UPKEEP AND MAINTENANCE : 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.
What is the difference between upkeep and maintenance?
Maintenance works better for structural or mechanical things, such as buildings and automobiles, upkeep works better for things that grow, such as hair and landscaping projects, and. sustainance is more fitting for nourishment, or for something abstract, such as government.
Upkeep and maintenance of moulds consist of the following aspects:
1. Defining Upkeep
2. Defining Maintenance
3. Specification sheets for all moulds
4. History sheets
5. Instruction manual on upkeep and maintenance.
DEFINING UP KEEP: 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 MAINTENANCE:
1. 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.
2. Preventive maintenance of the moulds would cover examining the mould for small damages
3. Increase in the clearance of the moving parts, the adjusting of the locking wedges
4. The cleaning of the water channels
5. 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.
SPECIFICATION SHEETS:
1. Specification may vary from mould to mould. It gives complete information about the mould, which can be stored in a computer.
2. Each sheet may be stored in a computer, allotting a suitable file number.
3. 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.
HISTORY SHEETS:
1. This Pinpoints the defects, which are occasional/Which are repetitive /which are chronic in nature.
2. This help to take appropriate steps to find the solutions to the defects and take corrective measures.
3. It also reveal the management a lot of information about the performance and capabilities of the shop flow personnel.
INSTRUCTION MANUAL:
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.
Maintenance 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 Maintenance
1. Break down maintenance done unexpectedly when an accident occurs to the mould is in production.
2. 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.
3. We have to study the problems along with production Engineers and to bag a last shot from the production.
4. 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 tool maintenance:
1. Assembly table: 3' x 3' x 6' (90cm x 90cm x 180cm) should be able to handle a minimum of 1 ton or 1000kg.
2. Good lighting: A high density portable lamp with a magnetic base is desirable.
3. Heat-treated rails: 36" x 1" x 1" (90cm x 2.5 cm x 2.5 cm) for molds to slide on.
4. Hammers: Heavy-duty plastic head, light duty plastic head, light weight (13 oz) machinists hammer (Ball Peen).
5. Hex wrenches and spanners to remove water line connections.
6. Ruby polishing stone (fine): To remove burrs or scratches on mold inserts.
7. Medium bench stone: To remove burrs or scratches on mold plates.
8..Polishing Kit and Die grinder
9. Cleaning solvent.
MAINTENANCE LIST:
1. Surface and air vents.
2. Slides,guides pins, ejector pins and slanting ejector pins. No severe wear and tear,
3. Sufficient Lubricant. Finger pins
4. Cooling connections.
5. Springs
6. Safety devices
7. Mould protection Correct settings.
8. Fasteners (Bolts, Nuts, etc.) All Securely tighten.
NOTE: All findings must be recorded in the mould history card.
Preventive Maintenance:
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:
1. 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.
2. Identifying steel for parts is important Stress relieve steel when appropriate.
3. Heat treatment of steels should be documented to insure that proper hardness have been achieved.
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.
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.
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.
Abuse can be incipient: 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:
1. Have a clean operation using well maintained tools and equipment. Use soft or treated water in cooling systems.
2. Blow out or drain the tool when it is pulled from the machine.
3. Seal the work area and mold storage area from outside Environment. Have outside, filtered, positively pressurized air circulated in.
QUALITY PLAN FOR MOULDS:
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:
1. Is the product design released for tooling? YES/NO
2. Will the mould fit the machine / machines in your shop? YES/NO
3. Is the projected area of the mould surface / cavities within machine capacity? YES/NO
4. Is the shot weight of the mould within the machine capacity? YES/NO
5. Has the shrinkage factor been agreed? YES/NO
6. Are the cooling / heating channels calculated and agreed?YES/NO
7. Is cavity numbering and position specified on the drawing?YES/NO
8. Are lifting arrangements specified on drawing? YES/NO
9. If a runner less mould, has the control system been agreed? YES/NO
10. Check for venting. YES/NO
11. 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
1. TOLERANCES
2. MATERIAL SHRINKAGE FACTOR
3. RADIUS
4. MACHINE FITTING
5. DRAFT ANGLES
6. POLISHING STANDARDS
CHECK LIST EXTRAS FOR RUNNERLESS MOULDS
1. Are multi-pin sockets and plunge fitted? YES/NO
2. Are plugs, sockets, and writing efficiently masked? YES/NO
3. Is the continuity of each heater positive? YES/NO
4. Is the continuity rating suitable for heater load? YES/NO
5. Check whether open or closed loop, or both on controllers to be used. YES/NO
6. Does the controller have heater drying facility? YES/NO
7. 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)
1. Are hydraulic fittings available? YES/NO
2. Is the hydraulic cylinder fitted securely? YES/NO
3. Is the sequence of the hydraulic cores known? YES/NO
4. Are the circuits identified on the mould? YES/NO
5. Check machine for hydraulic facilities. YES/NO
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
1. Check for continuity.
2. Make sure wiring is properly masked.
3. Make sure plug and socket is robust enough.
CHECK LIST FOR CARTRIDGE HEATERS
1. Before putting into tool, check heater for resistance and continuity.
2. If showing a virtual short, put in drying oven for an hour and check again.
3. Heater must shoe 0.5 meg ohms or above before putting into tool.
4. 10meg ohms are a dry heater; anything below needs a 2hour drying time minimum. very wet, an overnight soaking.
5. Heater drying out voltages should be 10% of total heater wattage.
6. 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:
1. C orrect 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 +70℃. 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.
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