(1) A mould is a tool that uses its own specific shape to shape a product of a certain shape and size.
A plastic molding tool is a tool that uses its own specific shape to mold a plastic product of a certain shape and size.
(2) Classification of Plastic Molding Molds
1.Injection moulds (injection moulds, injection moulds)
2.Extrusion moulds (extrusion moulds, machine heads)
3.Pressing moulds (pressing moulds, pressing film)
4.Die-casting mould (die-casting mould)
5.Hollow forming moulds (hollow moulds)
6.Vacuum and compressed air forming moulds
(3) What are the factors that affect the accuracy of the size of plastic parts?
1.Error caused by mould manufacturing accuracy
2.Error caused by mould wear
3.Error caused by fluctuations in plastic shrinkage
4.Errors caused by installation errors in the mould 5Errors caused by clearance of moving parts in the mould
(4) If the wall thickness difference of a plastic part is too large, what method should be used to reduce the wall thickness difference?
The wall thickness difference can be reduced by hollowing out the thick part of the part or by breaking the part into several parts and combining them again.
(5) What are the key points in the design of the release slope? How to mark
1.Highly accurate parts require a small release slope.
2.Smaller release slope for high size parts
3.The shape of the part is complex and not easy to release, use a larger slope
4.Use a larger release slope for reinforced plastics
5.High shrinkage, greater slope
Smaller release slope for plastics containing lubricants
Note: The shape is based on the large end and the slope is obtained from the shrinkage direction.
The inner shape is based on the small end and the slope is obtained from the enlargement direction.
(6) What are the characteristics of plastic products?
Uniform wall thickness and thin wall thickness
(7) What factors should be taken into account when designing plastic products?
1.The physical and mechanical properties of the raw materials
2.The moulding process of the raw materials
3.The shape of the plastic part should be conducive to the parting of the mould for air venting and cooling
4.The shrinkage of the product after moulding and the difference in shrinkage rate
5.The general structure of the mould and the structure of the mould parts
6.The working process of the mould parts
(8) What is the general structure of an injection mould? What is the main purpose of each component?
1.Use of moulding parts: to determine the shape and position of the product
2.Closing guide mechanism: to ensure accurate alignment between the moving and fixed moulds or other parts of the mould, so as to ensure the shape and size of the product.
To ensure the accuracy of the shape and size of the product, and to avoid collisions and interferences between parts of the mould.
3.The pouring system serves to direct the molten plastic injected by the injection machine into the closed cavity.
It has an important role in the flow characteristics of the melt and the quality of injection moulding.
4.Push-out mechanism: A device for releasing plastic products from the mould cavity.
5.Lateral parting and core extraction mechanism: A set of lateral movement devices for lateral core extraction of products with side holes or side recesses.
6.Air venting mechanism: A device for removing air from the mould cavity and various gases evolved by the plastic itself during the plastic melt punching process, in order to remove the air from the mould cavity.
The purpose of the air venting mechanism is to remove the air from the cavity and the gases evolved by the plastic itself during the plastic melt punching process so that they do not cause defects.
7.Cooling and heating device: To meet the requirements of the injection moulding process on the moulding process on the temperature of the mould.
The cooling and heating device is used to meet the requirements of the injection moulding process in order to ensure the filling of the mould with the melt and the curing of the product.
8.Supporting parts: Mainly used for mounting or supporting the seven functional structures mentioned above, such as moulding parts.
(9) What are the categories of injection moulds according to their structural features? Describe, with examples, the principles of operation?
1.single-face injection moulds
2.double-face injection moulds
3.lateral parting and core extraction moulds with oblique guide pillars
4.Injection moulds with lateral parting and core extraction with inclined slides
5.Injection moulds with movable inserts
6.Injection moulds with push-out mechanism for fixed moulds
7.No runner parting moulds
(10) What are the forms of parting faces? What are the principles for selecting a parting frame?
Form: Flat-frame sloping-frame stepped-frame curved-frame flanging
Principles for choosing the parting frame:
1.Good for demoulding
2.Good for ensuring the quality of the moulded part
3.Good for simplifying the mould structure
4.It is conducive to the processing of moulded parts.
5.It should be selected at the largest contour of the moulded part.
6.It is conducive to lateral parting and core extraction
7.It should minimise the difference in the size of the part caused by the slope of the release
8.The technical parameters of the injection machine should be taken into account
(11) What are the characteristics of integral and combined moulded parts?
1.Integral type: strong, not easily deformed, good quality parts. Large size, inconvenient to handle; too much cutting
Waste of steel; not easy to build heat treatment (hardened impervious), difficult to maintain.
2.Combined: simple shape, small size, easy to handle, easy to work on; saves steel, easy to heat-treat, easy to maintain.
(12) What are the working factors that affect the working size of moulded parts?
1.Manufacturing errors in moulded parts
2.Wear of moulded parts
3.Fluctuations in shrinkage of moulded parts
4.Fitting errors in mould installation
5.Error caused by gaps in the moving parts
(13) How are the strength and stiffness conditions for molded parts determined?
The wall thickness of the cavity of a large-size mold should be sufficient for stiffness, and the wall thickness of the cavity of a small-size mold should be sufficient for strength.
(14) What is the purpose of the mold closing guide mechanism? (to withstand lateral force)
1.Guiding: guide the mold in the correct position for closing the mold. The guide should be 6-8 mm higher than the main core.
2.Positioning: To ensure the correct shape of the cavity.
3.Withstand a certain amount of lateral force: when the part is not symmetrical or when a side sprue is used.
(15) What are the types of mould closing guides? What is the main purpose of these guides? What are the characteristics of each? (2 types, column guidance, column positioning)
(2 types, guide pillar guidance and guide pillar positioning) Mould closing guides are usually guided by guide pillars.
1.Features of column-guided mechanisms: simple structure, easy to work with, easy to install; low positioning accuracy and poor ability to withstand lateral forces.
2.Features of column-guided, tapered-frame positioning mechanism: high positioning accuracy, strong ability to withstand lateral force; complex structure.
Features of tapered-frame positioning mechanism: zero clearance for tapered-frame positioning, which can improve positioning accuracy.
(16) What issues should be considered in the design of guide columns? What are the different ways of distributing guide columns?
Principle: Ensure that the mould can only be moved and fixed in one position and along one die.
Layout: A isometric non-symmetrical B non-isometric symmetrical
(17) What are the components of a common pouring system? What are the design requirements for each part?
Design of the main runner:
1.The main runner is normally located on the centre line of the mould
2.The diameter of the main runner must be appropriate
3.In order to remove the condensate from the main runner cheaply
4.The outlet end of the main channel should be rounded at angle
5.The surface roughness of the wall of the main channel should be less than Ra0.63
6.In order to ensure that the product is formed
The main channel should be short in order to reduce the amount of pressure loss and waste.
(18) What are the basic types of pouring? What are the characteristics of each? What are their respective applications?
1.Advantages of direct pouring: The melt enters the cavity directly through the main flow channel, resulting in a short process, fast feed, low flow resistance and good pressure transfer.
It has a short process, fast feed, low flow resistance, good pressure transfer, strong pressure-holding and shrinkage, and is conducive to air venting and elimination of fusion marks. At the same time, the pouring system consumes less material and the mould structure is simple and compact, making it easy to manufacture.
Disadvantages: A. High internal stress, product deformation B. Difficulty in removing cold solids from runners.
Application: Suitable for moulding shell or box shaped products with deep cavities.
2.Side pouring (edge pouring) Characteristics: The closing time (replenishment time) of a rectangular shaped pouring is mainly determined by the thickness a value.
The shear rate during mould filling is mainly determined by the width b value.
Application: Suitable for thin, mature molded parts.
- Characteristics of the centre sprue: The core has a positioning function.
Use: This type of sprue is suitable for plastic parts that are carefully sized and where fusion marks are not allowed.
Advantages: easy to remove the sprue and facilitates automatic operation
Disadvantages: a Complicated mould structure, suitable for multi-cavity, three-panel, two-opening moulds, point sprue comes off automatically when the mould is opened.
4.Submerged sprue characteristics: The runner is set on the parting face and the sprue is often opened at the side of the product at an angle to the runner. The sprue is cut off automatically when the mould is opened. Application: Molding bushings and box parts, pushing out the product to cut off the sprue.
5.ears guarded sprue should be used: for flat, thin molded parts to reduce shear forces in the cavity.
(19) What are the forms of runner arrangement? What are the characteristics of each?
The centre of the cavity pressure coincides as closely as possible with the centre of the injection machine.
The characteristics of the natural balance: the flow rate and the time for the melt to reach the cavity are controlled using the thickness of the runner to achieve balance.
(20) What principles should be followed in selecting the location of the sprue?
1.Prevent the creation of jets at the sprue to create ripple marks during the filling process
2.Position the sprue to facilitate melt flow and shrinkage. The pouring should be at the thickest part of the product.
3.The location of the pouring gate and the warpage of the product
4.Prevent the melt from impacting directly on the slender core or insert
5.Pouring location should facilitate air venting to avoid wind packing
6.Pouring location should be in the area with the least energy loss during melt flow
7.The location of the sprue should avoid fusion marks as far as possible. If this cannot be avoided, it should be done in such a way that If they cannot be avoided, they should be located out of the functional, load and appearance zones.
(21) What are the factors that affect push-out force?
Positioning of the release force push-out piece
(22) What are the components of the push rod push-out mechanism? What issues should be noted when using the push rod push out mechanism?
1.Pusher fixing plate
2.Limit pins
3.Pusher and reset lever
Note:
1.Avoid the location of cooling channels
2.Generally allow the top bar to encroach no more than 0.1 mm into the moulded part, and generally do not allow the end of the top bar to fall below the moulded surface of the part
3.As long as the appearance of the part is not damaged, as many pushrods as possible should be provided to reduce the contact force for release of the part
4.Push rods should be located in locations where air venting is difficult and can be used for both purposes
(23) What are the components of a typical demoulding mechanism? What are the characteristics of each?
Positioning device guide device ejector device discharge device forming device
(24) How does a sequential demoulding mechanism work?
The mechanism for removing the moulded part and the pouring system from the mould cavity or core.
(25) What are the components of the inclined column side core extraction mechanism? What is the function of each part? Please illustrate with a drawing.
1.Slanting column for guidance
2.Slide-guide role:The slider should slide smoothly in the slide-guide without stalling or skipping.
3.Locking wedge:The clamping block used to close the slider should be able to withstand the lateral pressure during injection.
4.Limiting parts should be used:The slider limiting device should be flexible and reliable to ensure that the slider does not slide arbitrarily after opening the mould.
(26) What is the phenomenon of side core interference? How can it be avoided?
If the slider is reset first and the pusher is reset later, there is a risk that the side core will hit the pusher. How to avoid this: Use the reset mechanism first.
(27) What are the specific forms of side core extraction mechanisms used in inclined columns? What is the principle of operation of each form?
By type of drive.
1.Manual side core extraction mechanism principle: small batch production or no motorized core extraction mechanism can be used
2.Motorized side core extraction mechanism principle: Relying on mold opening force, the side core is extracted by means of drive parts
3.Principle of hydraulic or air-operated side core extraction mechanism: Rely on hydraulic system or its pressure system to extract side cores
By mould structure.
1.inclined column parting and core extraction mechanism principle: using the fixed distance parting tensioning mechanism to complete the fixed part of the mould first parting, complete the lateral core, then the dynamic mould with the product out of the cavity, and then rely on the push out mechanism to complete the entire demoulding action.
2.Principle of inclined slider parting and core extraction mechanism: When the mould is opened, the moulded part and slider are left at the side of the moving mould, and only after the core is set, the inclined slider is parted and core extracted from the product with the help of the push rod.
3.Other side core extraction mechanisms
