Good injection presses are expensive. And many factories in China are constrained in the amount of electricity they can consume. Hence the need to improve equipment efficiency.
Last week we looked into labor productivity in plastic injection molding. This week we'll cover machine efficiency.
1 The Problem of Low Machine Efficiency and its Causes
1.1 Operator Availability
Assuming the factory had a one-machine-one-person policy and that a single operator was responsible for running the machine to produce your parts, everything would be good, at least while they were operating their machine. However, this cannot always be the case. There are instances where that operator is not available (e.g. multiple shifts, holidays, and sick days). If the person is not working on the machine, the machine is not running thus not producing parts.
1.2 Overall Equipment Effectiveness (OEE)
The Overall Equipment Effectiveness ratio measures how close a factory is to perfect production (manufacturing only good parts, as fast as possible, with no down time). The true value of a factory’s OEE score is in understanding the underlying losses: availability loss, performance loss, and quality loss. By focusing on these losses and taking action to reduce these losses will naturally improve the OEE score.
An obvious loss in the case where we have one operator per machine is the loss to production while the machine is not running.
So in theory, for a single 8-hour shift per day, there would be a 15 minute morning break, 1 hour for lunch and a 15-minute break in the afternoon equating to a maximum machine running time of 6 ½ hours. A reality check on the 6 ½ hours running time would be closer to 6 hours due to machine not being ready and operator taking comfort breaks.
This has a direct effect on delivery times against planned schedules; it also increases the pressure on the operator if schedule looks to be slipping, which will impact quality.
Think also about rotating operators on machines so that the machine does not become set up for only one person. Rotating operators has the effect of having different people look at a process and being able to fix what another operator might miss.
1.3 One Operator Multi-Tasking
An injection mold machine does not work as soon as it is turned on. There is a warm-up period where temperatures have to be brought up to operating levels, hydraulic pressures have to be brought up to functioning levels, among other parameters that need time to reach the correct operating levels. The warm-up period could be over 2 hours for larger machines.
If the machine were switched on at the start of every day, this warm up period would be used to prepare everything for the day’s production. The operator would be responsible for ensuring the raw material is available and pre-dried ready to use. Any peripheral items required for the production activity would be checked to make sure all were in the correct place, items such as storage bins, trimming equipment, and inspection equipment.
These are all operations and jobs that could be assigned to other staff, allowing the machine operator to focus on doing his job, running the machine.
1.4 Limited Output
The net result of having a single operator per machine is low productivity. With the limited uptime per day, the maximum output is determined by the cycle time multiplied by the machine running hours, so in the example above where we have a running time of 6 hours per shift and with a product cycle time of 1 minute the daily output from this operator would be 360 parts (assuming 1 part per shot).
An order of 5000 items, this operator would complete the job in 14 shifts (instead of 11 shifts if the running time were 8 hours per shift). Note that we are assuming that the machine is already at running temperature.
2 Best Practices to Improve Machine Efficiency
From a business point of view, the more efficient production is the less waste the factory will produce. Optimizing each and every element within a factory is important and one way of achieving that is to implement best practices.
2.1 Staff Training
Training staff so they are proficient on a number of different mold machines provides flexibility within the mold shop, allowing production to be continuous through the use of staff rotation.
Ensuring each machine has different staff doing different jobs (to ensure everything is ready for a production run) will provide greater Overall Equipment Effectiveness as the machine can be kept running during the normal 8 hours shift instead of 6 hours.
A recent article by Debbie Zmorenski posted in the online magazine Reliable Plant, states:
Companies that increased their training after changes in the organization reported 63-percent higher productivity, 69-percent higher profits and 74-percent higher quality. In contrast, companies that did not increase training after changes in the organization observed significantly lower results, including a 34-percent productivity increase, 40-percent profit increase and a 24-percent quality increase.
These statistics are relevant not only to employees who have undergone change in an organization but also for employees who are new to an organization. Studies show that in all circumstances training increases profits by enhancing employee satisfaction, reducing stress and decreasing turnover.
2.2 Planned Maintenance
Planned or scheduled maintenance which is carried out during night shifts or over weekends, not only allows for the main production shift to operate without disruption but it is an important element in keeping the machines in the best working order and keeping up time to an absolute maximum.
Planned maintenance is a whole subject in its own right. I you would like more information regarding this please contact us.
2.3 System Parameter Optimization
Optimizing the overall system parameters means optimizing the machine settings, the material processing settings and the tool settings in order to generate the parts as quickly and as efficiently as possible. Once the overall system has been optimized, the parts being produced have a greater chance of being within specification and without any defects such as sink marks or flash.
It is important to have a record of all the parameter settings for each job so that set-up and start-up times are kept to a minimum and the use of set-up experts in a team will keep the machine downtime to a minimum.
2.4 Impact of Best Practice Implementation
Basically, implementing best practices within the mold shop allows the machine to run longer and more efficiently. The production yields more parts that are at an acceptable quality level. The holistic outcome to this is that the company runs more efficiently, and therefore is able to make your products within schedule and to the desired quality levels. It also makes your business more efficient if you are the customer, as less waste is coming in through your door.
The vast majority of Chinese factories we have worked with who have adopted best practice methods for their maintenance program have seen a high improvement in productivity (minimum 30%).
