August 19, 2015

Six Sigma: Control Phase : 3. Other: Pre-control Technique, TPM & Visual Management

Pre-control Technique rules advantages disadvantages Short Run SPC Visual Management TPM 8 Pillars Goal Main aspect   Preventive Corrective In‐built

The Pre-control Technique

An easy method of controlling the process average is known as “pre-control.” Pre-control was developed in 1954 by a group of consultants (including Dorin Shainin) in an attempt to replace the control chart. Pre-control is most successful with processes which are inherently stable and not subject to rapid process drifts once they are set up. Pre-control can act both as a guide in setting process aim and monitoring the continuing process.

The idea behind pre-control is to divide the total tolerance into zones. The two boundaries within the tolerance are called pre-control lines. The location of these lines is halfway between the center of thespecification and specification limits. It can be shown that 86%of the parts will be inside the P-C lines with 7% in each of the outer sections, if the process is normally distributed and Cpk= 1. Usually the process will occupy much less of the tolerance range, so this extreme case will not apply.

The chance that two parts in a row will fall outside either P-C line is 1/7 times 1/7, or 1/49. This means that only once in every 49 pieces can we expect to get two pieces in a row outside the P-C lines just due to chance. There is a much greater chance (48/49) that the process has shifted. It is advisable, therefore, to reset the process to the center. It is equally unlikely that one piece will be outside one P-C line and the next outside the other P-C line. This is a definite indication that a special factor has widened the variation and action must be taken to find that special cause before continuing.

Pre-control rules:

. Set-up: The job is OK to run if five pieces in a row are inside the target .

. Running: Sample two consecutive pieces

. If the first piece is within target, run (don’t measure the second piece)

. If the first piece is not within target, check the second piece

. If the second piece is within target, continue to run

. If both pieces are out of target, adjust the process, go back to set up

. Any time a reading is out-of-specification, stop and adjust

The ideal frequency of sampling is 25 checks until a reset is required. Sampling can be relaxed if the process does not need adjustment in greater than 25 checks. Sampling must be increased if the opposite is true. To make pre-control even easier to use, gauges for the target area may be painted green. Yellow is used for the outer zones and redfor out-of-specification.

The advantages of pre-control include:

. Shifts in process centering or increases in process spread can be detected

. The percentage of non-conforming product will not exceed a pre-determined level

. No recording, calculating or plotting is required

. Attribute or visual characteristics can be used

. Can serve as a set-up plan for short production runs, often found in job shops

. The specification tolerance is used directly

. Very simple instructions are needed for operators

The disadvantages of pre-control include:

. There is no permanent paper record of adjustments

. Subtle changes in process capability cannot be calculated

. It will not work for an unstable process

. It will not work effectively if the process spread is greater than the tolerance

Short Run SPC

In a data rich environment, the concepts and practice of traditional SPC techniques can present the possibility of so many control charts, for many different kinds of units and multiple variableson each unit, as to make implementation unwieldy and impractical. The development of traditional SPC techniques anticipated long, reasonably stable production runs. To construct a control chart that reflects Shewhart economic limits requires 20 to 30 subgroups or individual X’s (preferably a minimum of 100 data measurements). When there are relatively few variables and long runs, traditional control charts, are practical. Short run charting may be desirable when the production lot size is extremely small (10-20) pieces or when the sample size, under typical operating conditions, is small.

Visual Management

Visual Management provide real-time information on work place status by a combination of simple, effective visual information aids that allow employees to understand their influence on the organization overall performance hence allowing the employees to improve their performance.

Applications of Visual Management

1.Safety Warning: Display sign in work area to aware employee and customer, of safe practices. Like, for Chemical as Danger
2.Display working areas, paths: Marking area or path with color schemes, Such as yellow, if conveyor or any robot travel carrying the material.
3.Display instruments, pipes
4.Tools and supplies
5.Materials
6.Quality Control
7.Documentation…

 

Total Productive Maintenance (TPM)

Total productive maintenance (TPM) is an activity that promotes coordinated group activities for greater equipment effectivenessand requires operators to share responsibility for routine machine inspection, cleaning, maintenance, and minor repairs. The professional maintenance staff retains responsibility for major maintenance activities and act as coaches for the routine and minor items. Productive maintenance combines preventive, predictive, maintainability improvement techniques, and equipment life cycle costs of equipment to increase reliability and ease of maintenance. There are “six biglosses” that contribute negatively to equipment effectiveness: . Equipment failure: from breakdowns . Setup and adjustment: from setup changes . Idling and minor stoppages: defective sensors, parts caught on conveyor, etc. . Reduced speed: the loss between designed and actual operating speed . Process defects: scrap and quality defects . Reduced yields: loss of product from machine startups and shutdowns

8 Pillars of TPM

•Safety, Health and Environment •Education and Training •Autonomous Maintenance •FocusedImprovement (KAIZEN)•Planned Maintenance •QualitySystem Maintenance •SupplyChain / Office TPM •EquipmentEarly Management

Total Productive Maintenance
• Reasons for throughput losses on Machinery
Breakdown: Failed function and reduced function.
Setup and Changeover: Taking much longer than needed
Idling and minor stoppage: Sudden disruption
Reduced speed: Actual vs. designed
Quality defects and rework: Sporadic and chronic
Startup yield: Process instability

Goal of Total Productive Maintenance (TPM)
• The goal of TPM is to minimize downtime due to maintenance, and maximize machine uptime.

Importance of TPM
As buffer sizes and inventory levels are reduced, the uptime on the machinery becomes even more important. Because there is little inventory to buffer unplanned downtime in a lean environment, when a machine goes down the entire production line may go down; therefore, a formal TPM program is instrumental in supporting a lean manufacturing implementation.

Main Aspects of TPM
• Preventive Maintenance
• Corrective Maintenance
• Inbuilt Maintenance

Preventive Maintenance
• Preventive maintenance is concerned with the uptime or availability of equipment. The effort here is aimed at performing preventive maintenance action on equipment in a planned / scheduled and disciplined manner, as opposed to in an unplanned or chaotic manner.
• The operators are a central part of this program, specifically to conduct daily maintenance on the equipment and identify abnormalities as they occur. This is paramount to successful preventive
maintenance

Corrective Maintenance
Corrective maintenance concentrates on enhancing frequently failing equipment. The  idea here is that if components from the original equipment keep breaking, why not replace them with something better?

In‐built Maintenance
• Maintenance prevention is an area that most of companies neglect and pay very little attention to when designing or purchasing new equipment. Because one of the key ingredients of a successful TPM program is that of daily operator “autonomous maintenance”, it is imperative that equipment be easy to maintain on a recurring basis. If the new machinery is difficult to lubricate, if the bolts are difficult to tighten, and if it is impossible or difficult to check critical fluid levels, then it is very unlikely that operators will be motivated to monitor the equipment
on daily basis. The total life‐cycle cost on the equipment must be examined when Procuring new machines not Week #6 9 machines, just the one‐off, nonrecurring costs