Word for the day: EFFICIENCY

 

It is quite amusing but a little humorous to have 1^st of April as fool's day, especially when most of us will be tired of paying hefty taxes and have little money left, for financial year ending March 31^st in this sub-continent, at least. Someone in the past must have thought of having a good laugh after going bankrupt!

 

Well, at the same time it is also a period during which many targets, objectives and budgetary proposals will be set for another financial year. Although financial wizards mutter many confusing jargons, in this newsletter, let us try to understand EFFICIENCY, one of the commonly used objectives in a typical manufacturing unit (for that matter, efficiency can be used in any field).

 

EFFICIENCY: This is one of the most common & widely used parameter for determining how well or bad a single machine, an assembly (or process) line or an entire unit is performing. In very simple terms, efficiency – normally represented by Greek symbol η (ETA) – is the ratio of (OUTPUT / INPUT). In this simple yet powerful ratio, INPUT refers to a resource that is expected to undergo certain process and produce an OUTPUT. Any type of input that undergoes a conversion process will produce some losses along with output. Under no conditions will output be exactly equal to input. For many practical purposes – like in a production process – the efficiency can also be defined as the ratio of (ACTUAL RESULT / EXPECTED RESULT). Note: In time based calculations, the ratio has to be reversed since actual time will be more than or equal to expected time. Efficiency is usually expressed in percentage.

 

Let us write the formula for efficiency in percentage as: η =(OUTPUT / INPUT) X 100 = ((INPUT-LOSSES) / INPUT) X 100

 

Before measuring efficiency or declaring a magical number, it is important to understand few points:

 

1. The efficiency is an interdependent parameter that will be affected by all its inter-connected elements and their efficiencies. (Example: an inefficient motor will REDUCE the overall machine efficiency in which it is fixed)
   

   
    

2. When more than one activity is involved in the conversion process, efficiency should NOT be measured in isolation. Efficiency of all activities should be considered. This also applies to interdependent departments in a manufacturing set-up. (Example: if stores department does not release required material in time, efficiency of production department REDUCES which actually REDUCES the efficiency of the complete unit in totality)
   

   
    

3. When a mix of old and high-end machines or process exists in a line, the component with "least" efficiency decides the "overall" line or process efficiency. (Example: if a high speed robot is installed in a assembly line which has lot of manual operations, robot's high efficiency will NOT INCREASE overall line efficiency)
   

   
    

4. Efficiency should be a "dynamic" parameter measured regularly rather than a static one that will be calculated. (Example: in one month, if efficiency for one week was 90% and three weeks was 60%, the average efficiency will be 67.5% only, HIDING one week's good efficiency)
   

   
    

To obtain clarity on these points, let us take a small tour thru the process of an assembly machine producing some sub-assembly component for an automobile. This critical activity has three important components for accomplishing the job (Refer flow chart below):

 

• A pneumatic clamping system – This system is expected to clamp and unclamp the component.
  

  
   

  • Technical Requirements: Air Pressure: 5 to 6 Kg / cm² ( 73 to 88 PSI); Air Volume: 12 CFM (Cubic Feet per Minute) (0.334 Cubic Meter per Minute)
    
  • As per the design, the clamping time is 4 seconds and unclamping time is 2 seconds
    

  
   

• A stand alone hydraulic power pack – This system is expected to bend and create a profile on the component
  
  
  • Technical Specifications: Pump working pressure: 140 Kg / cm² (1991 PSI) Required Operating Pressure: 75 Kg / cm² (1066 PSI) Pump Volume: 20 LPM (Liters Per Minute) (5.38 Gallon Per Minute) Motor HP: 7.5 (5.5 Kilowatt) 3 Phase
    
  • As per the design, the total "hydraulic cycle time" is 6 seconds
    

    
     

• An inspection table – This is a manual process where a quality inspector is checking the produced components referring some dimensional and visual standards and his / her judgment skills.
  

  
   

  • From past experience it is agreed upon that one component can be inspected completely in
    12 seconds
    

 

At the outset, the total time required to make the component ready for next operation is 24 seconds (sum of all times). Ideally, it should be able to produce 150 pieces per hour. Now, let us build a flow chart for this production process.

The data from production record showed that the "average" output achieved from the process is 100 pieces per hour. When compared to the designed output, the efficiency will be only 66.6% (η = (ACTUAL RESULT / DESIRED RESULT) X 100 = (100 / 150) X 100 = 66.6%). Before investigating further on this, let us take a look at the process log book for twelve hours starting 6AM in the morning to check the hourly outputs and other details. This information was almost same for entire week.

 

6-7	7-8	8-9	9-10	10-11	11-12	12-13	13-14	14-15	15-16	16-17	17-18	AVG
85	100	125	85	90	90	125	100	85	85	110	125	100.4

 

Although output from the process has been less for many hours, it has increased predominantly in three different hours. Therefore, the first objective will be to elevate output of balance hours. A thorough data collection from the concerned personnel and log book revealed few reasons for reduced production.

 

• Pneumatic clamping is operating very slowly
  
• High oil temperature in hydraulic power pack is frequently stopping the process
  
• Inspection delay
  

 

Let us understand how individual efficiency of each of these reasons influences the overall efficiency of the process. Start with first one.

 

Pneumatic clamping is operating very slowly: For optimum operation, this pneumatic system requires minimum of 12 CFM (Cubic Feet per Minute) (0.334 Cubic Meter per Minute) air at a minimum pressure of 5 Kg / cm2 (73 PSI) to complete process within the rated time. If both of these values decrease, the efficiency of pneumatic system decreases.

 

On an hourly basis, pressure readings were taken from the gauge fitted to the INLET pipe of the assembly machine. Table below gives the values in Kg/cm2 (PSI). The readings were almost same for entire week.

 

6-7	7-8	8-9	9-10	10-11	11-12	12-13	13-14	14-15	15-16	16-17	17-18
5.2 (74)	5.9 (84)	5.8 (83)	4.7 (66.8)	4.7 (66.8)	4.5 (64)	5.8 (83)	5 (71.1)	5.5 (78.2)	5.5 (78.2)	6.0 (85.3)	6.2 (88)

 

As you can see from the above table, the air pressure is reduced below the required limit between 9 and 12 hours. Reduction in pressure also means reduction in the volume (CFM or Cubic Meter per minute) and hence the pneumatic system works slower. The production is less between 14 and 16 hours as well, but looks like air supply is not the cause.

 

During these hours, the duration for clamping and unclamping was recorded – using a simple stop-watch – at 5.5 and 3.2 seconds respectively. Now, let us calculate the pneumatic efficiency from these values. For the sake of simplicity, we will consider clamp and unclamp time together.

Pneumatic efficiency, Pη = (DESIRED TOTAL TIME / ACTUAL TOTAL TIME) X 100 = ((4+2) / (5.5 + 3.2)) X 100 = 69%. Since the pneumatic system did not clamp or unclamp within desired time, overall cycle time is increased and hence output is reduced.

 

On further investigation as to why pressure dropped specifically in these time windows, following points were discovered:

 

• A punching machine located upstream (before) of the assembly machine performs certain operations during this period and is consuming more air – This is a regular activity and cannot be avoided
  

  
   

• Compressor is running fully loaded to meet the sudden demand and it is running very hot – As the temperature of air increases, its density reduces. So, as the compressor starts running hot (beyond specified limits), its output efficiency (CFM or Cubic meter per minute) actually reduces
  

  
   

• The size of inlet pipe to assembly machine is found to be ½" (12.7mm) - The actual inlet size required is ¾" (19mm). As the size of pipe reduces, volume flowing thru the pipe also reduces.
  

  
   

For further discussion, let us assume that all components of the pneumatic system are in good, clean working condition. No component level problems exist.

 

All these three limitations should be eliminated to increase the production. Limitation III was immediately eliminated by replacing the specified pipe size. To eliminate limitations I & II, a brain storming session was conducted with and a YES / NO matrix with any readings / remarks was created to explain the situation. This will further help in taking a decision, which we will see very soon.

 

Question	YES	NO	Remark
Can the punching machine be stopped to reduce air consumption?		NO
Is it possible to reduce the air consumption of punching machine?		NO
Will a separate line from air receiver to assembly machine help?		NO	The compressor is running fully loaded. So re-piping may not help
Is compressor's capacity sufficient to meet this sudden demand?		NO	It is short by 12%
Can we buy a new large compressor to eliminate this shortage?		NO	No budget at this point of time. It is expensive also. Difficult for one more year, at least.
Is the present compressor running at its full efficiency?	YES		It is delivering at 90%
Is it acceptable to run assembly machine with reduced output?		NO	It has to produce minimum 125 pieces per hour (could be more, but later)
Is the punching machine running 24 hours?		NO	It runs only eight to nine hours in day shift
Which means big compressor is running rest of the day to support only the small assembly machine?]p	YES		Increased power cost / maintenance cost of compressor / early wear and tear
Can a small stand-alone compressor be bought for the assembly machine?	YES		A cost-benefit analysis report needs to be prepared considering following points i) Power saving by stopping big compressor ii) Consistent output from assembly machine iii) Return on investment for small compressor

 

The efficiency measurement at a higher level and further exploration using the above matrix gave a conclusion for this scenario: To buy new small low-cost compressor for the assembly machine, to have long term advantages and avoid running bigger compressor in then night shift.

 

Now let us revisit the list and take up second point.

 

High oil temperature in hydraulic power pack is frequently stopping the process: The hydraulic power pack fixed on this assembly machine uses water based oil. Its temperature must be maintained around 45°C (113°F) for optimum operation. If the temperature rises, oil viscosity reduces and performance of the system decreases. So, hydraulic system efficiency decreases.

 

Oil temperature can rise due to many reasons. Some causes are contaminated or degraded oil, excessive pressure settings, poor heat exchange, and choked filters. If the pump operates beyond required pressure for long time, the oil will be subjected to extreme pressure pulses and its temperature increases. And, the circulating oil needs to be cooled properly – either by air or water or other cooling medium – to maintain a constant operating temperature.

 

On an hourly basis, reading of working pressure and oil temperature were recorded. Table below gives the values in Kg/cm2 (PSI) and Degree Celsius (Degree Fahrenheit) respectively.

 

 

6-7	7-8	8-9	9-10	10-11	11-12	12-13	13-14	14-15	15-16	16-17	17-18
75 (1066)	74 (1052)	78 (1109)	75 (1066)	73 (1038)	75 (1066)	74 (1052)	78 (1109)	73 (1038)	72 (1024)	75 (1066)	74 (1052)
43 (116)	48 (118)	47 (116)	49 (120)	49 (120)	50 (122)	48 (118)	51 (124)	53 (127)	54 (129)	54 (129)	52 (125)

 

From this table, we can infer that the oil pressure is fairly constant throughout the 12-hour observation period and it has remained pretty much same for the whole week. Oil temperature seems to be on the high side always, reaching peak during afternoon between 14 and 17 hours. Between 14 and 16 hours, the power pack was forced to be stopped intermittently to let the oil cool and resume production.

 

In this scenario, even though the hydraulic power pack has a problem, measuring its efficiency is little difficult. Since this problem is reducing machine output, we can consider the PRODUCTION EFFICIENCY as an indirect indicator of power pack efficiency. To calculate, let us consider the realistic output of 125 per hour as DESIRED OUTPUT (Achieving 150 products per hour must be our ultimate goal). Consider it for the two hours when production was reduced due to frequent hydraulic power pack stoppages.

 

Production Efficiency, PE η =

(ACTUAL OUTPUT / DESIRED OUTPUT) X 100 = (85/125) X 100 = 68% = Indirect Hydraulic Efficiency

 

Since the working pressure is stable, we can safely confirm that the hydraulic system components are working normal and needs no further investigation. Following points were recorded with reference to the excessive oil temperature. The oil is cooled by a fan-assisted radiator.

 

• The high-pressure filter has not been replaced for long time – no record available
  
• The radiator was clogged with dust and was preventing free air circulation
  
• Due to space constraint in unit, the power pack was surrounded by lot of packing boxes, bins
  
• Suspicious radiator fan
  

 

We will go thru the same exercise of creating YES / NO matrix with any readings / values to justify and arrive at a conclusion for increasing the output. As obvious from the list, we will replace high-pressure filter. If this filter is blocked, it will restrict oil flow resulting in increased pressure and hence temperature.

 

An action will be immediately initiated to clean and service the radiator over weekend. It can be done in-house with the available technical personnel.

 

Question	YES	NO	Remark
Is the pump running at zero pressure when not working?	YES		We checked all the components. Pump is working fine.
Is radiator fan running at its rated speed?	YES
Is there any problem in the fan blade?	YES		Looks like the two blades have become somewhat flat reducing air flow
Should the fan blade be replaced?		NO	With little tinkering work, it can be corrected in house to match the profile of good blade
Is it not possible to clear the area around radiator to provide sufficient ventilation?		NO	Right now, the shop floor is overfilled with WIP material. Rack system will be ready only after eight months. Till then we have to somehow manage.
Can the radiator unit alone be located near window with some additional piping, temporarily?		NO	The window is too far
Can the radiator be elevated to roof level with additional piping?	YES		It is possible
Will elevating the radiator affect hydraulic system performance?		NO	May not be necessary since the elevation will be only about 10 feet

 

As the exploration revealed, fan blade modification, radiator servicing and elevating the radiator will provide better cooling and prevent minor stoppages. This will help in achieving the desired output of 125 pieces per hour.

Now let us revisit the list and take up third limitation.

Inspection Delay:
The production output numbers are considered only after inspection is complete. Due to space constraint, the component produced must be inspected continuously to avoid work-in-progress inventory. So any delay in inspection affects "inspection efficiency" and output is reduced.

 

It was observed that between 7 & 8 and 13 & 14 hours the output was reduced due to inspection delay. Since it is a combination of machine and human factor, very discrete measurement of efficiency is little difficult. So, like earlier case, reduced and desired outputs were taken for calculating the efficiency.

 

Production Efficiency, PE η=

(ACTUAL OUTPUT / DESIRED OUTPUT) X 100 = (100/125) X 100 = 80% = Indirect Inspection Efficiency

 

A small brainstorming session was conducted to understand the inspection process and following points were recorded:

 

• The inspector spends around fifteen minutes between 7 & 8 and 13 & 14 to prepare quality / inspection reports – it was agreed that machine should not run without "on-line" inspection
  

  
   

• A 100% inspection plan is in place to inspect every component produced
  

  
   

• Once in a while, inspector also takes additional work of auditing, inspection of other components
  

 

After a thorough exploration and cross consultation between departments – ideally production & quality – following points were considered to be implemented, as soon as possible.

 

• Since the machine has been producing consistent quality components, 100% inspection can be gradually reduced to a sampling plan, probably starting with 75% and reducing 25% every week till about 5 to 10% sample rate is established
  

  
   

• Once the sampling plan is implemented, inspector can utilize the balance time to fill quality / inspection reports without hampering output
  

  
   

• To standardize inspection procedure, fabricate special fixtures – like GO-NO GO gauges – to perform repetitive inspections, quicker
  

 

 

This small tour of an assembly machine showed us how efficiency can be discretely measured at every level without huge investments or additional resources. It requires one-time and focused effort to establish the procedures. A graphical representation of the efficiency effect in an organization is presented in next page for making the concept a bit clear.

 

If you have had some similar interesting experience, send it to us. Let our friends, colleagues know about it and benefit from it.

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Someone said, if some work is done today better than yesterday, then you are already efficient than yesterday. The journey never stops.

Good luck……

 

 

 

TECHUZZLE

 

 

Across

 

1.    Leading Generator manufacturing company

5.    Leading refrigerating compressor manufacturer

6.    Pioneers in electrical products, now in every field - & T?

8.    A leading air compressor manufacturer – Name of a city in USA

 

 

 

 

Down

 

2.    A big German company - makes everything, almost everything.

3.    Another generating set manufacturing company - becomes a butterfly later

4.    Leading Indian pump manufacturer - brothers?

7. Leaders in brushless alternators - not a ford product

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