Overview
ISO 7870-8:2017 - Control charts - Part 8: Charting techniques for short runs and small mixed batches provides guidance on applying regular variables control charts when monitoring samples of size one. The standard addresses modern manufacturing realities - frequent changeovers, many part numbers, short production runs and small batch sizes - by shifting the focus from product-oriented SPC to process-focused short-run SPC. It gives methods and chart types that let users plot similar characteristics from different items, or multiple characteristics of an item, on a single control chart to reveal process behavior and sources of variation.
Key Topics
- Scope and intent: Use of variables control charts where subgroup size is restricted to one; emphasis on understanding process variation rather than individual product characteristics.
- Chart selection: Guidance on how to select the correct Shewhart control chart for continuous-variable data and for characteristics without a constant aim or spread.
- Preparation procedures: Methods for grouping similar processes, preliminary process diagnosis, and establishing the correct initial setup of a process characteristic.
- Limit setting: Procedures to pre-establish control limits and initial control-chart setup for short runs and small mixed batches.
- Chart types covered: Variable-aim individual and moving range charts; variable-aim moving mean and moving range charts; universal individual and moving range charts; universal moving mean and moving range charts.
- Practical tools: Forms, reproducible chart templates and normal probability worksheets (informative annex) to facilitate implementation.
- Terminology and symbols: Uses ISO 3534-2 terms and defines symbols (e.g., C for centre line, UCL/LCL for limits, R for range, moving R).
Applications
ISO 7870-8:2017 is designed for environments with short runs or small mixed batches where traditional subgroup-based SPC is impractical. Typical applications include:
- Job shops and contract manufacturers with many part numbers and frequent changeovers.
- Operations with continuous activities applied to many parts (turning, drilling, grinding, extrusion).
- Small-batch stamping, bolt production, tube extrusion and similar processes where only a few items are produced between changeovers.
Who uses it:
- Quality engineers, process engineers and production managers implementing Statistical Process Control (SPC).
- Lean, Six Sigma and continuous improvement practitioners seeking practical control methods for flexible production.
- Technical specialists who need to consolidate sparse product data into meaningful process-focused control charts.
Related Standards
- ISO 7870-1 and ISO 7870-2 (recommended background reading for control-chart fundamentals).
- ISO 3534-2 (terms and definitions used in the document).
Note: For situations where subgroup size > 1, other ISO SPC standards are applicable.
Keywords: ISO 7870-8:2017, short-run SPC, control charts, small mixed batches, statistical process control, individuals and moving range, Shewhart control chart.