Mould Maintenance Presented By S.K Mandal

Factors to be considered Mould Check List. “Break-in” a NEW Mould. The Role of Mould Designer – Preventive Maintenance The Role of Mould Maker – Preventive Maintenance Causes of Wear & Damage to the mould. Program of Preventive Maintenance. Maintenance Records. Mould Surface Treatments. Mould Polishing. Mould Inspection & Maintenance Record.

Mould Check List Is the mould parting line chosen the most efficient for mould operation & tool construction ? Have the core & cavity been designed in the easiest manner for machining in the available equipments ? Will any slender blades or pins deform under cavity pressure / flow ? Is the cavity of adequate strength to resist internal cavity pressure ? Can all parts of the mould be dismantled or separated in the event of tool break-down or modifications ? Are all necessary parts hardened ? Have all the allowances for moulding shrinkage been provided ? Has sufficient mould taper / draft been allowed on relevant parts ?

Mould Check List Will the moulding remain on ejection side when the platen opens ? Has the ejector return mechanism been provided ? Have adequate guide pillars been provided between mould halves ? Are all inserts been located positively & prevented from displacing during tool closing or under cavity pressure ? Has adequate cooling channels been provided ? Are the runners of sufficient size ? Has a sprue - puller hook & cold slug well been provided ? Is the mould sufficiently vented ? Do the spherical nose & orifice of the nozzle mate with the spherical seating & bore of the sprue bush ?

“Break – in” a NEW Mould Obtain Sample & moulding Cycle information. Clean the mould. Visually inspect the mould. Check-out the actions of the mould on the bench ( cams, slides etc ). Install safety devices. Load the mould on the machine. Move ( open / close ) slowly under low pressure. Dry cycle the mould & inspect. At mould operating temperature Dry cycle again. Take a shot using maximum mould lubrication, low material feed & low pressure. Build up slowly to operating temperature. Record operating information. Check the part quality. Make required changes.

Causes of Wear & Damage to the mould Negligence. Abrasive Wear due to glass-filled plastics ( sprues, runners, gates, cavity & core parts – directly opposite to the gates ). Continue to run the mould after flashing occurs. Closing the mould on plastic material, like bits of flash, granules of raw material, foreign objects ( nuts, bolts, pins etc ). Using screw drivers, rods, knives etc to remove sticking mouldings, Corrosion due to leaking water from leaking water lines, leaking O – rings. Chemical corrosion due to over-heating plastics & gases evolution. Continue to run the mould on a mal-functioning machine. Improper assembly of the mould ( loose screws, metal chips, grinding / polishing dust, mould not cleaned & inspected ). Fatigue due to stresses during moulding cycles over long period of time. Thermal shocks due to rapid heating / cooling.

Role of a Mould Designer Sharp Corners, Inadequate Drafts, Limited Ejection results in fragile steel sections in the mould. Provisions for mould maintenance like :- Proper selection of Tool – Steel. provide Inserts in critical areas for ease of repair. Providing wear strips for slides. Largest possible diameter of ejector pins. Ignoring these points will add to the future mould maintenance costs.

The Role of Mould Maker Should follow the mould design. Modifications should be discussed. Steel identification of the components. Heat treatment should be documented. Again , ignoring these points will add to the future mould maintenance costs.

Preventive Maintenance for Moulds 1). Mould Plating :- New mould should be plated immediately after sample and mould operation are approved. Never run production before plating. Periodic checking of plating ( corners and high flow areas ). 2). Replacement parts :- Using replaceable inserts / parts, requires advance planning. 3). Control of Flash :- Cleaning is essential – parting lines, ejectors, slides. Check loose fastenings. Check machine platens. 4). Hand Tool Damages :- Use only soft brass / copper rods. contd…

Preventive Maintenance for Moulds 5). Water hazards :- Chrome plating the mould. Water condensation. Cleaning water lines – first disconnect the supply & then use air nozzle to blow the remaining water out. Nickel plating all water lines. 6). Acids :- Using corrosive plastics. Products of de-composition. Plating as per attacking medium. Proper Mould temperature control. Prevention of excess heating in barrel. Venting of runner system.

Preventive Maintenance for Moulds 7). Accidents :- Loose mould fastenings. Loose slides / split cavities. Low draft angles in multi-cavity mould. Moulding sticking plastics. Moulding in fast cycles.

Program of Preventive Maintenance Scheduling each mould out of production regularly into tool-room. Last shot moulded should be attached. Complete cleaning of the mould. Careful inspection of the mould. Lubrication of the moving parts. Spray anti-oxidants / rust preventives. Returned to storage / production.

Mould Maintenance Records Maintenance requirements notes during operation. Last and previous maintenance notes. Problems encountered during mould operation. Cycles to date. Parts produced till date. Cycles since last maintenance. Next scheduled maintenance. Areas to be checked – complete tear down / periodic inspection.