2. Injection Moulding

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Transcript of 2. Injection Moulding

INJECTION MOULDING

CORPORATE TRAINING AND PLANNING

Historical Background A single-action hydraulic injection machine was designed in the U.S.A. in 1870 by Hyatt Heating-cylinder design was first recognised in a patent issued to Adam Gastron in 1932. Large-scale development of injection moulding machinery design towards the machines we know today did not occur until the 1950's in Germany

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Injection Moulding Process Over ViewSolid Wide neck, Flat Product is made like bucket, cabinets, Automobile & Industrial parts etc. by injecting molten thermoplastic material in to a closed mould which is relatively cool.CORPORATE TRAINING AND PLANNING

Type of Injection Moulding Machine Hand Injection Moulding M/C Plunger type Injection Moulding M/C Reciprocating Screw Type Injection Moulding M/CCORPORATE TRAINING AND PLANNING

Hand Injection Moulding Machine

vertical machine consists of Barrel, Plunger, Band Heaters along with energy regulator, Rack & Pinion system for Injecting the material by the plunger, a torpedo and nozzle.CORPORATE TRAINING AND PLANNING

Plunger Type Injection Moulding Machine

Vertical & Horizontal Plunger Type Injection Moulding MachineCORPORATE TRAINING AND PLANNING

The Reciprocating Screw The feeding zone The compressing (or transition) zone The metering zone

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Machine components

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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. Refills the material for the next cycle. Ejects the Product. Closes the Mould for further cycle.

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Injection Moulded Items

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Injection Moulded Items

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Injection Moulded Items

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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.CORPORATE TRAINING AND PLANNING

Advantages of Injection Moulding Process Minimal scrap loss result as runners, gates, and rejects can be reground and reused. Same items can be moulded in different materials, without changing the machine or mould in some cases. Close dimensional tolerances can be maintained. Parts can be moulded with metallic and non-metallic inserts. Parts can be moulded in a combination of plastic and such fillers as glass, asbestos, talc and carbon. The inherent properties of the material give many advantages such as high strength-weight rates, corrosion resistance, strength and clarity.CORPORATE TRAINING AND PLANNING

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.CORPORATE TRAINING AND PLANNING

Machine operation sequenceThe mould closes and the screw begins moving forward for injection.

The cavity fills as the reciprocating screw moves forward, as a plunger.

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Machine operation sequenceThe cavity is packed as the screw continuously moves forward.

The cavity cools as the gate freezes off and the screw begins to retract to plasticize material for the next shot.

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Machine operation sequenceThe mould opens for part ejection

The mould closes and the next cycle begins

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Injection MouldCORPORATE TRAINING AND PLANNING

Mould systemA typical (three-plate) moulding system

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A two-plate mould.

A three-plate mould.

The moulded system includes a delivery system and moulded parts.CORPORATE TRAINING AND PLANNING

Screw Used in Injection Moulding Machines

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 root diameter; the Transition Zone, where the plastic is conveyed, compressed and melted along a root diameter that increases with a constant taper; and the Metering Zone, where the melting of the plastic is completed and the melt is conveyed forward along a constant root diameter reaching a temperature and viscosity to form parts.CORPORATE TRAINING AND PLANNING

L/D RATIO The L/D ratio is the ratio of the flighted length (Effective Length) of the screw to its 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 Thermoset it may range from 12:1 to 16:1.

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High L/D Ratio results the following .

More shear heat can be uniformly generated in the plastic without degradation; Greater the opportunity for mixing, resulting in a better homogeneity of the melt. Greater the residence time of the plastic in the barrel possibly permitting faster cycles of larger shots.

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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 3.0:1. Thermo set screws have a 1:1 ratio.CORPORATE TRAINING AND PLANNING

Higher the CR results the following . Greater shear heat imparted to the resin Greater heat uniformity of the melt High Potential for creating stresses in some resins High energy consumptionCORPORATE TRAINING AND PLANNING

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. Effect of Back Pressure More Homogeneous Mix Proper Melting More compact Sometime leads degradationCORPORATE TRAINING AND PLANNING

Injection Speed (cm/Sec)The injection speed is the forward speed of the screw during its injection operation per unit time. Effect of Injection Speed Easy Injection of Material Avoid Short-Shot Some times leads more orientation & burn marksCORPORATE TRAINING AND PLANNING

Screw Rotation SpeedThe screw rotation speed (RPM) is the rate at which the plasticizing screw rotates. The faster the screw rotation result the following .. Faster the material is compressed by the screw flights Increasing the amount of shear heating Low residence time, some less meltingCORPORATE TRAINING AND PLANNING

CushionThe 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 6 mm is used.CORPORATE TRAINING AND PLANNING

Materials for Injection Moulding Acrylonitrile butadiene styrene (ABS) Acetal Acrylic Polycarbonate (PC) Polyester Polyethylene Fluoroplastic Polyimide Nylon Polyphenylene oxide Polypropylene (PP) ** Polystyrene (PS) Polysulphone Polyvinyl chloride (PVC) TRAINING AND CORPORATEPLANNING

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Molecules lie in a definite fashion or regular arrangementCORPORATE TRAINING AND PLANNING

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Molecules fall in Crystalline & amorphous patternCORPORATE TRAINING AND PLANNING

Amorphous Polymer has

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While flowing in the channel or cavity of the Mould. As the melt touches the surface of the mould its viscosity increases because of lowering of melt temperature, So it slides on the Surface and the Molecules gets orientedCORPORATE TRAINING AND PLANNING

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Non Newtonian Plastics

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Non Newtonian Plastics

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Newtonian Plastic

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Broad Molecular weight Distribution shows broad Melting PointsCORPORATE TRAINING AND PLANNING

Narrow Molecular weight Distribution shows sharp Melting PointsCORPORATE TRAINING AND PLANNING

Plastic Product Properties can change 10% or more by changing Process ConditionsCORPORATE TRAINING AND PLANNING

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During Refilling

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During Injection

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Additive Filler Plasticizer Antioxidant Colorant Flame retardant Stabilizer Reinforcement

Function increase bulk density improve processability, reduce product brittleness prevent polymer oxidation provide desired part application color reduce polymer flammability stabilize polymer against heat or UV light improve strength

Examples calcium carbonate, talc, limestone phthalate esters, phosphate esters phenols, aromatic amines oil-soluble dyes, organic pigments antimony trioxide carbon black, hydroxybenzophenone E-glass, S-glass, carbon, Kevlar fibers

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TOGGLE TYPE CLAMPING A toggle is mechanically device to amplify force. In a moulding machine, which consists of two bars joined, together end 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 form a straight line.

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TOGGLE TYPE CLAMPING

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TOGGLE TYPE CLAMPINGADVANTAGE Low cost and lower horsepower 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.CORPORATE TRAINING AND PLANNING

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 ram come back and mould is open.

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HYDRAULIC CLAMPING

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HYDRAULIC CLAMPINGADVANTAGE Clamp speed easily controlled and stopped at any point. Direct a read out of clamp force. Easy adjustment of clamped force and easy mould set up. Low maintenance as part is self lubricated.

DISADVANTAGE It is higher cost and more expensive than toggle system. None positive clamp.CORPORATE TRAINING AND PLANNING

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. The main advantage of this system there is no limitation of mould platen size. As there is no tie bar so the mould dimension is not so important. Also mounting of the mould is easy and it is very useful when products eject from the mould is manual.CORPORATE TRAINING AND PLANNING

TIE-BAR LESS CLAMPING

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TIE-BAR LESS CLAMPING Much larger mould mounting area. Larger stroke compared to the toggle type machines. Full machine capacity can be utilised. Smaller machines can mould larger components. Saves floor space. Saves electrical energy because of reduction in the size of machine. Has the capacity to reduce weight of the moulded component because tiebar stretching is not there. Machine becomes very flexible for future modification. Easy access to mould cavity's because of the absence of the tie bars. Robotic arm movement becomes easy. Fewer moving parts so lesser wear and tear so longer life for machines. Lower lubrication required. Removal of mould plates much simple. Greater stability.

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Theoretical Calculation

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Example 1: POM has an S.G. of 1.42. It is to be moulded in an Injection Moulding Machine with a shot weight of 80 gms (in PS). This machine has a shot weight of 80 x 1.42 / 1.05 = 108.19 gms of POM. Example 2: PP has an S.G. of 0.90. It is to be moulded in an Injection Moulding Machine with a shot weight of 80 gms (in PS). This machine has a shot weight of 80 x 0.90 / 1.05 = 68.57 gms of PP.CORPORATE TRAINING AND PLANNING

Example 3: Figurines made of UPVC (S.G. 1.38) with a combined weight of figurine plus runners of 40 gms. are to be moulded. What size of machine is sufficient? Shot weight in terms of PS = 40 x 1.05/1.38 = 30.43 gms. Using the 85% guide line, the machine shot weight needed = 30.43/0.85 =35.80 gms. Example 4: The same figurine in example 3 is to be moulded in a big machine. What is the biggest machine that could be used? Using the 35% rule, the biggest machine that could be used has a shot weight = 30.43/0.35 = 86.94 gms.CORPORATE TRAINING AND PLANNING

Determining Projected Area

Projected area is calculated by multiplying length times width.CORPORATE TRAINING AND PLANNING

Determining Clamping Force (Tonnes)Projected Area = Length x Width and multiplying that area by a clamp factor of between 2 and 8. Most commonly factor 5 is used. Clamp Force = Projected Area x 5 For every inch of depth the clamp force must be increased by 10%.

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Example 5: What is the residence time of UPVC (S.G. 1.38) in a machine with screw diameter of 55 mm, injection stroke of 250 mm, shot weight (PS) of 567 g, and a cycle time of 10 s moulding shots weighing 260 g? Volume of melt in the barrel is estimated to be two times the injection volume = 2 * 3.1416 * 5.5 * 5.5 * 25 / 4 = 1188 cm3 Barrel residence time = 1188 * 1.38 * 10 / 260 = 63 s Example 6: A GPPS cup of diameter 79 mm is to be moulded. The cup is 0.6 mm at its thinnest section. Find a conservative clamping force which would be sufficient. The projected area of the cup (and runner) is 3.1416 * 7.92 / 4 = 49 cm2. This cup belongs to the thin wall domain. The conservative clamping force is 0.62 * 49 = 30.4 tonnes.CORPORATE TRAINING AND PLANNING

Example 7: The same GPPS cup has a flow path length of 104 mm. Find a more accurate clamping force needed. Flow path to thickness ratio (L/T Ratio) = 104 / 0.6 = 173. From Figure 2, at 0.6 mm wall thickness, the cavity pressure is 550 bar. 1 bar = 1.02 kg/cm2. The clamping force = 550 * 1.02 * 49 = 27,500 kg = 27.5 tonnes. The above calculation has not accounted for viscosity. It turns out to be still correct as the viscosity factor for GPPS is 1.0. Example 8: The same cup as in the above example is to be made out of ABS. Find the clamping force needed. Using the viscosity factor of 1.5, the clamping force needed = 1.5 * 27.5 tonnes = 41.3 tonnes.CORPORATE TRAINING AND PLANNING

Plastic flow

(a) Simple shear flow. (b) Simple extensional flow.

(c) Shear flow in cavity filling. (d) Extensional flow in cavity filling.

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where

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When Plastics flow in the cavity, the pressure decreases along the delivery system and the cavityCORPORATE TRAINING AND PLANNING

Injection pressure as a function of melt viscosity, flow length, volumetric flow rate, and part thicknessCORPORATE TRAINING AND PLANNING

Setting Machine Process Conditions1 2 3 4 5 6 7 8 9 10 Set the melt temperature Set the mold temperature Set the switch-over position Set the screw rotation speed Set the back pressure Set the injection pressure to the machine maximum Set the holding pressure at 0 MPa Set the injection velocity to the machine maximum Set the holding time Set ample remaining cooling timeCORPORATE TRAINING AND PLANNING

Setting Machine Process Conditions11 12 13 14 15 16 17 18 19 Set the mold open time Mold a short-shot series by increasing injection volume Switch to automatic operation Set the mold opening stroke Set the ejector stroke, start position, and velocity Set the injection volume to 99% mold filled Increase the holding pressure in steps Minimize the holding time Minimize the remaining cooling time

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Basic Process Factors in Injection Moulding

Material ParametersAmorphous, Semicrystalline, Blends and Filled Systems Pressure-Volume-Temperature (PVT) Behaviour Viscosity

Geometry ParametersWall Thickness of Part Number of Gates Gate Location Gate Thickness and Area Type of Gates: Manually or Automatically Trimmed Constraints from Ribs, Bosses and Inserts

Manufacturing ParametersFill Time Packing Pressure Level Mold Temperature Melt TemperatureCORPORATE TRAINING AND PLANNING

Residual stress

The development of residual flow stresses due to frozen-in molecular orientation during the filling and packing stages. (1) High cooling, shear, and orientation zone (2) Low cooling, shear, and orientation zoneCORPORATE TRAINING AND PLANNING

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Process ControlsInjection Moulding cycle can be broken down into four phases: Fill, Pack, Hold, and Cooling/plastication These phases can be controlled by following variables: Injection Speed, Plastic Temperature, Plastic Pressure, Cooling Temperature and Time.CORPORATE TRAINING AND PLANNING

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Cycle time in injection moulding

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Post Moulding Operation Heat inserting Chrome Plating In Mould Insert Moulding Post Mould Inserting Drilling Polishing AssemblyCORPORATE TRAINING AND PLANNING

Secondary operations Bonding Welding Inserting Staking Swaging Assembling with fasteners

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Secondary operations Appliqu: 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 Metallizing/shielding Surface treatment Annealing Machining

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Benefits of Post Moulding Operations Reduced costs by carrying out post moulding operations in house, and utilising lean manufacturing tools, we can greatly reduce component costs and the complexity of work that our customers would ordinarily undertake. High level of quality performing post-moulding operations on products helps 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 standards. Reduction of Customers stock holding Assembly of components will reduce the cost of customers stock holding due to delivery of an assembly rather than a range of components. Reduced production times post moulding operations mean there is very little time between 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 between moulding and assembly operations.CORPORATE TRAINING AND PLANNING

Heat inserting is the addition of inserts into a part increases the functionality of a part by which components can be assembled.

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Benefits of Heat Inserting Increased functionality by adding inserts to mouldings the part can more easily be used for its designed purpose. For example by adding threaded inserts parts can be easily be screwed to their fixings or other parts, increasing their functionality. Low part degradation the process of heat inserting means that the heating/melting of the part is very localised to where the insert will be pressed in. this means that parts do not suffer warping, or any other distortion effects, due to being heated again. High level of quality due to the known challenges with heat inserting extra measures are taken to ensure the processes is repeated to as high a level as possible, meaning part quality is kept very high.CORPORATE TRAINING AND PLANNING

Chrome Plating

Due to the chrome plating process requiring the part to be electrically conductive, a series of steps are required before the chrome can be deposited onto the surface of the product.CORPORATE TRAINING AND PLANNING

Benefits of Chrome Plating Metal finish - Metal finishes can be very popular and, by coating plastics, advantage can be taken of characteristics from both materials. Wear resistant as chrome is a metal rather than a plastic its wear resistance properties are much greater than those of the plastic it covers. This means for applications where a part might be handled repeatedly, such as a shower handset, a chrome finish is likely to wear better than its plastic counterpart. Electrically conductive parts by chrome or nickel plating a part it is possible to give a plastic component the ability to conduct electricity. This gives the advantage of being able to create electrical components that are light weight and less costly to produce than completely metal parts. Attractive mouldings by applying chrome finish to CORPORATE TRAINING AND mouldings a PLANNING

In Mould Insert Moulding

In mould insert moulding is the process by which a metal, or preformed plastic, insert is incorporated in to the component during the moulding stage.CORPORATE TRAINING AND PLANNING

Benefits Of In Mould Insert Moulding Reduced post-moulding operations With in mould insert moulding the need for post moulding operations is greatly reduced. This helps with ease of assembly and reduces the labour necessary for products. Increased part consistency Insert Moulding has major benefits in the consistency of parts produced. As the inserts are placed in the same locations in tools for every cycle each of the mouldings produced will be exactly the same. This helps reduce costs, as rejected parts will be kept to a minimum. Ease of assembly Due to inserts being incorporated into parts during the moulding stage this eases the assembly of the part. Instead of having to place fittings to attach parts fittings can be incorporated during the moulding stage so that parts can be simply clipped together. Reduced production time when vertical moulding machines, that are equipped with a rotary table, are used for production there is the opportunity to have two halves of the lower part of the tool. This means that production is almost constant with mouldings being formed at the same time as fresh inserts are being loaded into the second half of the tool. This lowers overall production times and can also reduce the amount of labour needed.

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Post Mould Inserting

Post mould inserting is the process by which a metal, or preformed plastic, insert is incorporated into a moulding by means of a secondary process once the component has already been moulded.CORPORATE TRAINING AND PLANNING

Benefits of Post Mould Inserting Ease of assembly by adding inserts to a moulding the ease by which it can be assembled is greatly increased. Inserts such as clips or screw bolts can be incorporated into mouldings which greatly assist assembly operations and subsequent product performance. Increased part functionality besides adding inserts to aid assembly inserts that improve a parts functionality can also be used. For example, terminal fittings for wires, or seals to make parts watertight. Increased component value any second operation carried out on a part will add value to it. By adding inserts to help assembly or increase functionality, product value will be raised. This helps to compensate for the extra time involved in second operations and ensure products remain cost effective. Good part consistency to carry out post mould inserting jigs are used to hold mouldings while they are inserted. This means that the repeatability of the operation is very good and all parts inserted will be of the same quality.CORPORATE TRAINING AND PLANNING

DrillingThe 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 mouldings.

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PolishingFor products that have a high quality gloss finish a post moulding polishing operation is often a useful extra process. Even though 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 packaging gives a part the high gloss finish that will have been specified.. Polishing operations are carried out on a softpolishing wheel with high quality wax to ensure that a part is polished to a perfect finish without leaving any marks.CORPORATE TRAINING AND PLANNING

AssemblyFor products that require assembly we are able to carry out this operation in our assembly facility. We can demonstrate examples of assemblies where we mould all the separate components in house and assemble the parts either as a whole in the assembly facility or as a step by step process on the press as each part is produced. By carrying out assembly in house we can reduce costs for our customers while still producing products to a high standard.CORPORATE TRAINING AND PLANNING

Faults & Remedies

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Sink MarksDepression in a moulded part caused by shrinking or collapsing of the resin during cooling.CORPORATE TRAINING AND PLANNING

Sink Marks - Problems Resin feed inadequate Improper mould design. Parts cool too rapidly Rib section in part too wide. Temperature of mould surface opposite rib too hot. Entrapped gas. Nozzle too restrictive, land length too long. Pressure too low. Mould temperature too low or high Stock temperature too high Gate too small Improper gate location Nozzle and metering zone temperatures too high. Excessive cooling time in mould Unbalanced flow pattern. Bad check valve.

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JettingTurbulence in the resin melt flow caused by undersized gate, abrupt change in cavity volume, or too high injection pressure.CORPORATE TRAINING AND PLANNING

Jetting - Problems Excessive injection speed. Melt temperature too high. Melt temperature too low. mould Temperature too low. Nozzle opening too small. Gate and length too long. Sprue, runner, and/or gate size too small. Nozzle heating band malfunction. Inefficient gate location.CORPORATE TRAINING AND PLANNING

Splay Marks (Silver Streaking, Splash Marks)Marks or droplet type imperfections formed on the surface of a finished part.CORPORATE TRAINING AND PLANNING

Splay Marks (Silver Streaking, Splash Marks) - Problems Obstruction in nozzle. Screw rpm too high. Back pressure too low. Melt temperature too high. Nozzle too hot. Nozzle too small. Gates too small. Sprue too small. Insufficient venting. Burr in runner or gate. Cracked mould. Trapped volatiles. Excessive moisture. Resin contaminated. mould cavity contamination. Excessive shot size.

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BlushDiscoloration generally appearing at gates, around inserts, or other obstructions along the flow path. Usually indicates weak points.CORPORATE TRAINING AND PLANNING

Blush - Problems mould temperature too cold Injection fill speed too fast Melt stock temperature too high or too low. Improper gate location Sprue and nozzle diameter too small. Nozzle temperature too low. Insufficient cold slug well. Sharp Corners in gate area Resin excessively moist. Inadequate injection pressure.CORPORATE TRAINING AND PLANNING

Burn MarksBlack marks or scorch marks on surface moulded part; usually on the side of the part opposite the gate or in a deep cavity.

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Burn Marks - Problems Excessive Injection speed Excessive injection pressure. Inefficient mould temperature. Excessive amount of volatiles due to improper Venting. Improper gate location Front zone temperature too high. Screw speed too high. Excessive back pressure. Compression ratio of screw too high. Faulty temperature controllers. Frictional burring--gates too small Dead material hung up on screw or nozzle. Melt stock temperature too high or too low. Nozzle diameter too small Over-heated heater band Incorrect screw rpm.

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Poor Weld Lines (Knit Lines)Inability of two melt fronts to knit together in a homogeneous fashion during the moulding process, resulting in weak areas in the part of varying severity.CORPORATE TRAINING AND PLANNING

Poor Weld Lines - Problems Material too cold. Injection speed too slow Entrapment of air at weld line. Improper mould design. Contamination of poorly dispersed pigments. Core shifting. mould temperature to low. Injection speed too slow. Melt stock temperature to low. Injection pressure too low. Insufficient mould venting Cylinder temperature too low. Injection back pressure too low. Nozzle diameter too small. Excessive screw flights in metering zone. Improper gate locations and/or size. Distance from gate excessive. Ineffective flow pattern. mould release agent (brittle weld lines). Inadequate flow.

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Voids (Bubbles)An unfilled space of such size that it scatters radiant energy such as light.

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Voids - Problems Injection pressure too low Packing time too short Insufficient feed of material mould temperature too low. Injection speed too high Excessive cushion At the side of a rib; rib too thick. Runners or gate too small or badly positioned.CORPORATE TRAINING AND PLANNING

Delamination (Skinning)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.CORPORATE TRAINING AND PLANNING

Delamination - Problems Contamination of resin by additives or other foreign materials. Resin temperature too low. Non-uniformity of resin temperature. Wrong mould temperature. Excessive material moisture. Inadequate injection speed. Sharp corners at gate. Incompatible polymers.CORPORATE TRAINING AND PLANNING

Flow Lines and FoldsMark visible on the finished item that indicate the direction of flow in the cavity.

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Flow Lines and Folds - Problems Stock temperature too low. Runners too small Improper gate size and/or location. mould temperature too low. Inadequate cold slug well.

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Excessive Warpage/ ShrinkageExcessive dimensional change in a part after processing, or the excessive decrease in dimension in a part through cooling.CORPORATE TRAINING AND PLANNING

Warpage / Shrinkage -Problems mould closed time too short. Inefficient injection forward time. Ram speed too high or too low. Injection and holding pressure too high or low. Melt temperature inadequate. Excessive nozzle and metering zone temperatures. mould temperature too high (for thick wall sections). Parts cool unevenly. Parts underpacked. Improper gate location. Gate too restrictive Unequal temperature between mould halves. Non-uniform part ejection. Parts mishandled after ejection. Unbalanced gates on multiple gated part. Too many stresses in part.

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Black SpecksParticles in the surface of an opaque part and visible throughout a transparent part.

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Black Specks - Problems Contamination of material. Holdup of molten resin moulding machine or mould runner system. Press Contamination. Local over-heating in the injection cylinder. Defective closure of the nozzle. Oxidation by occluded air or inadequate air venting mould contains grease. Trapped air Inefficient injection speed.CORPORATE TRAINING AND PLANNING

BrittlenessTendency of a moulded part to break, crack, shatter, etc. under conditions which it would not normally do so.CORPORATE TRAINING AND PLANNING

Brittleness - Problems mould temperature too high Inadequate cooling in gate area Gate section of item too thin (gate brittleness) Resin too cold. Non-uniformity of resin temperature. Undried material. Contamination. Poor part design. Material degraded. Non-compatible mould release. Packing the mould. Melt temperature too cold. Excessive amounts of regrind.CORPORATE TRAINING AND PLANNING

Brittleness - Problems Inadequate mould temperature Excessive screw rpm Excessive back pressure Insufficient venting. Improper gate location. Excessive injection speed. Excessive residence timed Melt temperature too high. Nozzle too hot. Injection pressure too low (weld lines). Runners and gates in adequate (weld lines). Dwell time in the injection cylinder too long (material degraded). Material degraded during drying or pre-heatingCORPORATE TRAINING AND PLANNING

FlashExcess plastic around the area of the mould parting line on a moulded part.CORPORATE TRAINING AND PLANNING

Flash - Problems mould parting surfaces do not seal properly. Injection pressure too high. Clamp pressure set too low or projected area or item too large for clamp pressure of the machine. Injection temperature too high. Feed needs adjustment. Hold time too long. Inadequate mould supports. Oversize vents.CORPORATE TRAINING AND PLANNING

BlisterDefect on the surface of a moulded part caused by gases trapped within the part during curing.CORPORATE TRAINING AND PLANNING

Blister - Problems Screw rpm too high Back pressure too low mould temperature too low. Gate improperly located Insufficient venting. Regrind too coarse

CORPORATE TRAINING AND PLANNING

CrazingFine cracks in part surface. May extend in a network over the surface or through the part.CORPORATE TRAINING AND PLANNING

Crazing - Problems Insufficient drying of the material. Contamination. Injection temperature too high (crazing accompanied by dis-coloring or yellowing). mould surface contaminated Inadequate injection speed. Inefficient injection forward time. Excessive injection pressure. mould temperature too low. Gate too large.CORPORATE TRAINING AND PLANNING

CrackingFracture of the plastic material in an area around a boss, projection, or moulded insert.CORPORATE TRAINING AND PLANNING

Cracking - Problems Parts cool too quickly moulded-in stress Wall thickness too heavy for compound.

CORPORATE TRAINING AND PLANNING

Low GlossSurface roughness resulting from high speed fill which causes surface wrinkling as the polymer melt flows along the wall of the mould.CORPORATE TRAINING AND PLANNING

Low Gloss - Problems Inadequate polish of mould surface. Material or mould too cold. Air entrapment. Melt index of material too low. Improper mould design. Wrong injection pressure. Excessive injection speed.CORPORATE TRAINING AND PLANNING

Low Gloss - Problems Inadequate flow. Contamination Resin excessively moist Sprue, runners, and/or gate size too small. Pigment agglomerates. Oil or grease on knockout pins.CORPORATE TRAINING AND PLANNING

Short ShotInjection of insufficient material to fill the mould.CORPORATE TRAINING AND PLANNING

Short Shot - Problems Insufficient feed, cushion. Inadequate injection pressure. Inadequate injection speed. Insufficient booster or injection highpressure time. Inefficient screw delay. Inadequate injection back pressure. Melt temperature too low. Cylinder temperature inadequate. mould temperature too low.CORPORATE TRAINING AND PLANNING

Short Shot - Problems Gates, sprues, and/or runners too small. Excessive screw flights in metering zone. Insufficient venting. Improper gate location. Melt index of resin too low. Excessive clearance between non-return valve and barrel. Screw bridging. Injection press of insufficient capacity.CORPORATE TRAINING AND PLANNING

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CORPORATE TRAINING AND PLANNING