SPC For Short Runs and Small Runs

SPC For Short Runs and Small Runs

Small production runs (batches) and short runs require a specific type of SPC. The standard average and range chart does not work for short runs. There are several control charts available that give you an accurate picture of your process.

Short Runs v. Small Runs

A short run is one that gets over quickly. A short run may produce a large number of units, but the runs are short by the virtue of their high production rate. Small runs are defined as runs with a small number of parts or pieces. Small Runs need not be short, but only have a small output number. A classic example stated is that of the Hubble Space Telescope program that produced only one piece but took 15 years to get it into orbit.

SPC for short runs and small runs use the same type of chart for the most part.

Approaches To SPC For Short and Small Runs

1. Exact Method: Control Limits are calculated on the basis of production study carried out on limited number of subgroups. The constants used for calculating the control limits on limited data come from special tables. These control limits are updated as more data becomes available, until enough data is available to calculate control limits the regular way. The process control is thus implemented in three phases.

2. Code Value Charts: Code value charts are plotted on transformed data. They are typically created by subtracting the nominal from the reading so that they represent only the deviation from the nominal. Code value charts enable different parts from the same process or many features from the same part on a single control chart. In case the initial data is limited, the exact method can be used to compute the initial control limits. A typical example of these is a grinding process producing thread plug gauges, each gauge with a different nominal size.

3. Stabilized Control Charts: Stabilized control charts are scaled in such a way that they are independent of the unit of measure, and several different characteristics, irrespective of their units can be plotted on the same control chart. Stabilized control charts can be useful to get an overview of processes since they encompass a broad range of features of a process.

Example of Exact Method

One of the most used charts in SPC for short runs is the individual and moving range chart. This chart requires only one part be measured and recorded giving an relatively accurate picture of the process' stability. The individual and moving range chart uses the exact data as measured and collected. The control limits are updated as more measurements are taken and analyzed. This chart along with several others are used during the course allowing the students a wide choice for their specific process.

Class content

Learn how to apply SPC to short runs and small batches in just one day. Save your company money on scrap and rework by using SPC.

This dynamic seminar presents a practical "hands on" approach to Short Run SPC.

You can have this class presented at your business for as little as $54.00 per person. Call us or click here to send us a message.

This class is 1 day and includes:

1.       Introduction and overview

2.       Rules for short run SPC

3.       Control charts for short runs

4.       Applying the knowledge

5.       Short run process capability

6.       Problem solving techniques for short runs

7.       Workshops

8.       CEU and RU credits are awarded

One of the best books that covers short and small run SPC, as well as hundreds of other quality topics is the  Quality Engineering Handbook, Second... Edition.   

Additional Information Resources