The CPI is based on the scientific method. The 6 steps are as follows:
- Select the process to be studied,
- Record the existing method to collect the necessary data in a useful form, - Analyze the recorded data to generated alternative improved methods, - Evaluates the alternatives to develop the best method of doing the work, - Install the method as standard practise by training the operator,
- Maintain the new method.
Select the process
This depends on the ability to recognize situations that have good potential for improvement.
Observe. Any situation can be improved but some have better potential than others. Indicators that show areas most needing improvement include:
- High scrap, reprocessing, rework and repair costs;
- Backtracking of material flow caused by poor plant layout;
- Bottlenecks;
- Excessive overtime;
- Excessive manual handling of materials, both from workplace to workplace and at the workplace;
- Employee grievances without true assignable causes.
Select. The purpose of CPI is to improve productivity, to reduce operating, product or service costs. In selecting jobs or operations for method improvement, there are 2 major considerations: economic and human.
Economic considerations. The cost of the improvement must be justified. The cost of making the study and installing the improvement must be recovered from the savings in a reasonable time. 1 to 2 years is a commonly used period.
The human factor. The resistance to change, by both management and worker, must always be remembered. Working situations characterized by high fatigue, accident hazards, absenteeism and dirty and unpleasant conditions should be identified and improved. Sometimes it is difficult to give specific economic
justification for such improvements, but the intangible benefits are extensive and should weigh heavily in selecting studies.
Pareto diagrams. Pareto analysis can be used to select problems with the greatest economic impact. It separates the vital few from the trivial many. The steps in making a Pareto analysis are as follows:
- Determine the method of classifying the data: by problem, cause, nonconformity and so forth;
- Select the unit of measure;
- Collect data for an appropriate time interval, usually long enough to include all likely conditions;
- Summarize the data by ranking the items in descending order according to the select unit of measure;
- Calculate the total cost;
- Calculate the percentage for each item;
- Construct a bar graph showing the percentage for each item and a line graph of the cumulative percentage.
Note that Pareto analysis does not report what the problems are, only where they seems to occur.
Cause-and-effect diagram. Sometimes called fishbone or an Ishikawa diagram, the cause-and-effect diagram is a very useful tool for identifying root causes. It is best used by a group or a team working together. The steps in developing a fishbone diagram are:
- Identify the problem to be studied and state it in a few words;
- Generate some ideas about the main causes of the problem. Usually all probable root causes can be classified into 6 categories: materials, machines, people, methods, measurement and environment;
- Brainstorm all possible causes for each of the main causes;
- Once all the causes have been listed, try to identify the most likely root causes and work on these.
Record
To be able to understand what to record, it is necessary to define the process being studied. The following must be determined to properly define the process:
- The process boundaries. Starting and ending points form the boundaries of the process;
- Process flow. This is a description of what happens between the starting and ending points;
- Process inputs and outputs. The things, that are changed by processes, are called inputs and they may be physical or information. Outputs are the result of what goes on in the process;
- Components are the resources used in changing inputs to outputs. They are composed of people, methods and equipment;
- Customer. Processes exist to serve customers and customers ultimately define what a process is supposed to do;
- Suppliers are those who provide the inputs. They may be internal to the organization or external;
- Environment. The process is controlled or regulated by external and internal factors. The external factors are beyond control and include customers’ acceptance of the process output, competitors and government regulation. Internal factors are in the organization and can be controlled.
The record of the present method also provides the basis for both the critical examination and the development of an improved method.
Classes of activity. All activities can generally be classified into 1 of 6 types.
There are 6 universally used symbols for these activities.
Operation. The main step in process, method or procedure.
Usually the part, material or product is modified during the operation;
Inspection. An inspection for quality or a check for quantity;
Movement. The movement of workers, material, equipment or information from place to place;
Storage. A controlled storage from which material is issued or received;
Delay. A delay in the sequence of events;
Decision. Where a decision is made.
Following are descriptions of some of the various charting techniques.
Operations process charts. Operations process charts record in sequence only the main operation and inspections. They are useful for preliminary investigation and give a bird’s-eye view of the process. The description, and sometimes the time, for each operation are also shown. An operation process chart would be used to record product movement.
Process flow diagram. A process flow diagram shows graphically and sequentially the various steps, events and operations that make up a process. It provides a picture, in the form of a diagram, of what actually happens when a product is made or a service performed.
Analyze
Examination and analyze are the key steps in CPI. This step involves analyzing every aspect of the present method and evaluating all proposed possible methods.
Find the root cause. Often symptoms are what we see and it is difficult to trace back to the root cause. To find the root causes you must have a questioning attitude (what, why, when, how, where and who).
3 approaches can help in examining:
- A questioning attitude. This implies an open mind, examining the facts as they are, not as they seem, avoiding preconceived ideas and avoiding hasty judgements;
- Examining the total process to define what is accomplished, how and why.
The answers will determine the effectiveness of the total process;
- Examining the parts of the process. Activities can be divided into 2 major categories: those in which something is happening to the product (worked on, inspected or moved) and those in which nothing constructive is happening to the product (delay or storage). In the first category, value is added only when the part is being worked on. Setup, put away and move add cost to the product but do not increase its value. The goal is to maximize the productivity of these operations.
Develop
When developing possible solutions, there are 4 approaches to take to help develop a better method:
- Eliminate all unnecessary work;
- Combine operations wherever possible. Thus materials handling will be reduced, space saved and the throughput time reduced. This is a major thrust of JIT manufacturing;
- Rearrange the sequence of operations for more effective results. If sequences are changed, then possibly they can be combined;
- Simplify wherever possible by making the necessary operations less complex. If the questioning attitude is used, then complexity should be reduced.
Principles of motion economy. There are several principles of motion economy, among which are the following:
- Locate materials, tools, and workplace within normal working areas and pre-position tools and materials;
- Locate the work done most frequently in the normal working areas and everything else within the maximum grasp areas;
- Arrange work so motions of hands, arms, legs and so on are balanced by being made simultaneously, in opposite directions, and over symmetrical paths. Both hands should be working together and should start and finish at the same time. The end of one cycle should be located near the start of the next cycle;
- Conditions contributing to operator fatigue must be reduced to a minimum.
Provide good lightning, keep tools and materials within maximum working areas, provide for alternate sitting and standing at work and design workplaces of proper height to eliminate stooping.
Human and environmental factors. These include safety, comfort, cleanliness and personal care; so provision must be made for lightning, ventilation and heating, noise reduction, seating and stimulation.
Methods improvement is based on the concepts of scientific management. Job design is an attempt to provide more satisfying meaningful jobs and to use the
- Job enlargement expands a worker’s job by clustering similar or related tasks into one job. This is called horizontal enlargement;
- Job enrichment adds more meaningful, satisfying and fulfilling tasks. The job not only includes production operations but many setup, scheduling, maintenance and control responsibilities;
- Job rotation trains workers to do several jobs so they can be moved from one job to another. This is called cross training.
All these factors help to produce a more motivated and flexible workforce.
Install
So far, the work done by the analyst has been planning. Now the plans must be put into action by installing the new method. In planning the installation, consideration must be given to the best time to install, the method of installing and the people involved. Then the analyst needs to be sure that equipment, tooling, information and the people are all available. At installation time, a dry run will show whether all equipment and tooling are working properly.
Training the operator is the most important part of installation. If the operator has been involved in designing the method change, this should not be difficult. The worker will be familiar and comfortable with the change and will probably feel some sense of ownership.
Learning curve. Over time, as the operator does the task repetitively, speed will increase and errors decrease. This process is known as the learning curve.
Depending on the task, a worker may progress through the learning curve in a few minutes or, for high-skill jobs, several months or years.
Maintain
Maintaining is a follow-up activity that has 2 parts. The first is to be sure that the new method is being done as it should be. This is most critical for the first few days and close supervision may be necessary. The second is to evaluate the change to be sure that the planned benefits are accomplished. If not, the method must be changed.