting, core-pulling and resetting. This kind of mechanism has relatively stable action, large pulling force, long core pulling distance, time sequence of core pulling can be set freely according to needs. Modern injection machines usually have a core-pulling hydraulic pipeline and control system, so it is very convenient to use hydraulic pressure for lateral parting and core-pulling.

Motorized lateral parting and core-pulling mechanism uses mold opening force of injection machine as driving force when opening mold, force is applied to lateral molded part through mechanical transmission part (such as oblique guide posts, bending pins, etc.) to make it laterally split or core-pulling it laterally; when mold is closed, lateral molded parts are reset by transmission parts. Although structure of this kind of mechanism is relatively complicated, its core pulling force is high, production efficiency is high, and it is easy to realize automatic production, so it is the most widely used in production. According to different transmission parts, motorized lateral parting and core pulling mechanism can be divided into different types such as oblique guide pillars, bending pins, oblique guide grooves, oblique sliders and gear racks. Among them, inclined guide post lateral parting and core pulling mechanism is the most commonly used.

Because plastic wraps tightly on side core or adheres to side cavity, in various types of side parting and core pulling mechanisms, drawing resistance will inevitably be encountered when performing lateral parting and core pulling. Force of lateral parting and core pulling (or called pulling force) must be greater than pulling resistance.
There are many factors that affect size of core-pulling force, and they are also very complex. They can be summarized as follows: the larger surface area of lateral concave-convex shape of molded plastic part, the more complex surface geometry, the greater required core-pulling force; the greater wall thickness of plastic part of core part, the greater solidification shrinkage and the greater core pulling force required; the more upper core of same core pulling mechanism, the greater required core pulling force; the smaller demolding slope of side core forming part, the greater required core-pulling force; the larger injection pressure, the tighter force of opposite core will increase and core pulling force will increase. In addition, holding time of injection, mold temperature, paint spraying, and plastic varieties will all affect core pulling force.
 

When designing lateral parting and core pulling mechanism, in addition to calculating lateral pulling force, issue of lateral core pulling distance must also be considered. Lateral core-pulling distance is generally 2~3mm larger than depth of concave side hole of plastic part or height of lateral boss, as shown in Figure 5-7-1. Formula is:
 
In formula: s—— core pulling distance, mm;
s——depth of undercut and side hole on plastic part or height of lateral boss, mm.

 

Figure 5-7-1 Core-pulling distance of lateral core-pulling mechanism
When structure of plastic part is special, it is necessary to comprehensively consider influence of shape of plastic part and mold structure on core-pulling distance. For example, when shape of plastic part is round and side core pulling of split slider is adopted (as shown in Figure 5-7-2), core pulling distance is:
 
In formula: R——radius of outer circle, mm;
r——Minimum radius of shape that hinders demolding of plastic part, mm

 

Figure 5-7-2 Core pulling distance of split slider

Lateral parting and core-pulling mechanism of oblique guide column is compact in structure, reliable in action, and convenient to manufacture. Therefore, it is the most widely used in production. However, due to limitation of mold structure and core-pulling force, it is generally used in occasions where pulling force is not large and core pulling distance is small.

(1) Composition of oblique guide post lateral parting and core pulling mechanism 

Figure 5-7-9 shows oblique guide post lateral parting and core pulling mechanism. Figure 5-7-9a shows closed state after injection; Figure 5-7-9b shows opened state. Let's take this as an example to introduce composition of lateral parting and core pulling mechanism of inclined guide column.

 

Figure 5-7-9 Composition of lateral parting and core pulling mechanism of inclined guide column
1—Pushing plate; 2, 14—stop block; 3—spring; 4—rod; 5—side slider; 6, 13—wedge block; 7. 11—oblique guide column; 8—side core; 9—punch mold; 10—fixed mold plate; 12—lateral forming block
1) Lateral molding parts
It refers to parts of side concave and convex (or side hole) of molded plastic part, including side core and side molding block, such as side core 8 and side molding block 12 in Figure 5-7-9.
2) Moving parts
It refers to part that drives lateral molding block or lateral core and moves in mold guide chute when mold is opened and closed, such as side slider 5 and lateral molding block 12 in Figure 5-7-9.
3) Transmission parts
It refers to part that drives moving parts for lateral parting or core pulling when mold is opened, and resets them when mold is closed, such as inclined guide posts 7 and 11 in Figure 5-7-9.
4) Locking parts
In order to prevent moving parts from being subjected to lateral bulging force during injection, parts set up are called locking parts, such as wedge blocks 6 and 13 in Figure 5-7-9.
5) Limiting parts
It refers to part set in order to make moving parts stay in required position after side parting or side core pulling, to ensure that transmission parts can be reset smoothly when mold is closed. Its function is not only to ensure core pulling distance, but also to ensure that inclined guide pin is accurately inserted into inclined hole when mold is closed, so that core can be reset. As shown in Figure 5-7-9, spring pull rod stopper mechanism composed of parts 2, 3, 4 and so on.

Figure 5-7-9a shows mold clamping state after injection is finished. Side sliders 5 and 12 are locked by wedge blocks 6, 13 respectively; when mold is opened, movable mold part moves to left, plastic part is wrapped on punch and moves along with movable mold. Under action of inclined guide post 7, side slider 5 drives side core 8 to pull side core in guide chute on pusher plate. Under action of oblique guide post 11, lateral forming block 12 is laterally divided into lower side in guide chute on pusher plate. After lateral parting is finished, inclined guide post is separated from side slider, side slider 5 is pressed against limit stop 2 under action of spring 3, side forming block 12 abuts against stop 14 due to its own gravity, so that inclined guide post can be accurately inserted into inclined hole of side slider when mold is closed again, forcing it to reset, as shown in Figure 5-7-9b.

Basic form of oblique guide column is shown in Figure 5-7-10. L1 is part fixed in mold plate and adopts transitional fit of H7/m6 with mounting hole in mold plate; L2 is working part to complete core pulling; α is inclination angle of inclined guide post; L3 is lead-in part of end of inclined guide post, and θ is bevel angle of lead-in part, usually θ=α+(2～3)°; keep a gap of 0.5～1mm between inclined guide post and slide hole.

 

Figure 5-7-10 Basic form of oblique guide column

In lateral parting and core pulling mechanism of oblique guide post, angle between oblique guide post and mold opening and closing direction is called inclination angle α of oblique guide post. Selection of inclination angle of inclined guide post is not only related to core pulling distance and length of inclined guide post, but also determines force condition of inclined guide post. It can be seen from research that when core-pulling resistance is constant and inclination angle α increases, bending force on inclined guide column increases, but mold opening stroke required to complete core-pulling decreases, working length of inclined guide column also decreases. When determining inclination angle of oblique guide column, usually α may be larger when core pulling distance is long, α may be appropriately smaller when core pulling distance is short; α may be smaller when core pulling force is large, and α may be larger when core pulling force is small. Therefore, determination of inclination angle α of oblique guide column should be considered comprehensively.
Inclination angle of oblique guide column can be divided into two situations, which are described as follows:

When core pulling direction of side core slider is perpendicular to opening and closing direction of mold (as shown in Figure 5-7-11), it can be known from force analysis and theoretical calculation that α≤25° is generally used in design, and the most commonly used is 12°≤α≤25°. Relationship between inclination angle of inclined guide column α, core pulling distance s, and working length of inclined guide column is as follows:

 
In formula, s—— core pulling distance, mm;
L4——Length of working part of inclined guide column, mm;
α——Inclination angle of oblique guide column;
H——Mold opening stroke required when core pulling distance is s.

 

Figure 5-7-11 Core pulling perpendicular to direction of mold opening and closing

 

Figure 5-7-12 Core pulling not perpendicular to direction of mold opening and closing
2) When core pulling direction of side core slider is not perpendicular to opening and closing direction (as shown in Figure 5-7-12), it can be used only when β angle is not large. Figure 5-7-12a shows case where core-pulling direction is inclined by β angle to side of movable mold. At this time, effective inclination angle that affects core-pulling effect is α1=α+β, value of installation inclination angle α of inclined guide column should be selected within α+β≤25°, which is smaller than when it is not inclined; Figure 5-7-12b shows case where core-pulling direction is inclined by β angle to fixed mold side. At this time, effective inclination angle that affects core-pulling effect is α2=α-β, value of installation inclination angle α of inclined guide column should be selected within α-β≤25°, which is larger than when it is not inclined.
From Figure 5-7-12, it can be seen that no matter whether core pulling direction is inclined to dynamic mode or fixed mode direction by angle β, following relationship exists:
 

Calculation of length of inclined guide column is shown in Figure 5-7-13, and its total length is:
 
Substituting formula (5-7-4) into formula (5-7-8), according to trigonometric function relationship:
 
In formula, L——total length of inclined guide column, mm;
d2——Diameter of large end of fixed part of oblique guide column, mm;
h——Thickness of fixed plate of inclined guide column, mm;
d——Diameter of working part of inclined guide column, mm;
s——Lateral core pulling distance, mm.

 

Figure 5-7-13 Length of oblique guide post
If core pulling direction of side core slider is not perpendicular to opening and closing direction of mold, simply substituting formula (5-7-5) into formula (5-7-7) to calculate length of inclined guide post.

Diameter of ordinary oblique guide column depends on maximum bending force it bears. Therefore, before calculating diameter of oblique guide column, force of oblique guide column should be analyzed to calculate bending force Fw of oblique guide column.

 

Figure 5-7-14 Force analysis of inclined guide column
Bending force Fw on inclined guide column is shown in Figure 5-7-14a. Figure 5-7-14 shows force analysis diagram of side core slider. In figure, F is positive pressure exerted by oblique guide post on slider through oblique hole on slider when core is pulled, Fw is its reaction force; extraction resistance (ie demolding force) Ft is reaction force of extraction force Fc ; Fk is mold opening force, which is applied to slider through guide chute; F1 is friction force between inclined guide post and slider, direction is opposite to direction of slider moving along inclined guide post when core is pulled; F2 is friction force between slider and guide chute, direction is opposite to direction slider moves along guide chute when core is pulled. Assuming that friction coefficients between inclined guide post and sliding block, guide sliding groove and sliding block are all μ, following force balance equation can be established:
 
Where F1=μF F2=μFk
Solve by formula (5-7-9) and formula (5-7-10):
 
Since friction force is generally small compared with other forces, it can often be omitted (ie μ=0), so above formula is:
 
In formula, Mw——bending moment of inclined guide column;
Fw——bending force on inclined guide column;
Lw——Bending arm of inclined guide column.
From knowledge of material mechanics:
 
In formula, [σw]——allowable bending stress of material used for inclined guide column, generally 3*108Pa for carbon steel;
W-bending section coefficient.
Cross section of oblique guide column is generally circular, and its bending section coefficient is:
 
From equations (5-7-12) to (5-7-15), diameter of oblique guide column can be deduced as:
 
Where
Hw——Distance between intersection of line of action of side core slider subjected to demolding force and center line of oblique guide post to fixed plate of oblique guide post. Its size depends on mold structure and is not necessarily equal to half of height of slider.
In mold design, due to complicated calculation, method of looking up table is often used to determine diameter of oblique guide column. For details, please refer to "Plastic Mold Design Manual".

 

Side slider is an important part of lateral parting and core pulling mechanism of inclined guide column. Generally, it is combined with side core (or side molding block) to form side slider core, called a combined side slider. In the case that side core is simple and easy to process, there is also a one that integrates side slider and side core, which is called an integral side slider. In the process of lateral parting or core pulling, dimensional accuracy of plastic part and reliability of movement of side slider must be guaranteed by accuracy of its movement.
The most widely used is T-shaped slider. Figure 5-7-15a shows form of T-shaped sliding guide surface designed at the bottom of slider. Center of side core is closer to T-shaped sliding guide surface. Slider has better stability when core pulling, and is often used in relatively small areas. Figure 5-7-15b shows form of T-shaped sliding guide surface designed in the middle of slider, so that center of side core is as close as possible to T-shaped sliding surface to improve stability of slider during core pulling. It is suitable for thicker sliders.
In combined side slider structure, several common connection forms of side cores and side sliders are shown in Figure 5-7-16. Figure 5-7-16a and Figure 5-7-16b show form of positioning with cylindrical pins after side core is inserted. The former uses a single cylindrical pin, and the latter uses two seam cylindrical pins. If side core is large enough, there is no need to increase size at its fixed end; Figure 5-7-16c shows that side core adopts a dovetail fixed form; Figure 5-7-16d is a form in which sheet-shaped side core is inserted into slotted side slider and then positioned with two cylindrical pins; Figure 5-7-16e is suitable for multiple small cores, that is, after inserting each core into a fixed plate, use screws and pins to connect, position it with side slider from front. If molding is affected, screws and pins can also be connected, positioned from back of side slider and side core fixing plate.
Side core is forming part of mold, usually made of T8, T10, 45 steel, CrWMn and other materials, heat treatment hardness requires HRC≥50 (for 45 steel, HRC≥40). Side slider is made of 45 steel, T8, T10, etc., and hardness requires HRC≥40. Material roughness of inlay combination is Ra=0.8μm, and matching accuracy of inlay is H7/m6.

 

Figure 5-7-16 Connection form of side core and side slider

When inclined guide post lateral core-pulling mechanism works, side sliding block moves reciprocatingly in a certain direction in guide chute with a certain precision requirement. The most commonly used guide chute forms are T-slots and dovetail grooves, as shown in Figure 5-7-17. Figure 5-7-17a shows integral T-shaped groove with compact structure. Groove body is milled with a T-shaped milling cutter, which requires high machining accuracy. Figures 5-7-17b and c are integral cover plate type, but guide chute of Figure 5-7-17b is opened on cover plate, guide chute of Figure 5-7-17c is opened on bottom plate; Figure 5- 7-17d is a partially covered form; Figure 5-7-17e is designed as a separate press block form on both sides of side core, all of which solve problem of processing difficulties. In Figure 5-7-17f, height direction of side slider is still guided by T-shaped groove, its moving direction is guided by insert inserted in the middle; Figure 5-7-17g is form of integral dovetail groove guide. Sliding accuracy is higher, but machining is more difficult. In order to facilitate processing of dovetail groove, one side of dovetail groove can be replaced with a partial mosaic form.
Since slider is required to move back and forth in guide chute during injection molding, there are certain requirements for hardness and wear resistance of parts that make up guide chute. Integral guide chute is usually processed directly on fixed mold plate or movable mold plate. Since commonly used material of movable and fixed mold plate is 45 steel, in order to facilitate processing, it is often quenched and tempered to 28-32HRC, then milled into shape. Material of cover plate is usually T8 and T10, heat treatment hardness requires HRC≥50.
When designing guide chute and side slider, fit between them must be selected correctly. Cooperation of sliding part generally adopts H8/f8. If it is in contact with molten material when forming on mating surface, in order to prevent leakage at mating part, mating accuracy should be appropriately improved, fitting H8/f7 or H8/g7 can be used, and a gap of about 0.5mm should be left in remaining places. Roughness of mating part requires Ra≤0.8μm.
In order to allow side slider to move flexibly in guide chute without being stuck, guide chute and side slider are required to maintain a certain mating length. After side slide has been pulled out, all or part of its sliding part should remain in guide chute. Generally, length of side slider retained in guide chute should not be less than 2/3 of total mating length of guide chute. In addition, it is also required that length of sliding block with sliding part is more than 1.5 times width. If width of side slider is larger than its length due to special shape of plastic part and restriction of mold structure, number of side inclined guide posts should be increased to solve this problem.

 

Figure 5-7-17 Structure of guide chute

During injection molding process, laterally molded parts will displace side slider outwards under molding pressure, which reduces lateral dimensional accuracy of plastic part, lateral bulging force is also transmitted to oblique guide post through side sliders, which will seriously deform inclined guide post. Therefore, when designing lateral core-pulling mechanism of oblique guide column, locking problem of side slider must be considered.
Various structural forms of wedge block are shown in Figure 5-7-18. Figure 15-7-18a adopts form of pin positioning and screw fixation, with simple structure, convenient processing, and wider application. Its disadvantage is that lateral force it withstands is small; Figure 5-7-18b is a form in which wedge block is fitted into mold mplate. Its rigidity is improved and lateral force it bears is also slightly larger; Figures 5-7-18c and d are double-wedge tightening forms. The former uses an auxiliary wedge block to wedge main wedge block, the latter uses a wedge taper and a wedge block to double wedge tightly; Figure 5-7-18e is an integral wedge form, which is firm, reliable and rigid, suitable for occasions with large lateral forces, but wastes materials, consumes processing man-hours, and requires high processing accuracy.

 

Figure 5-7-18 Structure of wedge block
Wedging angle α'of wedge block (see Figure 5-7-18a) should be greater than inclination angle α of oblique guide column, otherwise wedge block will affect side core pulling action when mold is opened. When core pulling direction of side slider is perpendicular to mold clamping direction, α′=α+(2～3)°; when core pulling direction of side slider is inclined to side of movable mold by an angle of β, α′=α+(2 ～3)°=α1-β+(2～3)°; when core pulling direction of side slider is inclined to fixed mold side by an angle of β, α′=α+(2～3)°=α2+β+( 2～3)°.

In order to allow inclined guide post to be accurately inserted into inclined hole of side slider during mold clamping, side slider must be positioned when it is just separated from inclined guide post during mold opening, otherwise mold will be damaged when mold is closed. Depending on position of side slider, different positioning forms can be selected. Figure 5-7-19 shows several common forms of side slider positioning devices.
Figure 5-7-19a shows structure that uses elastic force of compression spring to keep side slider at limit stop. It is commonly known as spring rod stop type. It is suitable for lateral core pulling in any orientation, especially suitable for lateral core pulling in upward direction. Another form of spring positioning is shown in Figure 5-7-19b. It is to place spring on inner side of side slider. After side core is pulled, side slider is positioned against outer stopper under action of spring, which is suitable for small molds with a small core-pulling distance. Figure 5-7-19c shows structure suitable for pulling down core. After side core pulling is completed, dead weight of side slider is used for positioning against stopper. Figure 5-7-19d shows positioning form of spring ejector pin, commonly known as spring ejector pin type. It is suitable for occasion of side core pulling in horizontal direction. Ejector pin can also be replaced with a steel ball with a diameter of 5-10mm, which is called a spring steel ball type. Applicable occasions are same.

 

Figure 5-7-19 Positioning device of side slider

Different installation positions of oblique guide column and side slide block on mold constitute different application forms of lateral parting and core pulling mechanism. Various application forms have different characteristics and problems that need attention, should be selected reasonably according to specific conditions and technical requirements of plastic parts during design.

Structure in which inclined guide column is fixed on fixed mold and side slider is installed on movable mold is the most widely used form of lateral parting and core pulling mechanism of inclined guide column. It can be used for single parting surface injection molds and double parting surface injection molds. When designing molds with side core-pulling plastic parts, this form should be considered first.
Figure 5-7-20 shows side parting and core-pulling structure of double parting surface. Oblique guide post 5 is fixed on intermediate plate 8. In order to prevent oblique guide post from moving backward when side core is pulled during parting process, a backing plate 10 is arranged at its fixed end to fix it. When mold is opened, A parting surface is first parted. When parting surface reaches point where condensate of gate gating system can be taken out, left end of tie rod guide post 11 contacts guide sleeve 12, parting of parting surface A is finished, mold continues to be opened, then parting surface B is parted. Inclined guide column 5 drives side core slider 6 in guide chute of movable mold plate 4 for lateral core pulling. After inclined guide column is separated from slider, mold continues to be opened, finally ejection mechanism starts to work, push tube 2 pushes plastic part out of core 1 and movable mold insert 3.
In side core pulling mechanism of double parting surface inclined guide column, inclined guide column can also be fixed on fixed mold seat plate, so that inclined guide column will be stressed during parting, drive-side core slider is used for lateral parting and core pulling. In order to ensure that parting surface is parted first, a fixed-distance sequential parting mechanism must be used in fixed mold part, which will increase complexity of mold structure, so try not to use this method in design.

 

Figure 5-7-20 Double parting surface injection mold with oblique guide column fixed on fixed mold and side slider installed on movable mold
1—core; 2—push tube; 3—moving mold insert; 4—moving template; 5—oblique guide column; 6—side core slider; 7—Wedge block; 8—Intermediate plate; 9—Fixed mold seat plate; 10—Backing plate; 11—Tie rod guide post; 12—Guide sleeve
When designing lateral core-pulling mechanism where inclined guide column is fixed on fixed mold and side slider is installed on movable mold, care must be taken that side slider and push rod cannot interfere during mold closing and resetting process. Interference phenomenon refers to an accident in which resetting of side slider before resetting of push rod causes movable side core to collide with push rod during mold clamping process, causing movable side core or push rod to be damaged.
Possibility of interference between side slider core and push rod occurs when projections of two on parting surface overlap, as shown in Figure 5-7-21. Figure 5-7-21a shows clamping state, and a push rod is set under projection of side core. Figure 5-7-21b shows state that inclined guide column is reset to right when inclined guide column is just inserted into inclined hole of side slider during mold clamping process, reset lever of mold has not yet reset push rod. This will cause interference phenomenon of side core colliding with push rod.

 

Figure 5-7-21 Interference between side slider core and push rod
If mold structure permits, try to avoid setting push rod in projection range of side core. If push rod must be set under side core due to restriction of mold structure, first consideration should be whether push rod can still be lower than the lowest surface of side core after a certain distance. When this condition cannot be met, it is necessary to analyze critical conditions for interference and take measures to reset ejection mechanism first, then allow side core slider to reset, so as to avoid interference.

 

Figure 5-7-22 Conditions for no interference between side slider core and push rod
1—Reset bar; 2—Moving mold plate; 3—Push rod; 4—Side core slider; 5—Slanted guide column; 6—Fixed mold seat plate; 7—Wedge block
Figure 5-7-22 is a schematic diagram of analyzing critical conditions for interference. Figure 5-7-22a shows state of push rod pushing out plastic part after mold is opened and side core is pulled out. Figure 5-7-22b shows critical state in which reset rod resets push rod and inclined guide post resets side core without interference between side core and push rod when mold is reset. Figure 5-7-22c shows state where mold clamping is completed, side core and push rod coincide with Sc within projection range of parting surface. It can be seen from figure that in critical state of no interference, side core has been reset to S', length that needs to be reset is SS'=Sc, and length of push rod to be reset is hc. If it is completely reset, following conditions should be met:
 
In the case of no interference, there should be a small distance between side core and push rod when it is necessary to be in a critical state. Therefore, conditions for no interference are:
 
In formula, hc——the shortest distance between end face of push rod and side core when mold is fully closed, mm;
Sc——Overlapping length of side core and push rod within projection range of parting surface, mm;
α——Inclination angle of oblique guide column.
Under normal circumstances, interference can be avoided as long as hctanα-Sc>0.5mm. If actual situation cannot meet this condition, first reset mechanism of push rod must be designed. Following introduces several commonly used first reset mechanisms.
1) Spring type first reset mechanism
Spring first reset mechanism is a kind of first reset mechanism that uses elastic force of spring to reset ejection mechanism before mold is closed, that is, spring is compressed and installed between push rod fixed plate and movable mold support plate, as shown in Figure 5-7- 23. Figure 5-7-23a shows form where spring is mounted on reset rod, which is the most commonly used form of small and medium-sized injection molds. In Figure 5-7-23b, spring is installed on an additional pole, which is the most commonly used form of large injection molds. Spring in Figure 5-7-23c is directly installed on push rod, which is suitable for occasions where push rod is distributed symmetrically and distance is far away.
In spring-type first-return mechanism, it is generally necessary to set 4 springs and evenly arrange them around fixed plate of push rod so that push rod can be reset smoothly. Spring reset mechanism is simple in structure and easy to install, so mold designers like to use it, but spring has a small force, it is prone to fatigue failure, and reliability will be worse. Generally, it is only suitable for occasions where restoring force is not large, spring needs to be inspected and replaced regularly.

 

Figure 5-7-23 Spring type first reset mechanism
1—Reset bar; 2—Moving template; 3—Push rod; 4—Side core slider; 5—Slanted guide column; 6—Fixed mold seat plate; 7—Wedge block
2) Wedge rod triangle slider type first reset mechanism
Wedge-rod triangle-slider type first reset mechanism is shown in Figure 5-7-24. Wedge rod 1 is fixed in fixed mold, triangular sliding block 4 is installed in guide sliding groove of push tube fixing plate 6. When mold is fully closed, wedge rod 1 is in contact with inclined surface of triangular slider 4, as shown in Figure 5-7-24a. Figure 5-7-24b shows initial state of wedge rod contacting triangular slider when mold is first closed after plastic part is pushed out. Under action of wedge rod, triangular slider 4 moves down in guide chute of push tube fixing plate 6. At the same time, push tube fixing plate is pushed to move to left, so that reset of push tube 5 is before reset of side core slider, so as to avoid interference between two.

 

Figure 5-7-24 Wedge bar triangle slider type first reset mechanism
1—wedge bar; 2—oblique guide column; 3—side core slider; 4—triangular slider; 5—push tube; 6—push tube fixing plate
3) Wedge bar swing bar type first reset mechanism
Wedge rod swing rod type first reset mechanism is shown in Figure 5-7-25. Figure 5-7-25a shows mold clamping state. One end of swing rod 4 is fixed on support plate with a rotating shaft, the other end is equipped with a roller. When clamping mold, push roller on pendulum rod on wedge rod 1, forcing pendulum rod to rotate counterclockwise around shaft, and at the same time it pushes push rod fixed plate to move to left, so that reset of push rod is before reset of side core slider. In order to prevent wear between roller and push plate, push plate is often inlaid with a quenched backing plate.

 

Figure 5-7-25 Wedge bar swing bar type first reset mechanism
1—Wedge rod; 2—Push rod; 3—Support plate; 4—Swing rod; 5—Push rod fixed plate; 6—Push plate
Figure 5-7-26 shows wedge rod double swing rod type first reset mechanism. When working, first reset speed of push rod is faster than wedge rod pendulum rod type first reset mechanism, its working principle is similar to wedge rod pendulum rod type first reset mechanism.

 

Figure 5-7-26 Wedge rod double swing rod type first reset mechanism
1—Wedge bar; 2—Push rod; 3,5—Swing rod; 4—Support plate; 6—Push rod fixing plate; 7—Push plate
4) Link type first reset mechanism
Linkage type first reset mechanism is shown in Figure 5-7-27. Figure 5-7-27a shows mold clamping state, connecting rod 4 uses cylindrical pin 5 fixed on movable template 10 as fulcrum, one end is installed on side core slider 7 with rotating shaft 6, the other end is in contact with push rod fixing plate 2. When molding, oblique guide post fixed in fixed mold part approaches slider; Figure 5-7-27b shows initial state of oblique guide post contacting slider. Once inclined guide post starts to drive side core slider to reset, connecting rod 4 must rotate clockwise around cylindrical pin 5, so that push rod fixing plate 2 drives push rod 3 to quickly reset, so as to avoid interference between lateral core and push rod.

When mold is opened, plastic part is generally required to stay on movable mold, but inclined guide post is fixed on movable mold, when side core is installed on fixed mold, if side core pulling and demolding are carried out at the same time, due to obstruction of side core in mold opening direction, plastic part is forced out of movable mold part and stays in fixed mold. After side core pulling is completed, plastic part cannot be taken out from fixed mold cavity, causing mold to fail to work normally. Therefore, characteristic of mold with inclined guide column fixed on movable mold and side slider installed on fixed mold is that side core pulling and demolding cannot be performed at the same time, either side core pulling and then demolding, or demoulding first and side core pulling.

 

Figure 5-7-27 Link type first reset mechanism
1—Pushing plate; 2—Pushing rod fixing plate; 3—Pushing rod; 4—Connecting rod; 5—Cylinder pin; 6—rotating shaft; 7—side core slider; 8—inclined guide column; 9—fixed template; 10—moving mold plate

 

Figure 5-7-28 Punch Floating Type Inclined Guide Pillar Fixed Mould Side Core Pulling Figure 5-7-29 Elastic Pressure Type Inclined Guide Pillar Fixed Mould Side Core Pulling
1—support plate; 2—moving mold plate; 3—punch mold; 4—pushing piece plate; 1—moving mold support plate; 2—oblique guide column; 3—side core; 5—Wedge block; 6—oblique guide column; 7—side core slider; 8-limit pin 4—fixed distance screw; 5—spring; 6—punch mold
Figure 5-7-28 shows a typical mechanism that first pulls core from side and then demolds. It is also called floating type of convex mold with inclined guide column and fixed mold side core. Punch 3 is installed in movable mold plate with a H8/f8 fit, distance between its bottom end and movable mold support plate 2 is h. When mold is opened, because plastic part has sufficient tightening force on convex mold, convex mold stays relatively still with plastic part within mold opening distance h, that is, convex mold 3 floats by distance h, so that side slider 7 completes lateral core pulling under action of inclined guide post 6. Continue to open mold, plastic part and punch 3 retreat together with movable mold, push plate 4 pushes plastic part out of punch 3 when ejection mechanism is working. When designing core-pulling mechanism on the side of punch floating inclined guide column, resetting of the punch 3 should be considered when mold is closed.
Structure shown in Figure 5-7-29 is called elastic-compression type inclined guide column fixed mold side core pull, which is characterized by adding a parting surface to movable mold part, parting is performed by spring set in parting surface. When mold is opened, under action of spring 5, A parting surface is divided first. During parting process, inclined guide post 2 fixed on movable mold support plate 1 drives side core slider 3 for lateral core pulling. After core pulling is finished, fixed distance screw 4 is restricted, movable mold continues to retreat, then B parting surface is divided, plastic part is wrapped on convex mold and moves back with movable mold until ejection mechanism pushes plastic part out.
Structure shown in Fig. 5-7-30 is a mold structure with core pulling on fixed mold side of inclined guide column after demolding. Concave mold 3 is a side sliding block that can be moved laterally, there is a large gap C between inclined guide post 5 and inclined hole on concave mold side sliding block 3. When opening mold, before concave mold side slider 3 moves laterally, moving and fixed molds will be separated by a certain distance. At the same time, due to constraint of concave mold side slider 3, plastic part and convex mold 4 will also be separated by a certain distance, then inclined guide post 5 contacts side slider 3, lateral parting and core pulling actions begin. This kind of mold has simple structure and convenient processing, but plastic parts need to be manually taken out from between split side sliders, which is inconvenient to operate, has high labor intensity and low productivity. Therefore, it is only suitable for production of small batches of simple plastic parts.

 

Figure 5-7-30 First demoulding, then oblique guide pillar and fixed mold side core pulling
1—Fixed mold base plate; 2—Guide chute; 3—Concave mold side slider; 4—Punch mold; 5—Slanted guide post; 6—Moving mold plate; 7—Moving mold base plate

In structure where oblique guide column and side slide block are installed in fixed mold at the same time, in general, oblique guide pillar is fixed on fixed mold seat plate, side slide block is installed in guide slide groove on fixed mold plate. In order to form relative movement between inclined guide column and side slider, a parting surface must be added between fixed mold base plate and fixed mold plate. Therefore, a fixed distance sequential parting mechanism is required, that is, when mold is opened, main parting surface will not be divided for time being, but let parting surface added in fixed mold part be separated by a fixed distance, and let inclined guide column drive side slider to perform side core pulling. After core pulling is completed, main parting surface starts to be parted. Since oblique guide post and side core are set in fixed mold part at the same time, oblique guide post can be appropriately lengthened in design to ensure that side slider will never leave oblique guide post when side core is pulled, so there is no need to set side slider positioning device.
Structure shown in Figure 5-7-31 is a swing-hook type fixed-distance sequential parting of oblique guide column lateral core pulling mechanism. When mold is closed, under action of spring 7, swing hook 8 fixed on fixed mold plate 10 by rotating shaft 6 hooks stopper 12 fixed on movable mold plate 11. When mold is opened, because swing hook 8 hooks stopper, mold is first parted from parting surface A. At the same time, under action of inclined guide column 2, side core slider 1 starts to pull side core. After side core pulling is completed, inclined surface of pressing block 9 fixed on fixed mold seat plate presses swing hook 8 to swing in a counterclockwise direction to escape stop 12, under restriction of distance screw 5, parting of A parting surface is finished. Movable mold continues to retreat, B parting surface is divided. Plastic part stays on the side of movable mold with punch 3, finally pusher plate 4 releases plastic part from mold under action of push rod 13.
Structure shown in Figs. 5-7-32 is a spring-loaded fixed-distance sequential parting of oblique guide column side core-pulling mechanism, fixed-distance screw 6 is fixed on fixed mold plate 5. When mold is closed, spring 7 is compressed. When mold is opened, under action of spring 7, A parting surface is divided first, inclined guide column 2 drives side core slider 1 to do lateral core pulling. After side core pulling is finished, distance screw 6 is restricted, movable mold continues to move backward, parting surface B begins to separate, finally push-out mechanism works, and push rod 8 pushes pusher plate 4 to eject plastic part from punch 3 . 

 

Figure 5-7-31 Swing hook type fixed distance sequence parting of inclined guide column side core pulling mechanism
1—side core slider; 2—oblique guide column; 3—punch mold; 4—pushing plate; 5—fixed distance screw; 6—rotating shaft; 7—spring; 8—swing hook; 9—press block; 10—fixed template; 11—moving template; 12—stop block; 13—push rod
 
Figure 5-7-32 Bouncing type fixed pitch sequence parting of inclined guide pillar side core pulling mechanism
1—side core slider; 2—oblique guide column; 3—punch mold; 4—pushing plate; 5—fixed template; 6—fixed screw; 7—spring; 8—push rod

(4) Inclined guide column and side slider are installed in movable mold at the same time

Structure in which oblique guide column and side slide block are installed in movable mold at the same time, relative movement of oblique guide column and side core slide block is generally realized by a pusher plate ejection mechanism.
In side core pulling mechanism of inclined guide column shown in Figure 5-7-33, inclined guide column 3 is fixed on movable mold plate 5, side core slider 2 is installed in guide chute of pusher plate 4, mold is locked by wedge block 1 set on fixed mold plate when mold is closed. When mold is opened, side core slider 2 and inclined guide post 3 move back together with movable mold. When ejection mechanism is working, push rod 6 pushes pusher plate 4 to demold plastic part, and at the same time, side core slider 2 slides to both sides in guide sliding groove of pusher plate 4 under action of inclined guide post 3 to perform lateral core pulling. For mold with this structure, since inclined guide post and side slider are on same side of movable mold, inclined guide post must be appropriately lengthened during design so that inclined slider does not depart from inclined guide post during whole process of side core pulling. There is no need to provide a side slider positioning device. This side core pulling mechanism is mainly suitable for occasions where pulling distance and core pulling force are not too large.
 
Figure 5-7-33 Structure of inclined guide column and side slider in same movable mold
1—wedge block; 2—side core slider; 3—oblique guide column; 4—pushing plate; 5—moving template; 6—pushing rod; 7—punch mold

Lateral parting and core-pulling mechanism of oblique guide column can not only perform outer parting and core-pulling of plastic part, but also can also perform inner core-pulling of plastic part.

 

Figure 5-7-34 Inclined guide pillar inner core pulling of fixed mold Figure 5-7-35 Inclined guide pillar inner core pulling of movable mold
1—core; 2—side core slider; 3—inclined guide post; 1—fixed mold plate; 2—inclined guide post; 3—side core slider; 4—small spring; 5—large spring; 6—limit screw 4—punch mold; 5—push rod; 6—moving mold plate
Structure shown in Figure 5-7-34 is a structure in which inner core of fixed mold is pulled by elastic force of spring. After mold is opened, under elastic action of large spring 5, parting surface of fixed mold part is divided first, inclined guide post 3 drives side core slider 2 to pull inner core of plastic part. After inner core pulling is finished, side core slider 2 is positioned on core under  action of small spring 4, at the same time limit screw is limited, then mold is opened, plastic part is brought to movable mold, finally ejection mechanism works, plastic part is pushed out of mold by push rod.
Structure shown in Figure 5-7-35 is a core-pulling structure inside movable mold of inclined guide column. Inclined guide post 2 is fixed on fixed mold plate 1, side core slider 3 is installed in guide chute of movable mold plate 6 to move inner core pulling, finally push rod 5 pushes plastic part out of punch 4. When designing this type of mold, there are two ways to position side core slider when it is separated from inclined guide post: one is to set side slider above mold position, use self-weight positioning of side slider, structure shown in Figure 5-7-35 is this positioning; the other is when side core is installed below, a compression spring is set on non-forming end of side slider. After core is pulled inside inclined guide column, side slider is positioned against large core of movable mold by force of compression spring.

 

Figure 5-7-36 Bent pin lateral core pulling mechanism
1—stop block; 2—fixed template; 3—wedge block; 4—Bent pin; 5—Side core slider; 6—Moving mold plate
Working principle of bending pin lateral parting and core pulling mechanism is similar to working principle of inclined guide column, except that in structure, inclined guide column is replaced by a rectangular bearing surface, its typical structure is shown in Figure 5-7-36. Bending pin 4 and wedge block 3 are fixed in fixed mold plate 2, side core slider 5 is installed in guide chute of movable mold plate 6, gap between bending pin 4 and hole on side core slider 5 is usually about 0.5 mm. When mold is opened, movable mold part retreats, side core slider 5 is used for lateral core pulling under action of bending pin 4. After core pulling is completed, side core slider 5 is positioned by spring pull rod stop device, finally plastic part is pushed out by push tube.
Bending pin lateral core pulling mechanism has several obvious characteristics: First feature is that because bending pin has a rectangular cross-section, its bending section coefficient is larger than that of a circular inclined guide column. Therefore, a larger inclination angle α can be used than that of inclined guide column, it can generally be selected reasonably within range of less than 30°; second feature is that bending pin can be delayed core-pulling, gap between bending pin and side slider is designed according to needs of delayed core-pulling. As shown in Figure 5-7-37, because plastic part has a relatively large tightening force on core of fixed mold, inner hole of plastic part is not allowed to have an inclination, when mold is opened, inclined guide post will only start to pull core after a certain distance. After such a delay of core-pulling, plastic part has basically separated from core under restriction of side slider before side core-pulling, mold injection production can proceed smoothly; the third feature is that bent pin side core-pulling mechanism can change angle of side-pulling core. As shown in Figure 5-7-38, because side core to be drawn is longer and plastic part has a greater tightening force, a variable angle bend pin is used to pull core. In process of opening mold, bending pin is first acted by a smaller inclination angle to have a larger initial extraction force. After driving side slider to move, larger inclination angle acts to extract a longer core pulling distance, thereby completing entire side core pulling action.
 
Figure 5-7-37 Delayed core-pulling of bent pins Figure 5-7-38 Variable-angle core-pulling of bent pins
According to different installation methods, installation of bending pins on mold can be divided into in-mold installation and out-of-mold installation. Structures shown in Figure 5-7-37 and Figure 5-7-38 are all in form of bending pins installed in mold. Structure shown in Figure 5-7-39 is a form in which bending pin is installed outside mold.

 

Figure 5-7-39 Structure of bending pin installed outside mold Figure 5-7-40 Diagonal inner core pulling of bending pin
1—Moving mold seat plate; 2—Pushing plate; 3—Pushing rod fixing plate; Pin fixing plate; 2—Backing plate; 3—Limiting screw; 4—Side core; 4—Push rod; 5—Moving template; 6—Block; 7—Bent pin; 5—Bent pin; 6—Punch mold; 7—Pushing plate; 8—Moving mold plate; 8—stop pin; 9—side core slider; 10—fixed mold seat plate 9—retractor hook; 10-press block; 11—slider; 12—spring
Bending pin can not only pull core outside, but also pull inside. Figure 5-7-40 shows inner core pulling structure of bending pin. Bending pin 5 is fixed in bending pin fixing plate 1, side core 4 is installed in oblique square hole of punch 6. When mold is opened, due to action of sequential fixed-distance parting mechanism, hook 9 pulls slider 11, mold is parted from A parting surface first, bending pin 5 acts on side core 4 to draw a certain distance. After oblique side core-pulling is completed, inclined surface of pressing block 10 contacts slider 11, causes slider to retreat and disengages. Limit screw 3 limits position, pulls movable mold and continues to retreat to make B parting surface parting, finally pushing mechanism works, pushing plate 7 pushes plastic part out of mold. Since a part of length of working end of bending pin remains in the hole of side core 4 after side core-pulling is completed, bending pin does not depart from sliding block after side core-pulling is completed and acts as a lock. When mold is closed, bending pin resets and locks side core.
In fact, bending pin lateral parting has a similar structure to core pulling mechanism and inclined guide column side core pulling. It can also be divided into four types: bending pin is fixed on fixed mold side, core is installed on movable mold, bending pin is fixed on movable mold side, core is installed on fixed mold, bending pin and side core are installed on fixed mold at the same time or movable mold is installed at the same time. These types are not introduced one by one here.

Lateral parting and core pulling mechanism of oblique guide groove is formed by connecting oblique guide groove fixed outside mold and cylindrical pin fixed on side core slider, as shown in Figure 5-7-41. Oblique guide groove is fixed on the outside of fixed mold plate 9 with four screws and two pins. Movement of side core slider 6 in guide chute of movable mold plate is restricted by movement track of cylindrical pin 8 fixed on it in oblique guide groove. After mold is opened, because cylindrical pin 8 first moves in the direction where oblique guide slot plate and mold opening direction form an angle of 0°, at this time, only parting is performed without core pulling. After stop pin 7 is separated from side core slider 6, cylindrical pin 8 moves in oblique guide groove along a direction at a certain angle to mold opening direction, and at this time, side core is pulled. Figure 5-7-41a shows mold clamping state, Figure 5-7-41b shows eject state after core is pulled out.
The whole process of core pulling action of lateral core pulling mechanism of oblique guide groove is actually controlled by shape of oblique guide groove. Figure 5-7-42 shows three different forms of oblique guide plate. In the form of Fig. 5-7-42a, there is only a chute with an inclination angle of α on oblique guide groove plate, so side core pulling starts when mold is opened, but inclination angle should be α<25° at this time; in the form of Figure 5-7-42b, there is a delay of core-pulling after mold is opened, side core-pulling does not start until it enters chute part; in the form of Figure 5-7-42c, core is pulled from inner side of oblique guide groove with a small inclination angle, then core is pulled in oblique guide groove with a large inclination angle. This form is suitable for occasions where pulling force is large and core pulling distance is long. Since initial drawing force is large, inclination angle α1 of first stage is less than 25°. Once side core and plastic part become loose, subsequent drawing force will be relatively small, so inclination angle of second stage can be appropriately increased, but should still be α2<25°.
When designing lateral parting and core-pulling mechanism of inclined guide groove, attention should also be paid to three major design elements of sliding guide when slider is driven, locking during injection, positioning at the end of side core-pulling. Inclined guide groove plates and cylindrical pins are commonly used as T8, T10, etc., with hardness HRC≥55, and surface roughness of working part Ra≤0.8μm.

 

Figure 5-7-41 Side core pulling mechanism of inclined guide groove
1—Push rod; 2—Moving template; 3—Spring; 4—Ejector pin; 5—Slanted guide groove plate; 6—Side core slider; 7—stop pin; 8—cylindrical pin; 9—Defined mold plate

 

Figure 5-7-42 Form of oblique guide groove

When undercut of plastic part is shallow, required core-pulling distance is not large, but molding area of undercut is relatively large, so a larger core-pulling force is required, or when other lateral core-pulling forms are not suitable due to limitation of mold structure, inclined slider lateral parting and core-pulling mechanism can be used. Characteristic of lateral parting and core-pulling mechanism of oblique slider is to use pushing force of mold ejection mechanism to drive oblique slider to move obliquely. When plastic part is ejected and demolded, side parting and core pulling action is completed by inclined slider.
This type of mechanism is simpler than lateral core pulling mechanism of inclined guide column. Generally, it can be divided into two categories: inclined slider and inclined guide rod sliding. Each type is divided into two types: outer part and inner part.

Figure 5-7-43 shows structure of outer parting and core pulling of inclined sliding block. Plastic part is a winding wheel type product with a shallower but larger undercut on outside. Oblique slider is designed as two split concave mold inserts, that is, cavity is composed of two oblique sliders. Core of large hole inside plastic part is set in movable mold part. After mold is opened, plastic part is wrapped tightly on movable mold core 5 and moves to left with inclined slider 2. Under action of push rod 3, oblique slider 2 moves forward relative to each other in oblique guide chute of movable mold plate. Under restriction of inclined sliding block 2, plastic part is released from movable mold core 5 while inclined sliding block is divided laterally. Limit screw 6 is set to prevent inclined slider 3 from sliding out of movable mold plate when it is pushed out. When clamping mold, return of inclined sliding block is carried out by pressing upper end surface of inclined sliding block 2 by fixed mold plate.
 
Figure 5-7-43 Outer parting and core pulling of inclined slider
1—moving mold plate; 2—inclined sliding block; 3—push rod; 4—fixed model core; 5—moving model core; 6—limit screw; 7—core fixing plate 
 
1—inclined slider; 2—core; 3—limit pin; 4—inlay block; 5—push rod
Figure 5-7-44 shows structure of inner core pulling of inclined slider guide. Upper end of inclined slider 1 is a concave-convex shape inside molded plastic part. Upper side of insert 4 is in a dovetail shape and can slide in dovetail groove of core 2, the other side is embedded in inclined slider 1. When pushing out, under action of push rod 5, inclined slider 1 shrinks inwardly while pushing out plastic part to complete inner core pulling action. Limit pin 3 acts as a limit to pushing out of inclined slider 1.
Figure 5-7-45a shows use of lateral parting structure on outside of inclined slider to realize automatic demoulding of external thread of plastic part; Figure 5-7-45b shows use of a lateral core-pulling structure on inner side of inclined slider to realize automatic demoulding of internal thread of plastic part. Structure of thread-removing mechanism of these two methods is simple and reliable, but there is a parting line on thread of plastic part.
Installation form of inclined slider in movable mold plate is shown in Figure 5-7-46. Figure 5-7-46a shows integral T-shaped guide chute, which is neither easy to process nor heat-treatable, but it has a compact structure and is suitable for small and medium-sized molds. Figure 5-7-46b is a dovetail guide chute, which is difficult to manufacture, but position is relatively compact, which is suitable for form of small molds and multiple sliders. Figure 5-7-46c shows inlaid guide rail. Front and rear splitting wedges, left and right locking wedges are separately manufactured, then inserted into mold frame. They are easy to process and can be heat treated, which improves accuracy and grindability. In Fig. 5-7-46d, guide post inserted obliquely is used as guide rail, which is convenient to manufacture and easy to ensure accuracy. However, it should be noted that bevel angle of guide post is smaller than bevel angle of die sleeve. Figure 5-7-46e uses a cylindrical hole as guide rail of inclined slider, which is convenient to manufacture and easy to ensure accuracy. It is used in the case of partial core pulling. Figure 5-7-46f uses core block as guide of inclined slider, position is very compact when inner core is pulled. Figure 5-7-46g shows form in which oblique sliding block directly fits oblique hole on mold plate and rear end is provided with a push rod.

 

Figure 5-7-45 Forming thread with inclined slider
1—Moving template; 2—Reset rod; 3—Push rod fixed plate; 4—Threaded oblique slider; 5—Slanted push rod; 6—Core

 

Figure 5-7-46 Guide sliding form of inclined slider