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Chapter 16: Waste of motion  

2012-06-24 12:12:57|  分类: Buffer Mentality |  标签: |举报 |字号 订阅

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NatSteel Ltd set up its subsidiary, Eastern Steel Services, to offer cut-and-bend rebars (abbreviation for reinforcement steel bars used in concrete structures) service to its clients. The company aimed to help the clients save on yield loss by providing cut-and-bend services to them. Due to the design of the civil works and building construction structures, rebars of various lengths were cut from rebars of 12-meter standard length. The remnant pieces were often useless and were sold back to NatSteel Ltd as scrap.

In ten years, NatSteel Ltd had appointed seven different General Managers for Eastern Steel Services. The average length of service for these general managers was less than one and a half years. They were either transferred out to other divisions or outright asked to leave the company. This is because they failed to increase the production output beyond 3,000 tons per month. In other words, none of them could assist NatSteel Ltd to sell more rebars to the construction industry in Singapore.

In 1992, the General Manager who just came on board realized that he did not know what to do to increase the factory output. Everyday he was busy attending to customer complaints. The number of complaints amounted to more than twenty a day. More than 90% of these complaints were made up of two issues - Late delivery and missing parts.

He couldn’t figure out what to do to reduce the number of customer complaints either. It seemed to him the factory had done all things possible to ensure on-time delivery and no missing parts. He asked me for help.

I went down to the factory floor. It was a very simple operation. Only two work stations: Two shearing machines and eight bending machines. The two shearing machines were placed adjacent to the raw material stock of rebars of 12-meter standard length and in sizes varying from 16 mm, 20 mm, 25 mm, ,28 mm, 32 mm to 40 mm in diameter were located at the front-end of the factory.

These two machines cut the standard 12-meter length rebars into various lengths dictated by a piece of software that feeds information to the shearing machines by a barcode reader that reads the bar tags. Information in the bar tags indicated the rebar diameter to be used and the length to be cut.

The software was specially designed and developed to reduce the length of the remnant end from a standard 12-meter length rebar. The shorter the length of the remnants means the lower percentage of the standard 12-meter length rebars is scrapped. The scrapped percentage was around 1.5%.

To optimize the yield of the rebars, the software allows the production planner to load into the production schedule as many job orders as possible. Each job order usually consists of many parts of various diameters and lengths ranging from as short as 1.2 meters to the full length of 12 meters.

Common sense tells us that as more batches of job orders are mixed into a single production schedule, the lower the scrap level. Since a ton of steel bar costs more than $550, a 1.5% yield loss amounts to $8.25 per ton of rebars lost in the cut-and-bend operations. It was quite substantial and therefore, as many as twenty five job orders were usually mixed into one production schedule.

The eight benders were placed after the two shearing machines. In between the shearing and bending machines was an empty floor space about 2,000 square feet in area. Cut rebars of the same size and length were bundled together and hoisted away from the shearing machines and placed all over the shop floor. There were easily fifty to a hundred bundles of cut rebars on the floor in-between the shearing and bending machines.

One bundle of rebars at a time was hoisted to a bending machine where two operators bend the rebars to the correct shape. After they finished bending the bundle of rebars which are of the same shape and size, the bundle of rebars were tied by pieces of tying wires and the bar tag was firmly re-attached to the bundle. The bundle of bent rebars was then hoisted away from the bending machine and placed onto the floor towards the back-end of the factory.

Over at the other end of the factory, about fifty to a hundred bundles of rebars were randomly placed over an area of 8,000 square feet in area. Nearer to the back-end of the factory, cut-and-bent rebars were stacked up on top of one another separated by different job order numbers.

Altogether, there could easily be twenty to fifty different piles of rebars stacked together with bar tags identifying them as coming from the same job order. After checking that all the rebars that make up a job order were grouped together, they were ready to be hoisted up onto a trailer. A truck then came in to tow it away to be delivered to the construction site.

 

FFigure 16-1: Before the implementation of the lean production system



     The factory was observed to be doing all the right things. They were hoisting cut rebars away from the shear machines and putting them onto the floor, hoisting the cut rebars from the floor to the top of the bending machines, hoisting bent rebars away from the bending machines to the floor, hoisting bent rebars from the floor to be stacked up together by job order and finally, hoisting the stack of rebars from the floor onto trailers. The frequent hoisting of rebars was deemed necessary.

But the problem I saw was not in the hoisting operations alone. I saw the difficulties in finding the bundle of cut rebars needed by the bending machines and the bent rebars to be stacked together in a pile identified by the job orders. With more than fifty to a hundred bundles of rebars on the floor, hunting for the right bundle of rebars was very slow and tedious.

Every time, the bar tag had to be read to identify which job order it belonged to. Operators at the bending machines were observed to be idling frequently while waiting for the material handlers to hoist the cut rebars to them. A quick estimate indicated they were idle for more than 70% of the time.

Meanwhile, the material handlers at the back-end of the factory have to search the factory floor high and low just to find the bundles of bent rebars that go into making the full job order. Often, a bundle or two were missed and were not hoisted onto the trailer. This caused missing parts upon delivery to the customers.

In summary, the process of hoisting the rebars onto the floor and then picking them up again from the floor is a complete waste of motion. The waste of motion had effectively strangled the productivity of the factory!

I reckoned if much fewer number of bundles of rebars were left lying on the floor, the time required to search for the bundles of rebars could be shortened tremendously. The factory’s overall productivity could jump up by three folds. Not only that, the probability of not finding a bundle of rebars for delivery would go down to zero.

I introduced into the shop floor a number of lean production methods. The increase in yield loss was insignificant but the number of bundles of rebar placed onto the factory floor was reduced by more than two-third.

The bending machines were observed to be idle for a very short period of time. I reckoned the bending machines were idle for a cumulative of much less than 30% of the time. The time taken to search for the bundles of rebars to be re-grouped into each job order was cut by more than half.

 

Figure 16-2: After the implementation of lean production system


     Suddenly, the factory was found to have been given a steroid injection. The productivity increased by more than 100%. The general manager was very happy. For the first time in their history, the factory managed to break the 3,000 tons per month hurdle and it by surpassed the previous record by more than double. That was amazing.

Building upon the above success, I recommended the installations of roller conveyors to replace the hoisting of rebars in-between these two machines. This waste of motion was eliminated completely. Productivity went up further. The entire piece of floor space was freed up.

In less than a year the total tonnage of rebars cut-and-bent increased from less than 3,000 tons per month to 12,000 ton per month. The productivity increased by four times. The mere elimination of the waste of motion alone had contributed to 400 percent increase in productivity! That was simply marvelous.

 

Illustration #1: Tenets of industrial engineering

 

I am a lean production consultant. I first broke into China with a lean production consulting project with AAC Acoustics Technologies’ plant at Fuyong, Shenzhen. AAC Acoustics Technologies is a Hong Kong-listed, HK$12 billion company. At the end of the third month, I managed to increase the productivity of its mobile phone buzzer assembly line by 33%. That was slightly higher than my promised delivery of 30% increased in productivity.

During the proposal stage of the project, AAC’s CEO Benjamin Pan Zheng Min did not believe I can increase the productivity by 30%. At the very most, “in the teens”, that was what he said.

I have twenty-three years of experiences in the implementation of lean production system. I saw two key potentials. One, AAC management did not carry out time motion study for its assembly processes. Two, at the assembly line, work-in-progress (WIP) piled up to several thousands pieces at every work stations. I conservatively estimated these two weaknesses alone would provide me with a room of improvement of around 15% each.  

I began working on the project in Oct 2006 by conducting a motion time study for all the process steps. Based on the time study of every assembly processes, I did a task analysis and re-distributed the tasks among the work stations to achieve a balanced Kanban[1] assembly line. The productivity of the first assembly line shot up by 15% immediately.

In the second phase, I carried out finite motion study on every assembly processes and recommended changes in work flow, use of jig and fixtures and quality improvement. I began this series of business re-engineering process starting from the elimination of the bottle-neck of the last work station.

Next I moved on to work on removing the bottle-neck of the immediate upstream station. I repeated this process ten times working diligently to remove each new found bottle-neck progressing moving back upstream. This effort accounted for another 15% increased in productivity.

Following picture is one of the examples where I reduced the travel distance of the hand to save on about 0.1 seconds per cycle. A saving of mere 0.1 seconds resulted in a saving of 40 minutes in a ten-hour shift. 


Figure 16-3a: Before improvement

 

Figure 16-3b: After improvement

When I asked Liqunthe plant manager of this factory what were the obvious differences of the assembly line, before and after, he replied, “Two major achievements.

One, the WIP inventories were all gone. When a minor hiccup happened in the Kanban assembly line, it showed up immediately as either a small build-up in inventory or the operators idles without any material to work on.

Two, before the implementation, the hourly output fluctuated from 1,200 pieces an hour to as high as 2,000 pieces an hour. After the implementation, the output rate was very steady, hovering between 1,900 and 2,100 pieces an hour.

For these two reasons alone, I have ordered my people to quickly duplicate the Kanban assembly lines to all five other similar assembly lines.”

Lean production system comprises IE (Industrial Engineering) and many other techniques applicable to all manufacturing companies. No doubt all these techniques can be applied to any company, however, which techniques would be the most appropriate and should be applied first to a particular company depends on the result of existing performance level of the factory.

Assume a pond is full of rocks where one piece of rock occupies 80% of the volume of the pond while the remaining small pieces occupy the remaining 20%. However submerged in waters it is not easy to see what are the rocks and which one of them is the biggest piece. Likened it to draining all the water in pond all at once, I identified the biggest piece of rock (problem) and therefore, able to offer a solution(s) to achieve not less than 30% increased in productivity for AAC Acoustics Technologies.

Unnecessary motion, which appeared necessary as part and parcel of most production operations, can form a bottle-neck that chokes the factory’s ability to produce at its optimum production capacity.

Waste of motion can be a major cause of low productivity because it causes other operations to be idle for a substantial part of the time.

 


 



[1] Kanban is a Japanese term. In this context, the word, Kanban refers to a carrier to circulate the work-in-progress in between tow adjacent work stations.

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