Injection moulding is a manufacturing technique for making parts from both thermoplastic and thermosetting. Plastic material in production molten plastic is injected at high pressure into a mould.
1. Seminar on: INJECTION MOULDING
BY:-KUNDAN KUMAR
(Department of Mechanical Engg.)
Camellia Institute of Technology & Management
2. Historical Background
• In 1868 john wesley hyatt become the first to inject
hot celluloid in to a mould, producing billiard balls.
• He and his brother patented an injection moulding
machine that used a plunger in 1872, this process is
work until 1946.
• In 1946 James Hendry built the first screw injection
moulding machine.
3. Injection Moulding process – over
view
Solid wide neck, flat product is made like bucket, cabinets,
Automobile & Industrial parts etc.. By injecting molten
thermoplastic material into a closed mould which is
relatively cool.
Type of Injection Moulding Machine
Hand Injection Moulding M/C
Plunger Type Injection Moulding M/C
Reciprocating Screw Type Injection Moulding M/C
4. Hand Injection Moulding Machine
Vertical machine consist
of Barallel, Plunger,
Band Heaters along with
energy regulator, Rack &
Pinion system for
injecting the material by
the plunger, a torpedo
and nozzle.
5. Plunger Type Injection Moulding machine
Vertical and Horizontal plunger type
injection moulding machine:
6. Reciprocating Screw Type Injection Moulding Machine
• The feeding zone
• The compressing (or transition) zone
• The metering zone
8. The injection process
Plasticises the material by reciprocating screw.
Injects the molten material to a closed mould
-via a channel system of gates and runners.
Cools the Mould.
Refill the material for the next cycle
Eject the product.
Closes the mould for further cycle.
11. Screw Used in Injection Moulding machine
The screw has three zones with a ring-plunger assembly. The
Feed Zone. Where the plastic first enters the screw and is
conveyed along a constant compressed and melted along a root
diameter; the Transition zone, where the plastic is conveyed,
compressed and melted along the root diameter that increases
with a constant taper; and the Metering Zone. Where the meting
of the plastic is completed and the melt is conveyed forward
along a constant root diameter reaching a temperature and
viscosity to form parts.
12. L/D Ratio
The L/D ratio is the ratio of the flighted length (Effective Length)
of the outside diameter.
Most injection screws use a 20:1 L/D ratio. But it may range
from 18:1 to 24:1
In the case of Thermoplastic it may range from 12:1 to 16:1
Compression Ratio
(CR)
The ratio of the first flight depth of feed zone to the last flight depth
of meter zone.
Or,
First channel Volume of feed zone to last channel volume of
metering zone.
Typically ranges from 1.5:1 to 4.5:1 for most thermoplastic
materials.
Most Injection screws classified as general purpose have a
compression ratio of 2.5:1 to 3:1.
Thermo set screws have a 1:1 ratio.
13. Back pressure(Kg/Cm2 or bar )
Back pressure is the amount of pressure exerted by the
material ahead of the screw, as the screw is pushed back
in preparation for the next shot.
Injection speed (Cm/Sec )
The injection speed is the forward speed of the screw
during its injection operation per unit time.
Screw Rotation Speed
The screw rotation speed (RPM) is the rate at which the
plasticizing screw rotates.
14. Cushion
The cushion is the difference in the final forward position of the
screw and its maximum allowable forward position.
•More cushion results more residence time, some time degrades.
•If the screw were allowed to travel its full stroke and stop mechanically
against the nozzle, the cushion would be zero.
•With zero cushion no hold on works.
•Typically a cushion of 3 to 6mm is used.
16. Advantages of Injection Moulding process
Parts can be produced at high production rates.
Large volume production is possible.
Relatively low labour cost per unit is obtainable.
Process is highly susceptible to automation.
Parts require little or no finishing.
Many different surfaces, colours, and finishes are available.
Good decoration is possible.
For many shapes this process is the most economical way to
fabricate.
Process permits the manufacture of very small parts which are
almost impossible to fabricate in quantities by other methods.
Minimal scrap loss result as runners, gates and rejects can be
reground and reused.
17. Limitations of Injection Moulding
Intense industry competition often results in low profit
margins.
Mould costs are high.
Moulding machinery and auxiliary equipment costs are high.
Lack of Knowledge about the fundamentals of the process
causes problems.
Lack of knowledge about the long term properties of the
materials may result in long-term failures.
Materials for Injection Moulding
1. Acetal 8. Polyphenylene oxide
2. Acrylic 9. Polyphenylene
3. Polycarbonate (pc) 10. Polystyrene
4. Polyester 11. Polysulphone
5. Polyethylene 12. Polyvinyl chloride(PVC)
6. Fluoro plastic 13. Acrylonitrile butadiene styrene
7. Polyimide 14. Nylon
19. Setting Machine Process conditions
1. Set the melt temperature
2. Set the mould temperature
3. Set the switch-over position
4. Set the screw rotation speed
5. Set the back pressure
6. Set the injection pressure to the machine maximum.
7. Set the holding pressure at 0 Mpa
8. Set the injection velocity to the machine maximum
9. Set the holding time
10.Set ample remaining cooling time
11.Set mould open time
12.Mould a short-shot series by increasing injection volume
13.Switch to automatic operation
14.Set the mould opening stroke
15.Set the ejector stroke, start position and velocity
16.Set the injection volume to 99% mould filled
17. increase the holding pressure and minimize the holding
time
18.Minimize the remaining cooling time
20. Temperature History in an Injection Moulded part
Pressure History in an Injection Moulded part
22. Post Moulding Operation
1. Chrome Plating
2. In Mould Insert Moulding
3. Post Mould Inserting
4. Drilling
5. Polishing
6. Heat inserting
7. Assembly
23. Secondary Operations
Applique: A surface covering applied by heat and
pressure
Printing: A process of making a mark or impression
onto a substrate for decorative or informational
purposes.
Painting
Hard coating
Metalizing/shielding
Surface Treatment
Annealing
Machining
Injection moulding is a manufacturing technique for making parts from both thermoplastic and thermosetting. Plastic material in production molten plastic is injected at high pressure into a mould. Which is the inverse of the products shape. After a product is designed usually by an industrial designer or an engineer, moulds are made by mould maker (or tool maker) from metal , by either steel or aluminium and precision machined to from the features of the desired part. Injection moulding is widely used for manufacturing a verity of parts from the smaller components to either body panels of cars.
In 1868 john wesley Hyatt became the first to inject hot celluloid in to a mould producing billiard balls. He and his brothers Isalah patented an injection moulding machine that used a plunger in 1872, and the process remained more or less the same until 1946. When james Hendry built the first screw injection moulding machine, revolutionizing the plastic industry.
Roughly 95% of all moulding machine now use screws to efficiently heat mix and inject plastic in to moulds.
According to their divided Zone the work is run by the three parts of machine.
Pouring & maintenance :- I can say feeding, Here we produced the solid plastic grain in hopper and agent for colouring.
Heating and melting:- Here the plastic material is melt due to heat produced by electric heater which is wrapped the circular of the barrel and heated by electric.
Cooling and Removal :- After inject the melting material the product is required rapid cooling for that the parallel water based cooling pipe is on the all side of the mould cavity.
Injection processes
The reciprocating screw injection moulding machine operated by an cycle to repeat the four operations.
Plasticisation :- Here when the plastic material is comes in the barrel Is in solid form here the heater giving heat to the plastic material. The plastic material takes heat from heater comes in melting condition.
Injection:- this is the 2nd operation of injection process, here the plastic material inject in the mould at a specific high speed and pressure that the material totally fulfil the mould before cooling .
Cooling:- After proper fill the mould cavity by material screw rotates in reverse direction and the mould is in cooling process so the plastic material in mould cavity being solidify (Molecular orientation, stress between molecules, crystal form)
De mould or, Ejection:- After cooling the material is removed from mould and Now we prepare for next cycle.
Mould in injection moulding machine nothing but same as green sand mould. It has also runner, sprue, gate, mould core etc. But some others parts are ejection pin, cooling channel, ejector box, ejector bar etc.
Designing of mould product should be done to fulfil demanded characteristics of desired product and need to evaluate materials particle physically, mould ability, liquid and mould designing condition for that point should be care.
Try not to make the thickness excessively thick and try to keep it even, so that rapid change in thickness will not happen.
Try not to make the undercut.
Consider the draft angle
Try not to make sharp corner
Also we have to careful in the gate designing in injection moulding. Ex - Direct sprue gate, Side gate, Fan gate, Disk gate, ring gate, film gate, rib gate, submarine gate.
Blow moulding process and mould:- It’s used the making toy, bottle, poly bag etc. In them after the inject the material in the mould cavity, at a pressure air is produce in side the mould and material. Which force is same in all direction and due to this blow air plastic material taking the shape of mould. And then after cooling it remove automatically. It’s also used to make cool drinks bottle, plastic box, plastic rod, water tank.
In the blow moulding a big advantage is that we make a material of multi layer of different quality and colour of plastic. Ex:- water tank
Result due to higher L/D ratio :
More shear heat can be uniformly generated in the plastic without degradation.
Great the opportunity for mixing, resulting in a better homogeneity of the melt.
Greater the resistance time of the plastic in the barrel possibly permitting faster cycles of larger shots.
2. Result due to higher CR.
Greater shear heat imparted to the resin.
Greater heat uniformity of the melt.
High potential for creating stresses in some resins.
High energy consumption.
Back pressure effect
More homogeneous mixture
Proper melting.
More compact
Sometimes leads degradation
2. Injection speed effect:
Easy injection of material
Avoid short-shot
Sometimes leads more orientation & burn marks.
3. The faster the screw rotation speed
Faster the material is compressed by the screw flights.
Increasing the amount of shear heating
Some less melting
Clamping is an machinery system to clamp the mould or mould cavity.
:- Mainly three types of clamping-
Toggle type clamping:-
A toggle is mechanically device to amplify force.
In a moulding machine which consists of two bars jointed together and to end with a pivot.
The end of one bar is attached to a stationary platen and the other end of a second bar is attached to the movable platen.
When the mould is open the toggle is in the shape of a V.
When pressure is applied to the pivot the two bars from a straight line.
:-ADVANTAGE:-
Low cost and lower horse power needed to run.
Positive clamp of the mould.
DISADVANTAGE:-
Do not read the clamp force.
Clamping is more difficult.
Higher maintenance as lubricant is provided.
2. HYDRAULIC CLAMPING:
A clamping unit actuated by hydraulic cylinder which is directly connected to the moving closed the mould. In this case ram of hydraulic system is attached to moving platen. There are two halves in hydraulic cylinder which is actually inlet and outlet of oil.
When oil goes to the cylinder with pressure oil pushes the ram to forward direction by which moving platen moves and mould closed and when oil. Comes from the cylinder the back and mould is open.
ADVANTAGE:
Clamp speed easily controlled and stopped at any point
Direct a read out of clamp force.
Easy adjustment of clapped force and easy mould setup
Low maintenance as part is self lubricated
DISADVANTAGE:-
It is higher cost and more expensive then toggle system.
None positive clamp.
3. TIE-BAR LESS CLAMPING.
Tie bar less clamping system is basically hydraulic clamping system without any tie-bar.
The platen is moved on a rail system.
ADVANTAGE:
There is no limitation of mould platen size.
There is no tie bar so the mould dimension is not so important.
Also moulding of the mould is easy any it is very useful when products eject from the mould is manual.
Large stroke compared to the toggle type machine.
Full machine capacity can be utilized.
Smaller machines can mould larger components.
Saves electrical energy because of reduction in the size of machine.
Lower lubrication required.
POST MOULDING OPERATION
Benefits of post moulding operation:-
Reduced costs:- By caring out post moulding operations in house, and utilise lean manufacturing tools, we can greatly reduce comfort costs and the complexity of work that our customers would ordinarily under marks would ordinary undertaken.
High level of quality:_ performing post moulding operations on products help ensure that a high level of quality is maintained. By checking parts from the moment they leave a press to final assembly quality levels can be maintained and ensure that components are only assembled to the highest standard.
Reduction of customers stock holding.
Reduced production time:- Post moulding operation mean there is a very little time b/w the production of components and their assembly. This means that a great deal of time can be saved when components would normally be transported or stored in b/w moulding and assembly operation.
TYPES OF POST MULDING OPERATION:
CHROME PLATING:- Due to the chrome plating process requiring the parts to be electrically conductive, a series of steps are required before the chrome can be deposited on the surface of the product.
BENEFITS:-
Metal finish:- Metal finishes can be very popular and by coating plastics advantage can be taken of characteristics from both materials.
Wear resistance:- as chrome is a metal rather then a plastic its were resistance properties are much greater then those of the plastic it covers, this means for application where a part might be handled repeatedly such as a shower handset, a chrome finish is likely to were better then its plastic counterpart.
IN MOULD INSERT MOULDING:- In mould insert moulding is the process by which a metal or performed plastic insert is incepted in to the components during the moulding stage.
BENEFITS:-
Increased part consistency:- Insert moulding has major benefits in the consistency of parts produced. As the inserts are pleased in the same location in tools for every cycle each of moulding produced will be exactly the same. This helps reduces costs as rejected parts will be kept to a minimum.
POST MOULD INSERTING:- Post mould inserting is the process by which a metal or preformed plastic, Insert is incorporated in to a moulding by means of a secondary process once the component has already been moulded.
BENEFITS:-
Easy to assembly:- By adding inserts to a moulding type ease by which it can be assembled is greatly increased. Insert such as clips or screw bolts can be incorporated in to mouldings which greatly assist assembly operation and subsequent product performance.
Increase part functionality:- Besides adding inserts to aid assembly inserts that improve a parts functionality can also be used. Ex:- thermal fitting for wires
DRILLING:- The drilling of parts is used. To remove any unnecessary polymer that may have been necessary in the moulding process by removing this extra material in house it means a ready – to – assemble moulding can be provided to the customer or the part can be assembled with other moulding.
POLISHING:- For products that have a high quality gloss finish a post moulding polishing operation is often a useful extra process even through the finish produced by the moulding tool may be of a very high quality a polishing operation to remove any dust from the product before final packing gives a part the high gloss finish that will have been specified. Polishing operations are carried. Out on a soft polishing wheel with high quality wax to ensure that a part is polished to a perfect finish without leaving any marks.
HEAT INSERTING:- Heat inserting is the addition of inserts into a part increases the functionality of a part by which components can be assembled.
BENEFITS:-
Increased functionality:- By adding inserts to moulding the part can more easily be used for part can more easily be used for its designed purpose. Ex:- by adding threaded inserts parts can be easily be screwed to their fixing of other parts, increasing their functionality.
Low part degradation:- The process of heat inserting means that the heating/ melting or the parts is very localised to where tyhe insert will be pressed in this means that parts done suffer carping or any other distortion effects due to being heated again.
High level of quality.
7. ASSEMBLY:- for products that require assembly we are able to caring out this operation in our assembly facility.
FAULTES AND REMEDIES.
SINK MARKS:- Depression in a moulded part caused by shrinking or collapsing of the resin during cooling. Problem due to:-
Improper mould design.
Parts cool too rapidly.
Rib section in part too wide.
Enter tapped gas.
Nozzle too resistive.
Pressure too low.
Gate too small.
Excessive cooling time in mould.
2. JETTING:- Turbulence in the resin melt flow caused by undersized gate, abrupt change in cavity volume, or too high injection pressure.
Problem due to:-
Excessive injection speed.
Melt temperature too high.
Melt temperature too low.
Gate and length too long.
Sprue, runner and/or gate size too small.
Nozzle heating band malfunction.
3. SPLAY MARKS:- Marks or droplet type imperfections formed on the surface of a finished part.
Problem due to:-
Obstruction in nozzle.
Screw rpm too high.
Nozzle too hot.
Nozzle, gate, or sprue too small.
Cracked mould.
Excessive moisture.
Insufficient venting.
4. BLUSH: Discoloration generally appearing at gates, around inserts, or other obstructions along the flow path usually indicates weak points.
Problem due to:-
Mould temperature too cold.
Injection fill speed too fast.
Improper gate location.
Sprue and nozzle diameter too small.
Sharp corners in gate area.
Inadequate injection pressure.
5. BURN MARKS:- Black marks or scorch marks on surface moulded part usually on the side of the part opposite the gate or in a deep cavity.
Problem due to:-
Excessive injection speed and pressure.
Screw speed too high.
Faulty temp. Controllers.
Compression ratio of screw too high.
Inefficient mould temp.
Excessive back pressure.
6. POOR WELD LINES:- In ability of too melt fronts to knit together in a homogeneous function during the moulding process, resulting in weak areas in the part of varying severity.
Problem due to:-
Material too cold.
Improper mould design.
Distance from gate excessive.
Injection pressure too low.
Core shifting.
Entrapment of air at weld line.
Inadequate flow.
7. VOIDS:- An unshelled space of such size that it scatters radiant energy such as light.
Problem due to:-
Injection pressure too low.
Packing time too short.
Insufficient feed of material.
Excessive cushion.
At the side of rib too thick.
Mould temperature too low.
8. DELAMINATION:- Surface of the finished part separates or appears to be composed. of layer of solidified resin strata or fish scale type appearance where the layers may be separated.
Problem due to:-
Resin temperature too low.
Non-uniformly of resin temperature.
Incompatible polymers.
Excessive material moisture.
9. FLOW LINES AND FOLDS:- Mark visible on the finished item that indicate the direction of flow in the cavity.
Problem due to:-
Stock temp. Too low.
Runner too small.
Improper gate size and/or location.
Inadequate cold slug well.
10. EXCESSIVE WARPAGE:- Excessive dimensional change in a part after processing of the excessive decrease in dimension in a part through cooling.
Problem due to:-
Mould closed time too short.
Inefficient injection forward time.
Ram speed too high or, too low.
Excessive nozzle and melting zone temperature.
Non-uniform part injection.
11. BLACK SPECKS:- Particles in the surface of an opaque part and visible throughout a transparent part.
Problem due to:-
Contamination of material.
Press contamination.
Local over- heating in the nozzle.
Tapped air.
Inefficient injection speed.
Oxidation by occluded air or inadequate air venting.
12. BRITTLENESS:- Tendency of a molded part to break creak, shatter etc., under condition which it would not normally do so.
Problem due to:-
Excessive amount of regrind.
Melt temperature too cold.
Material degraded.
Poor part design.
Undried material.
Non-uniformly of resin temperature.
Resin too cold.
FLASH:- Excess plastic around the area of the mould parting line on a moulded part.
Problem due to:-
Mould parting surfaces do not seal properly.
Injection pressure too high.
Feed needs adjustment.
Inadequate, mould support.
Oversized vent.
14. BLISTER:- Defect on the surface of a moulded part caused by gases trapped with in the part during curing.
Problem due to:-
Screw rpm too high.
Back pressure too low.
Regrind too coarse.
Gate improperly located.
Insufficient venting.
15. CRAZING:- Fine cracks in part surface. May extend in a network over the surface or through the parts.
Problem due to:-
Gate too large.
Inefficient injection forward time.
Mould surface contaminated.
Injection temperature too high.
16. CRACKING:- Fracture of the plastic material in an area around a bass, projection or moulded insert.
Problem due to:-
Parts cool too quickly.
Moulded in stress.
Well thickness too heavy for compound.
17. LOW GLOSS:- Surface roughness resulting from high speed fill which causes surface wrinkling as the polymer melt flow along the wall of the mould.
Problem due to:-
Air intrapment.
Melt inbox of material too low.
Inadequate polish of mould surface.
Inadequate flow.
Resin excessively moist.
Oil or grease on knockout pins.
Pigment agglomerates.
18. SHORT SHOT:- Injection of insufficient material to fill the mould.
Problem due to:-
Insufficient feed, cushion.
Inefficient screw delay.
Mould temperature too low.
Inadequate injection speed or pressure.
Melt temperature too low.
Screw bridging.
Injection press to insufficient capacity.
Improper gate location.
