How to achieve quicker mould changes
Minimising unproductive mould changing time is a key task for all operators of injection moulding machines. The total time taken to change moulds is determined by the sequence of the specific steps involved. Each changeover will require the disconnection and reconnection of the mould’s cooling water and other services such as hydraulics and electrics, the mechanical handling of the moulds onto and off the injection moulding machine and the heating of the mould to operating temperature. A detailed review of each of these stages is required to ensure that mould changeover times are reduced to a minimum.
Quick Release Connectors
One of the first improvements to be considered should be the method used to make connections to the mould for cooling water, hydraulics, nitrogen, electronics etc. From simple and cost effective, full flow quick disconnect couplings for water cooling applications to completely valved quick connection solutions for oil heating or temperature control circuits, the appropriate quick release coupling can be selected for any application.
Identification of sockets and plugs by coloured rings also helps, as on Stäubli’s RPL range for water and temperature control circuits; this makes circuit identification quicker and easier. The rings can also serve to number the circuits (on the socket side) and a strengthened locking system ensures the security of the circuits. The locked position is instantly visible by the coloured ring on the socket. The non-spill design of the Stäubli CBI range typically used on temperature control circuits, guarantees perfect sealing during connection and disconnection of circuits; no air is introduced into the circuits and there is no pollution to the work environment through leakage.
The use of quick release connectors in place of fixed connections for these applications often brings the single most significant reduction in mould change times.
Multi –Couplings
Further reduction in changeover times can be achieved by a move to a multiple connection plate system. Placing all the quick release couplings together on a pair of plates enables all connections to be made safely and securely in one swift, lever controlled, robust locking operation, with the additional bonus that the chance of any wrong connection is eliminated. Connection of the plate is only possible in the correct position and a foolproof keying system prevents any cross connection where several plates are being used on the same mould.
Multi-coupling plates can be designed to match the specific requirements of each application, taking into account the type of fluids used in each circuit as well as the pressure, temperature and flow rate required; couplings can be either single or double shut-off or unvalved. Electrical connections can also be included on the plates to correspond to the voltage and amperage required.
A fully automatic multi coupling system should also be considered at this stage. This can bring additional savings in downtime and reduces the operators’ machine servicing requirements, frequently allowing a larger batch of moulding machines to be monitored, reducing manning levels.
An example of the benefits to be achieved through the use of mutli-coupling plates is at Triumph Motorcycles in Hinckley where mould change times in the injection moulding shop were reduced by 30%.
A target time of 20 minutes for the tool change was set, which with tools weighing up to 8 tonnes, a rapid automatic multi-coupling system was needed. Stäubli RMI 212 couplings were selected for the water system, which was operating at high pressure (6 bar) and RMP 48 couplings for the hydraulics. Both connectors were placed on a multi-coupling plate and connection to the mould made via special brackets located on the tool side.
Tool change times at Triumph reduced to 22 minutes on the 420 Tonne IMM and 26 minutes on the 1300 Tonne machine. The multi-coupling removed any danger of wrong connection and shaved at least 10 minutes off the tool change time. Times are expected to reduce further as the operators become practised in using the system.
Transfer Tables
The mechanical handling of moulds onto and away from the injection moulding machine can be a slow process. Datum lines on the tool holders and crane positions can save time in positioning the mould. Balance weights on the lifting straps, to avoid tilting, is also a useful idea that can save time manoeuvring the mould into place on the machine. With side loaded moulds a dedicated loading and/or insertion table may be required to ease handling of the mould. This may be a simple scissor lift roller table or a tailor made handling system fully integrated in to the control systems of the moulding machine.
Moulds need to be heated to operating temperature before moulding can take place. The installation of a specially designed pre-heat station can ensure that the next mould is brought up to temperature and ready for production just when required. This improvement alone has frequently reduced changeover times for moulds dramatically.
Finally, after each of the above improvements has been implemented, investment in a quick mould clamping system should be evaluated. There are three different technologies available – mechanical, hydraulic and magnetic, each one with their own benefits and several different design approaches in each technology. Selecting the most appropriate for each application requires detailed analysis.
Through this rigorous, step-by-step, evaluation process, mould changeover times can be reduced significantly. As a rule of thumb, if your mould changeover time is reduced to below 10 minutes then it is at this stage that the additional benefits of installing a quick mould clamping system should be evaluated.