Simul8 Tips, Technical Corner

Stop a conveyor to carry out a quality control check

Liam Hastie  /   Feb 7, 2018

SIMUL8 Consultant Liam Hastie shows you how to quickly simulate a conveyor quality control check and identify the impact of inspections on processed Jobs Per Hour.

Quality control inspections are used to identify, contain and resolve production issues as quickly as possible. Minimizing production defects by implementing quality checks also helps to maintain customer satisfaction, encourage repeat business, ensure product safety and reduce liability risks.

Although there are obviously benefits of conducting quality control checks – are there any downsides to consider? For example, what would the impact be of introducing these checks on KPIs like Jobs per Hour (JPH)?

In this tip, I’ll show you three simple steps to simulate a quality check on a conveyor process in SIMUL8:

  • Setting up the conveyor process and the JPH KPI
  • Adding an inspection Activity
  • Routing a percent of work items to inspection and stopping conveyor flow

We’ll randomly select and check 10% of the parts going through the conveyor to see how this impacts the current output average of 6.4 JPH. We can also try increasing the inspection percentage to discover when this will start to become a bottleneck on our processed Jobs per Hour.


Download the example simulation

Follow the steps below or download the example quality control check simulation to quickly try it out for yourself.



Step 1: Setting up the conveyor process and adding Jobs Per Hour

  1. Use the ‘Building Blocks’ and ‘Advanced Building Blocks’ menus to add a Start Point, Queue, Conveyor and End Point.
  2. Select the Conveyor and set Length to 20 and Speed to 1.
  3. Change the ‘Routing In’ on the Conveyor from ‘Passive’ to ‘Priority’ to pull in work items without using an Activity.
  4. Add a Queue with a minimum wait time of 60 minutes and an Activity with a fixed zero process time.
  5. Run the simulation and pause to select the Queue to add a contents chart – the dashed line in this contents chart displays the average rate of jobs per hour.


Step 2: Add the inspection Activity

  1. Change the Conveyor length from 20 to 10 and make a copy of the Conveyor by holding down the Ctrl Key and dragging the object with left mouse button.
  2. Position and reconnect the Conveyors so that we now have 2 x 10 length conveyors.
  3. Add an Activity named ‘Check Needed’ between the Conveyors and set it to have a zero process time – this activity will define if each work item is tested or not.
  4. Add a Queue and another Activity named ‘Inspect’, connecting it to the Conveyor.
  5. Give the Inspect Activity an average process time of 30 minutes and add connections to the Queue.


Step 3: Routing a percent of work items to inspection and stopping conveyor flow

  1. Set the ‘Routing Out’ from the Check Needed Activity to ‘Percent’ and set 10% of work items to go to the Inspect Activity.
  2. Select both of the Activities and the Queue together by holding down the Ctrl Key and clicking on each object.
  3. Once all are selected right-click on top of an object and select the option ‘Create Group’.
  4. This creates a group (‘Group 1’). In the Group window set option to ‘Limit work items in the group’ to 1. This means that when a work item is present anywhere across these 3 objects then no other work items can enter those objects. This will stop the Conveyor 1 flow while an work item is being inspected.


So, what is the impact of introducing the inspection?

By resetting and running the simulation, we can see the impact of introducing the 10% product inspection. We can see that although there is some build-up on Conveyor 1, we are still able to achieve the pre-inspection output rate of 6.4 Jobs per hour.

But what happens when we increase the inspection rate to 30%? To test this, edit Routing-out on Check Needed Activity to have 30% of work items go to Inspect.

After resetting and running the simulation again we can see at a 30% product inspection that our Jobs per hour has now reduced to an average of 5.7 Jobs per Hour.


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About the author

Liam Hastie

Liam Hastie

Liam Hastie is a Specialist Consultant at SIMUL8 Corporation providing insight, support and skills to help you get the most from process simulation. With a Masters in Industrial Design Engineering and over 10 years’ experience in Lean Six Sigma Process Improvement, Liam offers unique perspective on how to use simulation to boost your process improvement projects and transform your decision making.