Code for design of plastic molding technology and mold design course

Design topic: design of injection mold for cold water pot cover

Designer: Li Li

Major: mold design and manufacturing

Class: Class 2005 Mould (Class 3)

Design time: 2007. 12

Teaching and research section: mold teaching and research section

Instructor: Liu Quanxin

Ezhou university machinery department

Course Design Task Book of "Plastic Molding Technology and Mold Design"

Project design name: Design of injection mold for cold water pot cover

Plastic Drawing: (Mold Course Design Guidance-Plastic Drawing Compilation: Legend 3- 18 on page P68)

Name of plastic parts PE-HD cold water pot cover thickness 1 workpiece accuracy 5

Design content:

1. Prepare the molding process specification (that is, fill in the "Plastic Parts Molding Process Card")

2. Draw the assembly drawing of injection mold for plastic parts (A3 drawing 1)

3. Draw a set of parts drawings (multiple A3 drawings) of the punch and die of the mold.

4, write and improve the mold design instructions (according to A4 printing paper binding)

catalogue

A, the preparation of plastic molding process card

Second, the plastic molding process analysis and design

1. Raw material characteristics of plastic parts

2. Moldability of raw materials for plastic parts

3. Analysis of the structure, dimensional accuracy and surface quality of plastic parts.

4. Determination of plastic molding method

Third, the plastic molding die design

5. Number and arrangement of cavities

6. Select the model and parameters of injection molding machine.

7. Determine the parting surface

8. Selection and design of gating system

9. Design and calculation of molded parts 10.

10. ......................................... of lateral core-pulling mechanism 10

1 1. exhaust system design ....................................... 1 1.

12. Determination of formwork and selection of standard parts (schematic diagram) ............................ 1 1

13. Design of temperature regulation system .......................................................... 12

14. Ejection mechanism (demoulding) ................................................................. 12

15. Steering mechanism ............................................................ 13.

16. Experience in mold design ....................................................... 13.

17. Refer to ................................................... 13.

18. Die assembly drawing and parts drawing ........................................... 13.

Plastic molding process card

Plastic parts are called sketches of high-density polyethylene plastic parts.

Material brand number PE-HD

The weight of a single piece is 25.9g.

Modeling equipment model XS-ZY- 1000

Number of modules per module 4

Forming process parameters

Name of material drying equipment oven

Temperature/℃

Time/hour 1~2

The barrel temperature in the later stage of molding process /℃ 140~ 160.

Middle section /℃ 180~200

The former /℃ 180~ 190

Nozzle /℃ 150~ 180

Mold temperature is 30 ~ 60/℃

Time injection/sec 0~5

Maintain pressure /s 15~60

Cooling /s 15~60

Pressure injection /MPa 70~ 105

Maintain pressure/MPa

Post-treatment temperature/℃ _ _ _

Time/minute _ _ _

Compilation date and approval date

Ber Ber 2007. 12.4

Design calculation and explanation

Analysis and design of 1. plastic molding process

1 High density polyethylene

(1) chemical and physical properties

The high crystallinity of PE-HD leads to its high density, tensile strength, high temperature deformation temperature, viscosity and chemical stability. PE-HD has stronger permeability resistance than PE-LD. PE-HD has low impact strength. The characteristics of PH-HD are mainly controlled by density and molecular weight distribution. The molecular weight distribution of PE-HD suitable for injection molding is very narrow. The density is 0.9 1- 0.925g/cm3, and the flow characteristics of the material are very good, and the MFR is between 0. 1-28. The higher the molecular weight, the worse the flow characteristics of PH-LD, but the better the impact strength. PE-LD is a semi-crystalline material, and the shrinkage rate after molding is high, which is 1.5%-4%. PE-HD is prone to environmental stress cracking. By using materials with very low flow characteristics to reduce internal stress, the cracking phenomenon can be alleviated. PE-HD is easily soluble in hydrocarbon solvents when the temperature is higher than 60℃, but its solubility resistance is better than PE-LD.

(2) Typical application scope

Refrigerator container, storage container, household kitchenware, sealing cover, etc.

(3) Process conditions of PE-HD injection mold

Drying: If stored properly, there is no need to dry.

Melting temperature: 220-260℃. For materials with larger molecules, it is suggested that the melting temperature range is between 200-250℃. Mold temperature: 50-95℃. Plastic parts with wall thickness less than 6mm should adopt higher mold temperature, and plastic parts with wall thickness greater than 6mm should adopt lower mold temperature. The cooling temperature of plastic parts should be uniform to reduce the shrinkage difference. In order to obtain the best machining cycle time, the diameter of the cooling channel should be not less than 8mm, and the distance from the die surface should be within 1.3d ("D" is the diameter of the cooling channel).

Injection pressure: 70-105 MPa; Injection speed: high-speed injection is adopted. Runner and gate: the diameter of runner is between 7.5mm, and the length of runner is as short as possible. Various types of gates can be used, and the gate length should not exceed 0.75 mm When polyethylene is molded, the shrinkage in the flow direction and the vertical direction is very different, and the shrinkage in the injection direction is greater than that in the vertical direction, which is easy to deform and increases the brittleness around the gate. The molding shrinkage is large, which is easy to cause shrinkage cavity; If the cooling speed is slow, it must be fully cooled and the cooling speed should be uniform; Soft and easy to demould, and can be forcibly demoulded when there is shallow side concave. Especially suitable for using hot runner mold.

2. Moldability of raw materials for plastic parts

? Crystalline material, low hygroscopicity

? Excellent fluidity, the overflow value is about 0.02mm, and the fluidity is sensitive to pressure changes.

? Melting cracking may occur, and cracking may occur in contact with organic solvents.

? Heating for a long time will lead to decomposition and burns.

? The cooling speed is slow, so it must be fully cooled. It is appropriate to set cold holes, and the mold should have a cooling system.

? Wide shrinkage rate, large shrinkage value, obvious directionality and easy deformation and warping. The crystallinity and cooling conditions of the die have great influence on the shrinkage. The mold temperature should be controlled to keep the cooling uniform and stable.

? High pressure injection should be used, the material temperature should be uniform, the filling speed should be fast, and the pressure should be fully maintained.

? It is not suitable to use sprue, which will easily increase internal stress or cause uneven shrinkage and obvious directional deformation. Pay attention to the location of the feed inlet to prevent shrinkage and deformation.

? Soft and easy to demould, plastic parts can be forcibly demoulded when there are shallow side grooves.

3. Analysis of the structure, dimensional accuracy and surface quality of plastic parts.

? Structural analysis: According to the part drawing, the part has a round edge and six rectangular holes of 4 mm× 22 mm.. When designing the mold, it is necessary to set up a side parting core-pulling mechanism and a small workbench at the mouth of the part.

? Dimensional accuracy: the accuracy of this plastic part is grade 7, and the accuracy requirement is low.

? Surface quality analysis:

The surface of this part is required to be free from defects and burrs. Because the cold water pot cover is often in contact with people's hands, it is required that the surface be smooth, and it is best to naturally form rounded corners.

4. Determination of molding method of plastic parts

To sum up, the plastic part has simple structure, uniform wall thickness and good molding technology, and can be produced by injection molding.

Second, the plastic molding die design

5. Number and arrangement of cavities

The precision of plastic parts is not high, and it is a small plastic part with simple shape and mass production. Initially identified as a mold with four cavities. The arrangement of cavities adopts symmetrical H-shaped arrangement, as shown in the following figure: In order to ensure the surface quality requirements of plastic parts, point gate is selected for molding, and the gate position is arranged at the top of plastic parts.

The mold adopts double parting surface injection mold (three plates).

6. Select the model and parameters of the injection molding machine.

(1) Calculation of injection quantity: Through Pro/E modeling and analysis, the volume of plastic parts is 27,265 ㎜, and the quality of plastic parts: at this time, the volume of condensate in runner is unknown, which can be estimated as 0.6 times of the quality of plastic parts, so the injection quantity is:

(2) Calculation of clamping force: At this time, the projected area of runner condensate (including gate) on the parting surface is unknown. According to the empirical formula: (the projected area of each plastic part on the parting surface), it is estimated by the following formula:

? formula

? The injection pressure required for checking plastic parts is 70- 105Mpa, and the average pressure of cavity is 30%-65% of the injection pressure. Because the plastic part is a thin-walled plastic part, and the gate is a point gate, the pressure loss is relatively large, so take a bigger one, and then

(3) Selection of injection molding machine: According to the injection quantity and clamping force calculated above, domestic XS-ZY- 1000 screw injection molding machine can be selected, and its related parameters are as follows:

Nominal injection volume/

1000 maximum thickness of formwork /mm 700

Screw diameter/mm 55 Minimum thickness of formwork/mm 300

Clamping force /N

Template size 690×790

Injection pressure /MPa 12 1 rod spacing /mm 650×550.

Injection stroke /mm 280 hydraulic machinery with clamping mode

Screw speed/(rpm) 0~47 Motor power/kW 22

Maximum travel of formwork /mm 700 locating ring size /mm 150

Nozzle ball radius/mm 18 nozzle hole diameter/mm 7.5

Maximum molding area of injection screw/

1800

Positioning ring size /mm 150 injection time /s 4

(4) Check the related parameters of the blaster.

? Check the number of cavities.

According to the rated injection quantity of the injection machine, check the number of mold cavities;

The number of cavities is qualified.

Where, the volume required for solidification and flash evaporation of Vj injection system.

Vz is the volume of each plastic part.

Vg is the rated injection volume of the injection machine.

? Inspection of injection pressure

Injection pressure inspection is qualified.

Where k is the injection pressure, and the safety factor is generally 1.25- 1.4.

? Verification of clamping force

Clamping force is qualified.

K is the safety factor of clamping force, which is generally taken as1.1-1.2.

Other dimensions can only be checked after the template is selected and the structural dimensions are determined.

7. Determine the parting surface

This plastic part requires a smooth outer surface and no gate marks on the outer edge of the lower end. According to the selection principle of parting surface, the parting surface of plastic parts should be selected as shown in the following figure A-A, so that the concave cavity can be integrally processed and molded, and the outer surface of plastic parts is smooth and easy to demould.

8. Selection and design of gating system

(1) main channel design

? Main channel size

Diameter of small end of main groove:

The spherical radius of the main runner is:

Cone angle of main groove: take; Main channel length: l = 70mm；;

Diameter of large end of main channel:

? Form of main runner bushing

Because the inlet of the main channel is in repeated contact with the nozzle of the injection machine, it is easy to be damaged and requires high materials. Therefore, the main runner is designed as a sprue sleeve, T 10A, and heat-treated for 50HRC-55HRC, as shown in the above figure:

The structure of the matching locating ring is shown in the following figure:

(2) Design of shunt.

? Layout of the distributary channel: In order to ensure that the distributary channel can meet the requirements of good pressure transmission, maintain an ideal filling state, and enable the condensed melt to be distributed to various cavities as soon as possible, the balanced distributary channel structure shown in the following figure is adopted:

? Shape and cross-sectional dimensions of the diverter:

Because of the good fluidity of polyethylene, the semi-circular flow channel with good processability is selected, and the look-up table shows d= 10㎜.

? Surface roughness of diverter:

The surface roughness Ra of the runner is not required to be very low, and is generally 0.8- 1.6, here it is 1.6, as shown in the above figure.

(3) Design of gate

Because the appearance and surface quality requirements of plastic parts are relatively high, there can be no obvious burn marks, so use the point gate lookup table shown on the right to get the size:

(4) Check the injection stroke

Check that the injection stroke of XS-ZY- 1000 is 280, and the length of gating system is:

Established.

9. Design and calculation of mould forming parts

By analyzing the structure of plastic parts, we can know that the tolerance grade of plastic parts in radial direction is MT7 (GB4458.5-84), and the accuracy is medium for this kind of plastic. Through the analysis of plastic parts structure, it can be seen that the moving mold part cannot be processed by using the integral structure, so the combined core structure is adopted.

? Cylindrical core

The shoulder is fixed, and its lower bottom surface is pressed by the die core.

Size calculation. Check its dimensional tolerance:

Because the dimensional accuracy is moderate, the manufacturing deviation is taken as the dimensional tolerance 1/3, and the wear deviation is taken as the dimensional tolerance.

1/6, namely:.

Plastic shrinkage range: 1.5-2.0%, then the average shrinkage rate is:

Therefore, the dimensions of the cavity core are: (See the part drawing for design dimensions).

? Dynamic core cavity

Assemble the movable die core, fix it on the movable template with screws, and check its dimensional tolerance:

Cavity size:

(See part drawing for design dimensions)

? Fixed die core cavity

After the die core is assembled, fix it on the movable template with screws, and check its dimensional tolerance: cavity size:

(See part drawing for design dimensions)

? Sliding block core

The slider core is designed as an integral structure with four * * *, and the corresponding side hole sizes are as follows:

10.9, lateral core-pulling mechanism

? Selection of lateral core-pulling mechanism

There are six square holes in the side wall of the plastic part, which are perpendicular to the demoulding direction to prevent the molded plastic part from coming out of the mold. Therefore, the lateral parting core-pulling mechanism must be set during molding. After analysis, the die adopts inclined column core-pulling mechanism.

Determine the core-pulling distance: if the depth of the side hole of the plastic part is 1mm, then S = h+(2-3) = 4 mm.

Determine the inclination angle of the inclined guide post: because the core-pulling distance of the die is relatively short, the inclination angle can be smaller, which is 12.

? Determine the size of the inclined guide post:

, look up the table to get d= 18mm.

After calculation, the length of standard inclined guide pillar is 100㎜.

1 1. Determination of the die set and selection of standard parts.

According to the large layout and mutual position size of the front cavity, combined with the plastic parts size of the standard frame of the mold base and the standard mold base of P4 structure, the size of 500×560 mold base can meet the requirements.

Check parameters related to cavity parts.

? Verify the distance between I-shaped edges.

Pass the inspection

For the allowable application of cavity materials, the allowable stress of Cr 12MoV is 245MPa.

P is the average pressure of the cavity.

? Check the thickness of the cavity floor.

, inspection qualified.

? The closing height of the mold. cheque

Calculate the closing height of the mold as follows:

Check xs-zy- 1000, that is, the mold meets the requirements.

Installation requirements of.

? Check the shape of the mold;

The overall dimensions of the mold are XS-ZY- 1000. The maximum installation dimension of the injection molding machine template is, which can meet the installation requirements of the mold.

? Inspection of mold opening stroke;

The mold stroke is XS-ZY- 1000, and the maximum mold opening stroke is 700 mm >: 183mm, which can meet the mold opening requirements of injection molding machines.

12. exhaust system design

This plastic part is a small reverse part, which can be discharged through the gap between the push rod, the moving core and the template, with a gap of.

13. 1 1, design of temperature control system

Look-up table shows that the mold temperature required for polyethylene molding is 30-60℃, and the mold temperature is 40℃.

? Volume flow of cooling water

? Cooling water pipe diameter

In order to keep the water turbulent, it is necessary to look up the table.

? Velocity of cooling water in pipeline

According to formula

It is higher than the minimum flow rate 1. 10m/s, and reaches a turbulent state, so the pipe diameter is reasonably selected.

? Heat transfer film coefficient between cooling pipe hole wall and cooling water

Look-up table f=7.22 (when the water temperature is 30℃), so

? Total heat transfer area of cooling pipe:

? Number of cooling water holes to be opened on the mold:

14. Ejection mechanism (demoulding)

? Determination of the form of pushing mechanism;

This plastic part is pushed out by the thimble, and the push rod is designed at the step of the plastic part. Each plastic part is pushed out by 8 push rods, which are evenly distributed in a circle at the step, with a total of 32 push rods. Its structure is shown in the assembly drawing.

? Calculation of demoulding force:

Coefficient of demoulding force coefficient of linear expansion of plastics

Elastic tensile modulus of plastics at demoulding temperature and softening temperature.

Temperature and thickness of plastic parts when demoulding.

Core height in demoulding direction

? Verification of demoulding force

Check whether the jacking force of XS-ZY- 1000 can meet the requirements of the injection machine.

15. Guiding mechanism

The guide post adopts the specifications of the die frame itself, but its length is related to the die opening stroke and must be designed and selected separately. After calculation, the length of long guide pillar is, and the length of guide pillar is.

The relevant cooperation is shown in the assembly drawing, and the corresponding guide sleeve is selected according to the specifications of the mold base.

16. Reference

1. Wu Xianming, etc? Plastic mold design guidance? Beijing: National Defense Industry Press, 2006? five

2. Yu Dongrong, where is Cheng? Plastic molding technology and mold design? Beijing Science Press 2005.

3. China Mechanical Engineering Society, Editorial Board of China Mould Design Ceremony? China Mould Design Festival. Nanchang: Jiangxi Science and Technology Press, 1998.

17. Experience in mold design

Through this mold design, my professional knowledge is more systematic and complete. In the design, I have mastered the relevant technical standards and specifications, and learned how to learn and use the valuable design experience and information accumulated by predecessors. It also exercised my ability to comprehensively consider structure, technology, economy and standardization, and consolidated the professional course knowledge I learned in the past. I have mastered the basic process of injection mold design, and also exercised my hands-on ability and rigor in engineering technology. In a word, my professional level has been further improved through this mold design.

18. Die assembly drawing and parts drawing: (with engineering drawing) Results

The molding process of this plastic part is good.

Point gate pouring adopts three-plate structure, one mold and four cavities.

Choose XS-ZY- 1000 screw for injection molding.

The shunt is semicircular, D= 10.

millimetre

Adopt a combined core structure

The specifications of the inclined guide post are as follows

Its dip angle is 12.

P4 standard template is selected, and the template size is 500×560.

Cavity parts passed the inspection.

The mold closing height is qualified.