2023年12月27日星期三

mold design

Design of compound core pulling mechanism with built-in inclined top block

With rapid development of economy, automobiles as consumer goods have increasingly entered thousands of households, and automotive molds have also experienced nearly two decades of development. In the context of continuous development of injection technology, automotive industry has become increasingly demanding on appearance and function of plastic products, which puts higher requirements on design and manufacture of injection molds.

1 Product analysis

Figure 1 Car handrail

Product is a car handrail, external dimensions are 84.46mm * 249.97mm * 105.08mm, as shown in Figure 1, molding material is ABS, which has good moldability and paintability. Molded product has good surface roughness and high impact strength. Product structure feature is that there are many reverse buckles. There is also a small vertical buckle on large reverse buckle. This feature adds difficulty to design and manufacture of mold. When designing mold, it is necessary to design lifter block in the slider, slider is formed at large reverse buckle, and lifter block is formed at small reverse buckle. Mold opening direction is shown in Fig. 2. Slider is cored and demoulded in Y direction, slider block is cored and demoulded in X direction.

Fig. 2 Demoulding direction of composite core pulling mechanism

There are usually two design schemes for formation of products with similar structures above: ① Install a spring in slider, and use spring force to complete core pulling of lifter block in the slider; ② Lifter block and slider are respectively equipped with a hydraulic cylinder. Core pulling of lifter block in the slider is completed by double power. These two design schemes have shortcomings. The former spring mechanism is unstable, strength of spring will decrease with increase of number of uses. On the other hand, processing position of spring hole will also affect smoothness of movement of lifter block. Mechanism is easy to fail and can not accurately complete core pulling, reduce molding quality of product, or even scrap. The latter double hydraulic cylinder structure occupies a large space, increases overall size of mold, increases manufacturing cost. Compound core pulling mechanism introduced now is simple and stable in structure, low in manufacturing cost, and occupies less space. It can successfully complete core-pulling work and ensure molding quality of products.

2 Compound core pulling mechanism structure

01 Hydraulic cylinder slider mechanism

Figure 3 Composite core pulling mechanism

Figure 4 Hydraulic cylinder slider mechanism components

Hydraulic cylinder 2. T-shaped block 3. Slider

Figure 5 Slider bottom view

Figure 3 shows assembly structure of composite core-pulling mechanism. Large inverted part of product to be formed is designed as a slider forming. In hydraulic cylinder slider mechanism assembly shown in Figure 4, hydraulic cylinder and slider are connected by a T-shaped block, power is provided by hydraulic cylinder to push slider core to complete demolding and mold closing action of slider in Y direction. Slider is provided with a tunnel and a groove inside. Tunnel is used to install a lifter block. Groove can catch a movable insert that moves upward, as shown in FIG. 5.

02 Inclined top block mechanism

Figure 6 lifter block mechanism components

1. Stopping block 2. Wear-resistant block 3. Movable insert set 4. Slanted top block fixing block 5. Spring 6. Movable insert 7. Slanted top block 8. Small inverted parts of pressed product are formed by lifter block. In lifter block mechanism assembly, there is a inclined groove on the stop block, and movable insert can be pushed upward through inclined surface, as shown in FIG. 6. Movable insert sleeve is fixed on fixed block of lifter block to guide movable insert and move with fixed block of lifter block, spring can provide a restoring force for movable insert.

Figure 7 Top view of lifter block mechanism assembly

1. Lifter block fixing block 2. Oblique top block
Fixed block of lifter block is designed with a inclined groove. Lifter block can slide back and forth on inclined groove to complete demolding and mold close action of lifter block in X direction, as shown in FIG. 7.

03 Rack components

Figure 8 Rack components

1. Stop block 2. Wear-resistant block 3. Moving template 4. Guide rail I 5. Guide rail II
In Fig. 8, stopper block, wear-resistant block and guide rail II are fixedly installed on moving mold plate, and form a rack system with moving mold plate. Guide rail I is installed on slider, and slider can slide relatively on guide rail II.

3 Process principle

Slider has a built-in composite core pulling mechanism for lifter block, and a tunnel is designed inside slider to install slider block. When mold is opened, piston rod of hydraulic cylinder drives slider to move in Y direction, and slider is detached from large undercut of product. At the same time, slider uses tunnel slope to push lifter block to move in X direction, lifter block is separated from small inverted of plastic part buckle. After a period of movement, demolding of lifter block in X direction is completed, piston rod of hydraulic cylinder drives slider and lifter block to continue to move in Y direction, thereby completing core pulling.

01 Mold opening process

Figure 9 assembly of pressure block and slider

Press block 2. Slider

Figure 10 Cross-sectional structure of first stage mold

1. Slanted top block 2. Slider 3. Slanted top block fixed block 4. Movable insert sleeve 5. Press block 6. Movable template 7. Stop block 8. Movable insert 9. SpringThe first stage opened. Pressing block is fixedly installed on slider and moves with slider, as shown in FIG. 9. As shown in Figure 10, between slider and fixed block of lifter block, pressing block and hydraulic cylinder of movable insert sleeve drive slider to move 26mm in Y direction first, lifter block moves along X direction of slide groove on inclined surface of slider tunnel and lifter fixed block, slider and inclined roof block simultaneously separate reverse buckling of product. At this time, core pulling of inclined roof block in X direction has been completed. In the first stage of mold opening, chute on stop block catches movable insert, so that fixed block and lifter block will not follow slider in Y direction due to sliding friction generated by movement of slider, lifter block is now holding product, restraining movement of product in Y direction, when anti-slip block is separated from product, product will adhere to slider and move with slider, resulting in defects such as product deformation, damage or unqualified dimensions.

Figure 11 Organization status at the end of first phase

Figure 12 Core section to complete cross-sectional structure of mold

1. Slanted top block 2. Slider 3. Slanted top block fixed block 4. Movable insert sleeve 5. Press block 6. Movable template 7. Stop block 8. Movable insert 9. SpringThe second stage mold opening. Figure 11 shows state at the end of the first stage. After slider moves 26mm, slider and pressing block respectively contact fixed block of lifter block and movable insert sleeve, then slider and pressing block together push fixed block and lifter block to move in Y direction together. At this time, lifter block and slider do not move relative to each other, and lifter block will not move in X direction. During demoulding process of core pulling mechanism in Y direction, movable insert passes through chute of stop block, pushes out along slope of chute, and finally stuck on the insert above slider tunnel, and product is separated to a safe position with core pulling mechanism, and core pulling is completed, as shown in Figure 12.

02 Mold clamping process

Figure 13 State of mechanism after completing core pulling

State that mechanism has completed core pulling is shown in Figure 13. After taking out product, mechanism starts mold clamping movement. Piston rod of hydraulic cylinder pushes slider and pressing block to move 26mm in -Y direction first. In this process, slider pushes lifter block through tunnel slope to move in -X direction. After 26mm of movement, slider and pressing block push fixed block of lifter block and movable panel piece sleeve to continue to move, and movable insert can return to stop block chute by restoring force of spring. At this point, all components of core pulling mechanism are reset, and mold is smoothly closed to complete a molding cycle.

Mold design

Things you need to know about how to design of mold slide.

Posted on : March 11, 2022 By GREFEE

Undercuts treatment

Movement principles & design elements of diagonal bracing pin block

Undercuts treatment uses the mold opening movement and ejection force to causes the tendency of relatively motion between angle pin and slider. There are two movements to make it separate from the undercut : mold opening direction & horizontal direction. As the below pic shows:

in the pic:

β=α+2°～3°(avoid any parts contacts or blocks when group molding & reduce friction when opening molds)

α≦25°(α is the obliquity of taper pin)

L=1.5D （L is matching length）

S=T+2～3mm(S, the distance of horizontal movement of slider, T, the end product undercut

S=(L1xsina-δ)/cosα(δ – the space between taper pin and slider, normally is 0.5MM,L1is the taper pin vertical distance inside the slider)

Clamping methods & applicable situations of diagonal bracing tip

Movement principles & design elements of pulling block

The mold opening movement of molding machine causes a tendency of relatively motion between pulling blocks and sliders.

See pic below:

in the pic above:

β=α≦25°　(α – the obliquity of pulling block)

H1≧1.5W 　(H1-matching distance)

S=T+2～3mm　(S-distance of horizontal movement of slider, T- end product undercut)

S=H*sinα-δ/cosα(δ – the space between diagonal bracing tip and sliders, normally is 0.5MM,L1is the vertical distance of

H-vertical distance of pulling block inside the slider)

C- motion stopping surface so the pulling block form doesn’t need motion-stoping surface(no space)

Slider locking & fixing solutions

There is a huge pressure during the molding machine injection process. To avoid affecting the side and appearance（eg. burrs) of end products, we should keep the slider and core unmoved when molding machine injection. So the slider should use locking fixed method to keep it stay. normally, this part is motion-stoping block or heel.

Some common locking methods：

Fixed methods of slider

The slider will move a certain distance in mold opening. One way to make the slider return back smoothly is to use equipment to fix it and it should be flexible and stable so that the slider will stay at where it should be. Some exceptional situations do not need fixed equipments, like left to right slider, so it is suggested to apply a fixed equipment.

Connecting method of slide insert

How slider head insert connected is controlled by end product. Different end products have different connecting methods.

The slider head insert connected methods details:

Guide form of sliding block

In the slide guiding, the slider must be smooth and stable so that no stutters or beats, which will affect the aspects, like quality and service life of mold. (Link for the specifications of platen)

The common sliding guide forms are shown in the figure below.

Calculation of tilt slider index

Due to the undercut surface of the end product is tilt, so the move direction of slider should follow the direction of end products’ undercut surface, otherwise it will cause damages when pulling the end product.

When the angle situation between the slider core pulling and the parting surface is called the slider pulling direction moving-die.

Shown as pic:

Situation when the angle between slide core pulling direction and parting surface is slider pulling direction fixed-die.

Shown as below：

master mold runner slider

application features：

Undercuts forming on the side of master mold

Marks are allowed on the appearance

Medium slider forming area

Shown as below:

Undercut forming on the side of master mold. No marks allowed on appearance. Need to switch to master mold runner slider.

Master mold tunnel block shown as below：

gst mold opening：

second mold opening：

second mold Designing tips

a. Thickness of top clamping plate H2≧1.5D (D – diameter of large tie rod; hyperlink of large tie rod diameter calculation, three play mold large tie rod calculation; H2- thickness of top clamping plate).

b. Depth of pulling block inserted on the top clamping plate H≧2/3H2

c. There should has taper on SPRUE BUSHING head to fit for clamping and should be on the top clamping plate to avoid brush nozzle on the molding machine separating from SPRUE BUSHING and then result in brush, which is inconvenient to take out and affects next injection.

d.when pulling block inside the cavity plate, should reduce material.

e.The wearable plate should be 0.5mm higher than master mold plate to protect the taste mold plate and support the support pulling block to prevent it from distorting due to the external force.

f. Small pull rod limit stroke: S≦2/3H1 assist with mold clamping. (H1 – height of the slider)

g. It is best to have fixed block on the front of pole, easy to adjust and processing, consist three point bearing, increase the strength of pulling block.

h.To make the wearable block assemble smoothly, E point should on the right of D point. Shown as below:

I. When assembling slide base and pulling block, need to notice about the relationship between size B and B1, it shoulbe B>B1, while in order to assemble smoothly, can also dig through the rear mold located after the slide base.

Dos and don’ts & calculation formula of double “T” groove

Shown as above:

S3=H*tgγ;

(H – the decreased height of slide block which is the small pull rod stroke; γ – the angle of pulling block)

S2=δ2*cosγ；

(δ2 – the space between pulling block and slide block, normally is 0.5mm)

S=S3-S2=H*tgγ-δ2*cosγ=(H*sinγ-δ2)/cosγ；

　(S — horizontal moving distance of slide block)

S4=δ1/cosα;

(δ1 – slider insert and space between sliders；α -tilt angle of slider insert)

S1=(H*sinβ-δ1)/sin(α+β)；　

（β – space between grooves，normally is 0.5mm；S1- distance of slider insert out from the undercut）

Dos and donts：

a. Assemble requirements: assemble the slider insert and inclined insert hole, it should notice the relationship between the size A and A1, should be A>A1.

b. Double “T” groove tolerance, shown as below:

Case of Assemble matters

Die sketch

pic above :

Slide insert can be put inside the core insert without problems, required S1>S or open the core plate.

β=α+2°~3° (easy to open mold and reduce scratches)

H≧1.5D H is diagonal brace pin matching length; D is diameter of diagonal brace pin)

Double “T” groove structure model:

Cavity explosive slider

applicable situations of explosive slide block

Generally, forming on the cavity side and large slider forming area, especially using slider when the cavity side is very deep.

Explosive slider as blow pic shows:

mold opening state：

Stroke calculation:

Shown in the pic below:

S=L*sinβ (β- “T” groove angle；L stroke along the “T” groove direction; S – distance of slide block horizontal movement)

H=L*cosβ (H distance of slide block vertical distance)

Design tips and notices of explosive slide block

Shown as the pic on the right:

a.bottom wearable plate needs bevel, reduce loss between slide block and core plate, normally takes 1.5˚~3˚, assemble location be at the 3 / 4 of the center of gravity of the slide block.

　　b.S1>S　(S – distance of slide block horizontal movement）

c. the wearable plate on the back of slide block and should be 0.5 mm higher than slide block’s back.

e. The angle between block and grab hook γ＞ the wearable plate obliquity.

　　f.β＝α （β is “T” groove angle；α is lmit rod angle）

g. T – block should be longer and 10 mm higher than cavity plate.

h. Slide block head should have die screw, easy to group the mold. Need to take down when testing mold

i. Lock T-block screw should be vertical to T block.

j. The spring at the head, should calculate the weight of slide block.

k. The back of the slide block should be tool setting plane.

l. Both flanks of slide block should have limit groove.

m. The slide block head must have datum plane to provide convenience for grouping mold. The processing base level is normally over 8mm.

n. Explosive slide block must have shoulder (wings for fixing) to provide convenience for grouping mold and also a base level is necessary, cannot reduce the material)

The assemble location depends on the location of the gravity of slide block.

Dos and don’ts of Extra deep explosive slide block

the guide rod should assemble from the cavity plate

a、Cavity plate should be embedded into the core plate,avoid the cavity plate outward lift, enhance the mold strength

b.wearable plates needed at the protruding side of cavity plate, avoid scratches, easy to adjust.

c. Other precautions are the same as above

Place ejector pin inside slider

Generally, for thick and deep products’ wall, the side of the wall has many core pulling holes. The core pulling force is strong, so when moving the slide block, the product might be distorted or scratched. To avoid these happening, we need to place the ejector pin inside the slide block to stop the distortion or scratches.

A. Place ejector pin inside slide block (example 1)

B. Two common ways to place the ejector pin inside slide block, shown as below:

Delay slider

1. The outside product pulling force is strong, avoid distortion.

2. Use delay slider to operate forced demolding.

The pic below is water pipe and water pipe delay diagram:

1st mold

Finishing state after 2nd mold opening

oblique slider

1. Application range of oblique slider Normally applied in the products with slider structure, at the same time, along the slider’s direction, the end product also has undercut, which indicates that we can apply oblique slider.

note:

Pic on the right is typical case of oblique slider

2. Oblique slider diagram:

3.internal slider

(1) use boss form (seen as below)

Use the form of diagonal brace pin (as shown below）

S1 = S + 1mm above（S, undercut distance；S1 distance of slider moving

S2=S1/cosβ (S2, horizontal distance of slider；β obliquity of slider)

S2=S3=(H1*sinα-0.5)/cosα (H1, relative vertical height； obliquity of diagonal brace pin ≦25)°　

γ＝α＋2°~3°

H≧1.5D (D, diameter of diagonal brace pin; H, matching distance of diagonal brace pin)

*Detailed dimension calculation hyperlink oblique slider calculation*

Calculation of core pulling force & strength checking

1. Calculation of core pulling force

After cooling, the plastic will be narrowing and shortening, including the die core and the other parts (like oblique tip, slider, insert etc)Therefore, we must consider the enclosed strength that end product impact on slider, stress state, see pic on the right

note:

F=F4*cosα-F3cosα=(F4-F3)*cosα

F—core pulling force(N);

F3—F2 lateral component(N)

F4— core pulling resistance(N);

α—obliquity of de-molding. as α is normally low, so cosα=1

That is F=F4-F3

But F2=F1-cosα

F3=F2tgα=F1cosα*tgα=F1*sinα

F4=F2*μ=μ-F1cosα

So F=F4-F3=μ*F1cosα-F1sinα=F1(μcosα-sinα)

F1——the enclosed strength that plastic on core (N)

F2—perpendicular to positive pressure on the surface of core(N)

μ—the friction coefficient between palstic and steel, normally is around 0.2

While F1=CLF.

The average circumference of core cross-section part which enclosed by plastic.

L—the distance of core part enclosed by plastic (CM)

F0—enclosed strength of unit area, normally 7.85～11.77MPA

Namely F=100CLF0(μcosα-sinα) (N)

2. Diagonal bracing tip diameter checking:

The diameter of diagonal bracing tip is affected by many factors, like obliquity, length, and required de-molding distance. Thus, in designing, some parameters should be adjusted and matched to obtain the best result to make sure the slider to move smoothly. Calculation formula:

Note:P – maximum bending force on taper pin

L— bending moment

P1—core pulling resistance

H— distance from core pulling hole center to point A

α°—obliquity of taper pin

P2—mold opening force

From the pic we know:

P=P1/cosα (KN)

M curve=PL (KN)

Which is M curve≦[σcurve]*W (KN)

namely PL=[σ curve]*W (KN)

W—bending section coefficient

[σ curve]—permissible bending stress(for carbon steel – 13.7KN/CM2 (137MPA)

M curve—maximum moment on taper pin

Namely: W=(πd4/64)/(D/2)= πd3/32=0.1d3

0.1d3=pL/[σ]=PH/([σ]cosα)

0.1d3=pL/[σ]curve=PH/([σ]curve cosα)

D=3√(ph/0.1[σ]cosα (cm)

D=3√(ph/0.1[σ] curve cosα (cm)

3.size of pulling block section checking

The size of pulling block section checking is as same as the calculation of diagonal bracing tip. It only needs to alter the last step. Formula:

W=bh2/b

When b=2/3h, W=h3/9

h3/9=pL/[σ] curve =PH/([σ] curve cosα)

H=3√9PH/([σ] curve cosα) (cm)

When b=h, W=H3/b]

H=3√(6ph/[σ] curve*cosα) (cm)

h—long side of puling block section(cm)

b—short side of pulling block section(cm)

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Diagram	Description
	Suits for situations, like thin mold and the top clamping plate and cavity plate are closed. The contact area is long and stable.
	Suits for situations, like thick mold, large mold cavity. applicable to two plate mold/three plate mold.The contact area L≧1.5D(D is diameter of diagonal bracing tip), good stability
	Suits for thick mold applicable to two plate mold/three plate mold contact area L≧1.5D(D is diameter of angle pin), poor stability, hard to processing
	Suits for situations, like thin mold and the top plate mold and cavity plate can be separated. Long contact area, good stability

Diagram	Description	Diagram	Description
	The sliders are pieced together, normally used for standard products. Normally used standard products, check standard parts catalogue. Good structure and hardness. Applicable to situations needing strong locking force.		Use insert mode to lock. Applicable to wide sliders.
	Use integrated locking mode. Good rigidity and structure. Hard to processing. Short Demolding distance. Applicable to small molds		Use insert mode Applicable to wide sliders
	Pulling or stopping Poor stability Applicable to situations of small slider space		Are pieced together Good rigidity Applicable to situations of large space

Equipment for fixing: diagram	Description
	Fixing slider with spring screw, the strength of spring is 1.5-2 times the weight of slider. Applicable to upward or lateral core pulling.
	Fixed by spring steel ball. Normally for small sliders for lateral core pulling.
	Fixed by spring screw and guard. Strength of spring is 1.5-2 times the weight of slider. Applicable to upward and lateral core pulling.
	Fixed by spring guard, Strength of spring is 1.5-2 times the weight of slider. Applicable to big slider, upward and lateral core pulling.

Diagram	Description	Diagram	Description
	Integrated structure Applicable to situations of large cores, good strength.		Fixed by screw. Applicable to situations of cores, round, or cores are small.
	Fixed by screw. Applicable to situations of square cores/small or medium cores		Fixed by screw. Applicable to situations of square cores/small or medium cores

Diagram	Description	Diagram	Description
	Integrated manufacturing mode, hard to manufacture, applicable to small mold manufacturing.		Clamping plate ¢ral rail mode. Applicable to situations of long slider and high cavity temperate.
	Rectangle platen. Easy to manufacture. Fine strength, wide range of application, the specifications of platen is on standard parts list.		“T” groove inside the slider. Applicable to situations of small space, like slide inside the slider.
	Applied “7” shaped clamping plate. Easy to manufacture, good strength. normally fixing with pinhole together.		Inserted “T” groove, good stability, hard to manufacture.