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Project: Evaluate a Manufacturing Process

Manufacturing processes for any product is like putting together a puzzle. Products are pieced together step by step, and keeping a close eye on the process is important.

For this project, you're supporting a team that wants to improve how they monitor and control a manufacturing process. The goal is to implement a more methodical approach known as statistical process control (SPC). SPC is an established strategy that uses data to determine whether the process works well. Processes are only adjusted if measurements fall outside of an acceptable range.

This acceptable range is defined by an upper control limit (UCL) and a lower control limit (LCL), the formulas for which are:

The UCL defines the highest acceptable height for the parts, while the LCL defines the lowest acceptable height for the parts. Ideally, parts should fall between the two limits.

Using SQL window functions and nested queries, you'll analyze historical manufacturing data to define this acceptable range and identify any points in the process that fall outside of the range and therefore require adjustments. This will ensure a smooth running manufacturing process consistently making high-quality products.

The data

The data is available in the manufacturing_parts table which has the following fields:

  • item_no: the item number
  • length: the length of the item made
  • width: the width of the item made
  • height: the height of the item made
  • operator: the operating machine
Spinner
DataFrameavailable as
alerts
variable
SELECT 
outer_subquery.*, 
CASE WHEN outer_subquery.height NOT BETWEEN outer_subquery.lcl AND outer_subquery.ucl
	THEN TRUE
	ELSE FALSE
	END AS alert
--OUTER_SUBQUERY
FROM (
	SELECT
	inner_subquery.*,
	inner_subquery.avg_height+3*inner_subquery.stddev_height/SQRT(5) AS ucl, --Upper control height limit
	inner_subquery.avg_height-3*inner_subquery.stddev_height/SQRT(5) AS lcl  --Lower Control height limit
	-- INNER SUBQUERY
	FROM (SELECT
		  --Operator
		  operator,
		  --Row number
		  ROW_NUMBER() OVER(PARTITION BY operator ORDER BY item_no ROWS BETWEEN 4 PRECEDING AND CURRENT ROW) 
	AS row_number,
		  --Height
		  height,
		  --Moving average height
		  AVG(height) OVER(PARTITION BY operator ORDER BY item_no ROWS BETWEEN 4 PRECEDING AND CURRENT ROW) 
	AS avg_height,
		  --Moving standard deviation from height
		  STDDEV(height) OVER(PARTITION BY operator ORDER BY item_no ROWS BETWEEN 4 PRECEDING AND CURRENT ROW) 
	AS stddev_height
		  FROM manufacturing_parts
		 ) as inner_subquery -- inner_subquery
	WHERE inner_subquery.row_number >= 5
	) as outer_subquery -- outer_subquery