Process Input, machine - Jigs and fixture from qualification to maintenance in mass production

In this article, I shall focus on variations contributed by process input, machine.  The word “machine” in this context span from small jigs and fixture, semi automatic equipment to high technology fully automated robotic manufacturing line. 

In electronic industry ecosystem, high tech commodity product such as IC, semiconductor components, battery cells, PCB,  mechanical piece part, memory modules, LCD display,  are produce using  semi to fully automated equipment.  Therefore machine could be the major contributor of process input variations.

Assembly process of fitting all the above high tech commodity parts together to form a finish electronic gadget such smart phone or tablet is more manual process.  Most the assembly process are still make by human hand.  In good manufacturing practices,  we would use jig and fixture  to aid operator in assembly process,  therefore machine is still a contributor to a certain extend.

Machine use to aid manufacturing need to be qualified,  setup by expert and maintained correctly in order to minimize the variation contributed by “machine”.  In part 1 of this article we shall concentrate on jig and fixture qualification  and maintenance in mass production. 

Jig and fixture is used under 2 main situations

Situation	Purpose	Results
Manual manufacturing process	To aid operator in transformation process  such as simple cutting jig or To help support part and guide operator to assemble parts	More consistent part,  such as cutting part with cutting jig,  length will be more uniform
High technology manufacturing process equipment	To reduce the changeover time of equipment by converting a portion of the equipment for changeover of parts	Shorter equipment conversion time

There is a subtle difference between jig and fixture.  Jig is use to aid operator in the transformation of part and fixture main purpose is to support the part during transformation/assembly process.  Good reference to jig and fixture could be found in this link http://engineeringhut.blogspot.my/2010/11/jigs-and-fixtures.html

Jig and fixture  as part of process input, machine, need to be qualified, setup and maintained properly to ensure it helps to reduce process variation to get consistent good quality part.

Recommended practice for Qualification of Jig and fixture

1. Understand why a process needs a jig or fixture,  and conceptualize the design 
2. Design of the jig should into consideration if it will cause handling, ESD problem to the part.  Material selected should not be easily subjected to wear and tear. 
3. Develop jig and fixture drawing with necessary details  :-  dimension and tolerance, critical dimension clearly marked and specify material required for the jig and fixture.
4. Jig and fixture supplier should fabricate the jigs and fixture according to drawing and buyoff the jig and fixture according to design drawing with official first article inspection report.
5. Manufacturer must have identification system which ensure all jig and fixture had a unique identification number for traceability.
6. Manufacturer should create a masterlist for all the jigs and fixture in factory which consist of the following information :-  Jig ID,  Jig name/description,  purpose of the jig,  process used,  FAI date,  drawing,  qualification date and results,  PM required.
7. User factory of jig and fixture should create a process to buy-off jig and fixture which comprise of  :-

• Checking the jig and fixture per drawing and first article with proper report

• Trial  the jig and fixture in production line and record the results of the parts and cycle time. 

• Specify the length of evaluation and how many parts need to be evaluated.

•  Evaluate the key process input Y of the part such as attribute  reject rate, critical to quality parameter variable output.  The qualification best practice would be using process capability index (Cpk/Ppk) of the impacted critical to quality process output Y.  

Fixture which help to support the part , operator do not need to hold part and apply glue result in more consistent gluing process

Typical drawing of fixture

 Jig and fixture could be subjected to wear and tear or shift in performance over time in production,  therefore preventive maintenance is necessary  to verify the jig/fixture on regular basis.

The preventive maintenance of jig and fixture should include the following

1.   Determine the preventive maintenance base on production volume or  interval (months or quarterly)

2.   Establish all the checking criteria for jig and fixture  clearly documented in procedure

3.   There should a master list to track the preventive maintenance due date and auto trigger to the jig and fixture owner in the process.

4.   Create checklist on checking items and record all checking items and condition of jig and fixture. 

5.   Assess if there is any part of the jig and fixture which need to be replaced and record the replacement if necessary.  This can be used to determine if the frequency of the preventive maintenance.

Jig and fixture could help to create a consistent good products if  qualification, set up and maintenance is done properly.  On the flip side it will create problem if there is governance process to manage jig and fixture used.