MOULD MAINTENANCE

By

A. KUMARCentral Institute Of Plastics Engineering &

Technology (CIPET) CHENNAI

Injection moulds play a vital role in production of qualified quality components. Consistency in the quality of component would also depend on the quality of mould. Unreliable mould would need frequent adjustment, repairs etc. it is therefore necessary that mould should be reliable in its function and moulding of qualified components.

INTRODUCTIINTRODUCTIONON

UPKEEP AND UPKEEP AND MAINTENANCEMAINTENANCE

PURPOSE

SCOPE

RESPONSIBILITY

FACTORS – MOLD LIFE

DEFINITION

To provide a systematic approach to the maintenance requirements of molds.

Purpose Purpose ::

In order to maintain quality parts, they must be produced in quality molds. The best quality parts are produced from precision molds. Molds, quite like cars, begin to wear with use and maintaining a tool is an investment in precision.

Scope :Scope :

Proper tool maintenance is a matter of attention to detail. As things begin to wear, they must be noted and attended to. This is a simple matter of keeping a molding log for maintenance as little things come up and performing periodic maintenance as the tool is run in production.

The maintenance procedure is a guideline provided to

the customers for the proper maintenance of molds. It is the

customer's responsibility to determine a maintenance

schedule and follow it.

Responsibility :Responsibility :

It is one of the prime objectives of any moulder that the moulds in use should function well to the maximum possible production quantities. A mould nicely designed and made may not remain necessarily nice, unless kept and maintained in a nice manner. Therefore, upkeep and maintenance of moulds are important practical aspects of a moulding shop.

UPKEEP UPKEEP ANDAND MAINTENANCEMAINTENANCE

Defining ‘Upkeep’

Upkeep and maintenance of Upkeep and maintenance of moulds consist of the following moulds consist of the following

aspects:aspects:

Defining ‘Maintenance’

Specification sheets for all moulds

History sheets

Instruction manual on upkeep and maintenance.

The up-keep of a mould means that the mould should be kept well cleaned.

An antirust spray may be used to prevent the rusting of the mould parts.

The moulds should be stored preferably at a place where the humidity is low

and the ambient temperature is not excessive. Sometimes, moulding shops

are situated in the vicinity of other factories or shops having chemical

processing or labs. It is practically found that even small traces of chemical

fumes do come in contact with mould surfaces. Hence a fine layer of ‘rust’

appears on the cores, cavities and other parts of the mould. This happens if

the core and the cavities are not chromium plated.

‘Rusting’ can be very much minimised if the moulds are kept covered by PVC

sheet covers.

DEFINING UP KEEPDEFINING UP KEEP

In General terms, maintenance means to keep the moulds

and bring them to production in a worthy condition, some

essential aspects of mould maintenance are covered here. Preventive maintenance of the moulds would cover examining

the mould for small damages Increase in the clearance of the moving parts, the adjusting of the

locking wedges The cleaning of the water channels Sometimes, any guide pin or cam pin may found shaky in its

holding hole. In that event, as a maintenance action, either a new

pin may be put or the existing one may be copper plated at the

holding surface.

DEFINING DEFINING MAINTENANCEMAINTENANCE

SPECIFICATIONSPECIFICATION SHEETSSHEETS

This also helps to the persons, who are not familiar with the moulds and might have an occasions to handle maintenance and upkeep of moulds.

Specification may vary from mould to mould. It gives complete information about the mould, which can be stored in a computer.

Each sheet may be stored in a computer, allotting a suitable file number.

HISTORY SHEETSHISTORY SHEETS

It also reveal the management a lot of information about the performance and capabilities of the shop flow personnel.

This Pinpoints the defects, which are occasional

/Which are repetitive /which are chronic in nature.

This help to take appropriate steps to find the solutions to the defects and take corrective measures.

INSTRUCTIONINSTRUCTION MANUALMANUAL

Upkeep and maintenance actions are almost

similar for all the moulds. But some special

precautions may be needed for some moulds. It is

therefore a good practice to thoughtfully prepare a

manual on MOULDS UPKEEP AND

MAINTENANCE. Technical personnel involved in

upkeep and maintenance can follow it.

What affects Physical Mould What affects Physical Mould Life?Life?

Inadequate physical strength of mould parts to withstand the loads encountered and caused by clamping force injection pressure, ejection forces etc.,Improper mould makes selection.Improper allowance for fatique in mould studies in a frequent cause for breakage,Improper heat treat specifications.Lack of lubrication of sliding faces.Incorrect machine setup.Poor maintenance practices and rough handling of the mould, especially if the moulder does not adhere to the suggested start up and maintenance procedure.The use of dirty and contaminated plastics.Abrasive, erosion or corrosive fillers such as glass and some other additives.Corrosive plastics, which may attack (corrode) poorly suited mould materials.High humidity.Dirty and corrosive cooling water.

In general, for physical mould life for most products is practically unlimited, provided the mould is properly designed and engineered and not damaged by neglect, poor operation and maintenance or by accidents.

Maintenance FrequencyMaintenance Frequency Level 1: Every time the mold is pulled from production or put

back into production, Routine Maintenance.

Level 2: 20,000 cycles or nine production shifts for Inspection

Maintenance.

Level 3: 100,000 cycles or every 10 production runs for General

Maintenance.

Level 4: 250,000 cycles or half the anticipated life time volume,

whichever comes first for Major Maintenance.

Break Down MaintenanceBreak Down Maintenance

Break down maintenance done unexpectedly when an

accident occurs to the mould is in production.

The problem may be, water leak, core or cavity damage,

cooling line blocked, ejection system failure and heater failure

in case of hot runner, etc.

We have to study the problems along with production

Engineers and to bag a last shot from the production.

The maintenance of the mould is done with reference to the

decision taken in the out come of the meeting.

Suggested tools available for proper Suggested tools available for proper tool maintenance:tool maintenance:

Assembly table: 3' x 3' x 6' (90cm x 90cm x 180cm) should be able to handle a

minimum of 1 ton or 1000kg.

Good lighting: A high density portable lamp with a magnetic base is desirable.

(2) Heat-treated rails: 36" x 1" x 1" (90cm x 2.5 cm x 2.5 cm) for molds to slide

on.

(3) Hammers: Heavy-duty plastic head, light duty plastic head, light weight

(13 oz) machinists hammer (Ball Peen).

Hex wrenches and spanners to remove water line connections.

(1) Ruby polishing stone (fine): To remove burrs or scratches on mold inserts.

(1) Medium bench stone: To remove burrs or scratches on mold plates.

Polishing Kit and Die grinder

Cleaning solvent.

MAINTENANCE LISTMAINTENANCE LIST Surface and air vents.

No Plastic particles, oils and Impurities. Slides,guides pins, ejector pins and slanting ejector pins.

No severe wear and tear,Sufficient Lubricant.

Finger pinsNo bending and tearing.

Cooling connections.Proper connection, no blockage and leakage.

SpringsNo breakage or distortion.

Safety devices.Micro switch properly connected etc.

Mould protectionCorrect settings.

Fasteners (Bolts, Nuts, etc.)All Securely tighten.

NOTE: All findings must be recorded in the mould history card.

Preventive Maintenance:Preventive Maintenance:

The role of Designer:The role of Designer:Initial study on part drawing – Identify the areas of concerns- to be discussed with customer to avoid on going mould and moulding problems.

Part design which include sharp corners, in adequate draft, limited areas of ejection etc., which call fragile steel section in the mould should be discussed to determine and modifications can be made in the part design. Such changes will have positive results in reducing future mould maintenance cost

Mould designer should incorporate into the mould design provision for mould maintenance. Critical areas should be inserted for ease of repair. Materials, should be used which are resistant to galling when slides are required and wear strips and locks should be accessible and adjustable.

Steel should be selected for strength and hardness properties that will ensure reliable performance.

Mould bases for high production moulds should be fabricated from steel that will not collapse and more under stresses induced by the moulding operation.

THE ROLE OF THE MOULD BUILDER:THE ROLE OF THE MOULD BUILDER:

To follow the mould design changes in construction should be

with concurrence of the mould designer if a mistake in design

has been made, the mould builders should inform the designers

so that the correction can be made & recorded.

Identifying steel for parts is important

Stress relieve steel when appropriate.

Heat treatment of steels should be documented to insure that

proper hardness have been achieved.

Complexity: Molds with intricate mechanisms or parts requiring unreasonably high precision will require more maintenance than a simple two plate tool making a low precision parts. Slides, lifters, internal cores, hydraulic and mechanical systems, hot runners, complex ejector systems or mechanisms with small, therefore weak, components all add to the maintenance schedule.

Procedure:Procedure:The degree and frequency of maintenance are determined by

four factors.

Material: Aluminium or soft tools will suffer wear and tear in a shorter period of time than tools made of conventional tool steel. Molds made of hardened steel will last longer than those made of conventional mold steel.

Molding material: Materials with high melt temperatures wear out molds quicker than those with low temperatures. Higher melt temperatures will expose the metals to more heat and enhance material wear. Filled materials are abrasive because the fillers are not liquid. Fiberglass, mineral fillers (Usually Mica), etc. are very abrasive to metal, they will tend to wash the mold steel away after thousands of cycles. Abuse: Excessive clamp pressures, high injection pressures, jerking the mold open and closed, not lubricating the appropriate components, multiple ejection, crashing the mold closed or closing up on partially ejected parts are a sure road to increased maintenance.Abuse can also be defined at the work place. A shop that is dirty, open to the outside dust and dirt, machines with grease and absorbent on the floor, all create an atmosphere that will cause the molds to wear out quicker. Areas exposed to acid vapours, such as a molding area located near a plating operation will corrode the steel. Areas of high uncontrolled humidity or salt water will also enhance corrosion. Dry areas with constant wind and dust will cause premature wear on the mold.

Using untreated coolant in the tool can cause a scale build up in the water lines. Build up can be noticed by an increase in the differential of temperatures and pressures from the inlet and outlet of the cooling circuit. This scaling dramatically decreases the heat transfer ability of the tool and therefore affects the process capability and dimensional stability of the parts. While the tool steel may seem in perfect working order, clogged or restricted cooling circuits can seriously affect part quality. Solutions to environmental abuse:

Have a clean operation using well maintained tools and equipment.

Use soft or treated water in cooling systems.

Blow out or drain the tool when it is pulled from the machine.

Seal the work area and mold storage area from outside Environment.

Have outside, filtered, positively pressurized air circulated in.

Abuse can be Abuse can be incipient:incipient:

MOULD REMOVING, CLEANING AND MOULD REMOVING, CLEANING AND STORAGE:STORAGE:

Heat the mould to room temperature before removal to evaporate any surface condensation.

Using a mild, clean shop safety solvent and soft, clean towels, gently clean internal mould surfaces to remove residual dirt and grime.

More the ejector system fully forward and spray both mould halves with a shop-approved, protective rust preventive before retracting the ejector and closing the mould.

Drain and blow free all residual water to avoid rust buildup. No water should be trapped inside the mould and it is critical.

Make sure all bolts plates and clamps are properly placed and the safety straps are secured and tightened.

Remove mould, check and clean it again, if required.

Bag the last two or four shots to store with the mould (including parts, sprue and runner) as examples of the expected run quality.

Store the moulds on storage racks-notably out of shop floor.

Don’t let water lines stick out when storing moulds on racks.

Wrap the mould with plastics. Ensure that air is dry when wrapping, or put a desicant air absorption bag inside so that temperature changes don’t cause condensation inside the wrapping that could form rusting.

QUALITY PLAN FOR MOULDS

QUALITY PLAN -MOLDS

INSPECTION AND PROGRESS

Inspection and progressing a mould and

its design at every stage is more important than

its first test. The following check list should be

completed before the first test.

ORDER STAGE:

•Is the product design released for tooling? YES/NO•Will the mould fit the machine / machines in your shop? YES/NO•Is the projected area of the mould surface / cavities within machine

capacity? YES/NO•Is the shot weight of the mould within the machine capacity?

YES/NO•Has the shrinkage factor been agreed? YES/NO•Are the cooling / heating channels calculated and agreed?YES/NO•Is cavity numbering and position specified on the drawing?YES/NO•Are lifting arrangements specified on drawing? YES/NO•If a runner less mould, has the control system been agreed? YES/NO•Check for venting. YES/NO•Extras, e.g. core pulling, check machine for facilities. YES/NO

The Mould Drawings are now ready for release: ORDER RECEIVED ON :

PRODUCT DRAWING RELEASED ON :

MOULD DRAWING RELEASED ON : 

Released by:

Name: Signature:Name: Signature

POINTS THAT LEAD TO DISPUTES LATER ON 

•TOLERANCES

• MATERIAL SHRINKAGE FACTOR

• RADIUS

• MACHINE FITTING

• DRAFT ANGLES

• POLISHING STANDARDS 

CHECK AND AGREE THESE between Moulder / Toolmaker / Material

Manufacturer/Industrial Designer/Customer, etc.

FIRST-OFF MOULD INSPECTION 

CARRIED OUT BY: MOULDER/YPEC NAME 

IT WILL SAVE TIME AND TIME MEANS MONEY

CHECK LIST (Standard for Conventional Moulds)

• Sprue bushing size / radius suite machine?YES/NO

• Ejector bar length suits machine /mould?YES/NO(Also check type of ejection, i.e. centre or edge)

3. Size of mould fits machine available for test?YES/NO

4. Lifting eye-bolt installed is an approved make and a good fit in tool? YES/NO5. If unorthodox loading of mould to machine, is it clearly stamped on tool?

YES/NO6. Are air, oil, grease, hydraulics inlets clearly marked?

YES/NO 7. Cavities are polished to agreed standard?

YES/NO 8. Cores are polished to agreed standard? YES/NO9. Cavities and cores are hardened? If NO, has this been agreed between YES/NO

moulder/mould maker? 10. Check if die plates are hardened or soft YES/NO11. Cooling channels been bench tested for leaks? YES/NO12. Has the mould been vented? YES/NO13. If multi-cavity mould, are the cavities numbered and correctly sequenced?

YES/NO14. Are water fittings available for mould? YES/NO15. Does ejection move freely? YES/NO

CHECK LIST EXTRAS FOR RUNNERLESS MOULDS

•Are multi-pin sockets and plunge fitted? YES/NO

•Are plugs, sockets, and writing efficiently masked? YES/NO

•Is the continuity of each heater positive? YES/NO

•Is the continuity rating suitable for heater load? YES/NO

•Check whether open or closed loop, or both on controllers to be used.

YES/NO

•Does the controller have heater drying facility? YES/NO

•Are all the gate orifices clear of all obstructions? YES/NO

(Check with airline from sprue bush end to gate.)

CHECK LIST FOR HYDRAULICALLY-OPERATED MOULD(SIDE CORES) 

•Are hydraulic fittings available? YES/NO

•Is the hydraulic cylinder fitted securely? YES/NO

•Is the sequence of the hydraulic cores known? YES/N

•Are the circuits identified on the mould? YES/N

•Check machine for hydraulic facilities.

If there is one ‘NO’ or a doubtful ‘YES’, check the point with

toolmaker before authorising tool to go on machine for a test.

CHECK LIST FOR PRESSURE TRANSDUCERS 

•Check for continuity.•Make sure wiring is properly masked.•Make sure plug and socket is robust enough. 

CHECK LIST FOR CARTRIDGE HEATERS 

•Before putting into tool, check heater for resistance and continuity.

•If showing a virtual short, put in drying oven for an hour and check again.

•Heater must shoe 0.5 meg ohms or above before putting into tool.

•10meg ohms are a dry heater; anything below needs a 2hour drying time

minimum. very wet, an overnight soaking.

•Heater drying out voltages should be 10% of total heater wattage.

•Heaters should be brought up to temperature slowly to avoid overloading.

•IF HEATER FOTS LOOSELY, DO NOT SWITCH ON.

The moulding shop supervisor is responsible for following and updating the contents.

The first priority on completion of a mould and its receipt by

the moulding shop,

1.The mould is fitted to the machine securely.

2.There are no oil /water leaks under pressure.

3.The mould opens and closes without any resistance.

4.The mould safety sensing device is on.

5.For a runner less (hot-runner) mould, all wires and

thermocouples are secured away from the die faces.

6.All controllers are connected to correct heating circuits and

are identified.

7.Estimate shot weight of component and set machine

marginally under rather over for the first shape.

THE MOULD TEST

 This is a critical stage of the mould, and any undue haste could well

damage months of planning and craftsmanship. Testing or proving

recommended procedure to be followed:

• Set the mould on the machine. Check:

ALIGNMENT – MOULD SAFETY – WATERWAYS

Open and close at low pressure and slow speed to check:

CORRECT FUNCTIONING OF ALL MECHANICAL MOVEMENTS.

2. Dry cycle mould for 10 to 20 shots, first on slow speed, then fast.

3. Dry cycle mould for 25 shots with mould temperature at +70oC.

These cycles will establish any areas where fittings were are too tight

and seizure is likely.

4. Purge machine barrel and fill with test material. Ensure polymer is in

correct state for moulding.

  

5.      Inject material on slow cycles for 10 shots or so. The wrong

speed can break core pins or cavity parts.

6. Eject components on low setting initially.

7. If mould is filling and ejecting satisfactory, start semi –

automatic cycle, moving on to automatic if the mould is designed to

run automatically.

DO NOT RUSH.

8. Reject the first 30 to 50 shots.

9. a) Produce 20 to 100 shots after establishing cycle conditions.

Keep samples in strict sequence order.

b) Record your conditions on test data sheet

     10. Alter only one setting at a time and wait for the alteration to take

effect.

DO NOT ALTER every two or three shots

POST TEST ACTION

1.      Seal in polythene bag and mark four sets of samples selected at random from the test run. Distribute samples as follows:One set to Inspection Department.One set to Product DesignerOne set to ToolmakerOne set to Records for future reference.Always date your samples and identify them with time data sheet number.

2.     2. First-off detail inspection should be carried out at least 24 hours after moulding.3. DO NOT use wooden jigs to reduce distortion without consulting or advising customer/toolmaker/end-user etc. Mouldings will revert back to the original shape if they reach or approach their softening point in service.4. LOOK for any scoring or scars on sample due to light ejections as in a new mould some of the moving parts may be tight.5. DO NOT rush your assessment of part quality.6. DO NOT asks for the tooling changes on the same day the mould was tested. Consider the change, evaluate costs, but wait a day or two before authorising tool change.TRY components functionally in use to see if they will fit and perform in actual use. Consult the product designer, there is usually a good reason for tight or close tolerances but sometimes a ‘tight or close’ tolerance is put in for safety, as behaviour of the polymer may not be known fully.

7.    7.The moulder and the mould maker should be consulted on all changes to the mould. RECORD ALL CHANGES IN THIS MANUAL THE SAME DAY

MOULD STORAGE RECORD 

All moulds should be inspected on the machine before storage.

Moulds should be stored on racks or blocks of wood at least 6’’ (150mm) off

ground level in a dry store.

Spray mould with “MOULD PROTECTOR” or grease/oil before storage. The last

shot off the mould should be stored with the mould.

DATE STORED

CONDITION ON RECEIPT FOR STORAGE

ACTION REQUIRED

ACTION COMPLETED

DATE RELEASD